全文获取类型
收费全文 | 5103篇 |
免费 | 361篇 |
国内免费 | 277篇 |
专业分类
航空 | 2723篇 |
航天技术 | 1648篇 |
综合类 | 219篇 |
航天 | 1151篇 |
出版年
2023年 | 27篇 |
2022年 | 96篇 |
2021年 | 103篇 |
2020年 | 71篇 |
2019年 | 90篇 |
2018年 | 124篇 |
2017年 | 125篇 |
2016年 | 103篇 |
2015年 | 127篇 |
2014年 | 184篇 |
2013年 | 194篇 |
2012年 | 217篇 |
2011年 | 279篇 |
2010年 | 238篇 |
2009年 | 255篇 |
2008年 | 294篇 |
2007年 | 187篇 |
2006年 | 193篇 |
2005年 | 166篇 |
2004年 | 136篇 |
2003年 | 174篇 |
2002年 | 146篇 |
2001年 | 140篇 |
2000年 | 114篇 |
1999年 | 125篇 |
1998年 | 132篇 |
1997年 | 118篇 |
1996年 | 96篇 |
1995年 | 115篇 |
1994年 | 117篇 |
1993年 | 73篇 |
1992年 | 85篇 |
1991年 | 43篇 |
1990年 | 46篇 |
1989年 | 82篇 |
1988年 | 41篇 |
1987年 | 33篇 |
1986年 | 36篇 |
1985年 | 114篇 |
1984年 | 80篇 |
1983年 | 80篇 |
1982年 | 60篇 |
1981年 | 103篇 |
1980年 | 25篇 |
1979年 | 27篇 |
1978年 | 33篇 |
1977年 | 25篇 |
1975年 | 39篇 |
1972年 | 33篇 |
1971年 | 25篇 |
排序方式: 共有5741条查询结果,搜索用时 46 毫秒
121.
122.
面向对象的双轴混排加力涡扇发动机详细非线性实时仿真模型研究 总被引:1,自引:5,他引:1
本文就双轴加力涡扇发动机详细非线性实时仿真模型进行了研究。采用框架灵活方便、具有可扩展性的 VC 语言 ,在 P 45 0计算机上实现了一台双轴混排加力涡扇发动机的实时仿真 ,可准确模拟发动机及其部件的工作状况。发动机流路的平均计算时间为 0 .5 42 ms,一个工作点的计算时间小于 2 5 ms。此模型的建模方法具有通用性 ,可适用于其他类型发动机的实时建模要求。经在火力 /飞行 /推进综合控制仿真系统中的应用 ,证明此模型完全满足实时模拟真实发动机的要求 相似文献
123.
美陆军制导武器试验半实物仿真技术综述 总被引:6,自引:0,他引:6
主要综述美国陆军制导武器试验的仿真技术和设施,同时介绍仿真试验中使用的几种典型的目标景象投影技术,并说明了它们的应用范围和优缺点。最后介绍了当前制导武器试验仿真技术的发展趋势。 相似文献
124.
L. Jacquin D. Fabre D. Sipp V. Theofilis H. Vollmers 《Aerospace Science and Technology》2003,7(8):94-593
This paper presents a review of theoretical and experimental results on stability and other unsteady properties of aircraft wakes. The basic mechanisms responsible for the propagation and the amplification of perturbation along vortices, namely the Kelvin waves and the cooperative instabilities, are first detailed. These two generic unsteady mechanisms are described by considering asymptotic linear stability analysis of model flows such as vortex filaments or Lamb–Oseen vortices. Extension of the linear analysis to more representative flows, using a biglobal stability approach, is also described. Experimental results obtained using LDV, hot wire and PIV in wind tunnels are presented and they are commented upon the light of theory. 相似文献
125.
The application of existing estimation theory to the problem of specification and performance of passive sonar spectral estimators is considered. The classification function is addressed, so that the signal is assumed to be present, and so that the energy arrival angle is known. The spatial filter considered is a line array of M equally spaced omnidirectional hydrophones. Signal and ambient noise are both zero-mean, wide-sense, stationary Gaussian random processes that differ in their spatial correlation across the face of the array. The signal is a plane wave that can be made totally spacially corrected between array elements by inserting delays between sensors to invert the signal propagation delay. The noise correlation is a function of frequency, bandwidth, element separation, and the relative time delay between sensors. Under these assumptions, the Cramer-Rao lower bound is derived for the class of unbiased estimates of signal power in a narrow frequency band at the hydrophone in the presence of correlated ambient noise of known power. The bound is examined numerically, resulting in a threshold phenomenon with M that constitutes a new design consideration. In addition, there is a striking insensitivity to realistic values of ambient noise correlation, and there are ranges in signal-to-noise ratio for which one gains more by increasing M than by increasing the bandwidth-time product. Specific processors, including a new unbiased estimator when noise power is unknown, are developed. 相似文献
126.
The complex angle (CA) method for resolving a low angle target from its multipath signal is evaluated in the presence of system noise. It is shown that standard deviation improvements of around 3-to-1 can be achieved at a 20-dB signal-to-noise power ratio relative to a normal monopulse system without the CA. It is also shown that the CA method is unbiased, giving bias improvements of as much as 100 times relative to normal monopulse. Evaluation of the assumptions in the technique shows very little sensitivity to knowledge of the reflecting surface's conductivity or dielectric constant. However, the method is somewhat sensitive to knowledge of surface roughness. 相似文献
127.
128.
吴昌忠%陈静%陈怀宁%林泉洪 《宇航材料工艺》2005,35(3):17-20,30
综述了钛及钛合金高温钎焊结构在现代工业中的应用。在分析了钛基钎料应用和发展的基础上,重点分析了钎焊接头的组织与接头性能的关系以及影响因素。指明接头组织中脆性金属间化合物相的存在形态是决定接头性能的主要因素,接头间隙和钎焊时间决定了接头的组织形态,从而影响接头的性能。钛及钛合金高温钎焊接头的拉伸性能、高温性能和疲劳性能是优越的,而接头氧化后的性能急剧下降。并展望了钛基材料连接的发展方向。 相似文献
129.
130.
A scheme is presented for the identification of naval vessels via active multiple-frequency radar interrogation. A major virtue of the described method is the use of a response waveform synthesized using amplitude data only. A prediction correlation using natural resonances associated with substructures on the vessels is applied to synthetically generated matched-filter response waveforms. The identification scheme is tested using measured model data for 8 vessels on a simulated sea surface. A correct identification probability of roughly 77 percent is obtained. 相似文献