全文获取类型
收费全文 | 5172篇 |
免费 | 15篇 |
国内免费 | 16篇 |
专业分类
航空 | 2400篇 |
航天技术 | 1816篇 |
综合类 | 191篇 |
航天 | 796篇 |
出版年
2021年 | 37篇 |
2019年 | 32篇 |
2018年 | 85篇 |
2017年 | 51篇 |
2016年 | 58篇 |
2014年 | 113篇 |
2013年 | 123篇 |
2012年 | 117篇 |
2011年 | 196篇 |
2010年 | 124篇 |
2009年 | 204篇 |
2008年 | 237篇 |
2007年 | 125篇 |
2006年 | 119篇 |
2005年 | 136篇 |
2004年 | 135篇 |
2003年 | 158篇 |
2002年 | 192篇 |
2001年 | 205篇 |
2000年 | 84篇 |
1999年 | 123篇 |
1998年 | 152篇 |
1997年 | 106篇 |
1996年 | 153篇 |
1995年 | 177篇 |
1994年 | 132篇 |
1993年 | 85篇 |
1992年 | 127篇 |
1991年 | 53篇 |
1990年 | 46篇 |
1989年 | 105篇 |
1988年 | 49篇 |
1987年 | 42篇 |
1986年 | 47篇 |
1985年 | 174篇 |
1984年 | 141篇 |
1983年 | 101篇 |
1982年 | 131篇 |
1981年 | 158篇 |
1980年 | 46篇 |
1979年 | 44篇 |
1978年 | 46篇 |
1977年 | 44篇 |
1976年 | 33篇 |
1975年 | 37篇 |
1974年 | 44篇 |
1972年 | 32篇 |
1971年 | 27篇 |
1970年 | 36篇 |
1969年 | 41篇 |
排序方式: 共有5203条查询结果,搜索用时 140 毫秒
931.
Cosmic Research - We have considered procedure and results of the experimental study for spectral characteristics of self emission from laboratory models of electric thrusters with closed electron... 相似文献
932.
The techniques of forming the mobile sliding manifolds and vector controls, which bring these systems into the sliding modes under continuous action of uncertain factors, namely limited disturbances and total errors in measurements, are developed for dynamic systems with discontinuous control. The techniques are applicable for effective control of complex aerospace objects. 相似文献
933.
934.
Structures for radar detection in compound Gaussian clutter 总被引:1,自引:0,他引:1
Sangston K.J. Gini F. Greco M.V. Farina A. 《IEEE transactions on aerospace and electronic systems》1999,35(2):445-458
The problem of coherent radar target detection in a background of non-Gaussian clutter modeled by a compound Gaussian distribution is studied here. We show how the likelihood ratio may be recast into an estimator-correlator form that shows that an essential feature of the optimal detector is to compute an optimum estimate of the reciprocal of the unknown random local power level. We then proceed to show that the optimal detector may be recast into yet another form, namely a matched filter compared with a data-dependent threshold. With these reformulations of the optimal detector, the problem of obtaining suboptimal detectors may be systematically studied by either approximating the likelihood ratio directly, utilizing a suboptimal estimate in the estimator-correlator structure or utilizing a suboptimal function to model the data-dependent threshold in the matched filter interpretation. Each of these approaches is studied to obtain suboptimal detectors. The results indicate that for processing small numbers of pulses, a suboptimal detector that utilizes information about the nature of the non-Gaussian clutter can be implemented to obtain quasi-optimal performance. As the number of pulses to be processed increases, a suboptimal detector that does not require information about the specific nature of the non-Gaussian clutter may be implemented to obtain quasi-optimal performance 相似文献
935.
W. H. Matthaeus G. P. Zank R. J. Leamon C. W. Smith D. J. Mullan S. Oughton 《Space Science Reviews》1999,87(1-2):269-275
Mechanisms for the deposition of heat in the lower coronal plasma are discussed, emphasizing recent attempts to reconcile
the fluid and kinetic perspectives. Structures at the MHD scales are believed to act as reservoirs for fluctuation energy,
which in turn drive a nonlinear cascade process. Kinetic processes act at smaller spatial scales and more rapid time scales.
Cascade-driven processes are contrasted with direct cyclotron absorption, and this distinction is echoed in the contrast between
frequency and wavenumber spectra of the fluctuations. Observational constraints are also discussed, along with estimates of
the relative efficiency of cascade and cyclotron processes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
936.
M R Sims C T Pillinger I P Wright J Dowson S Whitehead A Wells J E Spragg G Fraser L Richter H Hamacher A Johnstone N P Meredith C de la Nougerede B Hancock R Turner S Peskett A Brack J Hobbs M Newns A Senior M Humphries H U Keller N Thomas J S Lingard T C Ng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(11):1925-1928
The aim of the proposed Beagle 2 small lander for ESA's 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X-ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies. 相似文献
937.
938.
Sai F. Lee 《航空学报》1993,14(12):596-602
<正> The terrain profile at several airports has caused some difficulty with autolands on the DC-10 and MD-80. Some operators have reported that the pilot had to disconnect the flight guidance system during flare and land manually. At present, the autoland guidance system is not uniquely designed to handle the variations of terrain. Since there is no accurate substitute for radio altitude(h_(rad)) the only variable left to improve is radio altitude rate (h_(rad)). 相似文献
939.
我们在进行某一环形燃烧室扇形形试验件的试验研究时,用热电偶测量了燃烧室内的温度分布。一般来说,热电偶不能获得与热燃气同样的温度,这是因为热电偶和周围环境有着辐射能量的交换。通常是热电偶节点向冷的壁面辐射能量。在稳态时,燃气通过对流传热向热电偶节点提供能量来平衡这一损失。这就是说,热电偶节点测得的温度较燃气的真实温度要低,这一温差就是由辐射热损失造成的。下面介绍对此热辐射损失进行修正的一个简化方法。 相似文献
940.