全文获取类型
收费全文 | 14213篇 |
免费 | 1335篇 |
国内免费 | 1098篇 |
专业分类
化学 | 1110篇 |
晶体学 | 52篇 |
力学 | 3161篇 |
综合类 | 204篇 |
数学 | 9573篇 |
物理学 | 2546篇 |
出版年
2024年 | 22篇 |
2023年 | 164篇 |
2022年 | 165篇 |
2021年 | 194篇 |
2020年 | 362篇 |
2019年 | 359篇 |
2018年 | 364篇 |
2017年 | 391篇 |
2016年 | 461篇 |
2015年 | 382篇 |
2014年 | 600篇 |
2013年 | 1220篇 |
2012年 | 605篇 |
2011年 | 781篇 |
2010年 | 630篇 |
2009年 | 838篇 |
2008年 | 943篇 |
2007年 | 898篇 |
2006年 | 812篇 |
2005年 | 742篇 |
2004年 | 661篇 |
2003年 | 651篇 |
2002年 | 578篇 |
2001年 | 478篇 |
2000年 | 496篇 |
1999年 | 430篇 |
1998年 | 401篇 |
1997年 | 341篇 |
1996年 | 260篇 |
1995年 | 178篇 |
1994年 | 186篇 |
1993年 | 138篇 |
1992年 | 151篇 |
1991年 | 124篇 |
1990年 | 96篇 |
1989年 | 68篇 |
1988年 | 49篇 |
1987年 | 43篇 |
1986年 | 36篇 |
1985年 | 52篇 |
1984年 | 70篇 |
1983年 | 41篇 |
1982年 | 51篇 |
1981年 | 32篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 8篇 |
1973年 | 10篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献
22.
就一般非完整约束系统,从约束方程满足的变分恒等式出发,利用增广位形流形上的向量场定义三类非自由变分,即非完整变分:vakonomic变分、Hlder变分、Suslov变分,并讨论它们之间的关系以及它们成为自由变分的充要条件.利用非完整变分以及相应的积分变分原理建立两类动力学方程:vakonomic方程和Routh方程或Chaplygin方程.通过vakonomic方程分别与Routh方程和Chaplygin方程比较,得到它们具有共同解的两类充分必要条件.这些条件并不是约束的可积性条件.
关键词:
非完整约束
非完整变分
Chetaev条件
vakonomic动力学 相似文献
23.
24.
25.
Cai Xiaochun 《Annals of Differential Equations》2006,22(1):1-6
In this paper, we apply a critical point theorem and obtain the condition for the existence of three solutions to two-point boundary value problem of a second order nonlinear difference equation. 相似文献
26.
We propose a framework, based on classical mixture theory, to describe the isothermal flow of an incompressible fluid through a deformable inelastic porous solid. The modeling of the behavior of the inelastic solid takes into account changes in the elastic response due to evolution in the microstructure of the material. We apply the model to a compression layer problem. The mathematical problem generated by the model is a free boundary problem. 相似文献
27.
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
28.
In this work we study nonnegativity and positivity of a discrete quadratic functional with separately varying endpoints. We introduce a notion of an interval coupled with 0, and hence, extend the notion of conjugate interval to 0 from the case of fixed to variable endpoint(s). We show that the nonnegativity of the discrete quadratic functional is equivalent to each of the following conditions: The nonexistence of intervals coupled with 0, the existence of a solution to Riccati matrix equation and its boundary conditions. Natural strengthening of each of these conditions yields a characterization of the positivity of the discrete quadratic functional. Since the quadratic functional under consideration could be a second variation of a discrete calculus of variations problem with varying endpoints, we apply our results to obtain necessary and sufficient optimality conditions for such problems. This paper generalizes our recent work in [R. Hilscher, V. Zeidan, Comput. Math. Appl., to appear], where the right endpoint is fixed. 相似文献
29.
方程w"-w+f(t,w)=O的Dirichlet边值问题的正解存在性与多解性 总被引:1,自引:0,他引:1
姚庆六 《应用泛函分析学报》2002,4(1):4-9
考察了下列常微分方程的Dirichlet边值问题的正解[w″(t)-w(t) f(t,w(t))=0,0≤t≤1 w(0)=w(1)=0建立了n正解的存在性,其中n是一个任意的自然数。 相似文献
30.
F. S. de Aguiar L. B. Bernardes S. Goulart Rosa Jr. 《Journal of statistical physics》1991,64(3-4):673-682
Metastability in the ferromagneticp-state Potts model defined on the Cayley tree is discussed. It is shown that the sign of the boundary fieldH
s
determines the order of the transition as well as the stability of the low-temperature phase. Lowering the temperature withH
s
>0, a system withp<2 (p>2) will display a second (first)-order transition to a metastable (stable) phase. ForH
s
>0 a second (first)-order transition to a metastable (stable) phase occurs ifp>2 (p<2). In this case the system also has a residual entropy which is negative forp<2. 相似文献