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   581584篇
  免费   48361篇
  国内免费   1035篇
  2018年   17164篇
  2017年   16048篇
  2016年   13965篇
  2015年   8690篇
  2014年   9535篇
  2013年   13875篇
  2012年   20029篇
  2011年   30157篇
  2010年   24048篇
  2009年   19501篇
  2008年   25029篇
  2007年   27753篇
  2006年   13983篇
  2005年   14530篇
  2004年   14489篇
  2003年   14298篇
  2002年   13774篇
  2001年   18287篇
  2000年   18117篇
  1999年   14717篇
  1998年   5770篇
  1997年   5833篇
  1996年   5576篇
  1995年   5268篇
  1994年   5159篇
  1993年   5192篇
  1992年   12781篇
  1991年   12535篇
  1990年   12453篇
  1989年   12238篇
  1988年   11550篇
  1987年   10833篇
  1986年   10142篇
  1985年   10593篇
  1984年   8859篇
  1983年   7639篇
  1982年   6055篇
  1981年   5397篇
  1980年   5027篇
  1979年   8300篇
  1978年   6570篇
  1977年   6202篇
  1976年   5883篇
  1975年   6328篇
  1974年   6918篇
  1973年   6769篇
  1972年   6846篇
  1971年   6232篇
  1970年   4895篇
  1969年   4888篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
63.
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   
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.
With DNA sequencing now getting cheaper more quickly than data storage or computation, the time may have come for genome informatics to migrate to the cloud.  相似文献   
68.
69.
Synthesis of prenylquinones in chloroplasts   总被引:3,自引:0,他引:3  
  相似文献   
70.
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   
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