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   797352篇
  免费   92674篇
  国内免费   435篇
  2018年   7078篇
  2016年   9827篇
  2015年   13707篇
  2014年   15803篇
  2013年   22165篇
  2012年   25314篇
  2011年   25897篇
  2010年   17442篇
  2009年   16156篇
  2008年   23048篇
  2007年   23964篇
  2006年   22133篇
  2005年   21497篇
  2004年   21248篇
  2003年   20115篇
  2002年   19556篇
  2001年   34312篇
  2000年   34297篇
  1999年   27588篇
  1998年   10197篇
  1997年   10531篇
  1996年   10102篇
  1995年   9301篇
  1994年   9236篇
  1993年   9130篇
  1992年   22594篇
  1991年   21983篇
  1990年   21479篇
  1989年   21081篇
  1988年   19522篇
  1987年   18799篇
  1986年   17381篇
  1985年   17181篇
  1984年   14504篇
  1983年   12543篇
  1982年   9827篇
  1981年   8834篇
  1980年   8425篇
  1979年   13839篇
  1978年   10803篇
  1977年   9989篇
  1976年   9501篇
  1975年   10086篇
  1974年   11177篇
  1973年   10923篇
  1972年   10071篇
  1971年   9236篇
  1970年   7918篇
  1969年   7846篇
  1968年   7235篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
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   
102.
Protein metal-binding sites.   总被引:2,自引:0,他引:2  
Metal ions have a role in a variety of important functions in proteins including protein folding, assembly, stability, conformational change, and catalysis. The presence or absence of a given metal ion is crucial to the conformation or activity of over one third of all proteins. Recent developments have been made in the understanding and design of metal-binding sites in proteins, an important and rapidly advancing area of protein engineering.  相似文献   
103.
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   
104.
105.
106.
Electron microscopy of the adrenal medulla and cortex during the intermediate period of endotoxin shock has revealed severe destructive changes in parenchymal cells. These changes are the reason for synthetic, secretory and trophic disturbances of glandular functions. Ultrastructural lesions indicate that stress exposure exceeds the adaptive capacity of cells, the majority of which are exhausted and killed.  相似文献   
107.
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   
108.
109.
Synthesis of prenylquinones in chloroplasts   总被引:3,自引:0,他引:3  
  相似文献   
110.
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