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   337733篇
  免费   37809篇
  国内免费   189篇
  2018年   2892篇
  2017年   2741篇
  2016年   3978篇
  2015年   5455篇
  2014年   6378篇
  2013年   8943篇
  2012年   10218篇
  2011年   10200篇
  2010年   6973篇
  2009年   6290篇
  2008年   9047篇
  2007年   9517篇
  2006年   8776篇
  2005年   8467篇
  2004年   8189篇
  2003年   7949篇
  2002年   7952篇
  2001年   18301篇
  2000年   18500篇
  1999年   14199篇
  1998年   4281篇
  1997年   4544篇
  1996年   4362篇
  1995年   4058篇
  1994年   3993篇
  1993年   3816篇
  1992年   11591篇
  1991年   11204篇
  1990年   10757篇
  1989年   10342篇
  1988年   9577篇
  1987年   8918篇
  1986年   8147篇
  1985年   8028篇
  1984年   6463篇
  1983年   5626篇
  1982年   4171篇
  1981年   3642篇
  1980年   3410篇
  1979年   6192篇
  1978年   4626篇
  1977年   4179篇
  1976年   3830篇
  1975年   4396篇
  1974年   4560篇
  1973年   4448篇
  1972年   4138篇
  1971年   3546篇
  1970年   3204篇
  1969年   3007篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
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   
992.
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   
993.
994.
995.
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   
996.
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   
997.
998.
999.
Summary Linkage analysis has been carried out in six German families with autosomal dominantly inherited myotonia congenita (Thomsen's disease) using five chromosome 19 markers known to be linked to the gene for myotonic dystrophy (DM). Two of the markers, APOC1 and APOC2, are tightly linked to DM. Close linkage between these markers and myotonia congenita (MC) has been excluded to a distance of 9cM (z=-2.158). These data support the clinical suggestion that MC and DM are non-allelic disorders.  相似文献   
1000.
This study was presented in part at the annual meeting of the Wilderness Medical Society at Aspen, Colorado, in August 1986 and at “Mountain Medicine 1987,” Leavenworth, Washington, in November 1987.We questioned 220 injured rock climbers or their partners seen consecutively at the Yosemite (California) Medical Clinic over 3 ½ years regarding details of their accidents. Injury type and location were extracted from medical records and severity quantified. The National Park Service rescued 27% of the climbers. Injured climbers were characteristically male (88%) and experienced (mean 5.9 years) and typically fell while leading climbs (66%). Among 451 injuries, 50% were to the skin or subcutaneous tissues, while 28% involved the lower extremity and were predominantly fractures. In terms of each climber''s most severe injury (n = 220), 45% involved the lower extremities (30% from the ankle alone). Head injury or hypothermia caused 12 of 13 fatalities, showing the lowest case-fatality rate reported to date among injured climbers (6%). Rescue personnel successfully managed airways in victims of head injuries, anticipated and treated complications of hypothermia, and stabilized fractures. Victims requiring immediate extensive surgical intervention or blood transfusion usually died before rescue could be effected.  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