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71.
F. Milde R.A. Römer M. Schreiber V. Uski 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):685-690
We study the three-dimensional Anderson model of localization with anisotropic hopping, i.e., weakly coupled chains and weakly coupled planes. In our extensive numerical study we identify and characterize the metal-insulator
transition by means of the transfer-matrix method. The values of the critical disorder obtained are consistent with results of previous studies, including multifractal analysis of the wave functions and energy-level
statistics. decreases from its isotropic value with a power law as a function of anisotropy. Using high accuracy data for large system
sizes we estimate the critical exponent as . This is in agreement with its value in the isotropic case and in other models of the orthogonal universality class.
Received 25 October 1999 相似文献
72.
In modern materials science the characterisation of nanostructures is becoming increasingly important. For measurement of the quality of nanoscale multilayer arrangement with high spatial resolution a method is described that is based on the broadening of the spots in the Fourier transformation of transmission electron microscopic images of multilayer cross-sections. Using this method on Si/Ge superlattices with periodic lengths between 4 and 12 nm it could be quantitatively shown that the layer perfection decreases with increasing periodic length. The transition from elastic to plastic deformation between the Si and Ge layers at larger periodic lengths can be the reason for this behaviour. 相似文献
73.
The negatively charged exciton in double-layer quantum dots 总被引:1,自引:0,他引:1
Wenfang Xie 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):385-389
The hyperangular equation for charged semiconductor complexes in a double-layer harmonic quantum dot was solved numerically
by using the correlated hyperspherical harmonics as basis functions. By using this method, we have calculated the energy spectra
of the low-lying states of a charged exciton as a function of the radius of the quantum dot and the binding energy spectra
of the ground state as a function of the radius of the quantum dot for a few values of the distance between the vertically
coupled dots and the electron-to-hole mass ratio.
Received 3 December 1999 相似文献
74.
75.
P.Y. Friot P. Turban S. Andrieu M. Piecuch E. Snoeck A. Traverse E. Foy C. Theodorescu 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):41-50
This study is dedicated to the growth of bcc Mn by molecular beam epitaxy, in order to look at the magnetic properties of
bcc Mn near room temperature. For this purpose, Mn is deposited on bcc MxV1-x(001) alloy lattices (M = Fe or Nb) for which the lattice spacing is tunable by varying the concentration x. We first show that the parameter of the MxV1-x alloy's buffer layers can be adjusted from 2.95 ? to 3.3 ? depending on x and M. Three different structures in Mn films grown on these buffer layers are observed depending on the in-plane spacing
of the initial MxV1-x lattice. Thick Mn films are always found to grow epitaxially in the Mnstructure. For moderate thicknesses larger than 4 atomic planes, Mn grows in an unidentified structure. Finally, up to four
deposited atomic planes, Mn is found to grow in a tetragonal structure close to a bcc one on Fe(001), FexV1-x(001) and NbxV1-x(001) for . This tetragonal structure is shown to be a distorsion of a Mn bcc structure with . Except for ultra-thin Mn films deposited on Fe(001), no macroscopic magnetization is detected in our strained bcc Mn samples.
These results are compared to theoretical predictions.
Received 21 June 1999 相似文献
76.
A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3(l00) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation of the intensity of reflection high-energy
electron diffraction (RHEED) in BaTiO3 and SrTiO3 layers was observed and attributed to the lattice-misfit-induced periodic variation of the terrace density in film surface.
The relationship between the second-order nonlinear optical susceptibilities and the superlattice structure was systematically
studied. The experimental and theoretical fitting results indicate that the second-order nonlinear optical susceptibilities
of BaTiO3/SrTiO3 superlattices were greatly enhanced with the maximum value being more than one order of magnitude larger than that of bulk
BaTiO3 crystal. The mechanism of the enhancement of the second-order optical nonlinearity was discussed by taking into account the
stress-induced lattice distortion and polarization enhancement. 相似文献
77.
In the asymptotic limit, the interlayer exchange coupling decays as D-2, where D is the spacer thickness. A systematic procedure for calculating the preasymptotic corrections, i.e., the terms of order D-n with ,is presented. The temperature dependence of the preasymptotic corrections is calculated. The results are used to discuss
the preasymptotic corrections for the Co/Cu/Co(001) system.
Received 7 January 1999 相似文献
78.
Q. Guo Y.P. Feng H.C. Poon C.K. Ong 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):29-36
A new approach based on the invariant embedding method for the self-consistent calculation of electronic structure of quantum
wells is presented and is applied to both neutral quantum well and parabolic quantum well. Numerical results obtained for
these structures agree very well with those of previous theoretical and experiment studies. The present approach is expected
to lead to a more efficient and stable scheme for the calculation of electronic band structure of quantum structures. Realistic
boundary conditions are naturally taken into account in the present calculation which provides a convenient way for studying
boundary effects.
Received 21 September 相似文献
79.
B. Tanatar N. Mutluay 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):409-417
We study the spin correlations in two- and three-dimensional electron liquids within the sum-rule version of the self-consistent
field approach of Singwi, Tosi, Land, and Sj?lander. Analytic expressions for the spin-antisymmetric static structure factor
and the corresponding local-field correction are obtained with density dependent coefficients. We calculate the spin-dependent
pair-correlation functions, paramagnon dispersion, and static spin-response function within the present model, and discuss
the spin-density wave instabilities in double-layer electron systems.
Received: 22 September 1997 / Revised: 1 December 1997 / Accepted: 4 December 1997 相似文献
80.
The irregular short period CdTe/ZnTe superlattice structure is investigated by both stationary and time-resolved optical spectroscopy with and without an external magnetic field as a perturbation. This study is aimed to emphasize the properties of radiative excitonic recombination in a superlattice of this type in comparison with the excitons confined in a single QW structure. The decay time of the excitons is about 400 ps which is deduced from the time-resolved measurements. Theg-factors of electrons and holes are obtained by the spin quantum beat measurements combined with Zeeman measurements. The experimental results show that theg-factors of holes in the irregular short period CdTe/ZnTe superlattice become dramatically different in comparison with the single CdTe/CdMgTe quantum wells. 相似文献