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   13393篇
  免费   201篇
  国内免费   21篇
教育   9343篇
科学研究   1521篇
各国文化   125篇
体育   1147篇
综合类   6篇
文化理论   98篇
信息传播   1375篇
  2021年   138篇
  2020年   195篇
  2019年   267篇
  2018年   367篇
  2017年   350篇
  2016年   356篇
  2015年   238篇
  2014年   315篇
  2013年   2306篇
  2012年   291篇
  2011年   315篇
  2010年   278篇
  2009年   218篇
  2008年   269篇
  2007年   238篇
  2006年   232篇
  2005年   207篇
  2004年   227篇
  2003年   204篇
  2002年   175篇
  2001年   444篇
  2000年   291篇
  1999年   253篇
  1998年   117篇
  1997年   155篇
  1996年   132篇
  1995年   123篇
  1994年   144篇
  1993年   110篇
  1992年   181篇
  1991年   191篇
  1990年   192篇
  1989年   198篇
  1988年   165篇
  1987年   158篇
  1986年   167篇
  1985年   205篇
  1984年   160篇
  1983年   148篇
  1982年   128篇
  1981年   121篇
  1980年   115篇
  1979年   163篇
  1978年   131篇
  1977年   116篇
  1976年   92篇
  1975年   112篇
  1974年   100篇
  1973年   107篇
  1971年   98篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Although the inventions embodied in the Internet originated in a diverse set of industrial economies, the US was consistently the source of critical innovations and an early adopter of new applications. Why did other nations, including several that made important inventive contributions to the Internet, not play a larger role in its development, particularly in the creation of new business organizations, governance institutions, and applications? We argue that the role of the US “national innovation system” in the creation of the Internet echoes several key themes of US technological development before 1940. The presence of a large domestic market, a set of antitrust and regulatory policies that weakened the power of incumbent telecommunications firms, and a diverse private/public research community that was willing to work with both domestic and foreign inventions were important preconditions for US leadership in computer networking innovation.  相似文献   
972.
Current citation-based document retrieval systems generally offer only limited search facilities, such as author search. In order to facilitate more advanced search functions, we have developed a significantly improved system that employs two novel techniques: Context-based Cluster Analysis (CCA) and Context-based Ontology Generation frAmework (COGA). CCA aims to extract relevant information from clusters originally obtained from disparate clustering methods by building relationships between them. The built relationships are then represented as formal context using the Formal Concept Analysis (FCA) technique. COGA aims to generate ontology from clusters relationship built by CCA. By combining these two techniques, we are able to perform ontology learning from a citation database using clustering results. We have implemented the improved system and have demonstrated its use for finding research domain expertise. We have also conducted performance evaluation on the system and the results are encouraging.  相似文献   
973.
Information Economy and Changing Occupational Structure in Singapore   总被引:1,自引:0,他引:1  
Using population census data since 1921, this article traces changes in employment and occupational structure in Singapore in the past 80 years. This is a follow-up to an earlier paper by Kuo and Chen (1987) that reported the nascent formation of the information society in Singapore till the 1980s. It also makes an assessment of the role of proactive government policies in directing industrial restructuring and occupational changes in this city-state. It is found that the long-term growing trend in information-related occupations has been in tandem and supportive of industrial changes in Singapore. One more wave of growth of information producers (and certainly, innovators) and information distributors is expected in the next couple of decades. The momentum has started, and competition from regional countries similarly aspiring to be information and knowledge economies will quicken the pace. The government has initiated fundamental changes in the educational system to meet the challenges of the knowledge-based economy. The small city-state has also long adopted an adaptive philosophy to be responsive to the ever-changing environment, either in technology or in regional politics. Based on the trend analysis, it is expected that the emergent information society will graduate into full status when Singapore attains a developed country status in the forthcoming decades.  相似文献   
974.
975.
If T maps a convex domain DT into itself, and if {ωn} is a real sequence with range in (0, 1] then the recursive averaging process,
Xn+1=(1?omega;n) XnnnTxn, x0=ξ?DT
generates a sequence {x?n}; with range in DT. Under suitable conditions on DT, T and {ωn} the sequence {x?n} will converge in some sense to a fixed point of T. We prove that if DT is a closed convex subset of a complex Hilbert space H, if Tω = (1 ? ω) I + ωT is a strict contraction for some ω ? (0, 1], and if {ωn} satisfies the conditions,
ωn → 0
and
n=0ωn=∞
then, for arbitrary ξ ? DT, {x?n} converges strongly to (the unique) fixed point of T. We also prove that if DT and {ωn} satisfy the foregoing conditions, if T has at least one fixed point, and if Tω is non-expansive for some ω ? (0, 1], then for all ξ ? DT, {x?n} converges at least weakly to some fixed point of T. Finally, we apply these results to linear equations involving bounded normal operators and obtain an extension of the classical Neumann operator series.  相似文献   
976.
A theory is developed to describe the propagation of characteristics waves through an infinite slab of irregularities in a magneto-ionic medium. The theory makes use of the asymptotic Green's dyadic. The results show that mode conversion is possible through scattering from irregularities in an anisotropic background. Some special cases are discussed and an example is given.  相似文献   
977.
多种原因造成了知识产权担保在发放信贷方面的重要性不如其他财产的担保。原因之一是知识产权具有一些特殊属性,一些潜在贷款人对这种财产属性缺乏了解。另一个原因是对许多知识产权的估价存在困难,相关法律在调整这些法定权利上的担保权益方面也不甚健全。尽管金融机构及其法律顾问已经越来越多地理解了知识产权担保借贷中的诸要素,但以知识产权担保的融资仍处在初期阶段。这是一个无论在法律领域,还是在信贷实践方面都很复杂的问题。立法者在回应专门立法需求以促进其发展方面也行动缓慢。这就进一步增加了用知识产权这种价值可能很大、但寿命又可能很短的财产做担保提供信贷的不确定性。  相似文献   
978.
Synchronous data transmission systems that transmit information over dispersive channels often employ adaptive equalization techniques in the processing of the received signals. Most equalizers presently used in communication systems are of the tapped delay line (TDL) type. In this paper, we propose a class of adaptive equalizers of which the TDL equalizer is a member. Another interesting member of this class is the Laguerre adaptive equalizer which is to be introduced in this paper. The configuration of the Laguerre equalizer is developed. It is found, as shown by the examples, that the Laguerre equalizer is more accurate, and is less sensitive to timing error than the conventional TDL equalizer.  相似文献   
979.
980.
Lymphatic filariasis caused mainly by infection fromWuchereria bancrofti andBrugia malayi remains as the major cause of clinical morbidity in tropical and subtropical countries. Development of vaccine against filarial infection can act as additional measure to the existing therapeutic and vector control methods in the control of this disease. The main hurdles in the development of anti-filarial vaccine are the strict primate specificity ofWuchereria bancrofti, the paucity of parasite material, the diversity of clinical manifestations and their associated complex immune responses, lack of clear understanding on host-parasite interactions and the mechanisms involved in protective immunity. However in the past few years, the information generated in immuno-epidemiological studies, correlated with observations in experimental animals suggests that a filarial vaccine is feasible. Initially live irradiated infective larvae have been successfully used to induce high level of protective immunity in several animal models. Applying diverse strategies, variety of purified or recombinant filarial antigens have been explored for their ability to induce protection in different host-parasite systems. Some of these targeted filarial antigens induced high level of resistance in experimental animals against challenge infections. More focussed studies on thorough characterization of parasitological and immunological changes associated with resistance induced by such candidate protective antigens and on delivery mechanisms and safety aspects will be crucial in their selection for possible use in humans.  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