首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1578篇
  免费   166篇
  国内免费   29篇
化学   53篇
力学   22篇
综合类   29篇
数学   1431篇
物理学   238篇
  2023年   17篇
  2022年   57篇
  2021年   53篇
  2020年   40篇
  2019年   44篇
  2018年   36篇
  2017年   78篇
  2016年   71篇
  2015年   44篇
  2014年   118篇
  2013年   108篇
  2012年   91篇
  2011年   68篇
  2010年   74篇
  2009年   116篇
  2008年   99篇
  2007年   100篇
  2006年   76篇
  2005年   68篇
  2004年   46篇
  2003年   34篇
  2002年   54篇
  2001年   30篇
  2000年   25篇
  1999年   14篇
  1998年   26篇
  1997年   27篇
  1996年   25篇
  1995年   20篇
  1994年   10篇
  1993年   10篇
  1992年   10篇
  1991年   8篇
  1990年   3篇
  1989年   6篇
  1988年   2篇
  1987年   3篇
  1986年   3篇
  1985年   9篇
  1984年   8篇
  1983年   4篇
  1982年   6篇
  1981年   6篇
  1980年   7篇
  1979年   2篇
  1978年   4篇
  1977年   4篇
  1976年   4篇
  1973年   2篇
  1957年   1篇
排序方式: 共有1773条查询结果,搜索用时 31 毫秒
161.
本文针对一类设备的最优分配问题,将利润表转化为边际利润表,并建立了相应的寻优方程,通过实例说明,在一定情况下,用改进后的算法比常规算法节省一定的计算工作量.  相似文献   
162.
The study aims to exploit incremental analysis or marginal analysis to overcome the drawbacks of ratio scales utilized in various multi-criteria or multi-attribute decision making (MCDM/MADM) techniques. In the proposed 11-step procedure, multiple criteria of alternatives are first reorganized as two categories – benefits and costs – and decision information will be manipulated separately. The performances of alternatives are then evaluated on their incremental benefit–cost ratio, and the rank can be obtained by applying the group TOPSIS (technique for order preference by similarity to ideal solution) model (Shih et al., 2007). Two representations of cost, i.e., a cost index and utility index, are proposed in the model to better-fit real-world situations. In addition, some considerations on costs and input–output relations are also discussed in order to understand the essentials of incremental analysis. In the final part, a case of robot selection demonstrates the suggested model to be both robust and efficient in a group decision-making environment.  相似文献   
163.
The parameter identification problem of constant parameters in the equation of membrane with strong viscosity is studied. The problem is formulated by a minimization of quadratic cost functionals by distributive measurements. The existence of optimal parameters and necessary optimality conditions for the parameters are proved.  相似文献   
164.
Steadily growing prices of oil and emissions coming from conventional vehicles, might force a switch to an alternative and less polluting fuel in the coming future. In this article we analyze the potential influence of selected factors for successful market penetration of hydrogen fuel cell vehicles in hydrogen based private transportation economy. Using a world scale, full energy system, bottom-up, optimization model (Global MARKAL Model—GMM) we address the possibility of supporting the fuel cell vehicle technology to become competitive in the markets. In a series of optimizations we evaluate the potential influence of governmental supports and the internalization of externalities related to CO2 and local pollution emissions originating from the transportation sector, as well as preferential crediting options and demonstration projects promoting fuel cell vehicles. The results suggest that the crucial element is the price of fuel cells and their further potential to reduce costs. This reduction of costs may be triggered by governmental support such as direct subsidies to fuel cells, preferential crediting options for the buildup of hydrogen infrastructure as well as penalization of emitters of CO2 and/or local pollutants.  相似文献   
165.
A linear programming model is constructed which enables a firm to estimate its competitor's cost structure when the competitor adheres to a non-randomized strategy. The existence of the model makes randomized bidding prudent apart from game theory considerations. The need for increased curriculum attention to optimal bidding is highlighted.  相似文献   
166.
The model estimates, subject to restrictions, the functional relationship between national sulfur dioxide discharges and investment in control technology development. Estimates may be made for different product demands, allowed cost increases, and clean fuel availabilities. Control technology development may be accelerated by increased investment. Both optimal and sub-optimal solutions are calculated for an example problem. A general computing method is provided.The model was presented at the Industrial Process Design for Pollution Control Workshop, Chicago, Illinois, Oct. 1973; copyright released by the American Institute of Chemical Engineers for publication for the first time in the monographNormative Analysis in Policy Decisions: Public and Private.  相似文献   
167.
We propose a tabu search heuristic for the location/allocation problem with balancing requirements. This problem typically arises in the context of the medium term management of a fleet of containers of multiple types, where container depots have to be selected, the assignment of customers to depots has to be established for each type of container, and the interdepot container traffic has to be planned to account for differences in supplies and demands in various zones of the geographical territory served by a container shipping company. It is modeled as a mixed integer program, which combines zero-one location variables and a multicommodity network flow structure. Extensive computational results on a set of benchmark problems and comparisons with an efficient dual ascent procedure are reported. These show that tabu search is a competitive approach for this class of problems.  相似文献   
168.
For allocation models consisting of n = 10, 6 and 4 equations, constrained generalized least squares coefficient estimates are compared with those obtained from the minimum information (MI) criterion in the sense of statistical information theory. The MI estimates are more efficient for n = 10. The bootstrap procedure is illustrated for the assessment of the variability of these estimates.  相似文献   
169.
Abbas  SH 《应用数学和力学》1996,17(12):1077-1083
本文讨论了求解密集型线性方程组的两种并行算法。这两种算法都在下上单元(LU)分解。法的基础上使用了前向和后向置换进行的。这些算法在数值上是稳定的,并在顺序平衡机上用各种处理程序进行试验,都得到良好效果。  相似文献   
170.
We show the existence ofaverage cost (AC-) optimal policy for an inventory system withuncountable state space; in fact, the AC-optimal cost and an AC-optimal stationary policy areexplicitly computed. In order to do this, we use a variant of thevanishing discount factor approach, which have been intensively studied in recent years but the available results not cover the inventory problem we are interested in.The work of the first author (OVA) was partially supported by Fondo del Sistema de Investigación del Mar de Cortéz under grant SIMAC/94/CT-005. The work of the second author (RMdO) was partially supported by Consejo Nacional de Ciencia y Tecnologia (CONACyT) under grant 0635P-E9506.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号