全文获取类型
收费全文 | 52314篇 |
免费 | 7140篇 |
国内免费 | 5315篇 |
专业分类
化学 | 15902篇 |
晶体学 | 189篇 |
力学 | 4223篇 |
综合类 | 606篇 |
数学 | 29645篇 |
物理学 | 14204篇 |
出版年
2024年 | 101篇 |
2023年 | 595篇 |
2022年 | 741篇 |
2021年 | 1127篇 |
2020年 | 1774篇 |
2019年 | 1794篇 |
2018年 | 1549篇 |
2017年 | 1601篇 |
2016年 | 2073篇 |
2015年 | 1851篇 |
2014年 | 2747篇 |
2013年 | 4902篇 |
2012年 | 2920篇 |
2011年 | 3354篇 |
2010年 | 3026篇 |
2009年 | 3428篇 |
2008年 | 3551篇 |
2007年 | 3528篇 |
2006年 | 3064篇 |
2005年 | 2823篇 |
2004年 | 2371篇 |
2003年 | 2286篇 |
2002年 | 1941篇 |
2001年 | 1565篇 |
2000年 | 1487篇 |
1999年 | 1345篇 |
1998年 | 1200篇 |
1997年 | 1073篇 |
1996年 | 713篇 |
1995年 | 604篇 |
1994年 | 497篇 |
1993年 | 346篇 |
1992年 | 333篇 |
1991年 | 305篇 |
1990年 | 258篇 |
1989年 | 186篇 |
1988年 | 174篇 |
1987年 | 161篇 |
1986年 | 151篇 |
1985年 | 185篇 |
1984年 | 164篇 |
1983年 | 83篇 |
1982年 | 147篇 |
1981年 | 124篇 |
1980年 | 108篇 |
1979年 | 105篇 |
1978年 | 70篇 |
1977年 | 64篇 |
1976年 | 58篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
151.
This paper presents an enhanced version of the elasto-plastic model for partially saturated soil first proposed by Bolzon,
Schrefler and Zienkiewicz in 1996, “BSZ” model, which uses the effective stress tensor and suction as independent stress variables.
It is recalled that the effective stress tensor proposed by Lewis and Schrefler in 1982 is thermodynamically consistent and,
compared with other choices of stress tensors, results particularly suitable for partially saturated soil mechanics. A hydraulic
constitutive relationship and a hydraulic hysteresis are introduced in the model, to take into account the irreversible deformation
during cyclic drying and wetting until structural collapse. For this reason the plastic rate of strain is split into the sum
of two components: one depending on the effective stress tensor and the other one on suction. This is the new feature of the
BSZ model. This enhanced model is then cast into a thermodynamical framework at macroscopic level and it is shown that it
is possible to derive the constitutive law from the Helmholtz free energy and a dissipation function, both for associative
and non- associative plasticity. Finally the model predictions have been compared with experimental data for Sion slime, with
particular emphasis on the deviatoric part, and model predictions of hysteretic behaviour have been investigated in case of
a wetting and drying cycle on compacted betonite–kaolin. 相似文献
152.
We discuss the problem of transmitting polarized pulses along optical fibers with variable dispersion. The dissipation and mean dispersion are assumed to be zero, which allows using the model of the vector nonlinear Schrödinger equation. We consider an optical fiber consisting of arms of equal length, which is assumed to be large. We propose an asymptotic recursive procedure for calculating the amplitude and the phase of an optical pulse propagating along the optical cable with variable dispersion. 相似文献
153.
We establish a relation between stable distributions in probability theory and the fractional integral. Moreover, it turns out that the parameter of the stable distribution coincides with the exponent of the fractional integral. It follows from an analysis of the obtained results that equations with the fractional time derivative describe the evolution of some physical system whose time degree of freedom becomes stochastic, i.e., presents a sum of random time intervals subject to a stable probability distribution. We discuss relations between the fractal Cantor set (Cantor strips) and the fractional integral. We show that the possibility to use this relation as an approximation of the fractional integral is rather limited. 相似文献
154.
155.
Geng Sheng WANG 《数学学报(英文版)》2005,21(5):1005-1014
This work is concerned with Pontryagin's maximum principle of optimal control problems governed by some non-well-posed semilinear heat equations. A type of approach to the non-well-posed optimal control problem is given. 相似文献
156.
Michael T. Jury David W. Kribs 《Proceedings of the American Mathematical Society》2005,133(1):213-222
Given a row contraction of operators on a Hilbert space and a family of projections on the space that stabilizes the operators, we show there is a unique minimal joint dilation to a row contraction of partial isometries that satisfy natural relations. For a fixed row contraction the set of all dilations forms a partially ordered set with a largest and smallest element. A key technical device in our analysis is a connection with directed graphs. We use a Wold decomposition for partial isometries to describe the models for these dilations, and we discuss how the basic properties of a dilation depend on the row contraction.
157.
TANG Chen ZHANG Fang YAN Hai-Qing CHEN Zhan-Qing LUO Tao 《理论物理通讯》2005,44(3):435-439
We develop the three-step explicit and implicit schemes of exponential fitting methods. We use the three- step explicit exponential fitting scheme to predict an approximation, then use the three-step implicit exponential fitting scheme to correct this prediction. This combination is called the three-step predictor-corrector of exponential fitting method. The three-step predictor-corrector of exponential fitting method is applied to numerically compute the coupled nonlinear Schroedinger equation and the nonlinear Schroedinger equation with varying coefficients. The numerical results show that the scheme is highly accurate. 相似文献
158.
一类混合型微分差分方程的周期解 总被引:1,自引:0,他引:1
利用Fenchel变换,我们推出一类微分差分方程存在周期解等价于某泛函具有临界点,并求出方程具有周期解的充分条件. 相似文献
159.
160.
李永祥 《数学物理学报(A辑)》2003,23(2):245-252
该文讨论四阶常微分方程边值问题u^(4)(t)=f(t,u,u″), t∈[0,1],u(0)=u(1)=u″(0)=u″(1)=0解的存在性, 其中f(t,u,v):[0,1]×R×R→R为Carathéodory函数. 在不限制f关于u,v的增长阶, 不假定f关于u,v的单调性的一般情形下, 用上下解方法获得了解的存在性结果,并讨论了单调迭代求解的有效性. 相似文献