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   649880篇
  免费   80784篇
  国内免费   361篇
  2016年   6988篇
  2015年   10104篇
  2014年   11768篇
  2013年   16858篇
  2012年   18828篇
  2011年   19114篇
  2010年   13008篇
  2009年   12103篇
  2008年   17046篇
  2007年   17579篇
  2006年   16449篇
  2005年   16014篇
  2004年   15520篇
  2003年   15644篇
  2002年   14951篇
  2001年   27653篇
  2000年   27860篇
  1999年   22458篇
  1998年   8284篇
  1997年   8896篇
  1996年   8247篇
  1995年   8019篇
  1994年   7929篇
  1993年   8064篇
  1992年   19416篇
  1991年   19065篇
  1990年   18324篇
  1989年   18105篇
  1988年   16654篇
  1987年   16359篇
  1986年   15222篇
  1985年   15366篇
  1984年   12890篇
  1983年   11307篇
  1982年   8908篇
  1981年   8216篇
  1980年   7690篇
  1979年   12648篇
  1978年   10065篇
  1977年   9350篇
  1976年   8871篇
  1975年   9722篇
  1974年   10279篇
  1973年   10132篇
  1972年   9328篇
  1971年   8471篇
  1970年   7265篇
  1969年   7169篇
  1968年   6395篇
  1967年   5594篇
排序方式: 共有10000条查询结果,搜索用时 216 毫秒
91.
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   
92.
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   
93.
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   
94.
95.
Synthesis of prenylquinones in chloroplasts   总被引:3,自引:0,他引:3  
  相似文献   
96.
The metabolism of the cholestatic triterpene acid reduced lantadene A has been studied in susceptible and resistant rats and in sheep which are susceptible to intoxication. Sheep and susceptible female rats produced a similar major metabolite and rats produced a second metabolite which was a glucuronide. These metabolites were also observed in extracts of bile canalicular membranes prepared from intoxicated rats. Resistant male and female rats produced a similar major metabolite which was different to those synthesized by susceptible animals. It is concluded that in rats and sheep there is a correlation between the type of metabolites produced in the liver and the susceptibility to intoxication by reduced lantadene A.  相似文献   
97.
98.
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   
99.
Pharmacology of DMSO   总被引:10,自引:0,他引:10  
A wide range of primary pharmacological actions of dimethyl sulfoxide (DMSO) has been documented in laboratory studies: membrane penetration, membrane transport, effects on connective tissue, anti-inflammation, nerve blockade (analgesia), bacteriostasis, diuresis, enhancement or reduction of the effectiveness of other drugs, cholinesterase inhibition, nonspecific enhancement of resistance to infection, vasodilation, muscle relaxation, antagonism to platelet aggregation, and influence on serum cholesterol in experimental hypercholesterolemia. This substance induces differentiation and function of leukemic and other malignant cells. DMSO also has prophylactic radioprotective properties and cryoprotective actions. It protects against ischemic injury.  相似文献   
100.
The absence of centromeric bands in the karyotype of Felis catus is confirmed. It is also confirmed that no satellite band is visible in CsCl density gradients. However, a satellite is observed both by recentrifuging the fraction of the DNA that bands at high density in CsCl and by using netropsin to enhance the resolution of a CsCl gradient containing total F. catus DNA. The satellite, about 0.5% of total DNA, was isolated by repeated centrifugation in CsCl alone and in CsCl with netropsin. Netropsin was removed and a pure satellite DNA obtained. The reassociation kinetics (C0t1/2 less than 10(-3) M . s) show that the satellite is of the simple sequence type and hence a candidate for centromeric heterochromatin. Its cytological localisation awaits in situ hybridisation experiments.  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