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   332649篇
  免费   37207篇
  国内免费   188篇
  2018年   2839篇
  2017年   2700篇
  2016年   3874篇
  2015年   5335篇
  2014年   6237篇
  2013年   8753篇
  2012年   9990篇
  2011年   9969篇
  2010年   6795篇
  2009年   6144篇
  2008年   8856篇
  2007年   9296篇
  2006年   8597篇
  2005年   8287篇
  2004年   8004篇
  2003年   7764篇
  2002年   7774篇
  2001年   18141篇
  2000年   18370篇
  1999年   14101篇
  1998年   4227篇
  1997年   4495篇
  1996年   4298篇
  1995年   4003篇
  1994年   3941篇
  1993年   3777篇
  1992年   11480篇
  1991年   11123篇
  1990年   10677篇
  1989年   10240篇
  1988年   9478篇
  1987年   8843篇
  1986年   8077篇
  1985年   7963篇
  1984年   6391篇
  1983年   5568篇
  1982年   4103篇
  1981年   3592篇
  1980年   3353篇
  1979年   6114篇
  1978年   4577篇
  1977年   4128篇
  1976年   3759篇
  1975年   4329篇
  1974年   4500篇
  1973年   4392篇
  1972年   4092篇
  1971年   3501篇
  1970年   3170篇
  1969年   2968篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A method for the extraction and quantitative determination of both the mass and radioactivity of glycolic acid from -14C-labeled leaf tissue is described. The recoveries of both mass and radioactivity from standard [1-14C]glycolic acid solutions averaged 98 percent, and recovery of radioactivity added to plant samples as [1-14C]glycolic acid was over 90 percent after the complete procedure. The method was reliable with total samples containing as little as 130 nmol of glycolic acid. The mass of glycolic acid recovered from sunflower leaf tissue was proportional to the amount of tissue extracted. In experiments with different plant material, the amount of glycolic acid varied between 530 and 1120 nmol/dm-2 of leaf tissue. The specific radioactivity of the glycolic acid in sunflower leaf tissue during photosynthesis in -14CO(2) was never more than 20 percent of the specific radioactivity of the -14CO(2) supplied.  相似文献   
952.
953.
Intermittent illumination increased H2 and C2H4 yields per unit of light from growing cells and from nitrogren-starved cells by 1.7- and 1.35-fold, respectively, as compared with continuous illumination.  相似文献   
954.
The release of alanine by rat diaphragm muscle in vitro.   总被引:13,自引:10,他引:3       下载免费PDF全文
Z discs were isolated from Lethocerus flight muscle by removing the contractile proteins from myofibrils with a solution of high ionic strength. The protein composition of the Z discs was analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis; the major proteins were alpha-actinin, actin and tropomyosin. Z lines were selectively removed from intact myofibrils by digestion with crude lipase and chymotrypsin, but not by purified lipase.  相似文献   
955.
956.
957.
Anaerobic rupture of the benzoic acid ring was investigated. Carbon 4 was converted primarily to carbon dioxide. Following ring rupture during methane fermentation, propanoic acid is an intermediate, and carbon 4 of benzoate becomes its carboxyl.Contribution No. 1285-j, Division of Biology, Kansas State University, Manhattan, KS 66506. This work was supported in part by funds from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506. Paper II of this series is Fina and Fiskin (1960)  相似文献   
958.
Bac. subtilis 168 (BD-25) cells were infected with DNA of plasmide R1drd19 isolated from E. coli strain; transformants resistant to streptomycin (500 microgram/ml) and kanamycin (40 microgram/ml) appeared with the frequency of 2.10(-6). These transformants retained resistance to the mentioned antibiotics stably. A satellite DNA peak was revealed in centrifugation in the density gradient of cesium chloride with ethidium bromide. It was possible to infect cells of Bac. subtilis 168 (BD-25) with plasmide DNA isolated from the transformants. Plasmide transduction with the aid of phages AR9 and PBSI multiplied on the transformant strains was also effected. Physico-chemical analysis of the transformed plasmide DNA was conducted; its molecular weight was determined.  相似文献   
959.
960.
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