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From 50 to 90% of wild plant species worldwide produce seeds that are dormant upon maturity, with specific dormancy traits driven by species' occurrence geography, growth form, and genetic factors. While dormancy is a beneficial adaptation for intact natural systems, it can limit plant recruitment in restoration scenarios because seeds may take several seasons to lose dormancy and consequently show low or erratic germination. During this time, seed predation, weed competition, soil erosion, and seed viability loss can lead to plant re‐establishment failure. Understanding and considering seed dormancy and germination traits in restoration planning are thus critical to ensuring effective seed management and seed use efficiency. There are five known dormancy classes (physiological, physical, combinational, morphological, and morphophysiological), each requiring specific cues to alleviate dormancy and enable germination. The dormancy status of a seed can be determined through a series of simple steps that account for initial seed quality and assess germination across a range of environmental conditions. In this article, we outline the steps of the dormancy classification process and the various corresponding methodologies for ex situ dormancy alleviation. We also highlight the importance of record‐keeping and reporting of seed accession information (e.g. geographic coordinates of the seed collection location, cleaning and quality information, storage conditions, and dormancy testing data) to ensure that these factors are adequately considered in restoration planning.  相似文献   
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Using a common temperate herbaceous terrestrial orchid from Australia (Caladenia latifolia) this study investigated 19 asymbiotic media variations comprising four commonly used basal media [half‐strength Murashige and Skoog (½MS), Knudson C (KC), Pa5, and Vacin and Went (VW), with combinations of the plant growth regulators 6‐benzylaminopurine (BA) and α‐naphthalene acetic acid (NAA) or coconut water (CW) and compared their performance with germination on a standard symbiotic germination medium, oatmeal agar (OMA). Percentage germination of seeds every 2 weeks for a total of 8 weeks (five replicates per treatment), time to germination, and growth and development phases in seedlings were recorded. ½MS with 5% (v/v) fresh CW delivered 93% germination, with seedling vigour and development indistinguishable from OMA (95% germination). The same protocol was applied to a further ten species (including the endangered Caladenia huegelii), demonstrating high asymbiotic germination performance (60–93%) across a wide phylogenetic range of terrestrial orchid species. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 556–566.  相似文献   
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Major histocompatibility complex (MHC) class II molecules exhibit conformational heterogeneity, which influences their ability to stimulate CD4 T cells and drive immune responses. Previous studies suggest a role for the transmembrane domain of the class II αβ heterodimer in determining molecular structure and function. Our previous studies identified an MHC class II conformer that is marked by the Ia.2 epitope. These Ia.2+ class II conformers are lipid raft-associated and able to drive both tyrosine kinase signaling and efficient antigen presentation to CD4 T cells. Here, we establish that the Ia.2+ I-Ak conformer is formed early in the class II biosynthetic pathway and that differential pairing of highly conserved transmembrane domain GXXXG dimerization motifs is responsible for formation of Ia.2+ versus Ia.2 I-Ak class II conformers and controlling lipid raft partitioning. These findings provide a molecular explanation for the formation of two distinct MHC class II conformers that differ in their inherent ability to signal and drive robust T cell activation, providing new insight into the role of MHC class II in regulating antigen-presenting cell-T cell interactions critical to the initiation and control of multiple aspects of the immune response.  相似文献   
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Although the effects of ethanol on protein receptors and lipid membranes have been studied extensively, ethanol’s effect on vesicles fusing to lipid bilayers is not known. To determine the effect of alcohols on fusion rates, we utilized the nystatin/ergosterol fusion assay to measure fusion of liposomes to a planar lipid bilayer (BLM). The addition of ethanol excited fusion when applied on the cis (vesicle) side, and inhibited fusion on the trans side. Other short-chain alcohols followed a similar pattern. In general, the inhibitory effect of alcohols (trans) occurs at lower doses than the excitatory (cis) effect, with a decrease of 29% in fusion rates at the legal driving limit of 0.08% (w/v) ethanol (IC50 = 0.2% v/v, 34 mM). Similar inhibitory effects were observed with methanol, propanol, and butanol, with ethanol being the most potent. Significant variability was observed with different alcohols when applied to the cis side. Ethanol and propanol enhanced fusion, butanol also enhanced fusion but was less potent, and low doses of methanol mildly inhibited fusion. The inhibition by trans addition of alcohols implies that they alter the planar membrane structure and thereby increase the activation energy required for fusion, likely through an increase in membrane fluidity. The cis data are likely a combination of the above effect and a proportionally greater lowering of the vesicle lysis tension and hydration repulsive pressure that combine to enhance fusion. Alternate hypotheses are also discussed. The inhibitory effect of ethanol on liposome-membrane fusion is large enough to provide a possible biophysical explanation of compromised neuronal behavior.  相似文献   
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J Aimi  H Qiu  J Williams  H Zalkin    J E Dixon 《Nucleic acids research》1990,18(22):6665-6672
The trifunctional enzyme encoding glycinamide ribonucleotide synthetase (GARS)-aminoimidazole ribonucleotide synthetase (AIRS)-glycinamide ribonucleotide transformylase (GART) was cloned by functional complementation of an E. coli mutant using an avian liver cDNA expression library. In E. coli, genes encoding these separate activities (purD, purM, and purN, respectively) produce three proteins. The avian cDNA, in contrast, encodes a single polypeptide with all three enzyme activities. Using the avian DNA as a probe, a cDNA encoding the complete coding sequence of the trifunctional human enzyme was also isolated and sequenced. The deduced amino acid sequence of the human and avian polyproteins show extensive sequence homologies to the bacterial purD, purM, and purN encoded proteins. Avian and human liver RNAs appear to encode both a trifunctional enzyme (G-ARS-AIRS-GART) as well as an RNA which encodes only GARS. The trifunctional protein has been implicated in the pathology of Downs Syndrome and molecular tools are now available to explore this hypothesis. Initial efforts to compare the expression of GARS-AIRS-GART between a normal fibroblast cell line and a Downs Syndrome cell line indicate that the levels of RNA are similar.  相似文献   
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A recombinant protein-tyrosine-phosphatase has been expressed in Escherichia coli and purified to a single band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis using affinity chromatography. When the phosphatase was allowed to react with 32P-labeled substrates and then rapidly denaturated, a 32P-labeled phosphoprotein could be visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Transient formation of a 32P-labeled phosphoprotein was observed, and the 32P-labeled protein disappeared as substrate was consumed. In the presence of 32P-labeled p-nitrophenyl phosphate, 0.27 mol of phosphate was incorporated per mol of protein-tyrosine-phosphatase. Site-directed mutagenesis of a catalytically essential cystine residue (position 215) in the recombinant protein resulted in an inactive enzyme, and no phosphoprotein was formed. The 32P-labeled phosphoprotein showed a maximum lability between pH 2.5 and 3.5 and was rapidly decomposed in the presence of iodine. These properties, along with additional site-directed mutations, suggest that the protein-tyrosine-phosphatase forms a covalent thiol phosphate linkage between Cys215 and phosphate.  相似文献   
10.
Active site labeling of a receptor-like protein tyrosine phosphatase.   总被引:1,自引:0,他引:1  
The inactivation of the cytoplasmic domain of rat LAR, a receptor-like protein tyrosine phosphatase (PTPase), by iodoacetate and not by iodoacetamide suggested that iodoacetate interacts in a highly selective manner with the enzyme. The data indicate that iodoacetate binds at the active site of the enzyme with a stoichiometry of 0.8 mol of iodoacetate bound per mol of rat LAR. A single [14C]iodoacetate-labeled peptide was isolated following endoproteinase Lys-C digestion of the radiolabeled PTPase. Sequence analysis of the active site labeled peptide demonstrates that Cys-1522 contains the radiolabel. This residue has been shown by site-directed mutagenesis to be essential for rat LAR activity (Pot, D. A., Woodford, T. A., Remboutsika, E., Haun, R. S., and Dixon, J. E. (1991) J. Biol. Chem. 266, 19688-19696). Iodoacetate reacts only with the first domain of this double domain PTPase. These results, for the first time, directly identify the highly reactive cysteine residue at the active site of a PTPase and highlight the ability of this residue to participate as a nucleophile in the hydrolysis of phosphate from tyrosine.  相似文献   
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