全文获取类型
收费全文 | 169983篇 |
免费 | 13534篇 |
国内免费 | 9893篇 |
专业分类
化学 | 69417篇 |
晶体学 | 1533篇 |
力学 | 10102篇 |
综合类 | 490篇 |
数学 | 38761篇 |
物理学 | 37742篇 |
无线电 | 35365篇 |
出版年
2024年 | 223篇 |
2023年 | 2158篇 |
2022年 | 2502篇 |
2021年 | 3460篇 |
2020年 | 3544篇 |
2019年 | 3321篇 |
2018年 | 13967篇 |
2017年 | 13622篇 |
2016年 | 10370篇 |
2015年 | 4982篇 |
2014年 | 5200篇 |
2013年 | 6368篇 |
2012年 | 11288篇 |
2011年 | 18505篇 |
2010年 | 11968篇 |
2009年 | 11736篇 |
2008年 | 12485篇 |
2007年 | 14297篇 |
2006年 | 4813篇 |
2005年 | 5501篇 |
2004年 | 4822篇 |
2003年 | 4858篇 |
2002年 | 3814篇 |
2001年 | 2576篇 |
2000年 | 2062篇 |
1999年 | 2118篇 |
1998年 | 1665篇 |
1997年 | 1488篇 |
1996年 | 1458篇 |
1995年 | 1226篇 |
1994年 | 997篇 |
1993年 | 881篇 |
1992年 | 734篇 |
1991年 | 654篇 |
1990年 | 527篇 |
1989年 | 400篇 |
1988年 | 312篇 |
1987年 | 259篇 |
1986年 | 267篇 |
1985年 | 227篇 |
1984年 | 162篇 |
1983年 | 146篇 |
1982年 | 105篇 |
1981年 | 85篇 |
1980年 | 77篇 |
1979年 | 65篇 |
1978年 | 44篇 |
1973年 | 41篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
941.
The possibility of ferromagnetic (FM) and antiferromagnetic (AFM) phase transitions in symmetric nuclear matter is analyzed
within the framework of a Fermi liquid theory with effective Gogny interaction. It is shown that, at some critical density,
nuclear matter with the D1S effective force undergoes a phase transition to the AFM spin state (opposite directions of neutron
and proton spins). The self-consistent equations of spin-polarized nuclear matter with the D1S force have no solutions corresponding
to FM spin ordering (the same direction of neutron and proton spins) and, hence, the FM transition does not appear. The AFM
spin polarization parameter is found for zero and finite temperature. It is shown that the AFM spin polarization parameter
of partially polarized nuclear matter at low enough temperatures increases with temperature. The entropy of the AFM spin state
for some temperature range is larger than the entropy of the normal state. Nevertheless, the free energy of the AFM spin state
is always less than the free energy of the normal state, and the AFM spin-polarized state is preferable for all temperatures
below the critical temperature.
The text was submitted by the authors in English. 相似文献
942.
De Ming ZHU Ying SUN 《数学学报(英文版)》2007,23(8):1495-1504
In this paper, we study the dynamical behavior for a 4-dimensional reversible system near its heteroclinic loop connecting a saddle-focus and a saddle. The existence of infinitely many reversible 1-homoclinic orbits to the saddle and 2-homoclinic orbits to the saddle-focus is shown. And it is also proved that, corresponding to each 1-homoclinic (resp. 2-homoclinic) orbit F, there is a spiral segment such that the associated orbits starting from the segment are all reversible 1-periodic (resp. 2-periodic) and accumulate onto F. Moreover, each 2-homoclinic orbit may be also accumulated by a sequence of reversible 4-homoclinic orbits. 相似文献
943.
Andreas Rößler 《BIT Numerical Mathematics》2007,47(3):657-680
The weak approximation of the solution of a system of Stratonovich stochastic differential equations with a m–dimensional Wiener process is studied. Therefore, a new class of stochastic Runge–Kutta methods is introduced. As the main
novelty, the number of stages does not depend on the dimension m of the driving Wiener process which reduces the computational effort significantly. The colored rooted tree analysis due
to the author is applied to determine order conditions for the new stochastic Runge–Kutta methods assuring convergence with
order two in the weak sense. Further, some coefficients for second order stochastic Runge–Kutta schemes are calculated explicitly.
AMS subject classification (2000) 65C30, 65L06, 60H35, 60H10 相似文献
944.
The compound binomial risk model with time-correlated claims 总被引:1,自引:0,他引:1
Yuntao Xiao 《Insurance: Mathematics and Economics》2007,41(1):124-133
In this paper, we consider the compound binomial risk model with the time-correlated claims. It is assumed that every main claim will produce a by-claim but the occurrence of the by-claim may be delayed. We obtain the recursive formula of the joint distribution of the surplus immediately prior to ruin and deficit at ruin. Furthermore, the ruin probability is given by means of ruin probability and the deficit at ruin of the classical compound binomial risk model. Finally, we derive an upper bound for the ruin probability. 相似文献
945.
Block-diagonalization of sparse equivariant discretization matrices is studied. Such matrices typically arise when partial
differential equations that evolve in symmetric geometries are discretized via the finite element method or via finite differences.
By considering sparse equivariant matrices as equivariant graphs, we identify a condition for when block-diagonalization via
a sparse variant of a generalized Fourier transform (GFT) becomes particularly simple and fast.
Characterizations for finite element triangulations of a symmetric domain are given, and formulas for assembling the block-diagonalized
matrix directly are presented. It is emphasized that the GFT preserves symmetric (Hermitian) properties of an equivariant
matrix.
By simulating the heat equation at the surface of a sphere discretized by an icosahedral grid, it is demonstrated that the
block-diagonalization is beneficial. The gain is significant for a direct method, and modest for an iterative method.
A comparison with a block-diagonalization approach based upon the continuous formulation is made. It is found that the sparse
GFT method is an appropriate way to discretize the resulting continuous subsystems, since the spectrum and the symmetry are
preserved.
AMS subject classification (2000) 43A30, 65T99, 20B25 相似文献
946.
Sedimentation and erosion processes in sedimentary basins can be modeled by a parabolic equation with a limiter on the fluxes and a constraint on the time variation.This limiter happens to satisfy a stationary scalar hyperbolic inequality,within a constraint,for which the authors prove the existence and the uniqueness of the solution.Actually,this solution is shown to be the maximal element of a convenient convex set of functions.The existence proof is obtained thanks to the use of a numerical scheme. 相似文献
947.
Jing-na Li Xiao-feng Wang Zheng-an Yao 《应用数学学报(英文版)》2007,23(3):421-432
In this paper, we propose a model in studying soft ferromagnetic films, which is readily accessible experimentally. By using penalty approximation and compensated compactness, we prove that the dynamical equation in thin film has a local weak solution. Moreover, the corresponding linear equation is also dealt with in great detail. 相似文献
948.
D Shaw 《The Journal of the Operational Research Society》2006,57(7):830-841
Problem-structuring group workshops can be used in organizations as a consulting tool and as a research tool. One example of the latter is using a problem-structuring method (PSM) to help a group tackle an organizational issue; meanwhile, researchers collect the participants’ initial views, discussion of divergent views, the negotiated agreement, and the reasoning for outcomes emerging. Technology can help by supporting participants in freely sharing their opinions and by logging data for post-workshop analyses. For example, computers let participants share views anonymously and without being influenced by others (as well as logging those views), and video-cameras can record discussions and intra-group dynamics. This paper evaluates whether technology-supported Journey Making workshops can be effective research tools that can capture quality research data when compared against theoretical performance benchmarks and other qualitative research tools. 相似文献
949.
Kang Hai TAN Xiao Ping YANG 《数学学报(英文版)》2006,22(3):701-710
In this paper we give a geometric interpretation of the notion of the horizontal mean curvature which is introduced by Danielli Garofalo-Nhieu and Pauls who recently introduced sub- Riemannian minimal surfaces in Carnot groups. This will be done by introducing a natural nonholonomic connection which is the restriction (projection) of the natural Riemannian connection on the horizontal bundle. For this nonholonomic connection and (intrinsic) regular hypersurfaces we introduce the notions of the horizontal second fundamental form and the horizontal shape operator. It turns out that the horizontal mean curvature is the trace of the horizontal shape operator. 相似文献
950.