全文获取类型
收费全文 | 728篇 |
免费 | 171篇 |
国内免费 | 41篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 44篇 |
2020年 | 25篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 30篇 |
2016年 | 10篇 |
2015年 | 35篇 |
2014年 | 51篇 |
2013年 | 48篇 |
2012年 | 53篇 |
2011年 | 44篇 |
2010年 | 52篇 |
2009年 | 71篇 |
2008年 | 47篇 |
2007年 | 54篇 |
2006年 | 38篇 |
2005年 | 33篇 |
2004年 | 21篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 28篇 |
2000年 | 15篇 |
1999年 | 33篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有940条查询结果,搜索用时 15 毫秒
681.
随着图像技术的广泛应用,图像的质量评估问题,即信息的可靠性问题,在自动化系统中的地位日益重要。全信息图像质量评估是针对目标原始图像和被测图像都已知时的被测图像评估。从历史发展角度系统地回顾了20世纪60年代以来全信息图像质量评估研究的发展历程和现状,并从算法的构成角度对代表性的全信息图像质量评估算法进行了分类与分析。由于图像质量评估函数的性能测定在其研究中具有重要的地位,对于图像质量评估函数的性能测定方案给予了说明。最后,从研究的深入角度上讨论图像质量评估研究的未来发展趋势。 相似文献
682.
683.
对高温燃气与带有平行冷却通道的再生冷却面板之间的三维耦合传热开展了数值研究,其中冷却通道内冷却剂为超临界压力煤油,并结合理论分析探讨了冷却面板构型对耦合传热的影响。结果表明:随燃气侧壁厚以及冷却通道宽度和高度的增大,燃气侧壁面温度升高,热流密度降低。研究还发现:冷却通道不同壁面传递给煤油的热量占比几乎不随燃气侧壁厚变化,但随冷却通道宽度和高度的改变而变化。 相似文献
684.
685.
机动目标跟踪是多机载预警雷达数据融合中的一个难点,传统的卡尔曼滤波本身不足以解决该问题.基于量测噪声协方差估计设计了一种可适用于机动目标的卡尔曼滤波器;引入了协方差交集,提出了一种针对多机载预警雷达数据融合中机动目标跟踪的新方法.仿真实验表明,该方法能够成功稳定地跟踪机动目标,与现有的主流方法相比,该方法的误差性能是最佳的. 相似文献
686.
687.
Ying Yuan Zhen-yang Liu Suo He Chao Ge Qing-bo Yu Yuan-feng Zheng Hai-fu Wang 《防务技术》2021,17(5):1687-1698
In this paper, the ballistic impact experiments, including impact test chamber and impact double-spaced plates, were conducted to study the reaction behaviors of a novel functionally graded reactive material (FGRM), which was composed of polytetrafluoroethylene/aluminum (PTFE/Al) and PTFE/Al/bismuth trioxide (Bi2O3). The experiments showed that the impact direction of the FGRM had a significant effect on the reaction. With the same impact velocity, when the first impact material was PTFE/Al/Bi2O3, compared with first impact material PTFE/Al, the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates. The theoretical model, which considered the shock wave generation and propagation, the effect of the shock wave on reaction efficiency, and penetration behaviors, was developed to analyze the reaction behaviors of the FGRM. The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials. The conclusion of this study provides significant information about the design and application of reactive materials. 相似文献
688.
Hong-bin Xie Hui-ya Yang Jian Yu Ming-yu Gao Jian-dong Shou You-tong Fang Jia-bin Liu Hong-tao Wang 《防务技术》2021,17(2):429-439
Electromagnetic railgun attracts more and more attention due to its advantage in speed,cost,and obscurity.It is found that the rail should withstand huge mechanical and thermal shocks during the launching operation.The forms of rail failure are accompanied by gouge,grooving,transition,and arc ablation,etc.The service life of the rail has become a bottleneck restricting the development of elec-tromagnetic railgun technology.A series of researches are carried out to solve rail failure,including analysing the failure mechanism and using various advanced rail materials.This paper provides a comprehensive review of rail materials,including material composition,preparation,microstructure,and properties.We begin from a short background of the requirement of the rail material.Then a detailed investigation of rail materials is described,and the performances of those materials are introduced.Finally,further development prospect of rail material is discussed. 相似文献
689.
Track tension is a major factor influencing the reliability of a track. In order to reduce the risk of track peel-off, it is necessary to keep track tension constant. However, it is difficult to measure the dynamic tension during off-road operation. Based on the analysis of the relation and external forces depending on free body diagrams of the idler, idler arm, road wheel and road arm, a theoretical estimation model of track tension is built. Comparing estimation results with multibody dynamics simulation results, the rationality of track tension monitor is validated. By the aid of this monitor, a track tension control system is designed, which includes a self-tuning proportional-integral-derivative (PID) controller based on radial basis function neural network, an electro-hydraulic servo system and an idler arm. The tightness of track can be adjusted by turning the idler arm. Simulation results of the vehicle starting process indicate that the controller can reach different expected tensions quickly and accurately. Compared with a traditional PID controller, the proposed controller has a stronger anti-disturbance ability by amending control pa-rameters online. 相似文献
690.