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   731887篇
  免费   82288篇
  国内免费   899篇
  2018年   6591篇
  2017年   6303篇
  2016年   9058篇
  2015年   12828篇
  2014年   15019篇
  2013年   20639篇
  2012年   23994篇
  2011年   24261篇
  2010年   16349篇
  2009年   14819篇
  2008年   21485篇
  2007年   22265篇
  2006年   20803篇
  2005年   19936篇
  2004年   19734篇
  2003年   18745篇
  2002年   18420篇
  2001年   33546篇
  2000年   33774篇
  1999年   26665篇
  1998年   9261篇
  1997年   9413篇
  1996年   8933篇
  1995年   8468篇
  1994年   8189篇
  1993年   8020篇
  1992年   22022篇
  1991年   21698篇
  1990年   21026篇
  1989年   20276篇
  1988年   18837篇
  1987年   17617篇
  1986年   16598篇
  1985年   16340篇
  1984年   13417篇
  1983年   11680篇
  1982年   8732篇
  1981年   7776篇
  1980年   7246篇
  1979年   12700篇
  1978年   10027篇
  1977年   8936篇
  1976年   8311篇
  1975年   9578篇
  1974年   10294篇
  1973年   10054篇
  1972年   9049篇
  1971年   8200篇
  1970年   7169篇
  1969年   6892篇
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
81.
S-adenosyl-L-homocysteine (S-AH), a potent inhibitor of biological transmethylation, decreased the response of rat retina adenylate cyclase to dopamine and to 2-amino-6, 7-dihydroxytetrahydronaphtalene (ADTN). This effect appeared for 10?7M of S-adenosyl-L-homocysteine and was linear for concentration ranging to 10?4M. S-adenosyl-L-homocysteine did not decrease the cyclic AMP accumulation with sodium fluoride, a non specific adenylate cyclase activator. On the other hand, the incorporation of methyl group was reduced in rat retina homogenates by S-adenosyl-L-homocysteine. These findings suggest that the activity of the dopamine dependent adenylate cyclase is linked to a methylation process.  相似文献   
82.
83.
84.
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   
85.
86.
87.
Puerto Rican populations of two species of sea anemones (Bunodosoma cavernata and B. granulifera) which had previously been considered one were assayed electrophoretically for enzymes encoded by 12 loci. The two species shared no common allozymes at 6 of the 12 loci. Genetic distance and identity values based on these allozymes were computed for the Puerto Rican populations and for B. cavernata from Florida and B. granulifera from Panama. The Puerto Rican populations of both species had much higher genetic identities for their geographically distant conspecifics than for each other. These results indicate that the two species are reproductively isolated and should be considered as separate valid species. Average heterozygosities are presented which are the first published for coelenterate species.  相似文献   
88.
89.
90.
Previous studies have shown that the concentration of red blood cell (RBC) magnesium is significantly lower in subjects carrying an HLA-BW 35 antigen (p less than 0.001) than in non-carriers. As this finding might be related to modifications of the RBC membrane sialoglycoconjugates, RBC sialic acid was comparatively determined in BW 35+ and BW 35- subjects. Pyruvate-kinase activity mean RBC volume, and reticulocyte count have also been determined in order to estimate whether some significant variations in the level of these age markers could be detected between the HLA BW 35+ and BW 35- subjects. A significant negative correlation between sialic acid and RBC magnesium concentrations was observed for the whole population tested (n 57, p less than 0.005), 61% of the BW 35+ and only 25% of the BW 35- individuals having sialic acid values above, and magnesium values below the overall mean (p less than 0.01). The variance of mean RBC volume was also larger for the BW 35+ group. Other determinations did not show any significant variations, suggesting that the results are not related to RBC age.  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