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   31365篇
  免费   1368篇
  国内免费   11篇
林业   1120篇
农学   916篇
基础科学   179篇
  4688篇
综合类   4160篇
农作物   1196篇
水产渔业   1286篇
畜牧兽医   17034篇
园艺   361篇
植物保护   1804篇
  2021年   248篇
  2020年   288篇
  2019年   362篇
  2018年   627篇
  2017年   697篇
  2016年   596篇
  2015年   386篇
  2014年   576篇
  2013年   1712篇
  2012年   926篇
  2011年   1183篇
  2010年   853篇
  2009年   799篇
  2008年   1135篇
  2007年   1117篇
  2006年   965篇
  2005年   771篇
  2004年   776篇
  2003年   714篇
  2002年   646篇
  2001年   769篇
  2000年   755篇
  1999年   557篇
  1998年   249篇
  1997年   232篇
  1995年   277篇
  1992年   413篇
  1991年   426篇
  1990年   442篇
  1989年   446篇
  1988年   355篇
  1987年   360篇
  1986年   392篇
  1985年   350篇
  1984年   338篇
  1983年   312篇
  1979年   487篇
  1978年   334篇
  1977年   371篇
  1976年   470篇
  1975年   485篇
  1974年   525篇
  1973年   480篇
  1972年   443篇
  1971年   356篇
  1970年   372篇
  1969年   436篇
  1968年   445篇
  1967年   449篇
  1966年   440篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
143.
Effect of testing environment on adrenal cortical responses to an injection of ACTH in clinically normal dogs was examined in three locations, presumably of increasing order of stress elicitation: in a home; veterinary hospital (VH), 4 hours in a cage; and VH, overnight in a cage. Basal cortisol (hydrocortisone) values for plasma were significantly lower (P less than 0.001) for the home group (1.8 microgram/dl) when compared with values for the VH, 4-hour cage (3.8 microgram/dl) or the VH, overnight cage (3.9 microgram/dl) groups. However, significant differences (P greater than 0.05) were not observed 2 hours after ACTH admininstration for the home group (13.7 microgram/dl); VH, 4-hour cage group (14.8 microgram/dl); or VH, overnight cage group (16.0 microgram/dl). Responses of individual dogs were consistent (P less than 0.005). The testing environment did not markedly affect results of adrenal cortical function tests for dogs when ACTH stimulation was utilized. The response of dogs to ACTH, as monitored by immunologic assay techniques (competitive protein-binding assay or radioimmunoassay), was consistent and was useful as a diagnostic aid for adrenal malfunction.  相似文献   
144.
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   
145.
146.
147.
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   
148.
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   
149.
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   
150.
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