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   1099782篇
  免费   88395篇
  国内免费   1350篇
  1189527篇
  2021年   17512篇
  2020年   12505篇
  2019年   16057篇
  2018年   16518篇
  2017年   15263篇
  2016年   27125篇
  2015年   41667篇
  2014年   49591篇
  2013年   75857篇
  2012年   28538篇
  2011年   14938篇
  2010年   40605篇
  2009年   42888篇
  2008年   15338篇
  2007年   12509篇
  2006年   19454篇
  2005年   20609篇
  2004年   20000篇
  2003年   17751篇
  2002年   15999篇
  2001年   19000篇
  2000年   15860篇
  1999年   20023篇
  1998年   23670篇
  1997年   23421篇
  1996年   23267篇
  1995年   21383篇
  1994年   21284篇
  1993年   20268篇
  1992年   18195篇
  1991年   16634篇
  1990年   15406篇
  1989年   16664篇
  1988年   15179篇
  1987年   14329篇
  1986年   13837篇
  1985年   15969篇
  1984年   17455篇
  1983年   15590篇
  1982年   17877篇
  1981年   17507篇
  1980年   16270篇
  1979年   13363篇
  1978年   13885篇
  1977年   13609篇
  1976年   13036篇
  1975年   11887篇
  1974年   11909篇
  1973年   12423篇
  1972年   10175篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
951.
Temperature affects both the biology and morphology of mosquito vectors. Geometric morphometrics is a useful new tool for capturing and analyzing differences in shape and size in many morphological parameters, including wings. We have used this technique for capturing the differences in the wings of the malaria vector Anopheles superpictus, using cohorts reared at six different constant temperatures (15°, 20°, 25°, 27°, 30°, and 35° C) and also searched for potential correlations with the life tables of the species. We studied wing shape in both male and female adults, using 22 landmarks on the wing in relation to ecological parameters, including the development rate. The ecological zero was calculated as 9.93° C and the thermal constant as 296.34 day‐degrees. The rearing temperature affects egg, larval, and pupal development and also the total time from egg to adult. As rearing temperatures increased, longevity decreased in both sexes. In An. superpictus, Ro value and productivity correlated with the statistically significant gradual deformations in the wing shape related to size in both sexes. These deformations directly linked to differences in immature rearing temperatures. Analysis using PCA and UPGMA phenograms showed that although wings of females became narrower dorsoventrally as the temperature increased, they became broader in males. Comparisons of the wing landmarks indicated the medial part of the wing was most affected by larval rearing temperatures, showing relatively more deformations. Algorithmic values of the life tables were determined in correlation with the results of geometric morphometrics. Comparisons of centroid sizes in the cohorts showed that overall wing size became smaller in both sexes in response to higher rearing temperatures.  相似文献   
952.
The detection of three classes of C-heterochromatin by in situ restriction endonuclease digestion allowed a karyotype differentiation between the American and the European eel.  相似文献   
953.
John R. Polito 《CMAJ》2008,179(10):1037-1038
  相似文献   
954.
955.
Effect of precursors on biosynthesis of monensins A and B   总被引:1,自引:0,他引:1  
Precursors of monensins (acetate, propionate, butyrate, isobutyrate) affect the total production and the relative proportion of monensins A and B. Addition of propionate into the fermentation medium causes a prevalence of monensin B whereas butyrate and isobutyrate stimulate the production of monensin A and suppress the production of monensin B.  相似文献   
956.
957.
A newly developed computer model is used to predict the aqueous salt solution concentration, breathing pattern, and inhaled droplet size distribution parameters that will maximize pulmonary deposition of hygroscopic medicinal aerosols. The parameter values providing maximum pulmonary deposition include 1) a NaCl concentration in the aerosolized solution of 0.035 g/ml or higher if the subject can tolerate it, 2) as nearly a monodispersed inhaled aerosol size distribution as possible, 3) an aerosol mass median diameter of 2-3 micron, and 4) slow (7 breaths/min) uninterrupted breathing of 1.5-2 liters of aerosol/breath. With these values, the model predicts that pulmonary deposition can be increased by greater than 100% relative to the deposition achieved in conventional inhalation therapy with isotonic saline-based medications.  相似文献   
958.
959.
960.
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