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   888443篇
  免费   101809篇
  国内免费   557篇
  2018年   8233篇
  2017年   7782篇
  2016年   11285篇
  2015年   15352篇
  2014年   17886篇
  2013年   25704篇
  2012年   28844篇
  2011年   29310篇
  2010年   19725篇
  2009年   18182篇
  2008年   25693篇
  2007年   26618篇
  2006年   24530篇
  2005年   23811篇
  2004年   23532篇
  2003年   22399篇
  2002年   21550篇
  2001年   42468篇
  2000年   42616篇
  1999年   33729篇
  1998年   11597篇
  1997年   12169篇
  1996年   11499篇
  1995年   10555篇
  1994年   10443篇
  1993年   10315篇
  1992年   27092篇
  1991年   25936篇
  1990年   25148篇
  1989年   24681篇
  1988年   22449篇
  1987年   21340篇
  1986年   19805篇
  1985年   19452篇
  1984年   16243篇
  1983年   13759篇
  1982年   10560篇
  1981年   9562篇
  1980年   9010篇
  1979年   15311篇
  1978年   11707篇
  1977年   10818篇
  1976年   9914篇
  1975年   10794篇
  1974年   11682篇
  1973年   11417篇
  1972年   10366篇
  1971年   9510篇
  1970年   8092篇
  1969年   7768篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
101.
Disseminated nocardiosis in three macaque monkeys   总被引:1,自引:0,他引:1  
Extrapulmonary nocardiosis was diagnosed at necropsy in two rhesus monkeys (Macaca mulatta) and one pigtailed monkey (M. nemestrina) over a four-year period in a large primate center. Typical lesions were multiple pyogranulomatous foci in the liver, intestines, peritoneum, lung and brain. Partially acid-fast, branching, filamentous organisms were seen in all lesions. Nocardia sp. was isolated from two cases. We postulate that two of the monkeys were infected by the oral route because of the distribution of lesions.  相似文献   
102.
The biologically important pyridoxinato(1−) ligand (anionic vitamin B6) shows the rare phenolate-hydroxymethyl chelation plus bridging mode through the pyridine-nitrogen atom towards zinc(II) to give the one-dimensional (1D) coordination polymer {(acetato-κO)-aqua-μ-[2-methyl-3-oxy-4,5-di(hydroxymethyl)pyridine-κN:O,O′]zinc(II)}·monohydrate with polar packing of adjacent chains along the polar c axis (in space group Pc) through strong inter-chain hydrogen bonding.  相似文献   
103.
Two A strain influenza viruses, A/Hong Kong/123/77 (A/HK/123/77) (H1N1) and A/Queensland/6/72 (A/Qld/6/72) (H3N2), and the two cold-adapted reassortants which possess the surface antigens of these strains (CR35 and CR6, respectively) were tested for their ability both to induce primary cytotoxic T-cell (Tc cell) responses in mice and to sensitize mice for a second Tc cell response when challenged with a distantly related A strain virus, A/Shearwater/72 (H6N5). After intranasal inoculation, A/Qld/6/72 replicated to higher titers in the lung (1 to 2 log10 50% egg infective doses) than did A/HK/123/77 or either of the reassortants. A/Qld/6/72 induced higher Tc cell responses in the lung than did CR6, and both were more effective than either A/HK/123/77 or CR35 in this respect. When similar doses (10 or 10(3) hemagglutinin units) of each virus were injected intravenously into mice and the spleens were tested for Tc cell activity 6 days later, both A/Qld/6/72 and CR6 were ca. 100-fold better at inducing a primary Tc cell response than A/HK/123/77 or CR35. In contrast, the H1N1 and H3N2 viruses gave rather similar anti-hemagglutinin antibody titers (after intravenous injection) and delayed-type hypersensitivity reactions (after subcutaneous injection). If mice were primed with a low dose of these viruses (10(4) 50% egg infective doses intranasally), A/Qld/6/72 and CR6 were more effective than A/HK/123/77 or CR35 at sensitizing for a secondary Tc cell response when challenged with A/Shearwater/72, but if larger doses were given either intranasally (10(6) 50% egg infective doses) or intravenously (10 to 10(3) hemagglutinin units), all viruses sensitized the mice equally well, despite the fact the A/Shearwater/72 gives a poor primary Tc cell response in mice. Thus, the viral glycoprotein antigens can be important in determining the immunogenicity of the virus and, particularly, the class I antigen-restricted Tc cell response of the host.  相似文献   
104.
105.
106.
107.
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   
108.
S-adenosyl-L-homocysteine (S-AH), a potent inhibitor of biological transmethylation, decreased the response of rat retina adenylate cyclase to dopamine and to 2-amino-6, 7-dihydroxytetrahydronaphtalene (ADTN). This effect appeared for 10?7M of S-adenosyl-L-homocysteine and was linear for concentration ranging to 10?4M. S-adenosyl-L-homocysteine did not decrease the cyclic AMP accumulation with sodium fluoride, a non specific adenylate cyclase activator. On the other hand, the incorporation of methyl group was reduced in rat retina homogenates by S-adenosyl-L-homocysteine. These findings suggest that the activity of the dopamine dependent adenylate cyclase is linked to a methylation process.  相似文献   
109.
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   
110.
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