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   338950篇
  免费   38016篇
  国内免费   189篇
  2018年   2908篇
  2017年   2763篇
  2016年   3964篇
  2015年   5483篇
  2014年   6410篇
  2013年   8983篇
  2012年   10258篇
  2011年   10231篇
  2010年   6999篇
  2009年   6288篇
  2008年   9108篇
  2007年   9527篇
  2006年   8827篇
  2005年   8474篇
  2004年   8222篇
  2003年   7991篇
  2002年   7959篇
  2001年   18307篇
  2000年   18520篇
  1999年   14249篇
  1998年   4328篇
  1997年   4585篇
  1996年   4387篇
  1995年   4087篇
  1994年   4017篇
  1993年   3851篇
  1992年   11590篇
  1991年   11264篇
  1990年   10834篇
  1989年   10348篇
  1988年   9603篇
  1987年   8965篇
  1986年   8200篇
  1985年   8075篇
  1984年   6492篇
  1983年   5654篇
  1982年   4190篇
  1981年   3680篇
  1980年   3438篇
  1979年   6205篇
  1978年   4665篇
  1977年   4201篇
  1976年   3826篇
  1975年   4392篇
  1974年   4581篇
  1973年   4473篇
  1972年   4167篇
  1971年   3568篇
  1970年   3209篇
  1969年   3025篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
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   
972.
973.
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   
974.
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   
975.
976.
977.
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   
978.
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   
979.
980.
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