全文获取类型
收费全文 | 3299篇 |
免费 | 23篇 |
国内免费 | 13篇 |
专业分类
航空 | 1598篇 |
航天技术 | 1156篇 |
综合类 | 4篇 |
航天 | 577篇 |
出版年
2021年 | 26篇 |
2019年 | 23篇 |
2018年 | 54篇 |
2017年 | 52篇 |
2016年 | 45篇 |
2015年 | 26篇 |
2014年 | 72篇 |
2013年 | 93篇 |
2012年 | 82篇 |
2011年 | 121篇 |
2010年 | 80篇 |
2009年 | 138篇 |
2008年 | 159篇 |
2007年 | 100篇 |
2006年 | 75篇 |
2005年 | 93篇 |
2004年 | 92篇 |
2003年 | 99篇 |
2002年 | 74篇 |
2001年 | 115篇 |
2000年 | 67篇 |
1999年 | 69篇 |
1998年 | 89篇 |
1997年 | 58篇 |
1996年 | 93篇 |
1995年 | 112篇 |
1994年 | 112篇 |
1993年 | 50篇 |
1992年 | 72篇 |
1991年 | 35篇 |
1990年 | 32篇 |
1989年 | 79篇 |
1988年 | 29篇 |
1987年 | 24篇 |
1986年 | 34篇 |
1985年 | 90篇 |
1984年 | 91篇 |
1983年 | 65篇 |
1982年 | 66篇 |
1981年 | 100篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1975年 | 29篇 |
1974年 | 23篇 |
1973年 | 21篇 |
1972年 | 20篇 |
1969年 | 21篇 |
1968年 | 19篇 |
排序方式: 共有3335条查询结果,搜索用时 31 毫秒
981.
用基于控制体的有限差分方法对一排射流横向喷入管流的流场进行了数值分析,以建立流场温度分布和上游流动条件及几何参数的关系,可变的参数包括:喷嘴直径,喷嘴数,圆柱管半径,射流与主流的体积流量比,温度比和动压比,结果发现,动压比,喷嘴个数和喷嘴间距是三个重要变量,通过对模拟结果的函数拟合,发现射流喷射深度与动压比除以喷嘴数的平方之间的关系可用一个对数函数很好地描述,给出了适用最佳混合的喷射深度和喷嘴间距,提出了可用于结构实设计的程序。 相似文献
982.
ARTEMIS Science Objectives 总被引:1,自引:0,他引:1
D. G. Sibeck V. Angelopoulos D. A. Brain G. T. Delory J. P. Eastwood W. M. Farrell R. E. Grimm J. S. Halekas H. Hasegawa P. Hellinger K. K. Khurana R. J. Lillis M. ?ieroset T.-D. Phan J. Raeder C. T. Russell D. Schriver J. A. Slavin P. M. Travnicek J. M. Weygand 《Space Science Reviews》2011,165(1-4):59-91
NASA??s two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of the Earth??s magnetotail; reconnection, particle acceleration, and turbulence in the Earth??s magnetosphere, at the bow shock, and in the solar wind; and the formation and structure of the lunar wake. Planetary topics include the lunar exosphere and its relationship to the composition of the lunar surface, the effects of electric fields on dust in the exosphere, internal structure of the Moon, and the lunar crustal magnetic field. This paper describes the expected contributions of ARTEMIS to these baseline scientific objectives. 相似文献
983.
P. C. Frisch M. Bzowski E. Grün V. Izmodenov H. Krüger J. L. Linsky D. J. McComas E. Möbius S. Redfield N. Schwadron R. Shelton J. D. Slavin B. E. Wood 《Space Science Reviews》2009,146(1-4):235-273
Interstellar material (ISMa) is observed both inside and outside of the heliosphere. Relating these diverse sets of ISMa data provides a richer understanding of both the interstellar medium and the heliosphere. The galactic environment of the Sun is dominated by warm, low-density, partially ionized interstellar material consisting of atoms and dust grains. The properties of the heliosphere are dependent on the pressure, composition, radiation field, ionization, and magnetic field of ambient ISMa. The very low-density interior of the Local Bubble, combined with an expanding superbubble shell associated with star formation in the Scorpius-Centaurus Association, dominate the properties of the local interstellar medium (LISM). Once the heliosphere boundaries and interaction mechanisms are understood, interstellar gas, dust, pickup ions, and anomalous cosmic rays inside of the heliosphere can be directly compared to ISMa outside of the heliosphere. Our understanding of ISMa at the Sun is further enriched when the circumheliospheric interstellar material is compared to observations of other nearby ISMa and the overall context of our galactic environment. The IBEX mission will map the interaction region between the heliosphere and ISMa, and improve the accuracy of comparisons between ISMa inside and outside the heliosphere. 相似文献
984.
O.J. Oyedokun A.O. Akala E.O. Oyeyemi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(4):1222-1243
This study investigates the morphology of the GPS TEC responses in the African Equatorial Ionization Anomaly (EIA) region to intense geomagnetic storms during the ascending and maximum phases of solar cycle 24 (2012–2014). Specifically, eight intense geomagnetic storms with Dst ≤ ?100 nT were considered in this investigation using TEC data obtained from 13 GNSS receivers in the East African region within 36–42°E geographic longitude; 29°N–10°S geographic latitude; ± 20°N magnetic latitude. The storm-time behavior of TEC shows clear positive and negative phases relative to the non-storm (median) behavior, with amplitudes being dependent on the time of sudden commencement of the storm and location. When a storm starts in the morning period, total electron content increases for all stations while a decrease in total electron content is manifested for a storm that had its sudden commencement in the afternoon period. The TEC and the EIA crest during the main phase of the storm is significantly impacted by the geomagnetic storm, which experiences an increase in the intensity of TEC while the location and spread of the crest usually manifest a poleward expansion. 相似文献
985.
CFAR behavior of adaptive detectors: an experimental analysis 总被引:1,自引:0,他引:1
De Maio A. Foglia G. Conte E. Farina A. 《IEEE transactions on aerospace and electronic systems》2005,41(1):233-251
We conduct an experimental analysis for assessing the constant false alarm rate (CFAR) behavior of four coherent adaptive radar detectors in the presence of experimentally measured clutter data. To this end we exploit several data files containing both land, lake, and mixed land and sea clutter, collected by two radar systems (the MIT Lincoln Laboratory Phase-One radar and the McMaster IPIX radar) at different polarizations, range resolutions, and frequency bands. The results show that all the receivers, in the presence of real data, don't respect their nominal probability of false alarm (P/sub fa/), namely they exhibit a false alarm rate higher than the value preassigned at the design stage. Nevertheless one of them, the recursive persymmetric adaptive normalized matched filter (RP-ANMF) is very robust, in the sense that it presents an acceptable displacement from the nominal P/sub fa/, in correspondence of all the analyzed scenarios. 相似文献
986.
987.
C. M. Cully R. E. Ergun K. Stevens A. Nammari J. Westfall 《Space Science Reviews》2008,141(1-4):343-355
The Digital Fields Board (DFB) performs the data acquisition and signal processing for the Electric Fields Instrument and Search Coil Magnetometer on each of the THEMIS (Time History of Events and Macroscale Interactions during Substorms) satellites. The processing is highly flexible and low-power (~1.1 watt orbit-averaged). The primary data products are time series waveforms and wave power spectra of the electric and magnetic fields. The power spectra can be computed either on the raw signals (i.e. in a system co-rotating with the spacecraft) or in a coordinate system aligned with the local DC magnetic field. Other data products include spectral power from multiple passbands (filter banks) and electric power in the 30–500 kHz band. The DFBs on all five spacecraft have been turned on and checked out in-flight, and are functioning as designed. 相似文献
988.
A model and a technique for calculating polymer composite materials with an ellipsoid-shaped filler that take into account the influence of system porosity, particle anisodiametry and a boundary layer on the effective heat conduction are proposed. The results of calculations made by numerical methods are in a good agreement with the well-known statistic and Odolevskii, Maxwell, and Dul’nev matrix models. 相似文献
989.
I. E. Lobanov 《Russian Aeronautics (Iz VUZ)》2008,51(2):160-165
A number of exact solutions of a problem on heat exchange in channels under unsteady conditions at the low Biot numbers and sufficiently low Brune numbers with and without consideration for a heat carrier stay period in a pipeline are obtained. 相似文献
990.
I. Molotov V. Agapov V. Titenko Z. Khutorovsky Yu. Burtsev I. Guseva V. Rumyantsev M. Ibrahimov G. Kornienko A. Erofeeva V. Biryukov V. Vlasjuk R. Kiladze R. Zalles P. Sukhov R. Inasaridze G. Abdullaeva V. Rychalsky V. Kouprianov O. Rusakov E. Litvinenko E. Filippov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(7):1022-1028
A joint team of researchers under the auspices of the Center for Space Debris Information Collection, Processing and Analysis of the Russian Academy of Sciences collaborates with 15 observatories around the world to perform observations of space debris. For this purpose, 14 telescopes were equipped with charge-coupled device (CCD) cameras, Global Positioning System (GPS) receivers, CCD frame processing and ephemeris computation software, with the support of the European and Russian grants. Many of the observation campaigns were carried out in collaboration with the Astronomical Institute of the University of Bern (AIUB) team operating at the Zimmerwald observatory and conducting research for the European Space Agency (ESA), using the Tenerife/Teide telescope for searching and tracking of unknown objects in the geostationary region (GEO). More than 130,000 measurements of space objects along a GEO arc of 340.9°, collected and processed at Space Debris Data Base in the Ballistic Center of the Keldysh Institute of Applied Mathematics (KIAM) in 2005–2006, allowed us to find 288 GEO objects that are absent in the public orbital databases and to determine their orbital elements. Methods of discovering and tracking small space debris fragments at high orbits were developed and tested. About 40 of 150 detected unknown objects of magnitudes 15–20.5 were tracked during many months. A series of dedicated 22-cm telescopes with large field of view for GEO survey tasks is in process of construction. 7 60-cm telescopes will be modernized in 2007. 相似文献