全文获取类型
收费全文 | 18772篇 |
免费 | 217篇 |
国内免费 | 119篇 |
专业分类
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 |
出版年
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.
R J Markert A J Parisi H V Barnes S Cohen K Goldenberg L E Mieczkowski M Dunn R M Siervogel 《Bulletin of the Medical Library Association》1989,77(2):133-138
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.
E. R. Sukiasyan 《Scientific and Technical Information Processing》2009,36(5):262-266
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.
Design and synthesis of chiral Ti-1,1′-bi-2-naphthol coordination polymers for heterogeneous catalytic asymmetric oxidation of sulfides
下载免费PDF全文
![点击此处可从《重庆大学学报(英文版)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
袁小亚 《重庆大学学报(英文版)》2008,(3)
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.