全文获取类型
收费全文 | 17877篇 |
免费 | 1708篇 |
国内免费 | 3篇 |
出版年
2023年 | 60篇 |
2021年 | 333篇 |
2020年 | 196篇 |
2019年 | 222篇 |
2018年 | 305篇 |
2017年 | 248篇 |
2016年 | 419篇 |
2015年 | 731篇 |
2014年 | 771篇 |
2013年 | 972篇 |
2012年 | 1346篇 |
2011年 | 1314篇 |
2010年 | 824篇 |
2009年 | 719篇 |
2008年 | 1087篇 |
2007年 | 1104篇 |
2006年 | 983篇 |
2005年 | 917篇 |
2004年 | 972篇 |
2003年 | 816篇 |
2002年 | 826篇 |
2001年 | 288篇 |
2000年 | 252篇 |
1999年 | 264篇 |
1998年 | 237篇 |
1997年 | 185篇 |
1996年 | 168篇 |
1995年 | 156篇 |
1994年 | 150篇 |
1993年 | 119篇 |
1992年 | 184篇 |
1991年 | 165篇 |
1990年 | 135篇 |
1989年 | 139篇 |
1988年 | 135篇 |
1987年 | 127篇 |
1986年 | 145篇 |
1985年 | 107篇 |
1984年 | 105篇 |
1983年 | 100篇 |
1982年 | 107篇 |
1981年 | 88篇 |
1980年 | 70篇 |
1979年 | 89篇 |
1978年 | 91篇 |
1977年 | 65篇 |
1976年 | 75篇 |
1975年 | 71篇 |
1974年 | 82篇 |
1973年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Mitochondrial protein import: identification of processing peptidase and of PEP, a processing enhancing protein 总被引:43,自引:0,他引:43
Transport of nuclear-encoded precursor proteins into mitochondria includes proteolytic cleavage of amino-terminal targeting sequences in the mitochondrial matrix. We have isolated the processing activity from Neurospora crassa. The final preparation (enriched ca. 10,000-fold over cell extracts) consists of two proteins, the matrix processing peptidase (MPP, 57 kd) and a processing enhancing protein (PEP, 52 kd). The two components were isolated as monomers. PEP is about 15-fold more abundant in mitochondria than MPP. It is partly associated with the inner membrane, while MPP is soluble in the matrix. MPP alone has a low processing activity whereas PEP alone has no apparent activity. Upon recombining both, full processing activity is restored. Our data indicate that MPP contains the catalytic site and that PEP has an enhancing function. The mitochondrial processing enzyme appears to represent a new type of "signal peptidase," different from the bacterial leader peptidase and the signal peptidase of the endoplasmic reticulum. 相似文献
92.
Wendell L. Combest Timothy J. Bloom Lawrence I. Gilbert 《Journal of neurochemistry》1988,51(5):1581-1591
The effects of the naturally occurring polyamines spermine and spermidine on phosphorylation promoted by cyclic AMP (cAMP)-dependent protein kinase (PK) (cAMP-PK; EC 2.7.1.37) were studied using the brain of the tobacco hornworm, Manduca sexta. Four particulate-associated peptides (280, 34, 21, and 19 kilodaltons) in day 1 pupal brains are endogenous substrates for a particulate type II cAMP-PK. These phosphoproteins are present in brain synaptosomal, as well as microsomal, particulate fractions but are not present in the cytosol. They are distributed throughout the CNS and PNS and are present in several nonneuronal tissues as well. Phosphorylation of these proteins via cAMP-PK was inhibited markedly by micromolar concentrations of spermine and spermidine. Other particulate-associated peptides phosphorylated via a Ca2+/calmodulin-PK or Ca2+ and cAMP-independent PKs were unaffected by polyamines, whereas the phosphorylation of a 260-kilodalton peptide was markedly enhanced. Spermine did not exert its inhibitory effect indirectly by enhancement of cAMP or ATP hydrolysis or via proteolysis, but its action appears to involve a substrate-directed inhibition of cAMP-PK-promoted phosphorylation as well as enhanced dephosphorylation. Although addition of spermine resulted in marked ribosome aggregation in synaptosomal and microsomal particulate fractions, this phenomenon was not involved in the inhibition of cAMP-PK-promoted phosphorylation. 相似文献
93.
94.
Monoclonal antibodies raised against purified chicken progesterone receptor (PgR) have been described and characterized recently. In this study we have screened these antibodies for cross-reactivity with murine PgR. Of the six anti-PgR antibodies tested, one (alpha PR6) precipitates murine PgR in an assay using protein A-sepharose as an absorbent for the antibody. The antibody is specific for PgR and does not react with the estrogen receptor or the glucocorticoid receptor in the same cytosol. In immunoblot experiments, both alpha PR6 and alpha PR11 recognize a 115,000 Da protein, however, alpha PR11 gives a weaker signal than alpha PR6. In photoaffinity labeling experiments, a 115,000 Da and an 83,000 Da protein covalently bind tritiated R5020 in a receptor-specific way. We conclude that the alpha PR6 antibody can be used as a tool to study the structure and function of the murine PgR. 相似文献
95.
96.
Mutations in the phosphorylation sites of simian virus 40 (SV40) T antigen alter its origin DNA-binding specificity for sites I or II and affect SV40 DNA replication activity 总被引:35,自引:22,他引:13 下载免费PDF全文
A series of mutants of simian virus 40 was constructed by oligonucleotide-directed mutagenesis to study the role of phosphorylation in the functions of large T antigen. Each of the previously mapped phosphorylated serine and threonine residues in large T antigen was replaced by an alanine or cysteine residue or, in one case, by glutamic acid. Mutant DNAs were assayed for plaque-forming activity, viral DNA replication, expression of T antigen, and morphological transformation of rat cells. Viable mutants were isolated, suggesting that modification of some residues is not essential for the biological functions of T antigen. Two of these mutants replicated more efficiently than did the wild type. Seven mutants were partially or completely deficient in viral DNA replication but retained cell transformation activity comparable with that of the wild-type protein. Biochemical analysis of the mutant T antigens demonstrated novel origin DNA-binding properties of several mutant proteins. The results are consistent with the idea that differential phosphorylation defines several functional subclasses of T-antigen molecules. 相似文献
97.
Summary The complete physical map of the mitochondrial genome of the Owen cytoplasm of sugar beet has been determined from overlapping cosmid clones. The genome is 386 kb in size and has a multicircular organisation generated by homologous recombination across repeated DNA elements. The location of the rRNA genes and several polypeptide genes has been determined. In addition the mitochondrial genome was found to contain a sequence of chloroplast DNA including part of the 16 S rRNA gene. 相似文献
98.
Mahan James R.; Sherman Timothy D.; Funkhouser Edward A. 《Plant & cell physiology》1988,29(4):735-737
The thermal dependence of two of the reactions catalyzed bythe nitrate reductase from Chlorella vulgaris was determined.The activation energies for NADH:nitrate oxidoreductase (EC1.6.6.1
[EC]
) and NADH:Cytochrome c oxidoreductase (EC 1.6.99.3
[EC]
)are 42.1 kJ?mol1 and 21.5 kJ?mol1, respectively.Since the thermal dependency of the two enzymes is different,ratios of the activities will vary with temperature. The importanceof both rigorous thermal control during nitrate reductase assaysas well as the need to specify the temperature at which theratio of activities for the enzyme are clearly established.
1Present Address: Cropping Systems Research Laboratory, USDA-ARS,Route 3, Box 215, Lubbock, TX 79401, U.S.A. (Received November 25, 1987; Accepted March 2, 1988) 相似文献
99.
Shmuel Muallem Stephen J. Pandol Timothy G. Beeker 《The Journal of membrane biology》1988,106(1):57-69
Summary
45Ca fluxes and free-cytosolic Ca2+ ([Ca2+]
i
) measurements were used to study the effect of Ca2+-mobilizing hormones on plasma membrane Ca2+ permeability and the plasma membrane Ca2+ pump of pancreatic acinar cells. We showed before (Pandol, S.J., et al., 1987.J. Biol. Chem.
262:16963–16968) that hormone stimulation of pancreatic acinar cells activated a plasma membrane Ca2+ entry pathway, which remains activated for as long as the intracellular stores are not loaded with Ca2+. In the present study, we show that activation of this pathway increases the plasma membrane Ca2+ permeability by approximately sevenfold. Despite that, the cells reduce [Ca2+]i back to near resting levels. To compensate for the increased plasma membrane Ca2+ permeability, a plasma membrane Ca2+ efflux mechanism is also activated by the hormones. This mechanism is likely to be the plasma membrane Ca2+ pump. Activation of the plasma membrane Ca2+ pump by the hormones is time dependent and 1.5–2 min of cell stimulation are required for maximal Ca2+ pump activation. From the effect of protein kinase inhibitors on hormone-mediated activation of the pump and the effect of the phorbol ester 12-0-tetradecanoyl phorbol, 13-acetate (TPA) on plasma membrane Ca+ efflux, it is suggested that stimulation of protein kinase C is required for the hormone-dependent activation of the plasma membrane Ca2+ pump. 相似文献
100.
The tensiometric properties of expanded guinea pig skin 总被引:12,自引:0,他引:12
M S Schneider J E Borkow I T Cruz R D Marangoni J Shaffer D Grove 《Plastic and reconstructive surgery》1988,81(3):398-405
Our purpose in this study was to evaluate the tensile properties of expanded skin. In five guinea pigs, 29-cc ovoid tissue expanders were placed and sequentially expanded every 4 days until maximum volume was achieved. Five control and five expanded skins were harvested. Using an Instron tensile testing apparatus, skins were evaluated for stress-strain, maximum stiffness, and tensile strength, and the results were statistically compared. Centrally located expanded specimens demonstrated significantly weaker stress-strain values: 9.51 in.lb/in3 for expanded versus 30.11 in.lb/in3 for control (p less than 0.001). Maximum stiffness was similarly reduced: 4.56 lb/mm2 for expanded vs. 12.98 lb/mm2 for control (p less than 0.001). This is a 67.4 and 64.9 percent reduction, respectively, for the stress-strain and maximum stiffness. No statistically significant difference was seen in peripherally located expanded specimens relative to the controls: stress-strain expanded, 28.7 in.lb/in3 (p greater than 0.5); maximum stiffness expanded, 12.84 lb/mm2 (p greater than 0.5). Expanded skin demonstrated an average 35 percent reduction in tensile strength. We conclude that the tensile properties of expanded skin are significantly less than unexpanded skin and are a function of the degree of expansion. 相似文献