全文获取类型
收费全文 | 87032篇 |
免费 | 328篇 |
国内免费 | 375篇 |
专业分类
化学 | 23979篇 |
晶体学 | 787篇 |
力学 | 6723篇 |
数学 | 31962篇 |
物理学 | 15009篇 |
无线电 | 9275篇 |
出版年
2018年 | 11819篇 |
2017年 | 11446篇 |
2016年 | 6939篇 |
2015年 | 895篇 |
2014年 | 341篇 |
2013年 | 327篇 |
2012年 | 4146篇 |
2011年 | 11621篇 |
2010年 | 6814篇 |
2009年 | 6767篇 |
2008年 | 7154篇 |
2007年 | 9605篇 |
2006年 | 202篇 |
2005年 | 1540篇 |
2004年 | 1740篇 |
2003年 | 2159篇 |
2002年 | 1066篇 |
2001年 | 247篇 |
2000年 | 288篇 |
1999年 | 151篇 |
1998年 | 191篇 |
1997年 | 144篇 |
1996年 | 198篇 |
1995年 | 119篇 |
1994年 | 76篇 |
1993年 | 95篇 |
1992年 | 54篇 |
1991年 | 62篇 |
1990年 | 50篇 |
1989年 | 59篇 |
1988年 | 60篇 |
1987年 | 58篇 |
1986年 | 57篇 |
1985年 | 46篇 |
1984年 | 42篇 |
1983年 | 37篇 |
1982年 | 41篇 |
1981年 | 39篇 |
1980年 | 46篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1973年 | 25篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1910年 | 24篇 |
1909年 | 41篇 |
1908年 | 40篇 |
1907年 | 32篇 |
1904年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
441.
Leo Brewin 《General Relativity and Gravitation》2007,39(4):521-528
We show by an almost elementary calculation that the ADM mass of an asymptotically flat space can be computed as a limit involving
a rate of change of area of a closed 2-surface. The result is essentially the same as that given by David Brown and York (Phys.
Rev. D 55, 1977–1984 1997; Phys. Rev. D 47, 1407–1419 1993). We will prove this result in two ways, first by direct calculation from the original formula as given by
Arnowitt, Deser and Misner and second as a corollary of an earlier result by Brewin for the case of simplicial spaces. 相似文献
442.
Hoshang Heydari 《International Journal of Theoretical Physics》2007,46(11):2801-2807
We construct a measure of entanglement for general pure multipartite states based on the Plücker coordinates of the Grassmann
variety. In particular, we step by step construct measures of entanglement for general pure bipartite, three-partite, four-partite,
and m-partite states. 相似文献
443.
László Erdős Manfred Salmhofer Horng-Tzer Yau 《Communications in Mathematical Physics》2007,271(1):1-53
We consider random Schrödinger equations on \({\mathbb{R}^{d}}\) for d≥ 3 with a homogeneous Anderson-Poisson type random potential. Denote by λ the coupling constant and ψ t the solution with initial data ψ0. The space and time variables scale as \({x\sim \lambda^{-2 -\kappa/2}, t \sim \lambda^{-2 -\kappa}}\) with 0 < κ < κ0(d). We prove that, in the limit λ → 0, the expectation of the Wigner distribution of ψ t converges weakly to the solution of a heat equation in the space variable x for arbitrary L 2 initial data. The proof is based on a rigorous analysis of Feynman diagrams. In the companion paper [10] the analysis of the non-repetition diagrams was presented. In this paper we complete the proof by estimating the recollision diagrams and showing that the main terms, i.e. the ladder diagrams with renormalized propagator, converge to the heat equation. 相似文献
444.
In this paper, we evaluated the quasinormal modes of electromagnetic perturbation in a Schwarzschild black hole surrounded
by the static spherically symmetric quintessence by using the third-order WKB approximation when the quintessential state
parameter w
q
in the range of −1/3 < w
q
< 0. Due to the presence of quintessence, Maxwell field damps more slowly. And when at −1 < w
q
< −1/3, it is similar to the black hole solution in the ds/Ads spacetime. The appropriate boundary conditions need to be
modified. 相似文献
445.
We study an initial boundary value problem for the equations of plane magnetohydrodynamic compressible flows, and prove that
as the shear viscosity goes to zero, global weak solutions converge to a solution of the original equations with zero shear
viscosity. As a by-product, this paper improves the related results obtained by Frid and Shelukhin for the case when the magnetic
effect is neglected.
Supported by NSFC (Grant No. 10301014, 10225105) and the National Basic Research Program (Grant No. 2005CB321700) of China. 相似文献
446.
Deutsch and Hayden have proposed an alternative formulation of quantum mechanics which is completely local. We argue that
their proposal must be understood as having a form of ‘gauge freedom’ according to which mathematically distinct states are
physically equivalent. Once this gauge freedom is taken into account, their formulation is no longer local.
相似文献
447.
The liquid to solid transformation of ternary Ag42.4Cu21.6Sb36 eutectic alloy was accomplished in an ultrasonic field with a frequency of 35 kHz, and the growth mechanism of this ternary eutectic was examined. Theoretical calculations predict that the sound intensity in the liquid phase at the solidification interface increases gradually as the interface moves up from the sample bottom to its top. The growth mode of (ε θ Sb) ternary eutectic exhibits a transition of "divorced eutectic- mixture of anomalous and regular structures-regular eutectic" along the sample axis due to the inhomogeneity of sound field distribution. In the top zone with the highest sound intensity, the cavitation effect promotes the three eutectic phases to nucleate independently, while the acoustic streaming efficiently suppresses the coupled growth of eutectic phases. In the meantime, the ultrasonic field accelerates the solute transportation at the solid-liquid interface, which reduces the solute solubility of eutectic phases. 相似文献
448.
The interactive two-state model of cell membrane ion channels in an electric field is formulated on the Bethe lattice by means
of the exact recursion relations. The probability of channel opening or maximum fractions of open potassium and sodium channels
are obtained by solving a non-linear algebraic equation. Using known parameters for the conventional mean-field theory the
model gives a good agreement with the experiment both at low and high trans-membrane potential values. For intermediate voltages,
the numerical results imply that collective effects are introduced by trans-membrane voltage. 相似文献
449.
Yun Chen Qing-sheng Wu Rong-hui Yin Ya-ping Ding 《Journal of nanoparticle research》2007,9(2):283-287
Uniform Pb(OH)Cl nanotubes were synthesized for the first time through a reverse micelles system. The system was consisting
of C12E9 as a surfactant, n-pentanol as a cosurfactant, hexamethylene as the continuous oil phase and lead acetate or sodium chloride
solution as the dispersed aqueous phase. The obtained Pb(OH)Cl nanotubes have an average outer diameter of 60 nm, inner diameter
of about 40 nm, and an length up to 3 μm as TEM picture showed. And the range of the nanotube diameter is from 50 nm to 70 nm.
XRD result indicated that Pb(OH)Cl crystallized in an orthorhombic phase. Photoluminescent (PL) spectrum showed that the product
emit in near ultraviolet region and visible region at 335 nm and 439 nm respectively. The experimental results show that reaction
temperature have effect on the shape of Pb(OH)Cl nanotubes. A possible formation mechanism was also discussed. 相似文献
450.
We explain the (non-)validity of close-to-equilibrium entropy production principles in the context of linear electrical circuits.
Both the minimum and the maximum entropy production principles are understood within dynamical fluctuation theory. The starting
point are Langevin equations obtained by combining Kirchoff’s laws with a Johnson-Nyquist noise at each dissipative element
in the circuit. The main observation is that the fluctuation functional for time averages, that can be read off from the path-space
action, is in first order around equilibrium given by an entropy production rate.
That allows to understand beyond the schemes of irreversible thermodynamics (1) the validity of the least dissipation, the
minimum entropy production, and the maximum entropy production principles close to equilibrium; (2) the role of the observables’
parity under time-reversal and, in particular, the origin of Landauer’s counterexample (1975) from the fact that the fluctuating
observable there is odd under time-reversal; (3) the critical remark of Jaynes (1980) concerning the apparent inappropriateness
of entropy production principles in temperature-inhomogeneous circuits. 相似文献