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   4401篇
  免费   14篇
  国内免费   11篇
航空   1685篇
航天技术   1498篇
综合类   20篇
航天   1223篇
  2022年   16篇
  2021年   49篇
  2019年   21篇
  2018年   151篇
  2017年   118篇
  2016年   128篇
  2015年   47篇
  2014年   144篇
  2013年   165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   119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4426条查询结果,搜索用时 15 毫秒
41.
A command and control (C/sup 2/) problem for military air operations is addressed. Specifically, we consider C/sup 2/ problems for air vehicles against ground-based targets and defensive systems. The problem is viewed as a stochastic game. We restrict our attention to the C/sup 2/ level where the problem may consist of a few unmanned combat air vehicles (UCAVs) or aircraft (or possibly teams of vehicles), less than say, a half-dozen enemy surface-to-air missile air defense units (SAMs), a few enemy assets (viewed as targets from our standpoint), and some enemy decoys (assumed to mimic SAM radar signatures). At this low level, some targets are mapped out and possible SAM sites that are unavoidably part of the situation are known. One may then employ a discrete stochastic game problem formulation to determine which of these SAMs should optimally be engaged (if any), and by what series of air vehicle operations. We provide analysis, numerical implementation, and simulation for full state-feedback and measurement feedback control within this C/sup 2/ context. Sensitivity to parameter uncertainty is discussed. Some insight into the structure of optimal and near-optimal strategies for C/sup 2/ is obtained. The analysis is extended to the case of observations which may be affected by adversarial inputs. A heuristic based on risk-sensitive control is applied, and it is found that this produces improved results over more standard approaches.  相似文献   
42.
43.
This paper reports the main characteristics of the deep space transponder (DST) equipment that has been designed, developed and tested by Thales Alenia Space—Italy (TAS-I) for the European Space Agency (ESA) BepiColombo mission to Mercury.  相似文献   
44.
The Mercury Magnetopsheric Orbiter (MMO) is one of the spacecraft of the BepiColombo mission; the mission is scheduled for launch in 2014 and plans to revisit Mercury with modern instrumentation. MMO is to elucidate the detailed plasma structure and dynamics around Mercury, one of the least-explored planets in our solar system. The Mercury Plasma Particle Experiment (MPPE) on board MMO is a comprehensive instrument package for plasma, high-energy particle, and energetic neutral particle atom measurements. The Mercury Ion Analyzer (MIA) is one of the plasma instruments of MPPE, and measures the three dimensional velocity distribution of low-energy ions (from 5 eV to 30 keV) by using a top-hat electrostatic analyzer for half a spin period (2 s). By combining both the mechanical and electrical sensitivity controls, MIA has a wide dynamic range of count rates for the proton flux expected around Mercury, which ranges from 106 to 1012 cm−2 s−1 str−1 keV−1, in the solar wind between 0.3 and 0.47 AU from the sun, and in both the hot and cold plasma sheet of Mercury’s magnetosphere. The geometrical factor of MIA is variable, ranging from 1.0 × 10−7 cm2 str keV/keV for large fluxes of solar wind ions to 4.7 × 10−4 cm2 str keV/keV for small fluxes of magnetospheric ions. The entrance grid used for the mechanical sensitivity control of incident ions also work to significantly reduce the contamination of solar UV radiation, whose intensity is about 10 times larger than that around Earth’s orbit.  相似文献   
45.
The calculation of the design parameters of lifting airscrew systems with fixed and tilted rotor, including the investigation of the operation schemes of actuators for the propeller control system, is carried out.  相似文献   
46.
In this paper, a research and development version of the computer-aided system of mass tensometry (SMT) for conduction of aircraft and rocket-space equipment vibration tests is considered. A technique of the system design and development that combines the advantages of the system and process approaches when using the modern element base around the high-performance integral microcircuits is a distinctive feature in this research and development problem solution. We describe the architecture and structure of the advanced computer-aided SMTs and present data on its basic components desigtn. Also determined are the list and functional parameters of ratio-measuring network modules as well as the scheme of their connection to the test object and the local computer network of the enterprise.  相似文献   
47.
The methodical grounds for helicopter operation with respect to the technical condition for the state of the art of aeronautical engineering are analyzed and generalized. The most essential engineering solutions on developing the systems for monitoring the helicopter operating conditions are considered. The promising lines for further development of these systems are designated.  相似文献   
48.
A novel modular multistep algorithm is proposed for multi-criteria analysis of fracture of aircraft structures with complex geometries. In order to evaluate the algorithm, the crack growth analysis is realized by the following three criteria, namely, the stress intensity factor, the strain energy release rate, and the J-integral. The algorithm implementation by the finite element method is considered and prospects of alternative implementation based on the meshfree methods are assigned.  相似文献   
49.
An algorithm to control the aircraft trajectory is proposed. This algorithm is based on the dynamic stochastic systems optimal control theory. The optimal control implementation is shown to reduce the deviation of the controlled trajectory from the predetermined one. The optimal control is based on estimating phase coordinates with the high accuracy by the global navigation satellite system.  相似文献   
50.
This paper presents the results of an investigation of ejectors with the low entrainment ratio. A technique for calculating the ejectors with a curvilinear axis has been developed. Comparative studies of the performance characteristics of ejectors with the rectilinear axis of the mixing chamber and the curvilinear initial section of the mixing chamber are carried out.  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