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51.
Presented here are procedural modifications whic permit the utilization of 125I-labeled Met-enkephalin as substrate in the assay of rat brain enkephalin amipeptidase. The hydrolysis of enkephalin is monitored by the release of [125I]tyrosine separated on Porapak Q. The release of tyrosine is proportionate with both increasing time and tissue concentration. The estimated Km is near 10?4 M and the enzyme activity can be inhibited more than 95% with puromycin. The majority of the enzyme activity remains in the 100 000 × g supernatant following differential centrifugation.  相似文献   
52.
The biosynthesis of mammalian mitochondrial cytochromes was explored in primary hepatocyte cultures. When these were pulsed with [35S]methionine in the presence of cycloheximide, eight discrete mitochondrial polypeptides were detected by fluorography after their resolution under denaturing conditions by polyacrylamide gel electrophoresis. Since the pulse labeling of the polypeptides was sensitive to chloramphenicol, an inhibitor of mitochondrial translation, they must be translated on mitochondrial ribosomes. Three were identified as the largest subunits of cytochrome oxidase by their immunoprecipitation with antibody directed against purified rat liver cytochrome oxidase. Another (Mr = 28,000) was identified as one of eight subunits of purified rat liver cytochrome b-c1 complex by its immunoprecipitation with antibody directed against bovine heart b-c1 complex. Since cytochrome b apoprotein is the only product of the mitochondrial genome in the yeast cytochrome b-c1 complex (Krieke, J., Bechmann, H., van Hemert, F. J., Schweyan, R. J., Boer, P. H., Kaudewitz, F., and Groot, G. S. P. (1979) Eur. J. Bio-chem. 101, 607-617), the results strongly suggest that the Mr = 28,000 subunit of liver b-c1 complex is cytochrome b apoprotein. Thus the contribution of the mitochondrial translation system to the cytochrome complexes in liver is identical to that of yeast and Neurospora, and there appears to be no deletion or transfer to the nuclear genome of structural genes for mitochondrially synthesized cytochromes during eukaryotic evolution.  相似文献   
53.
Summary The ultrastructure of the polymorphic vesicular component of the ultimobranchial gland of the domestic fowl (Gallus gallus domesticus) has been described in detail, together with the structure of the cell strands interconnecting the vesicles and the parathyroid nodules lying within the ultimobranchial stroma. The vesicles frequently appear to arise from the nodules by way of the cell strands. The strands show a structure of their component cells intermediate between that of the parathyroid and the vesicular cells, although the position at which the strand changes from an essentially parathyroid structure to an essentially vesicular structure is very variable. The degree and kind of secretory activity within different cell types has been described. A review of the structure of ultimobranchial glands throughout the vertebrates shows that similar tissue with a similar secretory potential has been observed in all vertebrate classes, suggesting a functional significance for this part of the gland.  相似文献   
54.
Although 1,6-anhydro-3,4-dideoxy-,β-d-glycero-hex-3-enopyranos-2-ulose (2) is produced by the acid-catalyzed pyrolysis of both cellulose and 1,6-anhydro-β-d-glucopyranose (1), data presented here show that the principal mechanism of its formation in the pyrolysis of cellulose is not via 1. Furthermore, the data provide evidence that 1 itself is not a primary product of cellulose pyrolysis, so that the principal mechanism of its formation must involve a precursor as yet unidentified.  相似文献   
55.
Aqueous solutions of 5-500 μg/ml aldicarb inhibited hatching of Heterodera schachtii. Addition of hatching agents, zinc chloride, or sugarbeet root diffusate, to the aldicarb solutions did not decrease the inhibition of hatching. When cysts were removed from the aldicarb solufions and then treated for 4 wk in sugarbeet root diffusate, larvae hatched and emerged. Treatments of newly hatched larvae of H. schachtii with 5-100 μg/ml aldicarb depressed later development of larvae on sugarbeet (Beta vulgaris). Similar treatments with aldicarb sulfoxide had less effect on larval development, and aldicarb sulfone had no effect. Numbers of treated larvae that survived and developed were inversely proportional to concentration (0.1-5.0 μg/ml) and duration (0-14 days) of aldicarb treatments. Development of H. schachtii on sugarbeet grown in aldicarb-treated soil was inversely proportional to the concentration of aldicarb in the tested range of 0.75 - 3.0 μg aldicarb/g of soil. Transfer of nematode-infected plants to soil with aldicarb retarded nematode development, whereas transfer of plants first grownin treated soil to nematode-infested soil only slightly suppressed nematode development. Development of H. schachtii was inhibited in slices of storage roots of table beet (B. vulgaris), sugarbeet and turnip, (Brassica rapa), that had grown in soil treated with aldicarb.  相似文献   
56.
ATPase activity of plasma membrane vesicles isolated from oat (Avena sativa L. cv. Goodfield) roots was examined in the presence of various concentrations of MgCl(2) and ATP. A Mg(2+): ATP ratio of about 1 was required for maximal activity regardless of the concentrations used; the optimum concentration for both Mg(2+) and ATP was 9 mm. Based on the ATPase activity at different concentrations of complexed Mg.ATP and free ATP, it is concluded that Mg.ATP is the true substrate of this enzyme.Under certain experimental conditions, high concentrations of MgCl(2) and ATP inhibited the plasma membrane ATPase. On the basis of the relative amounts of free and complexed ATP and Mg(2+), it was found that the different moieties caused different amounts of inhibition. Free ATP inhibited the ATPase at concentrations in excess of 2 mm. Mg.ATP concentrations above 11 mm inhibited the enzyme. Free Mg(2+) caused only a slight inhibition of the ATPase.The Km for Mg.ATP was found to vary from 0.64 to 1.24 mm depending on the experimental conditions. This variation is thought to be due to variable amounts of Mg.ATP, which serves as an inhibitor as well as the substrate, and free ATP, which also inhibits the enzyme.  相似文献   
57.
Comparative observations of Bipolaris sorokiniana and Curvularia geniculata conidia germination as influenced by culture age and temperature showed some distinct differences, but generally established the ability of these organisms to function under similar conditions. Total germination of B. sorokiniana conidia was favored by increasing culture age from 20 to 60 days and temperature to 25°C; total conidia germination of C. geniculata was favored by increasing temperature to 25°C, but increasing culture age decreased germination. These reactions seem associated with conidia age. Maximum proportional intra-population germination of conidia of each organism also varied with culture age and temperature. At temperatures of 5°C and 15°C, amplitude of maximum proportional germination of both organisms increased as culture age was increased from 20 to 40 days and then decreased among 60-day-old cultures. At 25°C and above, amplitude of maximum proportional germination of conidia of both organisms decreased from each older culture. Progressively increasing temperature at a given culture age increased the amplitude of maximum proportional germination up to 25°C for conidia of B. sorokiniana, but generally decreased it for conidia of C. geniculata (except 20-day-old cultures). Frequency (specific 2 h interval) of maximum proportional intrapopulation germination of B. sorokiniana shifted from 6 h to 2 h in response to increasing temperature and culture age; conidia from youngest cultures of C. geniculata shifted to intervals of 4 h and 2 h in response to increasing temperature to 25°C, but among conidia from 60-day-old cultures, frequency shifted to 6 h intervals at all temperatures. Above 25°C, maximum proportional germination of C. geniculata conidia from cultures of all ages occurred at 6 h. It was concluded that the germination response of B. sorokiniana and C. geniculata conidia to temperature and culture age (and, subsequently, conidia age) are enough similar that these organisms could function in a potential ‘disease complex’ on Poa pratensis and Agrostis palustris.  相似文献   
58.
Coral Reefs - The existence of coral reefs is dependent on the production and maintenance of calcium carbonate (CaCO3) framework that is produced through calcification. The net production of CaCO3...  相似文献   
59.
60.

Background  

A full understanding of the patterns and processes of biological diversification requires the dating of evolutionary events, yet the fossil record is inadequate for most lineages under study. Alternatively, a molecular clock approach, in which DNA or amino acid substitution rates are calibrated with fossils or geological/climatic events, can provide indirect estimates of clade ages and diversification rates. The utility of this approach depends on the rate constancy of molecular evolution at a genetic locus across time and across lineages. Although the nuclear ribosomal internal transcribed spacer region (nrITS) is increasingly being used to infer clade ages in plants, little is known about the sources or magnitude of variation in its substitution rate. Here, we systematically review the literature to assess substitution rate variation in nrITS among angiosperms, and we evaluate possible correlates of the variation.  相似文献   
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