全文获取类型
收费全文 | 3190篇 |
免费 | 455篇 |
国内免费 | 68篇 |
专业分类
化学 | 232篇 |
晶体学 | 6篇 |
力学 | 87篇 |
综合类 | 64篇 |
数学 | 1548篇 |
物理学 | 182篇 |
无线电 | 1594篇 |
出版年
2024年 | 12篇 |
2023年 | 47篇 |
2022年 | 75篇 |
2021年 | 84篇 |
2020年 | 91篇 |
2019年 | 106篇 |
2018年 | 91篇 |
2017年 | 123篇 |
2016年 | 121篇 |
2015年 | 138篇 |
2014年 | 224篇 |
2013年 | 195篇 |
2012年 | 195篇 |
2011年 | 205篇 |
2010年 | 199篇 |
2009年 | 212篇 |
2008年 | 223篇 |
2007年 | 217篇 |
2006年 | 178篇 |
2005年 | 155篇 |
2004年 | 118篇 |
2003年 | 104篇 |
2002年 | 106篇 |
2001年 | 95篇 |
2000年 | 82篇 |
1999年 | 62篇 |
1998年 | 41篇 |
1997年 | 35篇 |
1996年 | 32篇 |
1995年 | 24篇 |
1994年 | 10篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 15篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有3713条查询结果,搜索用时 0 毫秒
21.
Optimal production and rationing decisions in supply chains with information sharing 总被引:1,自引:0,他引:1
Boray Huang 《Operations Research Letters》2007,35(5):669-676
This paper considers a two-echelon capacitated supply chain with two non-identical retailers and information sharing. We characterize the optimal inventory policies. We also study the benefits of the optimal stock rationing policy over the first come first served (FCFS) and the modified echelon-stock rationing (MESR) policies. 相似文献
22.
We study the approximability of minimum total weighted tardiness with a modified objective which includes an additive constant. This ensures the existence of a positive lower bound for the minimum value. Moreover the new objective has a natural interpretation in just-in-time production systems. 相似文献
23.
给定一组工件的加工时间与工期,要求确定这些工件在一台机器上的加.工排列,使相应的总延误达到最小,这就是总延误问题.该问题在近年已被证明是NP困难的.由Wilkermn和Irwin(1971),林勋(1983)等所研究的顺时安排法能得到相邻交换意义下的局部解.在本文中,我们进一步证明该算法能得到前移邻域意义下的局部解,并确定了该算法的性能比. 相似文献
24.
The Effects of Filtered Channel Quality Feedback on Throughput of Proportional Fair Algorithm 总被引:1,自引:0,他引:1
1 IntroductionSchedulingalgorithmsarewidelystudiedforwirelesspacketdatasystems,whichgenerallyhavetwobasiccategories,oneisoptimizedforsystemthroughputandfairness[1~ 2 ] ,andtheotherisforthequalityofservice[3~6] .Forsystemswherepack etdataaretimedivisionmultiplexedacrossusersonthedownlink ,orfromBaseStation (BS)tomultipleMobileStations(MS) ,theBSusesschedulingalgo rithmstodecidewhichuseristransmittedto .ItisindicatedinRefs.[7,8]thatschedulingonlyoneus eratatimeisoptimalfromthepointofviewo… 相似文献
25.
26.
SINGLE MACHINE SCHEDULING WITH CONTROLLABLE PROCESSING TIMES AND COMPRESSION COSTS (PART I:EQUAL TIMES AND COSTS) 总被引:1,自引:0,他引:1
Most papers in scheduling research have treated individual job processing times as fixed parameters. However, in many practical situations, a manager may control processing time by realloeating resources. In this paper, authors consider a machine scheduling problemwith controllable processing times. In the first part of this paper, a special case where the pro-cessing times and compression costs are uniform among jobs is discussed. Theoretical results are derived that aid in developing an O(n^2) algorithm to slove the problem optimally. In the second part of this paper, authors generalize the discussion to general case, An effective heuristic to the genera/ problem will be presented. 相似文献
27.
设T是m-增生算子,I是恒等映射.本文通过一个反例说明(T+λI)-1(λ>0)不一定是非扩张映射. 相似文献
28.
Lufthansa Technical Training GmbH (LTT) performs training courses for Lufthansa Technik AG as well as for several other international airlines. Courses of about 670 different types are offered of which several hundred take place each year. The course scheduling problem faced by LTT is to construct a yearly schedule which maximizes the profit margin incurred while meeting a variety of complex precedence, temporal, and resource-related constraints. A “good” operational schedule should also meet a number of additional subordinate objectives. We formalize the problem and develop a heuristic scheme along with several priority rules, as well as a local search algorithm to determine well-suited weights for weighted composite rules. The operational planning situation of 1996 served as our major test instance; additional test instances were constructed by modifying this data. Several computational experiments were carried out to evaluate the performance of the algorithms. It turned out that the best so-found schedule is substantially better in terms of the profit margin incurred than the solution manually constructed by LTT. 相似文献
29.
The employment of the Zn(Se,Te) pseudo-graded contacting scheme to p-type ZnSe-based alloys contributes directly to the recent
demonstration of room temperature continuous-wave operation of II– VI green-blue laser diodes. Contact ohmicity is maintained
down to cryogenic temperatures which enabled the investigation of electrical transport properties associated with the p-type
nitrogen-doped ZnSe, Zn(S,Se), and (Zn,Mg)(S,Se). The observation of both persistent photoconductivity and a metastable population
of holes which are in thermodynamic equilibrium with hydrogenic acceptors having reduced activation energy suggests the presence
of a DX-like behavior for holes in p-type (Zn,Mg)(S,Se). 相似文献
30.
Hiroshi Konno 《Mathematical Programming》1988,41(1-3):185-193
We will consider a concave minimization problem associated with a series production system in which raw material is processed inm consecutive facilities. The products at some facility are either sent to the next facility or stocked in the warehouse. The amount of demand for the final products during periodi, i = 1,,n, are known in advance. Our problem is to minimize the sum of processing, holding and backlogging cost, all of which are assumed to be concave.The origin of this model is the classical economic lot size problem of Wagner and Whitin and was extensively studied by Zangwill. This model is very important from the theoretical as well as practical point of view and this is one of the very rare instances in which polynomial time algorithm has been constructed for concave minimization problems.The purpose of this paper is to extend the model further to the situation in which time lag is associated with processing at each facility. We will propose an efficient O(n
4
m) algorithm for this class of problems. 相似文献