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   331215篇
  免费   17350篇
  国内免费   700篇
林业   25154篇
农学   14377篇
基础科学   3024篇
  48979篇
综合类   43137篇
农作物   17976篇
水产渔业   18927篇
畜牧兽医   144632篇
园艺   6613篇
植物保护   26446篇
  2019年   3839篇
  2018年   4743篇
  2017年   5200篇
  2016年   5279篇
  2015年   4615篇
  2014年   6009篇
  2013年   16620篇
  2012年   8893篇
  2011年   11517篇
  2010年   8666篇
  2009年   8975篇
  2008年   10773篇
  2007年   10114篇
  2006年   10111篇
  2005年   9366篇
  2004年   9108篇
  2003年   8976篇
  2002年   8157篇
  2001年   9158篇
  2000年   8943篇
  1999年   7726篇
  1998年   4444篇
  1997年   4494篇
  1996年   4211篇
  1995年   4892篇
  1994年   4266篇
  1993年   3946篇
  1992年   6067篇
  1991年   6345篇
  1990年   6175篇
  1989年   6169篇
  1988年   5532篇
  1987年   5551篇
  1986年   5535篇
  1985年   5587篇
  1984年   4891篇
  1983年   4490篇
  1982年   3445篇
  1981年   3231篇
  1980年   3171篇
  1979年   4355篇
  1978年   3681篇
  1977年   3326篇
  1976年   3174篇
  1975年   3168篇
  1974年   3498篇
  1973年   3584篇
  1972年   3263篇
  1971年   3095篇
  1970年   3074篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
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   
993.
Quantitative and qualitative bacterial assays were performed on the skin of three dogs with endocrine-related primary metabolic seborrhea. After the dogs were treated (thyroid supplementation or castration, bacterial analyses were again performed on the same sites. Before therapy, the dogs had a cutaneous flora composed mainly of Staphylococcus aureus coagulase-positive organisms. After therapy, there was a significantly lower bacterial count, and two of the dogs had floras consisting mainly of coagulase-negative cocci. During the study, the two dogs that reverted bacteriologically to a normal cutaneous microenvironment became normal dermatologically. The third dog improved, but continued to have minor signs of seborrhea.  相似文献   
994.
Silicified anthoecia (fertile le'mmas and paleas) of grasses (Berriochloa communis, Berriochloa primaeva, and Berriohldoa cf. nova) were found in, the oral cavity and rib cage articulated skeletons of Teleoceras major buried in late Clarendonian volcanic ash in. Nebraska The plant fossils, thought to be food residues, help clarify, the enigmatic paleobiological role, of Teleocears, which had hippotamus-like porportions but very high-crowned teeth. Telecoceras was probably amphbious, but siliceous grasses formed a significant portion of its diet.  相似文献   
995.
The dioxin issue     
  相似文献   
996.
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   
997.
998.
999.
1000.
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