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   656072篇
  免费   81494篇
  国内免费   366篇
  2016年   7083篇
  2015年   10265篇
  2014年   11918篇
  2013年   17052篇
  2012年   19050篇
  2011年   19337篇
  2010年   13133篇
  2009年   12253篇
  2008年   17257篇
  2007年   17823篇
  2006年   16678篇
  2005年   16219篇
  2004年   15706篇
  2003年   15821篇
  2002年   15113篇
  2001年   27749篇
  2000年   27996篇
  1999年   22608篇
  1998年   8365篇
  1997年   8951篇
  1996年   8625篇
  1995年   8094篇
  1994年   8007篇
  1993年   8143篇
  1992年   19547篇
  1991年   19173篇
  1990年   18445篇
  1989年   18213篇
  1988年   16753篇
  1987年   16456篇
  1986年   15332篇
  1985年   15455篇
  1984年   12997篇
  1983年   11396篇
  1982年   8972篇
  1981年   8275篇
  1980年   7759篇
  1979年   12722篇
  1978年   10141篇
  1977年   9401篇
  1976年   8949篇
  1975年   9794篇
  1974年   10329篇
  1973年   10203篇
  1972年   9401篇
  1971年   8521篇
  1970年   7331篇
  1969年   7225篇
  1968年   6437篇
  1967年   5647篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Maleylated bovine serum albumin (maleyl-BSA) and other polyanionic polymers that are recognized by cell surface receptors on macrophages have been shown to induce chemotaxis, protease secretion, and tumoricidal function in this cell type. In this paper the effect of maleyl-BSA on Ia antigen expression has been evaluated. In a fashion similar to LPS, maleyl-BSA suppressed IFN-gamma-induced expression of Ia in a time- and dose-dependent manner. Also like LPS, maleyl-BSA stimulated the production and secretion of substantial amounts of PGE2 over a 24-hr period. This did not, however, appear to be the primary mechanism by which expression of Ia was suppressed, because co-treatment of the cells with indomethacin, which totally inhibited the production of PGE2, only minimally affected the suppressive activity. Surprisingly, the suppressive activity of both maleyl-BSA and LPS could be largely abrogated by co-treatment of the cells with cyclohexamide during the time period when Ia expression was sensitive to suppression. This effect was selective in that PGE2- or dibutyryl cyclic AMP-induced suppression of Ia expression was not affected by cyclohexamide treatment. The data support the concept that there are multiple molecular mechanisms involved in the negative regulation of IFN-gamma-induced Ia expression in macrophages. Such mechanisms may include, in addition to the synthesis of PGE2 and consequent elevation in intracellular levels of cyclic AMP, one or more proteins made early after treatment with either maleyl-BSA or LPS. Thus the function of some of these early gene products may be to regulate expression of functional genes such as that encoding Ia antigen.  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.
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   
94.
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   
95.
96.
Synthesis of prenylquinones in chloroplasts   总被引:3,自引:0,他引:3  
  相似文献   
97.
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   
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.
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   
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