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   1337092篇
  免费   145335篇
  国内免费   646篇
  1483073篇
  2018年   11896篇
  2016年   16413篇
  2015年   22392篇
  2014年   26349篇
  2013年   37682篇
  2012年   42311篇
  2011年   43037篇
  2010年   29568篇
  2009年   27544篇
  2008年   39068篇
  2007年   40405篇
  2006年   37738篇
  2005年   36395篇
  2004年   36078篇
  2003年   34725篇
  2002年   33868篇
  2001年   55215篇
  2000年   54908篇
  1999年   44425篇
  1998年   17347篇
  1997年   17751篇
  1996年   16831篇
  1995年   15799篇
  1994年   15458篇
  1993年   15434篇
  1992年   37293篇
  1991年   36606篇
  1990年   35850篇
  1989年   35011篇
  1988年   32396篇
  1987年   31406篇
  1986年   29140篇
  1985年   29272篇
  1984年   24392篇
  1983年   21398篇
  1982年   16650篇
  1981年   15031篇
  1980年   14165篇
  1979年   23324篇
  1978年   18676篇
  1977年   16937篇
  1976年   16087篇
  1975年   17837篇
  1974年   19238篇
  1973年   18953篇
  1972年   17179篇
  1971年   15687篇
  1970年   13573篇
  1969年   13174篇
  1968年   11672篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Dr A C Srivastava has written to us to describe a case that raises the suggestion that people infected with the human immuno-deficiency virus (HIV) should carry identity cards. We asked two physicians, a general practitioner working with patients with the acquired immune deficiency syndrome (AIDS), and a general practitioner with a special interest in medical ethics to respond to the broad issues raised by Dr Srivastava''s letter.  相似文献   
992.
993.
994.
995.
996.
997.
The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately these data have until now been scattered throughout the literature in a variety of books, proceedings and journals. The data have recently been compiled in a centralized database, LIPIDAT, with a view to providing ready access to the data and to the appropriate literature. LIPIDAT consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes for synthetic and biologically-derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc., on the thermodynamic values. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes comprehensive literature referencing and list of authors, but does not at the present time include article titles. As of this writing, the database is current through June, 1990 and is approaching 10,000 records in length. Each record contains 28 fields. In this paper we report the contents and present an analysis of LIPIDAT as it refers to fully hydrated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). This database subset represents about 7% of all LIPIDAT records. It includes data collected over a 23-year period from 1967 to 1989 and consists of 702 records obtained from 336 articles in 55 different journals. The number of records per year rises steadily beginning in 1971, reaches a maximum of 89 records/year in 1977 and remains relatively constant at 60-70 records/year in the succeeding period. Journals making the greatest contribution to the DMPC subset include Biochimica et Biophysica Acta, Biochemistry, Chemistry and Physics of Lipids and the Biophysical Journal. These four journals account for 71% of the total records in the database subset. The analysis shows that differential scanning calorimetry, electron spin resonance, fluorescence, nuclear magnetic resonance and Raman spectroscopy are the methods most commonly used for DMPC transition temperature determination. An interesting pattern emerges as to the place in time the different methods assume or loose popularity.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
998.
A face fly (Musca autumnalis) population near Wetaskiwin, central Alberta, Canada, was sampled 9 times from 26 July to 29 September 1988 for the early larval stages of Thelazia spp. Of 426 female flies examined, 159 (37%) contained Thelazia spp. (almost exclusively T. skrjabini), with an average worm burden of 4.2 larvae per infected fly. Prevalence ranged from 17 to 56% over 9 collections. This is the first report of Thelazia skrjabini in flies from western North America and the highest Thelazia prevalence in face flies yet reported in North America. The face fly population was also parasitized by Heterotylenchus autumnalis, with a prevalence of 5.5%.  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