全文获取类型
收费全文 | 7055篇 |
免费 | 15篇 |
国内免费 | 15篇 |
专业分类
航空 | 3657篇 |
航天技术 | 2536篇 |
综合类 | 28篇 |
航天 | 864篇 |
出版年
2019年 | 41篇 |
2018年 | 129篇 |
2017年 | 75篇 |
2016年 | 41篇 |
2014年 | 115篇 |
2013年 | 174篇 |
2012年 | 137篇 |
2011年 | 215篇 |
2010年 | 156篇 |
2009年 | 252篇 |
2008年 | 311篇 |
2007年 | 172篇 |
2006年 | 167篇 |
2005年 | 180篇 |
2004年 | 164篇 |
2003年 | 238篇 |
2002年 | 135篇 |
2001年 | 237篇 |
2000年 | 140篇 |
1999年 | 203篇 |
1998年 | 220篇 |
1997年 | 163篇 |
1996年 | 207篇 |
1995年 | 250篇 |
1994年 | 242篇 |
1993年 | 143篇 |
1992年 | 160篇 |
1991年 | 90篇 |
1990年 | 86篇 |
1989年 | 177篇 |
1988年 | 74篇 |
1987年 | 90篇 |
1986年 | 71篇 |
1985年 | 234篇 |
1984年 | 173篇 |
1983年 | 154篇 |
1982年 | 170篇 |
1981年 | 226篇 |
1980年 | 76篇 |
1979年 | 60篇 |
1978年 | 65篇 |
1977年 | 63篇 |
1976年 | 48篇 |
1975年 | 73篇 |
1974年 | 48篇 |
1973年 | 49篇 |
1972年 | 59篇 |
1971年 | 45篇 |
1970年 | 50篇 |
1969年 | 45篇 |
排序方式: 共有7085条查询结果,搜索用时 0 毫秒
111.
This paper presents a Lagrangian formulation for studying the dynamics and control of the proposed Space Station based Mobile Servicing System (MSS) for a particular case of inplane libration and maneuvers. The simplified case is purposely considered to help focus on the effects of structural and joint flexibility parameters of the MSS on the complex interactions between the station and manipulator dynamics during slewing and translational maneuvers. The response results suggest that under critical combinations of parameters, the system can become unstable. During maneuvers, the deflection of the MSS can become excessive, leading to positioning error of the payload. At the same time the libration error can also be significant. A linear quadratic regulator is designed to control the deflection of the manipulator and maintain the station at its operating configuration. 相似文献
112.
113.
Effect of bacterial population density on germination wheat seeds and dynamics of simple artificial ecosystems. 总被引:1,自引:0,他引:1
L A Somova N S Pechurkin A B Sarangova T I Pisman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(9):1611-1615
Effect of the size of rhizospheric bacterial populations on germination of seeds and development of simple terrestrial "wheat plants--rhizospheric microorganisms--artificial soil" and "wheat plants-artificial soil" systems has been studied. Experiments demonstrated that within specify ranges in the inoculate, the rhizospheric bacteria are capable of increasing the yield of germinated seeds and stimulate the growth of plantlets. Germination of seeds inoculated with bacteria was either stimulated, or inhibited or remained at control levels depending on the amount of bacteria. Plant biomass growth and total photoassimilation has been found to depend on the amount of bacteria on the plant roots: the higher the amount of bacteria on plant roots, the smaller is the biomass of plants but the total photoassimilation is, higher. Thus, depending on the amount of bacteria on the roots of plants the system either increases the biomass of plants or increases the total photoassimilation, i.e. "pumps" carbon through itself involving bacteria. Grant numbers: N99-04-96017, N15. 相似文献
114.
Rice M. Oliphant T. Haddadin O. McIntire W. 《IEEE transactions on aerospace and electronic systems》2007,43(4):1484-1495
This paper describes data-aided signal level and noise variance estimators for Gaussian minimum shift keying (GMSK) when the observations are limited to the output of a filter matched to the first pulse-amplitude modulation (PAM) pulse in the equivalent PAM representation. The estimators are based on the maximum likelihood (ML) principle and assume burst-mode transmission with known timing and a block of L0 known bits. While it is well known that ML estimators are asymptotically unbiased and efficient, the analysis quantifies the rate at which the estimators approach these asymptotic properties. It is shown that the carrier phase, amplitude, and noise variance estimators are unbiased and can achieve their corresponding Cramer-Rao bounds with modest combinations of signal-to-noise ratio and observation length. The estimates are used to estimate the signal-to-noise ratio. It is shown that the mean squared error performance of the ratio increases with signal-to-noise ratio while the mean squared error performance of the ratio in decibels decreases with signal-to-noise ratio. Simulation results are provided to confirm the accuracy of the analytic results. 相似文献
115.
A. Aboudan G. Colombatti C. Bettanini F. Ferri S. Lewis B. Van Hove O. Karatekin S. Debei 《Space Science Reviews》2018,214(5):97
On 19th October 2016 Schiaparelli module of the ExoMars 2016 mission flew through the Mars atmosphere. After successful entry and descent under parachute, the module failed the last part of the descent and crashed on the Mars surface. Nevertheless the data transmitted in real-time by Schiaparelli during the entry and descent, together with the entry state vector as initial condition, have been used to reconstruct both the trajectory and the profiles of atmospheric density, pressure and temperature along the traversed path.The available data-set is only a small sub-set of the whole data acquired by Schiaparelli, with a limited data rate (8 kbps) and a large gap during the entry because of the plasma blackout on the communications.This paper presents the work done by the AMELIA (Atmospheric Mars Entry and Landing Investigations and Analysis) team in the exploitation of the available inertial and radar data. First a reference trajectory is derived by direct integration of the inertial measurements and a strategy to overcome the entry data gap is proposed. First-order covariance analysis is used to estimate the uncertainties on all the derived parameters. Then a refined trajectory is computed incorporating the measurements provided by the on-board radar altimeter.The derived trajectory is consistent with the events reported in the telemetry and also with the impact point identified on the high-resolution images of the landing site.Finally, atmospheric profiles are computed tacking into account the aerodynamic properties of the module. Derived profiles result in good agreement with both atmospheric models and available remote sensing observations. 相似文献
116.
Both the Capon and APES estimators can be shown to belong to the class of matched-filterbank spectral estimators and can be used to obtain complex spectral estimates that have more narrow spectral peaks and lower sidelobe levels than the fast Fourier transform (FFT) methods. It can also be shown that APES has better statistical performance than Capon. In this paper, we address the issue of how to efficiently implement Capon and APES for spectral estimation 相似文献
117.
This paper studies the application of Kalman filtering to single-target track systems in airborne radar. An angle channel Kalman filter is configured which incorporates measures of range, range rate, and on-board dynamics. Theoretical performance results are given and a discussion of methods for reducing the complexity of the Kalman gain computation is presented. A suboptimal antenna controller which operates on the outputs of the angle Kalman filter is also described. In addition, methodological improvements are shown to exist in the design of range and range-rate trackers using the Kalman filter configuration. 相似文献
118.
The application of chaos theory has become popular to understand the nature of various features of solar activity because most of them are far from regular. The usual approach, however, that is based on finding low-dimensional structures of the underlying processes seems to be successful only in a few exceptional cases, such as in rather coherent phenomena as coronal pulsations. It is important to note that most phenomena in solar radio emission are more complex. We present two kinds of techniques from nonlinear dynamics which can be useful to analyse such phenomena:
- Fragmentation processes observed in solar spike events are studied by means of symbolic dynamics methods. Different measures of complexity calculated from such observations reveal that there is some order in this fragmentation.
- Bursts are a typical transient phenomenon. To study energization processes causing impulsive microwave bursts, the wavelet analysis is applied. It exhibits structural differences of the pre- and post-impulsive phase in cases where the power spectra of both are not distinct.
119.
L. G. Blomberg J. A. Cumnock 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(12):2161-2165
Mercury has a small but intriguing magnetosphere. In this brief review, we discuss some similarities and differences between Mercury’s and Earth’s magnetospheres. In particular, we discuss how electric and magnetic field measurements can be used as a diagnostic tool to improve our understanding of the dynamics of Mercury’s magnetosphere. These points are of interest to the upcoming ESA-JAXA BepiColombo mission to Mercury. 相似文献
120.