全文获取类型
收费全文 | 265303篇 |
免费 | 891篇 |
国内免费 | 285篇 |
专业分类
化学 | 116536篇 |
晶体学 | 3763篇 |
力学 | 15982篇 |
综合类 | 7篇 |
数学 | 43881篇 |
物理学 | 86310篇 |
出版年
2019年 | 2290篇 |
2018年 | 10872篇 |
2017年 | 11629篇 |
2016年 | 7726篇 |
2015年 | 2549篇 |
2014年 | 3693篇 |
2013年 | 7142篇 |
2012年 | 9361篇 |
2011年 | 17665篇 |
2010年 | 11663篇 |
2009年 | 12017篇 |
2008年 | 15703篇 |
2007年 | 18937篇 |
2006年 | 5794篇 |
2005年 | 10449篇 |
2004年 | 7570篇 |
2003年 | 7446篇 |
2002年 | 5839篇 |
2001年 | 5140篇 |
2000年 | 4006篇 |
1999年 | 2865篇 |
1998年 | 2645篇 |
1997年 | 2474篇 |
1996年 | 2441篇 |
1995年 | 2156篇 |
1994年 | 2100篇 |
1993年 | 2122篇 |
1992年 | 2146篇 |
1991年 | 2457篇 |
1990年 | 2387篇 |
1989年 | 2472篇 |
1988年 | 2361篇 |
1987年 | 2387篇 |
1986年 | 2207篇 |
1985年 | 2752篇 |
1984年 | 2783篇 |
1983年 | 2416篇 |
1982年 | 2463篇 |
1981年 | 2369篇 |
1980年 | 2171篇 |
1979年 | 2506篇 |
1978年 | 2668篇 |
1977年 | 2672篇 |
1976年 | 2800篇 |
1975年 | 2591篇 |
1974年 | 2519篇 |
1973年 | 2727篇 |
1972年 | 2192篇 |
1971年 | 2000篇 |
1970年 | 1880篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Given a map f: X→Y and a Nielsen root class, there is a number associated to this root class, which is the minimal number of points among all
root classes which are H-related to the given one for all homotopies H of the map f. We show that for maps between closed surfaces it is possible to deform f such that all the Nielsen root classes have cardinality equal to the minimal number if and only if either N R[f]≤1, or N R[f]>1 and f satisfies the Wecken property. Here N R[f] denotes the Nielsen root number. The condition “f satisfies the Wecken property is known to be equivalent to |deg(f)|≤N R[f]/(1−χ(M
2)−χ(M
10/(1−χ(M
2)) for maps between closed orientable surfaces. In the case of nonorientable surfaces the condition is A(f)≤N R[f]/(1−χ(M
2)−χ(M
2)/(1−χ(M
2)). Also we construct, for each integer n≥3, an example of a map f: K
n
→N from an n-dimensionally connected complex of dimension n to an n-dimensional manifold such that we cannot deform f in a way that all the Nielsen root classes reach the minimal number of points at the same time. 相似文献
972.
There are few techniques available to numerically solve sixth-order boundary-value problems with two-point boundary conditions. In this paper we show that the Sinc-Galerkin method is a very effective tool in numerically solving such problems. The method is then tested on examples with homogeneous and nonhomogeneous boundary conditions and a comparison with the modified decomposition method is made. It is shown that the Sinc-Galerkin method yields better results.
973.
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
974.
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
975.
This paper develops a theory for the global solution of nonconvex optimization problems with parameter-embedded linear dynamic systems. A quite general problem formulation is introduced and a solution is shown to exists. A convexity theory for integrals is then developed to construct convex relaxations for utilization in a branch-and-bound framework to calculate a global minimum. Interval analysis is employed to generate bounds on the state variables implied by the bounds on the embedded parameters. These bounds, along with basic integration theory, are used to prove convergence of the branch-and-bound algorithm to the global minimum of the optimization problem. The implementation of the algorithm is then considered and several numerical case studies are examined thoroughly 相似文献
976.
Azuelos G. Benslama K. Costanzo D. Couture G. Garcia J.E. Hinchliffe I. Kanaya N. Lechowski M. Mehdiyev R. Polesello G. Ros E. Rousseau D. 《The European Physical Journal C - Particles and Fields》2004,39(2):13-24
The European Physical Journal C - We discuss possible searches for the new particles predicted by Little Higgs Models at the LHC. By using a simulation of the ATLAS detector, we demonstrate how the... 相似文献
977.
O. N. Lyubenko I. G. Ermolenko L. D. Patsenker Krasovitskii I. N. Tur 《Chemistry of Heterocyclic Compounds》2003,39(4):511-519
The behavior of dimethylamino-substituted 7H-benzo[de]pyrazolo[5,1-a]isoquinoline-7-ones, synthesized for the first time, under conditions of the Vilsmeier-Haack reaction. It has been shown that, on heating with POCl3 and DMF, they are converted by electrophilic substitution at the position ortho to the dimethylamino group, followed by cyclization of the iminium adduct to a quinazolinium salt. When an acetyl group is present, the Arnold reaction, leading to the formation of a chloroaryl, accompanies the heterocyclization. The rates and proportion of the reaction products depend on the position of the dimethyl groups relative to the pyrazole ring. 相似文献
978.
Linear topology defined on an arbitrary right module over a right Noetherian serial ring R enables one to describe the reduced, pure injective R-modules as modules that are complete in this topology. With the use of the completion of modules, the pure injective envelope of any right R-module is constructed. Bibliography: 8 titles. 相似文献
979.
980.
G. S. Osipenko J. V. Romanovsky N. B. Ampilova E. I. Petrenko 《Journal of Mathematical Sciences》2004,120(2):1155-1166
The Morse spectrum is a limit set of Lyapunov exponents of periodic pseudo-trajectories. This notion is especially important in the case where a dynamical system has infinitely many periodic trajectories of large period. A method for estimating the Morse spectrum was suggested by the first author in J. Math. Anal. Appl., 252 (2000). This method is based on ideas of symbolic dynamics which reduces the study of a dynamical system to the study of a certain graph, called a symbolic image. Within the framework of this method, the computation of the Morse spectrum is connected with searching simple closed paths and extracting contours with suitable characteristics. However, under iterations of the symbolic image, the number of such paths sharply increases, which leads to huge expenses of memory and time. We suggest an algorithm for constructing contours with the maximal and minimal mean values. This algorithm is based on a special version of the simplex method. Numerical tests are also described. Bibliography: 13 titles. Illustrations: 3 figures. 相似文献