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   14531篇
  免费   187篇
  国内免费   11篇
教育   10151篇
科学研究   1742篇
各国文化   122篇
体育   1024篇
综合类   17篇
文化理论   170篇
信息传播   1503篇
  2021年   138篇
  2020年   208篇
  2019年   280篇
  2018年   404篇
  2017年   424篇
  2016年   388篇
  2015年   257篇
  2014年   383篇
  2013年   2444篇
  2012年   335篇
  2011年   322篇
  2010年   313篇
  2009年   284篇
  2008年   297篇
  2007年   308篇
  2006年   295篇
  2005年   251篇
  2004年   280篇
  2003年   243篇
  2002年   255篇
  2001年   324篇
  2000年   345篇
  1999年   264篇
  1998年   147篇
  1997年   192篇
  1996年   188篇
  1995年   132篇
  1994年   146篇
  1993年   135篇
  1992年   215篇
  1991年   197篇
  1990年   229篇
  1989年   232篇
  1988年   196篇
  1987年   215篇
  1986年   188篇
  1985年   233篇
  1984年   174篇
  1983年   156篇
  1982年   143篇
  1981年   141篇
  1980年   135篇
  1979年   200篇
  1978年   155篇
  1977年   130篇
  1976年   105篇
  1975年   103篇
  1974年   110篇
  1973年   110篇
  1971年   99篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
研究目的:假腮的功能早已引起科学家兴趣,但还有待阐明。本文通过研究硬骨鱼类品种虹鳟鱼(Oncorhynchus mykiss)的假腮碳酸酐酶的免疫定位,来探讨假腮碳酸酐酶的生理功能。研究方法:免疫组织化学染色技术。重要结论:免疫组化结果显示碳酸酐酶分布在假腮细胞中,更精确地说是在其细胞顶端分布。细胞基底端、管状系统、毛细血管和柱细胞均无免疫染色。免疫细胞化学定位进一步验证了这些结果,并显示一部分是细胞质碳酸酐酶,其余的与细胞膜结构连接。此外,腔隙层未显示出免疫过氧化物酶的活性。本研究揭示了假腮碳酸酐酶的功能与细胞外介质有关,碳酸酐酶能干预传入神经纤维刺激机制。  相似文献   
992.
Schools are an important context for both basic and applied scientific research. Unlike the laboratory, however, the physical and social conditions of schools are not under the exclusive control of scientists. In this article, we liken collecting data in schools to putting on a theatrical production. We begin by describing the large cast of characters whose collaborative efforts make school‐based research possible. Next, we address the critics, including the university Institutional Review Board (IRB) and school administrators, whose feedback often improves the final study design. We then turn our attention to set building, stage directions, and rehearsals—key steps in the iterative process of refining study procedures. We end with a discussion of the day of data collection itself and activities that take place after the curtain drops. Throughout, we make recommendations based on our recent experience collecting data at several high schools.  相似文献   
993.
994.
The main aspects related to the development of a system for the aggregation and use of scientific results (hereinafter, the System) are discussed. A unified comprehensive approach to the development of the System and the qualitative improvement of the information about the performance of the Russian research sector provided to the target audience is being suggested for use by academic institutions, government regulators, and the business community. The improvement is meant to be achieved through the development of technology that provides access to the relevant electronic resources. The presented conclusions lay the basis for a range of research and development works in the field related to the collection of scientific results.  相似文献   
995.
996.
Three groups of social bookmarking users, namely experienced users, users with moderate level of experience, and novice users, were investigated, in terms of their reported tagging behaviors, perceived usefulness of social bookmarking in information discovery and management, and perceived usefulness of the bookmarking features provided. Based on the empirical analysis of the Connotea users, who are primarily in academia, the study shows that experienced academic users generally prefer to use social bookmarking while moderately experienced and novice users still prefer to use the traditional bookmarking methods, such as creating and using bookmarks on a dedicated computer. Experienced academic users were also found to create more tags per bookmark comparing to the other two groups. Most novice academic users, however, only created one tag per bookmark, which just met Connotea's minimum requirement. Surprisingly different from the collaborative design nature of the social bookmarking systems, the study finds that our participants, particularly experienced academic users, prefer to create and use their own bookmarks rather than sharing bookmarks created by others. In fact, experienced users have significantly higher frequency (once every two weeks) of creating bookmarks than the other two groups (once a month or less). In addition, website design features and functions, such as automatic collection of bibliographic information, are regarded by all participants as helpful for information discovery. The in-depth examination and discussion of the opinions of Connotea users may be useful for further improvement of the design features and usage applications, particularly for academic social bookmarking websites. The results may also have potential implications to the future development of social bookmarking services in general.  相似文献   
997.
This article describes a half-day preconference that focused on the library as publisher. It examined how the movement from print to online publication has impacted the roles of libraries and their ability to take on new roles as publishers. The session explored the benefits of libraries becoming publishers, and discussed Open Access, what it is and is not and its importance to libraries and scholarly communication. A detailed case study of the publishing operations of the University Library System at the University of Pittsburgh was presented as an example of a successful library publishing program. The session provided an opportunity for participants to discover ways that libraries can be involved in publishing.  相似文献   
998.
A method is described for determining multiple loop feedback topologies which yield minimum sensitivities for symmetrical, all-pole bandpass filters. The procedure begins with a follow-the-leader feedback (FLF) topology and additional feedback loops are constructed until minimum sensitivity is achieved. Filters comprised of identical second-order sections and non-identical sections, respectively, are considered.  相似文献   
999.
1000.
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