全文获取类型
收费全文 | 2627篇 |
免费 | 737篇 |
国内免费 | 273篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 43篇 |
2021年 | 50篇 |
2020年 | 49篇 |
2019年 | 33篇 |
2018年 | 33篇 |
2017年 | 124篇 |
2016年 | 187篇 |
2015年 | 122篇 |
2014年 | 230篇 |
2013年 | 188篇 |
2012年 | 243篇 |
2011年 | 233篇 |
2010年 | 138篇 |
2009年 | 252篇 |
2008年 | 194篇 |
2007年 | 189篇 |
2006年 | 200篇 |
2005年 | 186篇 |
2004年 | 173篇 |
2003年 | 118篇 |
2002年 | 114篇 |
2001年 | 91篇 |
2000年 | 71篇 |
1999年 | 68篇 |
1998年 | 69篇 |
1997年 | 44篇 |
1996年 | 38篇 |
1995年 | 27篇 |
1994年 | 30篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 7篇 |
1988年 | 4篇 |
排序方式: 共有3637条查询结果,搜索用时 15 毫秒
941.
预警机作为C4ISR的空中情报探测中心及指挥控制中心,在信息化作战中具有十分重要的战略和战术价值。针对预警机执行作战任务的特点,通过对战场环境中影响预警机生存力的因素进行分析,结合预警机的作战模式和流程,定义出预警机的生存概率函数。基于该概率函数,建立了一种预警机战场生存力评估模型,并利用蒙特卡洛方法对4种典型的预警机作战场景进行了仿真评估,验证了模型的有效性。最后,结合该模型提出提高预警机在战场中生存的手段。 相似文献
942.
943.
利用2006—2012年北半球冬季低纬度地区(30°S~30°N)无线电探空站数据及全球大气成分和气候监测再分析数据对1000 h Pa~200 h Pa高度层的气象、电离层与气候星座观测系统全球定位系统掩星反演的比湿廓线进行了精度和可靠性验证。结果表明,水汽对气象、电离层与气候星座观测系统掩星反演影响较大,尤其在中、低对流层及热带地区等水汽含量比较大的地区,且气象、电离层与气候星座观测系统掩星数据在850 hpa以下可能并不太适用于评估其他数据。 相似文献
944.
945.
946.
947.
948.
949.
In the literature two common macroscopic evacuation planning approaches exist: The dynamic network flow approach and the Cell–Transmission–Based approach. Both approaches have advantages and disadvantages. Many efficient solution approaches for the dynamic network flow approach exist so that realistic problem instances can be considered. However, the consideration of (more) realistic aspects (eg, density dependent travel times) results in non‐linear model formulations. The Cell‐Transmission‐Based approach on the other hand considers realistic traffic phenomena like shock waves and traffic congestion, but this approach leads to long computational times for realistic problem instances. In this article, we combine the advantages of both approaches: We consider a Cell‐Transmission‐Based Evacuation Planning Model (CTEPM) and present a network flow formulation that is equivalent to the cell‐based model. Thus, the computational costs of the CTEPM are enormously reduced due to the reformulation and the detailed representation of the traffic flow dynamics is maintained. We investigate the impacts of various evacuation scenario parameters on the evacuation performance and on the computational times in a computational study including 90 realistic instances. 相似文献
950.
The idea of deploying noncollocated sources and receivers in multistatic sonar networks (MSNs) has emerged as a promising area of opportunity in sonar systems. This article is one of the first to address point coverage problems in MSNs, where a number of points of interest have to be monitored in order to protect them from hostile underwater assets. We consider discrete “definite range” sensors as well as various diffuse sensor models. We make several new contributions. By showing that the convex hull spanned by the targets is guaranteed to contain optimal sensor positions, we are able to limit the solution space. Under a definite range sensor model, we are able to exclude even more suboptimal solutions. We then formulate a nonlinear program and an integer nonlinear program to express the sensor placement problem. To address the nonconvex single‐source placement problem, we develop the Divide Best Sector (DiBS) algorithm, which quickly provides an optimal source position assuming fixed receivers. Starting with a basic implementation of DiBS, we show how incorporating advanced sector splitting methods and termination conditions further improve the algorithm. We also discuss two ways to use DiBS to find multiple source positions by placing sensors iteratively or simultaneously. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 287–304, 2017 相似文献