全文获取类型
收费全文 | 296475篇 |
免费 | 2165篇 |
国内免费 | 631篇 |
专业分类
化学 | 142847篇 |
晶体学 | 4810篇 |
力学 | 14644篇 |
综合类 | 4篇 |
数学 | 42873篇 |
物理学 | 94093篇 |
出版年
2018年 | 10454篇 |
2017年 | 11374篇 |
2016年 | 6455篇 |
2015年 | 2598篇 |
2014年 | 2519篇 |
2013年 | 7964篇 |
2012年 | 9660篇 |
2011年 | 19477篇 |
2010年 | 11925篇 |
2009年 | 11928篇 |
2008年 | 16978篇 |
2007年 | 20686篇 |
2006年 | 6102篇 |
2005年 | 12700篇 |
2004年 | 8645篇 |
2003年 | 7915篇 |
2002年 | 5724篇 |
2001年 | 5936篇 |
2000年 | 4692篇 |
1999年 | 3551篇 |
1998年 | 2789篇 |
1997年 | 2796篇 |
1996年 | 2899篇 |
1995年 | 2618篇 |
1994年 | 2480篇 |
1993年 | 2366篇 |
1992年 | 2846篇 |
1991年 | 2736篇 |
1990年 | 2687篇 |
1989年 | 2718篇 |
1988年 | 2669篇 |
1987年 | 2668篇 |
1986年 | 2479篇 |
1985年 | 3351篇 |
1984年 | 3384篇 |
1983年 | 2807篇 |
1982年 | 2997篇 |
1981年 | 2932篇 |
1980年 | 2839篇 |
1979年 | 2999篇 |
1978年 | 3252篇 |
1977年 | 2992篇 |
1976年 | 2956篇 |
1975年 | 2800篇 |
1974年 | 2748篇 |
1973年 | 2792篇 |
1972年 | 1792篇 |
1968年 | 2026篇 |
1967年 | 2165篇 |
1966年 | 1968篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
LetB
1
be a ball of radiusr
1
inS
n
(ℍn), and letB
0
be a smaller ball of radiusr
0
such thatB
0
⊂B
1
. ForS
n
we considerr
1
π. Let u be a solution of the problem- δm = 1 in Ω :=B
1
/B
0
vanishing on the boundary. It is shown that the associated functionalJ (Ω) is minimal if and only if the balls are concentric. It is also shown that the first Dirichlet eigenvalue of the Laplacian
on Ω is maximal if and only if the balls are concentric. 相似文献
992.
R. Alonderis 《Lithuanian Mathematical Journal》2005,45(1):1-15
We consider classical, multisuccedent intuitionistic, and intuitionistic sequent calculi for propositional likelihood logic. We prove the admissibility of structural rules and cut rule, invertibility of rules, correctness of the calculi, and completeness of the classical calculus with respect to given semantics.__________Published in Lietuvos Matematikos Rinkinys, Vol. 45, No. 1, pp. 3–21, January–March, 2005. 相似文献
993.
We examine the ferroelectric-relaxor behavior of (Ba0.65Sr0.35)(Zr0.35Ti0.65)O3 (BSZT) ceramics in the temperature range from 80 to 380 K. A broad dielectric maximum, which shifts to higher temperature with increasing frequency, signifies the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ∼2 estimated from the linear fit of the modified Curie-Weiss law, indicates the relaxor nature of the BSZT ceramics. The dielectric relaxation rate follows the Vogel-Fulcher relation with TVF=107 K, Ea=0.121 eV, and ν0=6.83×1014 Hz, further supports such relaxor nature. The slim P-E hysteresis loop and ‘butterfly’ shape dc bias field dependence of permittivity at T>Tm (Tm, the temperature of permittivity maximum) clearly signifies the occurrence of nanopolar clusters, which is the typical characteristic of ferroelectric relaxor. At 300 K and 10 kHz, the dielectric constant and loss tan δ are ∼1100 and 0.0015, respectively. The high tunability (∼25%) and figure of merit (∼130) at room temperature show that the BSZT ceramics could be a promising candidate for tunable capacitor applications. 相似文献
994.
Lancaster G.P.T. Häffner H. Wilson M.A. Becher C. Eschner J. Schmidt-Kaler F. Blatt R. 《Applied physics. B, Lasers and optics》2003,76(8):805-808
We present a scheme for employing a violet extended-cavity diode laser in experiments with single, trapped ions. For this the grating-stabilised laser is spatially and spectrally filtered and referenced to a Fabry–Pérot cavity. We measure an upper limit to the line width by observing a 305-kHz FWHM beat note with the second harmonic of a titanium sapphire laser. The laser is subsequently used to optically cool a single 40Ca+ ion close to the Doppler limit. PACS 03.67.Lx; 32.80.Pj; 42.55.Px 相似文献
995.
Harper equations are derived for a px, py electronic system. Analysis is carried out for extreme points of the quasi-continuous spectrum in the cases when the number of magnetic flux quanta through a unit cell is a rational number and calculations are made for square and triangular lattices as well as for a honeycomb lattice with two nonequivalent atoms. The possibility of application of the results for explaining the fractional Hall effect is considered. 相似文献
996.
A hybrid analytical/numerical method is proposed that permits the efficient dynamic analysis of planar serial-frame structures. The method utilizes a numerical implementation of a transfer matrix solution to the equation of motion. By analyzing the transverse and longitudinal motions of each segment simultaneously and considering the compatibility requirements across each frame angle, the undetermined variables of the entire frame structure system can be reduced to six which can be determined by application of the boundary conditions. The main feature of this method is to decrease the dimensions of the matrix involved in the finite element methods and certain other analytical methods. 相似文献
997.
V. P. Shilov 《Journal of Experimental and Theoretical Physics》2003,96(4):719-729
The supercritical Marangoni convection has been studied in a plane-parallel liquid layer, bounded by a free deformable gas-liquid interface from above and by a low-heat-conductivity wall from below, occurring under conditions of inhomogeneous heating in the horizontal plane. In a longwave approximation with a small inhomogeneity of heat flux, the process is described by a system of two-dimensional nonlinear equations for the temperature perturbations, vorticity, and free surface deformation. The concept of quasiequilibrium, implying stability of long-range flows, is introduced, which allows the inhomogeneous heat flux to be modeled by a step function. The linear stability is analyzed in the cases of planar and axisymmetric heat fluxes. The boundaries of stability of the convection regimes are determined on the plane of parameters characterizing the degree of supercriticity inside a heated spot and the depth of damping outside the spot. For an axisymmetric spot, the domains of stability with respect to perturbations for various azimuthal numbers are established. 相似文献
998.
J. Wang J. Kono A. Oiwa H. Munekata C. J. Stanton 《Superlattices and Microstructures》2003,34(3-6):563
We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period 20 ps, which we interpret as coherent acoustic phonons. 相似文献
999.
1000.
The logarithmic decrement and shear modulus of a bulk amorphous Zr52.5Ti5Cu17.9Ni14.6Al10 alloy were studied with an inverse torsion pendulum in the range from room temperature to the crystallization temperature and in the frequency range 5–40 Hz. The activation energy spectra of reversible and irreversible structural relaxation were estimated. The results obtained are discussed in the context of a two-energy-level model. 相似文献