全文获取类型
收费全文 | 17617篇 |
免费 | 1916篇 |
国内免费 | 604篇 |
专业分类
化学 | 5619篇 |
晶体学 | 23篇 |
力学 | 1225篇 |
综合类 | 110篇 |
数学 | 7728篇 |
物理学 | 5432篇 |
出版年
2024年 | 20篇 |
2023年 | 179篇 |
2022年 | 329篇 |
2021年 | 444篇 |
2020年 | 480篇 |
2019年 | 466篇 |
2018年 | 334篇 |
2017年 | 449篇 |
2016年 | 676篇 |
2015年 | 547篇 |
2014年 | 839篇 |
2013年 | 1369篇 |
2012年 | 780篇 |
2011年 | 863篇 |
2010年 | 778篇 |
2009年 | 987篇 |
2008年 | 1180篇 |
2007年 | 1178篇 |
2006年 | 1002篇 |
2005年 | 731篇 |
2004年 | 632篇 |
2003年 | 701篇 |
2002年 | 688篇 |
2001年 | 532篇 |
2000年 | 549篇 |
1999年 | 451篇 |
1998年 | 435篇 |
1997年 | 303篇 |
1996年 | 266篇 |
1995年 | 218篇 |
1994年 | 205篇 |
1993年 | 183篇 |
1992年 | 174篇 |
1991年 | 110篇 |
1990年 | 103篇 |
1989年 | 93篇 |
1988年 | 113篇 |
1987年 | 74篇 |
1986年 | 78篇 |
1985年 | 123篇 |
1984年 | 84篇 |
1983年 | 34篇 |
1982年 | 53篇 |
1981年 | 54篇 |
1980年 | 51篇 |
1979年 | 42篇 |
1978年 | 37篇 |
1977年 | 42篇 |
1976年 | 36篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
F. Prez-Willard C. Sürgers H. Von Lhneysen P. Pfundstein 《Physica E: Low-dimensional Systems and Nanostructures》2004,22(4):872-880
The electronic transport through nanostructured bismuth nanobridges has been investigated at low temperatures (T<2 K) and in magnetic fields B up to 8.5 T. The samples show reproducible resistance fluctuations as a function of B, superimposed on a large magnetoresistance of up to 50%. In addition, time-dependent resistance fluctuations in zero magnetic field demonstrate the presence of bistable scatterers in the constriction region of our samples, which are described by two-level systems. Their dynamics are shown to be sensitive to subtle modifications of the static scatterer configuration in their vicinity, which cannot be detected in the sample magnetofingerprint. 相似文献
42.
43.
Zi‐Niu Wu 《国际流体数值方法杂志》2005,48(5):541-564
The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. In this paper we consider the influence of the refined interfaces on the steady state errors for second‐order three‐point difference approximations of flow equations. Since the various characteristic components of the Euler equations should behave similarly on such grids with regard to refinement‐induced errors, it is sufficient enough to conduct the analysis on a scalar model problem. The error we consider is a global error, different to local truncation error, and reflects the interaction between multiple interfaces. The steady state error will be compared to the errors on smooth refinement grids and on uniform grids. The conclusion seems to support the numerical findings of Yamaleev and Carpenter (J. Comput. Phys. 2002; 181: 280–316) that refinement does not necessarily reduce the numerical error. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
44.
45.
Karl Gustafson 《Numerical Linear Algebra with Applications》2004,11(7):649-659
Given the operator product BA in which both A and B are symmetric positive‐definite operators, for which symmetric positive‐definite operators C is BA symmetric positive‐definite in the C inner product 〈x, y〉C? This question arises naturally in preconditioned iterative solution methods, and will be answered completely here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
46.
CONG Fuzhong & LI YongSchool of Mathematics Information Science Shandong Institute of Business Technology Yantai China Office of Mathematics Changchun Flight Academy of the Air Force Changchun China Department of Mathematics Jilin University Changchun China 《中国科学A辑(英文版)》2004,47(5):675-686
An effective stability result for generalized Hamiltonian systems is obtained by applying the simultaneous approximation technique due to Lochak. Among these systems, dimensions of action variables and angle variables might be distinct. 相似文献
47.
从决策有限理性角度,引入行为金融理论于机构投资风险优化系统,对多心理账户条件下机构投资的风险优化设计进行了研究。以Friedman和Savage之谜为释例,对机构投资风险优化中的诸多非标准金融异像进行了解释。以Shefrin和Statman行为证券组合理论为核心,建立了多心理账户条件下机构投资的风险优化模型,为机构投资的风险优化实践提供了一种量化分析工具。 相似文献
48.
49.
Hybrid numerical—experimental approach for investigation of dynamics of microcantilever relay system
V. Ostasevicius S. Tamulevicius A. Palevicius M. Ragulskis R. Palevicius V. Grigaliunas 《Optics and Lasers in Engineering》2005,43(1):199
The time average holography measurements of the vibrating microelectromechanical switch (MEMS) were performed in this study. Experimental measurement results exhibit good agreement with computer generated holographic interferogram analysis. The validation of experimental investigations versus numerical analysis provides the necessary background to analyze the dynamical characteristics of micromechanical systems in virtual numerical environments. Direct application of fringe counting techniques for reconstruction of motion from time average holograms cannot be straightforward if the analyzed micromechanical systems contain motion limiters. Modifications of a classical time average holographic technique enable qualitative analysis of MEMS and can be applied for investigation of dynamical properties of much broader classes of MEMS systems. 相似文献
50.
We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given. 相似文献