全文获取类型
收费全文 | 55368篇 |
免费 | 6721篇 |
国内免费 | 5097篇 |
专业分类
化学 | 12765篇 |
晶体学 | 992篇 |
力学 | 13026篇 |
综合类 | 760篇 |
数学 | 23000篇 |
物理学 | 16643篇 |
出版年
2024年 | 128篇 |
2023年 | 592篇 |
2022年 | 1057篇 |
2021年 | 1217篇 |
2020年 | 1560篇 |
2019年 | 1347篇 |
2018年 | 1387篇 |
2017年 | 1896篇 |
2016年 | 2111篇 |
2015年 | 1640篇 |
2014年 | 2718篇 |
2013年 | 4156篇 |
2012年 | 3116篇 |
2011年 | 3583篇 |
2010年 | 3067篇 |
2009年 | 3437篇 |
2008年 | 3358篇 |
2007年 | 3375篇 |
2006年 | 3158篇 |
2005年 | 2940篇 |
2004年 | 2523篇 |
2003年 | 2345篇 |
2002年 | 2103篇 |
2001年 | 1838篇 |
2000年 | 1753篇 |
1999年 | 1608篇 |
1998年 | 1451篇 |
1997年 | 1236篇 |
1996年 | 998篇 |
1995年 | 892篇 |
1994年 | 765篇 |
1993年 | 588篇 |
1992年 | 611篇 |
1991年 | 484篇 |
1990年 | 392篇 |
1989年 | 292篇 |
1988年 | 225篇 |
1987年 | 182篇 |
1986年 | 137篇 |
1985年 | 184篇 |
1984年 | 159篇 |
1983年 | 86篇 |
1982年 | 101篇 |
1981年 | 70篇 |
1980年 | 48篇 |
1979年 | 63篇 |
1978年 | 46篇 |
1977年 | 58篇 |
1976年 | 26篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
重力场与静电场特点的比较 总被引:1,自引:1,他引:1
“场”是一种客观存在的物质,但由于“场”具有不易直接感受的特殊存在形态,同学们对“场”的物质性的理解不够深刻,解决“场”的相关问题时也感到棘手.笔者就高中阶段最典型的两种场——“重力场”和“静电场”的力学性质与能量特点进行比较,使同学们对“场”的概念有更深刻的认识. 相似文献
993.
以“自主探索”的方式开展中学物理教学法实验课教学活动,在调动学生学习积极性、主动性,提高学生实验操作、设计、改进能力,培养师范生的教学素质等方面都优于传统的实验课开展方式. 相似文献
994.
995.
M. E. Fels 《Transactions of the American Mathematical Society》1996,348(12):5007-5029
A simple invariant characterization of the scalar fourth-order ordinary differential equations which admit a variational multiplier is given. The necessary and sufficient conditions for the existence of a multiplier are expressed in terms of the vanishing of two relative invariants which can be associated with any fourth-order equation through the application of Cartan's equivalence method. The solution to the inverse problem for fourth-order scalar equations provides the solution to an equivalence problem for second-order Lagrangians, as well as the precise relationship between the symmetry algebra of a variational equation and the divergence symmetry algebra of the associated Lagrangian.
996.
Xiao-Qing Jin 《Journal of Computational and Applied Mathematics》1996,70(2):225-230
We consider the solutions of block Toeplitz systems with Toeplitz blocks by the preconditioned conjugate gradient (PCG) method. Here the block Toeplitz matrices are generated by nonnegative functions f(x,y). We use band Toeplitz matrices as preconditioners. The generating functions g(x,y) of the preconditioners are trigonometric polynomials of fixed degree and are determined by minimizing (f − g)/f∞. We prove that the condition number of the preconditioned system is O(1). An a priori bound on the number of iterations for convergence is obtained. 相似文献
997.
E. P. Dolzhenko 《Mathematical Notes》1996,60(2):130-136
Letd(;z, t) be the smallest diameter of the arcs of a Jordan curve with endsz andt. Consider the rapidity of decreasing ofd(;)=sup{d(;z, t):z, t , ¦z–t¦} (as 0,0) as a measure of nicety of . Letg(x) (x0) be a continuous and nondecreasing function such thatg(x)x,g(0)=0. Put¯g(x)=g(x)+x, h(x)=(¯g(x))2. LetH(x) be an arbitrary primitive of 1/h
–1(x). Note that the functionH
–1
x is positive and increasing on (–, +),H
–1 0 asx– andH
–1+ asx +. The following statement is proved in the paper.Translated fromMatematicheskie Zametki, Vol. 60, No. 2, pp. 176–184, August, 1996.This research was supported by the Russian Foundation for Basic Research under grant No. 93-01-00236 and by the International Science Foundation under grant No. NCF000. 相似文献
998.
A. M. Chebotarev 《Mathematical Notes》1996,60(5):544-561
We prove that the Hudson-Parthasarathy equation corresponds, up to unitary equivalence, to the strong resolvent limit of Schrödinger Hamiltonians in Fock space and that the symmetric form of this equation corresponds to the weak limit of the Schrödinger Hamiltonians.Translated fromMatematicheskie Zametki, Vol. 60, No. 5, pp. 726–750, November, 1996. 相似文献
999.
Nahid Emad 《Numerical Algorithms》1996,11(1):159-179
We make use of the Padé approximants and the Krylov sequencex, Ax,,...,A
m–1
x in the projection methods to compute a few Ritz values of a large hermitian matrixA of ordern. This process consists in approaching the poles ofR
x()=((I–A)–1
x,x), the mean value of the resolvant ofA, by those of [m–1/m]Rx(), where [m–1/m]Rx() is the Padé approximant of orderm of the functionR
x(). This is equivalent to approaching some eigenvalues ofA by the roots of the polynomial of degreem of the denominator of [m–1/m]Rx(). This projection method, called the Padé-Rayleigh-Ritz (PRR) method, provides a simple way to determine the minimum polynomial ofx in the Krylov subspace methods for the symmetrical case. The numerical stability of the PRR method can be ensured if the projection subspacem is sufficiently small. The mainly expensive portion of this method is its projection phase, which is composed of the matrix-vector multiplications and, consequently, is well suited for parallel computing. This is also true when the matrices are sparse, as recently demonstrated, especially on massively parallel machines. This paper points out a relationship between the PRR and Lanczos methods and presents a theoretical comparison between them with regard to stability and parallelism. We then try to justify the use of this method under some assumptions. 相似文献
1000.
The nonsymmetric Lanczos method has recently received significant attention as a model reduction technique for large-scale systems. Unfortunately, the Lanczos method may produce an unstable partial realization for a given, stable system. To remedy this situation, unexpensive implicit restarts are developed which can be employed to stabilize the Lanczos generated model.This work was supported in part by ARPA (US Army ORA4466.01), by ARPA (Grant 60NANB2D1272), by the Department of Energy (Contract DE-FG0f-91ER25103) and by the National Science Foundation (Grants CCR-9209349 and CCR-9120008). 相似文献