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   718071篇
  免费   177500篇
  国内免费   30131篇
  2018年   7781篇
  2016年   9944篇
  2015年   13710篇
  2014年   15218篇
  2013年   20828篇
  2012年   23342篇
  2011年   24111篇
  2010年   18174篇
  2009年   21393篇
  2008年   22266篇
  2007年   22656篇
  2006年   20147篇
  2005年   19790篇
  2004年   19456篇
  2003年   18284篇
  2002年   18352篇
  2001年   33270篇
  2000年   31564篇
  1999年   29202篇
  1998年   15591篇
  1997年   15469篇
  1996年   14682篇
  1995年   14281篇
  1994年   13752篇
  1993年   13342篇
  1992年   24946篇
  1991年   24159篇
  1990年   24183篇
  1989年   23535篇
  1988年   21380篇
  1987年   20162篇
  1986年   18595篇
  1985年   18228篇
  1984年   15059篇
  1983年   12769篇
  1982年   10845篇
  1981年   9865篇
  1980年   9321篇
  1979年   14026篇
  1978年   11195篇
  1977年   10599篇
  1976年   9801篇
  1975年   10134篇
  1974年   11181篇
  1973年   11007篇
  1972年   10281篇
  1971年   9557篇
  1970年   8313篇
  1969年   8211篇
  1968年   7312篇
排序方式: 共有10000条查询结果,搜索用时 203 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.
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