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51.
Background
Many systems in nature are characterized by complex behaviour where large cascades of events, or avalanches, unpredictably alternate with periods of little activity. Snow avalanches are an example. Often the size distribution f(s) of a system's avalanches follows a power law, and the branching parameter sigma, the average number of events triggered by a single preceding event, is unity. A power law for f(s), and sigma = 1, are hallmark features of self-organized critical (SOC) systems, and both have been found for neuronal activity in vitro. Therefore, and since SOC systems and neuronal activity both show large variability, long-term stability and memory capabilities, SOC has been proposed to govern neuronal dynamics in vivo. Testing this hypothesis is difficult because neuronal activity is spatially or temporally subsampled, while theories of SOC systems assume full sampling. To close this gap, we investigated how subsampling affects f(s) and sigma by imposing subsampling on three different SOC models. We then compared f(s) and sigma of the subsampled models with those of multielectrode local field potential (LFP) activity recorded in three macaque monkeys performing a short term memory task. 相似文献52.
Robert T. Stibrany Harvey J. Schugar Joseph A. Potenza 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(6):o354-o357
Two of the title compounds, namely (E)‐1,2‐bis(1‐methylbenzimidazol‐2‐yl)ethene, C18H16N4, (Ib), and (E)‐1,2‐bis(1‐ethylbenzimidazol‐2‐yl)ethene, C20H20N4, (Ic), consist of centrosymmetric trans‐bis(1‐alkylbenzimidazol‐2‐yl)ethene molecules, while 3‐ethyl‐2‐[(E)‐2‐(1‐ethylbenzimidazol‐2‐yl)ethenyl]benzimidazol‐1‐ium perchlorate, C20H21N4+·ClO4−, (II), contains the monoprotonated analogue of compound (Ic). In the three structures, the benzimidazole and benzimidazolium moieties are essentially planar; the geometric parameters for the ethene linkages and their bonds to the aromatic groups are consistent with double and single bonds, respectively, implying little, if any, conjugation of the central C=C bonds with the nitrogen‐containing rings. The C—N bond lengths in the N=C—N part of the benzimidazole groups differ and are consistent with localized imine C=N and amine C—N linkages in (Ib) and (Ic); in contrast, the corresponding distances in the benzimidazolium cation are equal in (II), consistent with electron delocalization resulting from protonation of the amine N atom. Crystals of (Ib) and (Ic) contain columns of parallel molecules, which are linked by edge‐over‐edge C—H⋯π overlap. The columns are linked to one another by C—H⋯π interactions and, in the case of (Ib), C—H⋯N hydrogen bonds. Crystals of (II) contain layers of monocations linked by π–π interactions and separated by both perchlorate anions and the protruding ethyl groups; the cations and anions are linked by N—H⋯O hydrogen bonds. 相似文献
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Toman Rudolf Garidel Patrick Andrä Jörg Slaba Katarina Hussein Ahmed Koch Michel HJ Brandenburg Klaus 《BMC biochemistry》2004,5(1):1-14
Background
Coxiella burnetiiis the etiological agent of Q fever found worldwide. The microorganism has like other Gram-negative bacteria a lipopolysaccharide (LPS, endotoxin) in its outer membrane, which is important for the pathogenicity of the bacteria. In order to understand the biological activity of LPS, a detailed physico-chemical analysis of LPS is of utmost importace. 相似文献55.
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