全文获取类型
收费全文 | 3199篇 |
免费 | 10篇 |
国内免费 | 5篇 |
专业分类
航空 | 1192篇 |
航天技术 | 1041篇 |
综合类 | 19篇 |
航天 | 962篇 |
出版年
2022年 | 15篇 |
2021年 | 37篇 |
2019年 | 16篇 |
2018年 | 128篇 |
2017年 | 102篇 |
2016年 | 116篇 |
2015年 | 41篇 |
2014年 | 111篇 |
2013年 | 135篇 |
2012年 | 118篇 |
2011年 | 158篇 |
2010年 | 127篇 |
2009年 | 192篇 |
2008年 | 190篇 |
2007年 | 122篇 |
2006年 | 74篇 |
2005年 | 101篇 |
2004年 | 94篇 |
2003年 | 106篇 |
2002年 | 83篇 |
2001年 | 113篇 |
2000年 | 36篇 |
1999年 | 53篇 |
1998年 | 61篇 |
1997年 | 42篇 |
1996年 | 43篇 |
1995年 | 80篇 |
1994年 | 61篇 |
1993年 | 34篇 |
1992年 | 45篇 |
1991年 | 10篇 |
1990年 | 19篇 |
1989年 | 41篇 |
1988年 | 11篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 70篇 |
1984年 | 56篇 |
1983年 | 48篇 |
1982年 | 42篇 |
1981年 | 82篇 |
1980年 | 25篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1972年 | 13篇 |
1971年 | 11篇 |
排序方式: 共有3214条查询结果,搜索用时 15 毫秒
881.
B. V. Nerubailo 《Russian Aeronautics (Iz VUZ)》2014,57(2):127-133
The solution is obtained based on the differential equations for the general theory of shells and approximate equations that are the components of the method of asymptotic synthesis. Numerical results are presented. 相似文献
882.
In this paper, the results of investigating a coaxial gas ejector without increase of passive flow pressure are presented. A technique for calculation of coaxial ejectors has been developed. This investigation has resulted in the optimal structure of ejector with a high value of ejection coefficient. 相似文献
883.
L. S. Yanovskii V. M. Ezhov A. A. Molokanov R. M. Stepanova K. V. Sharanina A. V. Kirsanov 《Russian Aeronautics (Iz VUZ)》2014,57(2):193-197
The results of investigating a domestic synthetic hydraulic fluid of new generation are presented. By comparing with the existing domestic and foreign analogues, we specify the main advantages and disadvantages of this hydraulic fluid. 相似文献
884.
Prokhorov M. I. Bogomolov V. V. Bogomolov A. V. Iyudin A. F. Kalegaev V. V. Myagkova I. N. Osedlo V. I. Svertilov S. I. 《Cosmic Research》2022,60(4):241-253
Cosmic Research - The use of the normalized range method for an analysis of the fast variability of electron fluxes in near-Earth space is proposed. This method makes it possible to conclude... 相似文献
885.
Víctor Puente 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(8):2359-2367
Tropospheric delay is one of the major sources of error in VLBI (Very Long Baseline Interferometry) analysis. The principal component of this error can be accurately computed through reliable surface pressure data —hydrostatic delay— yet there is also a small but volatile component —wet delay— which is difficult to be modelled a priori. In VLBI analysis, troposphere delay is typically modelled in the theoretical delays using Zenith Hydrostatic Delays (ZHD) and a dry mapping function. Zenith Wet Delay (ZWD) is not modelled but estimated in the analysis process. This work studies inter alia the impact of including external GNSS estimates to model a priori ZWD in VLBI analysis, as well as other models of a priori ZWD.In a first stage, two different sources of GNSS troposphere products are compared to VLBI troposphere estimates in a period of 5 years. The solution with the best agreement to VLBI results is injected in the VLBI analysis as a priori ZWD value and is compared to other options to model a priori ZWD. The dataset used for this empirical analysis consists of the six CONT campaigns.It has been found that modelling a priori ZWD has no significant impact either on baseline length and coordinates repeatabilities. Nevertheless, modelling a priori ZWD can change the magnitude of the estimated coordinates a few millimeters in the up component with respect to the non-modelling approach. In addition, the influence of a priori ZWD on Earth Orientation Parameters (EOP) and troposphere estimates —Zenith Total Delays (ZTD) and gradients—has also been analysed, resulting in a small but significant impact on both geodetic products. 相似文献
886.
R.V. Garcia P.C.P.M. Pardal H.K. Kuga M.C. Zanardi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(2):1038-1050
This article compares the attitude estimated by nonlinear estimator Cubature Kalman Filter with results obtained by the Extended Kalman Filter and Unscented Kalman Filter. Currently these estimators are the subject of great interest in attitude estimation problems, however, mostly the Extended Kalman Filter has been applied to real problems of this nature. In order to evaluate the behavior of the Extended Kalman Filter, Unscented Kalman Filter and Cubature Kalman Filter algorithms when submitted to realistic situations, this paper uses real data of sensors on-board the CBERS-2 remote sensing satellite (China Brazil Earth Resources Satellite). It is observed that, for the case studied in this article, the filters are very competitive and present advantages and disadvantages that should be dealt with according to the requirements of the problem. 相似文献
887.
V.V. Kalegaev N.A. Vlasova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Dynamical features of proton fluxes at high and middle latitudes were studied based on data measured by Sun-synchronous low-altitude (800 km height) polar-orbiting three NOAA series satellites: POES 15, 16, and 17 during the geomagnetic storm on January, 21–22, 2005. Data from three satellites that passed the Northern hemisphere along different MLTs allow reconstructing the longitudinal distribution of the proton fluxes. Measurements of protons with energies of 30–80 keV and 80–240 keV (the ring current energy range) by 0- and 90-detectors were used to evaluate and compare the longitudinal asymmetry of proton flux distribution measured in the regions equatorward and poleward of the isotropic boundary. It was found that during all the phases of the geomagnetic storm distribution of the maximum flux of precipitating protons (0-detector data) is sufficiently asymmetric. The maximal flux position along MLT is moving from pre-midnight sector in quiet time to post-midnight one before and during SSC and moving back during recovery phase. The longitudinal distribution of precipitation maxima demonstrates the local increase in afternoon sector (approximately at 13:30 MLT) and decrease in the dusk one during SSC. These features are evident consequence of the magnetosphere compression. To identify the origin of the particles, the locations of maximum fluxes have been projected to the magnetosphere. It was determined that during geomagnetic storm main and recovery phases maximum fluxes were measured at latitudes poleward of the isotropic boundary. To evaluate the trapped particle flux asymmetry, the particle fluences (90-detector data) were calculated along the satellite orbit from L = 2 to the isotropic boundary. The total fluences of trapped particles calculated along the satellite orbit show regular asymmetry between dusk and dawn during main and recovery phases. The maximal intensity of proton fluxes of both investigated populations located poleward and equatorward of the isotropic boundary is achieved during SSC. The total flux measured during crossing the anisotropic region can be considered as a proxy for ring current injection rate. 相似文献
888.
I.S. Batista M.A. Abdu Paulo A.B. Nogueira R.R. Paes J.R. de Souza B.W. Reinisch V.H. Rios 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
This study reports on ionospheric disturbances that occurred in the early morning hours in the South American–Atlantic sector during a few intense/super storm events. The events were observed at latitudes close to the southern crest of the equatorial ionization anomaly (EIA) as an unusual intensification of the F region electron density peak at local times when the EIA is not usually developed. All the events were observed at pre dawn-morning hours, under conditions of northward interplanetary geomagnetic field. Large scale traveling ionospheric disturbances that are launched during highly disturbed conditions and/or equatorward surges in the thermospheric meridional winds seem to be the most probable causes of the observed disturbances. 相似文献
889.
Low thrust interplanetary flight is considered. Firstly, the fuel-optimal control is found. Then the angular motion is synthesized. This motion provides the thruster tracking of the required by optimal control direction. And, finally, reaction wheel control law for tracking this angular motion is proposed and implemented. The numerical example is given and total operation time for thrusters is found. Disturbances from solar pressure, thrust eccentricity, inaccuracy of reaction wheels installation and errors of inertia tensor are taken into account. 相似文献
890.
The minimal scale of the Alfvénic turbulence transverse to the external magnetic field in the topside auroral ionosphere is investigated using electric field observations of the FAST spacecraft (the resolution 512 s–1). The events in which the power law form of the electric fluctuation spectra with a 2.0–2.5 slope (typical of Alfvénic turbulence) remains unchanged down to acoustic gyroradius ρs or ion gyroradius ρi local values are illustrated for the first time. In this case, the character of spectrum variation does not change at the electron inertial length λe, which is much larger than ρs and ρi for FAST altitudes (apogee ~4000 km). We have tried to explain this experimental fact by consideration of the known scenarios of the appearance of a small transverse scale in an Alfvénic perturbation. It has been noted that the effects of front steepening in an inertial Alfvén wave with a finite amplitude, which propagates at an angle smaller than (me/mi)1/2 with respect to the transverse direction, can result in small transverse scales comparable with acoustic gyroradius appearing in a perturbation. 相似文献