全文获取类型
收费全文 | 151067篇 |
免费 | 12396篇 |
国内免费 | 9037篇 |
专业分类
172500篇 |
出版年
2023年 | 1528篇 |
2022年 | 3522篇 |
2021年 | 6077篇 |
2020年 | 4101篇 |
2019年 | 5074篇 |
2018年 | 4957篇 |
2017年 | 3729篇 |
2016年 | 5480篇 |
2015年 | 8209篇 |
2014年 | 9505篇 |
2013年 | 10421篇 |
2012年 | 12618篇 |
2011年 | 11692篇 |
2010年 | 7327篇 |
2009年 | 6698篇 |
2008年 | 8227篇 |
2007年 | 7661篇 |
2006年 | 6931篇 |
2005年 | 5928篇 |
2004年 | 5363篇 |
2003年 | 5075篇 |
2002年 | 4579篇 |
2001年 | 2354篇 |
2000年 | 2077篇 |
1999年 | 2233篇 |
1998年 | 1697篇 |
1997年 | 1476篇 |
1996年 | 1372篇 |
1995年 | 1234篇 |
1994年 | 1186篇 |
1993年 | 1019篇 |
1992年 | 1157篇 |
1991年 | 927篇 |
1990年 | 793篇 |
1989年 | 685篇 |
1988年 | 650篇 |
1987年 | 618篇 |
1986年 | 535篇 |
1985年 | 616篇 |
1984年 | 529篇 |
1983年 | 497篇 |
1982年 | 533篇 |
1981年 | 517篇 |
1980年 | 472篇 |
1979年 | 344篇 |
1978年 | 347篇 |
1977年 | 323篇 |
1976年 | 315篇 |
1974年 | 331篇 |
1973年 | 307篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
Characterization of phosphotyrosyl-protein phosphatase activity associated with calcineurin 总被引:3,自引:0,他引:3
J Chernoff M A Sells H C Li 《Biochemical and biophysical research communications》1984,121(1):141-148
Calcineurin purified from bovine brain is shown to possess phosphotyrosyl -protein phosphatase activity towards proteins phosphorylated by the epidermal growth factor receptor/kinase. The phosphatase activity is augmented by Ca2+/calmodulin or divalent cation (Ni2+ greater than Mn2+ greater than Mg2+ greater than Co2+). In the simultaneous presence of all three effectors, the enzymatic activity is synergistically increased. Ca2+/calmodulin activates the Mg2+-supported activity by decreasing the Km value for phosphotyrosyl -casein from 2.2 to 0.6 microM, and increasing the Vmax from 0.4 to 4.6 nmol/min/mg. These results represent the first demonstration that calcineurin can dephosphorylate phosphotyrosyl -proteins and suggest a novel mechanism of activation of this enzyme. 相似文献
6.
Victoria V. Hargreaves Scarlet S. Shell Dan J. Mazur Martin T. Hess Richard D. Kolodner 《The Journal of biological chemistry》2010,285(12):9301-9310
Indirect evidence has suggested that the Msh2-Msh6 mispair-binding complex undergoes conformational changes upon binding of ATP and mispairs, resulting in the formation of Msh2-Msh6 sliding clamps and licensing the formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes. Here, we have studied eight mutant Msh2-Msh6 complexes with defective responses to nucleotide binding and/or mispair binding and used them to study the conformational changes required for sliding clamp formation and ternary complex assembly. ATP binding to the Msh6 nucleotide-binding site results in a conformational change that allows binding of ATP to the Msh2 nucleotide-binding site, although ATP binding to the two nucleotide-binding sites appears to be uncoupled in some mutant complexes. The formation of Msh2-Msh6-Mlh1-Pms1 ternary complexes requires ATP binding to only the Msh6 nucleotide-binding site, whereas the formation of Msh2-Msh6 sliding clamps requires ATP binding to both the Msh2 and Msh6 nucleotide-binding sites. In addition, the properties of the different mutant complexes suggest that distinct conformational states mediated by communication between the Msh2 and Msh6 nucleotide-binding sites are required for the formation of ternary complexes and sliding clamps. 相似文献
7.
E Giannazzo F Licata G Li Volsi G Mio F Santangelo M Scivoli 《Bollettino della Società italiana di biologia sperimentale》1992,68(11):677-683
A computer-assisted analysis of the spatial distribution of neurons having homogeneous characteristics is described in this paper. The camera lucida drawings of sections of a brain nucleus and the points representing the neurons labeled on the basis of a specific behavior of discharge rates were digitized on a personal computer Amiga 2000 or IBM compatible. Our software provided: a) the computerized, stereotaxically oriented reconstruction of the stored sections and of the plotted neurons; b) the identification within each section of the mass center (MC) of the units sharing a given behavior and of the area where the density of such neurons was maximal (MDA). The routine was tested on the spatial distribution of neuronal responses to serotonin in the lateral vestibular nucleus. 相似文献
8.
Cynthia L. Deitrick Richard E. Katholi David J. Huddleston Kathy Hardiek Lucienne Burrus 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,751(2)
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation. 相似文献
9.
Richard D. Gregory 《Ecography》1998,21(1):92-96
10.
Concentration factor and biological half-life of 54Mn were determined in three species representing an ecologically and economically important food chain. Green algae (Chlorella spp.), Daphnia magna and yellow perch (Perca flavescens) were exposed to 54Mn in water and assayed for 54Mn uptake. Steady state concentration factors computed from the laboratory data for algae, Daphnia and perch were 4230, 17 000 and 11, respectively. Respective biological half-lives were 1.6, 1.2 and 8.3 days. 相似文献