全文获取类型
收费全文 | 75260篇 |
免费 | 6460篇 |
国内免费 | 7242篇 |
专业分类
化学 | 29661篇 |
晶体学 | 379篇 |
力学 | 7068篇 |
综合类 | 1281篇 |
数学 | 25190篇 |
物理学 | 25383篇 |
出版年
2023年 | 594篇 |
2022年 | 985篇 |
2021年 | 1348篇 |
2020年 | 1519篇 |
2019年 | 1728篇 |
2018年 | 1480篇 |
2017年 | 1832篇 |
2016年 | 2065篇 |
2015年 | 1887篇 |
2014年 | 2744篇 |
2013年 | 4926篇 |
2012年 | 3183篇 |
2011年 | 3509篇 |
2010年 | 3010篇 |
2009年 | 4139篇 |
2008年 | 4662篇 |
2007年 | 4832篇 |
2006年 | 4498篇 |
2005年 | 3832篇 |
2004年 | 3544篇 |
2003年 | 3543篇 |
2002年 | 3254篇 |
2001年 | 2738篇 |
2000年 | 2651篇 |
1999年 | 2397篇 |
1998年 | 2221篇 |
1997年 | 1846篇 |
1996年 | 1642篇 |
1995年 | 1511篇 |
1994年 | 1388篇 |
1993年 | 1164篇 |
1992年 | 1113篇 |
1991年 | 860篇 |
1990年 | 722篇 |
1989年 | 637篇 |
1988年 | 575篇 |
1987年 | 451篇 |
1986年 | 382篇 |
1985年 | 444篇 |
1984年 | 438篇 |
1983年 | 212篇 |
1982年 | 356篇 |
1981年 | 410篇 |
1980年 | 302篇 |
1979年 | 296篇 |
1978年 | 227篇 |
1977年 | 206篇 |
1976年 | 157篇 |
1974年 | 112篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Kenji Saijyou 《Applied Acoustics》2006,67(10):1031-1043
The relationship between the dominant mode of the submerged thin cylindrical shell and the flexural wave velocity is investigated. The natural frequency corresponding to the vibration mode is obtained as the solution of characteristic equation of thin cylindrical shell. However, it is difficult to estimate the dominant mode, especially if two or more vibration modes are involved. To estimate the dominant mode of a thin shell in vacuo, the concept of “modified bending stiffness” has been introduced. In this paper, the concept of modified bending stiffness is extended to estimate the dominant mode of a submerged thin cylindrical shell. The dominant mode of a submerged thin cylindrical shell is theoretically discriminated from the other mode based on the smallness of the modified bending stiffness of the submerged shell. The validity of our theory is confirmed by a good agreement between theoretical and experimental results on flexural wave velocity. 相似文献
72.
Abstract
In this note, we consider a Frémond model of shape memory alloys. Let us imagine a piece of a shape memory alloy which is
fixed on one part of its boundary, and assume that forcing terms, e.g., heat sources and external stress on the remaining
part of its boundary, converge to some time-independent functions, in appropriate senses, as time goes to infinity. Under
the above assumption, we shall discuss the asymptotic stability for the dynamical system from the viewpoint of the global
attractor. More precisely, we generalize the paper [12] dealing with the one-dimensional case. First, we show the existence
of the global attractor for the limiting autonomous dynamical system; then we characterize the asymptotic stability for the
non-autonomous case by the limiting global attractor.
* Project supported by the MIUR-COFIN 2004 research program on “Mathematical Modelling and Analysis of Free Boundary Problems”. 相似文献
73.
Wei Gengping~ Shen Jianhua~ 《高校应用数学学报(英文版)》2006,21(3):320-326
This paper studies the nonautonomous nonlinear system of difference equationsΔx(n)=A(n)x(n)+f(n,x(n)),n∈Z,(*) where x(n)∈R~N,A(n)=(a_(ij)(n))N×N is an N×N matrix,with a-(ij)∈C(R,R) for i,j= 1,2,3,...,N,and f=(f_1,f_2,...,f_N)~T∈C(R×R~N,R~N),satisfying A(t+ω)=A(t),f(t+ω,z)=f(t,z) for any t∈R,(t,z)∈R×R~N andωis a positive integer.Sufficient conditions for the existence ofω-periodic solutions to equations (*) are obtained. 相似文献
74.
WANG Libin 《数学年刊B辑(英文版)》2002,23(4):439-454
The author gets a blow-up result of C1 solution to the Cauchy problem for a first order quasilinear non-strictly hyperbolic system in one space dimension. 相似文献
75.
76.
利用Riccati变换求解同谐谐振子的定态薛定谔方程,求得了能谱及态函数
关键词:
同调谐振子
本征值谱
Riccati变换法 相似文献
77.
为了描述复杂的噪声环境,考虑了一种具有频率结构的噪声——简谐速度噪声,包括它的产生、关联函数、功率谱以及作为热噪声时的频率特性所导致的一些行为.结果表明:在频谱空间中简谐速度噪声是一种带通噪声,存在一个峰值频率,且噪声带宽由参量Γ控制.当简谐势中的一个布朗粒子受热简谐速度噪声驱动时,粒子能量极大值出现在两种频率相等的情况下.这表明噪声和势场的频率之间存在动力学共振,决定着粒子能量的大小.
关键词:
简谐噪声
简谐速度噪声
功率谱
频率共振 相似文献
78.
79.
Maria Kordaki Athanasia Balomenou 《International Journal of Computers for Mathematical Learning》2006,11(1):99-135
This study focuses on the constructions in terms of area and perimeter in equivalent triangles developed by students aged 12–15 years-old, using the tools provided by Cabri-Geometry II [Labore (1990). Cabri-Geometry (software), Université de Grenoble]. Twenty-five students participated in a learning experiment where they were asked to construct: (a) pairs of equivalent triangles “in as many ways as possible” and to study their area and their perimeter using any of the tools provided and (b) “any possible sequence of modifications of an original triangle into other equivalent ones”. As regards the concept of area and in contrast to a paper and pencil environment, Cabri provided students with different and potential opportunities in terms of: (a) means of construction, (b) control, (c) variety of representations and (d) linking representations, by exploiting its capability for continuous modifications. By exploiting these opportunities in the context of the given open tasks, students were helped by the tools provided to develop a broader view of the concept of area than the typical view they would construct in a typical paper and pencil environment. 相似文献
80.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献