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991.
Males and females can be under different evolutionary pressures if sexual and natural selection is differentially operating in each sex. As a result, many species have evolved sexual dichromatism, or differences in coloration between sexes. Although sexual dichromatism is often used as an index of the magnitude of sexual selection, sexual dichromatism is a composite trait. Here, we examine the evolution of sexual dichromatism in one of the largest and most ecologically diverse families of birds, the tanagers, using the avian visual perspective and a species‐level phylogeny. Our results demonstrate that the evolutionary decreases of sexual dichromatism are more often associated with larger and more frequent changes in male plumage coloration, and evolutionary increases are not more often associated with larger changes in either sex. Furthermore, we show that the crown and ventral plumage regions are correlated with sexual dichromatism in males, and that only male plumage complexity is positively correlated with sexual dichromatism. Finally, we demonstrate that light environment is important in shaping both plumage brilliance and complexity. By conducting a multilevel analysis of plumage evolution in males and females, we show that sexual dichromatism evolves via a mosaic of sexual and natural selection in both sexes.  相似文献   
992.
The ptl locus of Bordetella pertussis contains eight open reading frames which are predicted to encode proteins (PtlA to PtlH) that are essential for secretion of pertussis toxin from the bacterium and which are members of a family of transport proteins found in other types of bacteria. We have detected PtlE, PtlF, and PtlG in immunoblots of extracts of B. pertussis by using antibodies raised to fusion proteins consisting of maltose-binding protein and the individual Ptl proteins. These proteins have apparent molecular weights similar to those predicted by DNA sequence analysis. Cell fractionation studies indicated that all three Ptl proteins are associated with the membranes of B. pertussis, suggesting that the Ptl proteins form a gate or channel which facilitates transport of pertussis toxin. Cell extracts of other Bordetella spp. were probed with antibodies to Ptl proteins for the presence of these transport proteins. Neither Bordetella parapertussis nor Bordetella bronchiseptica contained detectable levels of PtlE or PtlF. This lack of detectable Ptl protein may provide an explanation for previous observations which indicated that introduction of the genes encoding pertussis toxin subunits from B. pertussis into other Bordetella spp. results in production of the toxin but not secretion of the toxin.  相似文献   
993.
We previously demonstrated that chronic morphine induces a change in G protein coupling by the mu opioid receptor (MOR) from Gi/o to Gs, concurrent with the instatement of an interaction between Gbetagamma and adenylyl cyclase types II and IV. These two signaling changes confer excitatory effects on the cell in place of the typical inhibition by opioids and are associated with morphine tolerance and dependence. Both signaling changes and these behavioral manifestations of chronic morphine are attenuated by cotreatment with ultra-low-dose naloxone. In the present work, using striatum from chronic morphine-treated rats, we isotyped the Gbeta within Gs and Go heterotrimers that coupled to MOR and compared these to the Gbeta isotype of the Gbetagamma that interacted with adenylyl cyclase II or IV after chronic morphine treatment. Isotyping results show that chronic morphine causes a Gs heterotrimer associated with MOR to release its Gbetagamma to interact with adenylyl cyclase. These data suggest that the switch to Gs coupling by MOR in response to chronic morphine, which is attenuated by ultra-low-dose opioid antagonist cotreatment, leads to a two-pronged stimulation of adenylyl cyclase utilizing both Galpha and Gbetagamma subunits of the Gs protein novel to this receptor.  相似文献   
994.
The authors describe the discovery of a new class of inhibitors to an essential Streptococcus pneumoniae cell wall biosyn-thesis enzyme, MurF, by a novel affinity screening method. The strategy involved screening very large mixtures of diverse small organic molecules against the protein target on the basis of equilibrium binding, followed by iterative ultrafiltration steps and ligand identification by mass spectrometry. Hits from any affinity-based screening method often can be relatively nonselective ligands, sometimes referred to as "nuisance" or "promiscuous" compounds. Ligands selective in their binding affinity for the MurF target were readily identified through electronic subtraction of an empirically determined subset of promiscuous compounds in the library without subsequent selectivity panels. The complete strategy for discovery and identification of novel specific ligands can be applied to all soluble protein targets and a wide variety of ligand libraries.  相似文献   
995.
996.
The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in tumor cell lines, whereas normal cells appear to be protected from its cytotoxic effects. Therefore TRAIL holds promise as a potential therapeutic agent against cancer. To elucidate some of the critical factors that contribute to TRAIL resistance, we performed a genetic screen in the human colon carcinoma cell line SW480 by infecting this TRAIL-sensitive cell line with a human placental cDNA retroviral library and isolating TRAIL-resistant clones. Characterization of the resulting clones for inhibitors of TRAIL-induced death (ITIDs) led to the isolation of c-FLIP(S), Bax inhibitor 1, and Bcl-XL as candidate suppressors of TRAIL signaling. We have demonstrated that c-FLIP(S) and Bcl-XL are sufficient when overexpressed to convey resistance to TRAIL treatment in previously sensitive cell lines. Furthermore both c-FLIP(S) and Bcl-XL protected against overexpression of the TRAIL receptors DR4 and KILLER/DR5. When c-FLIP(S) and Bcl-XL were overexpressed together in SW480 and HCT 116, an additive inhibitory effect was observed after TRAIL treatment suggesting that these two molecules function in the same pathway in the cell lines tested. Furthermore, we have demonstrated for the first time that a proapoptotic member of the Bcl-2 family, Bax, is required for TRAIL-mediated apoptosis in HCT 116 cells. Surprisingly, we have found that the serine/threonine protein kinase Akt, which is an upstream regulator of both c-FLIP(S) and Bcl-XL, is not sufficient when overexpressed to protect against TRAIL in the cell lines tested. These results suggest a key role for c-FLIP(S), Bcl-XL, and Bax in determining tumor cell sensitivity to TRAIL.  相似文献   
997.
Evaluations of plant water use in ecosystems around the world reveal a shared capacity by many different species to absorb rain, dew, or fog water directly into their leaves or plant crowns. This mode of water uptake provides an important water subsidy that relieves foliar water stress. Our study provides the first comparative evaluation of foliar uptake capacity among the dominant plant taxa from the coast redwood ecosystem of California where crown-wetting events by summertime fog frequently occur during an otherwise drought-prone season. Previous research demonstrated that the dominant overstory tree species, Sequoia sempervirens, takes up fog water by both its roots (via drip from the crown to the soil) and directly through its leaf surfaces. The present study adds to these early findings and shows that 80% of the dominant species from the redwood forest exhibit this foliar uptake water acquisition strategy. The plants studied include canopy trees, understory ferns, and shrubs. Our results also show that foliar uptake provides direct hydration to leaves, increasing leaf water content by 2–11%. In addition, 60% of redwood forest species investigated demonstrate nocturnal stomatal conductance to water vapor. Such findings indicate that even species unable to absorb water directly into their foliage may still receive indirect benefits from nocturnal leaf wetting through suppressed transpiration. For these species, leaf-wetting events enhance the efficacy of nighttime re-equilibration with available soil water and therefore also increase pre-dawn leaf water potentials.  相似文献   
998.
Shewanella oneidensis MR-1, a facultatively anaerobic gammaproteobacterium, respires a variety of anaerobic terminal electron acceptors, including the inorganic sulfur compounds sulfite (SO32−), thiosulfate (S2O32−), tetrathionate (S4O62−), and elemental sulfur (S0). The molecular mechanism of anaerobic respiration of inorganic sulfur compounds by S. oneidensis, however, is poorly understood. In the present study, we identified a three-gene cluster in the S. oneidensis genome whose translated products displayed 59 to 73% amino acid similarity to the products of phsABC, a gene cluster required for S0 and S2O32− respiration by Salmonella enterica serovar Typhimurium LT2. Homologs of phsA (annotated as psrA) were identified in the genomes of Shewanella strains that reduce S0 and S2O32− yet were missing from the genomes of Shewanella strains unable to reduce these electron acceptors. A new suicide vector was constructed and used to generate a markerless, in-frame deletion of psrA, the gene encoding the putative thiosulfate reductase. The psrA deletion mutant (PSRA1) retained expression of downstream genes psrB and psrC but was unable to respire S0 or S2O32− as the terminal electron acceptor. Based on these results, we postulate that PsrA functions as the main subunit of the S. oneidensis S2O32− terminal reductase whose end products (sulfide [HS] or SO32−) participate in an intraspecies sulfur cycle that drives S0 respiration.Microbial reduction of inorganic sulfur compounds is central to the biogeochemical cycling of sulfur and other elements such as carbon and metals (29). The ability to reduce elemental sulfur (S0) is found in members of both prokaryotic domains (20), including mesophilic deltaproteobacteria (Desulfovibrio vulgaris, Pelobacter carbinolicus, Geobacter sulfurreducens) (6, 9, 36, 51), thermophilic deltaproteobacteria (Desulfurella acetivorans) (39), gammaproteobacteria (Shewanella putrefaciens) (41), epsilonproteobacteria (Wolinella succinogenes) (49), cyanobacteria (“Oscillatoria limnetica”) (45), and hyperthermophilic archaea (1, 53). Partially reduced inorganic sulfur compounds such as tetrathionate (S4O62−), thiosulfate (S2O32−), and sulfite (SO32−) are also important electron acceptors in the biogeochemical cycling of sulfur (29, 51). S4O62−-reducing bacteria, for example, may produce S2O32− as a metabolic end product of S4O62− reduction, while S2O32− disproportionation is a key reaction catalyzed by sulfate-reducing bacteria, resulting in the formation of sulfate (SO42−) and sulfide (S2−) (26).Shewanella oneidensis MR-1, a facultatively anaerobic gammaproteobacterium, respires a variety of compounds as an anaerobic electron acceptor, including the inorganic sulfur compounds S0, SO32−, S2O32−, and S4O62−; transition metals [e.g., Fe(III) and Mn(IV)]; and radionuclides [e.g., U(VI) and Tc(VII)] (8, 21, 41, 44, 50, 55, 56). The majority of studies of anaerobic respiration by S. oneidensis have focused on the mechanism of electron transport to transition metals and radionuclides (11, 14, 34, 46, 58, 59), while the mechanism of electron transport to inorganic sulfur compounds has not been thoroughly examined.Microbial S0 respiration is postulated to occur via two pathways, both of which are based on an intraspecies sulfur cycle. In the first pathway (catalyzed by members of the genus Salmonella [20]), S2O32− is reduced, yielding HS and SO32− (24). SO32− diffuses from the cell and reacts chemically with extracellular S0 to form S2O32−, which reenters the periplasm and is rereduced, thereby sustaining an intraspecies sulfur cycle. In the second pathway (catalyzed by W. succinogenes [24]), water-soluble polysulfides (Sn2; n > 2), formed by chemical interactions of S0 at pHs >7 (52), are reduced stepwise in the periplasm to Sn 12− and HS. Similarly to what occurs with the first pathway, microbially produced HS diffuses from the cell and reacts chemically with S0 to produce additional Sn2, which reenters the periplasm and is rereduced to sustain an analogous intraspecies sulfur cycle (24).Genetic analyses of S2O32− reduction-deficient mutants of Salmonella enterica serovar Typhimurium have demonstrated that phsA (denoting production of hydrogen sulfide) is required for HS production during S2O32− respiration (10, 17, 22). In addition, phsA-deficient mutants are unable to reduce S0 as an electron acceptor (24). The phsA homolog of W. succinogenes (annotated as psrA, for polysulfide reduction) is required for S0 respiration (32, 37). W. succinogenes psrA is the first gene of a three-gene cluster (including psrA, psrB, and psrC) whose products encode a polysulfide reductase, a quinol oxidase, and a membrane anchor, respectively (15). In addition, the structure of the polysulfide reductase complex (PsrABC) from Thermus thermophilus has recently been solved, and results indicate that PsrC acts as a quinol oxidase that transfers electrons stepwise via PsrB and PsrA to Sn2 during anaerobic S0 respiration (27). The main objectives of the present study were to (i) identify the S. Typhimurium phsA homolog in the S. oneidensis genome, (ii) employ a newly constructed suicide cloning vector for in-frame gene deletion mutagenesis in S. oneidensis to delete the S. Typhimurium phsA homolog of S. oneidensis, and (iii) test the S. oneidensis psrA deletion mutant for respiratory activity on a combination of two electron donors and 11 electron acceptors, including the inorganic sulfur compounds S4O62−, S2O32−, and S0.  相似文献   
999.
A capillary electrophoresis method was used to measure albumin, immunoglobulin G (IgG), transferrin, and uric acid in 230 amniotic fluid (AF) samples collected at 15.15 ± 0.06 weeks gestation. Species were quantified by external calibration using thiamine as internal standard. All major components were detected within 10 min. Migration time reproducibility was 3.0% relative standard deviation (RSD) and normalized peak areas were 12% RSD or better at 190 nm from 81 measurements of a pooled AF sample. The separation profile was not affected by 10 h of storage at room temperature or by 10 freeze-thaw cycles, suggesting that frozen AF samples are suitable for protein biomarker studies.  相似文献   
1000.
Characterization of arginine transport in Helicobacter pylori   总被引:1,自引:0,他引:1  
Mendz GL  Burns BP 《Helicobacter》2003,8(4):245-251
Background. The amino acid L‐arginine is an essential requirement for growth of Helicobacter pylori. Several physiological roles of this amino acid have been identified in the bacterium, but very little is known about the transport of L‐arginine and of other amino acids into H. pylori. Methods. Radioactive tracer techniques using L‐(U‐14C) arginine and the centrifugation through oil method were employed to measure the kinetic parameters, temperature dependence, substrate specificity, and effects of analogues and inhibitors on L‐arginine transport. Results. The transport of arginine at millimolar concentrations was saturable with a Km of 2.4 ± 0.3 mM and Vmax of 1.3 ± 0.2 pmole min?1 (µl cell water)?1 or 31 ± 3 nmole per minute (mg protein)?1 at 20°C, depended on temperature between 4 and 40°C, and was susceptible to inhibitors. These characteristics suggested the presence of one or more arginine carriers. The substrate specificity of the transport system was studied by measuring the effects of L‐arginine analogues and amino acids on the rates of transport of L‐arginine. The absence of inhibition in competition experiments with L‐lysine and L‐ornithine indicated that the transport system was not of the Lysine‐Arginine‐Ornithine or Arginine‐Ornithine types. The presence of different monovalent cations did not affect the transport rates. Several properties of L‐arginine transport were elucidated by investigating the effects of potential inhibitors. Conclusions. The results provided evidence that the transport of L‐arginine into H. pylori cells was carrier‐mediated transport with the driving force supplied by the chemical gradient of the amino acid.  相似文献   
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