全文获取类型
收费全文 | 6296篇 |
免费 | 892篇 |
国内免费 | 198篇 |
专业分类
化学 | 236篇 |
晶体学 | 71篇 |
力学 | 2607篇 |
综合类 | 81篇 |
数学 | 1759篇 |
物理学 | 2632篇 |
出版年
2024年 | 4篇 |
2023年 | 44篇 |
2022年 | 89篇 |
2021年 | 141篇 |
2020年 | 164篇 |
2019年 | 123篇 |
2018年 | 129篇 |
2017年 | 177篇 |
2016年 | 167篇 |
2015年 | 157篇 |
2014年 | 222篇 |
2013年 | 378篇 |
2012年 | 329篇 |
2011年 | 383篇 |
2010年 | 283篇 |
2009年 | 347篇 |
2008年 | 378篇 |
2007年 | 420篇 |
2006年 | 449篇 |
2005年 | 383篇 |
2004年 | 301篇 |
2003年 | 311篇 |
2002年 | 282篇 |
2001年 | 261篇 |
2000年 | 223篇 |
1999年 | 198篇 |
1998年 | 164篇 |
1997年 | 144篇 |
1996年 | 104篇 |
1995年 | 101篇 |
1994年 | 88篇 |
1993年 | 67篇 |
1992年 | 62篇 |
1991年 | 46篇 |
1990年 | 50篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1957年 | 4篇 |
排序方式: 共有7386条查询结果,搜索用时 468 毫秒
41.
Quantitative H–Al distances in acid sites of two zeolites with MFI and IFR framework topology were obtained by numerical simulation of 1H{27Al} rotational echo adiabatic passage double resonance (REAPDOR) experiments. A 27Al offset-dependent data set yields for each resolved 1H NMR line a corresponding nuclear electric quadrupole coupling constant of the neighboring 27Al site. This information is used for analyzing a second data set for on-resonance irradiation, where the dipolar evolution time (number of rotor cycles) was varied, to yield the 1H–27Al dipolar coupling constant. Numerical simulations indicate that the REAPDOR method does not depend significantly on the polar angles, defining the orientation of the electric field gradient tensor of 27Al with respect to the Al–H dipolar vector. In contrast, the transfer of populations in double resonance sequence is sensitive to these angles, and it can be thus used to measure them. 相似文献
42.
43.
封闭圆内开缝圆自然对流换热的振荡特性 总被引:1,自引:0,他引:1
本文通过数值计算探讨了封闭圆内开缝圆自然对流换热的振荡特性。数值计算以整个圆为计算区域,采用了非稳态的数学模型和具有QUICK差分格式的SIMPLE算法。在相同条件下计算结果和实验结果符合很好。数值结果显示, 当几何结构一定时,Rayleigh数Ra小于某个临界值时,流动和换热处于稳态,并且关于垂直中心线对称;Ra大于这个临界值时,流动和换热是振荡的,非对称的。数值实验还表明,流动和换热出现振荡时的临界Rayleigh数Rac与开缝圆的开缝度有关,且流动和换热的振荡会出现对称振荡和非对称振荡两种情形。 相似文献
44.
45.
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
46.
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
47.
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
48.
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.
49.
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
50.