全文获取类型
收费全文 | 42420篇 |
免费 | 7043篇 |
国内免费 | 3989篇 |
专业分类
化学 | 9881篇 |
晶体学 | 321篇 |
力学 | 7693篇 |
综合类 | 722篇 |
数学 | 12539篇 |
物理学 | 22296篇 |
出版年
2024年 | 77篇 |
2023年 | 530篇 |
2022年 | 938篇 |
2021年 | 1182篇 |
2020年 | 1439篇 |
2019年 | 1203篇 |
2018年 | 1160篇 |
2017年 | 1595篇 |
2016年 | 1817篇 |
2015年 | 1421篇 |
2014年 | 2384篇 |
2013年 | 3349篇 |
2012年 | 2531篇 |
2011年 | 3145篇 |
2010年 | 2552篇 |
2009年 | 2912篇 |
2008年 | 2815篇 |
2007年 | 2806篇 |
2006年 | 2466篇 |
2005年 | 2138篇 |
2004年 | 1965篇 |
2003年 | 1681篇 |
2002年 | 1554篇 |
2001年 | 1306篇 |
2000年 | 1183篇 |
1999年 | 1020篇 |
1998年 | 925篇 |
1997年 | 723篇 |
1996年 | 622篇 |
1995年 | 589篇 |
1994年 | 479篇 |
1993年 | 422篇 |
1992年 | 384篇 |
1991年 | 309篇 |
1990年 | 258篇 |
1989年 | 200篇 |
1988年 | 179篇 |
1987年 | 178篇 |
1986年 | 135篇 |
1985年 | 159篇 |
1984年 | 160篇 |
1983年 | 83篇 |
1982年 | 112篇 |
1981年 | 80篇 |
1980年 | 47篇 |
1979年 | 52篇 |
1978年 | 38篇 |
1977年 | 32篇 |
1976年 | 23篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 159 毫秒
51.
Abstract
In this note, we consider a Frémond model of shape memory alloys. Let us imagine a piece of a shape memory alloy which is
fixed on one part of its boundary, and assume that forcing terms, e.g., heat sources and external stress on the remaining
part of its boundary, converge to some time-independent functions, in appropriate senses, as time goes to infinity. Under
the above assumption, we shall discuss the asymptotic stability for the dynamical system from the viewpoint of the global
attractor. More precisely, we generalize the paper [12] dealing with the one-dimensional case. First, we show the existence
of the global attractor for the limiting autonomous dynamical system; then we characterize the asymptotic stability for the
non-autonomous case by the limiting global attractor.
* Project supported by the MIUR-COFIN 2004 research program on “Mathematical Modelling and Analysis of Free Boundary Problems”. 相似文献
52.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献
53.
一类非线性Schr(o)dinger方程的守恒差分法与Fourier谱方法 总被引:1,自引:0,他引:1
考察了一类带导数项的非线性Schrodinger方程的周期边值问题,提出了一种守恒的差分格式,在空间方向上采用Fourier谱方法,证明了格式的稳定性和收敛性.数值试验得到了与理论分析一致的结果. 相似文献
54.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献
55.
56.
S. Sabchevski T. Idehara I. Ogawa M. Glyavin K. Ohashi 《International Journal of Infrared and Millimeter Waves》2002,23(5):675-692
A computer code for simulation of beam-field interaction in a resonant cavity of a gyrotron has been developed. It is based on a self-consistent, time-independent, single-mode physical model. The code has been applied to the analysis of the electrodynamical system of a novel high-harmonic gyrotron with axis-encircling beam and a permanent magnet. In this paper both the physical model and numerical techniques used are outlined. Some results of the numerical experiments are presented and discussed. 相似文献
57.
利用室温下压电调制反射光(PzR)谱技术系统测量了N掺杂浓度为0.0%—3%的分子束外延生长GaNxAs1-x薄膜,并对图谱中所观察的光学跃迁进行了指认.在GaN0.005As0.995和GaN0.01As0.99薄膜的PzR谱中观察到此前只在椭圆偏振谱中才看到的N掺杂相关能态E1+Δ1+ΔN.当N掺杂浓度达到
关键词:
压电调制反射光谱(PzR)
xAs1-x薄膜')" href="#">GaNxAs1-x薄膜
分子束外延(MBE) 相似文献
58.
使一对纠缠的二能级原子之一与单模真空腔场发生共振相互作用,通过选择不同的演化时间,对这个三体系统的其中之一做选择性测量,可调节另外两体的纠缠状态。在不做测量时,研究了在不同的初始状态下,三体纠缠及三体中两两纠缠的演化特性。结果表明,该体系纠缠都呈现周期性的振荡,特别是,通过选择合适的初始状态和演化时间可生成强壮纠缠态———W纠缠态;在特定演化时刻,可使两纠缠原子的纠缠信息完全转化到腔外原子和腔场中去。 相似文献
59.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
60.
Eva Lesanska 《Applications of Mathematics》2002,47(5):411-426
The problem is to determine nonsensitiveness regions for threshold ellipsoids within a regular mixed linear model. 相似文献