全文获取类型
收费全文 | 5415篇 |
免费 | 63篇 |
国内免费 | 48篇 |
专业分类
航空 | 2372篇 |
航天技术 | 1902篇 |
综合类 | 77篇 |
航天 | 1175篇 |
出版年
2022年 | 26篇 |
2021年 | 57篇 |
2018年 | 112篇 |
2017年 | 106篇 |
2016年 | 88篇 |
2015年 | 50篇 |
2014年 | 126篇 |
2013年 | 155篇 |
2012年 | 138篇 |
2011年 | 247篇 |
2010年 | 181篇 |
2009年 | 243篇 |
2008年 | 308篇 |
2007年 | 179篇 |
2006年 | 148篇 |
2005年 | 173篇 |
2004年 | 139篇 |
2003年 | 178篇 |
2002年 | 131篇 |
2001年 | 184篇 |
2000年 | 120篇 |
1999年 | 131篇 |
1998年 | 141篇 |
1997年 | 123篇 |
1996年 | 125篇 |
1995年 | 138篇 |
1994年 | 136篇 |
1993年 | 79篇 |
1992年 | 104篇 |
1991年 | 48篇 |
1990年 | 54篇 |
1989年 | 103篇 |
1988年 | 46篇 |
1987年 | 47篇 |
1986年 | 52篇 |
1985年 | 163篇 |
1984年 | 106篇 |
1983年 | 99篇 |
1982年 | 87篇 |
1981年 | 156篇 |
1980年 | 38篇 |
1979年 | 31篇 |
1978年 | 39篇 |
1977年 | 36篇 |
1976年 | 32篇 |
1975年 | 50篇 |
1974年 | 33篇 |
1972年 | 34篇 |
1971年 | 26篇 |
1967年 | 26篇 |
排序方式: 共有5526条查询结果,搜索用时 15 毫秒
851.
Sanchez-Reillo R. Mengibar-Pozo L. Sanchez-Avila C. 《Aerospace and Electronic Systems Magazine, IEEE》2003,18(3):22-24
Due to the great increase in Information Technology (IT) systems where user authentication is needed, security in those systems relies on using PINs or passwords. During recent years, the scientific community has been trying to improve biometric techniques to be accepted as an alternative to other user authentication schemes. One of the sectors where user identity must be verified, is the identification cards sector. In fact, if great security wants to be achieved, smart cards should be used. But cardholder verification is performed using Card Holder Verification Keys (CHV-Keys), which are PIN-based. The authors are trying to integrate fingerprint verification inside a smart card, following their works in the past. The fingerprint scheme used is shown, and the work to achieve the integration inside a commercial smart card is detailed. 相似文献
852.
853.
V V Akatov YuAArkhangelsky A P Aleksandrov I Feher S Deme B Szabo J Vagyolgyi P P Szabo A Csoke M Ranky B Farkas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(10):77-81
A small, vibration- and shock-resistant thermoluminescent dosemeter /TLD/ system--named PILLE--was developed at the Health Physics Department of the Central Research Institute for Physics, Budapest, to measure the cosmic radiation dose on board orbital stations. The first on-board measurements with this system were performed /by B. Farkas, the Hungarian astronaut/, on the Salyut-6 space station in 1980. The same instrument was used by other crews in the following years. Doses measured at different sites in Salyut-6 are presented. The dose rates varied from 0.07 to 0.11 mGy.day-1. After the first cosmic measurements, the system was further developed. The minimum detectable dose of the new TLD system is 1 microGy, i.e. less by on order of magnitude than that of the former system. The self-irradiation dose rate of the TLD bulbs is also reduced--by more than one order of magnitude--to 10 nGy.h-1, by the use of potassium-free glass for the bulb envelope. This new type of PILLE TLD system is currently on-board Salyut-7. The dose rates /0.12-0.23 mGy.day-1/ measured in 1983 are presented in detail. 相似文献
854.
L. Schaffer J.A. Burns 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(9):107-110
We outline an analytical method for studying the motion of charged dust particles that orbit an oblate planet having a tilted, offset, dipolar magnetic field. Our computed trajectories closely mimic previous numerical results; equilibrium dust potentials must be less then 10 volts or the Jovian ring would be thicker than observed. We identify several , where the periods of components of the Lorentz force, as seen by a reference particle moving in the equatorial plane, match the particle's orbital period; several seem to be near observed features of the Jovian ring system. 相似文献
855.
A. Berroir P. de Felice L. Pontier P. Sitbon 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(6):125-131
The principle of determination of wind fields by a tomographic method is described. The airborne stereoscopic radiometer JANUS has been built to assess the feasibility of such measurements. Results of preliminary flights over isolated cumulus compare favourably with direct measurements. New flights with improved auxiliary parameter determinations are ongoing. 相似文献
856.
Truly optimal weapon system performance is highly dependent on the level of man-machine cockpit integration resulting from the intelligent application of crew station technologies. Future cockpits will incorporate a wide range of enhancements. Heavy application of artificial intelligence techniques can be expected to encompass the entire spectrum of crew station technologies; from data fusion, to optimized display resource management, to real-time onboard maintenance and fault reporting, and even to the optimization of pilot physiological needs. Emphasis on exploiting applications of the ultimate human resource, the mind, can be expected through the use of biocybernetics; initially to control previously manual and/or automated cockpit functions, and eventually to allow bidirectional communications. Future enhancements can also be expected to improve aircrew performance by allowing the pilot to take full advantage of aircraft maneuvering capability, and to operate effectively in hostile chemical, biological and radiological environments. New high resolution, full color, three dimensional crew station display devices will complement enlarged sensor suites and enhance aircrew situational awareness. Does the pilot really need to see the outside world to fly and fight effectively? Or, can panoramic display techniques, in an encapsulated environment, coupled with 4? steradian sensor coverage, increase performance? This paper strives to illustrate some ``no holds barred' approaches to making future fighter cockpits an ``in-tune' extension of the operator, based on current and projected tactical needs. 相似文献
857.
S.L. Mandelstam A.M. Urnov I.A. Zhitnik 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):87-89
Results are given of the study of active regions and flares by a high resolution Mg XI ion spectra obtained aboard rockets and a satellite. It is shown that there is a noticable similarity in the physical conditions in the plasma of active regions and flares. Plasma of both sources consists okf a thermal component with the temperature T ~ 2.?3.106K for active regions and T ~ 1.5?2.5.107K for flares and in both cases of a relatively small number (~ 1–5%) of suprathermal electrons with an energy E ~ 3–6 kT. 相似文献
858.
859.
Livingstone C.E. Gray A.L. Hawkins R.K. Olsen R.B. 《Aerospace and Electronic Systems Magazine, IEEE》1988,3(10):11-20
The airborne synthetic-aperture radar (SAR) system developed for the Canada Centre for Remote Sensing (CCRS) is described. It consists of two radars, at C -band and X -band. Each radar incorporates the following features: dual-channel receivers and dual-polarized antennas; a high quality, 7-look, real-time processor; a sensitivity time control for range-dependent gain control; a motion-compensation system for antenna steering in azimuth and elevation; and baseband I and Q signal phase rotation. The system also uses a high-power transmitter with a low-power back-up. The SAR maps to either side of the aircraft, at high or low resolution, at incidence angles which in high resolution span 0° to 80°. Radar operating parameters, data products, key specifications and the motion compensation scheme used are presented. Properties of the real-time imagery are discussed and examples of C -band SAR data in the three operating modes are given 相似文献
860.
J.L. Matteson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(4):135-146
Contemporary gamma-ray spectroscopy instruments and their results are reviewed. Sensitivities of 10?4 to 10?3 ph/cm2-sec have been achieved for steady sources and 10?2 to 1 ph/cm2-sec for transient sources. This has led to the detection of gamma-ray lines from more than 40 objects representing 6 classes of astrophysical phenomena. The lines carry model-independent information and are of fundamental importance to theoretical modeling and our understanding of the objects. These results indicate that gamma-ray spectroscopy is relevant to a wide range of astrophysical problems and is becoming a major part of astronomy. The objectives and anticipated results of future instruments are discussed. Several instruments in development will have a factor of ~ 10 sensitivity improvement to certain phenomena over contemporary instruments. A factor of ~ 100 improvement in sensitivity will allow the full potential of gamma-ray spectroscopy to be realized. Instrument concepts which would achieve this with both present and advanced techniques are discussed. 相似文献