全文获取类型
收费全文 | 100952篇 |
免费 | 565篇 |
国内免费 | 478篇 |
专业分类
化学 | 36032篇 |
晶体学 | 1235篇 |
力学 | 7416篇 |
综合类 | 7篇 |
数学 | 34119篇 |
物理学 | 23186篇 |
出版年
2020年 | 206篇 |
2019年 | 237篇 |
2018年 | 10635篇 |
2017年 | 10466篇 |
2016年 | 6427篇 |
2015年 | 1108篇 |
2014年 | 701篇 |
2013年 | 1535篇 |
2012年 | 4499篇 |
2011年 | 11287篇 |
2010年 | 6196篇 |
2009年 | 6618篇 |
2008年 | 7365篇 |
2007年 | 9545篇 |
2006年 | 954篇 |
2005年 | 1951篇 |
2004年 | 2077篇 |
2003年 | 2496篇 |
2002年 | 1518篇 |
2001年 | 962篇 |
2000年 | 828篇 |
1999年 | 592篇 |
1998年 | 556篇 |
1997年 | 490篇 |
1996年 | 518篇 |
1995年 | 502篇 |
1994年 | 432篇 |
1993年 | 424篇 |
1992年 | 411篇 |
1991年 | 457篇 |
1990年 | 420篇 |
1989年 | 433篇 |
1988年 | 397篇 |
1987年 | 398篇 |
1986年 | 391篇 |
1985年 | 459篇 |
1984年 | 484篇 |
1983年 | 357篇 |
1982年 | 369篇 |
1981年 | 394篇 |
1980年 | 379篇 |
1979年 | 385篇 |
1978年 | 373篇 |
1977年 | 336篇 |
1976年 | 350篇 |
1975年 | 311篇 |
1974年 | 300篇 |
1973年 | 325篇 |
1967年 | 347篇 |
1966年 | 301篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
An efficient computational method for a stochastic dynamic lot-sizing problem under service-level constraints 总被引:1,自引:0,他引:1
S. Armagan Tarim Mustafa K. Dogˇru Ula? Özen Roberto Rossi 《European Journal of Operational Research》2011,215(3):563-571
We provide an efficient computational approach to solve the mixed integer programming (MIP) model developed by Tarim and Kingsman [8] for solving a stochastic lot-sizing problem with service level constraints under the static-dynamic uncertainty strategy. The effectiveness of the proposed method hinges on three novelties: (i) the proposed relaxation is computationally efficient and provides an optimal solution most of the time, (ii) if the relaxation produces an infeasible solution, then this solution yields a tight lower bound for the optimal cost, and (iii) it can be modified easily to obtain a feasible solution, which yields an upper bound. In case of infeasibility, the relaxation approach is implemented at each node of the search tree in a branch-and-bound procedure to efficiently search for an optimal solution. Extensive numerical tests show that our method dominates the MIP solution approach and can handle real-life size problems in trivial time. 相似文献
943.
We report on the development of a novel precision target for atomic physics with heavy ion beams, which consists of extremely cold and well localized, laser-cooled lithium atoms in a magneto-optical trap. First experiments are in preparation to study the collisional losses from the trap caused by the ion beam. The experimental set-up and the laser system, using exclusively 670 nm diode lasers, are described. 相似文献
944.
Petros Galanopoulos Daniel Girela Rodrigo Hernández 《Journal of Geometric Analysis》2011,21(3):665-682
This paper is concerned mainly with the logarithmic Bloch space ℬlog which consists of those functions f which are analytic in the unit disc
\mathbbD{\mathbb{D}} and satisfy
sup|z| < 1(1-|z|)log\frac11-|z||f¢(z)| < ¥\sup_{\vert z\vert <1}(1-\vert z\vert )\log\frac{1}{1-\vert z\vert}\vert f^{\prime}(z)\vert <\infty , and the analytic Besov spaces B
p
, 1≤p<∞. They are all subspaces of the space VMOA. We study the relation between these spaces, paying special attention to the membership of univalent functions in them. We
give explicit examples of:
• |
A bounded univalent function in $\bigcup_{p>1}B^{p}$\bigcup_{p>1}B^{p} but not in the logarithmic Bloch space. 相似文献
945.
José Fernando Gonçalves Mauricio G. C. Resende Jorge J. M. Mendes 《Journal of Heuristics》2011,17(5):467-486
This paper presents a biased random-key genetic algorithm for the resource constrained project scheduling problem. The chromosome
representation of the problem is based on random keys. Active schedules are constructed using a priority-rule heuristic in
which the priorities of the activities are defined by the genetic algorithm. A forward-backward improvement procedure is applied
to all solutions. The chromosomes supplied by the genetic algorithm are adjusted to reflect the solutions obtained by the
improvement procedure. The heuristic is tested on a set of standard problems taken from the literature and compared with other
approaches. The computational results validate the effectiveness of the proposed algorithm. 相似文献
946.
This paper deals with a control-constrained linear-quadratic optimal control problem governed by the Stokes equations. It
is concerned with situations where the gradient of the velocity field is not bounded. The control is discretized by piecewise
constant functions. The state and the adjoint state are discretized by finite element schemes that are not necessarily conforming.
The approximate control is constructed as projection of the discrete adjoint velocity in the set of admissible controls. It
is proved that under certain assumptions on the discretization of state and adjoint state this approximation is of order 2
in L
2(Ω). As first example a prismatic domain with a reentrant edge is considered where the impact of the edge singularity is counteracted
by anisotropic mesh grading and where the state and the adjoint state are approximated in the lower order Crouzeix-Raviart
finite element space. The second example concerns a nonconvex, plane domain, where the corner singularity is treated by isotropic
mesh grading and state and adjoint state can be approximated by a couple of standard element pairs. 相似文献
947.
Let K be an algebraic number field and f a complex-valued function on the ideal class group of K. Then, f extends in a natural way to the set of all non-zero ideals of the ring of integers of K and we can consider the Dirichlet series \({L(s,f) =\sum_{{\mathfrak a}} f({\mathfrak a}){\bf N}({\mathfrak a})^{-s}}\) which converges for \({{\mathfrak R}(s) >1 }\). After extending this function to \({{\mathfrak R}(s)=1}\), and in the case that f does not contain the trivial character, we study the special value L(1, f) when f is algebraic valued and K is an imaginary quadratic field. Applying Kronecker’s limit formula and Baker’s theory of linear forms in logarithms, we derive a variety of results related to the transcendence of this special value. 相似文献
948.
Let f:X→Y be an algebraic fiber space with general fiber F. If Y is of maximal Albanese dimension, we show that κ(X)≥κ(Y)+κ(F). 相似文献
949.
Dimitrios Bagkavos 《Annals of the Institute of Statistical Mathematics》2011,63(5):1019-1046
A new kernel based local linear estimate of the hazard rate, under the random right censorship model is proposed in this article.
We study its finite sample and asymptotic properties and prove its asymptotic normality. Then we bring in three popular methods
for bandwidth selection to the hazard setting as potential bandwidth choice rules for the estimate. We discuss their practical
implementation and through Monte Carlo simulations we use four distributions with different hazard rate shapes to compare
their performance over various sample sizes and levels of censoring. 相似文献
950.
In this paper, we show the following result: Let K
i
be a knot in a closed orientable 3-manifold M
i
such that (M
i
,K
i
) is not homeomorphic to (S
2 ×S
1, x
0 ×S
1), i = 1, 2. Suppose that the Euler Characteristic of any meridional essential surface in each knot complement E(K
i
) is less than the difference of one and twice of the tunnel number of K
i
. Then the tunnel number of their connected sum will not go down. If in addition that the distance of any minimal Heegaard
splitting of each knot complement is strictly more than 2, then the tunnel number of their connected sum is super additive. 相似文献
|