全文获取类型
收费全文 | 1055篇 |
免费 | 17篇 |
国内免费 | 3篇 |
专业分类
航空 | 477篇 |
航天技术 | 466篇 |
综合类 | 15篇 |
航天 | 117篇 |
出版年
2022年 | 5篇 |
2021年 | 12篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 22篇 |
2013年 | 21篇 |
2012年 | 31篇 |
2011年 | 43篇 |
2010年 | 28篇 |
2009年 | 49篇 |
2008年 | 94篇 |
2007年 | 26篇 |
2006年 | 28篇 |
2005年 | 45篇 |
2004年 | 36篇 |
2003年 | 30篇 |
2002年 | 25篇 |
2001年 | 50篇 |
2000年 | 19篇 |
1999年 | 35篇 |
1998年 | 36篇 |
1997年 | 13篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 33篇 |
1993年 | 21篇 |
1992年 | 29篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 31篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1984年 | 27篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有1075条查询结果,搜索用时 203 毫秒
81.
C.T. Russell T.L. Zhang R.J. Strangeway H.Y. Wei M. Delva W. Magnes 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(1):113-117
The magnetometer on Venus Express was designed to be able to obtain 128 Hz samples of the magnetic field from two sensors in a gradiometer configuration. This mode is used around periapsis to determine whether the signals reported at low altitudes near 100 Hz, had the properties of electromagnetic waves generated by electric discharges in the Venus atmosphere. The lack of a magnetic cleanliness program and the shortness of the magnetometer boom make this a challenging measurement. Fortunately the signals are sufficiently strong that they can be easily resolved with rather straightforward analysis techniques. 相似文献
82.
卢兴猷 《南京航空航天大学学报(英文版)》1998,(1)
香港工商企业的质量管理大部分都采用西方的质量管理概念。每当范畴扩展到建立人的优质思想和意识时,便遇到不少困难,基于上述问题,作者进行了一系列的研究,希望了解‘文化’与‘优质管理’之间的关系,并将中国的优良文化传统应用于现代质量管理之中。研究结果显示,‘管理哲学’是重要的一环,而我国的哲学极为丰富,作者借此文章,希望引起更多中国人在这方面的兴趣,从而进行更深入地研究和推广。 相似文献
83.
H.N. Wang Y.M. Cui R. Li L.Y. Zhang H. Han 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,42(9):1464-1468
Nowadays operational models for solar activity forecasting are still based on the statistical relationship between solar activity and solar magnetic field evolution. In order to set up this relationship, many parameters have been proposed to be the measures. Conventional measures are based on the sunspot group classification which provides limited information from sunspots. For this reason, new measures based on solar magnetic field observations are proposed and a solar flare forecasting model supported with an artificial neural network is introduced. This model is equivalent to a person with a long period of solar flare forecasting experience. 相似文献
84.
Track segment association, fine-step IMM and initialization with Doppler for improved track performance 总被引:2,自引:0,他引:2
Yeom S.-W. Kirubarajan T. Bar-Shalom Y. 《IEEE transactions on aerospace and electronic systems》2004,40(1):293-309
In this work we present a new track segment association technique to improve track continuity in large-scale target tracking problems where track breakages are common. A representative airborne early warning (AEW) system scenario, which is a challenging environment due to highly maneuvering targets, close target formations, large measurement errors, long sampling intervals, and low detection probabilities, provides the motivation for the new technique. Previously, a tracker using the interacting multiple model (IMM) estimator combined with an assignment algorithm was shown to be more reliable than a conventional Kalman filter based approach in tracking similar targets but it still yielded track breakages due to the difficult environment. In order to combine the broken track segments and improve track continuity, a new track segment association algorithm using a discrete optimization approach is presented. Simulation results show that track segment association yields significant improvements in mean track life as well as in position, speed, and course rms errors. Also presented is a modified one-point initialization technique with range rate measurements, which are typically ignored by other initialization techniques, and a fine-step IMM estimator, which improves performance in the presence of long revisit intervals. Another aspect that is investigated is the benefit of "deep" (multiframe or N-dimensional, with N > 2) association, which is shown to yield significant benefit in reducing the number of false tracks. 相似文献
85.
Y.S. Ge C.T. RussellT.-S. Hsu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1243-1251
In 2001, 2002 and 2003, the Polar spacecraft probed the near equatorial plasma sheet at 9 RE near local midnight. Using the magnetic field observations, the signatures at substorm onsets are studied. Close to the flux pile-up region, the Polar spacecraft readily detects the dipolarization front, especially for pseudo onsets. An event with two distinct onsets has been examined. The signatures are found to be consistent with the multiple-onset model suggested by Russell [Russell, C.T. How northward turnings of the IMF can lead to substorm expansion onsets. Geophys. Res. Lett. 27, 3257–3259, 2000] which is a modified Near-Earth Neutral Line (NENL) model. Another similar event is also examined showing the effects of different Interplanetary Magnetic Field (IMF) conditions upon substorms. Moreover, ground effects can be very weak compared to in situ observations, especially for pseudo onsets, because these signatures appear to be localized and not global. 相似文献
86.
A.T.Y. Lui 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2000,25(12):2389-2394
Substorm evolution of the near-Earth (|X|<15 RE) plasma sheet has been emphasized recently because the inner tail is thought to link closely to the substorm auroral activity in the ionosphere during the early stage of substorms. In this paper, we discuss how the inner tail substorm phenomena during the late substorm growth phase and early expansion phase are accounted for by the two prevailing substorm models, namely, the near-Earth neutral line model and the current disruption model. We find that the late growth phase features are more satisfactorily accounted for by the current disruption model than by the near-Earth neutral line model. In addition, detailed observations on current disruption show evidence inconsistent with the proposed idea of dipolarization being due to plasma flow braking from reconnection in the mid-tail region, which poses a difficulty to the near-Earth neutral line model as well. 相似文献
87.
T. Gerngross Y. XuS. Pellegrino 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
The lobes of the NASA ULDB pumpkin-shaped super-pressure balloons are made of a thin polymeric film that shows considerable time-dependent behaviour. A nonlinear viscoelastic model based on experimental measurements has been recently established for this film. This paper presents a simulation of the viscoelastic behaviour of ULDB balloons with the finite element software ABAQUS. First, the standard viscoelastic modelling capabilities available in ABAQUS are examined, but are found of limited accuracy even for the case of simple uniaxial creep tests on ULDB films. Then, a nonlinear viscoelastic constitutive model is implemented by means of a user-defined subroutine. This approach is verified by means of biaxial creep experiments on pressurized cylinders and is found to be accurate provided that the film anisotropy is also included in the model. A preliminary set of predictions for a single lobe of a ULDB is presented at the end of the paper. It indicates that time-dependent effects in a balloon structure can lead to significant stress redistribution and large increases in the transverse strains in the lobes. 相似文献
88.
Benchmark for radar allocation and tracking in ECM 总被引:4,自引:0,他引:4
89.
Yihua Zheng Anthony T.Y. Lui Mei-Ching Fok Brian J. Anderson Pontus C. Brandt Donald G. Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1234-1242
One essential component of magnetosphere and ionosphere coupling is the closure of the ring current through Region 2 field-aligned current (FAC). Using the Comprehensive Ring Current Model (CRCM), which includes magnetosphere and ionosphere coupling by solving the kinetic equation of ring current particles and the closure of the electric currents between the two regions, we have investigated the effects of high latitude potential, ionospheric conductivity, plasma sheet density and different magnetic field models on the development of Region 2 field-aligned currents, and the relationship between R2 FACs and the ring current. It is shown that an increase in high latitude potential, ionospheric conductivity or plasma sheet density generally results in an increase in Region 2 FACs’ intensity, but R2 FACs display different local time and latitudinal distributions for changes in each parameter due to the different mechanisms involved. Our simulation results show that the magnetic field configuration of the inner magnetosphere is also an important factor in the development of Region 2 field-aligned current. More numerical experiments and observational results are needed in further our understanding of the complex relationship of the two current systems. 相似文献
90.
S. Guo X. LiuW. Ai Y. TangJ. Zhu X. WangM. Wei L. QinY. Yang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(5):736-741
Based on a formerly developed ground-based prototype of space plant-growing facility, the development of its improved prototype has been finished, so as to make its operating principle better adapt to the space microgravity environment. According to the developing experience of its first generation prototype and detailed demonstration and design of technique plan, its blueprint design and machining of related components, whole facility installment, debugging and trial operations were all done gradually. Its growing chamber contains a volume of about 0.5 m3 and a growing area of approximate 0.5 m2; the atmospheric environmental parameters in the growing chamber and water content in the growing media were controlled totally and effectively; lighting source is a combination of both red and blue light emitting diodes (LED). The following demonstrating results showed that the entire system design of the prototype is reasonable and its operating principle can nearly meet the requirements of space microgravity environment. Therefore, our plant-growing technique in space was advanced further, which laid an important foundation for next development of the space plant-growing facility and plant-cultivating experimental research in space microgravity condition. 相似文献