全文获取类型
收费全文 | 55822篇 |
免费 | 278篇 |
国内免费 | 336篇 |
专业分类
化学 | 22618篇 |
晶体学 | 682篇 |
力学 | 2389篇 |
综合类 | 23篇 |
数学 | 12891篇 |
物理学 | 17833篇 |
出版年
2023年 | 37篇 |
2022年 | 261篇 |
2021年 | 521篇 |
2020年 | 486篇 |
2019年 | 709篇 |
2018年 | 2298篇 |
2017年 | 2649篇 |
2016年 | 2175篇 |
2015年 | 1193篇 |
2014年 | 1710篇 |
2013年 | 2488篇 |
2012年 | 4828篇 |
2011年 | 4133篇 |
2010年 | 3684篇 |
2009年 | 3390篇 |
2008年 | 2469篇 |
2007年 | 2420篇 |
2006年 | 2190篇 |
2005年 | 5423篇 |
2004年 | 4622篇 |
2003年 | 2700篇 |
2002年 | 885篇 |
2001年 | 638篇 |
2000年 | 725篇 |
1999年 | 544篇 |
1998年 | 586篇 |
1997年 | 522篇 |
1996年 | 172篇 |
1995年 | 83篇 |
1994年 | 74篇 |
1992年 | 187篇 |
1991年 | 171篇 |
1990年 | 153篇 |
1989年 | 113篇 |
1988年 | 107篇 |
1987年 | 67篇 |
1986年 | 48篇 |
1985年 | 47篇 |
1984年 | 36篇 |
1983年 | 39篇 |
1979年 | 36篇 |
1976年 | 84篇 |
1975年 | 43篇 |
1974年 | 46篇 |
1973年 | 52篇 |
1972年 | 44篇 |
1970年 | 36篇 |
1969年 | 41篇 |
1968年 | 45篇 |
1966年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 146 毫秒
111.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help. 相似文献
112.
E. D. Mishina N. É. Sherstyuk V. O. Val’dner A. V. Mishina K. A. Vorotilov V. A. Vasil’ev A. S. Sigov M. P. De Santo E. Cazzanelli R. Barberi Th. Rasing 《Physics of the Solid State》2006,48(6):1210-1213
Ferroelectric composite two-dimensional ferroelectric/aluminum oxide nanostructures were studied. A porous aluminum oxide matrix was used as a template into which a ferroelectric precursor was introduced, followed by annealing. The prepared nanostructures were studied using optical second harmonic generation and micro-Raman scattering. 相似文献
113.
A general method for solving the problem of quantization of a top is proposed that allows for finding the Hamiltonian eigenfunctions in the form of polynomials of various degree n in the Cartesian coordinates with the use of the Lamé functions. All three coordinates x, y, and z are equivalently involved in computations, as well as their relations with ellipsoidal coordinates, which makes the computations symmetric. 相似文献
114.
A. B. Vasil’eva A. A. Plotnikov 《Computational Mathematics and Mathematical Physics》2006,46(5):762-767
A singularly perturbed parabolic equation with a nonlinear right-hand side of a special form is examined. A numerical analytical study of such equations is performed. 相似文献
115.
V. V. Lozhkarev S. G. Garanin R. R. Gerke V. N. Ginzburg E. V. Katin A. V. Kirsanov G. A. Luchinin A. N. Mal’shakov M. A. Mart’yanov O. V. Palashov A. K. Poteomkin N. N. Rukavishnikov A. M. Sergeev S. A. Sukharev G. I. Freidman E. A. Khazanov A. V. Charukhchev A. A. Shaikin I. V. Yakovlev 《JETP Letters》2005,82(4):178-180
In experiments on the parametrical amplification of femtosecond pulses in wide-aperture DKDP crystals, a power of more than 100 TW has been reached, which is much higher than the record level achieved in such lasers. The energy efficiency obtained for the parametric amplifier is equal to 27%. The energy of a 72-fs pulse is equal to 10 J. 相似文献
116.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart. 相似文献
117.
Daniel Pa?ca 《Journal of Mathematical Analysis and Applications》2007,325(1):90-100
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian. 相似文献
118.
In this paper we prove existence results for semilinear neutral functional differential inclusions with finite or infinite
delay in Banach spaces. Our theory makes use of analytic semigroups and fractional powers of closed operators, integrated
semigroups and cosine families.
相似文献
119.
A. P. Solov’ev M. I. Perchenko Yu. P. Sinichkin O. V. Zyuryukina 《Technical Physics》2002,47(8):996-1001
An expression for a signal at the ultrasonic frequency from a photodetector arising when diffraction waves at the cathode
mix is obtained for the case when the optical and acoustic beams are space-limited and Bragg angles are small. The alternating
current generated when the scattering medium is crossed by a focused 3-MHz ultrasonic beam and illuminated by a cw He-Ne laser
is measured. Satisfactory agreement between experimental results and those calculated from the formulas obtained indicates
that our model treating acoustooptical interaction in the medium in terms of Raman-Nath diffraction is valid. Conditions for
measuring the alternating current (which is a parameter of acoustooptical imaging) that are optimal from the viewpoint of
maximizing the signal and signal-to-noise ratio are predicted theoretically and corroborated experimentally. 相似文献
120.
R. A. Kotel’nikova G. N. Bogdanov G. V. Zotina V. S. Romanova Z. N. Parnes 《Physics of the Solid State》2002,44(3):576-577
Efficient quenching of eosin phosphorescence by amino-acid derivatives of fullerene (AADFs) such as C60-alanine and C60-glycine in aqueous solutions indicates the possibility of transferring electrons from eosin to fullerene upon collisions or in the exciplex state. To investigate electron transfer in the protein structure, we studied the process of incorporation of C60-alanine and C60-glycine into the heme pocket of myoglobin by controlling Förster quenching. The dissociation constant for the protein-AADF complex was estimated. 相似文献