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   1769749篇
  免费   180559篇
  国内免费   3195篇
  2021年   19142篇
  2019年   17007篇
  2018年   19771篇
  2017年   18332篇
  2016年   29890篇
  2015年   44469篇
  2014年   52785篇
  2013年   79215篇
  2012年   52108篇
  2011年   43265篇
  2010年   48628篇
  2009年   48714篇
  2008年   39926篇
  2007年   38682篇
  2006年   41433篇
  2005年   41768篇
  2004年   40735篇
  2003年   38222篇
  2002年   35971篇
  2001年   57097篇
  2000年   55298篇
  1999年   48685篇
  1998年   28646篇
  1997年   28722篇
  1996年   27724篇
  1995年   25995篇
  1994年   25553篇
  1993年   25108篇
  1992年   41859篇
  1991年   40280篇
  1990年   38780篇
  1989年   38817篇
  1988年   35739篇
  1987年   34635篇
  1986年   32600篇
  1985年   34096篇
  1984年   31123篇
  1983年   27389篇
  1982年   25271篇
  1981年   23781篇
  1980年   22385篇
  1979年   28107篇
  1978年   24531篇
  1977年   22980篇
  1976年   21825篇
  1975年   22284篇
  1974年   23479篇
  1973年   23476篇
  1972年   20485篇
  1971年   18939篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
221.
With DNA sequencing now getting cheaper more quickly than data storage or computation, the time may have come for genome informatics to migrate to the cloud.  相似文献   
222.
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   
223.
224.
Synthesis of prenylquinones in chloroplasts   总被引:3,自引:0,他引:3  
  相似文献   
225.
226.
227.
228.
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   
229.
The Thom gradient model of morphogenesis poses the followinga posteriori problem: “From the observed morphology of a given natural process (effect) determine the dynamics of the process (cause)”. In this paper we consider the classicala priori problem: “Given the cause (dynamics) determine the effect (resultant morphology)”. We find that in biochemical processes the mechanisms for energy activation, energy-matter interaction and energy dissipation determine the dynamics. Furthermore there exists basic energy mechanisms which drive the equilibrium states through the elementary catastrophes of Thom. A comparison with current theories shows that our models describe open ecological food chains and their dynamical systems generalize the equations of organisation posed by M. Eigen. Work supported by a Research Associateship of the International Centre for Theoretical Physics, P.O.B. 586, Miramare, 34100 Trieste, Italy.  相似文献   
230.
Several topics and concepts in developmental biology, such as induction of secondary axes (as in amphibians), the rules of distal transformation (valid, e.g., for insect and vertebrate limbs), and the rule one piece regenerates, the other one duplicates (valid also for imaginal discs) originally emerged from pioneering studies in hydroids. In addition, one finds phenomena of intercalation, i.e., the insertion of intervening parts when tissues of distant origin are confronted with each other. However, since not only short-range but also long-range interactions contribute to pattern regulation, one observes more regulative flexibility as compared to insect systems.  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