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   89859篇
  免费   5529篇
  国内免费   46篇
林业   3742篇
农学   3467篇
基础科学   632篇
  11261篇
综合类   13530篇
农作物   3366篇
水产渔业   4949篇
畜牧兽医   47697篇
园艺   1173篇
植物保护   5617篇
  2020年   732篇
  2019年   957篇
  2018年   1585篇
  2017年   1848篇
  2016年   1663篇
  2015年   1404篇
  2014年   1719篇
  2013年   3729篇
  2012年   2933篇
  2011年   3592篇
  2010年   2343篇
  2009年   2332篇
  2008年   3473篇
  2007年   3213篇
  2006年   3146篇
  2005年   2677篇
  2004年   2581篇
  2003年   2599篇
  2002年   2376篇
  2001年   3397篇
  2000年   3311篇
  1999年   2559篇
  1998年   985篇
  1997年   1053篇
  1996年   884篇
  1995年   1022篇
  1994年   897篇
  1993年   896篇
  1992年   1845篇
  1991年   1919篇
  1990年   1856篇
  1989年   1860篇
  1988年   1607篇
  1987年   1594篇
  1986年   1627篇
  1985年   1526篇
  1984年   1225篇
  1983年   1032篇
  1982年   714篇
  1979年   1061篇
  1978年   816篇
  1975年   815篇
  1974年   898篇
  1973年   865篇
  1972年   805篇
  1971年   795篇
  1970年   801篇
  1969年   780篇
  1968年   708篇
  1967年   734篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
261.
262.
263.
264.
1. An experiment was conducted to determine the effect of different dietary protein contents on the performance of naked neck (Na/na) and normally feathered (na/na) broilers.

2. Chicks from the two genotypes were reared in wire‐floored cages and divided at random into 3 groups. Birds were fed on high protein (HP, 12.99 MJ ME, 238 g crude protein/kg and 12.94 MJ ME, 216 g crude protein/kg from 0 to 3 and 3 to 7 weeks, respectively), medium protein (MP, 12.99 MJ ME, 219 g crude protein/kg and 12.87 MJ ME, 201 g crude protein/kg from 0 to 3 and 3 to 7 weeks), and low protein (LP, 12.94 MJ ME, 205 g crude protein/kg and 12.75 MJ ME, 184 g protein/kg from 0 to 3 and 3 to 7 weeks) diets.

3. The LP diets resulted in a significantly lower daily body weight gain of males from 0 to 3 weeks. Dietary protein content had no effect on body weight gain from 3 to 7 weeks, body weight at 7 weeks, and the food intake of birds. Carcase composition of birds from both genotypes was unaffected by dietary protein.

4. Naked neck birds had significandy higher body weights at 7 weeks. Yields of carcase and breast of Na/na males were significantly higher than those of na/na males. There were no significant differences between females from the two genotypes as regards carcase yield.

5. It was concluded that the dietary protein requirements of naked neck birds were similar to those for normally feathered birds.  相似文献   

265.
Extreme eosinophilia with disseminated eosinophilic granulomatous disease is described in a 4-year-old Arabian mare. Clinical signs included weight loss, coughing, jugular distention, and ventral edema. Cutaneous lesions were not observed. Eosinophilic inflammation was observed in cytologic specimens from the respiratory tract, body cavities, and lymph nodes. At necropsy, a 20-cm diameter intrathoracic mass was observed. Smaller nodules were present in the lymph nodes, liver, spleen, adrenal glands, pancreas, and skeletal muscle. Histologically, these masses and nodules were characterized by infiltrates of eosinophils, macrophages, and multinucleated giant cells, reactive fibroplasia; and multifocal eosinophilic coagula. Microscopically, mild eosinophilic infiltrates were observed in sections of stomach, small intestine, colon, and pleura; however, gross lesions were not observed in these tissues at necropsy. The etiology of the extreme eosinophilia and disseminated eosinophilic granulomatous disease in this horse was not determined.  相似文献   
266.
Response     
  相似文献   
267.
The concept of a spatial-velocity hodograph is introduced to describe quantitatively the extrusion of a carbon tubule from a catalytic particle. The conditions under which a continuous tubular surface can be generated are discussed in terms of this hodograph, the shape of which determines the geometry of the initial nanotube. The model is consistent with all observed tubular shapes and explains why the formation process induces stresses that may lead to "spontaneous" plastic deformation of the tubule. This result is due to the violation of the continuity condition, that is, to the mismatch between the extrusion velocity by the catalytic particle, required to generate a continuous tubular surface, and the rate of carbon deposition.  相似文献   
268.
269.
270.
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