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   31016篇
  免费   1332篇
  国内免费   10篇
林业   1145篇
农学   904篇
基础科学   180篇
  4675篇
综合类   4090篇
农作物   1199篇
水产渔业   1215篇
畜牧兽医   16768篇
园艺   364篇
植物保护   1818篇
  2021年   252篇
  2020年   305篇
  2019年   378篇
  2018年   631篇
  2017年   705篇
  2016年   591篇
  2015年   382篇
  2014年   580篇
  2013年   1702篇
  2012年   921篇
  2011年   1168篇
  2010年   839篇
  2009年   787篇
  2008年   1124篇
  2007年   1095篇
  2006年   919篇
  2005年   737篇
  2004年   743篇
  2003年   675篇
  2002年   608篇
  2001年   750篇
  2000年   747篇
  1999年   548篇
  1998年   245篇
  1997年   229篇
  1995年   270篇
  1992年   403篇
  1991年   417篇
  1990年   435篇
  1989年   442篇
  1988年   345篇
  1987年   353篇
  1986年   384篇
  1985年   344篇
  1984年   335篇
  1983年   308篇
  1979年   484篇
  1978年   330篇
  1977年   377篇
  1976年   471篇
  1975年   487篇
  1974年   528篇
  1973年   485篇
  1972年   438篇
  1971年   354篇
  1970年   372篇
  1969年   435篇
  1968年   441篇
  1967年   447篇
  1966年   440篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Testing issues     
  相似文献   
72.
High electric fields have been used to extract organic cations from solutions of small organic molecules in polyphosphoric acid. The cations have been analyzed by mass spectrometry. Production of ions by this method is shown to be related to ease of protonation by acid rather than to ionization potential.  相似文献   
73.
74.
Two experiments, using the ligated intestinal segment technique, were conducted to determine whether the pituitary hormone prolactin (PRL) could reduce Escherichia coli-induced fluid loss into the small intestine of 2- to 3-week-old pigs. Inoculation of 10(6) to 10(8) enteropathogenic E coli organisms into ligated jejunal segments caused a significant accumulation of luminal fluid within 12 hours. In the first experiment, intraluminal inoculation with 0.5 mg of ovine PRL along with the bacteria did not have any effect on fluid accumulation. Systemic IV treatment of the animals with 1.0 mg of ovine PRL at 3-hour intervals, beginning either immediately after or 9 to 10 hours before intestinal ligation, did not significantly (P less than 0.05) reduce fluid accumulation as compared with control animals. In the second experiment, IM administration of 100 microgram of thyrotropin-releasing hormone (TRH) at 3-hour intervals, beginning 6 hours before intestinal ligation, significantly (P less than 0.05) increased circulating PRL concentrations, as measured by radioimmunoassay. However, TRH treatment did not reduce the accumulation of luminal fluid in E coli-inoculated segments.  相似文献   
75.
76.
The life cycle of Moniezia expansa was studied experimentally using 10 species of oribatid mites as intermediate hosts. Four of them became infected, namely Scheloribates laevigatus (76.2%), Sch. latipes (70.8%), Liacarus coracinus (20%) and Platynothrus peltifer (1.1%). The last was found for the first time to serve as intermediate host of M. expansa in Czechoslovakia. The development of the cysticercoid of M. expansa in the oribatid mites at 28 degrees C and 85% relative humidity is completed within 27 days. At 18-20 degrees C and the same relative humidity the development lasts even 97 days.  相似文献   
77.
Ultrastructure of the cuticle and pseudobursa of adult males of four species of Trichinella has been studied by SEM. T. nativa differs markedly from T. spiralis, T. nelsoni and Trichinella sp. in the form of the pseudobursa. Trichinella sp. differs only slightly from T. spiralis and T. nelsoni. The ultrastructure of the cuticle revealed no characters suitable for the differentiation of the taxons under study.  相似文献   
78.
The considerations involved in defining appropriate roles for the public and private sectors in agricultural research are examined with respect to mechanization, plant variety, and insecticide research and development. It is concluded that the public sector should continue to give mechanization a low priority. Varietal improvement should remain a relatively high priority until the effects of plant variety protection legislation become more apparent. Simultaneous achievement of safety, environmental, and productivity objectives in insect pest control will require that the public sector play a larger role in research and development.  相似文献   
79.
80.
Routine access to low earth orbit provided by the space shuttle holds great potential for global studies of the earth's resources and its environment. A successful test flight of the Columbia orbiter in November 1981 demonstrated the utility and versatility of the shuttle for earth-related research. A series of remote sensing experiments is currently planned for the mid-1980's that will more fully exploit the shuttle's earth observation capabilities.  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