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   18772篇
  免费   217篇
  国内免费   119篇
教育   13006篇
科学研究   2474篇
各国文化   109篇
体育   1422篇
综合类   11篇
文化理论   215篇
信息传播   1871篇
  2020年   209篇
  2019年   311篇
  2018年   1050篇
  2017年   1022篇
  2016年   825篇
  2015年   289篇
  2014年   326篇
  2013年   2625篇
  2012年   369篇
  2011年   618篇
  2010年   514篇
  2009年   382篇
  2008年   447篇
  2007年   562篇
  2006年   276篇
  2005年   346篇
  2004年   380篇
  2003年   328篇
  2002年   262篇
  2001年   257篇
  2000年   287篇
  1999年   274篇
  1998年   142篇
  1997年   155篇
  1996年   183篇
  1995年   170篇
  1994年   131篇
  1993年   143篇
  1992年   216篇
  1991年   223篇
  1990年   230篇
  1989年   258篇
  1988年   209篇
  1987年   225篇
  1986年   219篇
  1985年   250篇
  1984年   222篇
  1983年   211篇
  1982年   176篇
  1981年   168篇
  1980年   157篇
  1979年   244篇
  1978年   190篇
  1977年   180篇
  1976年   149篇
  1975年   132篇
  1974年   151篇
  1973年   132篇
  1972年   107篇
  1971年   119篇
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
991.
992.
The University of Oklahoma Health Sciences Center (OUHSC) Library mailed a MEDLINE End User Practice Survey Form to 310 health professionals who had attended MEDLINE seminars supported by a two-year NLM grant. The survey sought to determine how many respondents had obtained NLM codes, reasons for not obtaining a code, searching time done since the seminar, differences in the use of information since taking the seminar, factors helpful in successful searching, and factors contributing to frustrations. The most prevalent reasons for not obtaining a code were lack of a microcomputer and modem, infrequent use of MEDLINE, cost, lack of time, complications, and ability to obtain free searches.  相似文献   
993.
The study presents and synthesizes the results of a series of five experiments on human information-seeking behavior in three different information-seeking environments. The first three experiments utilized a highly-controlled, simulated information-seeking task developed to study human search strategies in citation networks. Emphasis in the fourth and fifth experiments was placed on assessing the value of information for humans in realistic search environments. Subjects search on a topic of their own choice in a data base of fiction in Experiment Four and a data base of technical literature in Experiment Five. After summarizing the experimental results, a conceptual model of how humans value information is presented. The model is then used as a basis for a broad interpretation of the empirical results. Implications of both the empirical and modeling results are considered for the areas of information retrieval logic, system flexibility, retrieval methods, types of aiding, online estimation of information value, and computerizing versus computer-aiding.  相似文献   
994.
The experiences of medical students, residents, and faculty with a computerized literature searching system were evaluated. Third-year medical students, internal medicine and family practice residents, and full-time and voluntary faculty at one medical school had the opportunity to use a full-text and bibliographic medical literature retrieval system free of charge for an eleven-month period. Subjects conducted nearly nine thousand literature searches over a period of 942 system hours. Questionnaire data showed that participants could learn to use and would use an electronic information system, felt capable of using the system, utilized the system for a variety of purposes and in a number of different ways, and viewed the system as a valuable tool in searching the medical literature. The results are discussed in the context of the educational needs of the four user-groups and medical education planning by institutions.  相似文献   
995.
996.
This paper examines the problems of searching for literature of a biographic character and the means of indexing such literature in the Universal Decimal Classification. Recommendations are given on the recording and searching of biographic data in the thematic catalogue.  相似文献   
997.
998.
999.
Polymer-immobilized catalysis has many advantages such as easy recovery and reuse of catalyst. We prepared three novel chiral 1,1′-bi-2-naphthol-Ti coordination polymers with properly designed ligands and Ti(OiPr)4 under mild conditions. The prepared polymers exhibited good activity and excellent enantioselectivity (over 99%ee) in catalyzing the asymmetric oxidation of sulfides. The bridge linker in the polymer and the reaction solvent noticeably affected the enantioselectivity. The chiral coordination poly...  相似文献   
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