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51.
52.
We study numerically the effect of an external magnetic or electric field on the director profiles of a nematic liquid crystal
around a spherical particle. We pay particular attention to the stability of a hyperbolic hedgehog defect accompanying the
particle, which transforms into a Saturn-ring defect encircling the particle under a sufficiently strong external field. We
focus on the particle size dependence of the two important threshold field strengths: the “thermodynamic-transition” field
strength H1 at which the hedgehog and the Saturn-ring configurations have the equal free energy, and the critical field strength H2 at which the hedgehog loses its (meta)stability. Our numerical results demonstrate that while H1 is non-monotonically dependent on the particle radius R0, H2 monotonically increases with R0 and the dependence of H2 is weak for large R0. The non-monotonic dependence of H1 on R0 can be explained by comparing the energies of the two configurations and assuming the dependence of those energies on a rescaled
field. A crude argument of the energetics of a hyperbolic hedgehog defect under an external field shows that for an asymptotically
large R0 the critical field strength is independent of R0, which agrees with our numerical finding. 相似文献
53.
T. Andrade-Filho T. C. S. Ribeiro J. Del Nero 《The European physical journal. E, Soft matter》2009,29(3):253-259
The UV-vis absorption spectrum of the solvated quercetin molecule in methanol was investigated theoretically by means of an
elegant type of QM/MM scheme better known as sequential Monte Carlo/quantum mechanics (S-MC/QM) methodology. A set of 125
uncorrelated Monte Carlo molecular liquid structures were properly selected through the autocorrelation function of the energy
in order to be used in the quantum mechanical calculations. These molecular liquid structures were obtained by means of the
radial and minimum distance distribution functions. A detailed account of the pattern of hydrogen bond structures obtained
in this study is also available. The computed results obtained here were directly compared with the available experimental
data in order to validate our theoretical model and through this comparison a very good conformity between theoretical and
available experimental results was found. 相似文献
54.
The influence of controllable parameters like temperature and wavelength on the trajectories of light in a nematic liquid crystal with topological defects is studied through a geometric model. The model incorporates phenomenological details as how the refractive indices depend on such parameters. The deflection of light by the topological defect is then shown to be greater at lower temperatures and shorter wavelengths. 相似文献
55.
We have investigated the effect of weakly coupled hot plasmas on the dipole polarizabilities of positronium negative ion and hydrogen negative ion. The plasma effect is taken care of by employing a screened Coulomb (Yukawa) potential of Debye type, and highly correlated exponential wave functions are used. Dipole polarizabilities for various screening parameters are reported. 相似文献
56.
Using first-principles total energy calculations within the full-potential linearized augmented plane wave (FP-LAPW) method, we have investigated the structural, electronic and thermodynamic properties of potassium halides (KClxBr1−x, KClxI1−x and KBrxI1−x), with x concentrations varying from 0% up to 100%. The effect of composition on lattice constants, bulk modulus, band gap and dielectric function was investigated. Deviations of the lattice constants from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the three alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and coworkers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram. 相似文献
57.
High-quality relaxed SiGe films on Si (0 0 1) have been demonstrated with a buffer layer containing modified SiGe (m-SiGe) islands in ultra-high vacuum chemical vapor deposition (UHV/CVD) system. The m-SiGe islands are smoothened by capping an appropriate amount of Si and the subsequent annealing for 10 min. This process leads to the formation of a smooth buffer layer with non-uniform Ge content. With the m-SiGe-dot multilayer as a buffer layer, the 500-nm-thick uniform Si0.8Ge0.2 layers were then grown. These m-SiGe islands can serve as effective nucleation centers for misfit dislocations to relax the SiGe overlayer. Surface roughness, strain relaxation, and crystalline quality of the relaxed SiGe overlayer were found to be a function of period's number of the m-SiGe-dot multilayer. By optimizing period number in the buffer, the relaxed Si0.8Ge0.2 film on the 10-period m-SiGe-dot multilayer was demonstrated to have a threading dislocation density of 2.0 × 105 cm−2 and a strain relaxation of 89%. 相似文献
58.
Ionization energies of beryllium-like ions for Z = 26 - 36 in hot ana aense plasmas (ne=10^22 -10^24 cm^-3,kT= 500 - 2000 eV) are obtained by using an approach developed for electronic structure and transition property of ions in hot and dense plasmas based on the multi-configuration Dirac-Fock model. Influence of the plasma environment is considered by introducing a correction to the one-electron potential to account for the screening of the ionized electrons. This correction is calculated from the ionized electron micro-space distribution, which is obtained based on an "average atom model for the temperature and density-dependent average ionization of atoms in plasmas. Comparison between the present and the ion sphere models is made to display the significance of the ionized electron micro-space distribution. 相似文献
59.
Hua Liu Jun Ni Binglin Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):261-265
In this paper, we have investigated the ground states of a few-layered fcc thin film of binary alloy with two surfaces in
the (001) direction under symmetric surface confinement. The phase diagram of the ground states is given according to the
energy analysis of binary alloy thin film composed of six atomic layers in the (001) direction. Surface confinement field
(SC field) is introduced as a term to describe the confinement on the two surfaces in the (001) direction. Using Monte Carlo
simulation, we have found that there are 17 different ground states occurring when both SC field and chemical potential vary
from - ∞ to + ∞. Antiphase boundary(APB) was found in 12 of the 17 ground states, and only nine configurations with different
symmetry were found among the 17 ground states.
Received 6 November 2001 and Received in final form 25 January 2002 相似文献
60.
We have used the density functional theory to study the effect of molecular elongation on the isotropic-nematic, isotropic-smectic A and nematic-smectic A phase transitions of a fluid of molecules interacting via the Gay-Berne intermolecular potential. We have considered a range of length-to-width parameter 3.0 ⩽ x0 ⩽ 4.0 in steps of 0.2 at different densities and temperatures. Pair correlation functions needed as input information in density functional theory are calculated using the Percus-Yevick integral equation theory. Within the small range of elongation, the phase diagram shows significant changes. The fluid at low temperature is found to freeze directly from isotropic to smectic A phase for all the values of x0 considered by us on increasing the density while the nematic phase stabilizes in between isotropic and smectic A phases only at high temperatures and densities. Both isotropic-nematic and nematic-smectic A transition density and pressure are found to decrease as we increase x0. The phase diagram obtained is compared with computer simulation result of the same model potential and is found to be in good qualitative agreement. 相似文献