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   4402篇
  免费   8篇
  国内免费   10篇
航空   1684篇
航天技术   1494篇
综合类   20篇
航天   1222篇
  2022年   16篇
  2021年   48篇
  2019年   21篇
  2018年   150篇
  2017年   118篇
  2016年   127篇
  2015年   47篇
  2014年   144篇
  2013年   164篇
  2012年   145篇
  2011年   220篇
  2010年   172篇
  2009年   264篇
  2008年   273篇
  2007年   167篇
  2006年   100篇
  2005年   127篇
  2004年   133篇
  2003年   148篇
  2002年   109篇
  2001年   163篇
  2000年   62篇
  1999年   79篇
  1998年   84篇
  1997年   63篇
  1996年   77篇
  1995年   104篇
  1994年   85篇
  1993年   48篇
  1992年   68篇
  1991年   18篇
  1990年   30篇
  1989年   66篇
  1988年   21篇
  1987年   31篇
  1986年   32篇
  1985年   118篇
  1984年   78篇
  1983年   66篇
  1982年   64篇
  1981年   119篇
  1980年   33篇
  1979年   21篇
  1978年   19篇
  1977年   25篇
  1976年   20篇
  1975年   24篇
  1974年   23篇
  1972年   15篇
  1971年   14篇
排序方式: 共有4420条查询结果,搜索用时 750 毫秒
581.
A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection.  相似文献   
582.
Experimental investigations of the 10 N catalytic hydrazine thruster are reported. These thrusters find applications in orbit raising functions of a spacecraft. The hardware was realized and tested in a vacuum chamber (10?3 mbar vacuum) for its performance. When tested at the design propellant supply pressure of 21.5 bar the thruster developed 10.25 N thrust at an operating chamber pressure of 16.4 bar. The thruster was also tested for off-design conditions (24, 18 and 14.5 bar propellant supply pressures) of operation to determine the steady-state performance. The chamber pressure and vacuum thrust follow more or less a linear law with the propellant-supply pressure. The thruster was also tested for its response characteristics for short (100 ms) firing durations at various propellant-supply pressures (15.5, 18.8, 22.5, 25.6 and 29.5 bar) and the experimental results are reported and discussed. The hydrazine was injected at the room temperature (300±5 K).  相似文献   
583.
Hardware-in-the-loop testing technology for automatic control, condition monitoring and diagnostics systems of gas turbine engines is described. The technology proposed makes it possible to simulate combinations and chains of unexpected and gradual failures of engines, transducers and actuators.  相似文献   
584.
The algorithmic support of a small-sized navigation system on the basis of the magnetoinertial course transmitter is considered; the support makes it possible to significantly reduce accumulating errors that are due to incomplete data on wind parameters and decrease requirements for random errors of initial data sensors.  相似文献   
585.
A set of systems for labor standard computer-aided design is described, namely, initial developments, advance and state-of-the art.  相似文献   
586.
Some experimental data on the process of impulsive ultrasonic machining are presented. Also given are the data on variations in the impulsive vibration frequency of a workpiece and a tool.  相似文献   
587.
588.
A technique of integral diagnostics for an RF inductively coupled plasma gas discharge unit of an ion thruster is proposed. This technique includes a priori measurements of antenna coil electrical parameters in free space and in assembled state as well as experimental determination of the antenna coil currents with and without discharge.  相似文献   
589.
An estimate of the feasibility of the ultrahigh-energy cosmic ray and neutrino detection using a lunar satellite-borne radio receiver is presented. The data obtained in the proposed experiment will make resolving the current contradictions in the ultrahigh-energy cosmic ray spectra measured with the major ground-based instruments possible. Moreover, they will enable us to considerably extend the accessible energy range and to check predictions of various models of the origin of the highest-energy particles in the Universe. At the same time the lunar radio detector provides a means of searching for ultrahigh-energy neutrinos with a high sensitivity combined with a very large target effective mass.  相似文献   
590.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material, i.e., 3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are needed to improve agreement between the simulations and observations.  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