全文获取类型
收费全文 | 28236篇 |
免费 | 1329篇 |
国内免费 | 436篇 |
专业分类
化学 | 14989篇 |
晶体学 | 134篇 |
力学 | 1867篇 |
数学 | 5605篇 |
物理学 | 7406篇 |
出版年
2024年 | 27篇 |
2023年 | 229篇 |
2022年 | 306篇 |
2021年 | 323篇 |
2020年 | 1089篇 |
2019年 | 520篇 |
2018年 | 1887篇 |
2017年 | 1915篇 |
2016年 | 1603篇 |
2015年 | 1059篇 |
2014年 | 1557篇 |
2013年 | 3070篇 |
2012年 | 2138篇 |
2011年 | 2342篇 |
2010年 | 1863篇 |
2009年 | 1741篇 |
2008年 | 1375篇 |
2007年 | 1210篇 |
2006年 | 885篇 |
2005年 | 689篇 |
2004年 | 520篇 |
2003年 | 483篇 |
2002年 | 389篇 |
2001年 | 509篇 |
2000年 | 221篇 |
1999年 | 453篇 |
1998年 | 242篇 |
1997年 | 181篇 |
1996年 | 128篇 |
1995年 | 124篇 |
1994年 | 74篇 |
1993年 | 64篇 |
1992年 | 65篇 |
1991年 | 50篇 |
1990年 | 46篇 |
1989年 | 53篇 |
1988年 | 322篇 |
1987年 | 48篇 |
1986年 | 9篇 |
1984年 | 8篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 33篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1976年 | 25篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
《Communications in Nonlinear Science & Numerical Simulation》2007,12(6):1101-1114
This study presents a simple formulation for the nonlinear dynamic analysis of shear-deformable laminated sector plates made up of cylindrically orthotropic layers. The non-axisymmetric formulation in cylindrical coordinates is discretized in space domain using two-dimensional Chebyshev polynomials. Houbolt time marching is used for temporal discretization. Quadratic extrapolation is used for linearization along with fixed-point iteration for obtaining the results. Several combinations of simply supported, clamped and free edge conditions are considered. Convergence study has been carried out and the results are compared with the results of square plates. Effects of boundary conditions, moduli ratio, lamination scheme, sector angle and annularity on the transient deflection response are plotted graphically. Transient responses are compared for step, saw-tooth and sinusoidal loadings. 相似文献
92.
S. Azimpour M. Chaichi M. Toomanian 《Journal of Contemporary Mathematical Analysis (Armenian Academy of Sciences)》2007,42(5):270-277
A 4-dimensional Walker metric on a semi Riemanian manifold M, for the canonical metric with c = 0, have been investigated by M. Chaichi, E. García—Río and Y. Matsushita. The paper generalizes these notions to the case of constant c ≠ 0. Specially the form of defining functions of this metric in locally conformally flat 4-dimensional Walker manifolds is found. 相似文献
93.
A. Aghajani 《Journal of Mathematical Analysis and Applications》2007,326(2):1076-1089
We consider the nonlinear Euler differential equation t2x″+g(x)=0. Here g(x) satisfies xg(x)>0 for x≠0, but is not assumed to be sublinear or superlinear. We present implicit necessary and sufficient condition for all nontrivial solutions of this system to be oscillatory or nonoscillatory. Also we prove that solutions of this system are all oscillatory or all nonoscillatory and cannot be both. We derive explicit conditions and improve the results presented in the previous literature. We extend our results to the extended equation t2x″+a(t)g(x)=0. 相似文献
94.
95.
We present an isovector Lagrangian, which admits stable, nonsingular soliton solutions in three space dimensions. The spherical solution and its total energy are obtained via a variational procedure. An antisymmetric, second-rank tensor is defined in terms of the isovector field and its derivatives. This tensor satisfies Maxwell's equations. The corresponding current is identically conserved and the total charge is topologically quantized. 相似文献
96.
Shayesteh S. Farjami B. Soltani M. A. Solimany 《International Journal of Infrared and Millimeter Waves》2002,23(12):1691-1697
We present and discuss infrared magnetoplasma reflectivity and surface polariton modes in Ga1–xNxAs. It assumed that the sample is characterized by a magnetoplasma dielectric tensor. Surface polariton dispersion for two component magnetoplasma was calculated from reflectivity spectra data. We detect transverse optic phonon of GaN sublattice in 470 cm-1. The origin of sharp feature in p-polarization reflectivity about 300 cm–1 as well as LO phonon frequency of GaAs sublattice is due to Brewster mode. An interesting feature of surface modes in Voigt geometry is nonreciprocalicity, which means that the frequency changes when the direction of propagation is reversed. Also, the infrared magnetoplasma reflectivity of GaNAs should be providing determination of the electrons and heavy holes effective mass and carrier's concentration. 相似文献
97.
Let G be a finite group. Let p(G) denote the minimal degree of a faithful permutation representation ofG and let q(G) and c(G) denote the minimal degree of a faithful representation of G by quasi-permutation matrices over the rational and the complex numbers, respectively. Finally r(G) denotes the minimal degree of a faithful rational valued complex character of G. The purpose of this paper is to calculate p(G), q(G), c(G) and r(G) for the group SP(4,q).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
98.
Mohammad Reza Ganjali Morteza Rezapour Mohammad Reza Pourjavid Masoud Salavati-Niasari 《Analytical sciences》2003,19(8):1127-1131
A cobalt(II) derivative was used as a suitable ionophore for the preparation of a polymeric membrane nitrite-selective electrode. The electrode reveals a Nemstian behavior over a very wide NO2- ion concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) and a very low detection limit (5.0 x 10(-7) M). The potentiometric response is independent of the pH of solution in the pH range 4.0-9.5. The electrode shows advantages such as low resistance, fast response and, most importantly, good selectivity relative to a wide variety of inorganic and organic anions. In fact, the selectivity behavior of the proposed NO2- ion-selective electrode shows great improvements compared to the previously reported electrodes for nitrite ion. The proposed electrodes could be used for at least 2 months without any significant changes in potentials. The electrode was successfully applied to the determination of nitrate ion concentrations in sausage and milk samples. 相似文献
99.
100.
《Chaos, solitons, and fractals》2007,31(2):371-379
In this paper, we apply the simple adaptive-feedback control scheme to synchronize a class of chaotic non-autonomous systems. Based on the invariance principle of differential equations, some generic sufficient conditions for global asymptotic synchronization are obtained. Unlike the usual linear feedback, the variable feedback strength is automatically adapted to completely synchronize two identical systems and simple to implement in practice. As illustrative examples, synchronization of two parametrically excited chaotic pendulums and that of two 4D new systems are considered here. Numerical simulations show the proposed method is effective and robust against the effect of noise. 相似文献