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91.
In socially monogamous species, extra‐pair paternity may increase the strength of intersexual selection by allowing males with preferred phenotypes to monopolize matings. Several studies have found relationships between male signals and extra‐pair mating, but many others fail to explain variation in extra‐pair mating success. A greater appreciation for the role that ecological contingencies play in structuring behavioural processes may help to reconcile contradictory results. We studied extra‐pair mating in a spatial context in the common yellowthroat (Geothlypis trichas), a territorial wood warbler. Over the course of 6 years, we observed 158 breeding attempts by 99 males, resulting in a total of 369 nests and 520 sampled nestlings. The spatial distribution of territories varied greatly, with males having between 0 and 10 close neighbours and between three and 39 neighbouring nestlings close enough to represent extra‐pair siring opportunities. Both within‐pair and extra‐pair reproductive success increased with breeding density, but the opportunity for sexual selection and strength of selection varied with density. Total variance in reproductive success was highest at low density and was mostly explained by variation in within‐pair success. In contrast, at high density, both within‐pair and extra‐pair successes contributed substantially to variance in reproductive success. The relationships between plumage and extra‐pair mating also varied by density; plumage was under strong sexual selection via extra‐pair mating success at high density, but no selection was detected at low density. Thus, ecological factors that structure social interactions can drive patterns of sexual selection by facilitating or constraining the expression of mating preferences.  相似文献   
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Landauer  Walter  Dunn  L. C. 《Journal of genetics》1930,23(3):397-413
Journal of Genetics -  相似文献   
95.
Summary An active transport system specific for ammonium and methylammonium is decribed in wild type cells of Aspergillus nidulans. This system has a Km of less than 5x10-5 M for ammonium as measured by the uptake of 15NH+ 4 and a Km of 2x10-5 M and apparent Vmax of 11 nanomoles/min/mg dry weight for methylammonium, by the uptake of 14C methylammonium. The system concentrates methylammonium at least 120-fold and is probably regulated by the concentration of internal ammonium.Cells of the mutant strain DER-3 possess a reduced rate of ammonium and methylammonium transport under all conditions tested. DER-3 is a double mutant, one mutation being allelic with meaA8 and designated meaA21, the other is unlinked to meaA and designated mod meaA. The heterozygous diploid DER3/+ has wild type transport, indicating that the mutations are recessive. Cells of the mutant strain amrA1 have impaired transport of ammonium and methylammonium, but only under some conditions. amrA1 is recessive. The possible defects of these mutants are discussed.  相似文献   
96.
Acronycine — an alkaloid with antineoplastic activity against a wide range of experimental tumors — at concentrations of 0.5-12 μg/ml rapidly inhibits RNA synthesis in L5178Y mouse lymphoma and IRC rat monocytic leukemia cultures. Culture growth is arrested only at acronycine concentrations which markedly inhibit RNA synthesis. DNA synthesis is inhibited at rather higher concentrations but this is not a prerequisite of the arrest of growth. It is suggested that the arrest of growth may be a consequence of the inhibition of RNA synthesis. In both cultures arrest of growth coincides with the appearance of many cells with two apparently normal nuclei. Cells are not arrested in mitosis. It is shown these binucleated cells very probably arise from an inhibition of cell cleavage. Studies with synchronized cultures show that at low drug concentrations, more than one cell cycle may elapse before growth is arrested and binucleated cells appear, indicating the effect on cytokinesis is not immediate. The results suggest that the arrest of growth may be a result of a slow depletion of a component essential for cell cleavage. The disturbance at division is a major factor in arresting growth at low drug concentrations. At higher acronycine concentrations, when RNA synthesis may be inhibited by 80–90%, the cytotoxic effects appear earlier and are less specifically directed at cytokinesis; DNA synthesis is then also rapidly and markedly inhibited.  相似文献   
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Single and dual amino acid substitution variants were generated in the TCR CDRs of three TCRs that recognize tumor-associated Ags. Substitutions that enhance the reactivity of TCR gene-modified T cells to the cognate Ag complex were identified using a rapid RNA-based transfection system. The screening of a panel of variants of the 1G4 TCR, that recognizes a peptide corresponding to amino acid residues 157-165 of the human cancer testis Ag NY-ESO-1 (SLLMWITQC) in the context of the HLA-A*02 class I allele, resulted in the identification of single and dual CDR3alpha and CDR2beta amino acid substitutions that dramatically enhanced the specific recognition of NY-ESO-1(+)/HLA-A*02(+) tumor cell lines by TCR gene-modified CD4(+) T cells. Within this group of improved TCRs, a dual substitution in the 1G4 TCR CDR3alpha chain was identified that enhanced Ag-specific reactivity in gene-modified CD4(+) and CD8(+) T cells. Separate experiments on two distinct TCRs that recognize the MART-1 27-35 (AAGIGILTV) peptide/HLA-A*02 Ag complex characterized single amino acid substitutions in both TCRs that enhanced CD4(+) T cell Ag-specific reactivity. These results indicate that simple TCR substitution variants that enhance T cell function can be identified by rapid transfection and assay techniques, providing the means for generating potent Ag complex-specific TCR genes for use in the study of T cell interactions and in T cell adoptive immunotherapy.  相似文献   
99.
The tumor suppressors Tsc1 and Tsc2 form the tuberous sclerosis complex (TSC), a regulator of mTOR activity. Tsc1 stabilizes Tsc2; however, the precise mechanism involved remains elusive. The molecular chaperone heat‐shock protein 90 (Hsp90) is an essential component of the cellular homeostatic machinery in eukaryotes. Here, we show that Tsc1 is a new co‐chaperone for Hsp90 that inhibits its ATPase activity. The C‐terminal domain of Tsc1 (998–1,164 aa) forms a homodimer and binds to both protomers of the Hsp90 middle domain. This ensures inhibition of both subunits of the Hsp90 dimer and prevents the activating co‐chaperone Aha1 from binding the middle domain of Hsp90. Conversely, phosphorylation of Aha1‐Y223 increases its affinity for Hsp90 and displaces Tsc1, thereby providing a mechanism for equilibrium between binding of these two co‐chaperones to Hsp90. Our findings establish an active role for Tsc1 as a facilitator of Hsp90‐mediated folding of kinase and non‐kinase clients—including Tsc2—thereby preventing their ubiquitination and proteasomal degradation.  相似文献   
100.
Oota H  Dunn CW  Speed WC  Pakstis AJ  Palmatier MA  Kidd JR  Kidd KK 《Gene》2007,392(1-2):64-76
Humans have seven alcohol dehydrogenase genes (ADH) falling into five classes. Three out of the seven genes (ADH1A, ADH1B and ADH1C) belonging to Class I are expressed primarily in liver and code the main enzymes catalyzing ethanol oxidization. The three genes are tandemly arrayed within the ADH cluster on chromosome 4 and have very high nucleotide similarity to each other (exons: >90%; introns: >70%), suggesting the genes have been generated by duplication event(s). One explanation for maintaining similarity of such clustered genes is homogenization via gene conversion(s). Alternatively, recency of the duplications or some other functional constraints might explain the high similarities among the genes. To test for gene conversion, we sequenced introns 2, 3, and 8 of all three Class I genes (total>15.0 kb) for five non-human primates--four great apes and one Old World Monkey (OWM)--and compared them with those of humans. The phylogenetic analysis shows each intron sequence clusters strongly within each gene, giving no evidence for gene conversion(s). Several lines of evidence indicate that the first split was between ADH1C and the gene that gave rise to ADH1A and ADH1B. We also analyzed cDNA sequences of the three genes that have been previously reported in mouse and Catarrhines (OWMs, chimpanzee, and humans) and found that the synonymous and non-synonymous substitution (dN/dS) ratios in all pairs are less than 1 representing purifying selection. This suggests that purifying selection is more important than gene conversion(s) in maintaining the overall sequence similarity among the Class I genes. We speculate that the highly conserved sequences on the three duplicated genes in primates have been achieved essentially by maintaining stability of the hetero-dimer formation that might have been related to dietary adaptation in primate evolution.  相似文献   
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