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   17955篇
  免费   116篇
  国内免费   121篇
系统科学   98篇
丛书文集   118篇
教育与普及   34篇
理论与方法论   49篇
现状及发展   8233篇
研究方法   851篇
综合类   8606篇
自然研究   203篇
  2012年   288篇
  2011年   469篇
  2010年   121篇
  2009年   117篇
  2008年   318篇
  2007年   380篇
  2006年   351篇
  2005年   340篇
  2004年   407篇
  2003年   298篇
  2002年   358篇
  2001年   624篇
  2000年   626篇
  1999年   445篇
  1992年   329篇
  1991年   288篇
  1990年   295篇
  1989年   269篇
  1988年   287篇
  1987年   307篇
  1986年   288篇
  1985年   373篇
  1984年   319篇
  1983年   252篇
  1982年   244篇
  1981年   270篇
  1980年   260篇
  1979年   605篇
  1978年   507篇
  1977年   401篇
  1976年   404篇
  1975年   399篇
  1974年   452篇
  1973年   381篇
  1972年   405篇
  1971年   494篇
  1970年   615篇
  1969年   443篇
  1968年   476篇
  1967年   478篇
  1966年   408篇
  1965年   311篇
  1964年   126篇
  1959年   134篇
  1958年   252篇
  1957年   168篇
  1956年   160篇
  1955年   132篇
  1954年   143篇
  1948年   110篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Summary Effects of N6, O2 dibutyryl adenosine 3,5-cyclic monophosphate (db-cAMP) and theophylline (Th) on cultured rat embryonic shields were studied. After addition of db-cAMP to the culture medium, an increase of the weight of explants and of the incidence of the skeletal muscle was observed. Theophylline seems to be ineffective.  相似文献   
92.
Summary Neurohypophyseal blood flow increases in water-deprived rats. This increase is independent of vasopressin release, since it occurs even in rats with hereditary defect of hypothalamic vasopressin synthesis.Acknowledgment. The technical assistance of D. Vilimovská is acknowledged.  相似文献   
93.
Summary The binding of coumarin to serum proteins of the rat has been demonstrated. Of the total bound coumarin (37% of injected dose), 36% was bound to the slow and fast 1 globulins, 11% to the post albumins, 10% to globulin and 9% to albumin.  相似文献   
94.
Summary Abnormal-8-tetrahydrocannabidiol (ABN-8-THC) failed to elicit central nervous system and cardiovascular effects in laboratory animals. Abnormal-cannabidiol (ABN-CBD) was also devoid of overt behavioral effects but produced marked hypotension with only slight bradycardia in anesthesized dogs.Acknowledgment. This work was supported by NIDA (grant No. DA-00574-01 and DA-00490) and Virginia Heart Society (grant No. RR-05697)  相似文献   
95.
Summary Naja mossambica pallida venom administered i.v. (300 /kg) produces an initial brief fall in blood pressure, due to a direct myocardial depressant effect, and a sustained fall due to central depressant effect.This study was supported by University of Nairobi research grants (670–376). We also thank Mr E. Njogu for photographic assistance.  相似文献   
96.
Proton pump coupled to cytochrome c oxidase in mitochondria.   总被引:1,自引:0,他引:1  
M K Wikstrom 《Nature》1977,266(5599):271-273
  相似文献   
97.
Summary The free radical oxidation of 1 and 6-tetrahydrocannabinol has been examined by spin trapping techniques and intermediates that would lead to cannabinol have been trapped. The 1st step in the oxidation of 1-THC involves the removal of 3-H, while for 6-THC, either 2-H or 5-H. Intermediates were isolated which could be pyrolysed to the diene and cannabinol.  相似文献   
98.
Summary Leydig cell nuclear area and 5-3-hydroxysteroid dehydrogenase activity were increased in the testis ofBufo melanostictus 2 days after a single short-term cold exposure. Both parameters returned to normal values 4 days later.  相似文献   
99.
Summary 4-Isothiocyanato-4-nitrodiphenylamine possessed anthelmintic activity againstNippostrongylus dubius andHymenolepis nana in mice andH. diminuta in rats as determined by both egg counts and recovery of parasites at autopsy. No activity was detected against the cestode,Spirometra mansonoides, in cats.This investigation was supported in part by grants AI-10512 and AI-09483 from the National Institutes of Health. The authors are indebted to Dr P.P. Weinstein for providing animals infected withSpirometra mansonoides.  相似文献   
100.
The antibodies against estrogen receptor were obtained after injecting Rabbits with a cytoplasmic receptor fraction isolated from Calf uterus. The estrogen receptor was partially proteolysed by the action of trypsin and subsequently purified by affinity chromatography (purification 4,000 to 10,000 fold, to a purity of 5-20%). The affinity of the antibody for the proteolysed receptor is KD approximately 1 nM and serum titres have reached values of approximately 50 nM. The values remained constant after the third injection. Preliminary results indicate that the antibody has approximately the same affinity for "native" cytoplasmic estrogen receptor from Calf uterus, as well as for the "trypsinized" forms of estrogen receptor isolated from Calf uterine cytosol and Hen oviduct nuclei.  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