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Neil L. Kelleher Colleen A. Costello Tadhg P. Begley Fred W. McLafferty 《Journal of the American Society for Mass Spectrometry》1995,6(10):981-984
Thiaminase I (E.C. 2.5. 1.2) from Bacillus thiaminolyticus catalyzes the degradation of thiamin (vitamin B1). Unexpected mass heterogeneity (MW 42,127, 42,197, and 42,254; 1:2:1) in recombinant thiaminase I from Escherichia coli was detected by electrospray ionization Fourier-transform mass spectrometry, resolving power 7×104. Nozzle-skimmer fragmentation data reveal an extra Ala (+71.02; 71.04=theory) and GlyAla (+128.04; 128.06=theory) on the N-terminus, in addition to the fully processed enzyme. However, the fragment ion masses were consistent only with this sequence through 330 N-terminal residues; resequencing of the last 150 bps of the thiaminase I gene yields a sequence consistent with the molecular weight values and all 61 fragment ion masses. Covalently labeling the active site with a 108-Da pyrimidine moiety via mechanism-based inhibition produces a corresponding molecular weight increase in all three thiaminase I components, which indicates that they are all enzymatically active. Inspection of the fragment ions that do and do not increase by 108 Da indicates that the active site nucleophile is located between Pro79 and Thr177 in the 379 amino acid enzyme. 相似文献
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Background
Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH. 相似文献5.
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This work describes the performance of poly(methyl methacrylate) (PMMA) microfluidic DNA purification devices with embedded microfabricated posts, functionalized with chitosan. PMMA is attractive as a substrate for creating high surface area (SA) posts for DNA capture because X-ray lithography can be exploited for extremely reproducible fabrication of high SA structures. However, this advantage is offset by the delicate nature of the posts when attempting bonding to create a closed system, and by the challenge of functionalizing the PMMA surface with a group that invokes DNA binding. Methods are described for covalent functionalization of the post surfaces with chitosan that binds DNA in a pH-dependent manner, as well as for bonding methods that avoid damaging the underlying post structure. A number of geometric posts designs are explored, with the goal of identifying post structures that provide the requisite surface area without a concurrent rise in fluidic resistance that promotes device failure. Initial proof-of-principle is shown by recovery of prepurified human genomic DNA (hgDNA), with real-world utility illustrated by purifying hgDNA from whole blood and demonstrating it to be PCR-amplifiable. 相似文献
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The propagation of pressure waves in fluidic channels with elastic covers is discussed in view of applications to flow control in microfluidic devices. A theory is presented which describes pressure waves in the fluid that are coupled to bending waves in the elastic cover. At low frequencies, the lateral bending of the cover dominates over longitudinal bending, leading to propagating, non-dispersive longitudinal pressure waves in the channel. The theory addresses effects due to both the finite viscosity and compressibility of the fluid. The coupled waves propagate without dispersion, as long as the wave length is larger than the channel width. It is shown that in channels of typical microfluidic dimensions, wave velocities in the range of a few 10 m s(-1) result if the channels are covered by films of a compliant material such as PDMS. The application of this principle to design microfluidic band pass filters based on standing waves is discussed. Characteristic frequencies in the range of a few kHz are readily achieved with quality factors above 30. 相似文献
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自旋极化光电子谱的实验表明位于铑{001}表面Brillouin区中K11=0.65ΓX处的表面态(其束缚能为-0.30 eV)和位于M点的表面共振态(其束缚能为-0.6eV)在室温下具有铁磁性.上述表面态的铁磁性随着温度的下降而增加.当表面被暴露了0.5Langmur(L)氧后,铁磁性消失.自旋分辨的光电子谱表明,上述峰的自旋交换分裂很小.由上述峰的极化率估得表面层中的原子磁矩在0.1~0.3个μB间. 相似文献
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The far infrared (84.2 cm?1) propagation distance of surface electromagnetic waves on samples of single crystal GaAs with varied carrier concentrations has been measured using the twoprism technique. The experimental propagation distances agree well with theoretical values obtained from computer calculations using the exact two media dispersion relation. It was found that the propagation of the SEW is strongly dependent upon the free carrier concentration of the GaAs sample as expected. It is demonstrated that a simple classical theory of SEW works for GaAs-air interfaces in the far infrared. 相似文献
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