全文获取类型
收费全文 | 5208篇 |
免费 | 8篇 |
国内免费 | 10篇 |
专业分类
航空 | 2206篇 |
航天技术 | 1757篇 |
综合类 | 24篇 |
航天 | 1239篇 |
出版年
2021年 | 48篇 |
2019年 | 31篇 |
2018年 | 166篇 |
2017年 | 122篇 |
2016年 | 133篇 |
2015年 | 52篇 |
2014年 | 146篇 |
2013年 | 195篇 |
2012年 | 162篇 |
2011年 | 225篇 |
2010年 | 178篇 |
2009年 | 282篇 |
2008年 | 294篇 |
2007年 | 163篇 |
2006年 | 122篇 |
2005年 | 153篇 |
2004年 | 142篇 |
2003年 | 176篇 |
2002年 | 119篇 |
2001年 | 191篇 |
2000年 | 78篇 |
1999年 | 105篇 |
1998年 | 114篇 |
1997年 | 99篇 |
1996年 | 95篇 |
1995年 | 156篇 |
1994年 | 128篇 |
1993年 | 62篇 |
1992年 | 88篇 |
1991年 | 24篇 |
1990年 | 39篇 |
1989年 | 83篇 |
1988年 | 40篇 |
1987年 | 34篇 |
1986年 | 40篇 |
1985年 | 133篇 |
1984年 | 115篇 |
1983年 | 85篇 |
1982年 | 100篇 |
1981年 | 138篇 |
1980年 | 38篇 |
1979年 | 24篇 |
1978年 | 43篇 |
1977年 | 25篇 |
1976年 | 19篇 |
1975年 | 37篇 |
1974年 | 26篇 |
1973年 | 21篇 |
1972年 | 28篇 |
1971年 | 19篇 |
排序方式: 共有5226条查询结果,搜索用时 100 毫秒
501.
Two versions of a microwave feedback radiometer have been built and tested. One used an electromechanical feedback system; the other, an all-electronic system. The response of the servo loops proved to be fast enough and linear enough for almost any radiometer application. The rms noise fluctuation was the same as that of a Dicke radiometer. Stability was excellent even under adverse environmental conditions. 相似文献
502.
Shtessel Yuri B. Shkolnikov Ilya A. Levant Arie 《IEEE transactions on aerospace and electronic systems》2009,45(1):110-124
A new smooth second-order sliding mode control (SSOSM) is proposed and proved for a system driven by uncertain sufficiently smooth disturbances. The main target application of this technique, the missile interceptor guidance-control system against targets performing evasive maneuvers, is considered to demonstrate benefits of this design for a two-loop integration of guidance and flight control systems. The designed guidance-control system performance is verified via computer simulations using a miniature hypervelocity kinetic energy endo-atmospheric interceptor planar model. 相似文献
503.
J.L. Hall D. Fairbrother T. Frederickson V.V. Kerzhanovich M. Said C. Sandy J. Ware C. Willey A.H. Yavrouian 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
This paper describes the design, fabrication and testing of a full scale prototype balloon intended for long duration flight in the upper atmosphere of Venus. The balloon is 5.5 m in diameter and is designed to carry a 45 kg payload at an altitude of 55 km. The balloon material is a 180 g/m2 multi-component laminate comprised of the following layers bonded together from outside to inside: aluminized Teflon film, aluminized Mylar film, Vectran fabric and a polyurethane coating. This construction provides the required balloon functional characteristics of low gas permeability, sulfuric acid resistance and high strength for superpressure operation. The design burst superpressure is 39,200 Pa which is predicted to be 3.3 times the worst case value expected during flight at the highest solar irradiance in the mission profile. The prototype is constructed from 16 gores with bi-taped seams employing a sulfuric acid resistant adhesive on the outside. Material coupon tests were performed to evaluate the optical and mechanical characteristics of the laminate. These were followed by full prototype tests for inflation, leakage and sulfuric acid tolerance. The results confirmed the suitability of this balloon design for use at Venus in a long duration mission. The various data are presented and the implications for mission design and operation are discussed. 相似文献
504.
505.
J.S. Kaastra R. Lieu T. Tamura F.B.S. Paerels J.W. den Herder 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2504-2508
We discuss the detection of soft excess X-ray emission in a sample of 19 clusters of galaxies observed by XMM-Newton. In 6/19 clusters evidence for a soft X-ray excess is found. Four of these clusters show soft X-ray and O VII line emission from gas with a temperature of 0.2 keV. The centroid of this oxygen line is consistent with the redshift of the cluster. The intensity and spatial extend of the soft excess agrees with previous PSPC measurements. These observations are interpreted as emission from warm-hot intergalactic medium filaments, with density enhancements near the cluster centers, consistent with theoretical predictions. In the other two soft excess clusters a non-thermal origin is consistent with the data. 相似文献
506.
S. I. Solovyev V. A. Mullayarov D. G. Baishev E. S. Barkova S. N. Samsonov 《Cosmic Research》2004,42(6):607-613
Modulation of the VLF emission and riometric absorption by Pc5 geomagnetic pulsations is studied in the period of strong geomagnetic disturbances on October 30–31, 2003. Some conclusions about the regime of pitch-angular diffusion into the loss cone are made. The better coincidence of VLF emission modulation with geomagnetic pulsations in other longitude sectors is explained by the global character of excitation of the pulsations and by damping of their amplitudes at the meridian of observation of the VLF emission, which is associated with intensification of auroral electrojets.Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 6, 2004, pp. 632–639.Original Russian Text Copyright © 2004 by Solovyev, Mullayarov, Baishev, Barkova, Samsonov. 相似文献
507.
Spatial structure of the magnetosheath of the Earth was studied under the conditions when no sharp (more than 40° during 5
min) changes in the interplanetary magnetic field direction were observed. On the basis of 24 flights of the Interball-1 satellite through the magnetosheath, it is found that three regions differing from each other by parameters of the field
and plasma can be observed in the magnetosheath under the above-indicated conditions. These regions also differ from the solar
wind region before front of the Earth’s magnetospheric bow shock. Empirical distributions of parameters were studied in each
region. Taking into account the influence of the interplanetary magnetic field direction on the processes in the magnetosheath,
the cases of quasi-perpendicular and quasi-parallel shock waves were considered separately. The study showed that the distribution
of parameters in the selected regions (in the solar wind before front of the bow shock, in the magnetosheath behind the bow
shock (post-shock), in the region of the magnetosheath with minimal fluctuations in the field, and in the inner magnetosheath)
differ from each other at any interplanetary magnetic field direction. 相似文献
508.
A. N. Denisov N. V. Kuznetsov R. A. Nymmik M. I. Panasyuk N. M. Sobolevskii 《Cosmic Research》2010,48(6):509-516
In connection with projects of manned bases on the Moon it becomes topical to estimate radiation danger for their inhabitants.
In this paper we describe a method of evaluation of the radiation environment on the lunar surface produced by galactic and
solar cosmic rays. The roles of both primary and secondary radiations generated in the depth of the lunar soil under the action
of high-energy protons and nuclei are taken into account. Calculated fluxes of particles are used in order to estimate annual
averaged absorbed and equivalent local dose rates in tissues. It is established that in the lunar rock the contribution of
secondary neutrons to the dose rate exceeds that of protons. The contribution of the secondary particles generated by nuclei
of galactic cosmic rays to the dose rate is estimated. 相似文献
509.
V. Génot C. Jacquey M. Bouchemit M. Gangloff A. Fedorov B. Lavraud N. André L. Broussillou C. Harvey E. Pallier E. Penou E. Budnik R. Hitier B. Cecconi F. Dériot D. Heulet J.-L. Pinçon 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
AMDA (Automated Multi-Dataset Analysis), a new data analysis service, recently opened at the French Plasma Physics Data Center (CDPP). AMDA is developed according to the Virtual Observatory paradigm: it is a web-based facility for on-line analyses of space physics. Data may come from its own local database as well as remote ones. This tool allows the user to perform classical manipulations such as data visualization, parameter computation and data extraction. AMDA also offers innovative functionalities such as event searches on the content of the data in either visual or automated ways, generation, use and management of time tables (event lists). The general functionalities of AMDA are presented in the context of Space Weather with example scientific use cases. 相似文献
510.
V. G. Gainutdinov 《Russian Aeronautics (Iz VUZ)》2010,53(3):277-282
An algorithm is proposed for computer-aided calculation of required values of aircraft controlling moments and aerodynamic
moment coefficients for stable fulfillment of flight trajectories specified by design flight performance. 相似文献