全文获取类型
收费全文 | 5859篇 |
免费 | 14篇 |
国内免费 | 13篇 |
专业分类
航空 | 2615篇 |
航天技术 | 2069篇 |
综合类 | 22篇 |
航天 | 1180篇 |
出版年
2021年 | 57篇 |
2019年 | 31篇 |
2018年 | 148篇 |
2017年 | 105篇 |
2016年 | 111篇 |
2015年 | 53篇 |
2014年 | 160篇 |
2013年 | 183篇 |
2012年 | 182篇 |
2011年 | 256篇 |
2010年 | 177篇 |
2009年 | 296篇 |
2008年 | 379篇 |
2007年 | 180篇 |
2006年 | 140篇 |
2005年 | 175篇 |
2004年 | 152篇 |
2003年 | 202篇 |
2002年 | 127篇 |
2001年 | 206篇 |
2000年 | 100篇 |
1999年 | 120篇 |
1998年 | 152篇 |
1997年 | 108篇 |
1996年 | 126篇 |
1995年 | 162篇 |
1994年 | 142篇 |
1993年 | 81篇 |
1992年 | 117篇 |
1991年 | 60篇 |
1990年 | 45篇 |
1989年 | 115篇 |
1988年 | 50篇 |
1987年 | 56篇 |
1986年 | 54篇 |
1985年 | 143篇 |
1984年 | 111篇 |
1983年 | 91篇 |
1982年 | 110篇 |
1981年 | 161篇 |
1980年 | 53篇 |
1979年 | 41篇 |
1978年 | 38篇 |
1977年 | 36篇 |
1976年 | 34篇 |
1975年 | 35篇 |
1974年 | 35篇 |
1973年 | 29篇 |
1972年 | 24篇 |
1970年 | 24篇 |
排序方式: 共有5886条查询结果,搜索用时 15 毫秒
621.
Dehbonei H. Lee S. R. Nehrir H. 《IEEE transactions on aerospace and electronic systems》2009,45(1):31-45
This two-part paper presents a comprehensive comparative study on parallel power processing (PPP) and standard schemes in dc/dc converters for photovoltaic (PV) energy systems. It is demonstrated how PPP can improve direct energy transfer (DET), which results in PV systems operating at higher voltage and efficiency. Discussions of the concepts, hypotheses and computer simulations are presented in Part I. Part II provides the experimental results, which confirm the validity of the analysis and simulations. 相似文献
622.
Chien S. Knight R. Stechert A. Sherwood R. Rabideau G. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(1):23-30
An autonomous spacecraft must balance long-term and short-term considerations. It must perform purposeful activities that ensure long-term science and engineering goals are achieved and ensure that it maintains positive resource margins. This requires planning in advance to avoid a series of shortsighted decisions that can lead to failure. However, it must also respond in a timely fashion to a somewhat dynamic and unpredictable environment. Thus, in terms of high-level, goal-oriented activity, spacecraft plans must often be modified due to fortuitous events such as early completion of observations and setbacks such as failure to acquire a guidestar for a science observation. This describes an integrated planning and execution architecture that supports continuous modification and updating of a current working plan in light of a changing operating context. 相似文献
623.
Chikovani V.V. Yatsenko Yu.A. Barabashov A.S. Marusyk P.I. Umakhanov E.O. Taturin V.N. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(5):40-43
Metallic resonator Q-factor is very sensitive to the resonator's material, its thermal and chemical treatment, design, and environment; i.e., pressure and temperature. In order to obtain higher accuracy for CVG it is necessary to use resonator evacuation. Resonator mass plays a very important role in sensitivity to angle rate, in stability of vibration, in response to environmental condition changes, and also to external vibration and shock resistance. tnnalabs Holding Inc. uses a cylindrical resonator with increased rim thickness of up to 2 mmn and more. This concerns resonator material and design parameters selection, material thermal treatment to increase resonator Q-factor, and improved control algorithms in order to increase metallic CVG accuracy. As a result, CVG bias instability of 0.025 degth and random walk of 0.008 degvh for the resonator diameter 43 mmn, and 0.2 deg/h for the resonator diameter 25 mm were obtained. Future opportunities for Innalabs CVG is also discussed herein. Test results are presented for CVG43 and CVG25. Three-axis CVG unit under control of one DSP "Sharc" and IMU parameters are forecasted. 相似文献
624.
Candamo J. Kasturi R. Goldgof D. Sarkar S. 《IEEE transactions on aerospace and electronic systems》2009,45(3):937-949
A novel thin line detection algorithm for use in low-altitude aerial vehicles is presented. This algorithm is able to detect thin obstacles such as cables, power lines, and wires. The system is intended to be used during urban search and rescue operations, capable of dealing with low-quality images, robust to image clutter, bad weather, and sensor artifacts. The detection process uses motion estimation at the pixel level, combined with edge detection, followed by a windowed Hough transform. The evidence of lines is tracked over time in the resulting parameter spaces using a dynamic line movement model. The algorithm's receiver operating characteristic curve (ROC) is shown, based on a multi-site dataset with 86 videos with 10160 wires spanning in 5576 frames. 相似文献
625.
P. P. Pavlov R. S. Litvinenko M. N. Mubarakhin I. O. Yushin V. M. Nigmatullin 《Russian Aeronautics (Iz VUZ)》2008,51(2):198-204
A technique for selecting a rational variant of a multifunctional aircraft system using the analytic hierarchy process is proposed and a solution of a practical problem is presented. 相似文献
626.
Observability Analysis and Active Control for Airborne SLAM 总被引:1,自引:0,他引:1
627.
628.
Lehman D. Clark K. Cook B. Gavit S. Kayali S. McKinney J. Milkovich D. Reh K. Taylor R. Casani J. Griebel T. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(3):12-21
Congress authorized NASA's Prometheus Project in February 2003, with the first Prometheus mission slated to explore the icy moons of Jupiter. The project had two major objectives: 1) to develop a nuclear reactor that would provide unprecedented levels of power and show that it could be processed safely and operated reliably in space for long-duration, deep-space exploration; and 2) to explore the three icy moons of Jupiter - Callisto, Ganymede, and Europa - and return science data that would meet the scientific goals as set forth in the Decadal Survey Report of the National Academy of Sciences. Early in project planning, it was determined that the development of the Prometheus nuclear-powered spaceship would be complex and require the intellectual knowledge residing at numerous organizations across the country. In addition, because of the complex nature of the project and the multiple partners, approaches beyond those successfully used to manage a typical JPL project would be needed. This describes the key experiences in managing Prometheus, which should prove useful for future projects of similar scope and magnitude. 相似文献
629.
Waveform Design for Multistatic Radar Detection 总被引:1,自引:0,他引:1
We derive the optimal Neyman-Pearson (NP) detector and its performance, and then present a methodology for the design of the transmit signal for a multistatic radar receiver. The detector assumes a Swerling I extended target model as well as signal-dependent noise, i.e., clutter. It is shown that the NP detection performance does not immediately lead to an obvious signal design criterion so that as an alternative, a divergence criterion is proposed for signal design. A simple method for maximizing the divergence, termed the maximum marginal allocation algorithm, is presented and is guaranteed to find the global maximum. The overall approach is a generalization of previous work that determined the optimal detector and transmit signal for a monostatic radar. 相似文献
630.
The telecommunications market is reaching new types of customers who require their applications anywhere and anyway. Therefore, the DVB-RCS standard, which had great success in the fixed version is changing in this direction. The main objective of this work is to give an overview of architectures and technologies that can be used for implementation of a first-generation of advanced mobile satellite systems for the provision of broadband multimedia services. 相似文献