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   604072篇
  免费   65388篇
  国内免费   374篇
  669834篇
  2018年   6037篇
  2017年   5879篇
  2016年   8055篇
  2015年   10049篇
  2014年   11977篇
  2013年   17436篇
  2012年   19262篇
  2011年   19659篇
  2010年   13430篇
  2009年   12274篇
  2008年   17290篇
  2007年   17786篇
  2006年   16654篇
  2005年   15966篇
  2004年   15783篇
  2003年   15068篇
  2002年   14506篇
  2001年   31184篇
  2000年   30982篇
  1999年   24077篇
  1998年   7522篇
  1997年   8082篇
  1996年   7413篇
  1995年   6841篇
  1994年   6604篇
  1993年   6607篇
  1992年   18767篇
  1991年   18056篇
  1990年   17426篇
  1989年   16825篇
  1988年   15428篇
  1987年   14416篇
  1986年   13403篇
  1985年   13151篇
  1984年   10806篇
  1983年   9059篇
  1982年   6721篇
  1981年   6090篇
  1980年   5724篇
  1979年   10057篇
  1978年   7692篇
  1977年   7070篇
  1976年   6422篇
  1975年   7193篇
  1974年   7808篇
  1973年   7658篇
  1972年   6973篇
  1971年   6294篇
  1970年   5469篇
  1969年   5214篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
1. High mol. wt kininogen (HMW kininogen) was purified to a homogeneous state from porcine plasma. 2. The protein exhibited a strong inhibitory activity for thiol proteinases such as ficin, papain and calpain I, whereas it did not inhibit serine proteinases, trypsin and chymotrypsin. 3. The mol. wt, isoelectric point, amino acid and carbohydrate compositions, stabilities to temperature and pH, kinetic constants, and immunological properties of the porcine HMW kininogen were determined and compared with those of human HMW kininogen.  相似文献   
22.
23.
L-lysine-alpha-oxidase, a new fungal enzyme catalyzing oxidative deamination of L-lysine, exerts an inhibitory effect on DNA, RNA and protein synthesis in human cells of carcinoma ovarius (CaOv) in vitro.  相似文献   
24.
As part of a program towards the development of novel antibiotics, a convenient method for solid-phase synthesis of the cyclic cationic peptide polymyxin B1 and analogues thereof is described. The methodology, based on cleavage-by-cyclization using Kenner's safety-catch linker, yields crude products with purities ranging from 37-67%. Antibacterial assays revealed that analogues 23-26, in which the (S)-6-methyloctanoic acid moiety is replaced with shorter acyl chains, exhibit distinct antimicrobial activity. The results suggest that the length of the acyl chain is rather critical for antimicrobial activity. On the other hand, substitution of the hydrophobic ring-segment D-Phe-6/Leu-7 in polymyxin B1 with dipeptide mimics (i.e. analogues 27-33) resulted in almost complete loss of antimicrobial activity.  相似文献   
25.
S Yokota  H Tsuji  K Kato 《Histochemistry》1985,82(2):141-148
Light and electron microscopic localization of cathepsin D in rat liver was investigated by post-embedding immunoenzyme and protein A-gold techniques. By light microscopy, cytoplasmic granules of parenchymal cells and Kupffer cells were stained for cathepsin D. Weak staining was also noted in sinusoidal endothelial cells. In the parenchymal cells many of positive granules located around bile canaliculi. In the Kupffer cells and the endothelial cells, diffuse staining was noted in the cytoplasm in addition to granular staining. By electron microscopy, gold particles representing the antigenic sites for cathepsin D were seen in typical secondary lysosomes and some multivesicular bodies of the parenchymal cells and Kupffer cells. The lysosomes of the endothelial cells and fat-storing cells were weakly labeled. Quantitative analysis of the labeling density in the lysosomes of these three types of cells demonstrated that the lysosomes of parenchymal cells and Kupffer cells are main containers of cathepsin D in rat liver. The results suggest that cathepsin D functions in the intracellular digestive system of parenchymal cells and Kupffer cells but not so much in that of the endothelial cells.  相似文献   
26.
27.
1. Examination of the cerebrospinal fluid (CSF) of head-injured patients reveals that the concentration of intraventricular xanthine is elevated and that of uridine is decreased relative to those of adult lumbar CSF. 2. No correlations were observed between CSF lactate and CSF hypoxanthine, xanthine, or uridine, suggesting that changes in purine metabolites and the pyrimidine nucleoside do not index similar cellular events as does lactic acid production. 3. Ventricular CSF from hydrocephalic infants had uridine and hypoxanthine concentrations not significantly different from those of normal adult lumbar CSF, but xanthine was significantly elevated. 4. Since uridine has anticonvulsant properties and is a crucial substrate for cerebral metabolism, it may be useful to evaluate this pyrimidine for use in the management of patients with head injury.  相似文献   
28.
29.
30.
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