首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   231篇
  免费   0篇
教育   20篇
科学研究   104篇
信息传播   107篇
  2016年   1篇
  2015年   1篇
  2014年   6篇
  2013年   20篇
  2012年   41篇
  2011年   86篇
  2010年   14篇
  2009年   16篇
  2008年   6篇
  2007年   5篇
  2006年   22篇
  2005年   2篇
  2004年   7篇
  2002年   4篇
排序方式: 共有231条查询结果,搜索用时 15 毫秒
181.
The scientific theme for the 2005 Bower Award was Chemistry, specifically the field of Catalysis. The Franklin Institute, Philadelphia, Pennsylvania, awarded the 2005 Bower Award and Prize for achievement in Science to Henri B. Kagan for his seminal discovery of fundamental chemical principles that explain the impact of catalyst shape on its effectiveness in controlling chemical reactions, thus greatly simplifying the manufacture of pharmaceutically important compounds. Henri Kagan is widely recognized as a pioneer in the field of asymmetric catalysis. Starting in the early 1970s, his reports of the synthesis of the chiral bidentate diphosphine ligand and the demonstration of its use with soluble rhodium compounds to catalyze the efficient production of large enantiomeric excesses of chiral molecules in asymmetric hydrogenations has had far reaching effects on research in the field asymmetric catalysis. The concept of using chiral bidentate ligands of C2 symmetry has led the way for numerous developments in asymmetric catalysis. Later in 1986 his introduction of the concept and investigations into “nonlinear effects in asymmetric synthesis” using catalysts with chiral ligands that were not optically pure challenged the widely accepted assumption that the enantiomeric excess which is possible correlates linearly with the optical purity of the chiral ligands. He reported the first example in asymmetric catalysis where the optical purity of the product significantly exceeded the optical purity of the chiral ligand.  相似文献   
182.
Recent studies have advocated different technological innovation capabilities (TICs) and discussed their impact on a firm’s competitive performance. This paper introduces a study framework of innovation audit and examines the relevance of seven TICs to building and sustaining the competitiveness of Chinese firms. Empirical data was acquired through a recent study of 213 Chinese firms in Beijing, China. Regression analysis was employed to examine the correlation between TICs and innovation rate, sales growth, and product competitiveness among these firms. The findings verify that R&D and resources allocation capabilities are the two most important TICs. A strong R&D capability could safeguard innovation rate and product competitiveness in large and medium-sized firms, whereas a resources allocation capability would enhance the sales growth in small firms. However, the impact of learning and organising capabilities on a firm’s innovation performance has yet to be investigated.The findings of this paper suggest that Chinese firms should consider a more balanced focus on their TICs’ harmonising enhancement. In order to maintain their sustainable development, effectively plan and implement their innovation strategies as well as enhance their whole innovation capability, Chinese firms should closely relate their TICs to the formulation of technology strategy and harmonisation of innovation and R&D activities.  相似文献   
183.
With increasing popularity of the Internet and tremendous amount of on-line text, automatic document classification is important for organizing huge amounts of data. Readers can know the subject of many document fields by reading only some specific Field Association (FA) words. Document fields can be decided efficiently if there are many FA words and if the frequency rate is high. This paper proposes a method for automatically building new FA words. A WWW search engine is used to extract FA word candidates from document corpora. New FA word candidates in each field are automatically compared with previously determined FA words. Then new FA words are appended to an FA word dictionary. From the experiential results, our new system can automatically appended around 44% of new FA words to the existence FA word dictionary. Moreover, the concentration ratio 0.9 is also effective for extracting relevant FA words that needed for the system design to build FA words automatically.  相似文献   
184.
The term technochange refers to technology-driven organizational changes and covers the broad spectrum of aspects that are related to and have an impact on changes within organizations. Technochange processes are usually managed by change managers, who are responsible for successfully accomplishing the IT-related tasks in their projects, as well as every other structural and organizational dimension related to the implementation of technochanges. This paper discusses what competencies managers should have to carry out these processes effectively. On the basis of the existing literature, interviews with experts and case study research, we identify and test a set of IT- and non-IT-related competencies that are essential for managing technochange processes within and among organizations. Further, this paper presents a model for assessing and allocating project managers to IT technochange projects that match their competencies and skills. This model could also serve as a tool for developing technochange management competencies via targeted training programmes. A case study demonstrates how the assessment model can be used in practice. Finally, we make some suggestions for future research in the fields of change management and IT.  相似文献   
185.
This paper applies concepts drawn from KM to Art Education. Specifically, the purpose of this paper is to study the knowledge types, knowledge sources, knowledge processes as well as factors affecting these processes in Art Education. The research was carried out using an interpretative case study methodology in Singapore. Apart from 26 one-to-one interviews conducted with various stakeholders of the Art Education community, on-site observations were made at 19 different Art Education events. Four major findings emerged. One, the knowledge types of Art Education in Singapore were a blend of different knowledge domains. Two, perceptible knowledge sources were those which conveyed an appearance of authority. Three, knowledge processes in Art Education were steeply humanistic. Finally, factors that affected knowledge processes were (i) the highly competitive Singapore education system, (ii) management support and policies, (iii) personal values and interests, (iv) workload and (v) the absorptive capacity of Art teachers. This paper concludes with a number of research and practical implications.  相似文献   
186.
Recent legislation in New Zealand has placed statutory obligations on its government organizations to introduce sound records management practices and to ensure long-term access to their digital records. To obtain a base level of knowledge on current digital preservation practices and on awareness of digital preservation issues, an online survey was conducted of the nation's government organizations in March 2006. The survey, which achieved a response rate of 42.4%, found that most organizations were knowledgeable about basic aspects of their digital resources but their awareness of digital preservation was generally low, and digital preservation activity was modest overall. To identify possible reasons for this situation, Rogers' (Diffusion of innovations. 5th ed. New York: Free Press. 2003) Diffusion of Innovations model is used to discuss digital preservation as an innovation and the level of readiness for digital preservation as the innovation's rate of adoption. The paper concludes by using Rogers' model as the basis for making recommendations aimed at helping the government's lead agencies to increase New Zealand's public sector readiness for digital preservation.  相似文献   
187.
Projective synchronization is a type of chaos synchronization where the response system states are scaled replicas of the drive system states. This paper deals with the propagation of projective synchronization in a series connection of N chaotic discrete-time drive systems and N response systems. By exploiting an observer-based approach, the paper demonstrates that dead-beat projective synchronization (i.e., exact synchronization in finite time for any scaling factor) is achieved between the nth drive and nth response systems. In particular, it is shown that projective synchronization starts from the innermost (Nth) drive-response system pair and propagates toward the outermost (first) drive-response system pair. Only a single scalar synchronizing signal connects the cascaded drive and response systems. Finally, an example illustrates the propagation of different types of chaos synchronization in a series connection consisting of a Gingerbreadman map, a third order hyperchaotic Henon map and a Lozi map.  相似文献   
188.
Organic synthesis of natural products began in 1828 with Wohler's synthesis of urea, the first time a substance derived from a living organism had been produced by combining inorganic materials. Progress in the field was slow at first, due to the limited purification and analytical methods. Advances in those areas gave rise to rapid progress in synthesis, as chemists could now focus their energies on devising new approaches to the preparation of increasingly complex molecules. While it is possible to prepare many molecules by using known chemistry in new combinations, real progress has been the result of keen insight and creativity on the part of only a few individuals.Professor Samuel J. Danishefsky established himself early on as a leader in this field when he recognized that a well-known ring forming reaction could be greatly extended by adding chemical functionality to one of the components. He then found that these new reactive components could react with heretofore unreactive components to produce new rings containing oxygen atoms both in the ring and as attachments to the ring. These products were very similar to naturally occurring sugars. Danishefsky realized that he could develop this chemistry further to produce precisely defined polysaccharides as well. Some of these polysaccharides occur on the surface of cancer cells. Using the chemistry he developed, he was able to prepare these cancer cell markers, and after combining them with certain proteins, showed that the resulting molecules behaved as cancer vaccines. Several have entered clinical trial.Danishefsky has synthesized many other natural products, but he is particularly interested in those that may be useful in treating cancer. His syntheses allow for the modification of the final product in ways that improve both safety and efficacy. Several of these compounds have also entered clinical trials. Thus his work has not only advanced the art and science of organic synthesis, but stands to make dramatic advances in the treatment of cancer as well.  相似文献   
189.
Significant public investments in rural broadband internet service authorized by the American Recovery and Reinvestment Act raise new questions regarding the impacts of broadband on rural residents and communities. The results of a natural field experiment involving broadband internet projects funded by the Community Connect program of the Rural Utilities Service are reviewed here to provide a context for future evaluations of the effects of broadband infrastructure deployment and efforts to stimulate sustainable broadband use in rural areas. Based on pre-post surveys conducted in four communities in 2005 and 2008, the implementation of broadband infrastructure grants increased broadband adoption, although penetration also increased where a grant was awarded but later terminated. Public education efforts in a community participating in the ConnectKentucky initiative had an incremental effect on broadband adoption by positively affecting residents' perceptions of broadband service. Impacts on individual economic development activities and community satisfaction were not found. Implications for rural broadband initiatives and future evaluations of their effects are drawn.  相似文献   
190.
Over the last decade many governments across the world have intensified their efforts to improve efficiency of public services through Information and Communication Technology (ICT)-enabled transformation of Local Government Authorities (LGAs). Many of these efforts involve implementing new Information Systems and Technology (IS/IT) and integrating various disparate legacy systems to deliver improved services. While there is a surfeit of literature that have outlined the various organizational and technical challenges posed by Technology Integration Solutions (TIS), few studies have examined the role of stakeholders and surrounding challenges when implementing TIS in LGAs. The TIS adoption process involves several stakeholders, each with specific domain knowledge and expertise that are crucial to the success of TIS projects. In this paper, the authors use the concept of stakeholder theory to analyze the role of stakeholders during the TIS adoption process with regards to their perceptions on the factors influencing TIS adoption in LGAs and their involvement on the adoption lifecycle phases. A qualitative multiple case study approach is adopted to empirically highlight the different categories of stakeholders involved in the TIS adoption process, the dynamic nature and importance of their role, and why their domain knowledge and expertise are vital for TIS projects.  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