全文获取类型
收费全文 | 586529篇 |
免费 | 22935篇 |
国内免费 | 13969篇 |
专业分类
化学 | 335338篇 |
晶体学 | 7983篇 |
力学 | 26425篇 |
综合类 | 732篇 |
数学 | 72047篇 |
物理学 | 180908篇 |
出版年
2022年 | 4606篇 |
2021年 | 6348篇 |
2020年 | 7394篇 |
2019年 | 7324篇 |
2018年 | 8396篇 |
2017年 | 8145篇 |
2016年 | 11943篇 |
2015年 | 9974篇 |
2014年 | 13008篇 |
2013年 | 28362篇 |
2012年 | 25577篇 |
2011年 | 29437篇 |
2010年 | 19874篇 |
2009年 | 19536篇 |
2008年 | 25191篇 |
2007年 | 24791篇 |
2006年 | 23668篇 |
2005年 | 23180篇 |
2004年 | 20516篇 |
2003年 | 17159篇 |
2002年 | 15731篇 |
2001年 | 16554篇 |
2000年 | 12972篇 |
1999年 | 10660篇 |
1998年 | 8739篇 |
1997年 | 8403篇 |
1996年 | 8538篇 |
1995年 | 7629篇 |
1994年 | 7347篇 |
1993年 | 6865篇 |
1992年 | 7400篇 |
1991年 | 7205篇 |
1990年 | 6675篇 |
1989年 | 6331篇 |
1988年 | 6385篇 |
1987年 | 6074篇 |
1986年 | 5945篇 |
1985年 | 8088篇 |
1984年 | 8170篇 |
1983年 | 6733篇 |
1982年 | 7264篇 |
1981年 | 7024篇 |
1980年 | 6634篇 |
1979年 | 6876篇 |
1978年 | 7032篇 |
1977年 | 7084篇 |
1976年 | 7084篇 |
1975年 | 6746篇 |
1974年 | 6688篇 |
1973年 | 6873篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
We present the cosmological solutions in the six-dimensional Einstein-gauge theory to which is added a matter term. The general behavior of the scale factors of the ordinary (R3) and extra (R2) dimensions can be depicted in four stages. Stage 1: Both R3 and R2 expand. Stage 2: R2 is a constant and R3 is an inflationary solution. Stage 3: R2 recollapses towards its minimum value, R3 will continue to increase monotonically. Stage 4: R2 stabilizes at RKK and R3 expands in the usual FRW way, while the four-dimensional cosmological constant becomes zero. 相似文献
932.
Time structure of iodine laser pulse in the free running mode of operation was studied using the power amplifier of laser system PERUN as the laser oscillator. Two characteristic shapes of laser pulse correspond to different regimes of laser operation, the existence of which is ascribed to the critical concentration of I2 molecules. Simultaneously an additional chemical pumping was proved at least in the initial phase of photodissociation and in a late-time lasing after the end of flashlamps pumping light. 相似文献
933.
934.
Dynamic stage repair policies where the stage repair probabilities are determined by the number of items in the buffer are examined through a model of a manufacturing system with two unreliable workstages connected by a minimal intermediate storage buffer. Definitions for workstage availability and line balance are extended for sequential manufacturing systems with dynamic repair policies. A measure for stage repair inputs and a general form of dynamic stage repair policies are presented. The steady-state probabilities of the resultant state-inhomogeneous Markov chain are computed by an efficient solution procedure. Insights obtained from extensive numerical studies are illustrated and discussed. 相似文献
935.
Z.J. Yang T.H. Johansen H. Bratsberg G. Helgesen A.T. Skjeltorp 《Physica C: Superconductivity and its Applications》1989,160(5-6):461-465
Based on a dipole-dipole interaction model, we discuss the levitation force and related vibration problems to understand the effects of flux pinning in type-II superconductors, and the applications of levitation in superconducting systems. 相似文献
936.
激光晶体YAG中Er3+的辐射跃迁 总被引:2,自引:0,他引:2
本文讨论和分析了激光晶体YAG中Er3+离子的激光上能级的4S3/2、4I11/2和4I13/2辐射跃迁的有关因素。 相似文献
937.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as
far as the calibration of a satellite altimeter is concerned. 相似文献
938.
V. A. Popova I. V. Podgornaya V. G. Lundina L. I. Kurnikova A. I. Tarasov 《Russian Chemical Bulletin》1987,36(11):2361-2364
Conclusions Complex compounds of bisacyl derivatives of diaminodibenzo-18-crown-6 ether are active catalysts of the two stages of the synthesis of poly(ethylene terephthalate).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2544–2547, November. 1987. 相似文献
939.
J. Giroire T. Ha‐Duong V. Moumas 《Mathematical Methods in the Applied Sciences》2005,28(13):1527-1552
This article deals with a boundary value problem for Laplace equation with a non‐linear and non‐local boundary condition. This problem comes from petroleum engineering and is used to obtain an estimation of well productivity. The non‐linear and non‐local boundary condition is written on the well boundary. On the outer reservoir boundaries, we have both Dirichlet and Neumann conditions. In this paper, we prove the existence and uniqueness of a solution to this problem. The existence is proved by Schauder theorem and the uniqueness is obtained under more restricted conditions, when the involved operator is a contraction. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
940.