全文获取类型
收费全文 | 247717篇 |
免费 | 4213篇 |
国内免费 | 677篇 |
专业分类
化学 | 141786篇 |
晶体学 | 3561篇 |
力学 | 9590篇 |
综合类 | 4篇 |
数学 | 27044篇 |
物理学 | 70622篇 |
出版年
2018年 | 2346篇 |
2017年 | 2102篇 |
2016年 | 3913篇 |
2015年 | 3206篇 |
2014年 | 3938篇 |
2013年 | 11033篇 |
2012年 | 8904篇 |
2011年 | 10320篇 |
2010年 | 6696篇 |
2009年 | 6229篇 |
2008年 | 9188篇 |
2007年 | 9323篇 |
2006年 | 8769篇 |
2005年 | 8119篇 |
2004年 | 7334篇 |
2003年 | 6357篇 |
2002年 | 5967篇 |
2001年 | 6755篇 |
2000年 | 5235篇 |
1999年 | 4097篇 |
1998年 | 3230篇 |
1997年 | 3198篇 |
1996年 | 3254篇 |
1995年 | 2853篇 |
1994年 | 2803篇 |
1993年 | 2673篇 |
1992年 | 3190篇 |
1991年 | 3018篇 |
1990年 | 2952篇 |
1989年 | 2992篇 |
1988年 | 2870篇 |
1987年 | 2853篇 |
1986年 | 2629篇 |
1985年 | 3671篇 |
1984年 | 3684篇 |
1983年 | 2979篇 |
1982年 | 3250篇 |
1981年 | 3178篇 |
1980年 | 3053篇 |
1979年 | 3183篇 |
1978年 | 3401篇 |
1977年 | 3199篇 |
1976年 | 3194篇 |
1975年 | 3005篇 |
1974年 | 2966篇 |
1973年 | 2969篇 |
1972年 | 1879篇 |
1968年 | 2005篇 |
1967年 | 2195篇 |
1966年 | 1967篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
We investigate carrier dynamics in a passive InAs/InP quantum dot (QD) waveguide using 255 fs optical pulses at a central wavelength of 1568 nm. We observe strong anisotropy of absorption saturation for different polarizations. Pump-probe measurements indicate the presence of carrier relaxation dynamics on a timescale in the order of tens of picoseconds due to cascaded relaxation of carriers generated by two-photon absorption (TPA) from the bulk region to the QDs via the wetting layer. These relaxation timescales are much longer than in QD amplifiers. Our observations are supported by a rate-equation model which includes TPA, showing good agreement with the pump-probe measurements. 相似文献
992.
Ph. Hägler B. Pire L. Szymanowski O.V. Teryaev 《The European Physical Journal C - Particles and Fields》2002,24(2):261-270
We study Pomeron-Odderon interference effects giving rise to charge and single-spin asymmetries in diffractive electroproduction
of a pair. We calculate these asymmetries, originating from both longitudinal and transverse polarizations of the virtual photon,
in the framework of QCD and in the Born approximation, in a kinematical domain accessible to HERA experiments. We predict
a sizable charge asymmetry with a characteristic dependence on the invariant mass of the pair, which makes this observable very important for establishing the magnitude of the Odderon exchange in hard processes.
The single-spin asymmetry turns out to be rather small. We briefly discuss future improvements of our calculations and their
possible effects on the results.
Received: 18 July 2002 / Published online: 25 October 2002 相似文献
993.
994.
995.
996.
We describe the formation of a narrow beam for intensity-modulated electromagnetic radiation propagating through highly scattering materials. We propose to use this beam to reconstruct images, similar to X-ray back-projection techniques. For sufficiently high modulation frequency, the photon density wave is primarily carried by photons that suffer small or no large-angle scattering, which gives rise to the beam’s narrow divergence. The beam-narrowing concept is supported by large-scale numerical simulations to examine the quality of the imaging. 相似文献
997.
H. Barentzen 《Annalen der Physik》2006,15(9):684-698
The eigenvalues of the weakly coupled T ? t Jahn‐Teller problem are known for several decades, and the same holds also true for the eigenstates. These, however, are only given in the traditional position representation, which proves inconvenient if one attempts to extend the weak‐coupling treatment into the region of stronger coupling. Here the solution of the T ? t eigenvalue problem at weak coupling is derived in terms of creation and annihilation operators. This reformulation of the problem is nontrivial, since the algebraic form of the oscillator eigenvectors, being simultaneous angular‐momentum eigenstates, has been worked out only recently and is probably still widely unknown. The electronic and oscillator eigenstates are then coupled to form eigenvectors of the total angular momentum. Finally, in preparation for an extension of the weak‐coupling treatment, the action of the boson creation and annihilation operators on the oscillator eigenvectors is calculated, thus completing the algebraic approach to the weakly coupled T ? t system. 相似文献
998.
Summary. The perfectly matched layer (PML) is an efficient tool to simulate propagation phenomena in free space on unbounded domain.
In this paper we consider a new type of absorbing layer for Maxwell's equations and the linearized Euler equations which is
also valid for several classes of first order hyperbolic systems. The definition of this layer appears as a slight modification
of the PML technique. We show that the associated Cauchy problem is well-posed in suitable spaces. This theory is finally
illustrated by some numerical results. It must be underlined that the discretization of this layer leads to a new discretization
of the classical PML formulation.
Received May 5, 2000 / Published online November 15, 2001 相似文献
999.
V.H. CORTÍNEZM.T. PIOVAN 《Journal of sound and vibration》2002,258(4):701-723
In this paper, a theoretical model is developed for the dynamic analysis of composite thin-walled beams with open or closed cross-sections. The present model incorporates, in a full form, the shear flexibility (bending and warping shear) as well as a state of initial stresses. This allows to study the free vibration and buckling problems in a unified fashion. An analytical solution of the developed equations is obtained for the case of simply supported thin-walled beams. Numerical examples are given to demonstrate the importance of the shear flexibility on the vibration and buckling behavior of the considered structures. 相似文献
1000.