全文获取类型
收费全文 | 3167篇 |
免费 | 4篇 |
国内免费 | 11篇 |
专业分类
航空 | 1335篇 |
航天技术 | 882篇 |
综合类 | 9篇 |
航天 | 956篇 |
出版年
2021年 | 26篇 |
2019年 | 10篇 |
2018年 | 181篇 |
2017年 | 158篇 |
2016年 | 86篇 |
2015年 | 37篇 |
2014年 | 79篇 |
2013年 | 84篇 |
2012年 | 95篇 |
2011年 | 207篇 |
2010年 | 172篇 |
2009年 | 223篇 |
2008年 | 228篇 |
2007年 | 190篇 |
2006年 | 59篇 |
2005年 | 111篇 |
2004年 | 87篇 |
2003年 | 88篇 |
2002年 | 58篇 |
2001年 | 99篇 |
2000年 | 39篇 |
1999年 | 42篇 |
1998年 | 52篇 |
1997年 | 35篇 |
1996年 | 52篇 |
1995年 | 51篇 |
1994年 | 36篇 |
1993年 | 25篇 |
1992年 | 41篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 40篇 |
1988年 | 16篇 |
1987年 | 23篇 |
1986年 | 22篇 |
1985年 | 72篇 |
1984年 | 43篇 |
1983年 | 34篇 |
1982年 | 43篇 |
1981年 | 76篇 |
1980年 | 18篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 15篇 |
1973年 | 9篇 |
1971年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有3182条查询结果,搜索用时 31 毫秒
951.
The flow-field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied.Results obtained from four combustion models,combined with the re-normalization group(RNG) k-ε turbulence model,discrete ordinates radiation model and enhanced wall treatment are presented and discussed.The results are compared with a comprehensive database obtained from a series of experimental measurements.The flow patterns and the recirculation zone length in the combustion chamber are accurately predicted,and the mean axial velocities are in fairly good agreement with the experimental data,particularly at downstream sections for all four combustion models.The mean temperature profiles are captured fairly well by the eddy dissipation(EDS),probability density function(PDF),and laminar flamelet combustion models.However,the EDS-finite-rate combustion model fails to provide an acceptable temperature field.In general,the flamelet model illustrates little superiority over the PDF model,and to some extent the PDF model shows better performance than the EDS model. 相似文献
952.
953.
Calorimeters are used in cosmic ray studies for a variety of purposes, such as measurements of particle energy, separation
of electrons and hadrons, formation of triggers (signals for activation of instruments), and so on. In this review we consider
the methods of energy reconstruct of protons and electrons (for particles with energies exceeding 10 GeV) in calorimeters
of various types that are used in astrophysical experiments of cosmic ray studies carried out with balloons and satellites. 相似文献
954.
One of the most important tasks of space research is to find a way of real-time monitoring of the space environment conditions around the Earth. This is necessary in order to provide warning about the threats of critical failures in ground-based and space technological systems, thus providing for their stable and secure operation. In view of this concern, methods of diagnostics of ionospheric energy and electrodynamic characteristics continue to be developed on the basis of spectral and photometric measurements, analyzing the glow intensity of emissions of the upper atmosphere observed from above. Serial panoramic monochromatic maps of the intensity of luminosity of the upper atmosphere emissions measured from orbiting detectors can serve as a main data source for such an analysis. In this paper we consider the principal aspects of the method, and, on this basis, the instrumentation requirements are formulated. 相似文献
955.
D.K. Callebaut V.I. Makarov A.G. Tlatov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2007,40(12):1917-1920
After a polar reversal in one hemisphere the Sun has two polar caps of the same sign, leaving it in a kind of monopolar state. It may take months before a polar reversal occurs in the other hemisphere. The situation may have been extreme in the Maunder Minimum where the northern hemisphere most probably did not have polar reversals during several cycles, while the southern hemisphere may have had some. This may affect the interplanetary field and thus the cosmic rays reaching the Earth. Using the relation between the Wolf number and the speed of the global magnetic field regions the yearly mean Wolf number has to exceed 40 in order to have polar reversals, hence per hemisphere we expect that it must exceed 20. This may be used to give a definition of a deep minimum. 相似文献
956.
Statistical study of radio drifting pulsation structures with associated CMEs and other observations
Chengming Tan Y.H. Yan Y.Y. Liu Q.J. Fu S.J. Wang H.R. Ji Z.J. Chen H.R. Jing 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(6):969-975
Solar radio burst, especially the fine structures (FSs) and the drifting pulsation structures (DPSs), may be used as an important diagnostics tool to draw the evolution map of the flare loop in the initial phase of solar flares. In this work, 52 radio events were found accompanying with DPSs. They were all observed with the Solar Radio Spectrometers (0.625–7.6 GHz) of China during 1998–2004. Combining the radio observations with LASCO-C2, Goes-8 SXR, Hα, EUV and Trace observations, we analyzed all these events and obtained some statistic conclusions: First, 88% DPSs take place at the initial phase of the radio burst, and their rich spectrum characteristics are helpful to understand the events further. Second, 83% DPSs are associated with CMEs or ejection events, and all the events are accompanied by Goes SXR flare. Third, for CMEs and DPSs, which take the first step, there is no significant predominance of either of them. The relationship between the DPSs and CMEs is still not clear in this study because of the lack of spatial resolution in the centimeter–decimeter band. However, the EIT or Trace ejection happened during the onset/end time of DPSs. They are signatures of the initial phase of CMEs. Two events will be illustrated to explain this. 相似文献
957.
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
958.
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
959.
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
960.
A. S. Meshchanov 《Russian Aeronautics (Iz VUZ)》2008,51(3):259-268
A system of differential equations for the angular motion of an observation satellite (OS) equipped with an inertial drive electromagnetic device (EMD) without a controlling flywheel engine is presented. Apart from lag, the calculated and uncertain limited external and parametric disturbances constantly acting on the OS control system are taken into account. It is proposed that the sliding conditions be used to obtain the high-precision OS control with the specified direct indices of the transient process quality in the angular motion. A problem of equivalent system transformation is solved to safely provide the invariance of the sliding conditions to all listed disturbances with respect to the Euler angles and their first and second derivatives. 相似文献