全文获取类型
收费全文 | 6701篇 |
免费 | 657篇 |
国内免费 | 485篇 |
专业分类
航空 | 3596篇 |
航天技术 | 1971篇 |
综合类 | 598篇 |
航天 | 1678篇 |
出版年
2023年 | 47篇 |
2022年 | 114篇 |
2021年 | 167篇 |
2020年 | 129篇 |
2019年 | 128篇 |
2018年 | 234篇 |
2017年 | 197篇 |
2016年 | 159篇 |
2015年 | 177篇 |
2014年 | 256篇 |
2013年 | 268篇 |
2012年 | 271篇 |
2011年 | 350篇 |
2010年 | 337篇 |
2009年 | 396篇 |
2008年 | 364篇 |
2007年 | 285篇 |
2006年 | 237篇 |
2005年 | 239篇 |
2004年 | 185篇 |
2003年 | 212篇 |
2002年 | 307篇 |
2001年 | 270篇 |
2000年 | 157篇 |
1999年 | 185篇 |
1998年 | 169篇 |
1997年 | 157篇 |
1996年 | 166篇 |
1995年 | 188篇 |
1994年 | 138篇 |
1993年 | 91篇 |
1992年 | 123篇 |
1991年 | 66篇 |
1990年 | 52篇 |
1989年 | 82篇 |
1988年 | 44篇 |
1987年 | 33篇 |
1986年 | 39篇 |
1985年 | 122篇 |
1984年 | 105篇 |
1983年 | 62篇 |
1982年 | 94篇 |
1981年 | 121篇 |
1980年 | 29篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1974年 | 28篇 |
1972年 | 21篇 |
1971年 | 21篇 |
1969年 | 24篇 |
排序方式: 共有7843条查询结果,搜索用时 15 毫秒
21.
以小车式起落架为例,利用ADAMS/Airc- raft建立了起落架滑跑试验仿真模型.给出了起落架滑跑运动方程,并进行了滑跑试验仿真分析。仿真结果与理论要求对比具有较好的一致性。 相似文献
22.
The problem of the optimal number of phased array faces for performing 360/spl deg/ horizon surveillance is considered. Assuming the detection performance is the same in all beam positions and the total number of T/R modules is constant, it is shown that the optimal number of array faces is three. This is true whether the arrays are operating simultaneously or sequentially. A parametric analysis is performed between the number of array faces operating simultaneously and the associated cost of simultaneous operation in terms of the size of the array. 相似文献
23.
24.
The robustness of a moving-bank multiple model adaptive estimator/controller to order reduction in the controller design model is examined. It is shown that the adaptive mechanism and bank-moving logic are not confounded by the effects of unmodeled higher order modes of a large flexible spacestructure. Control characteristics are achieved that are essentially equivalent to those of an artificially informed benchmark controller 相似文献
25.
Liu H. Ghafoor A. Stockmann P.H. 《IEEE transactions on aerospace and electronic systems》1992,28(2):324-334
The Gram-Schmidt orthogonalization (GSO) algorithm has excellent numerical performance and is readily applicable to systolic implementations such as in a field of adaptive cancellation systems. A modified GSO algorithm for a fully adaptive array is proposed and computer simulations show that the proposed algorithm gives superior performance. A systolic implementation of the proposed GSO algorithm for fully adaptive array is presented. A feedback mode GSO algorithm for use with analog weights is also presented and has been shown to have excellent performance in the presence of weight errors 相似文献
26.
S. Carnochan P. Moore S. Ehlers 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,16(12)
Achieving orbital accuracies in the radial direction for ERS-1 commensurate with those for TOPEX/Poseidon is of utmost importance for the integration of the two altimeter data sets. This paper outlines a procedure whereby the radial orbit error for ERS-1 is recovered as a time series expansion in the form of a finite Fourier series with additional terms for atmospheric drag, solar radiation pressure, and initial state vector mismodelling. Using a least squares collocation method with constraints derived from the JGM2 gravity field co-variance matrix, the radial error is recovered using both dual crossovers and ERS-1 single satellite crossovers. Aggregate arcs are then used to derive the ERS-1 orbit error over the repeat period of 35 days. The results are presented in the improvement of fit in the dual crossover, ERS-1 crossover and altimetry data sets as well as the recovery of an altimeter bias for the two satellites. 相似文献
27.
Stability of resonance rotation of a satellite with respect to its center of mass in the orbit plane
S. Yu. Sadov 《Cosmic Research》2006,44(2):160-171
The stability of resonance oscillations and rotations of a satellite in the plane of its orbit in the case when the difference of the moments of inertia with respect to the principal axes lying in the orbit plane is small is determined at a given rotation number m by the sign of function Φm(e), introduced by F.L. Chernous’ko in 1963. In this paper, convenient analytical representations of functions Φm(e) are described in the form of integrals and series of Bessel functions regular at e → 1?. Values of Φm(1) are calculated in explicit form. A theorem about the double asymptotic form of functions Φm(e) at m → ∞ and e → 1? is proved by the saddlepoint method. 相似文献
28.
Savkin A.V. Pathirana P.N. Faruqi F.A. 《IEEE transactions on aerospace and electronic systems》2003,39(3):901-910
Addressed here is the precision missile guidance problem where the successful intercept criterion has been defined in terms of both minimizing the miss distance and controlling the missile body attitude with respect to the target at the terminal point. We show that the H/sup /spl infin// control theory, when suitably modified, provides an effective framework for the precision missile guidance problem. The existence of feedback controllers (guidance laws) is investigated for the case of finite horizon and non-zero initial conditions. Both state feedback and output feedback implementations are explored. 相似文献
29.
P.B. Marty S. Bardeau O. Czoske H. Ebeling J.P. Kneib R. Sadat I. Smail 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2509-2515
We present an analysis of seven clusters observed by XMM-Newton as part of our survey of 17 most X-ray luminous clusters of galaxies at z 0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using the public software FTOOLS and XMMSAS we have set up an automated pipeline to reduce the EPIC MOS and pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM-Newton deep spectro-imaging of these clusters allowed us to fit a standard β-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations. 相似文献
30.
A method is given to calculate the shape a high-altitude reflector must have to produce any intensity distribution inside the illuminated ground area. The method consists of setting up and solving a differential equation appropriate to the required ground intensity distribution. Cylindrical and spherical mirrors are discussed in detail, and mirror shapes for producing a particular type of uniform ground illumination are derived. These shapes approach paraboloids in the limit when the mirror altitude is much greater than the diameter of the illuminated area. 相似文献