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   62858篇
  免费   5913篇
  国内免费   32篇
  2022年   448篇
  2021年   916篇
  2020年   559篇
  2019年   673篇
  2018年   832篇
  2017年   782篇
  2016年   1249篇
  2015年   2086篇
  2014年   2365篇
  2013年   3102篇
  2012年   3807篇
  2011年   3868篇
  2010年   2522篇
  2009年   2205篇
  2008年   3165篇
  2007年   3352篇
  2006年   3201篇
  2005年   3107篇
  2004年   2973篇
  2003年   2791篇
  2002年   2740篇
  2001年   944篇
  2000年   839篇
  1999年   946篇
  1998年   897篇
  1997年   696篇
  1996年   615篇
  1995年   550篇
  1994年   554篇
  1993年   567篇
  1992年   714篇
  1991年   648篇
  1990年   643篇
  1989年   608篇
  1988年   587篇
  1987年   566篇
  1986年   529篇
  1985年   578篇
  1984年   635篇
  1983年   550篇
  1982年   620篇
  1981年   621篇
  1980年   513篇
  1979年   496篇
  1978年   502篇
  1977年   420篇
  1976年   454篇
  1975年   358篇
  1974年   417篇
  1973年   394篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Mutations in Aprataxin cause the neurodegenerative syndrome ataxia oculomotor apraxia type 1. Aprataxin catalyzes removal of adenosine monophosphate (AMP) from the 5′ end of a DNA strand, which results from an aborted attempt to ligate a strand break containing a damaged end. To gain insight into which DNA lesions are substrates for Aprataxin action in vivo, we deleted the Saccharomyces cerevisiae HNT3 gene, which encodes the Aprataxin homolog, in combination with known DNA repair genes. While hnt3Δ single mutants were not sensitive to DNA damaging agents, loss of HNT3 caused synergistic sensitivity to H2O2 in backgrounds that accumulate strand breaks with blocked termini, including apn1Δ apn2Δ tpp1Δ and ntg1Δ ntg2Δ ogg1Δ. Loss of HNT3 in rad27Δ cells, which are deficient in long-patch base excision repair (LP-BER), resulted in synergistic sensitivity to H2O2 and MMS, indicating that Hnt3 and LP-BER provide parallel pathways for processing 5′ AMPs. Loss of HNT3 also increased the sister chromatid exchange frequency. Surprisingly, HNT3 deletion partially rescued H2O2 sensitivity in recombination-deficient rad51Δ and rad52Δ cells, suggesting that Hnt3 promotes formation of a repair intermediate that is resolved by recombination.  相似文献   
142.
143.
144.
145.
146.
147.
148.
Prostaglandins E1, F and A2 were covalently joined to the surface of Sepharose as carboxamide linkages. The insolubilized prostaglandins were shown to function effectively in the purification of 15(S) -hydroxyprostaglandin dehydrogenase.  相似文献   
149.
A 14 kDa polypeptide in rat ileal cytosol has been identified as the major intestinal cytosolic bile acid-binding protein (I-BABP) by photoaffinity labeling with the radiolabeled 7,7-azo derivative of taurocholate (7,7-azo-TC). To further characterize I-BABP, the protein was purified by lysylglycocholate Sepharose 4B affinity and DE-52 anion-exchange chromatography. The purified I-BABP contained a single 14 kDa band on SDS-PAGE. The 14 kDa protein showed a 26-fold increase in binding affinity for [3H]7,7-azo-TC compared to cytosolic protein. Immunoblotting of protein fractions separated by affinity chromatography showed that neither liver fatty acid binding protein (L-FABP) nor intestinal fatty acid binding protein (I-FABP) bind to the affinity column and that the 14 kDa protein which bound to the column and was subsequently eluted with detergent did not cross-react with anti-L-FABP or anti-I-FABP. The 14 kDa protein labeled with [3H]7,7-azo-TC was radioimmunoprecipitated from cytosol by rabbit antiserum raised against purified I-BABP. I-BABP was shown to have a blocked N-terminus; however, its mixed internal sequence generated from cyanogen bromide-cleaved protein and amino acid composition indicated that it was related to (although clearly distinct from) both I-FABP and L-FABP. These studies have isolated a 14 kDa bile acid-binding protein from rat ileal cytosol which is immunologically and biochemically distinct from I-FABP and L-FABP.  相似文献   
150.
Energy calculations have been carried out on high-symmetry cuboctahedral Ni-Al nanoalloy clusters, of varying composition, with the interatomic interactions modelled by the Gupta many-body potential. Relaxations of cuboctahedral fragments cut from the bulk lattice of Ni3Al, with 13-561 atoms, were undertaken, as were relaxations of high symmetry clusters with 55 and 147 atoms. The lowest energy isomers were found to be dominated by three factors: the tendency toward mixing due to the favourable energy of mixing, ΔmixE; the size difference between nickel and aluminium; and the higher cohesive and surface energy of nickel compared to aluminium. The latter two factors favour Al-segregation to the surface. The most stable Ni:Al composition approaches 3:1 for larger clusters.  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