全文获取类型
收费全文 | 6402篇 |
免费 | 16篇 |
国内免费 | 14篇 |
专业分类
航空 | 2966篇 |
航天技术 | 2068篇 |
综合类 | 22篇 |
航天 | 1376篇 |
出版年
2021年 | 58篇 |
2019年 | 31篇 |
2018年 | 223篇 |
2017年 | 168篇 |
2016年 | 124篇 |
2015年 | 61篇 |
2014年 | 162篇 |
2013年 | 184篇 |
2012年 | 196篇 |
2011年 | 325篇 |
2010年 | 242篇 |
2009年 | 369篇 |
2008年 | 427篇 |
2007年 | 258篇 |
2006年 | 141篇 |
2005年 | 198篇 |
2004年 | 161篇 |
2003年 | 202篇 |
2002年 | 127篇 |
2001年 | 208篇 |
2000年 | 100篇 |
1999年 | 120篇 |
1998年 | 151篇 |
1997年 | 108篇 |
1996年 | 126篇 |
1995年 | 161篇 |
1994年 | 142篇 |
1993年 | 85篇 |
1992年 | 119篇 |
1991年 | 60篇 |
1990年 | 45篇 |
1989年 | 115篇 |
1988年 | 50篇 |
1987年 | 56篇 |
1986年 | 53篇 |
1985年 | 143篇 |
1984年 | 111篇 |
1983年 | 90篇 |
1982年 | 110篇 |
1981年 | 160篇 |
1980年 | 53篇 |
1979年 | 41篇 |
1978年 | 38篇 |
1977年 | 36篇 |
1976年 | 34篇 |
1975年 | 35篇 |
1974年 | 35篇 |
1973年 | 29篇 |
1972年 | 24篇 |
1970年 | 24篇 |
排序方式: 共有6432条查询结果,搜索用时 15 毫秒
11.
Burns T.J. Rogers S.K. Oxley M.E. Ruck D.W. 《IEEE transactions on aerospace and electronic systems》1996,32(2):628-649
The wavelet filters of the conventional 3D multiresolution analysis possess homogeneous spatial and temporal frequency characteristics which limits one's ability to match filter frequency characteristics to signal frequency behavior. Also, the conventional 3D multiresolution analysis employs an oct-tree decomposition structure which restricts the analysis of signal details to identical resolutions in space and time. This paper presents a 3D wavelet multiresolution analysis constructed from nonhomogeneous spatial and temporal filters, and an orthogonal sub-band coding scheme that decouples the spatial and temporal decomposition processes 相似文献
12.
T. K. Sirazetdinov 《Russian Aeronautics (Iz VUZ)》2007,50(1):30-36
A brief review of studies on simulation and control of a porous cooling process taking into account material transpiration is given. An approximated solution for an equation of the one-dimensional problem of fast ablation is also presented. 相似文献
13.
S. K. Solanki M. Fligge 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,29(12):L169-1940
The contribution to total solar irradiance variations by the magnetic field at the solar surface is estimated. Detailed models of the irradiance changes on the basis of magnetograms show that magnetic features at the solar surface account for over 90% of the irradiance variations on a solar rotation time scale and at least 70% on a solar cycle time scale. If the correction to the VIRGO record proposed by Fröhlich & Finsterle (2001) is accepted, then magnetic features at the solar surface are responsible for over 90% of the solar cycle irradiance variations as well. 相似文献
14.
Ahmad F. Frazer G.J. Kassam S.A. Amin M.G. 《IEEE transactions on aerospace and electronic systems》2004,40(1):206-220
A coarray-based near-field, wideband synthetic aperture beamformer using stepped-frequency signal synthesis and post-data acquisition processing is presented. While coarray techniques offer significant reduction in the number of array elements for a given angular resolution, the hybrid subarray-stepped frequency realization of wideband systems simplifies implementations and offers flexibility in beamforming. Proof of concept is provided using real data collected in an anechoic chamber for several pulse shapes and array weightings. 相似文献
15.
The results of the experimental studies of damping characteristics of a composite torsion bar in the helicopter main rotor
hingeless hub are presented. A variant of their improvement is considered. 相似文献
16.
We present an algorithm for calculating the shells of revolution with the branching meridian using the triangular finite elements, the rigidity matrices of which are formed based on the vector method of displacement interpolation [1]. The correct kinematic and static conditions of shell conjugation on the line of their coupling have been developed. The shell structure consisting of a cylinder and adjacent shells is calculated under various conditions of support. 相似文献
17.
I. S. Akhmed’yanov 《Russian Aeronautics (Iz VUZ)》2009,52(4):383-389
The application of the quadrature method [1] to analyzing the shells of revolution under symmetrical loading relative to the
zero meridian is considered. The method can be treated as a generalization of the method presented in [2] to solve the Volterra
integral equation of the second kind. 相似文献
18.
A problem of determining a shape of the airfoil being streamlined by a potential incompressible inviscid flow is solved by
the successive approximation method using a specified chord velocity diagram. It is shown that a closed airfoil that possesses
a specified chord velocity diagram can be constructed with a sufficient accuracy; if the chord diagram is unsuccessfully specified,
the closed airfoil may prove to be not univalent, that is, physically unrealizable. 相似文献
19.
Leblang M. Dunham S.J. Pappalardi F. 《Aerospace and Electronic Systems Magazine, IEEE》2004,19(11):18-23
HMS SCOTT is a United Kingdom ocean survey vessel that hosts a state-of-the-art deep ocean mapping system which was designed, developed, and is currently maintained and periodically updated by the Space and Naval Warfare Systems Center, San Diego, (SSC San Diego). A recent update of this system consisted of the replacement of an obsolete and very costly to maintain inertial navigation system. Another reason for updating the ship's inertial system was to provide higher accuracy attitude data, than was previously available with the old inertial system, to the high resolution multi-beam sonar system in order to produce improved bathymetric charts. After conducting a market survey of suitable inertial navigator systems, the Kearfott SEANAV ring laser gyro navigator (RLGN) system, using a monolithic T-24 gyro, was selected to replace the old inertial system. The selection of the SEANAV RLGN was based on its relatively low cost, high reliability, and, particularly, the roll and pitch data accuracies of typically less than 1-arc-minute. This attitude data accuracy was key to enable a significant improvement in the bathymetry data accuracy. Two SEANAV systems were integrated with GPS receivers, a system master time code generator, and electro magnetic (EM) log and Doppler sonar speed sensors to provide the navigation portion of the mapping data. Operational testing of this updated system aboard HMS SCOTT, in November, 2003, showed a marked improvement in the quality of the map product due, in part, to the improved attitude data provided by the SEANAV RLGN system. 相似文献
20.
Performance evaluation for MAP state estimate fusion 总被引:1,自引:0,他引:1
Chang K.C. Zhi Tian Mori S. 《IEEE transactions on aerospace and electronic systems》2004,40(2):706-714
This paper presents a quantitative performance evaluation method for the maximum a posteriori (MAP) state estimate fusion algorithm. Under ideal conditions where data association is assumed to be perfect, it has been shown that the MAP or best linear unbiased estimate (BLUE) fusion formula provides the best linear minimum mean squared estimate (LMMSE) given local estimates under the linear Gaussian assumption for a static system. However, for a dynamic system where fusion is recursively performed by the fusion center on local estimates generated from local measurements, it is not obvious how the MAP algorithm will perform. In the past, several performance evaluation methods have been proposed for various fusion algorithms, including simple convex combination, cross-covariance combination, information matrix, and MAP fusion. However, not much has been done to quantify the steady state behavior of these fusion methods for a dynamic system. The goal of this work is to present analytical fusion performance results for MAP state estimate fusion without extensive Monte Carlo simulations, using an approach developed for steady state performance evaluation for track fusion. Two different communication strategies are considered: fusion with and without feedback to the sensors. Analytic curves for the steady state performance of the fusion algorithm for various communication patterns are presented under different operating conditions. 相似文献