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   18331篇
  免费   44篇
  国内免费   70篇
系统科学   114篇
丛书文集   277篇
教育与普及   33篇
理论与方法论   115篇
现状及发展   8652篇
研究方法   806篇
综合类   8245篇
自然研究   203篇
  2013年   112篇
  2012年   235篇
  2011年   434篇
  2010年   91篇
  2008年   258篇
  2007年   282篇
  2006年   337篇
  2005年   304篇
  2004年   425篇
  2003年   336篇
  2002年   369篇
  2001年   609篇
  2000年   525篇
  1999年   376篇
  1992年   303篇
  1991年   227篇
  1990年   250篇
  1989年   247篇
  1988年   220篇
  1987年   246篇
  1986年   286篇
  1985年   353篇
  1984年   246篇
  1983年   238篇
  1982年   212篇
  1981年   230篇
  1980年   243篇
  1979年   591篇
  1978年   497篇
  1977年   469篇
  1976年   362篇
  1975年   432篇
  1974年   588篇
  1973年   473篇
  1972年   506篇
  1971年   585篇
  1970年   720篇
  1969年   563篇
  1968年   557篇
  1967年   557篇
  1966年   457篇
  1965年   388篇
  1964年   125篇
  1959年   194篇
  1958年   336篇
  1957年   251篇
  1956年   192篇
  1955年   193篇
  1954年   196篇
  1948年   129篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
(3H)-Ouabain binding to liver and kidney preparations was utilized to estimate the number of Na+, K+-ATPase enzyme units in livers and kidneys from rats fed 2% corn oil supplemented or fat-free diets. The specific (3H)-ouabain binding in liver and kidney preparations from fatty acid deficient rats was increased approximately 40%, but the affinity of the binding sites for ouabain (Kd-value) remained unchanged. The increased concentration of Na+, K+-ATPase enzyme units observed in the essential fatty acid deficient rats may contribute to the reduced body fat accumulation and elevated heat production observed in these animals.  相似文献   
142.
Summary An intermediate stage between the elementary and the initial bodies of theRickettsiella genus is defined as the beginning of an intracellular cycle. It is characterized by several structural changes in the dense elementary body: the cytoplasm becomes less electron-dense; thus, the nucleoid and the ribosomes are visible. The inner layer of the cell-wall becomes progressively clearer and the trilamellar structure of the inner and outer membranes appears distinctly. Preinitial body is proposed as name of this stage of development.  相似文献   
143.
Summary 2 new limonoid-type terpenes have been isolated from an aqueous extract of seeds produced by the Eastern Himalayan (India) plantAphanamixis grandifolia Bl. By interpreting principally mass spectral and nuclear magnetic resonance data, the structures of 12-hydroxyamoorastatin (2b) and amoorastatone (3) were elucidated. Unequivocal evidence for the 12-hydroxyamoorastatin structural assignment was obtained by chemical conversion to sendanin (4). Amoorastatin derivative2b was found to significantly inhibit growth of the murine P388 lymphocytic leukemia cell lines but amoorastatone in the same system was inactive. In a comparative biological study, sendanin (4) and anthothecol (7) were also found significantly to inhibit growth of the P388 cell line, while rohitukin (8) and limonin (9) were found to be inactive.Part 63 of the series Antineoplastic Agents. For the previous contribution refer to G.R. Pettit, T.S. Krupa and R.M. Reynolds, Int. J. Peptide Protein Res., in preparation. The present investigation was supported in part by Public Health Research Grant No. CA-16049-05 from the National Cancer Institute, the Fannie E. Rippel Foundation, Mrs Mary Dell Pritzlaff, the Spencer T. and Ann W. Olin Foundation, Mr John F. Schmidt, and the Phoenix Coca-Cola Bottling Company.  相似文献   
144.
Summary Viable cerebellar perikarya of mixed cell type obtained from 7–9-day-old rats were maintained in monolayer culture for up to 12 days. During this time extensive neurite formation and outgrowth occurred. The large majority of the cells developing in culture were tentatively identified as granule neurons. This identification was based on the large number isolated from the starting tissue, and the cells general morphological features in culture such as perikaryal and nuclear size, the bipolar nature of neurite extension, and their migratory behaviour.D.N. Currie was supported by a grant from Hoechst Pharmaceuticals, Ld, U.K.J.C. was supported by an S.R.C. Grant to S.P.R. RoseThe authors would like to thank Kathleen Tear for excellent technical assistance and members of the Brain Research Group for helpful discussions.  相似文献   
145.
Summary The insulinemic response to 1 g of tolbutamide i.v. is greatly enhanced (+145%) after a 60-min infusion of the -lytic dihydrogenated ergot alkaloid, dihydroergocristine (83.3 m/min, corresponding to a total dose of 5 mg) in 7 healthy subjects. No differences are observed in the glycemic responses.Acknowledgment. The authors are grateful to Mr Franco Della Sala, M.D., for his skillful technical assistance.  相似文献   
146.
147.
High-frequency generalised transduction by bacteriophage T4   总被引:30,自引:0,他引:30  
Wilson GG  Young KY  Edlin GJ  Konigsberg W 《Nature》1979,280(5717):80-82
  相似文献   
148.
149.
Summary In 10 human subjects plasma dopamine--hydroxylase activity was found in the adrenal vein blood to be as high as in the periphery of the circulation. Adrenaline concentration in the adrenal vein blood was in the mean 170 times, noradrenaline concentration 11 times and dopamine concentration little higher than levels in the periphery.This study was supported by the Deutsche Forschungsgemeinschaft.  相似文献   
150.
G A Hashim 《Nature》1975,256(5518):953-955
  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