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排序方式: 共有246条查询结果,搜索用时 15 毫秒
21.
A rate dependent crystal plasticity model for the α/β Ti–Al alloy Ti–6Al–4V with duplex microstructure is developed and presented herein. Duplex Ti–6Al–4V is a dual-phase alloy consisting of an hcp structured matrix primary α-phase and secondary lamellar α + β domains that are composed of alternating layers of secondary α laths and bcc structured residual β laths. The model accounts for distinct three-dimensional slip geometry for each phase, anisotropic and length scale dependent slip system strengths, the non-planar dislocation core structure of prismatic screw dislocations in the primary α-phase, and crystallographic texture. The model is implemented in the general purpose finite element code (ABAQUS, 2005. Ver 6.5, Hibbitt, Karlsson, and Sorensen, Inc., Pawtucket, RI) via a UMAT subroutine. 相似文献
22.
Non-equilibrium grain boundary structure and inelastic deformation using atomistic simulations 总被引:1,自引:0,他引:1
Garritt J. TuckerDavid L. McDowell 《International Journal of Plasticity》2011,27(6):841-857
Grain boundary influence on material properties becomes increasingly significant as grain size is reduced to the nanoscale. Nanostructured materials produced by severe plastic deformation techniques often contain a higher percentage of high-angle grain boundaries in a non-equilibrium or energetically metastable state. Differences in the mechanical behavior and observed deformation mechanisms are common due to deviations in grain boundary structure. Fundamental interfacial attributes such as atomic mobility and energy are affected due to a higher non-equilibrium state, which in turn affects deformation response. In this research, atomistic simulations employing a biased Monte Carlo method are used to approximate representative non-equilibrium bicrystalline grain boundaries based on an embedded atom method potential, leveraging the concept of excess free volume. An advantage of this approach is that non-equilibrium boundaries can be instantiated without the need of simulating numerous defect/grain boundary interactions. Differences in grain boundary structure and deformation response are investigated as a function of non-equilibrium state using Molecular Dynamics. A detailed comparison between copper and aluminum bicrystals is provided with regard to boundary strength, observed deformation mechanisms, and stress-assisted free volume evolution during both tensile and shear simulations. 相似文献
23.
Communicated by J.M. Howie 相似文献
24.
Eric L. McDowell Sam B. Nadler Jr. 《Proceedings of the American Mathematical Society》1996,124(4):1271-1276
The notion of an absolute fixed point set in the setting of continuum-valued maps will be defined and characterized.
25.
Robin S. McDowell Melvin I. Buchwald Michael S. Sorem Alan G. Robiette Catherine M. Deeley Welf A. Kreiner 《Journal of Molecular Spectroscopy》1985,112(2):363-376
A Fourier transform infrared spectrum of 91% 13CD4 has been recorded between 885 and 1193 cm?1 with a resolution of 0.04 cm?1. The frequencies of 600 lines were measured with an accuracy of ±0.003 cm?1. Of these, approximately 368 are assigned as allowed transitions in ν4, 95 are forbidden ν4 transitions, and 137 belong to ν2; maximum upper state J values are 20 for ν4 and 19 for ν2. The ground state tensor constants Dt, H4t, and H6t were obtained by fitting them to four rotational transitions observed by Kreiner and Opferkuch in the infrared-microwave double-resonance spectrum. An interacting-band analysis of the diad then yields 22 spectroscopic constants for these Coriolis-coupled fundamentals and fits the experimental frequencies with an rms deviation of 0.0055 cm?1 for 432 unblended lines that were assigned unit weight. A ν4P+(12) transition at 943.3812 cm?1, nearly coincident with the 10P(22) emission of the 12C16O2 laser, has been investigated by heterodyne spectroscopy and its detuning (?64 MHz) and absorption coefficient have been determined. Such coincidences may lead to the development of laser analytical techniques for 13CD4, which is a useful nonradioactive atmospheric tracer. 13CD4 transitions that are within 300 MHz of isotopic CO2 laser lines are tabulated for this purpose and for use in double-resonance experiments. 相似文献
26.
Keith McDowell 《Chemical physics letters》1979,66(3):423-427
The perturbation expansion of Hartree-Fock potential energy surfaces of simple hydrides in a single-center scale 1/Z-expansion is carried out using diagrammatic methods. Diagrams having the topological structure of third-order diagrams are summed to all orders using an integral equation technique. The resulting one-electron wavefunction is used to generate a resummed perturbation series correct through fourth order. 相似文献
27.
28.
W.J. McDowell 《Trends in analytical chemistry : TRAC》1985,4(6):X-XIII
Finding a suitable method for a chemical separation in the literature is difficult. A new keywording/indexing method makes retrieval of information on a specific separation easy. 相似文献
29.
L. S. McDowell P. R. Giffen A. Chatt 《Journal of Radioanalytical and Nuclear Chemistry》1987,110(2):519-529
The selenium content of a variety of food items representing a normal hospital diet has been determined by cyclic instrumental neutron activation analysis (CINAA) through the 162-keV gamma-ray of the77mSe nuclide. The CINAA method is very simple and rapid. It involves irradiation of a sample for 20 s, decay for 20 s, and counting for 20 s. The precision of the method has been significantly improved by recycling the samples up to 4 times. The accuracy has been evaluated by analyzing a number of certified reference materials of varied selenium levels. 相似文献
30.