全文获取类型
收费全文 | 293117篇 |
免费 | 34540篇 |
国内免费 | 152篇 |
专业分类
327809篇 |
出版年
2018年 | 2400篇 |
2016年 | 3088篇 |
2015年 | 4038篇 |
2014年 | 4919篇 |
2013年 | 6741篇 |
2012年 | 7709篇 |
2011年 | 7917篇 |
2010年 | 5209篇 |
2009年 | 5037篇 |
2008年 | 7143篇 |
2007年 | 7321篇 |
2006年 | 7201篇 |
2005年 | 6927篇 |
2004年 | 6787篇 |
2003年 | 6620篇 |
2002年 | 6469篇 |
2001年 | 17261篇 |
2000年 | 17449篇 |
1999年 | 13301篇 |
1998年 | 3863篇 |
1997年 | 4127篇 |
1996年 | 3851篇 |
1995年 | 3487篇 |
1994年 | 3465篇 |
1993年 | 3541篇 |
1992年 | 10386篇 |
1991年 | 10316篇 |
1990年 | 9804篇 |
1989年 | 9635篇 |
1988年 | 8990篇 |
1987年 | 8356篇 |
1986年 | 7556篇 |
1985年 | 7408篇 |
1984年 | 5824篇 |
1983年 | 5074篇 |
1982年 | 3613篇 |
1981年 | 3180篇 |
1980年 | 3030篇 |
1979年 | 5349篇 |
1978年 | 4115篇 |
1977年 | 3749篇 |
1976年 | 3299篇 |
1975年 | 3776篇 |
1974年 | 3948篇 |
1973年 | 3891篇 |
1972年 | 3421篇 |
1971年 | 3183篇 |
1970年 | 2822篇 |
1969年 | 2741篇 |
1968年 | 2412篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
861.
862.
Protein kinase activity of FSV (Fujinami sarcoma virus) P130gag-fps shows a strict specificity for tyrosine residues 总被引:10,自引:0,他引:10
A number of oncogenic viruses encode transforming proteins with protein kinase activities apparently specific for tyrosine residues. Recent evidence has raised questions as to the substrate specificity of these kinases in general and the physiological relevance of tyrosine phosphorylation in particular. The P130gag-fps transforming protein of Fujinami sarcoma virus (FSV) is strongly phosphorylated at 2 tyrosine residues in FSV-transformed cells of which 1 (Tyr-1073) is also the major site of P130gag-fps intermolecular autophosphorylation in vitro. We have investigated the specificity of the protein kinase activity intrinsic to FSV P130gag-fps by using site-directed mutagenesis to change the codon for Tyr-1073 to those for the other commonly phosphorylated hydroxyamino acids, serine and threonine. This approach has some advantages over the use of synthetic peptides to define protein kinase recognition sites in that the protein containing the altered target site can be expressed in intact cells. In addition it allows higher order as well as primary structure of the enzyme recognition site to be considered. Neither serine nor threonine were phosphorylated when substituted for tyrosine at position 1073 of P130gag-fps indicating a stringent specificity for tyrosine as a substrate of the P130gag-fps protein kinase autophosphorylating activity. Consistent with the suggestion that tyrosine phosphorylation is of functional significance we find that these and other FSV Tyr-1073 mutants have depressed enzymatic and oncogenic capacities. 相似文献
863.
864.
Edmund H. Frank Boyce W. Burge Boleslaw H. Liwnicz Linda J. Lotspeich Jocelyn C. White Steven L. Wechsler Frank H. Mayfield Jeffrey T. Keller 《Experimental cell research》1983,146(2):371-376
Cells from cranial and spinal arachnoid membranes of humans were grown in culture. Their growth characteristics, morphology and details of their cytoskeletal composition are described. Arachnoid membranes, obtained at autopsy, were finely minced and incubated in tissue culture medium. Monolayers of cells of homogeneous morphology grew from these tissue fragments. The cells were flat and polygonal. They divided slowly to form non-overlapping monolayers of low cell density. Electron microscopic examination of cultured arachnoid cells revealed numerous desmosome-like tight junctions and abundant intermediate filaments (tonofilaments). Both morphological features are characteristic of arachnoid cells in situ, but not of cells in the fibroblast-rich dura mater. Immunofluorescence microscopy with monoclonal antibodies demonstrated cytokeratin in the cytoplasm of primary cultures of arachnoid cells. Thus we demonstrated that these cultured cells retained certain of the specific differentiated properties of arachnoid cells in situ and that they are not fibroblasts (which lack tight junctions and cytokeratins). To our knowledge, there have been no previous reports of in vitro growth of arachnoid cells. This in vitro model should be useful in studying the response of arachnoid cells to a variety of substances thought to be involved in the chronic inflammatory condition of the meninges known as arachnoiditis. 相似文献
865.
866.
867.
868.
869.
A G Chuchalin V A Babushkina V Ia Arion R D Aspetov T B Sha?khinova 《Biulleten' eksperimental'no? biologii i meditsiny》1984,98(7):76-78
A study was made of the effect of T-activin on the biosynthesis of immune gamma-interferon. It was shown that in 27% of patients with chronic nonspecific pulmonary diseases, production of gamma-interferon by lymphocytes was substantially reduced during exacerbation of inflammatory process in the lungs. It was discovered that T-activin was not an interferon inductor but enhanced its synthesis in patients with a low capacity of producing immune interferon even at small doses of interferon inductor. The preparation does not produce any effect on this process in normal subjects and in patients showing the normal level of gamma-interferon. Thus T-activin can be used for stimulation of interferonogenesis. 相似文献
870.
N. I. Krikunova M. B. Terenina E. L. Ruchkina T. A. Misharina 《Applied Biochemistry and Microbiology》2006,42(3):335-338
Sorption of aromatic compounds from aqueous solutions by cryotextures and suspensions of native cornstarches was studied by capillary gas chromatography. Acetophenone and benzyl alcohol were not sorbed by cryotropic-cornstarch gel and native-cornstarch suspension. A linear concentration dependence was found for aldehydes. Phenylethyl alcohol was characterized by a nonlinear concentration dependence. The presence of a benzene ring contributed to decreased binding (relative to the level characteristic of aliphatic compounds). The degree of binding depended considerably on the type of functional group in the aromatic compounds. Cryotextures were more potent than granules of native cornstarch in binding aromatic compounds. 相似文献