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   38891篇
  免费   2359篇
  国内免费   285篇
林业   1576篇
农学   1412篇
基础科学   324篇
  5480篇
综合类   5650篇
农作物   1486篇
水产渔业   1796篇
畜牧兽医   20682篇
园艺   456篇
植物保护   2673篇
  2021年   363篇
  2020年   460篇
  2019年   469篇
  2018年   823篇
  2017年   864篇
  2016年   764篇
  2015年   656篇
  2014年   840篇
  2013年   1870篇
  2012年   1346篇
  2011年   1546篇
  2010年   1088篇
  2009年   1140篇
  2008年   1496篇
  2007年   1343篇
  2006年   1260篇
  2005年   1088篇
  2004年   1049篇
  2003年   1041篇
  2002年   930篇
  2001年   1268篇
  2000年   1246篇
  1999年   952篇
  1998年   403篇
  1997年   430篇
  1996年   361篇
  1995年   414篇
  1994年   354篇
  1992年   673篇
  1991年   801篇
  1990年   701篇
  1989年   738篇
  1988年   674篇
  1987年   641篇
  1986年   669篇
  1985年   601篇
  1984年   473篇
  1983年   422篇
  1979年   553篇
  1978年   431篇
  1977年   359篇
  1976年   365篇
  1975年   396篇
  1974年   459篇
  1973年   474篇
  1972年   448篇
  1970年   366篇
  1969年   400篇
  1968年   357篇
  1967年   359篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Sodium selenite was mixed in a commercial pig food so as to increase the original selenium content (0.126 ppm) by 1.2 ppm. The supplemented food was given to 7 pigs during 78 days. A control group of as many pigs was given the non-supplemented commercial food. The pigs were killed, starting 4 hours after the last selenium-supplemented food had been given and then with intervals during the next 14 days. Small but significant increases of tissue selenium were noticed in liver and striated muscle as compared with the control animals. The kidneys showed no increase.  相似文献   
53.
54.
55.
Four groups of five Romney lambs were treated by plunge dipping with one of four registered organophosphorus flystrike preventatives. Untreated lambs acted as controls. The sheep were challenged at weekly intervals with larval implants of organophosphate-susceptible and -resistant strains of Lucilia cuprina. All four treatments provided 19-21 weeks protection against susceptible larvae but chlorfenvinphos provided the longest protection (16-17 weeks), followed by propetamphos (15-16 weeks), dichlofenthion (10-13 weeks) and diazinon (9-13 weeks), against the resistant strain.  相似文献   
56.
Myers N 《Science (New York, N.Y.)》1995,269(5222):358-360
Among the environmental problems ahead, the most important ones could be those that are still unknown to us. This conceptual article explores this prospect on the grounds that it is important not only to supply answers to recognized questions but to raise appropriate new questions.  相似文献   
57.
58.
Intranuclear cisternal and vesicular structures, bound by a single membrane, were observed for the first time in some glandular "bird's eye" cells of canine circummanal gland carcinomas. The role of these intranuclear structures is not clear. It is suggested that they may be involved in cellular adaptation to an environment of nutrient deficiency, as a result of cell overcrowding.  相似文献   
59.
60.
Two strains of bovine Theileria from northern Nigeria were shown to be identical to Theileria mutans in the indirect immunofluorescent antibody test. One of the strains was transmitted by the tick Amblyomma variegatum; large macroschizonts, typical for T mutans, could be demonstrated in infected cattle. It is concluded from these experiments and from the literature that there is reliable evidence so far for the occurrence in Nigeria of only two bovine Tehileria species, T mutans and T velifera.  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