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   763429篇
  免费   87245篇
  国内免费   565篇
  2018年   6830篇
  2017年   6393篇
  2016年   9608篇
  2015年   13888篇
  2014年   15871篇
  2013年   22174篇
  2012年   25496篇
  2011年   25444篇
  2010年   16971篇
  2009年   15317篇
  2008年   22325篇
  2007年   23218篇
  2006年   21331篇
  2005年   20787篇
  2004年   20202篇
  2003年   19292篇
  2002年   18925篇
  2001年   36216篇
  2000年   36678篇
  1999年   28916篇
  1998年   9920篇
  1997年   10330篇
  1996年   9914篇
  1995年   9062篇
  1994年   9138篇
  1993年   8858篇
  1992年   23377篇
  1991年   22525篇
  1990年   21787篇
  1989年   21305篇
  1988年   19410篇
  1987年   18439篇
  1986年   16970篇
  1985年   16692篇
  1984年   13873篇
  1983年   12069篇
  1982年   9265篇
  1981年   8340篇
  1980年   7693篇
  1979年   13243篇
  1978年   10092篇
  1977年   9192篇
  1976年   8518篇
  1975年   9367篇
  1974年   9962篇
  1973年   9767篇
  1972年   8932篇
  1971年   8030篇
  1970年   6954篇
  1969年   6707篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
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   
93.
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   
94.
95.
96.
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   
97.
98.
99.
100.
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   
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