全文获取类型
收费全文 | 10153篇 |
免费 | 31篇 |
国内免费 | 30篇 |
专业分类
航空 | 5188篇 |
航天技术 | 3376篇 |
综合类 | 212篇 |
航天 | 1438篇 |
出版年
2021年 | 73篇 |
2018年 | 139篇 |
2017年 | 75篇 |
2016年 | 76篇 |
2014年 | 179篇 |
2013年 | 227篇 |
2012年 | 223篇 |
2011年 | 323篇 |
2010年 | 219篇 |
2009年 | 354篇 |
2008年 | 427篇 |
2007年 | 240篇 |
2006年 | 228篇 |
2005年 | 236篇 |
2004年 | 224篇 |
2003年 | 309篇 |
2002年 | 288篇 |
2001年 | 377篇 |
2000年 | 200篇 |
1999年 | 246篇 |
1998年 | 308篇 |
1997年 | 214篇 |
1996年 | 272篇 |
1995年 | 340篇 |
1994年 | 326篇 |
1993年 | 186篇 |
1992年 | 234篇 |
1991年 | 136篇 |
1990年 | 128篇 |
1989年 | 258篇 |
1988年 | 124篇 |
1987年 | 125篇 |
1986年 | 122篇 |
1985年 | 328篇 |
1984年 | 270篇 |
1983年 | 227篇 |
1982年 | 251篇 |
1981年 | 312篇 |
1980年 | 117篇 |
1979年 | 95篇 |
1978年 | 100篇 |
1977年 | 84篇 |
1976年 | 74篇 |
1975年 | 113篇 |
1974年 | 83篇 |
1973年 | 70篇 |
1972年 | 106篇 |
1971年 | 85篇 |
1970年 | 70篇 |
1969年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Y. Yan J. Huang B. Chen Y. Liu C. Tan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Radio bursts with fine structures in decimetric–centimetric wave range are generally believed to manifest the primary energy release process during flare/CME events. By spectropolarimeters in 1–2 GHz, 2.6–3.8 GHz, and 5.2–7.6 GHz at NAOC/Huairou with very high temporal (1.25–8 ms) and spectral (4–20 MHz) resolutions, the zebra patterns, spikes, and new types of radio fine structures with mixed frequency drift features are observed during several significant flare/CME events. In this paper we will discuss the occurrence of radio fine structures during the impulsive phase of flares and/or CME initiations, which may be connected to the magnetic reconnection processes. 相似文献
912.
Alicia L. Clúa de Gonzalez Walter D. Gonzalez 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
In the present paper the local-time variations in the disturbance of the geomagnetic-field horizontal component (H) for eight intense geomagnetic storms that occurred during the descending phase of solar cycle 23 have been analyzed. The study was based on the plot of contour lines of the H-depletion intensity in the plane local time versus universal time (LT–UT maps) with the objective of observing how the morphology and evolution of the ring current is mapped into the surface of the Earth in presence of intense geomagnetic storms. 相似文献
913.
C. Satirapod I. Trisirisatayawong L. Fleitout J.D. Garaud W.J.F. Simons 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Following previous findings from ongoing GPS research in Thailand since 2004 we continue to exploit the GPS technique to monitor and model land motions induced by the Sumatra–Andaman Earthquake. Our latest results show that up to the end of 2010, Thailand has been co-seismically displaced and is subsequently undergoing a post-seismic horizontal deformation with total displacements (co-seismic plus post-seismic) ranging from 10.5 to 74.7 cm. We observed the largest horizontal displacements in the southern part of Thailand and moderate and small displacements in the central and northern parts. In addition to horizontal displacements throughout Thailand, continuous GPS measurements show that large parts of Thailand are subsiding at rates up to 1 cm/yr. It is the first time that such vertical post-seismic deformations at large distances (650–1500 km away from the Earthquake’s epicentre) have been recorded. We have investigated the physical processes leading to the observed subsidence. While after-slip on the subduction interface induces negligible or even slightly positive vertical motions, relaxation in the asthenosphere is associated with a sizable subsidence. Predictions from a 3D finite element model feature an asthenosphere with an effective viscosity of the order of 3 * 1018 Pas, fit the horizontal post-seismic data and the observed subsidence well. This model is then used to predict the subsidence over the whole seismic cycle. The subsidence should go on with a diminishing rate through the next two decades and its final magnitude should not exceed 10 cm in the Bangkok area. 相似文献
914.
W. Menn O. Adriani G.C. Barbarino G.A. Bazilevskaya R. Bellotti M. Boezio E.A. Bogomolov L. Bonechi M. Bongi V. Bonvicini S. Borisov S. Bottai A. Bruno F. Cafagna D. Campana R. Carbone P. Carlson M. Casolino G. Castellini L. Consiglio M.P. De Pascale C. De Santis N. De Simone V. Di Felice A.M. Galper W. Gillard L. Grishantseva G. Jerse A.V. Karelin S.V. Koldashov S.Y. Krutkov A.N. Kvashnin A. Leonov V. Malakhov V. Malvezzi L. Marcelli A.G. Mayorov V.V. Mikhailov E. Mocchiutti A. Monaco N. Mori N. Nikonov G. Osteria F. Palma P. Papini M. Pearce P. Picozza C. Pizzolotto M. Ricci S.B. Ricciarini 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
915.
Rajat Acharya Bijoy Roy M.R. Sivaraman Ashish Dasgupta 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
It is important to use models developed specifically for the equatorial ionospheric estimation for real-time applications, particularly in Satellite Navigation. This work demonstrates a methodology for improved predictions of VTEC in real time using the model developed for the equatorial ionosphere by the authors. This work has been done using TEC data of the low solar activity period of 2005 obtained using dual frequency GPS receivers installed under the GAGAN project of ISRO. For the purpose, the model is first used in conjunction with Kriging technique. Improvement in accuracy is observed when compared with the estimations from the model alone using the measurements as true reference. Further improvement is obtained by Bayesian combination of these estimates with independent Neural Network based predictions. Statistical performance of improvement is provided. An improvement of ∼1 m in confidence level of estimation of VTEC is obtained. 相似文献
916.
Le Cadre J.-P. Jaetffret C. 《IEEE transactions on aerospace and electronic systems》1999,35(3):801-818
This paper deals with the analysis of the convergence of iterative methods for bearings only tracking (BOT). A geometric and unified framework is developed. Explicit sufficient conditions ensuring convergence of iterative methods for maximization of the likelihood functional are then derived 相似文献
917.
918.
A fast feature ranking algorithm for classification in the presence of high dimensionahty and small sample size is proposed. The basic idea is that the important features force the data points of the same class to maintain their intrinsic neighbor relations, whereas neighboring points of different classes are no longer to stick to one an- other. Applying this assumption, an optimization problem weighting each feature is derived. The algorithm does not involve the dense matrix eigen-decomposition which can be computationally expensive in time. Extensive exper- iments are conducted to validate the significance of selected features using the Yale, Extended YaleB and PIE data- sets. The thorough evaluation shows that, using one-nearest neighbor classifier, the recognition rates using 100-- 500 leading features selected by the algorithm distinctively outperform those with features selected by the baseline feature selection algorithms, while using support vector machine features selected by the algorithm show less prominent improvement. Moreover, the experiments demonstrate that the proposed algorithm is particularly effi- cient for multi-class face recognition problem. 相似文献
919.
R. R. Brown 《Space Science Reviews》1966,5(3):311-387
The present experimental knowledge of electron precipitation in the auroral zone is summarized, using observations primarily
from riometer, balloon, rocket and satellite studies. This includes the association of electron precipitation events with
aurora, magnetic disturbances as well as temporal and spatial aspects of the particle bombardment. 相似文献
920.