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371.
Susanne Müller Sarah N. Strack Sarah E. Ryan Daniel B. Kearns John R. Kirby 《Applied and environmental microbiology》2015,81(1):203-210
Biofilm formation is a common mechanism for surviving environmental stress and can be triggered by both intraspecies and interspecies interactions. Prolonged predator-prey interactions between the soil bacterium Myxococcus xanthus and Bacillus subtilis were found to induce the formation of a new type of B. subtilis biofilm, termed megastructures. Megastructures are tree-like brachiations that are as large as 500 μm in diameter, are raised above the surface between 150 and 200 μm, and are filled with viable endospores embedded within a dense matrix. Megastructure formation did not depend on TasA, EpsE, SinI, RemA, or surfactin production and thus is genetically distinguishable from colony biofilm formation on MSgg medium. As B. subtilis endospores are not susceptible to predation by M. xanthus, megastructures appear to provide an alternative mechanism for survival. In addition, M. xanthus fruiting bodies were found immediately adjacent to the megastructures in nearly all instances, suggesting that M. xanthus is unable to acquire sufficient nutrients from cells housed within the megastructures. Lastly, a B. subtilis mutant lacking the ability to defend itself via bacillaene production formed megastructures more rapidly than the parent. Together, the results indicate that production of the megastructure facilitates B. subtilis escape into dormancy via sporulation. 相似文献
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Historic species lists for a region can be of great interest to biologists surveying modern faunas. In 2001, we initiated
a 5-year field study to examine the status of insect pollinators in Boulder County grasslands, Boulder, Colorado. Century-old
records of the bee fauna were available from bee specialist Cockerell’s publication (University of Colorado Studies, Boulder,
1907) The Bees of Boulder County. We predicted that 116 species originally found by Cockerell would occur in grassland habitats. We recorded 110 species,
including several species not present in the 1907 collection. We conclude that the bees of the grasslands of Boulder County
have been largely conserved, and we hypothesize that the large amount of preserved habitat in the county has contributed to
maintaining the insects. 相似文献
374.
Gas phase oxygen concentrations of materially closed, energetically open miniature microbial ecosystems were measured periodically. Our results indicate: (i) closed systems remain biologically active for at least 9 years, (ii) Po2 values might serve as an indicator of stability, (iii) each closed ecosystem seems to seek its own unique final Po2 state, and (iv) ecosystem response to experimentally depleted Po2 suggests the presence of positive feedback control. 相似文献
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Initiation of chondroitin sulfate biosynthesis: a kinetic analysis of UDP-D-xylose: core protein beta-D-xylosyltransferase 总被引:1,自引:0,他引:1
The nature of the primary signals important for the addition of xylose to serines on the core protein of the cartilage chondroitin sulfate proteoglycan has been investigated. The importance of consensus sequence elements (Acidic-Acidic-Xxx-Ser-Gly-Xxx-Gly) in the natural acceptor was shown by the significant decrease in acceptor capability of peptide fragments derived by digestion of deglycosylated core protein with Staphylococcus aureus V8 protease, which cleaves within the consensus sequence, compared to the similar reactivity of trypsin-derived peptide fragments, in which consensus sequences remain intact. A comparison of the acceptor efficiencies (Vmax/Km) of synthetic peptides containing the proposed xylosylation consensus sequence and the natural acceptor (deglycosylated core protein) was then made by use of the in vitro xylosyltransferase assay. The two types of substrates were found to have nearly equivalent acceptor efficiencies and to be competitive inhibitors of each other's acceptor capability, with Km = Kiapparent. These results suggest that the artificial peptides containing the consensus sequence are analogues of individual substitution sites on the core protein and allowed the kinetic mechanism of the xylosyltransferase reaction to be investigated, with one of the artificial peptides as a model substrate. The most probable kinetic mechanism for the xylosyltransferase reaction was found to be an ordered single displacement with UDP-xylose as the leading substrate and the xylosylated peptide as the first product released. This represents the first reported formal kinetic mechanism for this glycosyltransferase and the only one reported for a nucleotide sugar:protein transferase. 相似文献