首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   315篇
  免费   33篇
  国内免费   35篇
航空   200篇
航天技术   71篇
综合类   27篇
航天   85篇
  2022年   4篇
  2021年   13篇
  2020年   7篇
  2019年   6篇
  2018年   6篇
  2017年   9篇
  2016年   8篇
  2015年   9篇
  2014年   19篇
  2013年   14篇
  2012年   6篇
  2011年   22篇
  2010年   5篇
  2009年   13篇
  2008年   9篇
  2007年   6篇
  2006年   7篇
  2005年   19篇
  2004年   15篇
  2003年   34篇
  2002年   41篇
  2001年   12篇
  2000年   6篇
  1999年   9篇
  1997年   4篇
  1996年   5篇
  1995年   5篇
  1994年   6篇
  1993年   8篇
  1991年   2篇
  1989年   6篇
  1986年   3篇
  1985年   3篇
  1984年   3篇
  1981年   2篇
  1980年   2篇
  1978年   3篇
  1976年   1篇
  1975年   4篇
  1974年   1篇
  1973年   1篇
  1972年   6篇
  1971年   1篇
  1970年   3篇
  1969年   1篇
  1968年   1篇
  1967年   4篇
  1966年   2篇
  1963年   2篇
  1962年   1篇
排序方式: 共有383条查询结果,搜索用时 187 毫秒
241.
Book review     
  相似文献   
242.
This study presents a new approach to the concept of cosmic consciousness integrated in current neuroscience knowledge and discusses implications for the search for extraterrestrial intelligence. It also examines different aspects related to consciousness and how it may play a key role in the understanding of the search for extraterrestrial intelligence and life in the Universe and its implications. Subjects (n=116) were college students from Spain, the United States, and Italy. Subjects responded to a questionnaire comprising five different sections: (A) religious beliefs, (B) environment and general opinion, (C) astronomy, (D) contact, and (E) attention and perception. The results showed the importance of several modular aspects that affect Space awareness in humans. Preliminary results are discussed with regard to current neuroscience, factor analysis, and possible implications for the understanding of contact with extraterrestrial intelligence. The roles of education, new search strategies, and possible contact scenarios are also discussed.  相似文献   
243.
In this paper we discuss the combined use of a priori information and adaptive signal processing techniques for the design and the analysis of a knowledge-aided (KA) radar receiver for Doppler processing. To this end, resorting to the generalized likelihood function (GLF) criterion (both one-step and two-step), we design and assess data-adaptive procedures for the selection of training data. Then we introduce a KA radar detector composed of three elements: a geographic-map-based data selector, which exploits some a priori information concerning the topography of the observed scene, a data-adaptive training selector which removes dynamic outliers from the training data, and an adaptive radar detector which performs the final decision about the target presence. The performance of the KA algorithm is analyzed both on simulated as well as on real radar data collected by the McMaster University IPIX radar. The results show that the new KA system achieves a satisfactory performance level and can outperform some previously proposed adaptive detection schemes  相似文献   
244.
The PAMELA experiment is devoted to the study of cosmic rays in Low Earth Orbit with an apparatus optimized to perform a precise determination of the galactic antimatter component of c.r. It is constituted by a number of detectors built around a permanent magnet spectrometer. PAMELA was launched in space on June 15th 2006 on board the Russian Resurs-DK1 satellite for a mission duration of 3 years. The characteristics of the detectors, the long lifetime and the orbit of the satellite, will allow to address several aspects of cosmic-ray physics. In this work we discuss the observational capabilities of PAMELA to detect the electron component above 50 MeV. The magnetic spectrometer allows a detailed measurement of the energy spectrum of electrons of galactic and Jovian origin. Long term measurements and correlations with Earth–Jupiter 13 months synodic period will allow to separate these two contributions and to measure the primary electron Jovian component, dominant in the 50–70 MeV energy range. With this technique it will also be possible to study the contribution to the electron spectrum of Jovian e reaccelerated up to 2 GeV at the Solar Wind Termination Shock.  相似文献   
245.
A non-empirical algorithm is presented to retrieve the optical depth in the 750–1250 cm−1 spectral range, of aerosol located in the boundary layer over the ocean, from nadir high-resolution radiance spectra in the thermal infrared. The algorithm is based on a line-by-line radiative transfer forward model and used the Optimal Estimation Method for the retrieval. Its performance strongly depends on the quality of the a priori temperature and H2O atmospheric profiles. To demonstrate the relevance of the algorithm, distributions of maritime aerosol parameters have been retrieved from IMG/ADEOS data for December 1996, using the algorithm with the LBLRTM radiative transfer code, and ERA40 (ECMWF) a priori atmospheric profiles and surface conditions.  相似文献   
246.
Transient effects of microgravity on early embryos of Xenopus laevis.   总被引:1,自引:0,他引:1  
In order to study the role of gravity on the early development of the clawed toad Xenopus laevis, we performed an experiment on the Maser-6 sounding rocket launched from Kiruna (Sweden) on 4 Nov 1993. The aim was to find out whether a short period of microgravity during fertilization and the first few minutes of development does indeed result in abnormal axis formation as was suggested by a pilot experiment on the Maser 3 in 1989. On the Maser 6 we used two new technical additions in the Fokker CIS unit, viz. a 1-g control centrifuge and a video recording unit which both worked successfully. The 1-g control centrifuge was used to discriminate between the influences of flight perturbations and microgravity. After fertilization shortly before launch, one of the first indications of successful egg activation, the cortical contraction, was registered in microgravity and on earth. Analysis of the video tapes revealed that the cortical contraction in microgravity starts earlier than at 1 g on earth. After recovery of the eggs fertilized in microgravity and culture of the embryos on earth, the morphology of the blastocoel has some consistent differences from blastulae from eggs fertilized in the 1-g centrifuge of the rocket. However from the gastrula stage onward, the microgravity embryos apparently recover and resume normal development: the XBra gene is normally expressed, and histological examination shows normal axis formation.  相似文献   
247.
248.
249.
The present paper summarizes fundamental evolutionary parameters of primaries of close binaries with initial masses between 9 and 60 M and initial composition appropriate for the Galaxy, the LMC and the SMC. The primary timescales and WR binary timescales are compared with corresponding recent single star predictions.  相似文献   
250.
A series of nine programs are developed for the design of the inductors of single-winding flyback converters. Three converter types are considered: voltage step-up, current step-up, and voltage step-up/current step-up. For each of the converter types, three pulse modulators are considered: constant frequency, constant transistor on-time, and constant transistor off-time. Computer-graphics displays are used to assist in evaluating characteristics of the various converter-modulator combinations.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号