全文获取类型
收费全文 | 86565篇 |
免费 | 594篇 |
国内免费 | 416篇 |
专业分类
化学 | 29459篇 |
晶体学 | 864篇 |
力学 | 6862篇 |
数学 | 33704篇 |
物理学 | 16686篇 |
出版年
2023年 | 56篇 |
2022年 | 69篇 |
2021年 | 122篇 |
2020年 | 129篇 |
2019年 | 129篇 |
2018年 | 10542篇 |
2017年 | 10365篇 |
2016年 | 6290篇 |
2015年 | 1086篇 |
2014年 | 583篇 |
2013年 | 871篇 |
2012年 | 4274篇 |
2011年 | 10973篇 |
2010年 | 5983篇 |
2009年 | 6363篇 |
2008年 | 7010篇 |
2007年 | 9181篇 |
2006年 | 667篇 |
2005年 | 1685篇 |
2004年 | 1869篇 |
2003年 | 2222篇 |
2002年 | 1266篇 |
2001年 | 395篇 |
2000年 | 456篇 |
1999年 | 278篇 |
1998年 | 300篇 |
1997年 | 237篇 |
1996年 | 300篇 |
1995年 | 179篇 |
1994年 | 156篇 |
1993年 | 166篇 |
1992年 | 131篇 |
1991年 | 140篇 |
1990年 | 116篇 |
1989年 | 137篇 |
1988年 | 120篇 |
1987年 | 118篇 |
1986年 | 116篇 |
1985年 | 104篇 |
1984年 | 107篇 |
1983年 | 83篇 |
1982年 | 93篇 |
1981年 | 102篇 |
1980年 | 78篇 |
1979年 | 99篇 |
1978年 | 87篇 |
1977年 | 61篇 |
1976年 | 74篇 |
1974年 | 55篇 |
1973年 | 73篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Jablonsk Josef ern Michal Pekr Juraj 《Central European Journal of Operations Research》2022,30(2):435-447
Central European Journal of Operations Research - The paper discusses operations research (OR) history and achievements in Czechia and Slovakia in 2010–2021 including the most significant OR... 相似文献
992.
LetK be a convex domain. A maximal snake of sizen is a set of non-overlapping translatesK
1, ...,K
N
ofK, whereK
i
touchesK
j
if and only if |i –j|=1 and no translate ofK can touchK
1 orK
n
without intersecting an additionalK
i
,i=1, ...,n. The size of the smallest maximal snake is proved to be 11 ifK is a parallelogram and to be 10 otherwise. 相似文献
993.
John M. Charnes Howard Marmorstein Walter Zinn 《The Journal of the Operational Research Society》1995,46(8):1006-1013
We consider a periodic-review inventory replenishment model with an order-up-to-R operating doctrine for the case of deterministic lead times and a covariance-stationary stochastic demand process. A method is derived for setting the inventory safety stock to achieve an exact desired stockout probability when the autocovariance function for Gaussian demand is known. Because the method does not require that parametric time-series models be fit to the data, it is easily implemented in practice. Moreover, the method is shown to be asymptotically valid when the autocovariance function of demand is estimated from historical data. The effects on the stockout rate of various levels of autocorrelated demand are demonstrated for situations in which autocorrelation in demand goes undetected or is ignored by the inventory manager. Similarly, the changes to the required level of safety stock are demonstrated for varying levels of autocorrelation. 相似文献
994.
This paper studies the optimal operation of an M/E k /1 queueing system with a removable service station under steady-state conditions. Analytic closed-form solutions of the controllable M/E k /1 queueing system are derived. This is a generalization of the controllable M/M/1, the ordinary M/E k /1, and the ordinary M/M/1 queueing systems in the literature. We prove that the probability that the service station is busy in the steady-state is equal to the traffic intensity. Following the construction of the expected cost function per unit time, we determine the optimal operating policy at minimum cost. 相似文献
995.
Kun-Jen Chung 《The Journal of the Operational Research Society》1995,46(11):1374-1385
Chiu, in 1976, studied the economic design of np charts for processes subject to a multiplicity of assignable causes. Chiu developed a two-step minimization procedure to obtain the three control variables, namely, the sampling interval, the sample size and the acceptance number. Although Chiu's two-step minimization procedure is simple, applicable and down to earth, it is rather inefficient and has some drawbacks. This paper presents an algorithm to overcome these drawbacks. The results and the execution times of all numerical examples show that the accuracy and the efficiency of the algorithm is reasonably good. 相似文献
996.
Karin Krüger Natalia V. Shakhlevich Yuri N. Sotskov Frank Werner 《The Journal of the Operational Research Society》1995,46(12):1481-1497
We consider a scheduling problem where a set of n jobs has to be processed on a set of m machines and arbitrary precedence constraints between operations are given. Moreover, for any two operations i and j values a ij >0 and a ji >0 may be given where a ij is the minimal difference between the starting times of operations i and j when operation i is processed first. Often, the objective is to minimize the makespan but we consider also arbitrary regular criteria. Even the special cases of the classical job shop problem J//Cmax belong to the set of NP-hard problems. Therefore, approximation or heuristic algorithms are necessary to handle large-dimension problems. Based on the mixed graph model we give a heuristic decomposition algorithm for such a problem, i.e. the initial problem is partitioned into subproblems that can be solved exactly or approximately with a small error bound. These subproblems are obtained by a relaxation of a subset of the set of undirected edges of the mixed graph. The subproblems are successively solved and a proportion of the results obtained for one subproblem is kept for further subproblem definitions. Numerical results of the algorithm presented here are given. 相似文献
997.
Yi-Chih Hsieh Mark S. Andersland 《The Journal of the Operational Research Society》1995,46(6):747-752
We develop an exact closed-form expression for the steady-state availability of a repairable, N-server system in which the ith server contains n i identical, reconfigurable, breakdown-prone units. Our approach, which follows from the Markov chain balance equations and the recursive properties of Hessenberg matrix determinants, is simpler than previously proposed matrix geometric approaches, and can readily be adapted to the availability analysis of more complicated structures. We illustrate this by computing the steady-state availability of a mixed parallel-serial gracefully degrading replicated system. 相似文献
998.
Eric Séré 《Communications in Mathematical Physics》1995,172(2):293-316
Consider a smooth Hamiltonian system in 2N
,
, the energy surface ={x/H(x)=H(0)} being compact, and 0 being a hyperbolic equilibrium. We assume, moreover, that {0} is of restricted contact type. These conditions are symplectically invariant. By a variational method, we prove the existence of an orbit homoclinic, i.e. non-constant and doubly asymptotic, to 0. 相似文献
999.
Recently B.Y. CHEN initiated the study of the tensor product immersion of two immersions of a given Riemannian manifold [3]. In [6] the particular case of tensor product of two Euclidean plane curves was studied. The minimal one were classified, and necessary and sufficient conditions for such a tensor product to be totally real or complex or slant were established. In the present paper we study for tensor product of Euclidean plane curves the problem of B.Y. CHEN: to what extent do the properties of the tensor product immersion f ? h of two immersions f, h determines the immersions f, h ? [3] 相似文献
1000.