全文获取类型
收费全文 | 15373篇 |
免费 | 1491篇 |
国内免费 | 572篇 |
专业分类
化学 | 5439篇 |
晶体学 | 18篇 |
力学 | 845篇 |
综合类 | 64篇 |
数学 | 6489篇 |
物理学 | 4581篇 |
出版年
2024年 | 21篇 |
2023年 | 212篇 |
2022年 | 170篇 |
2021年 | 370篇 |
2020年 | 420篇 |
2019年 | 414篇 |
2018年 | 286篇 |
2017年 | 330篇 |
2016年 | 553篇 |
2015年 | 467篇 |
2014年 | 705篇 |
2013年 | 1155篇 |
2012年 | 687篇 |
2011年 | 747篇 |
2010年 | 649篇 |
2009年 | 908篇 |
2008年 | 1073篇 |
2007年 | 1059篇 |
2006年 | 885篇 |
2005年 | 645篇 |
2004年 | 557篇 |
2003年 | 589篇 |
2002年 | 591篇 |
2001年 | 452篇 |
2000年 | 468篇 |
1999年 | 397篇 |
1998年 | 389篇 |
1997年 | 270篇 |
1996年 | 215篇 |
1995年 | 193篇 |
1994年 | 183篇 |
1993年 | 160篇 |
1992年 | 151篇 |
1991年 | 99篇 |
1990年 | 93篇 |
1989年 | 94篇 |
1988年 | 108篇 |
1987年 | 74篇 |
1986年 | 68篇 |
1985年 | 105篇 |
1984年 | 80篇 |
1983年 | 24篇 |
1982年 | 50篇 |
1981年 | 48篇 |
1980年 | 49篇 |
1979年 | 38篇 |
1978年 | 33篇 |
1977年 | 35篇 |
1976年 | 30篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We study the propagation of the light mesons σ,ω,ρ, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible
to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric
nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in β-equilibrium. The equation
of state and the potential contribution to the symmetry coefficient arising from the mean-field approximation are investigated.
Received: 16 October 2001 / Accepted: 10 January 2002 相似文献
82.
Ying Zhang Gang Hu Shigang Chen H.A. Cerdeira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):381-384
A method of controlling global stochasticity in Hamiltonian systems by applying nonlinear perturbation is proposed. With the
well-known standard map we demonstrate that this control method can convert global stochasticity into regular motion in a
wide chaotic region for arbitrary initial condition, in which the control signal remains very weak after a few kicks. The
system in which chaos has been controlled approximates to the original Hamiltonian system, and this approach appears robust
against small external noise. The mechanism underlying this high control efficiency is intuitively explained.
Received 15 January 2002 Published online 6 June 2002 相似文献
83.
D.A. Garanin E.M. Chudnovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):3-7
We compute the width and shape of the EPR and tunneling resonances due to dislocations in Mn12 acetate crystals. Uncorrelated dislocations produce the Gaussian shape of resonances while dislocations bound in pairs produce
the Lorentzian shape. We stress that the uniaxial spin Hamiltonian together with crystal defects can explain the totality
of experimental data on Mn12.
Received 2 August 2001 / Received in final form 15 March 2002 Published online 17 September 2002 相似文献
84.
External difference families (EDFs) are a type of new combinatorial designs originated from cryptography. In this paper, some
earlier ideas of recursive and cyclotomic constructions of combinatorial designs are extended, and a number of classes of
EDFs and disjoint difference families are presented. A link between a subclass of EDFs and a special type of (almost) difference
sets is set up. 相似文献
85.
This paper proposes a new method that extends the efficient global optimization to address stochastic black-box systems. The
method is based on a kriging meta-model that provides a global prediction of the objective values and a measure of prediction
uncertainty at every point. The criterion for the infill sample selection is an augmented expected improvement function with
desirable properties for stochastic responses. The method is empirically compared with the revised simplex search, the simultaneous
perturbation stochastic approximation, and the DIRECT methods using six test problems from the literature. An application
case study on an inventory system is also documented. The results suggest that the proposed method has excellent consistency
and efficiency in finding global optimal solutions, and is particularly useful for expensive systems. 相似文献
86.
87.
Christoph Elschenbroich Jrn Plackmeyer Klaus Harms Olaf Burghaus Jürgen Pebler 《无机化学与普通化学杂志》2006,632(5):819-827
Trovacene Chemistry. 13 [1] On Being Lead and Mislead in the Synthesis of Di([5]trovacenyl)ketone Di([5]trovacenyl)ketone ( 3¨ ) has been prepared from lithio‐[5]trovacene and dimethylcarbamoyl chloride and studied by X‐ray diffraction, cyclic voltammetry, magnetic susceptometry and EPR spectroscopy. Slight variation of the synthetic protocol affords an unusual trinuclear complex 5 ? that is also fully characterized. Spin‐spin exchange interaction is smaller in 3¨ than in 1,1‐di([5]trovacenylethene ( 2¨ ), which differs from 3¨ by a replacement of O for CH2. The novel trinuclear complex 5 ? , however, displays exchange coupling very similar to that observed in 1‐methoxy‐2,5,6‐tri([5]trovacenyl)benzene ( 7 ? ). In both cases, an unsymmetrical triangular arrangement of S = 1/2 centers is encountered. These findings are discussed in terms of the nature of the respective spacers. 相似文献
88.
The objective of this paper is to analyze under what well-known operations the class of quasipolyhedral convex functions,
which can be regarded as an extension of that of polyhedral convex functions, is closed. The operations that will be considered
are those that preserve polyhedral convexity, such that the image and the inverse image under linear transformations, right
scalar multiplication (including the case where λ=0+) and pointwise addition.
相似文献
89.
A direct central collision of two identical bodies of revolution is studied. A nonstationary mixed boundary-value problem with an unknown moving boundary is formulated. Its solution is represented by a series in term of Bessel functions. An infinite system of Volterra equations of the second kind for the unknown expansion coefficients is derived by satisfying the boundary conditions. The basic characteristics of the collision process are determined depending on the curvature of the frontal surface of the bodies 相似文献
90.
The motion of a particle in the field of an electromagnetic monopole (in the Coulomb–Dirac field) perturbed by an axially symmetric potential after quantum averaging is described by an integrable system. Its Hamiltonian can be written in terms of the generators of an algebra with quadratic commutation relations. We construct the irreducible representations of this algebra in terms of second-order differential operators; we also construct its hypergeometric coherent states. We use these states in the first-order approximation with respect to the perturbing field to obtain the integral representation of the eigenfunctions of the original problem in terms of solutions of the model Heun-type second-order ordinary differential equation and present the asymptotic approximation of the corresponding eigenvalues. 相似文献