首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The Harappan civilization, the world's fourth great civilization after those of Egypt, Mesopotamia, and China flourished in the valley of the Indus three thousand years ago. As yet little is known about it, but one enormous town — Mohenjo-Daro — has survived. This has been only partially excavated and has yielded just a few scraps of information which have provided the basis for some fanciful theories. The author of this article had developed an interesting new approach. Combining a re-examination of the documentation that has accumulated over the past 50 years with an investigation of the actual remains, he has obtained some exciting results which shed new light on the overall planning, architecture, and development of the town over the centuries, thus providing a fresh understanding of the Harappan civilization itself.  相似文献   

2.
Of all the senses, that of taste is perhaps the hardest to define and quantify and elucidation of the underlying mechanisms is unrespondingly difficult. This article describes a conceptual model — at the molecular level — for the four basic taste modalities, using apparent specific volume as a fundamental parameter. It also considers possible practical applications.  相似文献   

3.
The need for collaborative ventures in Europe has long been stressed in the editorial pages of this journal, and more than ten years ago (Endeavour, 28, 54, 1969) we gave strong support for a proposal to establish a European Laboratory of Molecular Biology. For this we then incurred some criticism, on the ground that such a laboratory would weaken national academic institutes striving to establish themselves in this rapidly developing field. Nevertheless, we continued to maintain (30, 2, '71) ‘the great political and scientific importance of this [concept]—and of other such collaborative enterprises—if Europe is to maintain the initiative in fields where the great institutions of the United States have established a dominant position.’ In the event, the Laboratory was established at Heidelberg in 1974, though not formally opened until 1978. The Director-General, Sir John Kendrew, here surveys the policy and achievements of this important new institute.  相似文献   

4.
Until a century or more ago disease was generally attributed to the presence of some undesirable feature. The realization that disease could be due to the absence of a desirable factor was revolutionary. During the 18th and 19th centuries, however, foundations were laid for the recognition in the 20th century that to prevent some diseases certain ‘accessory substances’—the vitamins—were essential in the diet. This article tells the story of their discovery, their current significance, and future trends in vitamin research.  相似文献   

5.
The biotechnological exploitation of fungi is becoming more and more important both for industrial purposes and in the field of cultivation of edible mushrooms. In the past, breeding of fungi was restricted mainly to selection of better strains after spontaneous or induced mutations. Today, the inclusion of genetic recombination—based on better knowledge of how to handle fungi under controlled conditions, of their life cycles, and of their breeding systems—has given the possibility of ‘concerted breeding’. In addition, some recent basic research provides means of preventing ageing and death of fungal strains, by either genetic alterations or therapeutic treatment. Examples of the application of these ideas and results are given.  相似文献   

6.
Of the animal artifacts encountered by archaeologists, bones and teeth are the ones most commonly found. Systematic study of these — particularly of their distribution and the different species involved —can throw much light on the diet and eating habits of people in the past.  相似文献   

7.
Until recently the identification of the authorship of written works has—like that of paintings—been largely subjective, but the application of the computer to analysis of literary structure has opened up important new possibilities. It has shown that simple frequency patterns are of much less diagnostic value than groupings of words and their position in sentences. Stylometry, as this new investigative method is called, has the merit of knowing no language barriers—it is equally applicable, for example, to classical Greek, English, and Swedish.  相似文献   

8.
The oil palm is a major factor in the economy of much of South East Asia and maximising the harvest is of major consequence. One important source of loss is the shedding of ripe fruit from the bunches before they reach the factories. Study of the course of abscission reveals unusual processes in the oil palm — and in a few other plantation crops such as dates and coconuts — which suggest practical means of achieving better harvesting regimes and regulation of fruit shedding.  相似文献   

9.
Croplands are the single largest anthropogenic source of nitrous oxide (N2O) globally, yet their estimates remain difficult to verify when using Tier 1 and 3 methods of the Intergovernmental Panel on Climate Change (IPCC). Here, we re-evaluate global cropland-N2O emissions in 1961–2014, using N-rate-dependent emission factors (EFs) upscaled from 1206 field observations in 180 global distributed sites and high-resolution N inputs disaggregated from sub-national surveys covering 15593 administrative units. Our results confirm IPCC Tier 1 default EFs for upland crops in 1990–2014, but give a ∼15% lower EF in 1961–1989 and a ∼67% larger EF for paddy rice over the full period. Associated emissions (0.82 ± 0.34 Tg N yr–1) are probably one-quarter lower than IPCC Tier 1 global inventories but close to Tier 3 estimates. The use of survey-based gridded N-input data contributes 58% of this emission reduction, the rest being explained by the use of observation-based non-linear EFs. We conclude that upscaling N2O emissions from site-level observations to global croplands provides a new benchmark for constraining IPCC Tier 1 and 3 methods. The detailed spatial distribution of emission data is expected to inform advancement towards more realistic and effective mitigation pathways.  相似文献   

10.
The river dolphins, of which there are now five species, are among the world's most endangered animals. This article describes the steps that have been taken — based on systematic study of its anatomy, ecology, and breeding and behavioural habits — to preserve the rare Chinese river dolphin. This is now limited to about 300 individuals in the middle and lower reaches of the Changjiang River.  相似文献   

11.
This paper analyses information system implementation from an innovation research perspective. The basic assumption is that information systems can be regarded as special types of innovation, so that the results of research concerning innovations may be of value within information system implementation research. The paper gives a brief overview of innovation research, identifying the characteristics of innovations as its most distinctive research area. Principal attention is paid to the analysis of four characteristics — complexity, radicalness, originality and divisibility — as factors influencing the implementability of innovations and information systems.  相似文献   

12.
Although relevance judgments are fundamental to the design and evaluation of all information retrieval systems, information scientists have not reached a consensus in defining the central concept of relevance. In this paper we ask two questions: What is the meaning of relevance? and What role does relevance play in information behavior? We attempt to address these questions by reviewing literature over the last 30 years that presents various views of relevance as topical, user-oriented, multidimensional, cognitive, and dynamic. We then discuss traditional assumptions on which most research in the field has been based and begin building a case for an approach to the problem of definition based on alternative assumptions. The dynamic, situational approach we suggest views the user — regardless of system — as the central and active determinant of the dimensions of relevance. We believe that relevance is a multidimensional concept; that it is dependent on both internal (cognitive) and external (situational) factors; that it is based on a dynamic human judgment process; and that it is a complex but systematic and measurable phenomenon.  相似文献   

13.
This paper presents a model that incorporates contemporary theories of tense and aspect and develops a new framework for extracting temporal relations between two sentence-internal events, given their tense, aspect, and a temporal connecting word relating the two events. A linguistic constraint on event combination has been implemented to detect incorrect parser analyses and potentially apply syntactic reanalysis or semantic reinterpretation—in preparation for subsequent processing for multi-document summarization. An important contribution of this work is the extension of two different existing theoretical frameworks—Hornstein’s 1990 theory of tense analysis and Allen’s 1984 theory on event ordering—and the combination of both into a unified system for representing and constraining combinations of different event types (points, closed intervals, and open-ended intervals). We show that our theoretical results have been verified in a large-scale corpus analysis. The framework is designed to inform a temporally motivated sentence-ordering module in an implemented multi-document summarization system.  相似文献   

14.
Recent simulations by Chen and Dorfman [Electrophoresis 35, 405–411 (2014)] suggested that “tilting” the electric field with respect to the lattice vectors of a hexagonal post array would lead to a substantial improvement in electrophoretic DNA separations therein. We constructed such an array where the electric field is applied at an angle equidistant between the two lattice vectors. This tilted array leads to (i) baseline resolution of 20 kbp DNA and λ DNA (48.5 kbp) in a 4 mm channel and (ii) measurable separation resolutions for electric fields up to 50 V/cm, both of which are improvements over untilted post arrays of the same post density. The predicted time required to reach a resolution of unity is approximately 5 min, independent of electric field. The separations are more reproducible at higher fields.  相似文献   

15.
We investigate the prevalence of the motive to source technological knowledge externally through corporate acquisition. Drawing on make-or-buy and organizational learning theories, we infer the implications of this explanation for the acquirers' pre-acquisition innovative characteristics. Using an international sample of 6106 high technology acquisitions during 1984–2000, we assess the contribution of innovative characteristics to the acquisition likelihood. For firms acquiring small private firms and former subsidiaries—but not public targets—the evidence is consistent with three propositions: (1) A firm's commitment to internal R&D is negatively affected by the decision to acquire; (2) Low R&D productivity increases the likelihood of acquisition; (3) A large knowledge stock predisposes firms to acquire because they perceive they are capable of selecting and absorbing targets. We conclude that acquisitions of small private firms and former subsidiaries are a viable R&D strategy to explore a range of potential future innovation trajectories for large public firms.  相似文献   

16.
Task-based evaluation of text summarization using Relevance Prediction   总被引:2,自引:0,他引:2  
This article introduces a new task-based evaluation measure called Relevance Prediction that is a more intuitive measure of an individual’s performance on a real-world task than interannotator agreement. Relevance Prediction parallels what a user does in the real world task of browsing a set of documents using standard search tools, i.e., the user judges relevance based on a short summary and then that same user—not an independent user—decides whether to open (and judge) the corresponding document. This measure is shown to be a more reliable measure of task performance than LDC Agreement, a current gold-standard based measure used in the summarization evaluation community. Our goal is to provide a stable framework within which developers of new automatic measures may make stronger statistical statements about the effectiveness of their measures in predicting summary usefulness. We demonstrate—as a proof-of-concept methodology for automatic metric developers—that a current automatic evaluation measure has a better correlation with Relevance Prediction than with LDC Agreement and that the significance level for detected differences is higher for the former than for the latter.  相似文献   

17.
While the phrase energy crisis is widely used in the context of the rising cost and diminishing availability of fossil fuels, there is in fact no lack of energy from alternative sources. The present situation has led to much more intensive investigation of these, which has revealed formidable—but certainly not insuperable—technological and economic obstacles to their exploitation. This article reviews the prospects for generating power on a large scale from the warm surface waters of the ocean, which represent a massive energy storage system.  相似文献   

18.
This article examines the application of two single-document sentence compression techniques to the problem of multi-document summarization—a “parse-and-trim” approach and a statistical noisy-channel approach. We introduce the multi-candidate reduction (MCR) framework for multi-document summarization, in which many compressed candidates are generated for each source sentence. These candidates are then selected for inclusion in the final summary based on a combination of static and dynamic features. Evaluations demonstrate that sentence compression is a valuable component of a larger multi-document summarization framework.  相似文献   

19.
By introducing the concept of innovation regimes, the aim of this article is to show how the rapid pace of technological development in the telecom sector may be explained by the close links between the sector's own R&D and the creation of numerous innovations, many of which are radical. In contemporary innovation theory, a theoretical antinomy exists: Whereas, the creation of incremental innovations is variously explained in terms of «rational» responses to markets, dynamics of technological regimes, dominant design, etc., radical innovations, in contrast, are explained in terms of serendipity, chance or haphazard scientific discoveries. Evidence from analysis of innovations in the telecom sector suggests that innovation regimes have provided a capability of coordination, direction and leadership in the creation of many of the radical technological innovations that have emerged in the sector. Thus, one may claim that the strong innovation regimes and high R&D intensity of the telecom sector, at least until recently, have provided a capability of creating innovations on purpose — for a purpose. The policy implications of this contradict some of the assumptions on which the prevailing market-oriented R&D governance models and policies are based — and which are supported by contemporary innovation theories.  相似文献   

20.
The separation of simple organic substances by distribution between two immiscible phases is a traditional technique in preparative and analytical chemistry. Latterly, the method has been extended to cover the increasingly important field of polymers—especially those of biological importance—and the micro constituents of cells. By appropriate choice of phases the method can be made highly selective, and it is particularly valuable for the treatment of labile substances that may be irreversibly damaged by conventional methods.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号