全文获取类型
收费全文 | 8808篇 |
免费 | 1591篇 |
国内免费 | 2435篇 |
专业分类
化学 | 4226篇 |
晶体学 | 35篇 |
力学 | 1342篇 |
综合类 | 71篇 |
数学 | 2373篇 |
物理学 | 4787篇 |
出版年
2023年 | 174篇 |
2022年 | 186篇 |
2021年 | 152篇 |
2020年 | 152篇 |
2019年 | 126篇 |
2018年 | 181篇 |
2017年 | 79篇 |
2016年 | 183篇 |
2015年 | 217篇 |
2014年 | 366篇 |
2013年 | 327篇 |
2012年 | 425篇 |
2011年 | 414篇 |
2010年 | 389篇 |
2009年 | 309篇 |
2008年 | 223篇 |
2007年 | 463篇 |
2006年 | 445篇 |
2005年 | 546篇 |
2004年 | 521篇 |
2003年 | 345篇 |
2002年 | 427篇 |
2001年 | 527篇 |
2000年 | 418篇 |
1999年 | 510篇 |
1998年 | 225篇 |
1997年 | 148篇 |
1996年 | 196篇 |
1995年 | 259篇 |
1994年 | 210篇 |
1993年 | 212篇 |
1992年 | 206篇 |
1991年 | 156篇 |
1990年 | 193篇 |
1989年 | 189篇 |
1988年 | 221篇 |
1987年 | 225篇 |
1986年 | 193篇 |
1985年 | 255篇 |
1984年 | 169篇 |
1983年 | 116篇 |
1982年 | 108篇 |
1981年 | 90篇 |
1975年 | 114篇 |
1959年 | 90篇 |
1958年 | 129篇 |
1957年 | 127篇 |
1956年 | 109篇 |
1955年 | 118篇 |
1954年 | 93篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
A Kind of direct methods is presented for the solution of optimal control problems with state constraints.These methods are sequential quadratic programming methods.At every iteration a quadratic programming which is obtained by quadratic approximation to Lagrangian function and Linear approximations to constraints is solved to get a search direction for a merit function.The merit function is formulated by augmenting the Lagrangian funetion with a penalty term.A line search is carried out along the search direction to determine a step length such that the merit function is decreased.The methods presented in this paper include continuous sequential quadratic programming methods and discreate sequential quadrade programming methods. 相似文献
72.
COMPLETE EIGEN-SOLUTIONS FOR ANTI-PLANE NOTCHES WITH MULTI-MATERIALS BY SUPER-INVERSE ITERATION 总被引:2,自引:0,他引:2
Xu Yongjun Yuan Si 《Acta Mechanica Solida Sinica》1997,10(2):157-166
In this paper,the super-inverse iterative method is proposed to compute the accurateand complete eigen-solutions for anti-plane cracks/notches with multi-materials,arbitrary opening an-gles and various surface conditions.Taking the advantage of the knowledge of the variation forms ofthe eigen-functions,a series of numerical techniques are proposed to simplify the computation andspeed up the convergence rate of the inverse iteration.A number of numerical examples are given todemonstrate the excellent accuracy,efficiency and reliability of the proposed approach. 相似文献
73.
SINGLE MACHINE SCHEDULING WITH CONTROLLABLE PROCESSING TIMES AND COMPRESSION COSTS (PART I:EQUAL TIMES AND COSTS) 总被引:1,自引:0,他引:1
Most papers in scheduling research have treated individual job processing times as fixed parameters. However, in many practical situations, a manager may control processing time by realloeating resources. In this paper, authors consider a machine scheduling problemwith controllable processing times. In the first part of this paper, a special case where the pro-cessing times and compression costs are uniform among jobs is discussed. Theoretical results are derived that aid in developing an O(n^2) algorithm to slove the problem optimally. In the second part of this paper, authors generalize the discussion to general case, An effective heuristic to the genera/ problem will be presented. 相似文献
74.
Xiugui LIU Xiangjun WANG Department of Mathematics LPMC Nankai University Tianjin China. 《数学年刊B辑(英文版)》2006,(3)
This paper computes the Thorn map onγ2 and proves that it is represented by 2b2,0h1,2 in the ASS. The authors also compute the higher May differential of 62,0, from which it is proved thatγs(b0hn-h1bn-1) for 2≤s < p - 1 are permanent cycles in the ASS. 相似文献
75.
Positron-Lithium Atom and Electron-Lithium Atom Scattering Systems at Intermediate and High Energies 下载免费PDF全文
K. Ratnavelu S. Y. Ng 《中国物理快报》2006,23(7):1753-1756
The coupled-channel optical method is used to study positron scattering by atomic lithium at energies ranging from the ionization threshold to 60eV, The present method simultaneously treats the target channels and the positronium (Ps) channels in the coupled-channel method together with the continuum effects via an ab-initio optical potential. Ionization, elastic and inelastic cross sections in target channels, and the total cross section are also reported and compared with other theoretical and experimental data. A comparative study with the corresponding electron-lithium data is also reported. 相似文献
76.
LIBAOLING G.F.DOMANTARY 《数学研究》1994,27(1):89-91
The V^t-integral as defined in[2], which is eqnivalent to M^2-integrsl as defined in Trigonometre series by Zygmund is used to sum trigonometric seies in[1]. In this paper, some convergent theorems of V^2-integral are established. 相似文献
77.
We present a Schrodinger (Liouville) type of equation for a quantum open system.It has a correlated part,and various master equations may be its special cases.It also has significant applications for constructing decoherencefree subspace for quantum computation.It is related to the original Schrodinger (Liouville)equation for the total system through a non-unitary similarity transformation.It is unnecessary for its correlated part to be self-adjoint,so there is a complex spectrum for the corresponding Hamiltonian (Liouvillian),which enables the time evolution of states to be asymmetric.This shows just the correlation to produce evolution of world. 相似文献
78.
This paper tries to introduce the reader to the method of using photochemical re-action to copy holographic optical elements(HOEs)in relief.The holographic blazing gratingso copied is groove depth adjustable phase modulability enlarged through copying and 3.3times the diffraction efficiency(DE)of the original grating.It is expected that the newmethod will lead to the mass production of the light-weight HOEs at low cost. 相似文献
79.
80.
张玉虎 王华磊 柳敏良 周小红 郭文涛 G.de Angelis N.Marginean A.Gadea D.R.Napoli M.Axiotis C.Rusu T.Martinez 许甫荣 《中国物理 C》2004,28(9):907-913
利用重离子熔合蒸发反应和在束γ谱学实验方法,研究了双奇核184?Au的高自旋态能级结构.扩展了基于πh9/2ν7/2–[514]和πi13/2νi13/22准粒子组态下的转动带能级纲图,建立了两个转动带之间以及πh9/2ν7/2-[514]带与基态的谱学连接.从而确定了πi13/2νi13/2带能级的自旋和宇称,证实了此转动带在低自旋区出现旋称反转.分析了πi13/2νi13/2带和相邻核转动带的准粒子顺排特征,指出此带的第一回弯以及相邻核转动带在低频观测到的顺排异常可能与h9/2质子顺排有关. 相似文献