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   5165篇
  免费   282篇
  国内免费   299篇
系统科学   243篇
丛书文集   140篇
教育与普及   88篇
理论与方法论   17篇
现状及发展   47篇
研究方法   24篇
综合类   5185篇
自然研究   2篇
  2024年   16篇
  2023年   60篇
  2022年   94篇
  2021年   82篇
  2020年   78篇
  2019年   18篇
  2018年   55篇
  2017年   64篇
  2016年   64篇
  2015年   113篇
  2014年   168篇
  2013年   156篇
  2012年   161篇
  2011年   175篇
  2010年   155篇
  2009年   206篇
  2008年   236篇
  2007年   244篇
  2006年   192篇
  2005年   183篇
  2004年   133篇
  2003年   129篇
  2002年   124篇
  2001年   159篇
  2000年   172篇
  1999年   328篇
  1998年   284篇
  1997年   283篇
  1996年   272篇
  1995年   228篇
  1994年   183篇
  1993年   174篇
  1992年   151篇
  1991年   146篇
  1990年   128篇
  1989年   101篇
  1988年   92篇
  1987年   68篇
  1986年   44篇
  1985年   13篇
  1984年   2篇
  1983年   1篇
  1982年   3篇
  1978年   1篇
  1974年   2篇
  1971年   1篇
  1967年   2篇
  1957年   2篇
排序方式: 共有5746条查询结果,搜索用时 15 毫秒
1.
This paper considers how information from the implied volatility (IV) term structure can be harnessed to improve stock return volatility forecasting within the state-of-the-art HAR model. Factors are extracted from the IV term structure and included as exogenous variables in the HAR framework. We found that including slope and curvature factors leads to significant forecast improvements over the HAR benchmark at a range of forecast horizons, compared with the standard HAR model and HAR model with VIX as IV information set.  相似文献   
2.
With increasing demand diversification and short product lifecycles, industries now encounter challenges of demand uncertainty. The Japanese seru production system has received increased attention owing to its high efficiency and flexibility. In this paper, the problem of seru production system formation under uncertain demand is researched. A multi-objective optimization model for a seru production system formation problem is developed to minimize the cost and maximize the service level of the system. The purpose of this paper is to formulate a robust production system that can respond efficiently to the stochastic demand. Sample average approximation (SAA) is used to approximate the expected objective of the stochastic programming. The non-dominated sorting genetic algorithm II (NSGA-II) is improved to solve the multi-objective optimization model. Numerical experiments are conducted to test the tradeoff between cost and service level, and how the performance of the seru production system varies with the number of product types, mean and deviation of product volume, and skill-level-based cost.  相似文献   
3.
Existing Side-Channel Attacks(SCAs) have several limitations and, rather than to be real attack methods,can only be considered to be security evaluation methods. Their limitations are mainly related to the sampling conditions, such as the trigger signal embedded in the source code of the encryption device, and the acquisition device that serves as the encryption-device controller. Apart from it being very difficult for an attacker to add a trigger into the original design before making an attack or to control the encryption device, there is a big gap in the capacity of existing SCAs to pose real threats to cipher devices. In this paper, we propose a new method, the sliding window SCA(SW-SCA), which can be applied in scenarios in which the acquisition device is independent of the encryption device and for which the encryption source code requires no trigger signal or modification. First,we describe the main issues in existing SCAs, then we theoretically analyze the effectiveness and complexity of our proposed SW-SCA —a method that can incorporate a sliding-window mechanism into almost all of the existing non-profiled SCAs. The experimental results for both simulated and physical traces verify the effectiveness of the SW-SCA and the appropriateness of its theoretical complexity.  相似文献   
4.
5.
本文在分析动车组一级修作业流程特点的基础上,将动车所调车作业计划优化问题构建为整数规划模型并设计了融合"股道均衡分配规则""股道无效占用时间最小化规则""冲突消解策略"的启发式算法对问题进行求解,以动车所实际案例为背景验证了模型和算法的有效性。结果表明,所提出优化模型和算法是有效的;所提启发式算法相比三类常见的调度方法具有明显的优越性。  相似文献   
6.
为了提高机器人足球的整体攻防能力,在动态攻防转换策略中建立了基于蚁群系统的混合通信机制,既增强了足球机器人的协作能力,又避免了足球机器人陷入冲突或任务死锁状态,增加了攻防转换的灵活性。在该通信机制的基础上采用攻防区域划分的方法,以球的位置为驱动信息,通过信息素来确定变换队形。在FIRA仿真平台中实验表明,基于蚁群混合通信机制的动态攻防转换策略使得仿真足球机器人在比赛过程中表现出更优异的性能,改善了球队的整体攻防能力,可有效应用于机器人足球比赛中。  相似文献   
7.
针对传统方法难以分析掺烧生活垃圾后的水泥窑复杂燃烧特性的问题,引入数据挖掘技术,以国内某水泥厂为对象,采集相关参数数据,使用稳定性选择算法分析各参数对煤耗与NOx排量的影响系数,通过随机森林算法建立煤耗与NOx排量的数学模型,结合K-means聚类算法得出关键优化参数及其最优值。结果表明,该方法能够建立精确的煤耗与NOx排量模型,挖掘出节能减排的关键优化参数及其最优目标值。通过改善关键优化参数至最优值,能够大大降低煤耗与NOx排量,可指导水泥厂优化窑内燃烧特性。  相似文献   
8.
Financial distress prediction (FDP) has been widely considered as a promising approach to reducing financial losses. While financial information comprises the traditional factors involved in FDP, nonfinancial factors have also been examined in recent studies. In light of this, the purpose of this study is to explore the integrated factors and multiple models that can improve the predictive performance of FDP models. This study proposes an FDP framework to reveal the financial distress features of listed Chinese companies, incorporating financial, management, and textual factors, and evaluating the prediction performance of multiple models in different time spans. To develop this framework, this study employs the wrapper-based feature selection method to extract valuable features, and then constructs multiple single classifiers, ensemble classifiers, and deep learning models in order to predict financial distress. The experiment results indicate that management and textual factors can supplement traditional financial factors in FDP, especially textual ones. This study also discovers that integrated factors collected 4 years prior to the predicted benchmark year enable a more accurate prediction, and the ensemble classifiers and deep learning models developed can achieve satisfactory FDP performance. This study makes a novel contribution as it expands the predictive factors of financial distress and provides new findings that can have important implications for providing early warning signals of financial risk.  相似文献   
9.
10.
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