全文获取类型
收费全文 | 1627篇 |
免费 | 307篇 |
国内免费 | 320篇 |
专业分类
航空 | 1070篇 |
航天技术 | 478篇 |
综合类 | 285篇 |
航天 | 421篇 |
出版年
2024年 | 9篇 |
2023年 | 21篇 |
2022年 | 57篇 |
2021年 | 64篇 |
2020年 | 66篇 |
2019年 | 53篇 |
2018年 | 65篇 |
2017年 | 58篇 |
2016年 | 34篇 |
2015年 | 52篇 |
2014年 | 86篇 |
2013年 | 82篇 |
2012年 | 98篇 |
2011年 | 106篇 |
2010年 | 118篇 |
2009年 | 123篇 |
2008年 | 104篇 |
2007年 | 83篇 |
2006年 | 82篇 |
2005年 | 64篇 |
2004年 | 43篇 |
2003年 | 55篇 |
2002年 | 47篇 |
2001年 | 50篇 |
2000年 | 65篇 |
1999年 | 76篇 |
1998年 | 69篇 |
1997年 | 50篇 |
1996年 | 60篇 |
1995年 | 43篇 |
1994年 | 53篇 |
1993年 | 41篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 28篇 |
1989年 | 29篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2254条查询结果,搜索用时 801 毫秒
701.
702.
基于神经网络的超精密车床圆柱度误差补偿技术研究 总被引:1,自引:0,他引:1
根据所研制的超精密亚微米车床的具体特点,提出了一种基于神经网络的工件圆柱度误差补偿方法,并据此建立了误差补偿控制系统,实验结果证明所提方法简单易行,在超精密车削中应用前景广阔。 相似文献
703.
Minghui Li Yilong Lu 《IEEE transactions on aerospace and electronic systems》2006,42(1):103-112
We present a robust solution for data reduction in array processing. The purpose is to reduce the computation and improve the performance of applied signal processing algorithms by mapping the data into a lower dimension beamspace (BS) through a transformation. Nulls steering to interference are incorporated into a transformation using the subspace projection technique, and the BS spatial spectrum estimation accuracy is evaluated and maximized with a measure. The derived transformation tries to preserve the full-dimension Cramer-Rao bounds (CRBs) for the parameters of interest while rejecting undesired signals effectively. When compared with an optimal method and an adaptive approach, simulation results show that significant improvements are obtained in terms of BS direction-of-arrival (DOA) estimation root-mean-squared error (RMSE), bias, and resolution probability. 相似文献
704.
FSS基本缝隙单元频率特性的实验研究 总被引:1,自引:0,他引:1
频率选择表面 (FSS )受到众多的设计参数的影响 ,十分复杂 ,通过实验手段研究FSS结构的基本振子的谐振特性是十分重要的。本文针对矩形缝隙这种基本FSS缝隙单元 ,在 8~ 1 7GHz频段上进行了扫频实验 ,由此分析和总结了几何参数和物理参数对其频率特性的影响 ,最后给出了频率特性随几何参数和物理参数变化而变化的趋势 相似文献
705.
Ultra-wideband radar and random signal radar are two types of newly-developed radar systems. This paper introduces the special advantages of the combination of ultra-wideband technology and random signal radar to the international radar community. It shows that these two radar systems have a very close relationship in nature and can gain significant benefits from each other. It can be anticipated that the random signal modulated waveform will open many potential possibilities for the applications of ultra-wideband radar systems to civilian operating environments. 相似文献
706.
707.
本文介绍了一种测液体粘滞系数的方法-“落球法”,该方法装置简单,原理清楚,有利于拓宽学生的视野,培养和提高学生的实际技能和处理数据的能力。 相似文献
708.
Weixian Liu Yilong Lu Fu J.S. 《IEEE transactions on aerospace and electronic systems》2002,38(2):601-612
Detection system with distributed sensors and data fusion. are increasingly being used by surveillance systems. There has been a great deal of theoretical study on decentralized detection networks composed of identical or non-identical sensors. To solve the resulting nonlinear system, exhaustive search and some crude approximations are adopted. However, those methods often cause either the system to be insensitive to some parameters or the suboptimal results. In this paper, a novel flexible genetic algorithm is investigated to obtain the optimal results on constant false alarm rate data fusion. Using this approach, all system parameters are directly coded in decimal chromosomes and they can be optimized simultaneously. The simulation results show that adopting the proposed approach, one can achieve better performances than the reported methods and results 相似文献
709.
Detonation waves induced by a confined wedge 总被引:2,自引:0,他引:2
An auto-ignition detonation phenomenon can be initiated by a wedge confined in a channel. A new, self-sustaining, normal detonation wave engine concept is proposed. The detonation processes were numerically modeled with a simplified two-dimensional wedged channel flow that was deemed to emulate a real three-dimensional configuration. The results showed that within certain ranges of incoming flow Mach number or wedge angle, detonation could be self ignited in the channel. The study furthermore investigated the detonation waves based on three different detonation initiation positions. Different configurations of the detonation waves were observed and analyzed. The performance of the different detonation wave configurations was estimated and compared. 相似文献
710.
本文根据液晶的减摩作用,研究了液晶作为润滑添加剂在改善机床爬行状况,即降低其爬行临界速度方面的实际应用。我们选择了三种液晶,每种液晶都按6种不同的浓度加入到N32(旧标准HJ20)机械油中,在M7130型平面磨床上进行了试验。试验结果表明,液晶作为润滑添加剂确定具有良好的防爬作用,且防爬效果与液晶的种类及其添加浓度有关。 相似文献