全文获取类型
收费全文 | 28350篇 |
免费 | 3628篇 |
国内免费 | 3197篇 |
专业分类
化学 | 8306篇 |
晶体学 | 189篇 |
力学 | 1879篇 |
综合类 | 219篇 |
数学 | 3179篇 |
物理学 | 10021篇 |
综合类 | 11382篇 |
出版年
2024年 | 90篇 |
2023年 | 297篇 |
2022年 | 709篇 |
2021年 | 759篇 |
2020年 | 842篇 |
2019年 | 746篇 |
2018年 | 713篇 |
2017年 | 926篇 |
2016年 | 1033篇 |
2015年 | 906篇 |
2014年 | 1409篇 |
2013年 | 2021篇 |
2012年 | 1635篇 |
2011年 | 1735篇 |
2010年 | 1382篇 |
2009年 | 1662篇 |
2008年 | 1686篇 |
2007年 | 1824篇 |
2006年 | 1776篇 |
2005年 | 1490篇 |
2004年 | 1402篇 |
2003年 | 1203篇 |
2002年 | 1123篇 |
2001年 | 992篇 |
2000年 | 909篇 |
1999年 | 691篇 |
1998年 | 723篇 |
1997年 | 635篇 |
1996年 | 571篇 |
1995年 | 516篇 |
1994年 | 463篇 |
1993年 | 393篇 |
1992年 | 357篇 |
1991年 | 290篇 |
1990年 | 261篇 |
1989年 | 235篇 |
1988年 | 228篇 |
1987年 | 137篇 |
1986年 | 89篇 |
1985年 | 58篇 |
1984年 | 52篇 |
1983年 | 20篇 |
1982年 | 36篇 |
1981年 | 25篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 26篇 |
1977年 | 17篇 |
1976年 | 8篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The paper outlines a procedure to identify the space-and time-dependent external nonstationary load acting on a closed circular
cylindrical shell of medium thickness. Time-dependent deflections at several points of the shell are used as input data to
solve the inverse problem. Examples of numerical identification of various nonstationary loads, including moving ones are
presented. The relationship between the external load and the stress-strain state of the shell is described by the Volterra
equation of the first kind. The identification problem is solved using Tikhonov's regularization method and Apartsin's h-regularization method
__________
Translated from Prikladnaya Mekhanika, Vol. 44, No. 7, pp. 91–100, July 2008. 相似文献
92.
应用密度矩阵方程计算了四能级原子系统中三阶非线性极化率随信号光和探针光频率失谐的变化关系。结果表明,由于量子干涉对信号光强度的敏感性,使四能级原子介质的交叉Kerr非线性作用大大增强,与三能级系统相比,四能级原子介质的Kerr非线性系数可增强两个数量级。 相似文献
93.
Scaling impacted structures 总被引:1,自引:0,他引:1
Summary The problem of non-scalability of structures under impact loads caused by strain-rate effects is solved in this article by properly correcting the impact velocity. The technique relies on the use of an alternative dimensionless basis, together with a mathematical model which allows the calculation of a correction factor for the impact velocity. This new velocity, when applied to the model, makes it to assure the satisfaction of the scaling laws. The indirect similitude method detailed here is applied to two strain-rate sensitive structures, a double plate under in-plane impact and a beam subjected to a blast load. The results show a very good agreement so that the model and a prototype made from strain rate sensitive materials behave the same.accepted for publication 3 March 2004 相似文献
94.
S. Sasa A. Nakashima Y. Nakajima M. Inoue 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):224
We fabricated nanoscale open-dot structures in an InAs surface inversion layer using an atomic-force-microscope oxidation process. Due to its superior nanofabrication capability, small open-dot structures with the feature size ranging between 100 and 300 nm were successfully fabricated. The magnetoresistance signal measured at 4.2 K showed reproducible fluctuations and a periodic oscillation component that varies in both amplitude and periodicity depending on the dot size. We show that the period of the oscillations corresponds to that of the Aharonov–Bohm effect and propose that the possible mechanism for the oscillations is due to the formation of a one-dimensional electron channel enclosing the open-dot structure as a result of the electron transfer from the InAs oxide to InAs. 相似文献
95.
K. Suzuki S. Miyashita K. Takashina Y. Hirayama 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):232
We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron–hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the extended states of the original electron and hole LLs make the QHE regions along integer-νnet discontinuous. Under tilted magnetic fields, these Rxx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron–hole hybridization and the formation of minigaps at LL crossings. 相似文献
96.
The patterns of absorption and reflection of an ultrashort laser pulse by a plasma with a solid-state density, which are realized in the mode of the normal skin effect, are studied. It is shown that a decrease in low-power pulse duration shorter than the period corresponding to the fundamental frequency of radiation leads to an increase in the absorption coefficient. If the pulse power is so high as to provide electron heating during a time shorter than the reciprocal fundamental frequency, nonlinear suppression of absorption takes place and the spectrum of the reflected radiation contains odd harmonics of the fundamental frequency. 相似文献
97.
广义酉矩阵与广义Hermite矩阵 总被引:22,自引:3,他引:19
给出了广义酉矩阵与广义(斜)Hermite矩阵的概念,研究了它们的性质及其与酉阵、共轭辛阵、Hermite阵、Hamilton及广义逆矩阵之间的联系;取得了许多新的结果;推广了酉矩阵、Hermite阵与斜Hermite阵间的相应结果,特别将正交阵的广义Cayley分解推广到了广义酉矩阵上;将各类酉矩阵、Hermite矩阵及广义逆矩阵统一了起来. 相似文献
98.
99.
We solve the problem of describing compatible nonlocal Poisson brackets of hydrodynamic type. We prove that for nonsingular pairs of compatible nonlocal Poisson brackets of hydrodynamic type, there exist special local coordinates such that the metrics and the Weingarten operators of both brackets are diagonal. The nonlinear evolution equations describing all nonsingular pairs of compatible nonlocal Poisson brackets of hydrodynamic type are derived in these special coordinates, and the integrability of these equations is proved using the inverse scattering transform. The Lax pairs with a spectral parameter for these equations are found. We construct various classes of integrable reductions of the derived equations. These classes of reductions are of an independent differential-geometric and applied interest. In particular, if one of the compatible Poisson brackets is local, we obtain integrable reductions of the classical Lamé equations describing all orthogonal curvilinear coordinate systems in a flat space; if one of the compatible brackets is generated by a constant-curvature metric, the corresponding equations describe integrable reductions of the equations for orthogonal curvilinear coordinate systems in a space of constant curvature. 相似文献
100.
M. R. Setare 《International Journal of Theoretical Physics》2004,43(11):2237-2242
We compute particle creation for a real massive scalar field conformally coupled to a spatially closed Robertson–Walker space-time background, with time-dependent scale factor. This is a dynamical Casimir effect with moving boundaries. 相似文献