全文获取类型
收费全文 | 355946篇 |
免费 | 158347篇 |
国内免费 | 29883篇 |
出版年
2016年 | 5027篇 |
2015年 | 6616篇 |
2014年 | 7424篇 |
2013年 | 9421篇 |
2012年 | 10658篇 |
2011年 | 11031篇 |
2010年 | 9855篇 |
2009年 | 14313篇 |
2008年 | 10973篇 |
2007年 | 11074篇 |
2006年 | 9620篇 |
2005年 | 9597篇 |
2004年 | 9416篇 |
2003年 | 9037篇 |
2002年 | 9419篇 |
2001年 | 15066篇 |
2000年 | 13055篇 |
1999年 | 15410篇 |
1998年 | 11688篇 |
1997年 | 11740篇 |
1996年 | 11098篇 |
1995年 | 11152篇 |
1994年 | 10594篇 |
1993年 | 10271篇 |
1992年 | 14990篇 |
1991年 | 14788篇 |
1990年 | 15277篇 |
1989年 | 14544篇 |
1988年 | 13507篇 |
1987年 | 12591篇 |
1986年 | 11712篇 |
1985年 | 11358篇 |
1984年 | 9263篇 |
1983年 | 7990篇 |
1982年 | 7218篇 |
1981年 | 6766篇 |
1980年 | 6329篇 |
1979年 | 8831篇 |
1978年 | 7280篇 |
1977年 | 6987篇 |
1976年 | 6684篇 |
1975年 | 6636篇 |
1974年 | 7228篇 |
1973年 | 7140篇 |
1972年 | 7057篇 |
1971年 | 6381篇 |
1970年 | 5665篇 |
1969年 | 5725篇 |
1968年 | 5024篇 |
1967年 | 4302篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
881.
Y W Yang J A Romanus T Y Liu S P Nissley M M Rechler 《The Journal of biological chemistry》1985,260(4):2570-2577
BRL-3A rat liver cells synthesize mature 7484-dalton rat insulin-like growth factor II (rIGF-II) as a approximately 22-kDa precursor, presumably prepro-rIGF-II. In the present study, we have biosynthetically labeled intact BRL-3A cells with [35S]cysteine and immunoprecipitated cell lysates and media with antisera to rIGF-II. A approximately 20-kDa protein was identified in immunoprecipitates of cell lysates having properties consistent with pro-rIGF-II. The approximately 20-kDa protein is precipitated by immune sera but not by nonimmune serum. Its immunoprecipitation is specifically inhibited by unlabeled rIGF-II but not by insulin. It is not precipitated from labeled lysates of a subclone of BRL-3A cells (BRL-3A2) that does not synthesize rIGF-II. The approximately 20-kDa protein is rapidly labeled intracellularly (10 min) but is not detected in BRL-3A media. In pulse-chase experiments, radioactivity in the approximately 20-kDa protein disappears during the chase and appears, at later times, in specifically immunoprecipitated approximately 19-, approximately 10-, approximately 8-, and approximately 7-kDa proteins in media and, to a limited extent, intracellularly. A protein with electrophoretic mobility identical to that of the approximately 20-kDa protein observed in cell lysates is immunoprecipitated from 35S-proteins whose synthesis is directed by BRL-3A RNA in a reticulocyte lysate cell-free translation system supplemented with microsomal membranes, and presumably arises by cotranslational removal of the signal peptide from approximately 22-kDa prepro-rIGF-II. Processing of the approximately 20-kDa protein in intact BRL-3A cells to intermediate and mature rIGF-II species appears to occur at the time of secretion and/or shortly thereafter, with the different forms appearing at approximately the same time. 相似文献
882.
883.
884.
885.
Subnuclear localization and antitransforming activity of N-myc:beta-galactosidase fusion proteins. 总被引:3,自引:2,他引:1
N-myc expression is under stage- and tissue-specific regulation in mammalian development, but its function is totally unknown. We sought agents to block N-myc activity in order to infer from the effect the possible function of N-myc in the apparently complex processes. As candidates for such agents, we tested fusion genes encoding N-myc:beta-galactosidase fusion proteins for their effects on the formation of transformed foci of rat embryo primary fibroblasts as the result of transfection with N-myc and activated H-ras. One of the gene constructs very efficiently antagonized N-myc activity, as assessed by its effect on focus formation, but did not appreciably affect cell viability. The product of this gene was not only targeted to the nucleus but also accumulated in subnuclear loci which may represent the sites where normal N-myc proteins reside. The occurrence of antagonistic effect at a low stoichiometric ratio suggested that the fusion protein gene competed with the N-myc gene in a fashion analogous to a dominant negative mutation. 相似文献
886.
Aliphatic aldehydes of different chain lengths were found to differ in their reaction at 22 °C with the B. harveyi luciferase peroxyflavin intermediate. Although similar quantum yields were obtained in the luciferase reaction with the different chain-length aldehydes, the catalytic turnover rates differed. The kinetics of a reaction utilizing two aldehydes of different chain lengths can thus indicate the degree to which the aldehyde reaction is reversible. By such criteria the reactions of octanal and decanal were found to be readily reversible, while that of dodecanal was not. This conclusion was supported both by the effects of long-chain alcohols, which are competitive inhibitors, and by the secondary addition of hydroxylamine, an aldehyde trapping agent. The results are consistent with a model in which there are many intermediates along the reaction path. Since the reactions are monitored by decay of luminescence intensity, it is difficult to determine the position of the rate-determining step. For octanal and decanal the rate-limiting step could be at an early reversible stage of the reaction, but later for dodecanal, subsequent to a less reversible step, but still prior to the final irreversible step which populates the excited state. 相似文献
887.
888.
889.
Isolation of Temperature-Sensitive Membrane Mutants of Escherichia coli K-12 总被引:1,自引:1,他引:0
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Johan F. Steenbakkers J. H. F. F. Broekman A. Kerkenaar P. G. De Haan 《Journal of bacteriology》1973,116(2):535-540
Mutants with impaired biosynthesis of unsaturated fatty acids or altered metabolism of the phospholipids were isolated at a rather high frequency from a set of temperature-sensitive lysis mutants. It is suggested that preselection for the lysis phenotype makes it possible to isolate several kinds of mutants affected in the integrity of the cytoplasmic membrane. 相似文献
890.