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   651805篇
  免费   68526篇
  国内免费   799篇
  721130篇
  2016年   7368篇
  2015年   9976篇
  2014年   11579篇
  2013年   17313篇
  2012年   18770篇
  2011年   19360篇
  2010年   13039篇
  2009年   11979篇
  2008年   17300篇
  2007年   18026篇
  2006年   17019篇
  2005年   16220篇
  2004年   16146篇
  2003年   15781篇
  2002年   15362篇
  2001年   26412篇
  2000年   26514篇
  1999年   21230篇
  1998年   7747篇
  1997年   8257篇
  1996年   7877篇
  1995年   7253篇
  1994年   7121篇
  1993年   7160篇
  1992年   18397篇
  1991年   18194篇
  1990年   17938篇
  1989年   17733篇
  1988年   16532篇
  1987年   15699篇
  1986年   14523篇
  1985年   15132篇
  1984年   12562篇
  1983年   10756篇
  1982年   8370篇
  1981年   7568篇
  1980年   7112篇
  1979年   12066篇
  1978年   9437篇
  1977年   8978篇
  1976年   8451篇
  1975年   9204篇
  1974年   10129篇
  1973年   9963篇
  1972年   9139篇
  1971年   8378篇
  1970年   7345篇
  1969年   7255篇
  1968年   6674篇
  1967年   5794篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Anatomical and neurophysiological findings have demonstrated neuronal connections between the diencephalic habenular nuclei and brain stem serotonergic raphe nuclei. Therefore we examined some neurochemical consequences of habenular lesions. Sixteen hours and one week after bilateral lesions serotonin metabolism (as reflected by concentrations of its metabolite, 5-hydroxyindoleacetic acid) was significantly increased in the dorsal but not the median raphe nuclei. Unilateral lesions produced a proportionally smaller augmentation. Motron locomotor activity was enhanced during the light and dark illumination phases in lesioned animals but only attained statistical significance during the day.  相似文献   
62.
It has been found by gel-penetrating chromatography and quantitative 13C NMR spectroscopy that mechanochemical processing of arabinogalactan isolated from the wood of the Siberian larch changes the molecular mass distribution, monosaccharide composition, and the degree of branching of its macromolecules. This is due to the partial destruction of polysaccharide macromolecules and subsequent recombination of resulting fragments. The intensity of these processes depends on the conditions of mechanochemical processing. Based on the data of IR and 13C NMR spectra, the conclusion has been drawn that no functionalization of arabinogalactan macromolecules occurs under these conditions. The toxicopharmacological properties of mechanically processed arabinogalactan have been studied. Its acute toxicity is >5000 mg/kg.  相似文献   
63.
64.
Experiments were made on rabbit fed an atherogenic diet (0.5 g/kg cholesterol) singly for 15 and 24 h and repeatedly for 3, 9 and 30 days. At early stages of lipid metabolism distress the interrelationship was established between blood rheological disorders and microcirculatory abnormalities. The dependence of the initial reaction of some rheological characteristics on their initial level was marked.  相似文献   
65.
66.
Electron microscopy of the adrenal medulla and cortex during the intermediate period of endotoxin shock has revealed severe destructive changes in parenchymal cells. These changes are the reason for synthetic, secretory and trophic disturbances of glandular functions. Ultrastructural lesions indicate that stress exposure exceeds the adaptive capacity of cells, the majority of which are exhausted and killed.  相似文献   
67.
68.
Synthesis of prenylquinones in chloroplasts   总被引:3,自引:0,他引:3  
  相似文献   
69.
Growth of fathead minnow yolk sac larvae was characterized from changes in dry weight and total content and concentrations of RNA, DNA and protein in fish exposed to a sublethal level of HCN (58 micrograms/l) and in age matched controls. Cyanide toxicosis occurred within 24 hr of exposure as evidenced by significant reductions in protein and RNA content and RNA/DNA ratio of larvae. After 96 hr exposure to HCN, larvae exhibited the same growth rate and protein synthetic rate (RNA/DNA) as control fish. HCN toxicosis and recovery is rapid and at least partial tolerance to HCN develops within 96 hr of exposure in larval fathead minnows.  相似文献   
70.
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