全文获取类型
收费全文 | 4492篇 |
免费 | 701篇 |
国内免费 | 421篇 |
专业分类
化学 | 528篇 |
晶体学 | 90篇 |
力学 | 411篇 |
综合类 | 50篇 |
数学 | 1526篇 |
物理学 | 3009篇 |
出版年
2024年 | 10篇 |
2023年 | 36篇 |
2022年 | 117篇 |
2021年 | 83篇 |
2020年 | 111篇 |
2019年 | 99篇 |
2018年 | 97篇 |
2017年 | 95篇 |
2016年 | 107篇 |
2015年 | 110篇 |
2014年 | 201篇 |
2013年 | 325篇 |
2012年 | 200篇 |
2011年 | 211篇 |
2010年 | 215篇 |
2009年 | 284篇 |
2008年 | 293篇 |
2007年 | 294篇 |
2006年 | 258篇 |
2005年 | 253篇 |
2004年 | 222篇 |
2003年 | 224篇 |
2002年 | 260篇 |
2001年 | 189篇 |
2000年 | 170篇 |
1999年 | 171篇 |
1998年 | 159篇 |
1997年 | 119篇 |
1996年 | 74篇 |
1995年 | 75篇 |
1994年 | 72篇 |
1993年 | 47篇 |
1992年 | 47篇 |
1991年 | 41篇 |
1990年 | 26篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 31篇 |
1986年 | 39篇 |
1985年 | 36篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 22篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1972年 | 5篇 |
排序方式: 共有5614条查询结果,搜索用时 15 毫秒
131.
A mathematical representation based on a linear elastic theory is proposed by which one may investigate the dependences of molecular orientation and crystallinity on the crystal lattice moduli and linear thermal expansion coefficients in the direction perpendicular to the chain axis as commonly measured by x-ray diffraction. In the theoretical calculation, a previously introduced model was employed in which oriented crystalline phase is surrounded by oriented amorphous phase and the strains of the two phases at the boundary are identical. The mathematical analysis indicated that the lateral crystal lattice moduli and linear thermal coefficients as measured by x-ray diffraction may be different from the intrinsic crystal moduli and linear thermal coefficients of a crystal unit cell, depending on the structure of the polymer solid. The numerical calculation was applied to nylon 6. As a result, it may be confirmed that the lateral crystal lattice moduli measured by x-ray diffraction are sensitive to the morphology of the bulk speciments and close to the intrinsic crystal moduli if the morphology of the test specimen can be represented by a parallel model with respect to the original stretching longitudinal direction. 相似文献
132.
Ivo Klik 《Journal of statistical physics》1991,62(1-2):389-397
The influence of the Bardeen-Herring back-jump correlations on the Fermi-Dirac statistics of the one-dimensional nonhomogeneous fermionic lattice gas is studied by the Monte Carlo simulation technique and semianalytically. The resulting distribution is obtained, exhibiting increased population of the lower levels in comparison to the Fermi-Dirac statistics. 相似文献
133.
Jiři Votinský Jaroslava Kalousová Ludvík Beneš 《Journal of inclusion phenomena and macrocyclic chemistry》1992,14(1):19-24
The paper deals with the relations between host lattices and guest molecules. Several types of interaction of the guest molecules and the host material are explained and some conclusions are made about the arrangement of various guest molecules in the van der Waals' gap. 相似文献
134.
Let H=1/2+V on l2(B), whereB is the Bethe lattice andV(x),x
B, are i.i.d.r.v.'s with common probability distribution. It is shown that for distributions sufficiently close to the Cauchy distribution, the density of states(E) is analytic in a strip about the real axis. 相似文献
135.
D. Shalitin 《Journal of statistical physics》1982,28(1):99-110
By decomposing certain lattices into two sublattices, and examining at percolation threshold the structure of their infinite clusters, an approximate relation between p
c
0
, of the original lattice and p
c
1
, of the sublattice is established: p
c
0
(p
c
1
)1/2. It is conjectured that an inequality always holds: p
c
0
(p
c
1
)1/2, and heuristic arguments are given to substantiate it. By similar considerations good estimates forp
c
of certain correlated percolation problems are also obtained. 相似文献
136.
The phonon dispersion curves, phonon frequency distribution function as well as the lattice specific heat of body-centred
tetragonal indium have been deduced using a lattice dynamical model which includes central, angular and volume forces. Six
elastic constants, four zone boundary frequencies and an equilibrium condition were used in the evaluation of the force constants.
It is shown that this model is elastically consistent and satisfies the symmetry requirements of the lattice, the phonon frequencies
of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical
values of Garrett and Swihart, and theθ
D values compare well with the experimental values over a wide temperature range. The apparent discrepancies in the phonon
dispersion curves and theθ
D-T curves obtained from deficient models, importance of umklapp processes and the significance of angular forces in the lattice
dynamical models are discussed. 相似文献
137.
The third law of thermodynamics, in the sense that the entropy per unit volume goes to zero as the temperature goes to zero, is investigated within the framework of statistical mechanics for quantum and classical lattice models. We present two main results: (i) For all models the question of whether the third law is satisfied can be decided completely in terms of ground-state degeneracies alone, provided these are computed for all possible boundary conditions. In principle, there is no need to investigate possible entropy contributions from low-lying excited states, (ii) The third law is shown to hold for ferromagnetic models by an analysis of the ground states.Dedicated to Pierre Résibois. Work supported in part by NSF grant PHY-7825390 A01. 相似文献
138.
Free vibration problems of lattice sandwich beams under several typical boundary conditions are investigated in the present paper. The lattice sandwich beam is transformed to an equivalent homogeneous three-layered sandwich beam. Unlike the traditional analytical model in which the rotation angles of the face sheets and the core are assumed the same, different rotation angles are considered in this paper to characterize the real response of sandwich beams. The analytical solutions of the natural frequencies for several typical boundary conditions are obtained. The effects of material properties and geometric parameters on the natural frequencies are also investigated. 相似文献
139.
The properties of the transfer-matrix of U(1) lattice gauge theory in the Fourier basis are explored. Among other statements it is shown: (i) the transfer-matrix is block-diagonal, (ii) all consisting vectors of a block are known based on an arbitrary block vector, (iii) the ground-state belongs to the zero-mode's block. The emergence of maximum-points in matrix-elements as functions of the gauge coupling is clarified. Based on explicit expressions for the matrix-elements we present numerical results as tests of our statements. 相似文献
140.
In this work we present an optical lattice setup to realize a full Dirac Hamiltonian in 2+1 dimensions. We show how all possible external potentials coupled to the Dirac field can arise from perturbations of the existing couplings of the honeycomb lattice pattern. This greatly simplifies the proposed implementations, requiring only spatial modulations of the intensity of the laser beams to induce complex non-Abelian potentials. We finally suggest several experiments to observe the properties of the quantum field theory in the setup. 相似文献