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   1387篇
  免费   9篇
  国内免费   9篇
林业   46篇
农学   19篇
基础科学   16篇
  60篇
综合类   823篇
农作物   40篇
水产渔业   29篇
畜牧兽医   303篇
园艺   38篇
植物保护   31篇
  2023年   10篇
  2022年   12篇
  2021年   10篇
  2020年   7篇
  2019年   12篇
  2018年   7篇
  2017年   15篇
  2016年   8篇
  2015年   15篇
  2014年   20篇
  2013年   20篇
  2012年   69篇
  2011年   88篇
  2010年   22篇
  2009年   33篇
  2008年   76篇
  2007年   69篇
  2006年   79篇
  2005年   79篇
  2004年   73篇
  2003年   80篇
  2002年   55篇
  2001年   68篇
  2000年   65篇
  1999年   31篇
  1998年   8篇
  1997年   7篇
  1995年   21篇
  1994年   15篇
  1993年   11篇
  1992年   13篇
  1991年   8篇
  1990年   10篇
  1989年   13篇
  1986年   8篇
  1982年   9篇
  1979年   8篇
  1976年   9篇
  1973年   7篇
  1970年   8篇
  1966年   9篇
  1963年   12篇
  1960年   8篇
  1959年   8篇
  1958年   13篇
  1956年   10篇
  1953年   6篇
  1948年   6篇
  1947年   6篇
  1945年   9篇
排序方式: 共有1405条查询结果,搜索用时 15 毫秒
71.
Gene expression studies advance our understanding of the effects of stress and glucocorticoids on brain function and give a new direction to animal welfare research. In this context, the presence of messenger RNA s (m RNA s) for corticotrophin releasing hormone (CRH) and vasopressin (VP) in the porcine hypothalamus has recently been documented. This study investigated the expression of CRH, VP and ionotropic glutamate receptor (iGluR) subunit m RNA s in the brains of pigs treated with the synthetic glucocorticoid dexamethasone (Dex; 5 mg kg(-1)i.v.). In the hypothalamus, VP, but not CRH, m RNA was reduced 3 hours after Dex. In the hippocampus, expression of m RNA s for some iGluR subunits appeared to be differentially regulated 6 hours after Dex. In addition, CRH message was detected in the hippocampus and significantly upregulated in the CA1 region 3 hours after Dex. The relevance of these findings to stress neurobiology of the growing pig is discussed.  相似文献   
72.
Two naturally occurring antioxidants, ascorbic acid and turmeric, were effective in inhibiting formation of hexanal, (E)-2-penenal, (E)-2-hexenal, (E)-2-heptenal, and (E)-2-octenal when slurries of fermented cucumber tissue were exposed to oxygen. Added ascorbic acid prevented formation of most of these oxidative aldehydes at 175 ppm or greater. Turmeric, which is used commercially as a yellow coloring in cucumber pickle products, was found to almost completely prevent aldehyde formation at 40 ppm.  相似文献   
73.
This year's Nobel Prize in chemistry was awarded to a trio of researchers--Alan Heeger of the University of California, Santa Barbara; Alan MacDiarmid of the University of Pennsylvania in Philadelphia; and Hideki Shirakawa of the University of Tsukuba in Japan--for discovering that plastics can be made electrically conductive. The discovery paved the way for revolutionary applications such as full-color displays for cellular phones and plastic electronics for computerized merchandise.  相似文献   
74.
Many of today's lasers are made from ceramic chips that require expensive clean-room facilities to manufacture, and their color palette is somewhat limited. Researchers have long pinned their hopes on organic materials, which are typically easier and cheaper to process. Now, on page 599, a team reports that they've devised the first electrically powered solid state organic laser, a step that could open the floodgates for novel lasers that are cheaper and that shine in colors inorganics can't match.  相似文献   
75.
Copper and zinc are frequently added at high concentrations to pig diets as growth promoters. Livestock grazing pasture contaminated with pig slurry may, therefore, be at risk from excessive intake of these elements. High liver copper concentrations have been detected in cattle from the agricultural region of Galicia (NW Spain), especially where there is intensive pig farming. The aim of this study was to evaluate whether pig farming does affect accumulation of copper and zinc in cattle in Galicia. Hepatic copper and zinc concentrations in calves were elevated in areas with naturally high levels of these elements in the soil. The densities of young pigs (piglets and growing-finishing pigs), but not reproductive sows, also influenced copper accumulation in calves. Liver copper levels in calves were significantly and positively related to the density of young pigs in the region. In areas with the highest pig densities, more than 20% of the cattle analysed had hepatic copper concentrations that exceeded the potentially toxic concentration of 150 mg/kg fresh weight. There was no evidence that zinc accumulation in calves was affected by pig density.  相似文献   
76.
甜瓜可溶性固形物含量的遗传表现与基因效应分析   总被引:2,自引:0,他引:2  
通过半轮配双列杂交,分析了甜瓜可溶性固形物含量的遗传特性。研究结果表明,遗传方差组成中,基因的加性效应和显性效应都是显著的,但加性效应占相对主要优势,狭义遗传力(h2N)值为65%。基因的分布是不均衡的,控制该性状的基因W为显性基因,但表现为不完全显性,可溶性固形物含量选择的较好世代在F4代。  相似文献   
77.
在对鄂豫陕接壤区引种栽培的26个山楂品种进行品比试验和调查分析的基础上,对其中13个引种时间较长,栽培面积较大的品种,采用合理——满意度和多维价值理论的并合规则,进行了综合评价。结果表明,晋京南1号、山东大敞口、大红袍釉山西798202性状表现最佳,可以大力推广;山东大金星和豫北红等次之,可适当发展;北京小金星和朱砂红表现欠佳,应考虑及时淘汰。  相似文献   
78.
79.
高山 《百姓》2006,(4):48-50
最近,阿联酋国营公司杜拜港口世界(DPW)以68亿美元的价格接管英国铁行港口(P·O)在美六个主要港口的经营权。然而这笔交易刚一公布,共和党和民主党都有成员跳出来对这笔交易做出批评,指责由阿拉伯公司控制美国港口会导致美国更容易受到恐怖袭击,因此这笔交易可能影响到美国的国  相似文献   
80.
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