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   812122篇
  免费   88344篇
  国内免费   708篇
  2016年   8877篇
  2015年   11592篇
  2014年   13971篇
  2013年   19874篇
  2012年   22127篇
  2011年   22963篇
  2010年   15387篇
  2009年   14343篇
  2008年   20346篇
  2007年   21075篇
  2006年   20108篇
  2005年   19406篇
  2004年   19115篇
  2003年   18546篇
  2002年   18304篇
  2001年   37902篇
  2000年   38575篇
  1999年   30138篇
  1998年   9828篇
  1997年   10334篇
  1996年   9737篇
  1995年   9098篇
  1994年   8973篇
  1993年   9011篇
  1992年   24635篇
  1991年   24277篇
  1990年   23660篇
  1989年   23123篇
  1988年   21792篇
  1987年   20623篇
  1986年   19093篇
  1985年   19402篇
  1984年   15730篇
  1983年   13693篇
  1982年   10297篇
  1981年   9491篇
  1980年   8805篇
  1979年   15098篇
  1978年   11952篇
  1977年   10980篇
  1976年   10301篇
  1975年   11684篇
  1974年   12690篇
  1973年   12624篇
  1972年   11346篇
  1971年   10433篇
  1970年   9162篇
  1969年   8785篇
  1968年   8098篇
  1967年   6956篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Monosomy 21: a new case confirmed by in situ hybridization   总被引:4,自引:0,他引:4  
Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation.  相似文献   
132.
A series of measurements of blood pressure in normotensive and hypertensive subjects showed that measurements made with a sphygmomanometer with the arm dependent by the side were consistently higher than those made with the arm horizontal at heart level. The mean difference in a group of 90 hypertensive outpatients was 11/12 mm Hg. Failure to appreciate the importance of arm position may lead to erroneous measurements of blood pressure. This has important implications for clinical practice and research.  相似文献   
133.
134.
135.
The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards.  相似文献   
136.
137.
Spinosyns A and D are the active ingredients in an insect control agent produced by fermentation of Saccharopolyspora spinosa. Spinosyns are macrolides with a 21-carbon, tetracyclic lactone backbone to which the deoxysugars forosamine and tri-O-methylrhamnose are attached. The spinosyn biosynthesis genes, except for the rhamnose genes, are located in a cluster that spans 74 kb of the S. spinosa genome. DNA sequence analysis, targeted gene disruptions and bioconversion studies identified five large genes encoding type I polyketide synthase subunits, and 14 genes involved in sugar biosynthesis, sugar attachment to the polyketide or cross-bridging of the polyketide. Four rhamnose biosynthetic genes, two of which are also necessary for forosamine biosynthesis, are located outside the spinosyn gene cluster. Duplication of the spinosyn genes linked to the polyketide synthase genes stimulated the final step in the biosynthesis — the conversion of the forosamine-less pseudoaglycones to endproducts. Duplication of genes involved in the early steps of deoxysugar biosynthesis increased spinosyn yield significantly. Journal of Industrial Microbiology & Biotechnology (2001) 27, 399–402. Received 31 May 2001/ Accepted in revised form 09 July 2001  相似文献   
138.
In 1990 and 1994, two males of Golden Eagles were found with small lead particles in their stomachs. Both individuals died soon after they had been taken sitting on the soil in bad condition. There are some findings of dead eagles in the same area which showed no sign of having been injured. The two cases of presumed lead poisoning coincide with intense efforts to reduce the number of ChamoixRupicapra rupicapra by hunting. The bullets used contain a nucleus of lead and eagles were seen taking the entrails of the shot chamoix.  相似文献   
139.
140.
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