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   6851篇
  免费   16篇
  国内免费   20篇
航空   3067篇
航天技术   2406篇
综合类   21篇
航天   1393篇
  2021年   74篇
  2019年   45篇
  2018年   160篇
  2017年   107篇
  2016年   112篇
  2015年   51篇
  2014年   178篇
  2013年   222篇
  2012年   212篇
  2011年   322篇
  2010年   229篇
  2009年   329篇
  2008年   366篇
  2007年   220篇
  2006年   156篇
  2005年   185篇
  2004年   182篇
  2003年   205篇
  2002年   145篇
  2001年   218篇
  2000年   127篇
  1999年   162篇
  1998年   190篇
  1997年   109篇
  1996年   171篇
  1995年   203篇
  1994年   189篇
  1993年   120篇
  1992年   149篇
  1991年   47篇
  1990年   48篇
  1989年   139篇
  1988年   59篇
  1987年   56篇
  1986年   63篇
  1985年   183篇
  1984年   144篇
  1983年   107篇
  1982年   115篇
  1981年   214篇
  1980年   49篇
  1979年   45篇
  1978年   50篇
  1977年   42篇
  1975年   50篇
  1974年   38篇
  1973年   32篇
  1972年   35篇
  1971年   35篇
  1970年   37篇
排序方式: 共有6887条查询结果,搜索用时 15 毫秒
431.
The rapid rotation of the gas giant planets, Jupiter and Saturn, leads to the formation of magnetodisc regions in their magnetospheric environments. In these regions, relatively cold plasma is confined towards the equatorial regions, and the magnetic field generated by the azimuthal (ring) current adds to the planetary dipole, forming radially distended field lines near the equatorial plane. The ensuing force balance in the equatorial magnetodisc is strongly influenced by centrifugal stress and by the thermal pressure of hot ion populations, whose thermal energy is large compared to the magnitude of their centrifugal potential energy. The sources of plasma for the Jovian and Kronian magnetospheres are the respective satellites Io (a volcanic moon) and Enceladus (an icy moon). The plasma produced by these sources is globally transported outwards through the respective magnetosphere, and ultimately lost from the system. One of the most studied mechanisms for this transport is flux tube interchange, a plasma instability which displaces mass but does not displace magnetic flux—an important observational constraint for any transport process. Pressure anisotropy is likely to play a role in the loss of plasma from these magnetospheres. This is especially the case for the Jovian system, which can harbour strong parallel pressures at the equatorial segments of rotating, expanding flux tubes, leading to these regions becoming unstable, blowing open and releasing their plasma. Plasma mass loss is also associated with magnetic reconnection events in the magnetotail regions. In this overview, we summarise some important observational and theoretical concepts associated with the production and transport of plasma in giant planet magnetodiscs. We begin by considering aspects of force balance in these systems, and their coupling with the ionospheres of their parent planets. We then describe the role of the interaction between neutral and ionized species, and how it determines the rate at which plasma mass and momentum are added to the magnetodisc. Following this, we describe the observational properties of plasma injections, and the consequent implications for the nature of global plasma transport and magnetodisc stability. The theory of the flux tube interchange instability is reviewed, and the influences of gravity and magnetic curvature on the instability are described. The interaction between simulated interchange plasma structures and Saturn’s moon Titan is discussed, and its relationship to observed periodic phenomena at Saturn is described. Finally, the observation, generation and evolution of plasma waves associated with mass loading in the magnetodisc regions is reviewed.  相似文献   
432.
433.
434.
A methodology of creating a loading imitation model of a single-rotor helicopter with artificial neural network algorithms is considered. Stages of creation, the structure, and an algorithm of searching for an optimal neural networks configuration of loading imitation model are presented.  相似文献   
435.
Based on an integrated approach, we solve the optimization problem for energy content and weight-dimensional characteristics of the electric servo drive by synthesis of structure and analysis of characteristics for different power supplies. The generalized power supply model, developed for different power supply of drive control systems, is given.  相似文献   
436.
A method of technologic audit for technical re-equipment of enterprises is considered. The method developed is intended to verify technological solutions of projects of technical re-equipment of enterprises according to indicators of productivity.  相似文献   
437.
Transient performance of a single-axis rate gyroscope mounted in a spacecraft which is spinning about the spin axis of the gyro is presented. Analytical expressions for various time-domain and frequency-domain specifications as functions of the spin rate of the vehicle are obtained. Numerical results are presented which are useful in selecting the gyro parameters if it is to be used for the measurements of the angular velocity in spinning space vehicles.  相似文献   
438.
The receipt of the Pioneer Award has given me a chance to look back over my professional life and the opportunity to take stock of how I helped shape a small part of the world. While I hope this process entertains my contemporaries, more importantly, I hope it stimulates those that are engaged in actively shaping the present. To describe the need for automatic picture transmission (APT), I must retrace the historical development of meteorological satellites. The idea for weather observations from a satellite originated with a small group of meteorologists at the U.S. Army Signal Corps Research and Development Lab. at Ft. Monmouth, N.J., and resulted in the design of Vanguard II. The Tiros and TOS series of satellites, and the design of Nimbus, followed soon thereafter. However, a faster picture dissemination than was available at that time was needed, and it was this necessity that sparked the development of APT. Nimbus was originally intended to be an operational system, but the advent of simpler, less costly stabilization systems made the Tiros evolution the clear winner. The geosynchronous weather satellites started nearly a decade later and evolved from the NASA Application Technology Satellite (ATS) series. All three systems, existing polar orbiting weather satellites, APT, and geosynchronous weather satellites, have changed meteorology and the reliability of weather forecasting profoundly.  相似文献   
439.
Powered by free-piston Stirling engines, linear alternators are proposed for space power stations as well as for isolated domestic applications, automotive, and on-Earth solar power plants. As the literature on the subject is sparse and base-design oriented, we present the general equations for both three-phase and single-phase winding configurations having permanent-magnet field excitations.  相似文献   
440.
Basic design guidelines are presented for a three-phase tubular linear alternator (LA). A numerical example for the design of a 25 kVA, 14.4 mls, 120/220 V, 60 Hz alternator is used to illustrate the procedure.  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