全文获取类型
收费全文 | 9301篇 |
免费 | 891篇 |
国内免费 | 553篇 |
专业分类
化学 | 417篇 |
晶体学 | 7篇 |
力学 | 590篇 |
综合类 | 157篇 |
数学 | 3745篇 |
物理学 | 2049篇 |
综合类 | 3780篇 |
出版年
2024年 | 39篇 |
2023年 | 90篇 |
2022年 | 164篇 |
2021年 | 195篇 |
2020年 | 214篇 |
2019年 | 201篇 |
2018年 | 178篇 |
2017年 | 263篇 |
2016年 | 248篇 |
2015年 | 238篇 |
2014年 | 360篇 |
2013年 | 525篇 |
2012年 | 417篇 |
2011年 | 449篇 |
2010年 | 337篇 |
2009年 | 425篇 |
2008年 | 492篇 |
2007年 | 607篇 |
2006年 | 551篇 |
2005年 | 440篇 |
2004年 | 412篇 |
2003年 | 427篇 |
2002年 | 441篇 |
2001年 | 366篇 |
2000年 | 364篇 |
1999年 | 294篇 |
1998年 | 265篇 |
1997年 | 199篇 |
1996年 | 205篇 |
1995年 | 138篇 |
1994年 | 159篇 |
1993年 | 129篇 |
1992年 | 120篇 |
1991年 | 124篇 |
1990年 | 115篇 |
1989年 | 95篇 |
1988年 | 84篇 |
1987年 | 57篇 |
1986年 | 37篇 |
1985年 | 44篇 |
1984年 | 56篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1981年 | 30篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 11篇 |
1976年 | 14篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Renny Mathew Karolina A. Uchman Lydia Gkoura Chris J. Pickard Maria Baias 《Magnetic resonance in chemistry : MRC》2020,58(11):1018-1025
A combined experimental and computational approach was used to distinguish between different polymorphs of the pharmaceutical drug aspirin. This method involves the use of ab initio random structure searching (AIRSS), a density functional theory (DFT)-based crystal structure prediction method for the high-accuracy prediction of polymorphic structures, with DFT calculations of nuclear magnetic resonance (NMR) parameters and solid-state NMR experiments at natural abundance. AIRSS was used to predict the crystal structures of form-I and form-II of aspirin. The root-mean-square deviation between experimental and calculated 1H chemical shifts was used to identify form-I as the polymorph present in the experimental sample, the selection being successful despite the large similarities between the molecular environments in the crystals of the two polymorphs. 相似文献
2.
考虑带有白噪声的Berger方程解的随机渐近性行为, 用渐近先验估计技术和算子分解方法, 通过引入同构映射构造等价过程, 证明随机吸引子在(H2(U)∩H10(U))×L2(U)中的存在性. 相似文献
3.
文章提出一种新的改进隔离型随机N叉树形冲突分解算法,对VSAT随机接入多址接入系统中冲突分解进行了研究。给出了冲突信息分组分解所需平均时隙数和系统吞吐量的解析式,进一步给出了信息分组冲突分解的实验值。 相似文献
4.
王新华 《淮北煤炭师范学院学报(自然科学版)》1996,(3)
本文详细讨论了通用教材中对MB系统的定义及MB统计分布和各种表述形式,指出MB系统的最主要标记应是“粒子的可分辨性”,提出了讲述MB统计分布的一些建议. 相似文献
5.
Second-order random wave solutions for interfacial internal waves in N-layer density-stratified fluid
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper studies the random internal wave equations describing the density interface displacements and the velocity potentials of N-layer stratified fluid contained between two rigid walls at the top and bottom. The density interface displacements and the velocity potentials were solved to the second-order by an expansion approach used by Longuet-Higgins (1963) and Dean (1979) in the study of random surface waves and by Song (2004) in the study of second- order random wave solutions for internal waves in a two-layer fluid. The obtained results indicate that the first-order solutions are a linear superposition of many wave components with different amplitudes, wave numbers and frequencies, and that the amplitudes of first-order wave components with the same wave numbers and frequencies between the adjacent density interfaces are modulated by each other. They also show that the second-order solutions consist of two parts: the first one is the first-order solutions, and the second one is the solutions of the second-order asymptotic equations, which describe the second-order nonlinear modification and the second-order wave-wave interactions not only among the wave components on same density interfaces but also among the wave components between the adjacent density interfaces. Both the first-order and second-order solutions depend on the density and depth of each layer. It is also deduced that the results of the present work include those derived by Song (2004) for second-order random wave solutions for internal waves in a two-layer fluid as a particular case. 相似文献
6.
Jong Uhn Kim 《Transactions of the American Mathematical Society》2002,354(3):1117-1135
In this paper we discuss an initial-boundary value problem for a stochastic nonlinear equation arising in one-dimensional viscoelasticity. We propose to use a new direct method to obtain a solution. This method is expected to be applicable to a broad class of nonlinear stochastic partial differential equations.
7.
T. Temesvári C. De Dominicis I.R. Pimentel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(3):361-372
Symmetry considerations and a direct, Hubbard-Stratonovich type, derivation are used to construct a replica field-theory relevant
to the study of the spin glass transition of short range models in a magnetic field. A mean-field treatment reveals that two
different types of transitions exist, whenever the replica number n is kept larger than zero. The Sherrington-Kirkpatrick critical point in zero magnetic field between the paramagnet and replica
magnet (a replica symmetric phase with a nonzero spin glass order parameter) separates from the de Almeida-Thouless line,
along which replica symmetry breaking occurs. We argue that for studying the de Almeida-Thouless transition around the upper
critical dimension d = 6, it is necessary to use the generic cubic model with all the three bare masses and eight cubic couplings. The critical
role n may play is also emphasized. To make perturbative calculations feasible, a new representation of the cubic interaction is
introduced. To illustrate the method, we compute the masses in one-loop order. Some technical details and a list of vertex
rules are presented to help future renormalisation-group calculations.
Received 9 October 2001 相似文献
8.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献
9.
给出2005年全国部分高校研究生数学建模竞赛D题的研究背景,对参赛论文作了简要评注,并提供了一种参考解答. 相似文献
10.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献