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   449592篇
  免费   51918篇
  国内免费   747篇
  502257篇
  2018年   4217篇
  2017年   4040篇
  2016年   5795篇
  2015年   8379篇
  2014年   9759篇
  2013年   13135篇
  2012年   15601篇
  2011年   16032篇
  2010年   10621篇
  2009年   9670篇
  2008年   14065篇
  2007年   14546篇
  2006年   13607篇
  2005年   13015篇
  2004年   13072篇
  2003年   12201篇
  2002年   11848篇
  2001年   18984篇
  2000年   18902篇
  1999年   15144篇
  1998年   5701篇
  1997年   5683篇
  1996年   5405篇
  1995年   5198篇
  1994年   4903篇
  1993年   4900篇
  1992年   12525篇
  1991年   12482篇
  1990年   12245篇
  1989年   11715篇
  1988年   10878篇
  1987年   10248篇
  1986年   9765篇
  1985年   9539篇
  1984年   7910篇
  1983年   6870篇
  1982年   5170篇
  1981年   4669篇
  1980年   4352篇
  1979年   7392篇
  1978年   5994篇
  1977年   5314篇
  1976年   4992篇
  1975年   5790篇
  1974年   6328篇
  1973年   6143篇
  1972年   5476篇
  1971年   5096篇
  1970年   4289篇
  1969年   4214篇
排序方式: 共有10000条查询结果,搜索用时 0 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.
In de-rooted seedlings of Amaranthus caudatus L., betacyanin synthesis induced by white light or cytokinin was inhibited by abscisic acid (ABA) or a mixture of gibberellins A4 and A7 (GA4/7). The GA4/7 and ABA effects were additive. Thus ABA inhibited the cytokinin action but had no effect on the gibberellin response.  相似文献   
993.
994.
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   
995.
996.
997.
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   
998.
Vitamin B6 injected intraperitoneally into rats 400 mg/kg body weight, has produced a statistically significant decrease in GABA level concentrations in hippocampus and cerebellum. Cerebral cortex, caudate nucleus and thalamus have shown the decrease in GABA concentrations, but these changes were not statistically significant. No remarkable behavioural changes were noted under such circumstances. The possible functional meaning of these results is discussed in relation to the role of GABA distribution in different brain regions and development of convulsions.  相似文献   
999.
The hypothesis that limiting the knee-flexion range increases the peak hip-extension moment while transferring from sitting to standing was tested by filming (100 fps) ten normal human volunteers. With the knees flexed 105 degrees from full extension (0 degrees) the mean (+/- 1 S.D.) peak hip-extension moment was 142 (+/- 37) Nm. With the knees flexed only 75 degrees subjects threw their arms and trunks forward to a greater extent, with a peak moment of 253 (+/- 65) Nm (p less than 0.0001). If the peak moments rise to a similar degree in patients with arthritis and limited knee-flexion range, they may accelerate hip joint damage or the loosening of hip endoprostheses.  相似文献   
1000.
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