全文获取类型
| 收费全文 | 8988篇 |
| 免费 | 233篇 |
| 国内免费 | 42篇 |
专业分类
| 航空 | 4592篇 |
| 航天技术 | 3265篇 |
| 综合类 | 103篇 |
| 航天 | 1303篇 |
出版年
| 2021年 | 68篇 |
| 2019年 | 60篇 |
| 2018年 | 112篇 |
| 2017年 | 99篇 |
| 2016年 | 69篇 |
| 2014年 | 168篇 |
| 2013年 | 233篇 |
| 2012年 | 189篇 |
| 2011年 | 311篇 |
| 2010年 | 228篇 |
| 2009年 | 345篇 |
| 2008年 | 422篇 |
| 2007年 | 241篇 |
| 2006年 | 239篇 |
| 2005年 | 245篇 |
| 2004年 | 199篇 |
| 2003年 | 299篇 |
| 2002年 | 187篇 |
| 2001年 | 299篇 |
| 2000年 | 198篇 |
| 1999年 | 253篇 |
| 1998年 | 269篇 |
| 1997年 | 210篇 |
| 1996年 | 249篇 |
| 1995年 | 292篇 |
| 1994年 | 295篇 |
| 1993年 | 167篇 |
| 1992年 | 202篇 |
| 1991年 | 113篇 |
| 1990年 | 117篇 |
| 1989年 | 226篇 |
| 1988年 | 98篇 |
| 1987年 | 106篇 |
| 1986年 | 96篇 |
| 1985年 | 282篇 |
| 1984年 | 220篇 |
| 1983年 | 195篇 |
| 1982年 | 203篇 |
| 1981年 | 286篇 |
| 1980年 | 96篇 |
| 1979年 | 74篇 |
| 1978年 | 87篇 |
| 1977年 | 78篇 |
| 1976年 | 65篇 |
| 1975年 | 98篇 |
| 1974年 | 63篇 |
| 1972年 | 81篇 |
| 1971年 | 60篇 |
| 1970年 | 61篇 |
| 1969年 | 59篇 |
排序方式： 共有9263条查询结果，搜索用时 15 毫秒
111.
White R.L. Adams M.B. Geisler E.G. Grant F.D. 《IEEE transactions on aerospace and electronic systems》1975,(2):195-203
An extended Kalman filter is used to process line-of-sight measurements to stars and known landmarks providing a statistical indication of performance in estimating spacecraft attitude, orbital ephemeris, and the bias drift of a set of three strapdown gyros. The landmark measurements were assumed to have been taken from the imagery of an Earth-observing multispectral scanner. It is shown that filtering of these noisy measurements results in highly accurate estimates of the above parameters. Results are given showing the sensitivity of performance to various system parameters such as star tracker accuracy, errors in the knowledge of landmark position, and number of stars and landmarks processed. 相似文献
112.
The worst error performance of estimation filters is investigated for continuous systems in this paper. The pathological performance study, without assuming any dynamical model such as Markov processes for perturbations, except for its bounded amplitude, will give practical and dependable criteria in establishing the navigation and maneuver strategy in deep space missions. 相似文献
113.
Paulikas G.A. Blake J.B. Imamoto S.S. 《IEEE transactions on aerospace and electronic systems》1975,(6):1138-1144
The Aerospace Corporation energetic electron-proton spectrometer operating on Applications Technology Satellite-6 (ATS-6) detects energetic electrons in four channels between 140 keV and greater than 32 MeV, and measures energetic protons in five energy channels between 2.3 and 80 MeV and energetic alpha particles in three channels between 9.4 and 94 MeV. After more than a year of operation in orbit, the experiment continues to return excellent data on the behavior of energetic magnetospheric electrons as well as information regarding the fluxes of solar protons and alpha particles. 相似文献
114.
A low frequency, small signal model, valid for all types of converters, both in the heavy and the light mode of conduction, is developed in block diagram form. The model provides a clear insight into the behavior of such converters and enhances the respective contributions of input and output filters. 相似文献
115.
Spilker James J. Luby Donald D. 《IEEE transactions on aerospace and electronic systems》1967,(1):71-82
A special-purpose adaptive machine is described which carries out estimation in real time of an unknown binary waveform which is perturbed with additive Gaussian noise. Unknown waveforms of over 103 samples in duration can be recovered. The unknown waveforms are of unknown epoch and can reappear at either random or periodic time intervals. The observed signal is received at moderate or low signal-to-noise ratios so that a single observation of the received data (even if one knew the precise signal arrival time) is not sufficient to provide a good estimate of the signal waveshape. Experimental results are described which show transient behavior waveform estimate. The transient behavior is expressed as the number of errors in the current estimate of the signal plotted vs. time. In a noisy environment, each ``learning' transient is a random time function. These learning transients are shown for several different signal-to-noise ratios and indicate the threshold noise levels for various types of initial states of the machine memory. 相似文献
116.
117.
R.C Miller S.G Martin W.R Hanson S.A Marino E.J Hall 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(12):1719-1723
The oncogenic potential of high-energy 56Fe particles (1 GeV/nucleon) accelerated with the Alternating Gradient Synchrotron at the Brookhaven National Laboratory was examined utilizing the mouse C3H 10T1/2 cell model. The dose-averaged LET for high-energy 56Fe is estimated to be 143 keV/μm with the exposure conditions used in this study. For 56Fe ions, the maximum relative biological effectiveness (RBEmax) values for cell survival and oncogenic transformation were 7.71 and 16.5 respectively. Compared to 150 keV/μm 4He nuclei, high-energy 56Fe nuclei were significantly less effective in cell killing and oncogenic induction. The prostaglandin E1 analog misoprostol, an effective oncoprotector of C3H 10T1/2 cells exposed to X rays, was evaluated for its potential as a radioprotector of oncogenic transformation with high-energy 56Fe. Exposure of cells to misoprostol did not alter 56Fe cytotoxicity or the rate of 56Fe-induced oncogenic transformation. 相似文献
118.
M R Sims C T Pillinger I P Wright J Dowson S Whitehead A Wells J E Spragg G Fraser L Richter H Hamacher A Johnstone N P Meredith C de la Nougerede B Hancock R Turner S Peskett A Brack J Hobbs M Newns A Senior M Humphries H U Keller N Thomas J S Lingard T C Ng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(11):1925-1928
The aim of the proposed Beagle 2 small lander for ESA's 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X-ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies. 相似文献
119.
D Voeste L H Levine H G Levine V Blum 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(1):211-214
The Closed Equilibrated Biological Aquatic System (C.E.B.A.S.) Mini-Module, a Space Shuttle middeck locker payload which supports a variety of aquatic inhabitants (fish, snails, plants and bacteria) in an enclosed 8.6 L chamber, was tested for its biological stability in microgravity. The aquatic plant, Ceratophyllum demersum L., was critical for the vitality and functioning of this artificial mini-ecosystem. Its photosynthetic pigment concentrations were of interest due to their light harvesting and protective functions. \"Post-flight\" chlorophyll and carotenoid concentrations within Ceratophyllum apical segments were directly related to the quantities of light received in the experiments, with microgravity exposure (STS-89) failing to account for any significant deviation from ground control studies. 相似文献
120.
P A Craven M J Rycroft 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):45-49
Beyond the magnetic influence of the Earth, the flux of galactic cosmic radiation (GCR) represents a radiological concern for long-term manned space missions. Current concepts of radiation quality and equivalent dose are inadequate for accurately specifying the relative biological \"efficiency\" of low doses of such heavily ionising radiations, based as they are on the single parameter of Linear Energy Transfer (LET). Such methods take no account of the mechanisms, nor of the highly inhomogeneous spatial structure, of energy deposition in radiation tracks. DNA damage in the cell nucleus, which ultimately leads to the death or transformation of the cell, is usually initiated by electrons liberated from surrounding molecules by the incident projectile ion. The characteristics of these emitted \"delta-rays\", dependent primarily upon the charge and velocity of the ion, are considered in relation to an idealised representation of the cellular environment. Theoretically calculated delta-ray energy spectra are multiplied by a series of weighting algorithms designed to represent the potential for DNA insult in this environment, both in terms of the quantity and quality of damage. By evaluating the resulting curves, and taking into account the energy spectra of heavy ions in space, a relative measure of the biological relevance of the most abundant GCR species is obtained, behind several shielding configurations. It is hoped that this method of assessing the radiation quality of galactic cosmic rays will be of value when considering the safety of long-term manned space missions. 相似文献