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A. Haug 《Photochemistry and photobiology》1964,3(3):207-212
Abstract— In an aqueous buffered solution of TpC monochromatic ultraviolet light lowers the absorption peak to approximately half its value, characterized by a photostationary state. The quantum yield for this photochemical decomposition is independent of the wavelength between 2400 and 3000 Å.At pH 7 the quantum yield amounts to 0.006, at pH 2 to 0.002, respectively. At neutral pH about 85 per cent of the photochemical transformation produced are reversible in the dark, at pH 2 only 40 per cent. Three photoproducts, being non-reversible in the dark, were isolated electrophoretically and characterized by their absorption spectra. These three compounds have an absorption peak around 2680 Å, one compound has a second absorption maximum at 3120 Å (pH 7). 相似文献
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Interlaboratory comparsion exercises on the determination of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) and dioxin-like polychlorinated biphenyls (PCBs) in three natural foodstuffs have been performed annually since 2000 by the Norwegian Institute of Public Health. Up to 77 laboratories from 24 countries world-wide have reported results. The data have been statistically analysed in order to assess the comparability of both the reported individual congener concentrations and the calculated toxic equivalents (TEQ). Due to the low concentrations of PCDDs/PCDFs and dioxin-like PCBs in food, the treatment of congeners reported as “not detected” and the identification of outliers, influence the estimation of the consensus values considerably. Based on the experiences from the first two rounds, an approach for calculation of the consensus values was established, resulting in a non-skewed distribution of data. The relative standard deviation of consensus TEQs was 13–32% for PCDDs/PCDFs and 11–45% for PCBs. Z-scores were calculated for PCDD/PCDF-TEQs using a target value of ±20% for the deviation. For food samples with a PCDD/PCDF contamination of more than half of the EU maximum level, 63–87% of the participants achieved Z-scores ±1, while for low contaminated foodstuffs about 60% of the participants had Z-scores of ±2. After four rounds of interlaboratory comparisons it can be concluded that there is a good comparability of the analytical data for dioxins and dioxin-like PCBs in food at higher contamination levels. However, the laboratories need to improve their performance when determining levels in food with low contamination of dioxin-like compounds, due to the increasing demand for analyses of such food items. The importance of determining dioxin-like PCBs is demonstrated by their large contribution to the total TEQ, especially in food from the marine environment. 相似文献
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E. Haug 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,37(1):9-14
The triply differential cross section of unpolarized bremsstrahlung produced by polarized electrons in the Coulomb field of a nucleus is calculated with the aid of Sommerfeld-Maue wave functions. The photon asymmetry originating from transversely polarized electrons is calculated for various values of energies and angles, in particular for the parameters of recent experiments. As a function of the atomic number Z of the target nucleus, the asymmetry shows a distinct deviation from a linear dependence, in contrast to a previous calculation exact to lowest order in the Coulomb parameter Z/137. The cross-section formula is integrated numerically over the angles of the outgoing electrons to obtain the photon asymmetry observed in non-coincidence experiments. 相似文献
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A combination of gold(I) complexes and amine bases catalyzes the 5-exo-dig cyclization of formyl alkynes. This direct alpha-functionalization of aldehydes with unactivated alkynes does not involve the use of preformed enol equivalents. 相似文献
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ABSTRACT A finite element based method is developed for geometrically nonlinear dynamic analysis of spatial articulated structures; i.e., structures in which kinematic connections permit large relative displacement between components that undergo small elastic deformation. Vibration and static correction modes are used to account for linear elastic deformation of components. Kinematic constraints between components are used to define boundary conditions for vibration analysis and loads for static correction mode analysis. Constraint equations between flexible bodies are derived in a systematic way and a Lagrange multiplier formulation is used to generate the coupled large displacement-small deformation equations of motion. A lumped mass finite element structural analysis formulation is used to generate deformation modes. An intermediate-processor is used to calculate time-independent terms in the equations of motion and to generate input data for a large-scale dynamic analysis code that includes coupled effects of geometric nonlinearity and elastic deformation. Examples are presented and the effects of deformation mode selection on dynamic prediction are analyzed in Part II of the paper. 相似文献