全文获取类型
收费全文 | 6395篇 |
免费 | 50篇 |
国内免费 | 33篇 |
专业分类
航空 | 2960篇 |
航天技术 | 2256篇 |
综合类 | 251篇 |
航天 | 1011篇 |
出版年
2021年 | 51篇 |
2018年 | 94篇 |
2017年 | 85篇 |
2016年 | 61篇 |
2015年 | 53篇 |
2014年 | 133篇 |
2013年 | 171篇 |
2012年 | 145篇 |
2011年 | 244篇 |
2010年 | 168篇 |
2009年 | 253篇 |
2008年 | 327篇 |
2007年 | 183篇 |
2006年 | 180篇 |
2005年 | 189篇 |
2004年 | 152篇 |
2003年 | 195篇 |
2002年 | 237篇 |
2001年 | 248篇 |
2000年 | 128篇 |
1999年 | 170篇 |
1998年 | 185篇 |
1997年 | 156篇 |
1996年 | 168篇 |
1995年 | 194篇 |
1994年 | 174篇 |
1993年 | 105篇 |
1992年 | 137篇 |
1991年 | 67篇 |
1990年 | 67篇 |
1989年 | 123篇 |
1988年 | 59篇 |
1987年 | 52篇 |
1986年 | 57篇 |
1985年 | 190篇 |
1984年 | 164篇 |
1983年 | 122篇 |
1982年 | 131篇 |
1981年 | 188篇 |
1980年 | 48篇 |
1979年 | 41篇 |
1978年 | 49篇 |
1977年 | 45篇 |
1976年 | 34篇 |
1975年 | 54篇 |
1974年 | 42篇 |
1972年 | 51篇 |
1971年 | 43篇 |
1970年 | 36篇 |
1969年 | 40篇 |
排序方式: 共有6478条查询结果,搜索用时 15 毫秒
31.
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
32.
This paper discusses and evaluates two innovative SETI education programs conducted at the University of Western Sydney, viz: the SETI Pathways Program and the Life in the Universe Curriculum Project. 相似文献
33.
34.
An experimental investigation of three eigen DF techniques 总被引:1,自引:0,他引:1
The comparative direction-finding (DF) performance of multiple signal classification (MUSIC), ROOT-MUSIC, and estimation of signal parameters via rotational invariance techniques (ESPRIT) is considered. Data were collected from two target transmitters operating simultaneously. The objective of the experiment was to evaluate multipath resolution capability using measurement precision equivalent to that found in modern radio direction-finding systems 相似文献
35.
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
36.
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
37.
S. Carbone L.F. Padilha M.B. Rosa D.K. Pinheiro N.J. Schuch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,37(12):2178-II
The first estimations of the aerosol optical thickness (AOT) using Langley Method at Southern Space Observatory (SSO) at Southern Brazil (29.4°S, 53.8°W) are presented. In addition to ozone and sulphur dioxide columns, AOT can be obtained using Brewer Spectrophotometer at specific wavelengths: 306.3, 310.1, 313.5, 316.8 and 320.1 nm. The AOT was obtained for the period from November/2002 to May/2003. Very low AOT averages were obtained, whose values were about 0.21 ± 0.03 at 306.3 nm, 0.21 ± 0.02 at 310.1 nm, 0.19 ± 0.02 at 313.5 nm, 0.20 ± 0.02 at 316.8 nm and 0.20 ± 0.02 at 320.0 nm for all period analysed. Different behaviour of AOT were obtained at two daily specific periods of aerosol accumulation, one in the afternoons from November/2002 to February/2003, caused mainly by a mild biomass burning season’s in the region and other in the mornings from March to May/2003, due the high relative humidity presented in the region studied. 相似文献
38.
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
39.
L. V. Zasova V. I. Moroz V. M. Linkin I. V. Khatuntsev B. S. Maiorov 《Cosmic Research》2006,44(4):364-383
The goal of this paper is to summarize the experimental data on the atmosphere of Venus obtained after 1985, when the VIRA (Venus International Reference Atmosphere) or COSPAR model was published. Among the most important results that have appeared since then are the following: measurements of the vertical temperature profile by the VEGA spacecraft with high precision and high altitude resolution; measurements made with balloons of the VEGA spacecraft; radio occultation measurements of Magellan, Venera-15, and Venera-16; and temperature profiles derived from the data of infrared spectrometry obtained by Venera-15. The new result as compared to VIRA is the creation of a model of the atmosphere in the altitude range 55 to 100 km dependent on local time. This model is presented in our paper in tabulated form. 相似文献
40.
D L Stephens L W Townsend J Miller C Zeitlin L Heilbronn 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):901-905
Deep-space manned flight as a reality depends on a viable solution to the radiation problem. Both acute and chronic radiation health threats are known to exist, with solar particle events as an example of the former and galactic cosmic rays (GCR) of the latter. In this experiment Iron ions of 1A GeV are used to simulate GCR and to determine the secondary radiation field created as the GCR-like particles interact with a thick target. A NASA prepared food pantry locker was subjected to the iron beam and the secondary fluence recorded. A modified version of the Monte Carlo heavy ion transport code developed by Zeitlin at LBNL is compared with experimental fluence. The foodstuff is modeled as mixed nuts as defined by the 71st edition of the Chemical Rubber Company (CRC) Handbook of Physics and Chemistry. The results indicate a good agreement between the experimental data and the model. The agreement between model and experiment is determined using a linear fit to ordered pairs of data. The intercept is forced to zero. The slope fit is 0.825 and the R2 value is 0.429 over the resolved fluence region. The removal of an outlier, Z=14, gives values of 0.888 and 0.705 for slope and R2 respectively. 相似文献