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   723404篇
  免费   84712篇
  国内免费   436篇
  2018年   6195篇
  2016年   8656篇
  2015年   12457篇
  2014年   14300篇
  2013年   20104篇
  2012年   23018篇
  2011年   23137篇
  2010年   15554篇
  2009年   14195篇
  2008年   20373篇
  2007年   21246篇
  2006年   19378篇
  2005年   18957篇
  2004年   18390篇
  2003年   17630篇
  2002年   17285篇
  2001年   35433篇
  2000年   35831篇
  1999年   28220篇
  1998年   9586篇
  1997年   10048篇
  1996年   9320篇
  1995年   8820篇
  1994年   8880篇
  1993年   8595篇
  1992年   22891篇
  1991年   22055篇
  1990年   21324篇
  1989年   20854篇
  1988年   19003篇
  1987年   18080篇
  1986年   16621篇
  1985年   16356篇
  1984年   13558篇
  1983年   11791篇
  1982年   9017篇
  1981年   8083篇
  1980年   7501篇
  1979年   12948篇
  1978年   9845篇
  1977年   8986篇
  1976年   8331篇
  1975年   9105篇
  1974年   9722篇
  1973年   9546篇
  1972年   8698篇
  1971年   7807篇
  1970年   6778篇
  1969年   6508篇
  1968年   5804篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The effect of the chromosomal ends of Tetrahymena thermophila on the stability of linear transforming molecules in the filamentous fungus Podospora anserina was tested. A derivative of an integrative vector for this fungus has been constructed, so that after linearization, the ends of the plasmid are the telomeric sequences of T. thermophila. After transformation, this linear molecule was maintained as an extrachromosomal plasmid with no integrated copies in about 50% of the transformants. Under selective conditions, there was approximately one linear molecule per 5 to 10 nuclei, and these extrachromosomal molecules were rapidly lost under nonselective conditions. The circular plasmid carrying an inverted repeat of T. thermophila telomeres could be linearized and processed in vivo.  相似文献   
92.
Experiments were made on rabbit fed an atherogenic diet (0.5 g/kg cholesterol) singly for 15 and 24 h and repeatedly for 3, 9 and 30 days. At early stages of lipid metabolism distress the interrelationship was established between blood rheological disorders and microcirculatory abnormalities. The dependence of the initial reaction of some rheological characteristics on their initial level was marked.  相似文献   
93.
94.
95.
OBJECTIVE--To test the hypothesis that farmers are at high risk of hip osteoarthritis and to investigate possible causes for such a hazard. DESIGN--Cross sectional survey. SETTING--Five rural general practices. SUBJECTS--167 male farmers aged 60-76 and 83 controls from mainly sedentary jobs. All those without previous hip replacement underwent radiography of the hip. MAIN OUTCOME MEASURES--Hip replacement for osteoarthritis or radiological evidence of hip osteoarthritis. RESULTS--Prevalence of hip osteoarthritis was higher in farmers than controls and especially in those who had farmed for over 10 years (odds ratio 9.3, 95% confidence interval 1.9 to 44.5). The excess could not be attributed to any one type of farming, and heavy lifting seems the likely explanation. CONCLUSIONS--Manual handling in agriculture should be limited where possible. Consideration should be given to making hip osteoarthritis a prescribed industrial disease in farmers. There may be wider implications for the prevention of hip osteoarthritis in the general population.  相似文献   
96.
97.
98.
99.
An earlier report (1) of an adverse effect of high doses of oxytocin on human memory included results of studies on women receiving oxytocin as part of the treatment to induce 2nd trimester therapeutic abortion. These women served as their own controls. We have now been able to study a group of women who have been treated in all ways like the original group, with the exception that they did not receive oxytocin. The results from this external control corroborate the finding that oxytocin affected memory.  相似文献   
100.
The linear sweep voltammetric method is used as a new approach for kinetic determination with enzymes accepting reversible redox couples as cosubstrate. A monolayer of hydrogenase molecules is grafted onto a glassy carbon electrode which is both the support of the enzyme and the detector of the activity. Reduced viologen concentration in the enzyme microenvironment is controlled by the electrode potential. The catalytic current produced by the enzyme allows an easy kinetic constant determination without the classical constraints found in hydrogenase kinetic measurements.  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