全文获取类型
收费全文 | 32517篇 |
免费 | 3715篇 |
国内免费 | 2182篇 |
专业分类
化学 | 1889篇 |
晶体学 | 17篇 |
力学 | 3674篇 |
综合类 | 443篇 |
数学 | 23629篇 |
物理学 | 8762篇 |
出版年
2024年 | 65篇 |
2023年 | 318篇 |
2022年 | 343篇 |
2021年 | 479篇 |
2020年 | 939篇 |
2019年 | 917篇 |
2018年 | 859篇 |
2017年 | 826篇 |
2016年 | 907篇 |
2015年 | 758篇 |
2014年 | 1489篇 |
2013年 | 2825篇 |
2012年 | 1505篇 |
2011年 | 2033篇 |
2010年 | 1872篇 |
2009年 | 2087篇 |
2008年 | 2229篇 |
2007年 | 2127篇 |
2006年 | 1847篇 |
2005年 | 1819篇 |
2004年 | 1507篇 |
2003年 | 1468篇 |
2002年 | 1289篇 |
2001年 | 979篇 |
2000年 | 935篇 |
1999年 | 891篇 |
1998年 | 850篇 |
1997年 | 714篇 |
1996年 | 534篇 |
1995年 | 438篇 |
1994年 | 395篇 |
1993年 | 252篇 |
1992年 | 225篇 |
1991年 | 231篇 |
1990年 | 201篇 |
1989年 | 117篇 |
1988年 | 120篇 |
1987年 | 120篇 |
1986年 | 115篇 |
1985年 | 113篇 |
1984年 | 113篇 |
1983年 | 53篇 |
1982年 | 99篇 |
1981年 | 89篇 |
1980年 | 64篇 |
1979年 | 60篇 |
1978年 | 46篇 |
1977年 | 36篇 |
1976年 | 27篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
31.
施国勇 《宁波大学学报(理工版)》1998,(2)
提出了一个线性双向联想存储器的模型,一组有限个向量对由一线性算子建立起双向联想关系,此线性算于是一个网络的联结权重矩阵。该权矩阵由最小二乘法决定。由权矩阵的解导出一特殊类型的Lyapunov矩阵方程.本文提供了这种Lyapunov矩阵方程的解。 相似文献
32.
Summary This paper is concerned with the problem of developing numerical integration algorithms for differential equations that, when
viewed as equations in some Euclidean space, naturally evolve on some embedded submanifold. It is desired to construct algorithms
whose iterates also evolve on the same manifold. These algorithms can therefore be viewed as integrating ordinary differential
equations on manifolds. The basic method “decouples” the computation of flows on the submanifold from the numerical integration
process. It is shown that two classes of single-step and multistep algorithms can be posed and analyzed theoretically, using
the concept of “freezing” the coefficients of differential operators obtained from the defining vector field. Explicit third-order
algorithms are derived, with additional equations augmenting those of their classical counterparts, obtained from “obstructions”
defined by nonvanishing Lie brackets. 相似文献
33.
34.
We examine two criteria for balance of a gain graph, one based on binary cycles and one on circles. The graphs for which each criterion is valid depend on the set of allowed gain groups. The binary cycle test is invalid, except for forests, if any possible gain group has an element of odd order. Assuming all groups are allowed, or all abelian groups, or merely the cyclic group of order 3, we characterize, both constructively and by forbidden minors, the graphs for which the circle test is valid. It turns out that these three classes of groups have the same set of forbidden minors. The exact reason for the importance of the ternary cyclic group is not clear. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
35.
Lin Surong 《Annals of Differential Equations》2006,22(4):517-523
The singularly perturbed boundary value problem for nonlinear higher order ordinary differential equation involving two small parameters has been considered. Under appropriate assumptions, for the three cases:ε/μ2→0(μ→0),μ2/ε→0 (ε→0) andε=μ2, the uniformly valid asymptotic solution is obtained by using the expansion method of two small parameters and the theory of differential inequality. 相似文献
36.
一类非线性Schr(o)dinger方程的守恒差分法与Fourier谱方法 总被引:1,自引:0,他引:1
考察了一类带导数项的非线性Schrodinger方程的周期边值问题,提出了一种守恒的差分格式,在空间方向上采用Fourier谱方法,证明了格式的稳定性和收敛性.数值试验得到了与理论分析一致的结果. 相似文献
37.
Zhong-Qing Wang 《Journal of Mathematical Analysis and Applications》2002,274(1):374-403
An orthogonal system of rational functions is discussed. Some inverse inequalities, imbedding inequalities and approximation results are obtained. Two model problems are considered. The stabilities and convergences of proposed rational spectral schemes and rational pseudospectral schemes are proved. The techniques used in this paper are also applicable to other problems on the whole line. Numerical results show the efficiency of this approach. 相似文献
38.
39.
根据生产任务选择加工设备进行制造资源重组是实现可重构制造系统的关键问题之一,由于设备的选择涉及到多种因素,既有定量指标,又有定性指标,传统的依靠人工经验的方法显得力不从心。本文首先结合实际情况,提出了一套设备选择评价体系,通过对模糊判断矩阵采用最小对数二乘法确定各评价因素的权重系数,针对定性指标和定量指标采用不同的方法确定其性能指标值,通过模糊积分对评判指标进行综合评判,最后进行了实例研究。所提出的方法有效地简化了决策过程,为可重构制造系统设备选择提供了一套行之有效的方法。 相似文献
40.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献