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   7025篇
  免费   38篇
  国内免费   6篇
教育   4809篇
科学研究   975篇
各国文化   17篇
体育   358篇
综合类   8篇
文化理论   148篇
信息传播   754篇
  2022年   19篇
  2021年   22篇
  2020年   44篇
  2019年   66篇
  2018年   788篇
  2017年   816篇
  2016年   584篇
  2015年   119篇
  2014年   123篇
  2013年   548篇
  2012年   190篇
  2011年   412篇
  2010年   393篇
  2009年   234篇
  2008年   284篇
  2007年   413篇
  2006年   65篇
  2005年   165篇
  2004年   205篇
  2003年   147篇
  2002年   77篇
  2001年   90篇
  2000年   88篇
  1999年   65篇
  1998年   56篇
  1997年   53篇
  1996年   52篇
  1995年   25篇
  1994年   33篇
  1993年   20篇
  1992年   45篇
  1991年   45篇
  1990年   29篇
  1989年   38篇
  1988年   34篇
  1987年   31篇
  1986年   36篇
  1985年   40篇
  1984年   39篇
  1983年   22篇
  1982年   33篇
  1981年   24篇
  1980年   17篇
  1979年   35篇
  1978年   28篇
  1977年   23篇
  1976年   17篇
  1974年   23篇
  1972年   24篇
  1971年   18篇
排序方式: 共有7069条查询结果,搜索用时 15 毫秒
31.
32.
33.
A paper read at the first regular meeting of the Osler Society of McGill University, October 19, 1921.  相似文献   
34.
35.
36.
In Information Retrieval, since it is hard to identify users’ information needs, many approaches have been tried to solve this problem by expanding initial queries and reweighting the terms in the expanded queries using users’ relevance judgments. Although relevance feedback is most effective when relevance information about retrieved documents is provided by users, it is not always available. Another solution is to use correlated terms for query expansion. The main problem with this approach is how to construct the term-term correlations that can be used effectively to improve retrieval performance. In this study, we try to construct query concepts that denote users’ information needs from a document space, rather than to reformulate initial queries using the term correlations and/or users’ relevance feedback. To form query concepts, we extract features from each document, and then cluster the features into primitive concepts that are then used to form query concepts. Experiments are performed on the Associated Press (AP) dataset taken from the TREC collection. The experimental evaluation shows that our proposed framework called QCM (Query Concept Method) outperforms baseline probabilistic retrieval model on TREC retrieval.  相似文献   
37.
38.
39.
Analysis of Statistical Question Classification for Fact-Based Questions   总被引:1,自引:0,他引:1  
Question classification systems play an important role in question answering systems and can be used in a wide range of other domains. The goal of question classification is to accurately assign labels to questions based on expected answer type. Most approaches in the past have relied on matching questions against hand-crafted rules. However, rules require laborious effort to create and often suffer from being too specific. Statistical question classification methods overcome these issues by employing machine learning techniques. We empirically show that a statistical approach is robust and achieves good performance on three diverse data sets with little or no hand tuning. Furthermore, we examine the role different syntactic and semantic features have on performance. We find that semantic features tend to increase performance more than purely syntactic features. Finally, we analyze common causes of misclassification error and provide insight into ways they may be overcome.  相似文献   
40.
Although the USSR and the United States had a comparable number of employees in the field of scientific information, there was a substantial difference in funding, which resulted in a lack of information support for Soviet scientists. While 90% of the publications in the United States were available almost immediately after their release, in the USSR they were delayed by 1.5 to 2 years. Since the publication of the Abstracts Journal by VINITI (AJ), its content was consistently expanding and reached its peak in 1990 (1.5 million documents per year). The next quarter of a century was characterized by a decline in both the composition of the AJ and the time required for its document coverage. The steps for restructuring VINITI activities are discussed. The focus is made on improving the limited coverage of the Russian-language part of the global flow of scientific information by Western information systems.  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