全文获取类型
收费全文 | 8543篇 |
免费 | 18篇 |
国内免费 | 24篇 |
专业分类
航空 | 4234篇 |
航天技术 | 2994篇 |
综合类 | 38篇 |
航天 | 1319篇 |
出版年
2021年 | 65篇 |
2019年 | 52篇 |
2018年 | 144篇 |
2017年 | 89篇 |
2016年 | 86篇 |
2014年 | 181篇 |
2013年 | 227篇 |
2012年 | 206篇 |
2011年 | 290篇 |
2010年 | 204篇 |
2009年 | 339篇 |
2008年 | 428篇 |
2007年 | 223篇 |
2006年 | 210篇 |
2005年 | 236篇 |
2004年 | 190篇 |
2003年 | 274篇 |
2002年 | 169篇 |
2001年 | 290篇 |
2000年 | 156篇 |
1999年 | 203篇 |
1998年 | 237篇 |
1997年 | 180篇 |
1996年 | 220篇 |
1995年 | 278篇 |
1994年 | 259篇 |
1993年 | 160篇 |
1992年 | 192篇 |
1991年 | 113篇 |
1990年 | 84篇 |
1989年 | 199篇 |
1988年 | 99篇 |
1987年 | 105篇 |
1986年 | 85篇 |
1985年 | 263篇 |
1984年 | 210篇 |
1983年 | 181篇 |
1982年 | 201篇 |
1981年 | 262篇 |
1980年 | 92篇 |
1979年 | 72篇 |
1978年 | 74篇 |
1977年 | 66篇 |
1976年 | 63篇 |
1975年 | 75篇 |
1974年 | 56篇 |
1973年 | 58篇 |
1972年 | 69篇 |
1971年 | 59篇 |
1970年 | 59篇 |
排序方式: 共有8585条查询结果,搜索用时 968 毫秒
581.
582.
The problem treated here is the analysis of a class of nonlinear sampled-data systems with a Gaussian input signal. The nonlinear element is a symmetrical limiter (memoryless device) that feeds the linear element. Preceding the limiter is a sampler and zero-order hold unit for data reconstruction. The analysis is predicated on finding an equivalent gain for the nonlinear element such that the mean-square error is a minimum. The nonlinearity is thus replaced by a linear component and the system is then analyzed by conventional techniques. It is also shown that for appropriate sampling rates the sampled-data system is equivalent to a continuous system due to the action of the sampler-hold combination. All calculations pertaining to the limiter input signal require the use of a transfer function that is interior to the feedback loop. However, in developing this transfer function, the overall system is considered so that the system output may be evaluated after the value of equivalent gain has been found. 相似文献
583.
This paper analyzes a hybrid navigation concept that uses signals from a radio interferometer mounted on a spinning geostationary satellite, preliminary position estimates from self-contained equipment, and stored a priori information on the past performance of this equipment. The craft-borne processor, optimum in the maximum a posteriori (MAP) sense, is designed to estimate position coordinates using only the incoming radio signals, although improved estimates result if the other two items are available. An error analysis starts with the derivation of an estimation error covariance matrix, whose elements depend on additive receiver noise and the physical parameters of the system. A minimum 1? estimation error in position is obtained by trading off these parameters. The effects of other major error sources, such as tropospheric phase fluctuations, multipath, and craft altitude uncertainty, are added to the estimation error to give a total 1? position error on the order of 3.7 to 5.6 km. 相似文献
584.
Sarles F.W. Stanley A.G. Roberge J.K. Godfrey B.W. 《IEEE transactions on aerospace and electronic systems》1973,(6):921-924
For direct measurement of the integrated radiation dose experienced in Earth synchronous orbit, p-i-n diodes were flown as radiation dosimeters on LES-6. The diode, which has a lifetime of 10-4 seconds in the intrinsic region, was originally developed as a neutron dosimeter, but can detect 1-MeV electron fluences as low as 1013 e·cm-2. Observations over three years in orbit are presented. 相似文献
585.
A direction-finding technique is presented that is capable of simultaneously estimating the arrival angles of multiple signals. Pulsed as well as continuous signals can be handled with the signal form only approximately specified. An adaptive antenna array is used as a processing device in the estimation technique. The effect of input signal and feedback loop parameters upon estimate bias is discussed. 相似文献
586.
Yu. V. Klochkov A. P. Nikolaev A. A. Shubovich S. S. Marchenko 《Russian Aeronautics (Iz VUZ)》2013,56(4):327-334
In this paper, we present an algorithm for geometrically nonlinear finite element analysis of the shells of revolution. Use is made of the most proper algorithms for vector interpolation of displacements through the nodal unknowns and an efficient algorithm for obtaining the stress-strain increment relation at a step of loading. By comparing the results of analyzing a geometrically nonlinear shell of revolution obtained on the basis of the ANSYS software with the scalar interpolation of displacements with those obtained on the basis of an author-developed finite element, it has been shown that application of the FEM vector displacement interpolation leads to increasing the accuracy of the finite element solutions in analyzing the stress-strain state of the geometrically nonlinear shells. 相似文献
587.
Louise M. Prockter Rosaly M. C. Lopes Bernd Giese Ralf Jaumann Ralph D. Lorenz Robert T. Pappalardo Gerald W. Patterson Peter C. Thomas Elizabeth P. Turtle Roland J. Wagner 《Space Science Reviews》2010,153(1-4):63-111
The surfaces of the Solar System’s icy satellites show an extraordinary variety of morphological features, which bear witness to exchange processes between the surface and subsurface. In this paper we review the characteristics of surface features on the moons of Jupiter, Saturn, Uranus and Neptune. Using data from spacecraft missions, we discuss the detailed morphology, size, and topography of cryovolcanic, tectonic, aeolian, fluvial, and impact features of both large moons and smaller satellites. 相似文献
588.
AeroSuite给出了一个飞行器制造过程有效管理整个产品制造流程的解决方案。它包括FiberSIM复材工艺软件、SyncroFIT机身设计制造装配软件、对于首件鉴定过程的流程化的质量规划模块(QPE)。 相似文献
589.
B. Holback S. -E. Jansson L. Åhlén G. Lundgren L. Lyngdal S. Powell A. Meyer 《Space Science Reviews》1994,70(3-4):577-592
The Wave Experiment, F4, on the Swedish/German satelliteFreja, is designed to measure the electric wave fields up to 4 MHz, the magnetic wave fields up to 16 kHz and the plasma density and its relative variations up to 2 kHz. Six wave signals and four density probe signals can be measured simultaneously. The wave forms of all signals are transmitted to ground without any analysis onboard. The limited TM allocation does not allow continuous sampling of the wave signals, so normally the measurements are made in snapshots of various lengths dependent on sampling frequency, etc. Continuous sampling can be made for shorter time periods by using a 6 Mbyte memory as a buffer. 相似文献
590.
Bhanu B. Das S. Symosek P. Snyder S. Roberts B. 《IEEE transactions on aerospace and electronic systems》1994,30(3):709-721
Range measurements to objects in the world relative to mobile platforms such as ground or air vehicles are critical for visually aided navigation and obstacle detection/avoidance. An approach is presented that consists of a synergistic combination of two types of passive ranging method: binocular stereo and motion stereo. We show a new way to model the errors in binocular and motion stereo in conjunction with an inertial navigation system (INS) and derive the appropriate Kalman filter to refine the estimates from these two stereo ranging techniques. We present results using laboratory images that show that refined estimates can be optimally combined to give range values which are more accurate than any one of the individual estimates from binocular and motion stereo. By incorporating a blending filter, the approach has the potential of providing accurate, dense range measurements for all the pixels in the field of view (FOV) 相似文献