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   658991篇
  免费   73374篇
  国内免费   542篇
  2016年   7080篇
  2015年   10443篇
  2014年   11930篇
  2013年   17319篇
  2012年   19111篇
  2011年   19361篇
  2010年   12907篇
  2009年   11984篇
  2008年   17243篇
  2007年   17714篇
  2006年   16965篇
  2005年   16245篇
  2004年   16093篇
  2003年   15335篇
  2002年   15113篇
  2001年   28095篇
  2000年   28561篇
  1999年   22789篇
  1998年   8109篇
  1997年   8475篇
  1996年   8030篇
  1995年   7462篇
  1994年   7326篇
  1993年   7397篇
  1992年   18688篇
  1991年   18147篇
  1990年   17660篇
  1989年   17301篇
  1988年   16198篇
  1987年   15517篇
  1986年   14530篇
  1985年   14716篇
  1984年   12263篇
  1983年   10517篇
  1982年   8396篇
  1981年   7768篇
  1980年   7155篇
  1979年   11907篇
  1978年   9500篇
  1977年   8880篇
  1976年   8348篇
  1975年   9258篇
  1974年   10225篇
  1973年   10076篇
  1972年   9228篇
  1971年   8484篇
  1970年   7493篇
  1969年   7312篇
  1968年   6689篇
  1967年   5710篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Preventing the establishment of ectoparasitic poultry red mite (Dermanyssus gallinae) populations is key in ensuring welfare and egg production of laying hens and absence of allergic reactions of workers in poultry facilities. Using the Hazard Analysis and Critical Control Point method, a panel of experts identified hazards and associated risks concerning the introduction and spread of this mite in poultry facilities. Together we provide an overview of possible corrective actions that can be taken to prevent population establishment. Additionally, a checklist of the most critical control points has been devised as management tool for poultry farmers. This list was evaluated by Dutch and British poultry farmers. They found the checklist feasible and useful.  相似文献   
994.
995.
996.
In this study, 18 partly commercially available samples of rock salt from Austria, Germany, Pakistan, Poland, Switzerland, and Ukraine were investigated with respect to their content of trace elements using instrumental neutron activation analysis. Elements detected were Al, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, Hf, La, Mn, Na, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, and Zn, some of them only in individual cases. An estimation of the bioavailability of these trace elements was performed by dissolving an equivalent of the sodium chloride samples in diluted hydrochloric acid (simulating stomach acid), filtering off the insoluble components, and analyzing the evaporated filtrate. It could be shown that in most cases bioactive trace elements like Fe can be found in rock salt in the form of almost insoluble compounds and are therefore not significantly bioavailable, whereas thorium, for example, was partly bioavailable in two cases. A significant contribution to the recommended daily intake of metal trace elements by using rock salt for nutrition can be excluded.  相似文献   
997.
998.
999.
The epididymis of buffalo is differentiated into 6 regions. The head represents the first 3 regions, the body the 4th region and the tail the 5th and 6th region. At 3-30 weeks, the epithelium is simple high columnar with few basal cells in region I, simple low columnar with few basal cells in region II, pseudostratified low columnar in regions III, IV, V, and pseudostratified low columar in region VI. As age advances, the epithelium increases in height and shows a tendency toward advanced pseudostratification. The basal cells are greater in number in regions III, IV and V than in the other regions of the epididymis. The epithelial cells contain stereocilia in region I at 3 weeks and regions III, IV and V at 30 weeks, whereas they are absent in regions II and VI. The tubules in region I are the smallest in diameter while the tubules in region VI have the largest diameter.  相似文献   
1000.
A method for separation and visualization of the different apolipoprotein B species using 0.2% sodium dodecyl sulfate-1.5% agarose gel electrophoresis and immunoblotting is described. The method is capable of demonstrating the different forms of apolipoprotein B (apo B) in plasma volumes of 10-50 microliters without prior ultracentrifugation. After ultracentrifugation of samples, estimation of the ratio between apo B 48 and apo B 100 is possible by scanning of Coomassie-stained gels or immunoblots.  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