全文获取类型
收费全文 | 38599篇 |
免费 | 3629篇 |
国内免费 | 5335篇 |
出版年
2024年 | 90篇 |
2023年 | 481篇 |
2022年 | 1224篇 |
2021年 | 1985篇 |
2020年 | 1430篇 |
2019年 | 1833篇 |
2018年 | 1693篇 |
2017年 | 1308篇 |
2016年 | 1799篇 |
2015年 | 2592篇 |
2014年 | 3086篇 |
2013年 | 3207篇 |
2012年 | 3871篇 |
2011年 | 3523篇 |
2010年 | 2239篇 |
2009年 | 1974篇 |
2008年 | 2249篇 |
2007年 | 2038篇 |
2006年 | 1763篇 |
2005年 | 1468篇 |
2004年 | 1191篇 |
2003年 | 1124篇 |
2002年 | 943篇 |
2001年 | 624篇 |
2000年 | 529篇 |
1999年 | 486篇 |
1998年 | 320篇 |
1997年 | 295篇 |
1996年 | 269篇 |
1995年 | 214篇 |
1994年 | 209篇 |
1993年 | 145篇 |
1992年 | 176篇 |
1991年 | 128篇 |
1990年 | 123篇 |
1989年 | 112篇 |
1988年 | 87篇 |
1987年 | 79篇 |
1986年 | 77篇 |
1985年 | 85篇 |
1984年 | 45篇 |
1983年 | 41篇 |
1982年 | 48篇 |
1981年 | 32篇 |
1979年 | 37篇 |
1978年 | 22篇 |
1977年 | 23篇 |
1974年 | 22篇 |
1973年 | 29篇 |
1971年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
31.
Ke Wang Feiyun Xu Wei Yuan Dongping Zhang Jianping Liu Leyun Sun Liyou Cui Jianhua Zhang Weifeng Xu 《The Plant journal : for cell and molecular biology》2021,107(6):1603-1615
Heterotrimeric G protein is involved in plant growth and development, while the role of rice (Oryza sativa) G protein γ subunit qPE9-1 in response to low-phosphorus (LP) conditions remains unclear. The gene expression of qPE9-1 was significantly induced in rice roots under LP conditions. Rice varieties carrying the qPE9-1 allele showed a stronger primary root response to LP than the varieties carrying the qpe9-1 allele (mutant of the qPE9-1 allele). Transgenic rice plants with the qPE9-1 allele had longer primary roots and higher P concentrations than those with the qpe9-1 allele under LP conditions. The plasma membrane (PM) H+-ATPase was important for the qPE9-1-mediated response to LP. Furthermore, OsGF14b, a 14-3-3 protein that acts as a key component in activating PM H+-ATPase for root elongation, is also involved in the qPE9-1 mediation. Moreover, the overexpression of OsGF14b in WYJ8 (carrying the qpe9-1 allele) partially increased primary root length under LP conditions. Experiments using R18 peptide (a 14-3-3 protein inhibitor) showed that qPE9-1 is important for primary root elongation and H+ efflux under LP conditions by involving the 14-3-3 protein. In addition, rhizosheath weight, total P content, and the rhizosheath soil Olsen-P concentration of qPE9-1 lines were higher than those of qpe9-1 lines under soil drying and LP conditions. These results suggest that the G protein γ subunit qPE9-1 in rice plants modulates root elongation for phosphorus uptake by involving the 14-3-3 protein OsGF14b and PM H+-ATPase, which is required for rice P use. 相似文献
32.
33.
34.
Effects of menstrual cycle on metabolic responses to exercise 总被引:1,自引:0,他引:1
35.
36.
37.
Involvement of a low-molecular-weight substance in in vitro activation of the molybdoenzyme respiratory nitrate reductase from a chlB mutant of Escherichia coli. 总被引:2,自引:1,他引:1
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)
The soluble subcellular fraction of a chlB mutant contains an inactive precursor form of the molybdoenzyme nitrate reductase, which can be activated by the addition to the soluble fraction of protein FA, which is thought to be the active product of the chlB locus. Dialysis or desalting of the chlB soluble fraction leads to the loss of nitrate reductase activation, indicating that some low-molecular-weight material is required for the activation. The protein FA-dependent activation of nitrate reductase can be restored to the desalted chlB soluble fraction by the addition of a clarified extract obtained after heating the chlB soluble fraction at 100 degrees C for 8 min. The heat-stable substance present in this preparation has a molecular weight of approximately 1,000. This substance is distinct from the active molybdenum cofactor since its activity is unimpaired in heat-treated extracts prepared from the organism grown in the presence of tungstate, which leads to loss of cofactor activity. Mutations at the chlA or chlE locus, which are required for molybdenum cofactor biosynthesis, similarly do not affect the activity of the heat-treated extract in the in vitro activation process. Moreover, the active material can be separated from the molybdenum cofactor activity by gel filtration. None of the other known pleiotropic chlorate resistance loci (chlD, chlG) are required for the expression of its activity. Magnesium ATP appears to have a role in the formation of the active substance. We conclude that a low-molecular-weight substance, distinct from the active molybdenum cofactor, is required to bestow activity on the molybdoenzyme nitrate reductase during its biosynthesis. 相似文献
38.
M A Davitz A M Gurnett M G Low M J Turner V Nussenzweig 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(2):520-523
Decay-accelerating factor (DAF) is an integral membrane protein that inhibits amplification of the complement cascade on the cell surface. We and other investigators have shown that DAF is part of a newly characterized family of proteins that are anchored to the cell membrane by phosphatidylinositol (PI). The group includes the variant surface glycoprotein (VSG) of African trypanosomes, the p63 protein of Leishmania, acetylcholinesterase (AChE), alkaline phosphatase, Thy-1, 5'-nucleotidase, and RT6.2--an alloantigen from rat T cells. The structure of the membrane anchor has been best characterized for VSG, but chemical studies of the membrane anchors of AChE and Thy-1 suggest that similar glycolipid moieties anchor these proteins to the cell surface. In the VSG, the membrane anchor consists of an ethanolamine linked covalently to an oligosaccharide and glucosamine; the entire complex is anchored to the cell membrane by PI. Immunologically, this glycolipid defines an epitope, the cross-reacting determinant (CRD), that is only revealed after removal of the diacyl glycerol anchor by a phospholipase C. By Western blotting, we show here that DAF-S (DAF released from the membrane by PI-specific phospholipase C [PIPLC]) also contains CRD. Using a newly developed immunoradiometric assay (IRMA) in which the solid-phase capturing antibody is a monoclonal antibody to DAF and the second antibody is anti-CRD, we have been able to quantitate DAF-S. By IRMA, we show that the reaction between anti-CRD and DAF-S is specific, since the binding is competitively inhibited only by the soluble form of the VSG. These observations further support the concept that the glycolipid anchors of this new family of proteins have similar structures. DAF is also found as a soluble protein in various tissue fluids as well as in Hela cell supernatants. No evidence for the presence of the CRD epitope was found on these proteins, suggesting that these forms of DAF are not released from the surface of cells by endogenous phospholipases. 相似文献
39.
Phosphatidylinositol anchor of HeLa cell alkaline phosphatase 总被引:7,自引:0,他引:7
Alkaline phosphatase from cancer cells, HeLa TCRC-1, was biosynthetically labeled with either 3H-fatty acids or [3H]ethanolamine as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography of immunoprecipitated material. Phosphatidylinositol-specific phospholipase C (PI-PLC) released a substantial proportion of the 3H-fatty acid label from immunoaffinity-purified alkaline phosphatase but had no effect on the radioactivity of [3H]ethanolamine-labeled material. PI-PLC also liberated catalytically active alkaline phosphatase from viable cells, and this could be selectively blocked by monoclonal antibodies to alkaline phosphatase. However, the alkaline phosphatase released from 3H-fatty acid labeled cells by PI-PLC was not radioactive. By contrast, treatment with bromelain removed both the 3H-fatty acid and the [3H]ethanolamine label from the purified alkaline phosphatase. Subtilisin was also able to remove the [3H]ethanolamine-labeled from purified alkaline phosphatase. The 3H radioactivity in alkaline phosphatase purified from [3H]ethanolamine-labeled cells comigrated with authentic [3H]ethanolamine by anion-exchange chromatography after acid hydrolysis. The data suggest that the 3H-fatty acid and [3H]ethanolamine are covalently attached to the carboxyl-terminal segment since bromelain and subtilisin both release alkaline phosphatase from the membrane by cleavage at that end of the polypeptide chain. The data are consistent with findings for other proteins recently shown to be anchored in the membrane through a glycosylphosphatidylinositol structure and indicate that a similar structure contributes to the membrane anchoring of alkaline phosphatase. 相似文献