全文获取类型
收费全文 | 6557篇 |
免费 | 1048篇 |
国内免费 | 470篇 |
专业分类
化学 | 1909篇 |
晶体学 | 38篇 |
力学 | 379篇 |
综合类 | 30篇 |
数学 | 1493篇 |
物理学 | 4226篇 |
出版年
2024年 | 13篇 |
2023年 | 73篇 |
2022年 | 125篇 |
2021年 | 147篇 |
2020年 | 214篇 |
2019年 | 195篇 |
2018年 | 182篇 |
2017年 | 170篇 |
2016年 | 212篇 |
2015年 | 222篇 |
2014年 | 337篇 |
2013年 | 483篇 |
2012年 | 367篇 |
2011年 | 464篇 |
2010年 | 339篇 |
2009年 | 478篇 |
2008年 | 446篇 |
2007年 | 428篇 |
2006年 | 369篇 |
2005年 | 309篇 |
2004年 | 301篇 |
2003年 | 290篇 |
2002年 | 297篇 |
2001年 | 234篇 |
2000年 | 230篇 |
1999年 | 185篇 |
1998年 | 176篇 |
1997年 | 105篇 |
1996年 | 91篇 |
1995年 | 74篇 |
1994年 | 71篇 |
1993年 | 67篇 |
1992年 | 61篇 |
1991年 | 33篇 |
1990年 | 33篇 |
1989年 | 26篇 |
1988年 | 34篇 |
1987年 | 20篇 |
1986年 | 29篇 |
1985年 | 26篇 |
1984年 | 24篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1974年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有8075条查询结果,搜索用时 15 毫秒
41.
B R Sitaram 《Pramana》1995,44(4):295-302
The invariants of chaotic bounded Hamiltonian systems and their relation to the solutions of the first variational equations
of the equations of motion are studied. We show that these invariants are characterized by the fact that they either lose
the property of differentiability as functions on phase space or that a certain formal power series defined in terms of the
derivatives of the invariants has zero radius of convergence. For a specific example, we show that the former possibility
appears to apply. 相似文献
42.
S. Chen H. Büttner 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):15-18
We generalize the Shastry-Sutherland model to three dimensions. By representing the model as a sum of the semidefinite positive
projection operators, we exactly prove that the model has exact dimer ground state. Several schemes for constructing the three-dimensional
Shastry-Sutherland model are proposed.
Received 20 February 2002 / Received in final form 27 May 2002 Published online 17 September 2002 相似文献
43.
Marco Marletta 《Advances in Computational Mathematics》1994,2(2):155-184
This paper discusses the numerical solution of eigenvalue problems for Hamiltonian systems of ordinary differential equations.
Two new codes are presented which incorporate the algorithms described here; to the best of the author’s knowledge, these
are the first codes capable of solving numerically such general eigenvalue problems. One of these implements a new new method
of solving a differential equation whose solution is a unitary matrix. Both codes are fully documented and are written inPfort-verifiedFortran 77, and will be available in netlib/aicm/sl11f and netlib/aicm/sl12f. 相似文献
44.
REN QingBao ZHU WeiTing HONG Bo & ZHANG YuHeng Department of Physics Lishui University Lishui China National High Magnetic Field Laboratory University of Science Technology of China Hefei China 《中国科学G辑(英文版)》2007,(3)
Magnetic properties of Nd_(0.5)Sr_(0.5)Mn_(1-x)(Ga_x, Ti_x)O_3 system (0.04≤x≤0.4) were inves- tigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melt- ing of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-T curves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region. 相似文献
45.
Qin Jiang 《Journal of Mathematical Analysis and Applications》2007,328(1):380-389
Some solvability conditions of periodic and subharmonic solutions are obtained for a class of subquadratic nonautonomous second-order Hamiltonian systems by the minimax methods in critical point theory. 相似文献
47.
Yi Lin 《Advances in Mathematics》2007,208(2):699-709
In this paper we construct six-dimensional compact non-Kähler Hamiltonian circle manifolds which satisfy the strong Lefschetz property themselves but nevertheless have a non-Lefschetz symplectic quotient. This provides the first known counterexamples to the question whether the strong Lefschetz property descends to the symplectic quotient. We also give examples of Hamiltonian strong Lefschetz circle manifolds which have a non-Lefschetz fixed point submanifold. In addition, we establish a sufficient and necessary condition for a finitely presentable group to be the fundamental group of a strong Lefschetz manifold. We then use it to show the existence of Lefschetz four-manifolds with non-Lefschetz finite covering spaces. 相似文献
48.
Let G(x,y) and GD(x,y) be the Green functions of rotationally invariant symmetric α-stable process in Rd and in an open set D, respectively, where 0<α<2. The inequality GD(x,y)GD(y,z)/GD(x,z)?c(G(x,y)+G(y,z)) is a very useful tool in studying (local) Schrödinger operators. When the above inequality is true with c=c(D)∈(0,∞), then we say that the 3G theorem holds in D. In this paper, we establish a generalized version of 3G theorem when D is a bounded κ-fat open set, which includes a bounded John domain. The 3G we consider is of the form GD(x,y)GD(z,w)/GD(x,w), where y may be different from z. When y=z, we recover the usual 3G. The 3G form GD(x,y)GD(z,w)/GD(x,w) appears in non-local Schrödinger operator theory. Using our generalized 3G theorem, we give a concrete class of functions belonging to the non-local Kato class, introduced by Chen and Song, on κ-fat open sets. As an application, we discuss relativistic α-stable processes (relativistic Hamiltonian when α=1) in κ-fat open sets. We identify the Martin boundary and the minimal Martin boundary with the Euclidean boundary for relativistic α-stable processes in κ-fat open sets. Furthermore, we show that relative Fatou type theorem is true for relativistic stable processes in κ-fat open sets. The main results of this paper hold for a large class of symmetric Markov processes, as are illustrated in the last section of this paper. We also discuss the generalized 3G theorem for a large class of symmetric stable Lévy processes. 相似文献
49.
S. C. Tiwari 《Foundations of Physics Letters》2006,19(1):51-62
Advances in gauge theories and unified theories have not thrown light on the meaning of electron. The problem of the origin
of electronic charge is made precise, new insights gained from Weyl space are summarized, and the origin of charge in terms
of fractional spin is suggested. A new perspective on the abelian Chern-Simons theory is presented to explain charge. 相似文献
50.
提出了将哈密顿算符对角化的一种方法.围绕一维谐振子讨论了如何将哈密顿算符对角化、引进的是玻色算符还是费米算符的问题,并分析了能量量子化的原因及能量子与声子的区别. 相似文献