全文获取类型
收费全文 | 50206篇 |
免费 | 1837篇 |
国内免费 | 2193篇 |
专业分类
化学 | 2878篇 |
晶体学 | 61篇 |
力学 | 1086篇 |
综合类 | 453篇 |
数学 | 7290篇 |
物理学 | 4150篇 |
综合类 | 38318篇 |
出版年
2024年 | 74篇 |
2023年 | 208篇 |
2022年 | 430篇 |
2021年 | 505篇 |
2020年 | 551篇 |
2019年 | 531篇 |
2018年 | 554篇 |
2017年 | 669篇 |
2016年 | 743篇 |
2015年 | 1070篇 |
2014年 | 2294篇 |
2013年 | 2068篇 |
2012年 | 2715篇 |
2011年 | 2990篇 |
2010年 | 2584篇 |
2009年 | 3031篇 |
2008年 | 3288篇 |
2007年 | 3892篇 |
2006年 | 3914篇 |
2005年 | 3272篇 |
2004年 | 2860篇 |
2003年 | 2619篇 |
2002年 | 2247篇 |
2001年 | 1914篇 |
2000年 | 1534篇 |
1999年 | 1172篇 |
1998年 | 793篇 |
1997年 | 815篇 |
1996年 | 708篇 |
1995年 | 612篇 |
1994年 | 547篇 |
1993年 | 488篇 |
1992年 | 435篇 |
1991年 | 411篇 |
1990年 | 351篇 |
1989年 | 341篇 |
1988年 | 248篇 |
1987年 | 182篇 |
1986年 | 83篇 |
1985年 | 84篇 |
1984年 | 51篇 |
1983年 | 30篇 |
1982年 | 60篇 |
1981年 | 41篇 |
1980年 | 36篇 |
1979年 | 58篇 |
1978年 | 30篇 |
1977年 | 29篇 |
1976年 | 21篇 |
1974年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions. 相似文献
113.
114.
Bogdan Nita 《General Relativity and Gravitation》2003,35(10):1865-1868
Algebraically special gravitational fields are described using algebraic and differential invariants of the Weyl tensor. A type III invariant is also given and calculated for Robinson-Trautman spaces. 相似文献
115.
This paper is about algorithms that schedule tasks to be performed in a distributed failure‐prone environment, when processors communicate by message‐passing, and when tasks are independent and of unit length. The processors work under synchrony and may fail by crashing. Failure patterns are imposed by adversaries. Linearly‐bounded adversaries may fail up to a constant fraction of the processors. Weakly‐adaptive adversaries have to select, prior to the start of an execution, a subset of processors to be failure‐prone, and then may fail only the selected processors, at arbitrary steps, in the course of the execution. Strongly adaptive adversaries have a total number of failures as the only restriction on failure patterns. The measures of complexity are work, measured as the available processor steps, and communication, measured as the number of point‐to‐point messages. A randomized algorithm is developed, that attains both ??(n log*n) expected work and ??(n log*n) expected communication, against weakly‐adaptive linearly‐bounded adversaries, in the case when the numbers of tasks and processors are both equal to n. This is in contrast with performance of algorithms against strongly‐adaptive linearly‐bounded adversaries, which has to be Ω(n log n/log log n) in terms of work. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2004 相似文献
116.
Summary Our purpose is to extend results due to P. Chandra and L. Leindler concerning the order of approximation by means of Fourier series for functions belonging to generalized Lipschitz-classes. 相似文献
117.
Nikolaos S. PAPAGEORGIOU Nikolaos YANNAKAKIS 《数学学报(英文版)》2005,21(5):977-996
This is the first part of a work on second order nonlinear, nonmonotone evolution inclusions defined in the framework of an evolution triple of spaces and with a multivalued nonlinearity depending on both x(t) and x(t). In this first part we prove existence and relaxation theorems. We consider the case of an usc, convex valued nonlinearity and we show that for this problem the solution set is nonempty and compact in C^1 (T, H). Also we examine the Isc, nonconvex case and again we prove the existence of solutions. In addition we establish the existence of extremal solutions and by strengthening our hypotheses, we show that the extremal solutions are dense in C^1 (T, H) to the solutions of the original convex problem (strong relaxation). An example of a nonlinear hyperbolic optimal control problem is also discussed. 相似文献
118.
The problem of generating a matrix A with specified eigen‐pair, where A is a symmetric and anti‐persymmetric matrix, is presented. An existence theorem is given and proved. A general expression of such a matrix is provided. We denote the set of such matrices by ??????En. The optimal approximation problem associated with ??????En is discussed, that is: to find the nearest matrix to a given matrix A* by A∈??????En. The existence and uniqueness of the optimal approximation problem is proved and the expression is provided for this nearest matrix. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
119.
在总结铜氧化物高温超导体晶体结构特点的基础上,提出了以无限层结构Cu-O钙钛矿为核心的结构组装概念,通过和相关结构的外延组合,衍生出了高温超导体的主要晶体构型。进一步运用此观念,建立了新的三元数命名法,并对高温超导体的晶体结构进行了归类。 相似文献
120.
本文在阐述卢梭自然主义教育思想的理论基础和主要内容的基础上,理论联系实际,结合现代社会的教育问题,揭示了卢梭自然主义教育思想的现实意义。 相似文献