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911.
912.
Ivana Seccareccia Christian Kost Markus Nett 《Applied and environmental microbiology》2015,81(20):7098-7105
Bacteria of the genus Lysobacter are considered to be facultative predators that use a feeding strategy similar to that of myxobacteria. Experimental data supporting this assumption, however, are scarce. Therefore, the predatory activities of three Lysobacter species were tested in the prey spot plate assay and in the lawn predation assay, which are commonly used to analyze myxobacterial predation. Surprisingly, only one of the tested Lysobacter species showed predatory behavior in the two assays. This result suggested that not all Lysobacter strains are predatory or, alternatively, that the assays were not appropriate for determining the predatory potential of this bacterial group. To differentiate between the two scenarios, predation was tested in a CFU-based bioassay. For this purpose, defined numbers of Lysobacter cells were mixed together with potential prey bacteria featuring phenotypic markers, such as distinctive pigmentation or antibiotic resistance. After 24 h, cocultivated cells were streaked out on agar plates and sizes of bacterial populations were individually determined by counting the respective colonies. Using the CFU-based predation assay, we observed that Lysobacter spp. strongly antagonized other bacteria under nutrient-deficient conditions. Simultaneously, the Lysobacter population was increasing, which together with the killing of the cocultured bacteria indicated predation. Variation of the predator/prey ratio revealed that all three Lysobacter species tested needed to outnumber their prey for efficient predation, suggesting that they exclusively practiced group predation. In summary, the CFU-based predation assay not only enabled the quantification of prey killing and consumption by Lysobacter spp. but also provided insights into their mode of predation. 相似文献
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915.
Christoph Fertinger Alicja Franke Rudi van Eldik 《Journal of biological inorganic chemistry》2012,17(1):27-36
Compound I, an oxo–iron(IV) porphyrin π-cation radical species, and its one-electron-reduced form compound II are regarded as key intermediates in reactions catalyzed
by cytochrome P450. Although both reactive intermediates can be easily produced from model systems such as iron(III) meso-tetra(2,4,6-trimethylphenyl)porphyrin hydroxide by selecting appropriate reaction conditions, there are only a few thermal
activation parameters reported for the reactions of compound I analogues, whereas such parameters for the reactions of compound
II analogues have not been investigated so far. Our study demonstrates that ΔH
≠ and ΔS
≠ are closely related to the chemical nature of the substrate and the reactive intermediate (viz., compounds I and II) in epoxidation
and C–H abstraction reactions. Although most studied reactions appear to be enthalpy-controlled (i.e., ΔH
≠ > −TΔS
≠), different results were found for C–H abstractions catalyzed by compound I. Whereas the reaction with 9,10-dihydroanthracene
as a substrate is also dominated by the activation enthalpy (ΔH
≠ = 42 kJ/mol, ΔS
≠ = 41 J/Kmol), the same reaction with xanthene shows a large contribution from the activation entropy (ΔH
≠ = 24 kJ/mol, ΔS
≠ = −100 J/kmol). This is of special interest since the activation barrier for entropy-controlled reactions shows a significant
dependence on temperature, which can have an important impact on the relative reaction rates. As a consequence, a close correlation
between bond strength and reaction rate—as commonly assumed for C–H abstraction reactions—no longer exists. In this way, this
study can contribute to a proper evaluation of experimental and computational data, and to a deeper understanding of mechanistic
aspects that account for differences in the reactivity of compounds I and II. 相似文献
916.
Two percent dimethyl sulfoxide (DMSO) reversibly inhibited DNA synthesis in primary rat hepatocyte cultures maintained with epidermal growth factor (EGF) or hepatocyte growth factor (HGF). These data suggest that, in vitro, DMSO is a non-specific inhibitor of hepatocyte proliferation, regardless of the stimulating mitogen. In addition, removal of DMSO from mitogen-free cultures resulted in an increase in DNA synthesis. Protein synthesis gradually but irreversibly declined in all cultures after DMSO removal. The relevance of these findings to regulation of hepatocyte growth is discussed. 相似文献
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