全文获取类型
收费全文 | 27194篇 |
免费 | 3211篇 |
国内免费 | 1700篇 |
专业分类
化学 | 1682篇 |
晶体学 | 16篇 |
力学 | 3110篇 |
综合类 | 315篇 |
数学 | 18901篇 |
物理学 | 8081篇 |
出版年
2024年 | 60篇 |
2023年 | 277篇 |
2022年 | 322篇 |
2021年 | 424篇 |
2020年 | 826篇 |
2019年 | 815篇 |
2018年 | 755篇 |
2017年 | 688篇 |
2016年 | 774篇 |
2015年 | 664篇 |
2014年 | 1225篇 |
2013年 | 2385篇 |
2012年 | 1289篇 |
2011年 | 1626篇 |
2010年 | 1580篇 |
2009年 | 1731篇 |
2008年 | 1823篇 |
2007年 | 1772篇 |
2006年 | 1506篇 |
2005年 | 1523篇 |
2004年 | 1256篇 |
2003年 | 1215篇 |
2002年 | 1054篇 |
2001年 | 813篇 |
2000年 | 775篇 |
1999年 | 737篇 |
1998年 | 694篇 |
1997年 | 567篇 |
1996年 | 442篇 |
1995年 | 366篇 |
1994年 | 308篇 |
1993年 | 201篇 |
1992年 | 190篇 |
1991年 | 204篇 |
1990年 | 175篇 |
1989年 | 98篇 |
1988年 | 102篇 |
1987年 | 98篇 |
1986年 | 98篇 |
1985年 | 92篇 |
1984年 | 85篇 |
1983年 | 44篇 |
1982年 | 84篇 |
1981年 | 73篇 |
1980年 | 52篇 |
1979年 | 55篇 |
1978年 | 36篇 |
1977年 | 30篇 |
1976年 | 23篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
991.
992.
993.
V. Majerník 《Foundations of Physics Letters》1997,10(4):357-370
We propose a spacetime scheme representing the union of the real and non-real spacetime as a possible geometrical framework
for Caldirola’s idea, that the bradyonic motion can be regarded as a light-like motion in an additional extra space. The playground
of all physical processes is the union space. However, the physical processes in union space are differently projected on
the real and non-real spacetime. The waves linked with luxons in union space are projected on the real spacetime so that they
propagate here always with the velocity of light. The waves linked with bradyons in union space are projected on the non-real
spacetime so that they propagate here with the velocity of light. The wave linked with a bradyon in union space, which is
projected on the real spacetime, is here described by the Schroedinger and Dirac equations. There is proposed a symmetry which
demands that the physical world is in its law the same whether it is seen from real or non-real spacetime. We discuss some
consequences of this symmetry in the theory of elementary particles. 相似文献
994.
995.
作者在前文 ̄(1,2)中通过计算机模拟实验给出了由多缝衍射反演光谱学的积分方程─一种第一类Fredholm积分方程─获得稳定线性方程组的条件,本文将进一步从数学上利用积分方程的本征值理论分析计算机的实验结果,阐明这些条件使线性方程组稳定的机制。 相似文献
996.
Differential equations of different types and orders are of utmost importance for mathematical modeling of control system problems. State variable method uses the concept of expressing n number of first order differential equations in vector matrix form to model and analyze/synthesize control systems.The present work proposes a new set of orthogonal hybrid functions (HF) which evolved from synthesis of sample-and-hold functions (SHF) and triangular functions (TF). This HF set is used to approximate a time function in a piecewise linear manner with the mean integral square error (MISE) much less than block pulse function based approximation which always provides staircase solutions.The operational matrices for integration and differentiation in HF domain are also derived and employed for solving non-homogeneous and homogeneous differential equations of the first order as well as state equations. The results are compared with exact solutions, the 4th order Runge-Kutta method and its further improved versions proposed by Simos [6]. The presented HF domain theory is well supported by a few illustrations. 相似文献
997.
MeiJiao Wang 《Applied mathematics and computation》2012,218(9):5259-5264
By means of the Hermite transformation, a new general ansätz and the symbolic computation system Maple, we apply the Riccati equation rational expansion method [24] to uniformly construct a series of stochastic non-traveling wave solutions for stochastic differential equations. To illustrate the effectiveness of our method, we take the stochastic mKdV equation as an example, and successfully construct some new and more general solutions. The method can also be applied to solve other nonlinear stochastic differential equation or equations. 相似文献
998.
In this paper, we consider a renewal risk model with stochastic premiums income. We assume that the premium number process and the claim number process are a Poisson process and a generalized Erlang (n) processes, respectively. When the individual stochastic premium sizes are exponentially distributed, the Laplace transform and a defective renewal equation for the Gerber-Shiu discounted penalty function are obtained. Furthermore, the discounted joint distribution of the surplus just before ruin and the deficit at ruin is given. When the claim size distributions belong to the rational family, the explicit expression of the Gerber-Shiu discounted penalty function is derived. Finally, a specific example is provided. 相似文献
999.
针对约束块可分的最优化问题,引入序列线性方程组方法和有效集策略,提出了一个求解约束块可分优化问题的QP-free型并行变量分配(PVD)算法.算法中用三个系数具有对称结构的线性方程组来代替PVD算法中的二次规划问题以求解线搜索方向,避免了约束不相容,减小了计算量.并且算法不要求约束是凸的.最后证明了QP-free型PVD算法的全局收敛性. 相似文献
1000.
利用(G'/G)-展开法求广义的(2+1)维ZK-MEW方程的新精确解 总被引:1,自引:0,他引:1
结合齐次平衡法原理并利用(G'/G)-展开法,研究了广义的(2+1)维ZK-MEW方程的精确解,从而得到了广义的(2+1)维ZK-MEW方程的用双曲函数和三角函数表示的通解,当双曲函数通解中常数取特殊值时,便得到广义的(2+1)维ZK-MEW方程的孤立波解,获得了与现有文献不同的新精确解. 相似文献