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   72338篇
  免费   6186篇
  国内免费   359篇
  2022年   2321篇
  2021年   2958篇
  2020年   2318篇
  2019年   2628篇
  2018年   1176篇
  2017年   889篇
  2016年   909篇
  2015年   1151篇
  2014年   1144篇
  2013年   1430篇
  2012年   1429篇
  2011年   1522篇
  2010年   1127篇
  2009年   1296篇
  2008年   1193篇
  2007年   1188篇
  2006年   1194篇
  2005年   1081篇
  2004年   2461篇
  2003年   2967篇
  2002年   3135篇
  2001年   5056篇
  2000年   3789篇
  1999年   3021篇
  1998年   2023篇
  1997年   2313篇
  1996年   1211篇
  1995年   1264篇
  1994年   1487篇
  1993年   1428篇
  1992年   1429篇
  1991年   1207篇
  1990年   1288篇
  1989年   931篇
  1988年   957篇
  1987年   872篇
  1986年   692篇
  1985年   758篇
  1984年   701篇
  1983年   582篇
  1982年   419篇
  1981年   441篇
  1979年   475篇
  1978年   586篇
  1977年   542篇
  1976年   449篇
  1975年   424篇
  1972年   508篇
  1971年   567篇
  1970年   676篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
We have identified mouse and human FKBP60, a new member of the FKBP gene family. FKBP60 shares strongest homology with FKBP65 and SMAP. FKBP60 contains a hydrophobic signal peptide at the N-terminus, 4 peptidyl-prolyl cis/trans isomerase (PPIase) domains and an endoplasmic reticulum retention motif (HDEL) at the C-terminus. Immunodetection of HA-tagged FKBP60 in NIH-3T3 cells suggests that FKBP60 is segregated to the endoplasmic reticulum. Northern blot analysis shows that FKBP60 is predominantly expressed in heart, skeletal muscle, lung, liver and kidney. With N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as a substrate, recombinant GST-FKBP60 is shown to accelerate effectively the isomerization of the peptidyl-prolyl bond. This isomerization activity is inhibited by FK506. mFKBP60 binds Ca2+ in vitro, presumably by its C-terminal EF-hand Ca2+ binding motif, and is phosphorylated in vivo. hFKBP60 has been mapped to 7p12 and/or 7p14 by fluorescence in situ hybridization (FISH).  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.
4.
5.
International Journal of Primatology - The selection of sleeping sites and sleeping trees in nonhuman primates is related to social and ecological factors. We investigate the role of body...  相似文献   
6.
7.
ABSTRACT   The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship.  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