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   282286篇
  免费   24713篇
  国内免费   265篇
  307264篇
  2018年   3726篇
  2017年   3525篇
  2016年   4753篇
  2015年   5426篇
  2014年   6355篇
  2013年   8931篇
  2012年   9960篇
  2011年   10416篇
  2010年   6972篇
  2009年   5983篇
  2008年   8768篇
  2007年   8950篇
  2006年   8618篇
  2005年   7949篇
  2004年   7859篇
  2003年   7539篇
  2002年   7306篇
  2001年   12903篇
  2000年   12825篇
  1999年   9832篇
  1998年   2955篇
  1997年   2932篇
  1996年   2892篇
  1995年   2682篇
  1994年   2578篇
  1993年   2448篇
  1992年   7601篇
  1991年   7340篇
  1990年   7387篇
  1989年   7182篇
  1988年   6649篇
  1987年   6300篇
  1986年   5625篇
  1985年   5931篇
  1984年   4668篇
  1983年   4050篇
  1982年   2817篇
  1981年   2618篇
  1980年   2427篇
  1979年   4343篇
  1978年   3268篇
  1977年   3008篇
  1976年   2944篇
  1975年   3403篇
  1974年   3655篇
  1973年   3680篇
  1972年   3215篇
  1971年   2990篇
  1970年   2687篇
  1969年   2453篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
971.
972.
973.
Close inspection of surface bone in skulls of Neanderthal man reveals weathering cracks extensive enough in one specimen, La Chapelle-aux-Saints, to allow preliminary analysis of major patterns of orientation and to make inferences about functional relationships of structures. The fine structure of the bone of the brow ridges is very different from the rest of the skull in the two adults examined, having a peculiar vermiculate surface pattern. Weathering cracks do not appear in this region. This indicates that Neanderthal brow ridges are not closely related to normal mechanical forces such as chewing exertion. It may, however, give further support to theories of Neanderthal brow ridges as protection for the eyes. The localized structure of bone often differs from region to region, and offers new possibilities for the analysis of both contemporary and fossil forms.  相似文献   
974.
975.
Human metallothionein-specific riboprobes.   总被引:2,自引:1,他引:1       下载免费PDF全文
  相似文献   
976.
977.
978.
Clinical, bacteriological, serological and epidemiological studies of ozena morbidity among the population of Minsk were carried out in 1970-1980. On January 1, 1981, the ozena morbidity rate among the inhabitants of Minsk was 26.72%. Ozena was found to affect mainly children and women. A wide spread of the family foci of this disease (31.68%) was revealed. The results of this study indicate that the source of K. ozaenae is a sick person who begins to excrete the bacteria in the prodromal period of the disease and may continue to excrete them for many years. The transfer of K. ozaenae occurs probably by droplet or contact infection. The droplet infection is less active in the absence of symptoms (coughing, sneezing) facilitating excretion of the infective agent into the air and in cases of the low susceptibility of persons to ozena. The main measures for controlling ozena are the timely detection and sanitation of the sources of ozena, as well as the current disinfection of the infection foci in apartments.  相似文献   
979.
The reactions of NADPH oxidation by quinones and inorganic complexes catalyzed by NADPH: adrenodoxin reductase were studied. The catalytic constant for the enzyme at pH 7.0 is 20-25 s-1; the oxidative constants for the quinones vary from 5 X 10(5) to 1.1 X 10(3) M-1 s-1 and show an increase with a rise in the one-electron acceptor reduction potential. The mode of adrenodoxin reductase interaction with oxyquinones differs from that of the enzyme interaction with alkyl-substituted quinones and inorganic complexes. NADPH competitively inhibits electron acceptors, whereas NADP+ is a competitive inhibitor of NADPH and a uncompetitive inhibitor of electron acceptors. (Ki = 25 microM). The depth of FAD incorporation into the enzyme molecule as calculated according to the outer sphere electron transfer theory is 6.1 A.  相似文献   
980.
The addition of ATP or 3,5-AMP (but not UTP, GTP, CTP, AMP, 2,3-AMP, ADP, inorganic pyrophosphate) at a final concentration of 10(-1) M into streptokinase solution, pH 7.0 or 9.5, causes a dramatic inhibition of streptokinase-induced fibrinolysis. The specificity of ATP effect is fully lost at pH 3.0, when all nucleotides completely inhibit the activating function of streptokinase. Ribose-5-phosphate causes a similar effect at pH 3.0. The character of nucleotide action on the activating function of streptokinase considerably differs from their influence on proteolytic reactions.  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