全文获取类型
收费全文 | 5008篇 |
免费 | 658篇 |
国内免费 | 1篇 |
出版年
2021年 | 75篇 |
2018年 | 48篇 |
2017年 | 52篇 |
2016年 | 76篇 |
2015年 | 129篇 |
2014年 | 193篇 |
2013年 | 203篇 |
2012年 | 308篇 |
2011年 | 291篇 |
2010年 | 181篇 |
2009年 | 150篇 |
2008年 | 227篇 |
2007年 | 234篇 |
2006年 | 204篇 |
2005年 | 212篇 |
2004年 | 214篇 |
2003年 | 197篇 |
2002年 | 216篇 |
2001年 | 171篇 |
2000年 | 136篇 |
1999年 | 112篇 |
1998年 | 80篇 |
1997年 | 65篇 |
1996年 | 50篇 |
1995年 | 47篇 |
1994年 | 43篇 |
1993年 | 54篇 |
1992年 | 92篇 |
1991年 | 109篇 |
1990年 | 91篇 |
1989年 | 84篇 |
1988年 | 78篇 |
1987年 | 67篇 |
1986年 | 83篇 |
1985年 | 65篇 |
1984年 | 61篇 |
1983年 | 63篇 |
1982年 | 51篇 |
1981年 | 44篇 |
1980年 | 44篇 |
1979年 | 59篇 |
1978年 | 53篇 |
1977年 | 40篇 |
1976年 | 49篇 |
1975年 | 53篇 |
1974年 | 47篇 |
1973年 | 51篇 |
1972年 | 59篇 |
1971年 | 36篇 |
1969年 | 37篇 |
排序方式: 共有5667条查询结果,搜索用时 578 毫秒
971.
The gibberellin-induced, cysteine-rich protein GIP2 from Petunia hybrida exhibits in planta antioxidant activity 总被引:1,自引:0,他引:1
Wigoda N Ben-Nissan G Granot D Schwartz A Weiss D 《The Plant journal : for cell and molecular biology》2006,48(5):796-805
Numerous GAST-like genes have been identified in various plant species. All code for small proteins with a conserved C-terminal region in which 12 cysteines are located in exactly the same positions. We have previously identified five gibberellin (GA)-induced GAST1-like genes in petunia, GIP1-5. GIP2 is expressed in elongating zones, and its suppression in transgenic petunia plants inhibits stem elongation, suggesting a role for the protein in GA-induced cell growth. However, nothing is known about the biochemical activity of GIP2 or any other GAST-like protein. As all contain putative catalytic disulfide bonds (putative redox-active cysteines), we speculated that they might be involved in redox regulation. Expression analysis of GIP2, GIP4 and GIP5 revealed that they are induced by H(2)O(2). To study whether GIP2 modulates H(2)O(2) levels, we generated transgenic petunia plants expressing GIP2 under the regulation of the ubiquitous CaMV 35S promoter. The transgene reduced H(2)O(2) levels in leaves following wounding. It also reduced the levels of H(2)O(2) in guard cells following osmotic stress and ABA treatments, leading to the suppression of stomatal closure. In addition, the transgene promoted stem and corolla elongation. As reactive oxygen species (ROS) are involved in cell elongation, we suggest that GIP2 affects growth by regulating the levels of ROS. As all known GAST-like proteins contain putative redox-active cysteines, they may all act as antioxidants. 相似文献
972.
Forster R Weiss M Zimmermann T Reynaud EG Verissimo F Stephens DJ Pepperkok R 《Current biology : CB》2006,16(2):173-179
The COPII coat complex mediates the formation of transport carriers at specialized sites of the endoplasmic reticulum (ERES). It consists of the Sar1p GTPase and the Sec23/24p and the Sec13/31p subcomplexes . Both stimulate the GTPase activity of Sar1p , which itself triggers coat disassembly. This built-in GAP activity makes the COPII complex in principle unstable and raises the question of how sufficient stability required for cargo capture and carrier formation is achieved. To address this, we analyzed COPII turnover at single ERES in living cells. The half times for Sar1p, Sec23p, and Sec24p turnover are 1.1, 3.7, and 3.9 s, respectively. Decreasing the amount of transport-competent cargo in the endoplasmic reticulum accelerates turnover of the Sec23/24p and slows down that of Sar1p. A mathematical model of COPII membrane turnover that reproduces the experimental in vivo FRAP kinetics and is consistent with existing in vitro data predicts that Sec23/24p remains membrane associated even after GTP hydrolysis by Sar1p for a duration that is strongly increased by the presence of cargo. We conclude that secretory cargo retains the COPII complex on membranes, after Sar1p release has occurred, and prevents premature disassembly of COPII during cargo sorting and transport carrier formation. 相似文献
973.
Macaranga (Euphorbiaceae) includes about 280 species with a palaeotropic distribution. The genus not only comprises some of the most prominent pioneer tree species in Southeast Asian lowland dipterocarp forests, it also exhibits a substantial radiation of ant-plants (myrmecophytes). Obligate ant-plant mutualisms are formed by about 30 Macaranga species and 13 ant species of the genera Crematogaster or Camponotus. To improve our understanding of the co-evolution of the ants and their host plants, we aim at reconstructing comparative organellar phylogeographies of both partners across their distributional range. Preliminary evidence indicated that chloroplast DNA introgression among closely related Macaranga species might occur. We therefore constructed a comprehensive chloroplast genealogy based on DNA sequence data from the noncoding ccmp2, ccmp6, and atpB-rbcL regions for 144 individuals from 41 Macaranga species, covering all major evolutionary lineages within the three sections that contain myrmecophytes. A total of 88 chloroplast haplotypes were identified, and grouped into a statistical parsimony network that clearly distinguished sections and well-defined subsectional groups. Within these groups, the arrangement of haplotypes followed geographical rather than taxonomical criteria. Thus, up to six chloroplast haplotypes were found within single species, and up to seven species shared a single haplotype. The spatial distribution of the chloroplast types revealed several dispersals between the Malay Peninsula and Borneo, and a deep split between Sabah and the remainder of Borneo. Our large-scale chloroplast genealogy highlights the complex history of migration, hybridization, and speciation in the myrmecophytes of the genus Macaranga. It will serve as a guideline for adequate sampling and data interpretation in phylogeographic studies of individual Macaranga species and species groups. 相似文献
974.
Levin AM Coroneus JG Cocco MJ Weiss GA 《Protein science : a publication of the Protein Society》2006,15(3):478-486
The techniques of phage-displayed homolog shotgun scanning, oligomer complementation, NMR secondary structure analysis, and computational docking provide a complementary suite of tools for dissecting protein-protein interactions. Focusing these tools on the interaction between the catalytic sub-unit of protein kinase A (PKAcat) and caveolin-1 scaffolding domain (CSD) reveals the first structural model for the interaction. Homolog shotgun scanning varied each CSD residue as either a wild-type or a homologous amino acid. Wild-type to homolog ratios from 116 different homologous CSD variants identified side-chain functional groups responsible for precise contacts with PKAcat. Structural analysis by NMR assigned an alpha-helical conformation to the central residues 84- 97 of CSD. The extensive mutagenesis data and NMR secondary structure information provided constraints for developing a model for the PKAcat-CSD interaction. Addition of synthetic CSD to phage-displayed CSD resulted in oligomer complementation, or enhanced binding to PKAcat. Together with previous experiments examining the interaction between CSD and endothelial nitric oxide synthase (eNOS), the results suggest a general oligomerization-dependent enhancement of binding between signal transducing enzymes and caveolin-1. 相似文献
975.
976.
Izadi-Pruneyre N Huché F Lukat-Rodgers GS Lecroisey A Gilli R Rodgers KR Wandersman C Delepelaire P 《The Journal of biological chemistry》2006,281(35):25541-25550
HasA is an extracellular heme binding protein, and HasR is an outer membrane receptor protein from Serratia marcescens. They are the initial partners of a heme internalization system allowing S. marcescens to scavenge heme at very low concentrations due to the very high affinity of HasA for heme (Ka = 5,3 x 10(10) m(-1)). Heme is then transferred to HasR, which has a lower affinity for heme. The mechanism of the heme transfer between HasA and HasR is largely unknown. HasR has been overexpressed and purified in holo and apo forms. It binds one heme molecule with a Ka of 5 x 10(6) m(-1) and shows the characteristic absorbance spectrum of a low spin heme iron. Both holoHasA and apoHasA bind tightly to apoHasR in a 1:1 stoichiometry. In this study we show that heme transfer occurs in vitro in the purified HasA.HasR complex, demonstrating that heme transfer is energy- and TonB complex-independent and driven by a protein-protein interaction. We also show that heme binding to HasR involves two conserved histidine residues. 相似文献
977.
Lansky IB Lukat-Rodgers GS Block D Rodgers KR Ratliff M Wilks A 《The Journal of biological chemistry》2006,281(19):13652-13662
The uptake and utilization of heme as an iron source is a receptor-mediated process in bacterial pathogens and involves a number of proteins required for internalization and degradation of heme. In the following report we provide the first in-depth spectroscopic and functional characterization of a cytoplasmic heme-binding protein PhuS from the opportunistic pathogen Pseudomonas aeruginosa. Spectroscopic characterization of the heme-PhuS complex at neutral pH indicates that the heme is predominantly six-coordinate low spin. However, the resonance Raman spectra and global fit analysis of the UV-visible spectra show that at all pH values between 6 and 10 three distinct species are present to varying degrees. The distribution of the heme across multiple spin states and coordination number highlights the flexibility of the heme environment. We provide further evidence that the cytoplasmic heme-binding proteins, contrary to previous reports, are not heme oxygenases. The degradation of the heme-PhuS complex in the presence of a reducing agent is a result of H2O2 formed by direct reduction of molecular oxygen and does not yield biliverdin. In contrast, the heme-PhuS complex is an intracellular heme trafficking protein that specifically transfers heme to the previously characterized iron-regulated heme oxygenase pa-HO. Surface plasmon resonance experiments confirm that the transfer of heme is driven by a specific protein-protein interaction. This data taken together with the spectroscopic characterization is consistent with a protein that functions to shuttle heme within the cell. 相似文献
978.
Hua QX Liu M Hu SQ Jia W Arvan P Weiss MA 《The Journal of biological chemistry》2006,281(34):24889-24899
The insulins of eutherian mammals contain histidines at positions B5 and B10. The role of His(B10) is well defined: although not required in the mature hormone for receptor binding, in the islet beta cell this side chain functions in targeting proinsulin to glucose-regulated secretory granules and provides axial zincbinding sites in storage hexamers. In contrast, the role of His(B5) is less well understood. Here, we demonstrate that its substitution with Ala markedly impairs insulin chain combination in vitro and blocks the folding and secretion of human proinsulin in a transfected mammalian cell line. The structure and stability of an Ala(B5)-insulin analog were investigated in an engineered monomer (DKP-insulin). Despite its impaired foldability, the structure of the Ala(B5) analog retains a native-like T-state conformation. At the site of substitution, interchain nuclear Overhauser effects are observed between the methyl resonance of Ala(B5) and side chains in the A chain; these nuclear Overhauser effects resemble those characteristic of His(B5) in native insulin. Substantial receptor binding activity is retained (80 +/- 10% relative to the parent monomer). Although the thermodynamic stability of the Ala(B5) analog is decreased (DeltaDeltaG(u) = 1.7 +/- 0.1 kcal/mol), consistent with loss of His(B5)-related interchain packing and hydrogen bonds, control studies suggest that this decrement cannot account for its impaired foldability. We propose that nascent long-range interactions by His(B5) facilitate alignment of Cys(A7) and Cys(B7) in protein-folding intermediates; its conservation thus reflects mechanisms of oxidative folding rather than structure-function relationships in the native state. 相似文献
979.
O'Brien JE Peterson TJ Tong MH Lee EJ Pfaff LE Hewitt SC Korach KS Weiss J Jameson JL 《The Journal of biological chemistry》2006,281(36):26683-26692
980.
Irit Cohen Myriam Maoz Hagit Turm Sorina Grisaru-Granovsky Bella Maly Beatrice Uziely Einat Weiss Rinat Abramovitch Eithan Gross Oded Barzilay Yun Qiu Rachel Bar-Shavit 《PloS one》2010,5(6)