全文获取类型
收费全文 | 5102篇 |
免费 | 512篇 |
国内免费 | 464篇 |
专业分类
化学 | 847篇 |
晶体学 | 32篇 |
力学 | 560篇 |
综合类 | 81篇 |
数学 | 2890篇 |
物理学 | 1668篇 |
出版年
2024年 | 5篇 |
2023年 | 58篇 |
2022年 | 78篇 |
2021年 | 91篇 |
2020年 | 127篇 |
2019年 | 156篇 |
2018年 | 122篇 |
2017年 | 159篇 |
2016年 | 164篇 |
2015年 | 113篇 |
2014年 | 188篇 |
2013年 | 422篇 |
2012年 | 192篇 |
2011年 | 225篇 |
2010年 | 196篇 |
2009年 | 276篇 |
2008年 | 228篇 |
2007年 | 274篇 |
2006年 | 296篇 |
2005年 | 236篇 |
2004年 | 230篇 |
2003年 | 234篇 |
2002年 | 222篇 |
2001年 | 179篇 |
2000年 | 199篇 |
1999年 | 166篇 |
1998年 | 155篇 |
1997年 | 135篇 |
1996年 | 98篇 |
1995年 | 82篇 |
1994年 | 79篇 |
1993年 | 73篇 |
1992年 | 61篇 |
1991年 | 58篇 |
1990年 | 50篇 |
1989年 | 37篇 |
1988年 | 58篇 |
1987年 | 53篇 |
1986年 | 37篇 |
1985年 | 46篇 |
1984年 | 38篇 |
1983年 | 14篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 27篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有6078条查询结果,搜索用时 592 毫秒
111.
Norio Konno 《Journal of Theoretical Probability》1995,8(4):833-876
In this paper we consider the basic contact process with infection rate λ and stirring rateD. We study the asymptotic behavior of the critical value
and survival probability
asD→∞. 相似文献
112.
New calculations to over ten million time steps have revealed a more complex diffusive behavior than previously reported of a point particle on a square and triangular lattice randomly occupied by mirror or rotator scatterers. For the square lattice fully occupied by mirrors where extended closed particle orbits occur, anomalous diffusion was still found. However, for a not fully occupied lattice the superdiffusion, first noticed by Owczarek and Prellberg for a particular concentration, obtains for all concentrations. For the square lattice occupied by rotators and the triangular lattice occupied by mirrors or rotators, an absence of diffusion (trapping) was found for all concentrations, except on critical lines, where anomalous diffusion (extended closed orbits) occurs and hyperscaling holds for all closed orbits withuniversal exponentsd
f
=7/4 and =15/7. Only one point on these critical lines can be related to a corresponding percolation problem. The questions arise therefore whether the other critical points can be mapped onto a new percolation-like problem and of the dynamical significance of hyperscaling. 相似文献
113.
We make a high-precision Monte Carlo study of two- and three-dimensional self-avoiding walks (SAWs) of length up to 80,000 steps, using the pivot algorithm and the Karp-Luby algorithm. We study the critical exponentsv and 2
4 – as well as several universal amplitude ratios; in particular, we make an extremely sensitive test of the hyperscaling relationdv = 2
4 –. In two dimensions, we confirm the predicted exponentv=3/4 and the hyperscaling relation; we estimate the universal ratios <R
g
2
>/<R
e
2
>=0.14026±0.00007, <R
m
2
>/<R
e
2
>=0.43961±0.00034, and *=0.66296±0.00043 (68% confidence limits). In three dimensions, we estimatev=0.5877±0.0006 with a correctionto-scaling exponent
1=0.56±0.03 (subjective 68% confidence limits). This value forv agrees excellently with the field-theoretic renormalization-group prediction, but there is some discrepancy for
1. Earlier Monte Carlo estimates ofv, which were 0.592, are now seen to be biased by corrections to scaling. We estimate the universal ratios <R
g
2
>/<R
e
2
>=0.1599±0.0002 and *=0.2471±0.0003; since *>0, hyperscaling holds. The approach to * is from above, contrary to the prediction of the two-parameter renormalization-group theory. We critically reexamine this theory, and explain where the error lies. In an appendix, we prove rigorously (modulo some standard scaling assumptions) the hyperscaling relationdv = 2
4 – for two-dimensional SAWs. 相似文献
114.
Monte Carlo simulations of the bond fluctuation model of symmetrical polymer blends confined between two neutral repulsive walls are presented for chain lengthN
A=N
B=32 and a wide range of film thicknessD (fromD=8 toD=48 in units of the lattice spacing). The critical temperaturesT
c
(D) of unmixing are located by finite-size scaling methods, and it is shown that
, wherev
30.63 is the correlation length exponent of the three-dimensional Ising model universality class. Contrary to this result, it is argued that the critical behavior of the films is ruled by two-dimensional exponents, e.g., the coexistence curve (difference in volume fraction of A-rich and A-poor phases) scales as
, where
2 is the critical exponent of the two-dimensional Ising universality class (
2=1/8). Since for largeD this asymptotic critical behavior is confined to an extremely narrow vicinity ofT
c
(D), one observes in practice effective exponents which gradually cross over from
2 to
3 with increasing film thickness. This anomalous flattening of the coexistence curve should be observable experimentally. 相似文献
115.
G. M. Molchan 《Journal of statistical physics》1995,78(3-4):701-730
We present a method for the derivation of the generating function and computation of critical exponents for several cluster models (staircase, bar-graph, and directed column-convex polygons, as well as partially directed self-avoiding walks), starting with nonlinear functional equations for the generating function. By linearizing these equations, we first give a derivation of the generating functions. The nonlinear equations are further used to compute the thermodynamic critical exponents via a formal perturbation ansatz. Alternatively, taking the continuum limit leads to nonlinear differential equations, from which one can extract the scaling function. We find that all the above models are in the same universality class with exponents
u
=-1/2,
i
=-1/3, and =2/3. All models have as their scaling function the logarithmic derivative of the Airy function. 相似文献
116.
On invexity-type nonlinear programming problems 总被引:3,自引:0,他引:3
Z. K. Xu 《Journal of Optimization Theory and Applications》1994,80(1):135-148
In this paper, we propose a new class of nonlinear programing, called SFJ-invex programming. The optimality characterization shows that a problem is SFJ-invex if and only if a Fritz John point together with its multiplier, is a Fritz John saddle point of the problem. Under any constraint qualification assumption, a problem is SFJ-invex if and only if a Kuhn-Tucker point together with its multiplier is a Kuhn-Tucker saddle point of the problem. Furthermore, a generalization of the SFJ-invex, class is developed; the applications to (h, )-convex programming, particularly geometric programming, and to generalized fractional programming provide a relaxation in constraint qualification for differentiable problems to get saddle-point type optimality criteria.The author wishes to thank the referee for helpful comments. 相似文献
117.
Malte Henkel 《Journal of statistical physics》1994,75(5-6):1023-1061
The extension of strongly anisotropic or dynamical scaling to local scale invariance is investigated. For the special case of an anisotropy or dynamical exponent =z=2, the group of local scale transformation considered is the Schrödinger group, which can be obtained as the nonrelativistic limit of the conformal group. The requirement of Schrödinger invariance determines the two-point function in the bulk and reduces the three-point function to a scaling form of a single variable. Scaling forms are also derived for the two-point function close to a free surface which can be either spacelike or timelike. These results are reproduced in several exactly solvable statistical systems, namely the kinetic Ising model with Glauber dynamics, lattice diffusion, Lifshitz points in the spherical model, and critical dynamics of the spherical model with a nonconserved order parameter. For generic values of , evidence from higher-order Lifshitz points in the spherical model and from directed percolation suggests a simple scaling form of the two-point function. 相似文献
118.
It is known that at the critical temperature the Curie-Weiss mean-field model has non-Gaussian fluctuations and that internal fluctuations can be Gaussian. Here we compute the distribution of theq-mode magnetization fluctuations as a function of the temperature, the wave vectorq, and a fading out external field. We obtain new classes of probability distributions generated by this external field as well as new critical behavior in terms of its rate of fading out. We discuss also the susceptibility as the limitq tending to zero. 相似文献
119.
The three-component ionic microemulsion system consisting of AOT/water/decane shows an unusual phase behavior in the vicinity
of room temperature. The phase diagram in the temperature-volume fraction (of the dispersed phase) plane exhibits a lower
consolute critical point at about 40 degrees centigrades and 10% volume fraction. A percolation line, starting from the vicinity
of the critical point, cuts across the plane, extending to high volume fraction side at progressively lower temperatures.
In this paper we review the evidence that allows to interpret the phase behavior of our system in terms of interacting spherical
droplets. We also investigate the dynamics of droplets, below and approaching the critical point by dynamic light scattering.
The first cumulant and time evolution of the droplet density correlation function can be quantitatively calculated by assuming
the existence of polydispersed fractal clusters formed by the microemulsion droplets due to attraction. The relaxation phenomena
observed in an extensive set of measurements of electrical conductivity and permittivity close to percolation is also reviewed
and interpreted through the same cluster-forming mechanism, which reproduces the most relevant features of the frequency-dependent
complex dielectric constant of this system.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
120.
Gerard Misiolek 《Proceedings of the American Mathematical Society》1996,124(3):977-982
An example of a geodesic in with conjugate points is given, thus providing an affirmative answer to a question of V.I. Arnold.