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81.
The response of Duhem hysteretic system to externally and/or parametrically non-white random excitations is investigated by using the stochastic averaging method. A class of integrable Duhem hysteresis models covering many existing hysteresis models is identified and the potential energy and dissipated energy of Duhem hysteretic component are determined. The Duhem hysteretic system under random excitations is replaced equivalently by a non-hysteretic non-linear random system. The averaged Ito's stochastic differential equation for the total energy is derived and the Fokker-Planck-Kolmogorov equation associated with the averaged Ito's equation is solved to yield stationary probability density of total energy, from which the statistics of system response can be evaluated. It is observed that the numerical results by using the stochastic averaging method is in good agreement with that from digital simulation. 相似文献
82.
The kinetic coefficient, , is the constant of proportionality between the velocity of a solid-liquid interface and the interface undercooling. The value of and its anisotropy are critical parameters in phase field modeling of dendritic solidification. In this paper we review several different molecular dynamics simulation methods which have been proposed to compute the kinetic coefficient. Techniques based on forced velocity simulations, free solidification simulations and fluctuation analyses are discussed and compared. In addition, a model of crystalline growth kinetics due to Broughton, Gilmer and Jackson will be compared with available atomistic simulation data. 相似文献
83.
Monomeric imidozirconocene complexes of the type Cp2(L)Zr=NCMe3 (Cp = cyclopentadienyl, L = Lewis base) have been shown to activate the carbon-hydrogen bonds of benzene, but not the C-H bonds of saturated hydrocarbons. To our knowledge, this singularly important class of C-H activation reactions has heretofore not been observed in imidometallocene systems. The M=NR bond formed on heating the racemic ethylenebis(tetrahydro)indenyl methyl tert-butyl amide complex, however, cleanly and quantitatively activates a wide range of n-alkane, alkene, and arene C-H bonds. Mechanistic experiments support the proposal of intramolecular elimination of methane followed by a concerted addition of the hydrocarbon C-H bond. Products formed by activation of sp2 C-H bonds are generally more thermodynamically stable than those formed by activation of sp3 C-H bonds, and those resulting from reaction at primary C-H bonds are preferred over secondary sp3 C-H activation products. There is also evidence that thermodynamic selectivity among C-H bonds is sterically rather than electronically controlled. 相似文献
84.
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86.
How can a formulator have confidence that a preservative system will perform as expected under adverse conditions? Extreme conditions that can lead to the development of "off odors" in the product can be a serious challenge for companies providing home care products in the global market. Formulation and stability testing occur under controlled parameters that simulate limited environmental conditions and microbial challenges are typically performed with a standard inoculum level. While this is an acceptable and dependable process, it does not necessarily assess how well a preservative system can perform under extreme environmental conditions or against unusually high levels of bacterial challenges. This is especially true when formulations are diluted and stored by the end-user. By modifying microbial challenge testing of a liquid dishwashing product to include unexpected dilution schemes, increased microbial assaults, and elevated temperatures, a pattern of preservative efficacy was established. The resulting approach proved to be a useful tool when developing use directions, recommended dilution levels, the overall surfactant system, preservative type, and storage restrictions. 相似文献
87.
Taichenachev AV Yudin VI Oates CW Hoyt CW Barber ZW Hollberg L 《Physical review letters》2006,96(8):083001
We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes. 相似文献
88.
This paper compares the performance of various spectral shift estimators for use in spectral elastography, namely, the normalized cross-correlation (NCC), sum squared difference (SSD) and sum absolute difference (SAD). Simulation and experimental results demonstrate that the spectral SSD-based elastographic method exhibits no marked difference in performance compared to the more computationally costly NCC-based approach, which has conventionally been the preferred estimator in spectral elastography. The spectral SAD-based strain estimator, despite being computationally less burdening, failed to exhibit performance comparable to that of the NCC- and SSD-based techniques. Furthermore, though spectral subsample estimation techniques using a cosine-fit interpolation method outperformed that of the parabolic-fit method in terms of both reduced bias errors and standard deviations, the latter was analyzed in this study due to computational simplicity. The role of spectral density was evaluated without and with parabolic-based subsample interpolation. Based on minimizing computational complexity, it is concluded that a (low density) spectral SSD strain estimator coupled with parabolic-based subsample estimation is the preferred choice for spectral elastography. 相似文献
89.
The change in the energy barriers for the heterogeneous reduction of pyruvate decarboxylase (PDC) relative to its coenzyme, thiamin pyrophosphate (ThPP), was determined experimentally using square wave voltammetry (SWV) to be 5.3 kcal/mol. These results are in agreement with those of reaction rate acceleration provided by thiamin-dependent decarboxylases relative to their coenzyme as determined kinetically based on the pK(a) suppression by the enzyme environment. 相似文献
90.
Superconducting transition temperature measurements of the α-phase alloys CuSi, CuGe, AgGe, AgAl, AuGe, and AuZn are reported. It is found that for alloys with the same electron per atom ratio, Tc values are highest when the pure metal lattice is deformed the least by the solute. 相似文献