全文获取类型
收费全文 | 17432篇 |
免费 | 1639篇 |
国内免费 | 991篇 |
专业分类
化学 | 412篇 |
晶体学 | 16篇 |
力学 | 1600篇 |
综合类 | 221篇 |
数学 | 14470篇 |
物理学 | 3343篇 |
出版年
2024年 | 37篇 |
2023年 | 161篇 |
2022年 | 219篇 |
2021年 | 243篇 |
2020年 | 365篇 |
2019年 | 386篇 |
2018年 | 444篇 |
2017年 | 475篇 |
2016年 | 481篇 |
2015年 | 351篇 |
2014年 | 827篇 |
2013年 | 1388篇 |
2012年 | 820篇 |
2011年 | 956篇 |
2010年 | 858篇 |
2009年 | 1109篇 |
2008年 | 1177篇 |
2007年 | 1228篇 |
2006年 | 1099篇 |
2005年 | 879篇 |
2004年 | 743篇 |
2003年 | 817篇 |
2002年 | 721篇 |
2001年 | 541篇 |
2000年 | 547篇 |
1999年 | 497篇 |
1998年 | 441篇 |
1997年 | 433篇 |
1996年 | 307篇 |
1995年 | 262篇 |
1994年 | 193篇 |
1993年 | 140篇 |
1992年 | 148篇 |
1991年 | 127篇 |
1990年 | 98篇 |
1989年 | 53篇 |
1988年 | 56篇 |
1987年 | 54篇 |
1986年 | 50篇 |
1985年 | 62篇 |
1984年 | 65篇 |
1983年 | 32篇 |
1982年 | 38篇 |
1981年 | 36篇 |
1980年 | 23篇 |
1979年 | 21篇 |
1978年 | 14篇 |
1977年 | 18篇 |
1976年 | 10篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Yanghyun Byun 《Foundations of Physics》2004,34(6):987-1003
We consider a representation of the state reduction which depends neither on its reality nor on the details of when and how it emerges. Then by means of the representation we find necessary conditions, even if not the sufficient ones, for a decomposition of the state vector space to be a solution to the basis problem. The conditions are that the decomposition should be Lorentz invariant and orthogonal and that the associated projections should be continuous. They are shown to be able to determine a decomposition in each of a few examples considered if the other circumstances are taken into account together. 相似文献
62.
Capacity Constrained Transit Assignment with Common Lines 总被引:1,自引:0,他引:1
Fumitaka Kurauchi Michael G. H. Bell Jan-Dirk Schmöcker 《Journal of Mathematical Modelling and Algorithms》2003,2(4):309-327
This paper proposes the use of absorbing Markov chains to solve the capacity constrained transit network loading problem taking
common lines into account. The approach handles congested transit networks, where some passengers will not be able to board
because of the absence of sufficient space. The model also handles the common lines problem, where choice of route depends
on frequency of arrivals. The mathematical formulation of the problem is presented together with a numerical example.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
63.
64.
Comment on “A Hierarchy of Integrable Nonlinear Lattice Equations and New Integrable Symplectic Map“
Comment on a recent paper on Commun. Theor. Phys. (Beijing, China) 38 (2002) pp. 523-528. 相似文献
65.
高斯光束计算平板波导自由传输区远场分布及其修正 总被引:2,自引:2,他引:0
对近轴近似条件下求解亥姆霍兹方程得到的高斯光束显式传播公式做了分析,同时,基于基尔霍夫衍射理论,在菲涅耳近似的条件下给出了相应的高斯光束在远场的传播公式,在此基础上,对近轴近似条件做出了定量分析,给出了这个近似条件引入的误差,提出了一种计算高斯光束远场分布的修正方法,并采用有限差分-光束传播方法(FD-BPM)来检验各种方法的准确性。把这种修正方法应用到平面光集成波导器件,如阵列波导光栅(AWG)、蚀刻衍射光栅(EDG)等器件的设计和模拟中,可以大大降低工作的复杂性,同时可以得到精确的结果。 相似文献
66.
THE COUPLING OF NATURAL BOUNDARY ELEMENT AND FINITE ELEMENT METHOD FOR 2D HYPERBOLIC EQUATIONS 总被引:2,自引:0,他引:2
De-haoYu Qi-kuiDu 《计算数学(英文版)》2003,21(5):585-594
In this paper, we investigate the coupling of natural boundary element and finite element methods of exterior initial boundary value problems for hyperbolic equations. The governing equation is first discretized in time, leading to a time-step scheme, where an exterior elliptic problem has to be solved in each time step. Second, a circular artificial boundary FR consisting of a circle of radius R is introduced, the original problem in an unbounded domain is transformed into the nonlocal boundary value problem in abounded subdomain. And the natural integral equation and the Poisson integral formula are obtained in the infinite domainΩ2 outside circle of radius R. The coupled variational formulation is given. Only the function itself, not its normal derivative at artificial boundary ΓR, appears in the variational equation, so that the unknown numbers are reducedand the boundary element stiffness matrix has a few different elements. Such a coupled method is superior to the one based on direct boundary element method. This paper discusses finite element discretization for variational problem and its corresponding numerical technique, and the convergence for the numerical solutions. Finally, the numerical example is presented to illustrate feasibility and efficiency of this method. 相似文献
67.
A solution to the phase problem in optics is considered within the context of registration and analysis of two-dimensional stationary optical fields transformed by the object under study or fields forming an image. To obtain information on amplitude and phase distributions of the light field analyzed, a method of registration of two intensity distributions is used. The first distribution corresponds directly to the amplitude distribution. The other is formed for the sum of the initial field and the field shifted along a certain direction. The intensity distributions obtained allow one to calculate the two-dimensional structure of the field under study. It is noteworthy that the method requires no iteration procedures in solving the problem. This leads to speeding up of the processing and analysis of the information. Two variants of optical schemes for the analysis of light fields are considered. The first one corresponds to registration of the image of the analyzed plane and the second to registration of the spectrum of the spatial frequencies. 相似文献
68.
Yong Lee Kazuhiko Hosomi Hiroyuki Uchiyama Toshio Katsuyama Shinya Kominami Tomoyoshi Mishima 《Optical Review》2003,10(1):38-42
An InGaAsP slab-type asymmetric-coupled-waveguide-based dispersion compensator with a mode selector has been designed and fabricated. The mode selector is necessary to select either a symmetric [with a positive group-velocity dispersion (GVD)] or antisymmetric (with a negative GVD) supermode. These supermodes exist simultaneously in the dispersion-compensation region of the device. Pulse-compression experiments were used to test the dispersion compensator, evaluating the function of the mode selector. A theoretical study of the experimental results shows that the mode selector obtains a very strong selectivity (nearly 100%) for the antisymmetric supermode. 相似文献
69.
Mathematical Notes - 相似文献
70.
Yu Zanping Zhou Zheyan School of Math.and Computer Science Fujian Normal University Fuzhou ) Shen Jianhe 《Annals of Differential Equations》2007,23(3):365-372
The paper aims to obtain existence and uniqueness of the solution as well as asymptotic estimate of the solution for singularly perturbed nonlinear third- order Robin boundary value problem with a turning point.In order to achieve this aim,existence and uniqueness of the solution for third-order nonlinear Robin boundary value problem is derived first based on the upper and lower solutions method under relatively weaker conditions.In this manner,the goal of this paper is gained by applying the existence and uniqueness results mentioned above. 相似文献