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   509319篇
  免费   55284篇
  国内免费   202篇
  2018年   5248篇
  2017年   4934篇
  2016年   7256篇
  2015年   10322篇
  2014年   11998篇
  2013年   15910篇
  2012年   18985篇
  2011年   19304篇
  2010年   12933篇
  2009年   12093篇
  2008年   17202篇
  2007年   17772篇
  2006年   16647篇
  2005年   16016篇
  2004年   15897篇
  2003年   14928篇
  2002年   14547篇
  2001年   18307篇
  2000年   18107篇
  1999年   14832篇
  1998年   6191篇
  1997年   6059篇
  1996年   5671篇
  1995年   5332篇
  1994年   5093篇
  1993年   5214篇
  1992年   12217篇
  1991年   12073篇
  1990年   11820篇
  1989年   11437篇
  1988年   10964篇
  1987年   10516篇
  1986年   9790篇
  1985年   9803篇
  1984年   8378篇
  1983年   7270篇
  1982年   5818篇
  1981年   5215篇
  1980年   5068篇
  1979年   7765篇
  1978年   6277篇
  1977年   5748篇
  1976年   5565篇
  1975年   5870篇
  1974年   6630篇
  1973年   6488篇
  1972年   5950篇
  1971年   5398篇
  1970年   4780篇
  1969年   4736篇
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
61.
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   
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.
Protein metal-binding sites.   总被引:2,自引:0,他引:2  
Metal ions have a role in a variety of important functions in proteins including protein folding, assembly, stability, conformational change, and catalysis. The presence or absence of a given metal ion is crucial to the conformation or activity of over one third of all proteins. Recent developments have been made in the understanding and design of metal-binding sites in proteins, an important and rapidly advancing area of protein engineering.  相似文献   
65.
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   
66.
67.
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   
68.
Synthesis of prenylquinones in chloroplasts   总被引:3,自引:0,他引:3  
  相似文献   
69.
The Thom gradient model of morphogenesis poses the followinga posteriori problem: “From the observed morphology of a given natural process (effect) determine the dynamics of the process (cause)”. In this paper we consider the classicala priori problem: “Given the cause (dynamics) determine the effect (resultant morphology)”. We find that in biochemical processes the mechanisms for energy activation, energy-matter interaction and energy dissipation determine the dynamics. Furthermore there exists basic energy mechanisms which drive the equilibrium states through the elementary catastrophes of Thom. A comparison with current theories shows that our models describe open ecological food chains and their dynamical systems generalize the equations of organisation posed by M. Eigen. Work supported by a Research Associateship of the International Centre for Theoretical Physics, P.O.B. 586, Miramare, 34100 Trieste, Italy.  相似文献   
70.
The main hepatic change in erythropoietic protoporphyria is the deposition of protoporphyrin. Brown deposits of this pigment occur in bile canaliculi and ductules, discretely in hepatocytes, and secondarily in macrophages and Kupffer cells. The pigment is deposited in a crystalline form. Under the fluorescence microscope with a mercury maximum pressure burner (HO 50) at a wave length of 380--500 nm, it shows a typical red fluorescence even after paraffin embedding. Its crystalline structure results in a characteristic double refraction under the polarising microscope. Light-microscopically, hepatocellular reactions are characterised mainly by discrete alterations in the ergastoplasm. However, cell damage is indicated by diffusely distributed, hyaline single cell necrosis and by cytolytic piecemeal necrosis at the peripheries of hepatic lobules. Numerous, often disturbed mitoses produce binuclear and multinuclear hepatocytes. The obligatory secretion of protoporphyrin into the bile ducts leads to an alteration in the canalicular and ductular excretion apparatus which involves distinct ductular proliferation and accompanying fibrosis. Piecemeal necrosis is a further consequence of this process. The resulting histological picture is similar to sclerosing cholangitis with which it also has in common the slowly progressive development of hepatic cirrhosis.  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