全文获取类型
收费全文 | 6522篇 |
免费 | 685篇 |
国内免费 | 524篇 |
专业分类
化学 | 425篇 |
晶体学 | 5篇 |
力学 | 719篇 |
综合类 | 110篇 |
数学 | 4808篇 |
物理学 | 1664篇 |
出版年
2024年 | 5篇 |
2023年 | 61篇 |
2022年 | 78篇 |
2021年 | 152篇 |
2020年 | 136篇 |
2019年 | 164篇 |
2018年 | 145篇 |
2017年 | 159篇 |
2016年 | 210篇 |
2015年 | 143篇 |
2014年 | 238篇 |
2013年 | 635篇 |
2012年 | 282篇 |
2011年 | 346篇 |
2010年 | 317篇 |
2009年 | 380篇 |
2008年 | 454篇 |
2007年 | 460篇 |
2006年 | 413篇 |
2005年 | 362篇 |
2004年 | 276篇 |
2003年 | 330篇 |
2002年 | 295篇 |
2001年 | 219篇 |
2000年 | 215篇 |
1999年 | 183篇 |
1998年 | 192篇 |
1997年 | 158篇 |
1996年 | 107篇 |
1995年 | 99篇 |
1994年 | 66篇 |
1993年 | 54篇 |
1992年 | 43篇 |
1991年 | 30篇 |
1990年 | 39篇 |
1989年 | 31篇 |
1988年 | 38篇 |
1987年 | 34篇 |
1986年 | 23篇 |
1985年 | 32篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 22篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1973年 | 6篇 |
排序方式: 共有7731条查询结果,搜索用时 250 毫秒
1.
In this paper, we investigate the evolution of joint invariants under invariant geometric flows using the theory of equivariant moving frames and the induced invariant discrete variational complex. For certain arc length preserving planar curve flows invariant under the special Euclidean group , the special linear group , and the semidirect group , we find that the induced evolution of the discrete curvature satisfies the differential‐difference mKdV, KdV, and Burgers' equations, respectively. These three equations are completely integrable, and we show that a recursion operator can be constructed by precomposing the characteristic operator of the curvature by a certain invariant difference operator. Finally, we derive the constraint for the integrability of the discrete curvature evolution to lift to the evolution of the discrete curve itself. 相似文献
2.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献
3.
采用Cundari和Stevens等推导的有效芯势对镧系金属一氢化物进行了理论计算,以探讨镧系金属元素与氢的相互作用。结果表明所有镧系金属一氢化物基态时理论上是稳定的,最稳定的是SmH,最不稳定的是DyH;键长计算结果显示,基态时镧系金属一招兵买马花物有独立王国 收缩现象发生;红外振动频率理论计算值与实验结果一致;成键轨道中,金属原子轨道的贡献主要是s轨道和d轨道:从CeH至ErH(GdH)例外)随着外层电子的增加s轨道成分逐渐增大d轨道成分逐渐减小;从TmH和LuH(包括GdH),成键轨道中金属原子轨道的贡献主要是d轨道,约为90%;约大多数镧系金属一氧化物的成键轨道中金属原子轨道f成分小于1%。 相似文献
4.
Lance Nielsen 《Acta Appl Math》2002,74(3):265-292
Stability properties of Feynman's operational calculus are addressed in the setting of exponential functions of noncommuting operators. Applications of some of the stability results are presented. In particular, the time-dependent perturbation theory of nonrelativistic quantum mechanics is presented in the setting of the operational calculus and application of the stability results of this paper to the perturbation theory are discussed. 相似文献
5.
R. S. Martynov Yu. M. Nechepurenko 《Computational Mathematics and Mathematical Physics》2006,46(7):1155-1167
For a discrete linear stochastic dynamical system, computation of the response matrix to the external action from a subspace using given observational data is examined. An algorithm is proposed and substantiated that makes it possible to improve the numerical accuracy and to reduce the amount of observational data compared to the general case where an arbitrary external action is allowed. As an illustration, a discrete system arising in the analysis of a linear stochastic dynamical continuous-time system is considered more thoroughly. Some numerical results are presented. 相似文献
6.
High-temperature series expansions of the susceptibility and second moment to 15th order are calculated for zero external field on the linear chain (LC), plane square (PSQ), simple cubic (SC), and body-centered cubic (BCC) lattices. Checks for specific models against pertinent work in the literature are detailed. 相似文献
7.
8.
Teresa Regińska 《BIT Numerical Mathematics》2004,44(1):119-133
The paper concerns conditioning aspects of finite-dimensional problems arising when the Tikhonov regularization is applied
to discrete ill-posed problems. A relation between the regularization parameter and the sensitivity of the regularized solution
is investigated. The main conclusion is that the condition number can be decreased only to the square root of that for the
nonregularized problem. The convergence of solutions of regularized discrete problems to the exact generalized solution is
analyzed just in the case when the regularization corresponds to the minimal condition number. The convergence theorem is
proved under the assumption of the suitable relation between the discretization level and the data error. As an example the
method of truncated singular value decomposition with regularization is considered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
证明了当超越亚纯函数的级小于1时,其Norel例外值最多只有一个.由于存在任何级的整函数,因此一个例外值总可达到,故所得结果不能再改进。 相似文献
10.
A new prediction technique is proposed for chaotic time series. The usefulness of the technique is thatit can kick off some false neighbor points which are not suitable for the local estimation of the dynamics systems. Atime-delayed embedding is used to reconstruct the underlying attractor, and the prediction model is based on the timeevolution of the topological neighboring in the phase space. We use a feedforward neural network to approximate thelocal dominant Lyapunov exponent, and choose the spatial neighbors by the Lyapunov exponent. The model is testedfor the Mackey-Glass equation and the convection amplitude of lorenz systems. The results indicate that this predictiontechnique can improve the prediction of chaotic time series. 相似文献