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Comparison of the diversity and community structure of Coleoptera (Passalidae) collected in Los Tuxtlas, Veracruz, Mexico, in primary and secondary tropical forest has been carried out. The saproxylophagous beetles studied can be differentiated according to their presence in three distinct microhabitats of rotting logs: underbark, sapwood—heartwood and microhabitat generalists. Over the 2-year study period, 12 passalid species were recorded (six Passalini and six Proculini) represented by a total of 2971 individuals, collected from 234 rotting logs. The rarefaction method, the lognormal species—abundance relationship, and the nonparametric jackknife method were used to compare species richness between the habitats. The data were also fitted to log series, truncated lognormal, geometric, and broken-stick species abundance models to detect changes in community structure. The community composition of Passalidae in Los Tuxtlas did not differ ostensibly between the primary and secondary forests. Neither the mean number of individuals nor the biomass per log differed significantly. Furthermore, there were no significant differences between the two habitats in terms of the number of underbark, sapwood/heartwood, and microhabitat generalist species. Different richness estimators indicated that the primary forest community is only slightly richer. The slight decrease in richness of the secondary forest is related to a decrease in dominance by certain species, as well as to a more balanced abundance distribution, which is adequately described by the broken-stick model. Complementary explanations for this pattern may be: (1) that logging reduces the abundance of dominant species, thus preventing competitive exclusion in the secondary forest; and (2) that passalid diversity is not regulated by the diversity of tree species. 相似文献
993.
Biotransformation of Explosives by the Old Yellow Enzyme Family of Flavoproteins 总被引:7,自引:4,他引:3
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Richard E. Williams Deborah A. Rathbone Nigel S. Scrutton Neil C. Bruce 《Applied microbiology》2004,70(6):3566-3574
Several independent studies of bacterial degradation of nitrate ester explosives have demonstrated the involvement of flavin-dependent oxidoreductases related to the old yellow enzyme (OYE) of yeast. Some of these enzymes also transform the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT). In this work, catalytic capabilities of five members of the OYE family were compared, with a view to correlating structure and function. The activity profiles of the five enzymes differed substantially; no one compound proved to be a good substrate for all five enzymes. TNT is reduced, albeit slowly, by all five enzymes. The nature of the transformation products differed, with three of the five enzymes yielding products indicative of reduction of the aromatic ring. Our findings suggest two distinct pathways of TNT transformation, with the initial reduction of TNT being the key point of difference between the enzymes. Characterization of an active site mutant of one of the enzymes suggests a structural basis for this difference. 相似文献
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Mohamed Mohideen Quwailid Alison Hugill Neil Dear Lucie Vizor Sara Wells Emma Horner Shelly Fuller Jessica Weedon Hamish McMath Paul Woodman David Edwards David Campbell Susan Rodger Joanne Carey Ann Roberts Pete Glenister Zuzanna Lalanne Nick Parkinson Emma L. Coghill Richard McKeone Sam Cox John Willan Andy Greenfield David Keays Saffron Brady Nigel Spurr Ian Gray Jackie Hunter Steve D.M. Brown Roger D. Cox 《Mammalian genome》2004,15(8):585-591
N-ethyl-N-nitrosourea (ENU) introduces mutations throughout the mouse genome at relatively high efficiency. Successful high-throughput phenotype screens have been reported and alternative screens using sequence-based approaches have been proposed. For the purpose of generating an allelic series in selected genes by a sequence-based approach, we have constructed an archive of over 4000 DNA samples from individual F1 ENU-mutagenized mice paralleled by frozen sperm samples. Together with our previously reported archive, the total size now exceeds 6000 individuals. A gene-based screen of 27.4 Mbp of DNA, carried out using denaturing high-performance liquid chromatography (DHPLC), found a mutation rate of 1 in 1.01 Mbp of which 1 in 1.82 Mbp were potentially functional. Screening of whole or selected regions of genes on subsets of the archive has allowed us to identify 15 new alleles from 9 genes out of 15 tested. This is a powerful adjunct to conventional mutagenesis strategies and has the advantage of generating a variety of alleles with potentially different phenotypic outcomes that facilitate the investigation of gene function. It is now available to academic collaborators as a community resource. 相似文献
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Zhu F Davies P Thompsett AR Kelly SM Tranter GE Hecht L Isaacs NW Brown DR Barron LD 《Biochemistry》2008,47(8):2510-2517
The binding of divalent copper ions to the full-length recombinant murine prion protein PrP23-231 at neutral pH was studied using vibrational Raman optical activity (ROA) and ultraviolet circular dichroism (UV CD). The effect of the Cu2+ ions on PrP structure depends on whether they are added after refolding of the protein in water or are present during the refolding process. In the first case ROA reveals that the hydrated alpha-helix is lost, with UV CD revealing a drop from approximately 25% to approximately 18% in the total alpha-helix content. The lost alpha-helix could be that comprising residues 145-156, located within the region associated with scrapie PrP formation. In the second case, ROA reveals the protein's structure to be almost completely disordered/irregular, with UV CD revealing a drop in total alpha-helix content to approximately 5%. Hence, although Cu2+ binding takes place exclusively within the unfolded/disordered N-terminal region, it can profoundly affect the structure of the folded/alpha-helical C-terminal region. This is supported by the finding that refolding in the presence of Cu2+ of a mutant in which the first six histidines associated with copper binding to the N-terminal region are replaced by alanine has a similar alpha-helix content to the metal-free protein. In contrast, when the protein is refolded in the presence of divalent manganese ions, ROA indicates the alpha-helix is reinforced, with UV CD revealing an increase in total alpha-helix content to approximately 30%. The very different influence of Cu2+ and Mn2+ ions on prion protein structure may originate in the different stability constants and geometries of their complexes. 相似文献
999.
Bender RP Jablonksy MJ Shadid M Romaine I Dunlap N Anklin C Graves DE Osheroff N 《Biochemistry》2008,47(15):4501-4509
Etoposide is a widely prescribed anticancer agent that stabilizes topoisomerase II-mediated DNA strand breaks. The drug contains a polycyclic ring system (rings A-D), a glycosidic moiety at C4, and a pendant ring (E-ring) at C1. A recent study that focused on yeast topoisomerase II demonstrated that the H15 geminal protons of the etoposide A-ring, the H5 and H8 protons of the B-ring, and the H2', H6', 3'-methoxyl, and 5'-methoxyl protons of the E-ring contact topoisomerase II in the binary enzyme-drug complex [ Wilstermann et al. (2007) Biochemistry 46, 8217-8225 ]. No interactions with the C4 sugar were observed. The present study used DNA cleavage assays, saturation transfer difference [ (1)H] NMR spectroscopy, and enzyme-drug binding studies to further define interactions between etoposide and human topoisomerase IIalpha. Etoposide and three derivatives that lacked the C4 sugar were analyzed. Except for the sugar, 4'-demethyl epipodophyllotoxin is identical to etoposide, epipodophyllotoxin contains a 4'-methoxyl group on the E-ring, and 6,7- O, O-demethylenepipodophyllotoxin replaces the A-ring with a diol. Results suggest that etoposide-topoisomerase IIalpha binding is driven by interactions with the A- and B-rings and potentially by stacking interactions with the E-ring. We propose that the E-ring pocket on the enzyme is confined, because the addition of bulk to this ring adversely affects drug function. The A- and E-rings do not appear to contact DNA in the enzyme-drug-DNA complex. Conversely, the sugar moiety subtly alters DNA interactions. The identification of etoposide substituents that contact topoisomerase IIalpha in the binary complex has predictive value for drug behavior in the enzyme-etoposide-DNA complex. 相似文献
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