全文获取类型
收费全文 | 1750篇 |
免费 | 77篇 |
国内免费 | 141篇 |
专业分类
化学 | 611篇 |
晶体学 | 5篇 |
力学 | 176篇 |
综合类 | 10篇 |
数学 | 380篇 |
物理学 | 786篇 |
出版年
2024年 | 6篇 |
2023年 | 51篇 |
2022年 | 38篇 |
2021年 | 28篇 |
2020年 | 41篇 |
2019年 | 29篇 |
2018年 | 42篇 |
2017年 | 47篇 |
2016年 | 49篇 |
2015年 | 40篇 |
2014年 | 72篇 |
2013年 | 108篇 |
2012年 | 77篇 |
2011年 | 121篇 |
2010年 | 106篇 |
2009年 | 122篇 |
2008年 | 131篇 |
2007年 | 132篇 |
2006年 | 99篇 |
2005年 | 100篇 |
2004年 | 86篇 |
2003年 | 55篇 |
2002年 | 67篇 |
2001年 | 49篇 |
2000年 | 40篇 |
1999年 | 32篇 |
1998年 | 42篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 17篇 |
1994年 | 21篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1971年 | 1篇 |
排序方式: 共有1968条查询结果,搜索用时 15 毫秒
1.
一种区间数的因子分析技术及其在证券市场中的应用 总被引:1,自引:0,他引:1
传统的因子分析技术能够有效地对高维变量空间进行降维处理,但它对于样本空间却缺乏行之有效的降维效果.为了解决这一问题,一种针对大量样本数据、新的因子分析技术———区间数因子分析技术(intervaldatafactoranalysis,IFA)被提出并得到了迅速的发展。IFA方法对传统的数据概念做了本质性的扩张,运用'数据打包'的理念,对海量原始数据在不破坏其原有内在逻辑关系的前提下,可以进行变量和样本点维度的双重降维。本文详细阐述了区间数因子分析技术的原理,并以中国股票市场为案例研究背景,结果表明IFA分析技术对大规模多维数据系统做综合简化是十分有效的。 相似文献
2.
A multidimensional GC-system containing two capillary columns of different polarities, operated within a double oven instrument, was used for the optimized separation of complex isomeric mixtures of various types of chlorinated aromatic compounds such as PCB, PCDD, or PCDF. Electron capture was applied parallel to flame ionization detection to obtain sensitive signals of the PCB or PCDD and the n-alkane standards required for identification by Kovats indices, respectively. Electron capture detection within a valvelessly operated MDGC system forced changes in the usual instrumental set-up, the live-switching coupling piece being located within the second oven of the double oven instrument. This oven is operated isothermally to ensure optimal and interference-free detection, for stable flow conditions within the coupling piece and for the determination of the isothermal retention indices (Kovats), which are much more suitable for identification by retention than the so-called “linear” indices. 相似文献
3.
《Electroanalysis》2003,15(4):254-262
The new electrochemical double pulse technique, known as additive differential normal pulse voltammetry (ADNPV) when there is no restriction on the duration of both pulses, and additive differential pulse voltammetry (ADPV) when t2?t1, has been applied to a pseudo‐first‐order catalytic mechanism. The expressions obtained here are applicable to planar and spherical electrodes, of any radius. This is of great interest since the size of the electrode plays an important role in the preponderating of diffusive and kinetics processes. The signal obtained with this technique presents the same morphological characteristics as the triple pulse technique, double differential pulse voltammetry (DDPV) and is more advantageous than DDPV and than the double pulse one, differential pulse voltammetry (DPV). 相似文献
4.
This paper deals with secondary bifurcations near a double eigenvalue of a nonlinear equation with two parameters. Utilizing symmetries (or more generally, equivariances ) and introducing two new parameters, we give some extended systems so that the double singular points, secondary bifurcation points and initial secondary branches respectively become their regular solutions. The methods in this paper not only give more general conditions of secondary bifurcation but also avoid the adjacent singularities of existing extended systems for computing the simple bifurcation points on non-trivial solution branches A numerical example is presented, showing the effectiveness of our methods. 相似文献
5.
双函数法及一类非线性发展方程的精确行波解 总被引:5,自引:0,他引:5
给出一种求解非线性发展方程精确行波解的新方法:双函数法。使用此方法,获得了一类非线性发展方程的许多精确行波解,其中包括孤波解和周期解,推广了文献用其它方法取得的结果,同时还获得了许多新的弧波解和周期解,借助于Mathemat-ica,此方法能部分地在计算机上实现。 相似文献
6.
Vassilios Fessatidis Norman J.M. Horing 《Physica E: Low-dimensional Systems and Nanostructures》2005,27(4):487-494
We examine the collective mode spectrum for a double quantum-wire system embedded in semi-infinite polar medium, taking account of the role of optical phonons in interaction with the double quantum-wire plasmons and bulk/surface plasmons. The collective mode frequencies are exhibited as functions of qx (wavenumber parallel to the wires) and as functions of z0 (distance of first wire from the interface). We also find that the region of drift instability of the collective modes is split into two disjoint regions of instability by the optical phonons, with a region of stability between them. 相似文献
7.
Dynamical systems with nonlinear damping show interesting behavior in the periodic and chaotic phases. The Froude pendulum
with cubical and linear damping is a paradigm for such a system. In this work the driven Froude pendulum is studied by the
harmonic balancing method; the resulting nonlinear response curves are studied further for resonance and stability of symmetric
oscillations with relatively low damping. The stability analysis is carried out by transforming the system of equations to
the linear Mathieu equation. 相似文献
8.
受激拉曼散射和热效应会限制光纤激光器功率的提高。利用高功率光纤激光器的速率方程和热传导方程,理论研究了双端泵浦和分布泵浦下双包层光纤激光器的受激拉曼散射和热效应,得到了光纤中的泵浦光、激光和斯托克斯光的功率分布,光纤激光器的输出特性以及光纤中的温度分布。分析表明,当泵浦功率增大到一定值时,光纤激光器中出现SRS,一部分激光功率会转移给斯托克斯光,影响激光功率进一步提高;与双端泵浦方式相比,分布泵浦下光纤激光器的斜率效率和最大输出功率相差不大,但是,光纤中的温度分布被有效地降低,因此,分布泵浦方式更为有效。 相似文献
9.
10.
Impairments resulting from stroke lead to persistent difficulties with walking. Subsequently, an improved walking ability is one of the highest priorities for people living with stroke. The degree to which gait can be restored after a stroke is related to both the initial impairment in walking ability and the severity of paresis of the lower extremities. However, there are some patients with severe motor paralysis and a markedly disrupted corticospinal tract who regain their gait function. Recently, several case reports have described the recovery of gait function in stroke patients with severe hemiplegia by providing alternate gait training. Multiple studies have demonstrated that gait training can induce “locomotor-like” coordinated muscle activity of paralyzed lower limbs in people with spinal cord injury. In the present review, we discuss the neural mechanisms of gait, and then we review case reports on the restoration of gait function in stroke patients with severe hemiplegia. 相似文献