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   277篇
  免费   6篇
  283篇
  2025年   1篇
  2024年   2篇
  2023年   6篇
  2022年   3篇
  2021年   6篇
  2020年   8篇
  2019年   3篇
  2018年   2篇
  2017年   6篇
  2016年   4篇
  2015年   7篇
  2014年   18篇
  2013年   19篇
  2012年   11篇
  2011年   10篇
  2010年   13篇
  2009年   18篇
  2008年   15篇
  2007年   21篇
  2006年   11篇
  2005年   8篇
  2004年   3篇
  2003年   5篇
  2002年   7篇
  2001年   8篇
  2000年   7篇
  1999年   8篇
  1998年   11篇
  1997年   4篇
  1996年   6篇
  1995年   7篇
  1994年   4篇
  1993年   5篇
  1992年   3篇
  1991年   7篇
  1990年   3篇
  1989年   1篇
  1982年   1篇
  1972年   1篇
排序方式: 共有283条查询结果,搜索用时 15 毫秒
121.
认真学习胡锦涛总书记9月19日重要讲话精神,切实搞好深入学习实践科学发展观活动,是推动中国新一轮发展的强大动力。通过深入学习实践科学发展观活动,提高全党的思想理论水平,为推动科学发展提供强大思想动力;努力解决群众反映强烈、影响和制约科学发展的突出问题,为推动科学发展提供强大社会合力;构建有利于科学发展的体制机制,为推动科学发展提供制度保证;提高党的执政能力,为推动科学发展提供坚强组织保证;努力在改进作风上取得新成效,为推动科学发展提供更和谐的环境。  相似文献   
122.
清朝末年,由于海防力量薄弱,东南沿海频遭列强侵犯,杨昌浚采取了一系列的措施进行抵抗。此外,他还参与了海防大讨论,提出了一些有价值的建议。清政府决定建立台湾省后,杨昌浚即表服从,并主持了台湾的建省工作。  相似文献   
123.
为了探索研究实艇的流水孔方案设计,基于滑移网格和内外域交互的计算方法,以含上层建筑流水孔的局部艇体模型为研究对象,对不同缩比的方形流水孔在不同吃水下的溢流进行了数值模拟,并对比分析了不同缩比的方形流水孔的上层建筑余水容积、余水高度、孔口流量以及流量系数等参数的变化规律.研究结果表明:流水孔的缩比越小,即流水孔的尺寸越大...  相似文献   
124.
This paper reports an alternative approach to the evaluation of infrared camouflage effectiveness via a multi-fractal method. By calculating multi-fractal spectra of the target region and the background re-gions in an infrared image, the spectrum shape features and the discrete Fréchet distances among these spectra were used to analyze the camouflage effectiveness of the target qualitatively and quantitatively, and the correlation coefficients of the spectra were further used as the index of camouflage effectiveness. It was found that the camouflaged target had better camouflage effectiveness than the target without camouflage in the same one background, and the same one camouflaged target had different camouflage effectiveness in different backgrounds. On the whole, the target matching well with its background had high camouflage effectiveness value. This approach can expand the application of multi-fractal theory in infrared camouflage technology, which should be useful for the research of infrared camouflage mate-rials, the design of camouflage patterns as well as the deployment of military equipment in battlefield.  相似文献   
125.
When a penetrator with enhanced lateral effect (PELE) impacts on a reinforced concrete (RC) target, the target is damaged with a large opening. An understanding of how PELE projectile parameters affect the opening dimension, is essential for effective design of the PELE projectile. In this study, under the condition that the impact velocity and target parameters (strength and thickness) were fixed values, the important influence factors of the PELE (jacket wall thickness B, jacket material strength Y1, filling material strength Y2 and angle of monolithic jacketθ) were determined by a dimensional analysis. Tests and simulations of the PELE penetrating the RC target were conducted to analyze the influence of these factors on opening diameter ((D), an equivalent diameter under relative kinetic energy). Based on the test and simulation results, it is found that the influence of these factors B, Y1 andθon the deformation mode of the jacket shows a similar trend:as values of the three factors decrease, the jacket deforms from small bending deformation to large one, and then to curling deformation. This causes the opening diameter to first increase with the decrease of these three factors, and then decreases. It is well known that the bending resistance of the jacket is related to these factors B, Y1 andθ. Therefore, a plastic limit bending moment (M0) of the jacket was quoted to characterize the influence of these factors on the bending deformation of the jacket and the opening diameter of the target. The influence factor Y2 causes (D) to first increase with the increase of Y2, and then decreases. A formula was developed to predict the opening diameter, whose influence parameters were considered in a dimensionless way. It has been shown that the dimensionless opening diameter (D)/d1 is dependent on two dimensionless parameters Q = (d31fc/M0) and G = (fc/Y2), where d1 and fc are the outer diameter of the projectile and the compressive strength of the target, respectively.  相似文献   
126.
We consider the problem of scheduling a set of jobs with a common due-date on a single-machine where the release time of a job is related to the amount of resource consumed. The objective is to minimize the total resource consumption and the total tardiness. While the problem is strongly NP-hard in general, we discuss two different special cases for which special properties are identified and used to develop efficient pseudo-polynomial time algorithms. © 1995 John Wiley & Sons, Inc.  相似文献   
127.
为了解决许多交通流预测研究方法不能全面地挖掘交通数据中的动态隐藏相关性的问题,研究了动态时空变化特征,提出了一个基于编码器-解码器的交通预测模型。在模型中,编码器和解码器都主要由多头时空注意力机制组成,在两者中间加入了连接注意力机制,以分析路网时空相关性。模型还使用时空嵌入编码与自适应图卷积结合构成的动态嵌入模块来分析节点的动态和静态信息。在两个真实数据集上的实验,证明了该时空模型在长短期流量预测的效果优于其他方法。因此,时空编码器-解码器模型能有效处理复杂的时空序列,提升交通流预测的准确性。  相似文献   
128.
针对水面舰艇编队空中威胁扇面角的预测问题,分析了影响空中威胁扇面角大小的主要因素。以具有航路规划能力的远程反舰导弹为对象,从航空兵及远程反舰导弹的作战使用特点和装备性能限制着手,建立了计算威胁扇面角的数学模型。通过仿真分析,得出了主要参数对威胁扇面角的影响规律,为水面舰艇编队对空防御兵力的配置提供了依据。  相似文献   
129.
The quick response (QR) system that can cope with demand volatility by shortening lead time has been well studied in the literature. Much of the existing literature assumes implicitly or explicitly that the manufacturers under QR can always meet the demand because the production capacity is always sufficient. However, when the order comes with a short lead time under QR, availability of the manufacturer's production capacity is not guaranteed. This motivates us to explore QR in supply chains with stochastic production capacity. Specifically, we study QR in a two-echelon supply chain with Bayesian demand information updating. We consider the situation where the manufacturer's production capacity under QR is uncertain. We first explore how stochastic production capacity affects supply chain decisions and QR implementation. We then incorporate the manufacturer's ability to expand capacity into the model. We explore how the manufacturer determines the optimal capacity expansion decision, and the value of such an ability to the supply chain and its agents. Finally, we extend the model to the two-stage two-ordering case and derive the optimal ordering policy by dynamic programming. We compare the single-ordering and two-ordering cases to generate additional managerial insights about how ordering flexibility affects QR when production capacity is stochastic. We also explore the transparent supply chain and find that our main results still hold.  相似文献   
130.
    
We study the competition problem of purchase and multiretrieval of perishable seasonal produce, where wholesalers purchase and stock their products in the first period, and then retrieve and sell them in subsequent periods. We first consider the duopoly case and assume that the prices are exogenous and fluctuate. In each period, after the price realization, the wholesalers retrieve some stock from their warehouses to satisfy their demands. One wholesaler's unsatisfied customers can switch to another and be satisfied by its left retrieved products. Any unsold retrieved stock has no salvage value and any unsatisfied demand is lost. The unretrieved stock is carried to the next period at a perishable rate. The wholesalers compete for the substitute demand by determining their own purchase and retrieval quantities. We show the existence and uniqueness of a pure-strategy Nash equilibrium, and that the Nash equilibrium strategy has the simple “sell-down-to” structure. We also consider the general N-person game and show the existence of the Nash equilibrium, and characterize the structure of the equilibrium strategy for the symmetric case. In addition, we consider the case with endogenous prices, and show that the problem reduces to a repeated newsvendor game with price and inventory competition. We derive the conditions under which a unique Nash equilibrium exists and characterize the equilibrium strategy. Finally, we conduct numerical studies to examine the impacts of the model parameters on the equilibrium outcomes and to generate managerial insights.  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