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   19687篇
  免费   1811篇
  国内免费   1967篇
  2024年   45篇
  2023年   204篇
  2022年   590篇
  2021年   897篇
  2020年   673篇
  2019年   873篇
  2018年   863篇
  2017年   622篇
  2016年   855篇
  2015年   1292篇
  2014年   1576篇
  2013年   1533篇
  2012年   1923篇
  2011年   1773篇
  2010年   1098篇
  2009年   1010篇
  2008年   1238篇
  2007年   1095篇
  2006年   894篇
  2005年   786篇
  2004年   655篇
  2003年   604篇
  2002年   581篇
  2001年   299篇
  2000年   261篇
  1999年   230篇
  1998年   158篇
  1997年   129篇
  1996年   96篇
  1995年   94篇
  1994年   87篇
  1993年   56篇
  1992年   70篇
  1991年   53篇
  1990年   49篇
  1989年   35篇
  1988年   24篇
  1987年   20篇
  1986年   23篇
  1985年   14篇
  1984年   14篇
  1983年   12篇
  1982年   7篇
  1981年   4篇
  1979年   4篇
  1975年   6篇
  1970年   4篇
  1966年   3篇
  1965年   3篇
  1964年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
COVID-19, caused by SARS-CoV-2, is an acute and rapidly developing pandemic, which leads to a global health crisis. SARS-CoV-2 primarily attacks human alveoli and causes severe lung infection and damage. To better understand the molecular basis of this disease, we sought to characterize the responses of alveolar epithelium and its adjacent microvascular endothelium to viral infection under a co-culture system. SARS-CoV-2 infection caused massive virus replication and dramatic organelles remodeling in alveolar epithelial cells, alone. While, viral infection affected endothelial cells in an indirect manner, which was mediated by infected alveolar epithelium. Proteomics analysis and TEM examinations showed viral infection caused global proteomic modulations and marked ultrastructural changes in both epithelial cells and endothelial cells under the co-culture system. In particular, viral infection elicited global protein changes and structural reorganizations across many sub-cellular compartments in epithelial cells. Among the affected organelles, mitochondrion seems to be a primary target organelle. Besides, according to EM and proteomic results, we identified Daurisoline, a potent autophagy inhibitor, could inhibit virus replication effectively in host cells. Collectively, our study revealed an unrecognized cross-talk between epithelium and endothelium, which contributed to alveolar–capillary injury during SARS-CoV-2 infection. These new findings will expand our understanding of COVID-19 and may also be helpful for targeted drug development.Subject terms: Mechanisms of disease, Viral infection  相似文献   
3.
4.
Squalene is a lipophilic and non-volatile triterpene with many industrial applications for food, pharmaceuticals, and cosmetics. Metabolic engineering focused on optimization of the production pathway suffer from little success in improving titers because of a limited space of the cell membrane accommodating the lipophilic product. Extension of cell membrane would be a promising approach to overcome the storage limitation for successful production of squalene. In this study, Escherichia coli was engineered for squalene production by overexpression of some membrane proteins. The highest production of 612 mg/L was observed in the engineered E. coli with overexpression of Tsr, a serine chemoreceptor protein, which induced invagination of inner membrane to form multilayered structure. It was also observed an increase in unsaturated fatty acid in membrane lipids composition, suggesting cellular response to maintain membrane fluidity against squalene accumulation in the engineered strain. This study potentiates the capability of E. coli for squalene production and provides an effective strategy for the enhanced production of such compounds.  相似文献   
5.
6.
7.
8.
9.
B Kaluza  G Betzl  H Shao  T Diamantstein  U H Weidle 《Gene》1992,122(2):321-328
Chimerization of antibodies (Ab) by cloning the V (variable) regions encoding the light and heavy chains with degenerate oligodeoxyribonucleotide primers matching to framework region 1 and to the joining regions, leads to Ab with altered amino acids at the N-terminus compared to those of the parental Ab. This is due to N-terminal framework 1 sequences in the expression vectors [Larrick et al., Bio/Technology 7 (1989) 937-938; Le Boeuf et al., Gene (1989) 371-377; Orlandi et al., Proc. Natl. Acad. Sci. USA 86 (1989) 3833-3837]. This might lead to Ab with altered affinity to the antigen due to interaction of framework sequences with complementarity determining regions. Moreover, some V regions may be refractory to cloning by this procedure. Here, we describe a method to circumvent these potential problems. The V regions for both chains of the Ab are cloned by inverse polymerase chain reaction (PCR) with primers matching the known constant region sequences of the Ab. After sequencing, PCR fragments corresponding to the V regions of both chains are inserted in-frame into appropriate expression vectors leading to Ab with unaltered N-terminal sequences after expression in mammalian cells. The procedure is illustrated with an Ab directed against the beta chain of the human interleukin-2 receptor.  相似文献   
10.
新疆绿蟾蜍的染色体组型初步研究   总被引:2,自引:2,他引:0  
吴敏  赵亚江 《动物学研究》1987,8(4):339-342
近年来,有关两栖类的染色体组型已有不少报道。无尾两栖类中蜍蟾属(Bufo)的染色体数目分为两类:2n=22和2n=20(Blain,1972)。我们对采自新疆4个地区的绿蟾蜍进行了染色体组型分析,发现其二倍体细胞染色体数均为44,是四倍体。现将我们的初步研究报道如下。  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