全文获取类型
收费全文 | 80370篇 |
免费 | 6483篇 |
国内免费 | 5121篇 |
专业分类
化学 | 24201篇 |
晶体学 | 1809篇 |
力学 | 3523篇 |
综合类 | 364篇 |
数学 | 18612篇 |
物理学 | 43465篇 |
出版年
2022年 | 338篇 |
2021年 | 358篇 |
2020年 | 643篇 |
2019年 | 946篇 |
2018年 | 925篇 |
2017年 | 621篇 |
2016年 | 444篇 |
2015年 | 421篇 |
2014年 | 1069篇 |
2013年 | 1896篇 |
2012年 | 1160篇 |
2011年 | 1714篇 |
2010年 | 2296篇 |
2009年 | 6813篇 |
2008年 | 7892篇 |
2007年 | 6339篇 |
2006年 | 5814篇 |
2005年 | 3949篇 |
2004年 | 3776篇 |
2003年 | 4005篇 |
2002年 | 5246篇 |
2001年 | 3752篇 |
2000年 | 3528篇 |
1999年 | 3353篇 |
1998年 | 2764篇 |
1997年 | 1954篇 |
1996年 | 1731篇 |
1995年 | 2209篇 |
1994年 | 2137篇 |
1993年 | 1596篇 |
1992年 | 1098篇 |
1991年 | 830篇 |
1990年 | 677篇 |
1989年 | 604篇 |
1988年 | 562篇 |
1987年 | 403篇 |
1986年 | 192篇 |
1985年 | 942篇 |
1984年 | 616篇 |
1983年 | 487篇 |
1982年 | 638篇 |
1981年 | 792篇 |
1980年 | 719篇 |
1979年 | 558篇 |
1978年 | 581篇 |
1977年 | 538篇 |
1976年 | 540篇 |
1975年 | 319篇 |
1974年 | 355篇 |
1973年 | 462篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
基于BDF的无约束优化方法的收敛性分析 总被引:3,自引:0,他引:3
1.介 绍 在上个世纪的七十年代末、八十年代初,基于常微分方程的优化方法或者说同伦方法是一类与拟牛顿法和共轭梯度法等我们所熟知的优化方法相竞争的重要方法[1-6,8,13,14,16].由于这类方法只是简单地利用现成的数值求解常微分方程的软件包,如CVODE[7]、LSODE[12],对同伦方程(一般是一个常微分方程的初值问题)进行计算,除了一些特殊的病态问题 相似文献
62.
Jihua Zhang Xi WangWeidong Yu Tao FengFumin Zhang Zhihong ZhengQiong Li Xianghuai Liu 《Solid State Communications》2003,127(4):289-293
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips. 相似文献
63.
We treat here of the question of absorbing boundary conditionsfor nonlinear diffusion equations. We use the conditions designedfor the linear equation, we prove them to be well posed forthe nonlinear problem, and through numerical experiments thatthey are well suited for reactiondiffusion equations. 相似文献
64.
A one-dimensional bulk reaction model for the oxidation of nickeltitanium is formulated, with preferential oxidation of titaniumbeing included. The modelling is directed at the better understandingof the dominant mechanisms involved in the oxidation processand their significance for the biocompatibility of the alloy.Two different regimes for the relative diffusivities of oxygenand the metals are investigated. By assuming fast bulk reactions,different asymptotic structures emerge in different parameterregimes and the resulting models take the form of moving boundaryproblems. Different profiles of nickel concentration are obtained:in particular a nickel-rich layer (observed in practice) ispresent below the oxide/metal interface for the case when oxygenand the metals diffuse at comparable rates. 相似文献
65.
线性泛函方程解的振动性的新结果 总被引:1,自引:0,他引:1
本文研究高阶泛函方程x(g(t))=P(t)x(t)+Q1(t)x(g2(t))+…+Qk(t)x(gk+1(t))解的振动性,得到了一些新的振动条件.改进和推广了已有结果. 相似文献
66.
67.
We derive the Friedmann-like equations in braneworld cosmology by imposing the first law of thermodynamics and Bekenstein's area-entropy formula on the apparent horizon of a Friedmann–Robertson–Walker universe in both Randall–Sundrum II gravity and Dvali–Gabadadze–Porrati gravity models. Israel's boundary condition plays an important role in our calculations in both cases, besides the first law of thermodynamics and Bekenstein's area-entropy formula. The results indicate that thermodynamics on the brane world knows the behaviors of gravity. 相似文献
68.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
69.
曾六川 《高等学校计算数学学报(英文版)》2003,12(1)
The purpose of this paper is to investigate the problem of approximating fixed points of non-Lipschitizian asymptotically pseudocontractive mappings in an arbitrary real Banach space by the modified Ishikawa iterative sequences with errors. 相似文献
70.
H.L. Xu A. Persson S. Svanberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):233-236
New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity
levels belonging to the 4f5d26p and 4f
25d
2 configurations of Ce I and 6 even-parity levels belonging to the 5d26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II
levels range in energy from 26 545 to 29 102 cm-1, and 42 573 to 48 152 cm-1, respectively.
Received 25 September 2002 Published online 4 March 2003 相似文献