全文获取类型
| 收费全文 | 500篇 |
| 免费 | 16篇 |
| 国内免费 | 5篇 |
专业分类
| 521篇 |
出版年
| 2025年 | 5篇 |
| 2024年 | 3篇 |
| 2023年 | 8篇 |
| 2022年 | 7篇 |
| 2021年 | 7篇 |
| 2020年 | 8篇 |
| 2019年 | 8篇 |
| 2018年 | 4篇 |
| 2017年 | 17篇 |
| 2016年 | 19篇 |
| 2015年 | 15篇 |
| 2014年 | 20篇 |
| 2013年 | 22篇 |
| 2012年 | 30篇 |
| 2011年 | 37篇 |
| 2010年 | 19篇 |
| 2009年 | 40篇 |
| 2008年 | 32篇 |
| 2007年 | 27篇 |
| 2006年 | 30篇 |
| 2005年 | 18篇 |
| 2004年 | 26篇 |
| 2003年 | 21篇 |
| 2002年 | 25篇 |
| 2001年 | 11篇 |
| 2000年 | 8篇 |
| 1999年 | 10篇 |
| 1998年 | 4篇 |
| 1997年 | 8篇 |
| 1996年 | 8篇 |
| 1995年 | 9篇 |
| 1994年 | 2篇 |
| 1993年 | 3篇 |
| 1992年 | 2篇 |
| 1991年 | 2篇 |
| 1990年 | 4篇 |
| 1989年 | 1篇 |
| 1988年 | 1篇 |
排序方式： 共有521条查询结果，搜索用时 0 毫秒
101.
针对常用的运动声源定位方法存在计算量较大或测试难度大的问题,提出一种基于阵列信号短时处理的运动声源定位方法。分析单、双五元十字阵列的定位性能,并基于单阵列的高精度定向能力,借鉴波束形成中帧处理思想,使用双阵列方位交叉的方法实现声源运动定位。使用自行火炮的发动机周期噪声作为模拟声源,进行外场定位实验,对参与短时相关数据的截取原则和传播路径补偿进行研究。实验结果表明,该方法能够有效实现周期声源的运动定位,最大相对误差保持在5%的水平。 相似文献
102.
基于扩展Petri网的动态服务聚合流程描述模型及其BPEL4WS表示方法 总被引：2，自引：0，他引：2
针对现有服务聚合流程建模方法的不足,基于扩展Petri网提出了一种新的服务聚合流程/资源描述模型WSCP/R-net,有效解决了动态服务聚合流程模型中不确定路径选择和服务的动态变化性问题。给出了WSCP/R-net模型向BPEL4WS的转换算法,并以城市应急处理为例说明了转换算法的有效性。 相似文献
103.
We consider the problem of efficiently scheduling deliveries by an uncapacitated courier from a central location under online arrivals. We consider both adversary‐controlled and Poisson arrival processes. In the adversarial setting we provide a randomized (3βΔ/2δ ? 1) ‐competitive algorithm, where β is the approximation ratio of the traveling salesman problem, δ is the minimum distance between the central location and any customer, and Δ is the length of the optimal traveling salesman tour overall customer locations and the central location. We provide instances showing that this analysis is tight. We also prove a 1 + 0.271Δ/δ lower‐bound on the competitive ratio of any algorithm in this setting. In the Poisson setting, we relax our assumption of deterministic travel times by assuming that travel times are distributed with a mean equal to the excursion length. We prove that optimal policies in this setting follow a threshold structure and describe this structure. For the half‐line metric space we bound the performance of the randomized algorithm in the Poisson setting, and show through numerical experiments that the performance of the algorithm is often much better than this bound. 相似文献
104.
We consider a stochastic partially observable system that can switch between a normal state and a transient abnormal state before entering a persistent abnormal state. Only the persistent abnormal state requires alarms. The transient and persistent abnormal states may be similar in appearance, which can result in excess false alarms. We propose a partially observable Markov decision process model to minimize the false alarm rate, subject to a given upper bound on the expected alarm delay time. The cost parameter is treated as the Lagrange multiplier, which can be estimated from the bound of the alarm delay. We show that the optimal policy has a control‐limit structure on the probability of persistent abnormality, and derive closed‐form bounds for the control limit and present an algorithm to specify the Lagrange multiplier. We also study a specialized model where the transient and persistent abnormal states have the same observation distribution, in which case an intuitive “watchful‐waiting” policy is optimal. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 320–334, 2016 相似文献
105.
Conventional control charts are often designed to optimize out‐of‐control average run length (ARL), while constraining in‐control ARL to a desired value. The widely employed grid search approach in statistical process control (SPC) is time‐consuming with unsatisfactory accuracy. Although the simulation‐based ARL gradient estimators proposed by Fu and Hu [Manag Sci 45 (1999), 395–413] can alleviate this issue, it still requires a large number of simulation runs to significantly reduce the variance of gradient estimators. This article proposes a novel ARL gradient estimation approach based on integral equation for efficient analysis and design of control charts. Although this article compares with the results of Fu and Hu [Manag Sci 45 (1999), 395–413] based on the exponentially weighted moving average (EWMA) control chart, the proposed approach has wide applicability as it can generally fit into any control chart with Markovian property under any distributions. It is shown that the proposed method is able to provide a fast, accurate, and easy‐to‐implement algorithm for the design and analysis of EWMA charts, as compared to the simulation‐based gradient estimation method. Moreover, the proposed gradient estimation method facilitates the computation of high‐order derivatives that are valuable in sensitivity analysis. The code is written in Matlab, which is available on request. © 2014 Wiley Periodicals, Inc. Naval Research Logistics 61: 223–237, 2014 相似文献
106.
操作系统是紧靠硬件的基础软件,它既是应用软件安全的坚实基础,又是硬件不安全因素的屏蔽器.在操作系统安全隐患和嵌入式操作系统技术特点的基础上,提出信息保护、空间域保护和时间域保护等增强操作系统安全性的几种方法,以提高嵌入式系统抗击系统本身缺陷或敌方恶意攻击等安全威胁的能力.上述几种安全保护技术已在嵌入式Linux中进行验证,并取得满意的结果. 相似文献
107.
108.
109.
This study addresses cyclic scheduling in robotic flowshops with bounded work‐in‐process (WIP) levels. The objective is to minimize the cycle time or, equivalently, to maximize the throughput, under the condition that the WIP level is bounded from above by a given integer number. We present several strongly polynomial algorithms for the 2‐cyclic robotic flowshop scheduling problems for various WIP levels. © 2010 Wiley Periodicals, Inc. Naval Research Logistics 58: 1–16, 2011 相似文献
110.
Sub-Saharan Africa has witnessed the end of foreign colonial rule, the rise and fall of autocratic political regimes, and the disappearance of statist command economies. The challenges were to turn populations into coherent nations owing allegiance to the state; to democratise the state structures that govern these populations; and to liberalise the rules that regulate economic transactions. An important source to assess these prospects are the views and attitudes of ordinary Africans. This essay reflects on the original data derived from a crossnational research project. Nine African states were surveyed between 1999 and 2000. An attempt is made to gather some propositions from the analysis of the data. Many present serious challenges to common wisdom about African politics. It appears that the process of nationbuilding has created coherent political communities with high levels of national identity; that democratising the state in Africa builds on existing indigenous demands from ordinary Africans; and that economic liberalisation proceeds in the face of a mixed set of values about market and state. 相似文献