全文获取类型
收费全文 | 3483篇 |
免费 | 5篇 |
国内免费 | 6篇 |
专业分类
航空 | 1550篇 |
航天技术 | 1250篇 |
综合类 | 181篇 |
航天 | 513篇 |
出版年
2021年 | 21篇 |
2019年 | 23篇 |
2018年 | 62篇 |
2017年 | 36篇 |
2016年 | 38篇 |
2015年 | 21篇 |
2014年 | 77篇 |
2013年 | 92篇 |
2012年 | 79篇 |
2011年 | 128篇 |
2010年 | 75篇 |
2009年 | 142篇 |
2008年 | 175篇 |
2007年 | 95篇 |
2006年 | 87篇 |
2005年 | 91篇 |
2004年 | 97篇 |
2003年 | 100篇 |
2002年 | 164篇 |
2001年 | 165篇 |
2000年 | 53篇 |
1999年 | 86篇 |
1998年 | 101篇 |
1997年 | 80篇 |
1996年 | 102篇 |
1995年 | 121篇 |
1994年 | 85篇 |
1993年 | 52篇 |
1992年 | 78篇 |
1991年 | 32篇 |
1990年 | 27篇 |
1989年 | 67篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1985年 | 113篇 |
1984年 | 99篇 |
1983年 | 61篇 |
1982年 | 85篇 |
1981年 | 107篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1978年 | 24篇 |
1977年 | 23篇 |
1975年 | 19篇 |
1974年 | 25篇 |
1972年 | 20篇 |
1971年 | 21篇 |
1970年 | 20篇 |
1969年 | 24篇 |
排序方式: 共有3494条查询结果,搜索用时 572 毫秒
11.
Servidia P.A. Sanchez Pena R.S. 《IEEE transactions on aerospace and electronic systems》2005,41(2):584-598
The attitude stabilization of a spacecraft using thrusters is considered from a practical point of view, i.e., when actuator constraints, uncertainties and failures, measurement noise, fuel consumption, and inertia matrix uncertainty are considered. A variable structure controller based on sliding modes is obtained first, which guarantees global exponential stability under actuator constraints, uncertainties, and failures. The design is based on a continuous average-proportional torque selection function and a set of feasible sliding surfaces, which may be adapted to improve performance. Exponential convergence towards ultimate bounds is guaranteed when all other practical issues arise. 相似文献
12.
Wang L. Dawson J.M. Hornak L.A. Famouri P. Ghaffarian R. 《IEEE transactions on aerospace and electronic systems》2004,40(2):567-575
Closed-loop control has been successfully applied to a microelectromechanical systems (MEMS) lateral comb resonator device in real-time to perform impulse disturbance damping and sinusoidal position control, enabled by the use of a through-wafer optical microprobe to obtain position feedback. This result leverages the application of lifetime, in-situ control of MEMS in order to provide quality assurance of microsystems in safety critical applications. A position feedback signal produced by a through-wafer optical microprobe has been used for comb resonator system model identification by two independent methods to accurately determine the effective mass, damping, and spring constant values of the device. After accurate determination of system parameters, closed-loop impulse disturbance damping and proportional-integral-differential (PID) translational control were applied. Closed-loop control results presented indicate controllability of such microstructures and response times on the order of the natural frequency of the device. 相似文献
13.
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
14.
The James Webb Space Telescope (JWST) project at the NASA, Goddard Space Flight Center (GSFC) is responsible for the development, launch, flight, and science operations for the telescope. The project is in phase B with its launch scheduled for no earlier than June 2013. The project is a partnership among NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The JWST mission team is fully in place, including major ESA and CSA subcontractors. This provides an overview of the planned JWST science, current architecture focusing on the instrumentation, and mission status, including technology developments, and risks. 相似文献
15.
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
16.
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
17.
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
18.
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
19.
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
20.
With a precise geoid, GOCE will allow an estimation of absolute dynamic topography from altimetry. The projected benefits
to operational oceanography and its applications are analyzed herein. After a brief overview of operational oceanography,
we explain how the new geoids will be used in the future to improve real time altimeter products and to better constrain modelling
and data assimilation systems. A significant impact is expected both for mesoscale (e.g. better estimations and forecasts of currents for pollution monitoring, marine safety, offshore industry) and climate (better
initialization of coupled ocean/atmosphere models) applications.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献