全文获取类型
收费全文 | 666386篇 |
免费 | 72360篇 |
国内免费 | 188篇 |
出版年
2018年 | 5764篇 |
2016年 | 7676篇 |
2015年 | 10155篇 |
2014年 | 12102篇 |
2013年 | 16822篇 |
2012年 | 19033篇 |
2011年 | 19653篇 |
2010年 | 13302篇 |
2009年 | 12543篇 |
2008年 | 17869篇 |
2007年 | 18534篇 |
2006年 | 17652篇 |
2005年 | 16880篇 |
2004年 | 16782篇 |
2003年 | 16053篇 |
2002年 | 15681篇 |
2001年 | 31359篇 |
2000年 | 31512篇 |
1999年 | 24579篇 |
1998年 | 7941篇 |
1997年 | 8367篇 |
1996年 | 7793篇 |
1995年 | 7460篇 |
1994年 | 7317篇 |
1993年 | 7511篇 |
1992年 | 20152篇 |
1991年 | 20038篇 |
1990年 | 19352篇 |
1989年 | 18865篇 |
1988年 | 17964篇 |
1987年 | 17019篇 |
1986年 | 15678篇 |
1985年 | 15442篇 |
1984年 | 12603篇 |
1983年 | 10946篇 |
1982年 | 8192篇 |
1981年 | 7301篇 |
1980年 | 7031篇 |
1979年 | 11939篇 |
1978年 | 9333篇 |
1977年 | 8544篇 |
1976年 | 7964篇 |
1975年 | 8806篇 |
1974年 | 9679篇 |
1973年 | 9485篇 |
1972年 | 8671篇 |
1971年 | 7950篇 |
1970年 | 7034篇 |
1969年 | 6914篇 |
1968年 | 6448篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Bo R. Park Ryszard A. Zielke Igor H. Wierzbicki Kristie C. Mitchell Jeffrey H. Withey Aleksandra E. Sikora 《Journal of bacteriology》2015,197(6):1051-1064
Vibrio cholerae is autochthonous to various aquatic niches and is the etiological agent of the life-threatening diarrheal disease cholera. The persistence of V. cholerae in natural habitats is a crucial factor in the epidemiology of cholera. In contrast to the well-studied V. cholerae-chitin connection, scarce information is available about the factors employed by the bacteria for the interaction with collagens. Collagens might serve as biologically relevant substrates, because they are the most abundant protein constituents of metazoan tissues and V. cholerae has been identified in association with invertebrate and vertebrate marine animals, as well as in a benthic zone of the ocean where organic matter, including collagens, accumulates. Here, we describe the characterization of the V. cholerae putative collagenase, VchC, encoded by open reading frame VC1650 and belonging to the subfamily M9A peptidases. Our studies demonstrate that VchC is an extracellular collagenase degrading native type I collagen of fish and mammalian origin. Alteration of the predicted catalytic residues coordinating zinc ions completely abolished the protein enzymatic activity but did not affect the translocation of the protease by the type II secretion pathway into the extracellular milieu. We also show that the protease undergoes a maturation process with the aid of a secreted factor(s). Finally, we propose that V. cholerae is a collagenovorous bacterium, as it is able to utilize collagen as a sole nutrient source. This study initiates new lines of investigations aiming to uncover the structural and functional components of the V. cholerae collagen utilization program. 相似文献
2.
Ryan Roth Richard Swanson Gonzalo Izaguirre Susan C. Bock Peter G. W. Gettins Steven T. Olson 《The Journal of biological chemistry》2015,290(47):28020-28036
Past studies have suggested that a key feature of the mechanism of heparin allosteric activation of the anticoagulant serpin, antithrombin, is the release of the reactive center loop P14 residue from a native state stabilizing interaction with the hydrophobic core. However, more recent studies have indicated that this structural change plays a secondary role in the activation mechanism. To clarify this role, we expressed and characterized 15 antithrombin P14 variants. The variants exhibited basal reactivities with factors Xa and IXa, heparin affinities and thermal stabilities that were dramatically altered from wild type, consistent with the P14 mutations perturbing native state stability and shifting an allosteric equilibrium between native and activated states. Rapid kinetic studies confirmed that limiting rate constants for heparin allosteric activation of the mutants were altered in conjunction with the observed shifts of the allosteric equilibrium. However, correlations of the P14 mutations'' effects on parameters reflecting the allosteric activation state of the serpin were inconsistent with a two-state model of allosteric activation and suggested multiple activated states. Together, these findings support a minimal three-state model of allosteric activation in which the P14 mutations perturb equilibria involving distinct native, intermediate, and fully activated states wherein the P14 residue retains an interaction with the hydrophobic core in the intermediate state but is released from the core in the fully activated state, and the bulk of allosteric activation has occurred in the intermediate. 相似文献
3.
Alcione Miotto Carlos A. Ceretta Gustavo Brunetto Fernando T. Nicoloso Eduardo Girotto Júlia G. Farias Tadeu L. Tiecher Lessandro De Conti Gustavo Trentin 《Plant and Soil》2014,374(1-2):593-610
Aims
This study investigated Cu uptake and accumulation as well as physiological and biochemical changes in grapevines grown in soils containing excess Cu.Methods
The grapevines were collected during two productive cycles from three vineyards with increasing concentrations of Cu in the soil and at various growth stages, before and after the application of Cu-based fungicides. The Cu concentrations in the grapevine organs and the macronutrients and biochemical parameters in the leaf blades were analyzed.Results
At close to the flowering stage of the grapevines, the concentration and content of Cu in the leaves were increased. However, the Cu concentrations in the roots, stem, shoots and bunches did not correlate with the metal concentrations in the soil. The application of Cu-based fungicides to the leaves increased the Cu concentrations in the shoots, leaves and rachis; however, the effect of the fungicides on the Cu concentration in the berries was not significant. The biochemical analyses of the leaf blades demonstrated symptoms of oxidative stress that correlated with the Cu concentrations in soil.Conclusions
The increased availability of Cu in soil had a slight effect on the levels and accumulation of Cu in mature grapevines during the productive season and did not alter the nutritional status of the plant. However, increased Cu concentrations were observed in the leaves. The evidence of oxidative stress in the leaves correlated with the increased levels of Cu in soil. 相似文献4.
5.
6.
J. Kim Holloway Xianfei Sun Rayka Yokoo Anne M. Villeneuve Paula E. Cohen 《The Journal of cell biology》2014,205(5):633-641
Meiotic crossovers (COs) are crucial for ensuring accurate homologous chromosome segregation during meiosis I. Because the double-strand breaks (DSBs) that initiate meiotic recombination greatly outnumber eventual COs, this process requires exquisite regulation to narrow down the pool of DSB intermediates that may form COs. In this paper, we identify a cyclin-related protein, CNTD1, as a critical mediator of this process. Disruption of Cntd1 results in failure to localize CO-specific factors MutLγ and HEI10 at designated CO sites and also leads to prolonged high levels of pre-CO intermediates marked by MutSγ and RNF212. These data show that maturation of COs is intimately coupled to deselection of excess pre-CO sites to yield a limited number of COs and that CNTD1 coordinates these processes by regulating the association between the RING finger proteins HEI10 and RNF212 and components of the CO machinery. 相似文献
7.
Andrea Dichlberger Stefanie Schlager Katariina Maaninka Wolfgang J. Schneider Petri T. Kovanen 《Journal of lipid research》2014,55(12):2471-2478
Human mast cells (MCs) contain TG-rich cytoplasmic lipid droplets (LDs) with high arachidonic acid (AA) content. Here, we investigated the functional role of adipose TG lipase (ATGL) in TG hydrolysis and the ensuing release of AA as substrate for eicosanoid generation by activated human primary MCs in culture. Silencing of ATGL in MCs by siRNAs induced the accumulation of neutral lipids in LDs. IgE-dependent activation of MCs triggered the secretion of the two major eicosanoids, prostaglandin D2 (PGD2) and leukotriene C4 (LTC4). The immediate release of PGD2 from the activated MCs was solely dependent on cyclooxygenase (COX) 1, while during the delayed phase of lipid mediator production, the inducible COX-2 also contributed to its release. Importantly, when ATGL-silenced MCs were activated, the secretion of both PGD2 and LTC4 was significantly reduced. Interestingly, the inhibitory effect on the release of LTC4 was even more pronounced in ATGL-silenced MCs than in cytosolic phospholipase A2-silenced MCs. These data show that ATGL hydrolyzes AA-containing TGs present in human MC LDs and define ATGL as a novel regulator of the substrate availability of AA for eicosanoid generation upon MC activation. 相似文献
8.
Hemant Kulkarni Peter J. Meikle Manju Mamtani Jacquelyn M. Weir Marcio Almeida Vincent Diego Juan Manuel Peralta Christopher K. Barlow Claire Bellis Thomas D. Dyer Laura Almasy Michael C. Mahaney Anthony G. Comuzzie Harald H. H. G?ring Joanne E. Curran John Blangero 《Journal of lipid research》2014,55(5):939-946
Plasma lipidome is now increasingly recognized as a potentially important marker of chronic diseases, but the exact extent of its contribution to the interindividual phenotypic variability in family studies is unknown. Here, we used the rich data from the ongoing San Antonio Family Heart Study (SAFHS) and developed a novel statistical approach to quantify the independent and additive value of the plasma lipidome in explaining metabolic syndrome (MS) variability in Mexican American families recruited in the SAFHS. Our analytical approach included two preprocessing steps: principal components analysis of the high-resolution plasma lipidomics data and construction of a subject-subject lipidomic similarity matrix. We then used the Sequential Oligogenic Linkage Analysis Routines software to model the complex family relationships, lipidomic similarities, and other important covariates in a variance components framework. Our results suggested that even after accounting for the shared genetic influences, indicators of lipemic status (total serum cholesterol, TGs, and HDL cholesterol), and obesity, the plasma lipidome independently explained 22% of variability in the homeostatic model of assessment-insulin resistance trait and 16% to 22% variability in glucose, insulin, and waist circumference. Our results demonstrate that plasma lipidomic studies can additively contribute to an understanding of the interindividual variability in MS. 相似文献
9.
10.
Dayanjan S. Wijesinghe Matthew Brentnall Jennifer A. Mietla L. Alexis Hoeferlin Robert F. Diegelmann Lawrence H. Boise Charles E. Chalfant 《Journal of lipid research》2014,55(7):1298-1309
In these studies, the role of ceramide-1-phosphate (C1P) in the wound-healing process was investigated. Specifically, fibroblasts isolated from mice with the known anabolic enzyme for C1P, ceramide kinase (CERK), ablated (CERK−/− mice) and their wild-type littermates (CERK+/+) were subjected to in vitro wound-healing assays. Simulation of mechanical trauma of a wound by scratching a monolayer of fibroblasts from CERK+/+ mice demonstrated steadily increasing levels of arachidonic acid in a time-dependent manner in stark contrast to CERK−/− fibroblasts. This observed difference was reflected in scratch-induced eicosanoid levels. Similar, but somewhat less intense, changes were observed in a more complex system utilizing skin biopsies obtained from CERK-null mice. Importantly, C1P levels increased during the early stages of human wound healing correlating with the transition from the inflammatory stage to the peak of the fibroplasia stage (e.g., proliferation and migration of fibroblasts). Finally, the loss of proper eicosanoid response translated into an abnormal migration pattern for the fibroblasts isolated from CERK−/−. As the proper migration of fibroblasts is one of the necessary steps of wound healing, these studies demonstrate a novel requirement for the CERK-derived C1P in the proper healing response of wounds. 相似文献