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   149145篇
  免费   6606篇
  国内免费   68篇
  155819篇
  2021年   981篇
  2020年   916篇
  2019年   894篇
  2018年   2961篇
  2017年   2977篇
  2016年   5140篇
  2015年   9051篇
  2014年   8707篇
  2013年   9634篇
  2012年   9807篇
  2011年   6778篇
  2010年   5020篇
  2009年   4328篇
  2008年   4410篇
  2007年   4103篇
  2006年   3902篇
  2005年   9312篇
  2004年   7980篇
  2003年   5915篇
  2002年   3387篇
  2001年   2609篇
  2000年   1845篇
  1999年   2583篇
  1998年   821篇
  1992年   2473篇
  1991年   2480篇
  1990年   2519篇
  1989年   2451篇
  1988年   2400篇
  1987年   2207篇
  1986年   2002篇
  1985年   2050篇
  1984年   1469篇
  1983年   1103篇
  1982年   705篇
  1981年   598篇
  1979年   1318篇
  1978年   1003篇
  1977年   777篇
  1976年   782篇
  1975年   1096篇
  1974年   1230篇
  1973年   1240篇
  1972年   1161篇
  1971年   1092篇
  1970年   996篇
  1969年   1010篇
  1968年   900篇
  1967年   900篇
  1966年   701篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Desulfurization of model and diesel oils by resting cells of Gordona sp.   总被引:2,自引:0,他引:2  
The desulfurization activity of the resting cells of Gordona sp. CYKS1 was strongly depended on harvest time and the highest value when the cells had been harvested in the early growth phase (0.12 mg sulfur g–1 cell–1 h–1). For the model oil, hexadecane containing dibenzothiophene, the specific desulfurization rate decreased as the reaction proceeded. Both the specific and the volumetric desulfurization rates were not significantly affected by the aqueous-to-oil phase ratio. The diesel oils, light gas oil and a middle distillate unit feed were desulfurized at higher rates (ca. 0.34 mg sulfur g–1 cell–1 h–1) than the model oil (0.12 mg sulfur g–1 cell–1 h–1).  相似文献   
2.
The cotton bollworm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) is one of the most serious insect pests in Australia, India and China. The larva causes substantial economical losses to legume, fibre, cereal oilseed and vegetable crops. This pest has proven to be difficult to control by conventional means, mainly due to the development of pesticide resistance. We present here the 2.5 A crystal structure from the novel procarboxypeptidase (PCPAHa) found in the gut extracts from H. armigera larvae, the first one reported for an insect. This metalloprotease is synthesized as a zymogen of 46.6 kDa which, upon in vitro activation with Lys-C endoproteinase, yields a pro-segment of 91 residues and an active carboxypeptidase moiety of 318 residues. Both regions show a three-dimensional structure quite similar to the corresponding structures in mammalian digestive carboxypeptidases, the most relevant structural differences being located in the loops between conserved secondary structure elements, including the primary activation site. This activation site contains the motif (Ala)(5)Lys at the C terminus of the helix connecting the pro- and the carboxypeptidase domains. A remarkable feature of PCPAHa is the occurrence of the same (Ala)(6)Lys near the C terminus of the active enzyme. The presence of Ser255 in PCPAHa instead of Ile and Asp found in the pancreatic A and B forms, respectively, enlarges the S1' specificity pocket and influences the substrate preferences of the enzyme. The C-terminal tail of the leech carboxypeptidase inhibitor has been modelled into the PCPAHa active site to explore the substrate preferences and the enzymatic mechanism of this enzyme.  相似文献   
3.
Elevated levels of intracellular calcium are a major cause of myocardial dysfunction. To find possible mediators of the deregulated calcium we searched for EF-hand calcium-binding proteins of the S100 family. By PCR technology we identified three members of the S100 protein family (S100 alpha, CACY, and CAPL) in the human heart. We cloned the corresponding cDNAs and examined their expression levels in various human tissues by Northern blot analysis. All three proteins are expressed at high levels in the human heart. Whereas CACY and CAPL mRNAs are expressed ubiquitously, S100 alpha mRNA is restricted to heart, skeletal muscle, and brain. Interestingly, the expression pattern of S100 alpha, CACY, and CAPL in human tissues differs significantly from that in rodent tissues.  相似文献   
4.
5.
6.
7.
The Biopolymer Markup Language.   总被引:6,自引:0,他引:6  
SUMMARY: An XML derived from a data model designed to be a hierarchical representation of an organism has been specified and a browser to use this language has been developed. AVAILABILITY: The language definition is available in HTML form at http://www.proteometrics.com/BIOML/. The BioML browser is available on request from the author.  相似文献   
8.
9.
10.
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