全文获取类型
收费全文 | 16318篇 |
免费 | 1485篇 |
国内免费 | 989篇 |
专业分类
化学 | 1923篇 |
晶体学 | 54篇 |
力学 | 6331篇 |
综合类 | 176篇 |
数学 | 6880篇 |
物理学 | 3428篇 |
出版年
2024年 | 38篇 |
2023年 | 178篇 |
2022年 | 264篇 |
2021年 | 288篇 |
2020年 | 429篇 |
2019年 | 332篇 |
2018年 | 364篇 |
2017年 | 478篇 |
2016年 | 522篇 |
2015年 | 418篇 |
2014年 | 739篇 |
2013年 | 1119篇 |
2012年 | 681篇 |
2011年 | 853篇 |
2010年 | 718篇 |
2009年 | 878篇 |
2008年 | 870篇 |
2007年 | 911篇 |
2006年 | 880篇 |
2005年 | 846篇 |
2004年 | 755篇 |
2003年 | 754篇 |
2002年 | 678篇 |
2001年 | 637篇 |
2000年 | 582篇 |
1999年 | 589篇 |
1998年 | 513篇 |
1997年 | 442篇 |
1996年 | 359篇 |
1995年 | 333篇 |
1994年 | 237篇 |
1993年 | 175篇 |
1992年 | 212篇 |
1991年 | 168篇 |
1990年 | 136篇 |
1989年 | 84篇 |
1988年 | 54篇 |
1987年 | 52篇 |
1986年 | 32篇 |
1985年 | 46篇 |
1984年 | 40篇 |
1983年 | 30篇 |
1982年 | 26篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
This paper considers the streamline‐upwind Petrov–Galerkin (SUPG) method applied to the unsteady compressible Navier–Stokes equations in conservation‐variable form. The spatial discretization, including a modified approach for interpolating the inviscid flux terms in the SUPG finite element formulation, and the second‐order accurate time discretization are presented. The numerical method is discussed in detail. The performance of the algorithm is then investigated by considering inviscid flow past a circular cylinder. Validation of the finite element formulation via comparisons with experimental data for high‐Mach number perfect gas laminar flows is presented, with a specific focus on comparisons with experimentally measured skin friction and convective heat transfer on a 15° compression ramp. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
932.
均匀棒纯纵向运动方程初边值问题的有限体积法 总被引:2,自引:0,他引:2
提出了均匀棒纯纵向运动方程初边值问题的有限体积格式,给出了有限体积解的误差分析,得到了有限体积解的最优阶L2和H1误差估计及超收敛H1误差估计,提供了一个数值算例. 相似文献
933.
Ajit Patel Amiya K. Pani Neela Nataraj 《Numerical Methods for Partial Differential Equations》2008,24(6):1460-1484
In this article a standard mortar finite element method and a mortar element method with Lagrange multiplier are used for spatial discretization of a class of parabolic initial‐boundary value problems. Optimal error estimates in L∞(L2) and L∞(H1)‐norms for semidiscrete methods for both the cases are established. The key feature that we have adopted here is to introduce a modified elliptic projection. In the standard mortar element method, a completely discrete scheme using backward Euler scheme is discussed and optimal error estimates are derived. The results of numerical experiments support the theoretical results obtained in this article. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2008 相似文献
934.
D. O. Revin 《Algebra and Logic》2008,47(3):210-227
935.
V. A. Dougalis F. Sturm G. E. Zouraris 《Mathematical Methods in the Applied Sciences》2009,32(12):1519-1540
We consider the third‐order Claerbout‐type wide‐angle parabolic equation (PE) of underwater acoustics in a cylindrically symmetric medium consisting of water over a soft bottom B of range‐dependent topography. There is strong indication that the initial‐boundary value problem for this equation with just a homogeneous Dirichlet boundary condition posed on B may not be well‐posed, for example when B is downsloping. We impose, in addition to the above, another homogeneous, second‐order boundary condition, derived by assuming that the standard (narrow‐angle) PE holds on B, and establish a priori H2 estimates for the solution of the resulting initial‐boundary value problem for any bottom topography. After a change of the depth variable that makes B horizontal, we discretize the transformed problem by a second‐order accurate finite difference scheme and show, in the case of upsloping and downsloping wedge‐type domains, that the new model gives stable and accurate results. We also present an alternative set of boundary conditions that make the problem exactly energy conserving; one of these conditions may be viewed as a generalization of the Abrahamsson–Kreiss boundary condition in the wide‐angle case. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
936.
设$\varphi$为群${\rm Aut}(N)$的同态,记$H_\varphi\times N$为群$N$借助于群$H$的半直积.设$G$为有限不可解群,本文证明: 若$G$中最高阶元素个数为40, 则$G$同构于下列群之一:(1)~$Z_{4\varphi}\times A_5$,\,${\rm ker}\varphi=Z_2$; (2)~$D_{8\varphi}\times A_5,\,{\rm ker}\varphi=Z_2\times Z_2$; (3)~$G/N=S_5$, $N=Z(G)=Z_2$; (4)~$G/N=S_5$, $N=Z_2\times Z_2,\,N\cap Z(G)=Z_2$. 相似文献
937.
N. S. Romanovskii 《Algebra and Logic》2008,47(6):426-434
A soluble group G is rigid if it contains a normal series of the form G = G1 > G2 > … > Gp > Gp+1 = 1, whose quotients Gi/Gi+1 are Abelian and are torsion-free as right ℤ[G/Gi]-modules. The concept of a rigid group appeared in studying algebraic geometry over groups that are close to free soluble.
In the class of all rigid groups, we distinguish divisible groups the elements of whose quotients Gi/Gi+1 are divisible by any elements of respective groups rings Z[G/Gi]. It is reasonable to suppose that algebraic geometry over divisible rigid groups is rather well structured. Abstract properties
of such groups are investigated. It is proved that in every divisible rigid group H that contains G as a subgroup, there is
a minimal divisible subgroup including G, which we call a divisible closure of G in H. Among divisible closures of G are divisible
completions of G that are distinguished by some natural condition. It is shown that a divisible completion is defined uniquely
up to G-isomorphism.
Supported by the Council for Grants (under RF President) and State Aid of Leading Scientific Schools (grant NSh-344.2008.1).
Translated from Algebra i Logika, Vol. 47, No. 6, pp. 762–776, November–December, 2008. 相似文献
938.
Fei Xu 《Advances in Mathematics》2008,219(6):1872-1893
Let C be a small category and k a field. There are two interesting mathematical subjects: the category algebra kC and the classifying space |C|=BC. We study the ring homomorphism HH∗(kC)→H∗(|C|,k) and prove it is split surjective, using the factorization category of Quillen [D. Quillen, Higher algebraic K-theory I, in: Lecture Notes in Math., vol. 341, Springer-Verlag, Berlin, 1973, pp. 85-147] and certain techniques from functor cohomology theory. This generalizes the well-known theorems for groups and posets. Based on this result, we construct a seven-dimensional category algebra whose Hochschild cohomology ring modulo nilpotents is not finitely generated, disproving a conjecture of Snashall and Solberg [N. Snashall, Ø. Solberg, Support varieties and Hochschild cohomology rings, Proc. London Math. Soc. 88 (3) (2004) 705-732]. 相似文献
939.
We consider the approximation of trigonometric operator functions that arise in the numerical solution of wave equations by
trigonometric integrators. It is well known that Krylov subspace methods for matrix functions without exponential decay show
superlinear convergence behavior if the number of steps is larger than the norm of the operator. Thus, Krylov approximations
may fail to converge for unbounded operators. In this paper, we propose and analyze a rational Krylov subspace method which
converges not only for finite element or finite difference approximations to differential operators but even for abstract,
unbounded operators. In contrast to standard Krylov methods, the convergence will be independent of the norm of the operator
and thus of its spatial discretization. We will discuss efficient implementations for finite element discretizations and illustrate
our analysis with numerical experiments.
AMS subject classification (2000) 65F10, 65L60, 65M60, 65N22 相似文献
940.
This paper is devoted to the development of accurate high‐order interpolating schemes for semi‐Lagrangian advection. The characteristic‐Galerkin formulation is obtained by using a semi‐Lagrangian temporal discretization of the total derivative. The semi‐Lagrangian method requires high‐order interpolators for accuracy. A class of ??1 finite‐element interpolating schemes is developed and two semi‐Lagrangian methods are considered by tracking the feet of the characteristic lines either from the interpolation or from the integration nodes. Numerical stability and analytical results quantifying the amount of artificial viscosity induced by the two methods are presented in the case of the one‐dimensional linear advection equation, based on the modified equation approach. Results of test problems to simulate the linear advection of a cosine hill illustrate the performance of the proposed approach. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献