首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6521篇
  免费   9篇
  国内免费   13篇
航空   2851篇
航天技术   2124篇
综合类   26篇
航天   1542篇
  2021年   55篇
  2019年   32篇
  2018年   214篇
  2017年   167篇
  2016年   143篇
  2015年   59篇
  2014年   153篇
  2013年   203篇
  2012年   195篇
  2011年   305篇
  2010年   254篇
  2009年   344篇
  2008年   361篇
  2007年   250篇
  2006年   134篇
  2005年   194篇
  2004年   187篇
  2003年   199篇
  2002年   145篇
  2001年   206篇
  2000年   86篇
  1999年   126篇
  1998年   151篇
  1997年   104篇
  1996年   102篇
  1995年   178篇
  1994年   169篇
  1993年   90篇
  1992年   106篇
  1991年   40篇
  1990年   58篇
  1989年   100篇
  1988年   39篇
  1987年   39篇
  1986年   51篇
  1985年   177篇
  1984年   149篇
  1983年   124篇
  1982年   108篇
  1981年   208篇
  1980年   49篇
  1979年   45篇
  1978年   45篇
  1977年   41篇
  1976年   40篇
  1975年   44篇
  1974年   36篇
  1973年   34篇
  1972年   50篇
  1971年   27篇
排序方式: 共有6543条查询结果,搜索用时 15 毫秒
131.
Smirnova  N. V.  Lyakhov  A. N.  Setzer  Yu. I.  Osepian  A. P.  Meng  C.-I.  Smith  R.  Stenbaek-Nielsen  H. C. 《Cosmic Research》2004,42(3):210-218
Spatial distributions of the electron density in the latitude range 60°–90° N were calculated on the basis of a physical model of the E and lower Fregions of the high-latitude ionosphere using statistical models of auroral proton and electron precipitation. It is shown that precipitating protons can play the key role in the ionization of the Eregion in the dusk and midnight sectors of the auroral oval. However, quantitative estimates of the contribution of protons to the ionization depend on the used statistical models of electron precipitation. Comparison of the electron density profiles calculated for two incoherent scatter radars, EISCAT (Tromsö) and ESR (Svalbard), for simultaneous precipitation of electrons and protons and for electron precipitation only show that the influence of protons is the most significant in the dusk sector over the EISCAT radar and in the midnight sector over the ESR radar. The results presented indicate the need to take protons into account when radar data are used to derive precipitating electron spectra.  相似文献   
132.
Babkin  E. V.  Belyaev  M. Yu.  Efimov  N. I.  Sazonov  V. V.  Stazhkov  V. M. 《Cosmic Research》2004,42(2):155-164
A comparison of two methods of determination of the microacceleration quasisteady component arising onboard the International Space Station was performed. In the first method the acceleration was calculated using the relative motion of the station reconstructed on the basis of telemetry data. The second method was a direct measurement of the microacceleration by a low-frequency accelerometer and a smoothing of the data obtained. The used measurements were made by the American accelerometer MAMS. The above comparison can theoretically be used to refine the position of the station center of mass relative to its body.  相似文献   
133.
Zetzer  J. I.  Kozlov  S. I.  Rybakov  V. A.  Ponomarenko  A. V.  Smirnova  N. V.  Romanovsky  Yu. A.  Meng  C.-I.  Erlandson  R.  Stoyanov  B. 《Cosmic Research》2002,40(3):233-240
The measurements of infrared emission from an artificial structure, which was generated during the Fluxus experiment with plasma jet injection into the atmosphere, are obtained and discussed for the first time. Additional experimental data on the airglow in the visible spectral band of the disturbed region of the atmosphere are presented. A generalized analysis of the data is given.  相似文献   
134.
Eiges  P. E.  Zastenker  G. N.  Safrankova  J.  Nemecek  Z.  Eismont  N. A. 《Cosmic Research》2001,39(5):432-438
Based on simultaneous measurements of ion fluxes made onboard the closely separated satellites Interball-1and Magion-4, the propagation velocity of middle-scale plasma structures in the Earth's foreshock relative to the solar wind flow is estimated. The derived value of this velocity allows these structures to be identified as a fast magnetosonic wave propagating upstream of the solar wind inflowing the Earth's bow shock. An evaluation is also made of the correlation length of these disturbances in the plane perpendicular to the Sun–Earth line. This length is approximately equal to 2R E.  相似文献   
135.
Tether Satellite System Collision Study   总被引:1,自引:0,他引:1  
Chobotov  V.A.  Mains  D.L. 《Space Debris》1999,1(2):99-112
A study was performed to determine the probability of collision with resident space objects and untrackable debris for the tether component of the Tethered Satellite System (TSS) after it broke away from the Space Shuttle orbiter (mission STS-75) in February 1996. Both an analytical and a numerical approach were used in this study, and the results obtained with these two methods were found to be in good agreement. These results show that the deployed tether is expected to have been impacted by several particles 0.1mm or larger in size. The probability of collision with objects 10cm in size or larger was on the order of 10–3 per month. Since the severed tether reentered within one month after deployment, the collision hazard to other objects while in orbit was small. The analytical methods used in this study are useful for tether collision evaluations in general.  相似文献   
136.
An investigation of the effects of drying and drying-rewetting cycles under vacuum conditions of 10(-2) torr at -30 degrees C on conidia of the atmospheric strain Penicillium chrysogenum from 48-77 km heights, collected by meteorological rockets found that survival and restoration of the initial physiological properties were possible through some very efficient protective cellular mechanisms. Such adaptive possibilities explain the widespread diffusion of microbial cells throughout the biosphere of our planet.  相似文献   
137.
When discussing problems related to medical service in space flight, particular attention should be given to the specific living conditions and changes associated with space flight. In disease and injury, surgery can be provided only after conservative therapy has failed. In this context gnotobiological chambers allowing surgery in aseptic conditions seem promising. A portable set of interchangeable surgical tools should be made of light-weight alloys that can be readily sterilized. Electroanalgesia in combination with auriculoacupuncture as well as peridureal anesthesia may be used as they allow normal operations in autonomous space flight conditions. Changes in the sympatho-adrenal and kallikrein-kinin systems, as well as water-electrolyte balance, should be taken into account in developing methods and means of medical service in critical situations. Special attention should be given to the prevention and treatment of brain edema in view of weightlessness-induced cephalad fluid shifts.  相似文献   
138.
In August, 1981, the Westerbork Synthesis Radio Telescope was used for 4 h to search for narrowband pulsing radio beacons in the direction of the Galactic Center. By using both the spatial discrimination and temporal stability available to an interferometric measurement, weak intermittent signals can be detected even in the face of the strong, naturally caused radiation from this region. A radio beacon within our bandwidth, centered on the 21 cm neutral hydrogen line, would be recognizable if it had a repetition period between 40 sec and 1/2 h. The rms sensitivity to point sources was approximately 50 mJy/cycle, and the detection limit was 500 mJy/cycle. The limit degrades for pulse widths < 0.02s. No repetitive signals were found. For a swept, narrow-band radio beacon constrained to the Galactic Disk (beamwidth = 0.02 rad), our detection limit corresponds to a transmitter power of 10(11) MW at the Galactic Center.  相似文献   
139.
The creation of artificial plasma density irregularities (AI) with prescribed spectra in the ionospheric heating experiments is discussed. We show that periodic successions of powerful pulses, pumped into the F-region of the ionosphere lead to obtaining AI with the controlled stationary spatial spectrum and allow us to change power low spectral index 2β at least from 2β = 2.2 to 2β = 3.4 by changing of the powerful pulse time schedule.  相似文献   
140.
Eight characteristics of the unique suite of amino acids and hydroxy acids found in the Murchison meteorite can be recognized on the basis of detailed molecular and isotopic analyses. The marked structural correspondence between the alpha-amino acids and alpha-hydroxy acids and the high deuterium/hydrogen ratio argue persuasively for their formation by aqueous phase Strecker reactions in the meteorite parent body from presolar, i.e., interstellar, aldehydes, ketones, ammonia, and hydrogen cyanide. The characteristics of the meteoritic suite of amino acids and hydroxy acids are briefly enumerated and discussed with regard to their consonance with this interstellar-parent body formation hypothesis. The hypothesis has interesting implications for the organic composition of both the primitive parent body and the presolar nebula.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号