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   302139篇
  免费   35205篇
  国内免费   153篇
  337497篇
  2018年   2553篇
  2017年   2441篇
  2016年   3301篇
  2015年   4223篇
  2014年   5165篇
  2013年   7119篇
  2012年   8380篇
  2011年   8665篇
  2010年   5574篇
  2009年   5264篇
  2008年   7705篇
  2007年   7956篇
  2006年   7777篇
  2005年   7382篇
  2004年   7250篇
  2003年   7073篇
  2002年   6878篇
  2001年   17488篇
  2000年   17701篇
  1999年   13419篇
  1998年   3950篇
  1997年   4197篇
  1996年   3935篇
  1995年   3560篇
  1994年   3540篇
  1993年   3613篇
  1992年   10469篇
  1991年   10393篇
  1990年   9885篇
  1989年   9708篇
  1988年   9052篇
  1987年   8403篇
  1986年   7633篇
  1985年   7484篇
  1984年   5895篇
  1983年   5149篇
  1982年   3682篇
  1981年   3239篇
  1980年   3097篇
  1979年   5417篇
  1978年   4184篇
  1977年   3810篇
  1976年   3347篇
  1975年   3810篇
  1974年   3988篇
  1973年   3937篇
  1972年   3446篇
  1971年   3210篇
  1970年   2839篇
  1969年   2754篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
D-2 dopamine receptors in the frontal cortex of rat and human   总被引:2,自引:0,他引:2  
D R Liskowsky  L T Potter 《Life sciences》1985,36(16):1551-1559
D-2 dopamine receptors and serotonin receptors in the frontal cortex of rat and human were labelled with 3H-spiroperidol. The D-2 receptors were then distinguished in 4 ways. Dissociation of spiroperidol was biphasic, indicating two populations of sites. Cinanserin in competition with 3H-spiroperidol exhibited high (75%) and low (25%) affinity sites. Dopamine and LY 141865 in competition with 1.25 nM 3H-spiroperidol exhibited high (20-25%) and low (80-75%) affinity sites in the absence of cinanserin, while in the presence of 300 nM cinanserin only the high affinity sites remained. Lesioning of the dopaminergic meso-cortical pathway increased the number of cinanserin-resistant sites by 26%. Thus 3H-spiroperidol binding in the presence of cinanserin can be used to selectively label D-2 receptors in the frontal cortex.  相似文献   
62.
The effects on a cloned DNA fragment carrying an actinomycin resistance determinant on physiological processes in strains of streptomycetes with various potencies in producing this antibiotic, their inactive mutants, and the model strain ofStreptomyces lividans66 were studied. This fragment was shown to modulate bacterial resistance to actinomycin and biosynthesis of antibiotics.  相似文献   
63.
The nucleotide sequences of a partial cDNA and three pseudogenes of human cytochrome c were determined. The complete nucleotide sequences which encode human cytochrome c were constructed on the basis of one of the pseudogenes by in vitro mutagenesis. The constructed human cytochrome c was functionally expressed in Saccharomyces cerevisiae. The recombinant human cytochrome c was purified and characterized.  相似文献   
64.
65.
66.
67.
68.
Intraperitoneal stimulation of adoptively sensitized rats with bacterial antigen promotes the localization of lymphoblasts at the site of antigen deposition. Lymphoblast extravasation activity (LEA) is generated only when specifically immune donor lymphocytes and the recipients of these cells share at least on Ag-B haplotype. However, if the specificity criteria for its formation are satisfied, LEA promotes the local development of lymphoblasts of all available specificities and irrespective of their Ag-B genotype. Allogeneic lymphoblasts do not participate actively in the delayed inflammatory reaction even when they are passively recruited into exudates. The results suggest that LEA is a T cell-derived mediator that amplifies the delayed type hypersensitivity reaction by directing recently activated lymphocytes into lesions.  相似文献   
69.
From three Fouquieria sp. 12 iridoid glucosides were isolated and identified. Eight of these were structurally related to galioside (monotropein methylester), while four were hydroxy substitution products of deoxyloganin. In three cases the glucoside occurred together with the corresponding 10-O-acetate.  相似文献   
70.
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