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41.
The torsional barriers and nonlinear optical properties for all phenylpyridine molecules were calculated by using Hartree-Fock
(HF) theory and Becke three-parameter functional (B3LYP) hybrid approaches within the density functional theory framework
with the 6-31++G(d, p) basis set, and via the GAUSSIAN 98W. The torsional barrier computations show that dihedral angle between
the two rings increases with the number of H-H vicinal interactions and torsional barriers with dihedral angles for 3-, 4-phenylpyridines
are too similar for both HF and B3LYP level calculations. Also, HOMO-LUMO energy gaps, polarizabilities, anisotropy of polarizabilities,
and static hyperpolarizabilities are calculated as a function of dihedral angle between benzene and pyridine rings. The study
reveals that the phenylpyridines show very low nonlinear optical properties. The calculated torsional barrier, equilibrium
dihedral angle and molecular dipole moment results for these molecules were compared with available experimental and other
results determining from different computational methods. 相似文献
42.
Prabhakar P. Singh 《Solid State Communications》2003,125(6):323-326
We present a comparison of electron-phonon interaction in NbB2 and MgB2, calculated using full-potential, density-functional-based methods in P6/mmm crystal structure. Our results, described in terms of (i) electronic structure, (ii) phonon density of states F(ω), (iii) Eliashberg function α2F(ω), and (iv) the solutions of the isotropic Eliashberg gap equation, clearly show significant differences in the electron-phonon interaction in NbB2 and MgB2. We find that the average electron-phonon coupling constant λ is equal to 0.59 for MgB2 and 0.43 for NbB2, leading to superconducting transition temperatures Tc at around 22 K for MgB2 and 3 K for NbB2. 相似文献
43.
Douglas M. Ruthven 《Adsorption》2001,7(4):301-304
Recently reported diffusivity data for N2, CH4 and Kr in 4A zeolite pelleted adsorbent are compared with earlier data for the same sorbates in several different 4A samples. It is shown that, although there are large differences in diffusivity between the different adsorbent samples the activation energies are essentially constant. The data can be reconciled if it is assumed that the samples contain different fractions of open windows as a result of non-ideal distribution of the Na+ cations. 相似文献
44.
Let n 〉 r, let lr --- (dl,d2,-,dn) be a non-increasing sequence of nonnegative integers and let Kr+l - e be the graph obtained from Kr+l by deleting one edge. If zr has a realization G containing Kr+l - e as a subgraph, then r is said to be potentially Kr+l - e-graphic. In this paper, we give a characterization for a sequence π to be potentially Kr+l - e-graphic. 相似文献
45.
We study the effects of electron-phonon interaction on the electron ground state in a symmetric triangular quantum well, and calculate the ground state energy of an electron in the GaAs/Al0.96Ga0.04As triangular quantum well including the effects of the interaction between electrons and confined LO phonons by using a modified Lee-Low-Pines variational method. The electron wavefunction in the triangular well is chosen as the Airy function. The numerical results are given and discussed. 相似文献
46.
Tanaka H. Sawai S. Morimoto K. Hisano K. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):867-872
The hemispherical total emissivity of partially stabilized zirconia has been obtained by a spectral analysis of the normal
emission spectra between 400–850 K. Thermal conductivity was evaluated with this emissivity and temperature gradient in the
sample. Effects of the scattering of the radiation in a ceramic sample are also investigated. In addition, specific heat capacity
was measured by thermal radiation calorimetry. Current results are compared with those reported for tetragonal zirconia with
the same yttria content and for monoclinic phase.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
47.
M. Capone M. Grilli W. Stephan 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):551-557
We investigate polaron formation in a many-electron system in the presence of a local repulsion sufficiently strong to prevent
local-bipolaron formation. Specifically, we consider a Hubbard-Holstein model of interacting electrons coupled to dispersionless
phonons of frequency . Numerically solving the model in a small one-dimensional cluster, we find that in the nearly adiabatic case , the necessary and sufficient condition for the polaronic regime to occur is that the energy gain in the atomic (i.e., extremely localized) regime overcomes the energy of the purely electronic system . In the antiadiabatic case, , polaron formation is instead driven by the condition of a large ionic displacement (g being the electron-phonon coupling). Dynamical properties of the model in the weak and moderately strong coupling regimes
are also analyzed.
Received 15 February 1999 相似文献
48.
Polaronic effects on the energy levels of a double donor impurity in quantum wells in the presence of a magnetic field 总被引:3,自引:0,他引:3
Zi-xin Liu Zhen-jiang Lai Yong-chang Huang Ya Liu Guo-jun Cheng 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):347-350
In the presence of a magnetic field the Hamiltonian of the single or double polaron bound to a helium-type donor impurity
in semiconductor quantum wells (QWs) are given in the case of positively charged donor center and neutral donor center. The
couplings of an electron and the impurity with various phonon modes are considered. The binding energy of the single and double
bound polaron in AlxlGa 1-xlAs/GaAs/AlxrGa 1-xrAs QWs are calculated. The results show that for a thin well the cumulative effects of the electron-phonon coupling and the
impurity-phonon coupling can contribute appreciably to the binding energy in the case of ionized donor. In the case of neutral
donor the contribution of polaronic effects are not very important, however the magnetic field significantly modifies the
binding energy of the double donor. The comparison between the binding energies in the case of the impurity placed at the
quantum well center and at the quantum well edge is also given.
Received 16 February 1999 相似文献
49.
Qinghu Chen Yuhang Ren Zhengkuan Jiao Kelin Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):59-63
The Feynman-Haken variational path integral theory is, for the first time, generalized to calculate the ground-state energy
of an electron coupled simultaneously to a Coulomb potential and to a longitudinal-optical (LO) phonon field in parabolic
quantum wires. It is shown that the polaronic correction to the ground-state energy is more sensitive to the electron-phonon
coupling constant than the Coulomb binding parameter and monotonically stronger as the effective wire radius decreases. We
apply our calculations to several semiconductor quantum wires and find that the polaronic correction can be considerably large.
Received 16 November 1998 相似文献
50.
Jun-Jie Shi 《Solid State Communications》2003,127(1):51-55
Within the framework of the dielectric-continuum model and Loudon's uniaxial crystal model, the equation of motion for the p-polarization field in a wurtzite quasi-two-dimensional multilayer heterostructure is solved exactly for the interface optical-phonon modes. The eigenvector, the dispersion relation and the electron-interface-phonon interaction Fröhlich-like Hamiltonian are derived using the transfer-matrix method. The analytical formulas are universal and can be applied to single heterojunctions, single/multiple quantum wells and superlattices. 相似文献