全文获取类型
收费全文 | 19076篇 |
免费 | 1974篇 |
国内免费 | 892篇 |
专业分类
化学 | 1612篇 |
晶体学 | 103篇 |
力学 | 3066篇 |
综合类 | 100篇 |
数学 | 2020篇 |
物理学 | 4689篇 |
综合类 | 10352篇 |
出版年
2024年 | 84篇 |
2023年 | 230篇 |
2022年 | 331篇 |
2021年 | 447篇 |
2020年 | 468篇 |
2019年 | 359篇 |
2018年 | 377篇 |
2017年 | 511篇 |
2016年 | 544篇 |
2015年 | 616篇 |
2014年 | 917篇 |
2013年 | 1084篇 |
2012年 | 1148篇 |
2011年 | 1213篇 |
2010年 | 858篇 |
2009年 | 1075篇 |
2008年 | 1096篇 |
2007年 | 1306篇 |
2006年 | 1160篇 |
2005年 | 1062篇 |
2004年 | 965篇 |
2003年 | 825篇 |
2002年 | 703篇 |
2001年 | 675篇 |
2000年 | 589篇 |
1999年 | 479篇 |
1998年 | 449篇 |
1997年 | 385篇 |
1996年 | 294篇 |
1995年 | 277篇 |
1994年 | 244篇 |
1993年 | 212篇 |
1992年 | 180篇 |
1991年 | 154篇 |
1990年 | 137篇 |
1989年 | 89篇 |
1988年 | 86篇 |
1987年 | 66篇 |
1986年 | 56篇 |
1985年 | 39篇 |
1984年 | 31篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 15篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 345 毫秒
61.
S. P. Popov 《Computational Mathematics and Mathematical Physics》2006,46(6):983-994
Numerical solutions to three systems of integrable evolutionary equations from the Toda lattice hierarchy are analyzed. These are the classical Toda lattice, the second local dispersive flow, and the second extended dispersive flow. Special attention is given to the properties of soliton solutions. For the equations of the second local flow, two types of solitons interacting in a special manner are found. Solutions corresponding to various initial data are qualitatively outlined. 相似文献
62.
A. V. Kel’manov L. V. Mikhailova 《Computational Mathematics and Mathematical Physics》2006,46(1):165-181
The problem of joint a posteriori detection of reference fragments in a quasi-periodic sequence and its partition into segments containing series of recurring fragments from the reference tuple is solved. It is assumed that (i) an ordered reference tuple of sequences to be detected is given, (ii) the number of desired fragments is known, (iii) the index of the sequence term corresponding to the beginning of a fragment is a deterministic (not random) value, and (iv) a sequence distorted by an additive uncorrelated Gaussian noise is available for observation. It is established that the problem consists in testing a set of hypotheses about the mean of a random Gaussian vector. The cardinality of the set grows exponentially as the vector dimension (i.e., the sequence length) increases. An efficient a posteriori algorithm producing a maximum-likelihood optimal solution to the problem is substantiated. Time and space complexity bounds related to the parameters of the problem are derived. The results of numerical simulation are presented. 相似文献
63.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
64.
随着光纤传输技术的不断发展,在传输领域中光传输已占主导地位。光纤存在巨大的频带资源和优异的传输性能,是实现高速、大容量传输的最理想的传输媒质。对光纤传输的要求是传的距离越远越好。从光纤传输距离的计算方法入手,结合影响传输距离的几个因素来分析可以从哪些方面入手来延长光纤通信的传输距离。 相似文献
65.
There are few techniques available to numerically solve sixth-order boundary-value problems with two-point boundary conditions. In this paper we show that the Sinc-Galerkin method is a very effective tool in numerically solving such problems. The method is then tested on examples with homogeneous and nonhomogeneous boundary conditions and a comparison with the modified decomposition method is made. It is shown that the Sinc-Galerkin method yields better results.
66.
混凝土动态劈裂拉伸试验的数值模拟 总被引:4,自引:0,他引:4
采用LS-DYNA有限元编码程序,对混凝土的动态劈裂拉伸试验进行了数值模拟,给出了混凝土试样在不同类型加载情况下应力分布之间的差异,证实了动态劈裂拉伸试验的有效性,提出了改进试验方法的若干结论. 相似文献
67.
68.
The time delay experiment proposed by I.I. Shapiro in 1964 and conducted in the seventies was the most precise experiment
of general relativity until that time. Further experimentation has improved the accuracy level of both the time delay and
the light deflection experiments. A simulation model is proposed that involves only a simple mass and time transformation
factor involving velocity of light. The light deflection and the time delay experiments are numerically simulated using this
model that does not use the general relativistic equations. The computed values presented in this paper compare well with
recent levels of accuracy of their respective experimental results. 相似文献
69.
AbbasA. Zaman 《Particle & Particle Systems Characterization》2003,20(5):342-350
Effects of a low molecular weight physically adsorbed polyethylene oxide (PEO) and the range of the electrostatic repulsion on the rheological behavior of silica dispersions (as a model system) has been investigated. Particular attention is given to the evolution of the rheological behavior with increasing the polymer concentration in the system and also effectiveness of the polymer as a dispersant under extreme conditions (high ionic strength). Results indicate that at small separation distances and low polymer coverage, the polymer chains are long enough to adsorb on the surface of two particles simultaneously causing bridging flocculation in the system and hence increasing the viscosity and linear viscoelastic functions of the dispersion. A significant increase was observed in the viscosity of the dispersion at salt concentrations high enough to eliminate electrostatics between the particles. Under these conditions,the viscosity of the system increased significantly when PEO was added to the dispersion showing that at high electrolyte concentrations, a neutral polymer such as PEO is not able to stabilize the system. 相似文献
70.