全文获取类型
收费全文 | 482579篇 |
免费 | 2624篇 |
国内免费 | 721篇 |
专业分类
化学 | 222065篇 |
晶体学 | 6915篇 |
力学 | 27604篇 |
综合类 | 9篇 |
数学 | 73872篇 |
物理学 | 155459篇 |
出版年
2020年 | 4251篇 |
2019年 | 5049篇 |
2018年 | 12379篇 |
2017年 | 12789篇 |
2016年 | 12272篇 |
2015年 | 5150篇 |
2014年 | 8734篇 |
2013年 | 17492篇 |
2012年 | 16884篇 |
2011年 | 24644篇 |
2010年 | 17663篇 |
2009年 | 17994篇 |
2008年 | 22665篇 |
2007年 | 24853篇 |
2006年 | 14478篇 |
2005年 | 16141篇 |
2004年 | 13639篇 |
2003年 | 13048篇 |
2002年 | 12084篇 |
2001年 | 11265篇 |
2000年 | 9051篇 |
1999年 | 6667篇 |
1998年 | 6122篇 |
1997年 | 5915篇 |
1996年 | 5520篇 |
1995年 | 5007篇 |
1994年 | 5034篇 |
1993年 | 4915篇 |
1992年 | 5121篇 |
1991年 | 5629篇 |
1990年 | 5404篇 |
1989年 | 5409篇 |
1988年 | 5157篇 |
1987年 | 5152篇 |
1986年 | 4775篇 |
1985年 | 5795篇 |
1984年 | 6138篇 |
1983年 | 5197篇 |
1982年 | 5528篇 |
1981年 | 5122篇 |
1980年 | 4827篇 |
1979年 | 5400篇 |
1978年 | 5645篇 |
1977年 | 5567篇 |
1976年 | 5718篇 |
1975年 | 5344篇 |
1974年 | 5258篇 |
1973年 | 5457篇 |
1972年 | 4273篇 |
1971年 | 3854篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
S. S. Andreev A. D. Akhsakhalyan M. A. Bibishkin N. I. Chkhalo S. V. Gaponov S. A. Gusev E. B. Kluenkov K. A. Prokhorov N. N. Salashchenko F. Schafers S. Yu. Zuev 《Central European Journal of Physics》2003,1(1):191-209
We present research investigations in the field of multilayer optics in X-ray and extreme ultra-violet ranges (XUV), aimed
at the development of optical elements for applications in experiments in physics and in scientific instrumentation. We discuss
normal incidence multilayer optics in the spectral region of “water window”, multilayer optics for collimation and focusing
of hard X-ray, multilayer dispersing elements for X-ray spectroscopy of high-temperature plasma, multilayer dispersing elements
for analysis of low Z-elements. Our research pays special attention to optimization of multilayer optics for projection EUV-lithography
(ψ-13nm) and short period multilayer optics. 相似文献
972.
M.V. Nazarov J.H. Kang E.-J. Popovici B.S. Tsukerblat 《Solid State Communications》2005,133(3):183-186
Samples of yttrium oxide doped with trivalent europium have been prepared by ceramic techniques, under different synthesis conditions; barium chloride (BaCl2) and sodium tetraborate (Na2B4O7) were tested as flux. The improvement of luminescence properties in dependence on substitution of Eu3+ for Y3+ in the host lattice, under electron and UV excitations is demonstrated. The lattice parameter as a quantitative assessment of activator incorporation degree is proposed. The obtained results are discussed with respect to the employed processing method. 相似文献
973.
Millard F. Beatty 《Journal of Elasticity》2003,70(1-3):65-86
Two constitutive models that are based on the classical non-Gaussian, Kuhn-Grün probability distribution function are reviewed. It is shown that all chains of a network cell structure comprised of a finite number of identical chains in an affine deformation referred to principal axes may have the same invariant stretch, if and only if the chains are oriented initially along any of eight directions forming the diagonals of a unit cube. The 4-chain tetrahedral and the 8-chain cubic cell structures are familiar admissible models having this property. An easy derivation of the constitutive equation for the Wu and van der Giessen full-network model of initially identical chains arbitrarily oriented in the undeformed state is presented. The constitutive equations for the neo-Hookean model, the 3 -chain model, and the equivalent 4- and 8-chain models are then derived from the Wu and van der Giessen equation. The squared chain stretch of an arbitrarily directed chain averaged over a unit sphere surrounding all chains radiating from a cross-link junction as its center is determined. An average-stretch, full-network constitutive equation is then derived by approximation of the Wu and van der Giessen equation. This result, though more general in that no special chain cell morphology is introduced, is the same as the constitutive equation for the 4- and 8-chain models. Some concluding remarks on extensions to amended models are presented. 相似文献
974.
K. Zhang 《Calculus of Variations and Partial Differential Equations》2003,17(1):85-103
Let be a linear subspace of real matrices without rank-one matrices and let be a finite set. Suppose is a bounded arcwise connected Lipschitz domain and is a sequence of bounded vector-valued mappings in such that in as , where is the closed -neighbourhood and the distance function to . We give estimates for such that up to a subsequence, in for some fixed . In other words, we give estimates on such that separates gradient Young measure. The two point set with is a special case of such sets up to a translation.
Received: 20 July 2001 / Accepted: 23 January 2002 / Published online: 5 September 2002 相似文献
975.
We consider some types of packet discretization for continuous spectra in quantum scattering problems. As we previously showed, this discretization leads to a convenient finite-dimensional (i.e., matrix) approximation for integral operators in the scattering theory and allows reducing the solution of singular integral equations connected with the scattering theory to some suitable purely algebraic equations on an analytic basis. All singularities are explicitly singled out. Our primary emphasis is on realizing the method practically. 相似文献
976.
We use the Jacobi method to construct various integrable systems, such as the Stäckel systems and Toda chains, related to various root systems. We find canonical transformations that relate integrals of motion for the generalized open Toda chains of types B
n, C
n, and D
n. 相似文献
977.
M F Anjos R C H Cheng C S M Currie 《The Journal of the Operational Research Society》2004,55(5):535-541
The paper describes a methodology that has been implemented in a major British airline to find the optimal price to charge for airline tickets under one-way pricing. An analytical model has been developed to describe the buying behaviour of customers for flights over the selling period. Using this model and a standard analytical method for constrained optimization, we can find an expression for the optimal price structure for a flight. The expected number of bookings made on each day of the selling period and in each fare class given these prices can then be easily calculated. A simulation model is used to find the confidence ranges on the numbers of bookings and these ranges can be used to regulate the sale of tickets. A procedure to update the price structure based on the remaining capacity has also been developed. 相似文献
978.
In this paper, we find the approximate solution of a second order nonlinear partial differential equation on a simple connected region inR 2. We transfer this problem to a new problem of second order nonlinear partial differential equation on a rectangle. Then, we transformed the later one to an equivalent optimization problem. Then we consider the optimization problem as a distributed parameter system with artificial controls. Finally, by using the theory of measure, we obtain the approximate solution of the original problem. In this paper also the global error inL 1 is controlled. 相似文献
979.
A band-dominant function on the Euclidean sphere embedded in R q+1 is the restriction to this sphere of an entire function of q+1 complex variables having a finite exponential type in each of its variables. We develop a method to represent such a function using finitely many bits, using the values of the function at scattered sites on the sphere. The number of bits required in our representation is asymptotically the same as the metric entropy of the class of such functions with respect to any of the L p norms on the sphere. 相似文献
980.
A. V. Yakovlev 《Journal of Mathematical Sciences》2004,120(4):1642-1644
It is proved that a Galois extension of a field of characteristic p is completely determined by its Galois group and the endomorphism of the additive group of the group algebra that corresponds to the raising to the power p. 相似文献