全文获取类型
收费全文 | 505篇 |
免费 | 10篇 |
国内免费 | 4篇 |
专业分类
航空 | 290篇 |
航天技术 | 162篇 |
综合类 | 11篇 |
航天 | 56篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2019年 | 7篇 |
2018年 | 20篇 |
2017年 | 8篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 22篇 |
2012年 | 10篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 23篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 23篇 |
2005年 | 19篇 |
2004年 | 12篇 |
2003年 | 16篇 |
2002年 | 4篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 5篇 |
1992年 | 12篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1986年 | 2篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 27篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1972年 | 6篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有519条查询结果,搜索用时 15 毫秒
511.
Eskelinen E. Ruuskanen P. Rasanen U. Kaleton M.-B. 《Aerospace and Electronic Systems Magazine, IEEE》1994,9(6):7-11
Most modern radar simulators are costly and need cumbersome operations while used. Besides, they have many features not suitable for preliminary level. Basic training of radio monitoring personnel can be carried out with a simple and inexpensive system capable of producing both staggered and frequency hopping pulse radar signals with radiation pattern modulation. For operator convenience the system is programmed with basic programming language 相似文献
512.
C. -U. Wagner D. Möhlmann K. Schäfer V. M. Mishin M. I. Matveev 《Space Science Reviews》1980,26(4):391-446
At the end of the sixties it became obvious that two-dimensional dynamo models can explain nearly all facts, which had been found morphologically for mean annual Sq-fields. During the recent decade new or improved methods to measure electric fields (e.g. incoherent scatter facilities) and to investigate great data files have been developed. New informations received with these methods about the existence of regular variations of the Sq-field in dependence on season and universal time and about the electric field have been summarized in Section 2. All attempts to describe also these variations with a two-dimensional dynamo model did not lead to any success, but showed a strong theoretical over-estimation of the asymmetries. Therefore, it must be concluded that three-dimensional plasmaspheric current systems, taking into consideration the coupling between both hemispheres along the high-conducting magnetic field lines, are needed in order to explain the regular variations of the Sq -field. The basic equations for two- and three-dimensional dynamo models, different methods for the solution of these equations and the resulting models from different authors are compiled and discussed (Section 3).Based on all morphological and theoretical results a plasmaspheric-ionospheric current system has been constructed and some properties of the plasmaspheric field-aligned current distribution, have been derived. 相似文献
513.
514.
K.U. Grossmann P. Barthol W. Frings R. Hennig D. Offermann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):111-114
Absolute zenith intensities of the atomic oxygen fine structure emission at 63 μm were measured above Kiruna, Sweden, on 9 December 1981 in the altitude regime of 85 km to 237 km. The measured data are compared with theoretical predictions for this emission. Both local thermodynamic equilibrium (LTE) and non-LTE conditions were assumed for the model intensity calculations. The importance of the 63 μm emission as a cooling mechanism of the thermosphere is briefly discussed. 相似文献
515.
D. Müller 《Space Science Reviews》2001,99(1-4):105-116
We briefly review the available data on cosmic rays beyond the `knee, i.e., over the energy range from 1015 to more than 1020 eV. We discuss the observational status of the field, review some of the current attempts to explain the origin of these particles, and briefly survey the prospects of future measurements. 相似文献
516.
Andrew W. Stephan R. R. Meier Scott L. England Stephen B. Mende Harald U. Frey Thomas J. Immel 《Space Science Reviews》2018,214(1):42
The NASA Ionospheric Connection Explorer Far-Ultraviolet spectrometer, ICON FUV, will measure altitude profiles of the daytime far-ultraviolet (FUV) OI 135.6 nm and N2 Lyman-Birge-Hopfield (LBH) band emissions that are used to determine thermospheric density profiles and state parameters related to thermospheric composition; specifically the thermospheric column O/N2 ratio (symbolized as \(\Sigma\)O/N2). This paper describes the algorithm concept that has been adapted and updated from one previously applied with success to limb data from the Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. We also describe the requirements that are imposed on the ICON FUV to measure \(\Sigma\)O/N2 over any 500-km sample in daytime with a precision of better than 8.7%. We present results from orbit-simulation testing that demonstrates that the ICON FUV and our thermospheric composition retrieval algorithm can meet these requirements and provide the measurements necessary to address ICON science objectives. 相似文献
517.
In this study, in-plane mixed mode-I/II fatigue crack growth simulations and experiments are performed for the Al 7075-T651 aluminum alloy which is widely used in the aerospace industry. Tests are carried out under different mode mixity ratios to evaluate the applicability of a fracture criterion developed in a previous study to mixed mode-I/II fatigue crack growth tests. Results obtained from the analyses and experiments are compared with existing and developed criteria in terms of crack growth lives. Compact Tension Shear (CTS) specimens, which enable mixed mode loading with loading devices under different loading angles, are used in the simulations and experiments. In an effort to model and simulate the actual conditions in the experiments, crack surfaces of fractured specimens are scanned, crack paths are modeled exactly, and contacts are defined between the contact surfaces of a specimen and the loading device for each crack propagation step in the analyses. Having computed the mixed mode stress intensity factors from the numerical analyses, propagation life cycles are predicted by existing and the developed mixed mode-I/II criteria and then compared with experimental results. 相似文献
518.
对巨磁电阻材料La1-xZnxMnO3(x=0.1,0.3,0.5,0.7,0.9,1.0)样品的制备工艺、晶体结构、微观结构进行研究。结果表明,样品ZnO与MnO2固相反应的烧结温度和时间分别大于1300℃和6h时,反应生成具有四面体结构的ZnMnO3化合物;压制成型的压力对结构具有一定影响;不同浓度的Zn2 (x=0.1,0.3,0.5,0.7,0.9)掺杂样品在1350℃烧结12h后,均具有钙钛矿结构,但掺杂浓度在大于x=0.5时有新的衍射峰,产生新的物相,从而影响巨磁电阻效应性能。 相似文献
519.
利用中国岢岚站(38.7°N,111.6°W)法布里-珀罗干涉仪2013年7月至2014年11月的水平风场数据,对87,97,250km风场长期变化和行星波特征进行了研究.通过分析年振荡(AO)和半年振荡(SAO)振幅相位,将午夜风场与HWM07数据对比发现:87km和97km处FPI纬向风变化趋势与HWM07相近,而经向风相位落后于HWM07,从振幅上看,HWM07振幅偏大;250km处风场月变化大,FPI与HWM07差异大,HWM07模式的准确性需进一步考虑太阳活动和行星际磁场的影响.利用Lomb-Scargle功率谱以及最小二乘谐波拟合提取了三个高度的行星波振幅,其特征表明87km和97km处纬向风16日波秋季及冬春季活动强,而6.5日波最强振幅出现在春季和秋季,在中间层顶附近两种行星波活动均较弱;250km处经向行星波活动略强于纬向,经向风不同周期带的行星波最强振幅主要出现在5-9月,与电离层f0F2振荡特性的研究结果一致. 相似文献