全文获取类型
收费全文 | 3866篇 |
免费 | 188篇 |
国内免费 | 304篇 |
专业分类
化学 | 1332篇 |
晶体学 | 3篇 |
力学 | 86篇 |
综合类 | 84篇 |
数学 | 2078篇 |
物理学 | 775篇 |
出版年
2024年 | 3篇 |
2023年 | 45篇 |
2022年 | 64篇 |
2021年 | 54篇 |
2020年 | 77篇 |
2019年 | 101篇 |
2018年 | 92篇 |
2017年 | 110篇 |
2016年 | 131篇 |
2015年 | 81篇 |
2014年 | 147篇 |
2013年 | 333篇 |
2012年 | 155篇 |
2011年 | 202篇 |
2010年 | 157篇 |
2009年 | 236篇 |
2008年 | 225篇 |
2007年 | 227篇 |
2006年 | 225篇 |
2005年 | 180篇 |
2004年 | 180篇 |
2003年 | 147篇 |
2002年 | 148篇 |
2001年 | 121篇 |
2000年 | 135篇 |
1999年 | 103篇 |
1998年 | 99篇 |
1997年 | 96篇 |
1996年 | 78篇 |
1995年 | 58篇 |
1994年 | 42篇 |
1993年 | 42篇 |
1992年 | 30篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 20篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 19篇 |
1978年 | 13篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1974年 | 3篇 |
排序方式: 共有4358条查询结果,搜索用时 0 毫秒
151.
CHEN Gang XUAN Pei-Cai CHEN Zi-Dong 《理论物理通讯》2006,46(1):39-42
In this paper, two novel semiclassical methods including the standard and supersymmetric WKB quantization conditions are suggested to discuss the Schroedinger equation with position-dependent effective mass. From a proper coordinate transformation, the formalism of the Schroedinger equation with position-dependent effective mass is mapped into isospectral one with constant mass and therefore for a given mass distribution and physical potential function the bound state energy spectrum can be determined easily by above method associated with a simple integral formula. It is shown that our method can give the analytical results for some exactly-solvable quantum systems. 相似文献
152.
We investigate the parameter dynamics of eigenvalues of Hamiltonians (‘level dynamics’) defined on symmetric spaces relevant to condensed matter and particle physics. In particular we: (1) identify the appropriate reduced manifold on which the motion takes place, (2) identify the correct Poisson structure ensuring the Hamiltonian character of the reduced dynamics, (3) determine the canonical measure on the reduced space, (4) calculate the resulting eigenvalue density. 相似文献
153.
为了说明原子光刻(Atom Lithography)在纳米计量及传递作用中的特殊地位,首先对纳米计量标准及其现状进行了简要介绍,提出纳米计量中原子光刻的基本概念和优势,结合原子光刻实验装置对原子光刻技术的工作机理进行了分析。结果表明,可以通过原子光刻技术得到纳米量级刻印条纹,为纳米计量及标准传递提供更加精确的手段。最后对常见的2种原子光刻技术——沉积型原子光刻和虚狭缝型原子光刻进行了阐述,指出2者的不同之处,为不同条件下原子光刻提供了一定的借鉴。 相似文献
154.
The mechanism of generation and annihilation of attractors during transition from a Hamiltonian system to a dissipative system is studied numerically using the dissipative standard map. The transient process related to the formation of attracting basins of periodic attractors is studied by discussing the evolution of the KAM tori of the standard map. The result shows that as damping increases, attractors are mainly generated from elliptic orbits of the Hamiltonian system and annihilated by colliding with unstable periodic orbits originating from the corresponding hyperbolic orbits of the Hamiltonian system. The transient process also exhibits the general feature of bifurcation. 相似文献
155.
156.
S. Al-Homidan 《Journal of Optimization Theory and Applications》2007,135(3):583-598
Given a data matrix, we find its nearest symmetric positive-semidefinite Toeplitz matrix. In this paper, we formulate the
problem as an optimization problem with a quadratic objective function and semidefinite constraints. In particular, instead
of solving the so-called normal equations, our algorithm eliminates the linear feasibility equations from the start to maintain
exact primal and dual feasibility during the course of the algorithm. Subsequently, the search direction is found using an
inexact Gauss-Newton method rather than a Newton method on a symmetrized system and is computed using a diagonal preconditioned
conjugate-gradient-type method. Computational results illustrate the robustness of the algorithm. 相似文献
157.
首先将常用类型的模糊矩阵都纳入到了二阶占优模糊矩阵的统一框架之内,然后利用模糊矩阵的有向伴随图,指出了强连通布尔矩阵振荡的一个充要条件,依次证明了强连通的二阶占优布尔矩阵的振荡指数为2n-2,非强连通的二阶占优布尔矩阵的振荡指数为3n-4. 相似文献
158.
For matrices whose eigenvalues are real (such as Hermitian or real symmetric matrices), we derive simple explicit estimates for the maximal (λmax) and the minimal (λmin) eigenvalues in terms of determinants of order less than 3. For 3 × 3 matrices, we derive sharper estimates, which use det A but do not require to solve cubic equations. 相似文献
159.
A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb 下载免费PDF全文
This paper reports that two identical external-cavity-diode-laser
(ECDL) based spectrometers are constructed at 634 nm referencing on
the hyperfine B-X transition R(80)8-4 of 127I2. The lasers
are stabilized on the Doppler-free absorption signals using the
third-harmonic detection technique. The instability of the
stabilized laser is measured to be 2.8×10-12 (after
1000 s) by counting the beat note between the two lasers. The
absolute optical frequency of the transition is, for the first time,
determined to be 472851936189.5 kHz by using an optical frequency
comb referenced on the microwave caesium atomic clock. The
uncertainty of the measurement is less than 4.9 kHz. 相似文献
160.
In this paper we consider certain matrix equations in the field of Mikusiński operators, and construct a method for obtaining an approximate solution which allows working with numerical constants instead of operators. The theory of diagonally dominant matrices is applied for the analysis, existence and character of the obtained solutions. We introduce a method for determining approximate solutions of a discrete analogue for operational differential equations and give conditions for their existence. The error of the approximation is estimated. 相似文献