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   5463篇
  免费   90篇
  国内免费   195篇
教育   3568篇
科学研究   1044篇
各国文化   18篇
体育   415篇
综合类   411篇
文化理论   3篇
信息传播   289篇
  2024年   1篇
  2023年   11篇
  2022年   44篇
  2021年   80篇
  2020年   106篇
  2019年   73篇
  2018年   51篇
  2017年   59篇
  2016年   58篇
  2015年   120篇
  2014年   275篇
  2013年   352篇
  2012年   377篇
  2011年   497篇
  2010年   427篇
  2009年   453篇
  2008年   440篇
  2007年   476篇
  2006年   404篇
  2005年   315篇
  2004年   242篇
  2003年   199篇
  2002年   161篇
  2001年   126篇
  2000年   88篇
  1999年   69篇
  1998年   30篇
  1997年   41篇
  1996年   28篇
  1995年   19篇
  1994年   24篇
  1993年   23篇
  1992年   15篇
  1991年   8篇
  1990年   9篇
  1989年   5篇
  1988年   3篇
  1986年   1篇
  1985年   8篇
  1984年   9篇
  1983年   3篇
  1982年   8篇
  1981年   2篇
  1980年   1篇
  1979年   3篇
  1978年   2篇
  1957年   2篇
排序方式: 共有5748条查询结果,搜索用时 281 毫秒
41.
构建基于J2EE规范的数字图书馆模型的探讨   总被引:2,自引:0,他引:2  
从软件工程的角度分析,数字图书馆实质是一个分布式管理信息系统。构建数字图书馆,就是构建一个分布式管理信息系统。J2EE的多层次的分布式应用模型和一系列开发技术规范,为构建数字图书馆平台提供了可靠保证。图1。参考文献11。  相似文献   
42.
基于P2P的适应性信息检索系统的设计   总被引:3,自引:1,他引:3  
针对现有搜索引擎的不足,提出了一个基于P2P的适应性信息检索系统设计方案,详细介绍了系统的各主要模块的功能和技术方法,进而分析了该模型的优势。  相似文献   
43.
44.
基于词向量扩展的学术资源语义检索技术   总被引:1,自引:0,他引:1  
[目的/意义] 尝试以统计的方法为指导思想,探究基于词向量扩展的语义检索技术来提升学术资源的语义检索能力。[方法/过程] 利用自然语言处理、文本挖掘技术,对采集来的学术资源(主要是学术论文)元数据进行预处理,结合word2vec词向量生成工具和elasticsearch全文检索引擎搭建语义检索系统,对学术资源进行语义检索的探索研究。[结果/结论] 本文提出的方法能够有效提升学术信息的检索效果,一定程度上实现学术资源的语义检索,并为后续语义检索的进一步研究提供借鉴。  相似文献   
45.
We have studied the efficiency of research in the EU by a percentile-based citation approach that analyzes the distribution of country papers among the world papers. Going up in the citation scale, the frequency of papers from efficient countries increases while the frequency from inefficient countries decreases. In the percentile-based approach, this trend, which is uniform at any citation level, is measured by the ep index that equals the Ptop 1%/Ptop 10% ratio. By using the ep index we demonstrate that EU research on fast-evolving technological topics is less efficient than the world average and that the EU is far from being able to compete with the most advanced countries. The ep index also shows that the USA is well ahead of the EU in both fast- and slow-evolving technologies, which suggests that the advantage of the USA over the EU in innovation is due to low research efficiency in the EU. In accord with some previous studies, our results show that the European Commission’s ongoing claims about the excellence of EU research are based on a wrong diagnosis. The EU must focus its research policy on the improvement of its inefficient research. Otherwise, the future of Europeans is at risk.  相似文献   
46.
The present study examined the effects of anticipated achievement feedback on students' semantic processing on the neural level, using event-related brain potentials (ERPs). Participants (N = 79) anticipated either self-referential or normative achievement feedback regarding an announced upcoming test. Additionally, their performance expectations (low vs. no expectations) were orthogonally manipulated. Subsequently, students' on-line semantic processing was assessed by measuring the N400 cloze effect, a component in the EEG signal of which the amplitude is associated with semantic processing. Within the low performance-expectation condition, no effect of anticipated feedback on semantic processing was found. Within the no-performance-expectation condition, participants anticipating self-referential feedback showed a more widely distributed N400 cloze effect than participants anticipating normative feedback. The results confirmed the hypothesis that the mere expectation of a particular type of feedback can affect students' semantic processes.  相似文献   
47.
The world has been turned upside down by a global health emergency caused by the Covid-19. Given the high contagiousness of the virus and the need to contain its spread, social distancing rules, self-isolation policies, and geographical lockdowns have been enforced globally. Over the pandemic emergency the majority of the planned in-person meetings and congresses of national and international anatomical societies have been postponed or canceled. It is unclear what the future holds, but times of crisis often present possibilities for re-thinking old ways to achieve a more critical approach. It has become increasingly clear that traditional in-person congress formats of scientific societies need to be reevaluated. Over the past year and a half, two types of congressional modalities have been trialed to address the challenge of the pandemic as far as scientific meetings are concerned: the fully virtual congress, in which case the conference program is live streamed to all of the attendees, and the hybrid congress, in which case some of the attendees physically participate at the congress's venue while others interact via a virtual platform. The current study set out to investigate the technical difficulties, social challenges, costs and sustainability, logistics and management issues linked to holding various types of congresses in the post-Covid world. Anatomical societies throughout the world are actively striving to reshape their response to the current global emergency and to uncover new types of conference modalities in the effort to keep scientific exchange alive and flourishing in the post-Covid era.  相似文献   
48.
In fall 2016, the Columbia-Cornell collaboration in the area of Slavic & East European resource coordination and sharing celebrated its sixth year. The author reviews particulars of the development, implementation, and function of this program as well as some of the challenges that face such cross-institutional efforts.  相似文献   
49.
We first report discovery of the spinel-garnet-orthopyroxene granulite with pure CO2 fluid inclusions from the Fuyun region of the late Paleozoic Altay orogenic belt in Central Asia, NW China. The rock is characterized by an assemblage of garnet, orthopyroxene, spinel, cordierite, biotite, plagioclase and quartz. Symplectites of orthopyroxene and spinel, and orthopyroxene and cordierite indicate decompression under UHT conditions. Mineral chemistry shows that the or-thopyroxenes have high XMg and A12O3 contents (up to 9.23 wt%). Biotites are enriched in TiO2 and XMg and are stable under granulite facies conditions. The garnet and quartz from the rock carry monophase fluid inclusions which show peak melting temperatures of around -56.7℃, indicating a pure CO2 species being presented during the ultrahigh-T metamorphism in the Altay orogenic belt. The inclusions homogenize into a liquid phase at temperatures around 15.3-23.8℃ translating into CO2 densities of the order of 0.86-0.88 g/cm3. Based on prelim  相似文献   
50.
本文分析了数据库系统的不安全因素.在简要介绍JAVA安全体系结构基础上结合JAAS来实现对用户身份的验证和授权以达到保护用户连接的目的、利用JSSE实现SSL隧道封装保护JDBC的传输,接着讨论了利用数据库管理系统提供的一些安全机制来加强数据库的安全.文章最后还提出了对高度机密的数据采用数据库加密的解决方案.  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