全文获取类型
收费全文 | 4203篇 |
免费 | 8篇 |
国内免费 | 7篇 |
专业分类
航空 | 2187篇 |
航天技术 | 1147篇 |
综合类 | 15篇 |
航天 | 869篇 |
出版年
2021年 | 33篇 |
2018年 | 183篇 |
2017年 | 154篇 |
2016年 | 72篇 |
2015年 | 43篇 |
2014年 | 68篇 |
2013年 | 102篇 |
2012年 | 116篇 |
2011年 | 222篇 |
2010年 | 196篇 |
2009年 | 233篇 |
2008年 | 273篇 |
2007年 | 191篇 |
2006年 | 56篇 |
2005年 | 127篇 |
2004年 | 101篇 |
2003年 | 97篇 |
2002年 | 55篇 |
2001年 | 93篇 |
2000年 | 60篇 |
1999年 | 39篇 |
1998年 | 101篇 |
1997年 | 58篇 |
1996年 | 80篇 |
1995年 | 85篇 |
1994年 | 110篇 |
1993年 | 62篇 |
1992年 | 87篇 |
1991年 | 32篇 |
1990年 | 34篇 |
1989年 | 80篇 |
1988年 | 30篇 |
1987年 | 38篇 |
1986年 | 53篇 |
1985年 | 110篇 |
1984年 | 70篇 |
1983年 | 69篇 |
1982年 | 66篇 |
1981年 | 84篇 |
1980年 | 39篇 |
1979年 | 30篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1975年 | 30篇 |
1974年 | 31篇 |
1973年 | 26篇 |
1972年 | 29篇 |
1971年 | 32篇 |
1969年 | 27篇 |
1967年 | 25篇 |
排序方式: 共有4218条查询结果,搜索用时 15 毫秒
991.
V. I. Bogdanov 《Russian Aeronautics (Iz VUZ)》2018,61(2):244-251
The new conceptual design of simple gas turbine engines for different purposes is presented. A choked-flow low-pressure turbine is used that allows reducing the number of stages and gas temperature in the relative motion ahead of blades. Application of such turbines with uncooled blades to reduce the cost of power-limited engines is considered. 相似文献
992.
993.
The multicriteria optimization problem on joint choice of a carrier aircraft and main design parameters of an air launcher
decoy are considered. The estimation of the design parameter values for the aerial decoy is based on the statistical data
processing with the use of the methods for constructing nonlinear regression. The result of solving this problem is a set
of Pareto-optimal geometry characteristics of the carrier aircraft and aerial decoy. A person who is responsible for decision-making
should choose the most reasonable variant from these characteristics. An example of solving the problem is presented. 相似文献
994.
995.
Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments 总被引:1,自引:0,他引:1
Paul B. Niles David C. Catling Gilles Berger Eric Chassefière Bethany L. Ehlmann Joseph R. Michalski Richard Morris Steven W. Ruff Brad Sutter 《Space Science Reviews》2013,174(1-4):301-328
Ongoing research on martian meteorites and a new set of observations of carbonate minerals provided by an unprecedented series of robotic missions to Mars in the past 15 years help define new constraints on the history of martian climate with important crosscutting themes including: the CO2 budget of Mars, the role of Mg-, Fe-rich fluids on Mars, and the interplay between carbonate formation and acidity. Carbonate minerals have now been identified in a wide range of localities on Mars as well as in several martian meteorites. The martian meteorites contain carbonates in low abundances (<1 vol.%) and with a wide range of chemistries. Carbonates have also been identified by remote sensing instruments on orbiting spacecraft in several surface locations as well as in low concentrations (2–5 wt.%) in the martian dust. The Spirit rover also identified an outcrop with 16 to 34 wt.% carbonate material in the Columbia Hills of Gusev Crater that strongly resembled the composition of carbonate found in martian meteorite ALH 84001. Finally, the Phoenix lander identified concentrations of 3–6 wt.% carbonate in the soils of the northern plains. The carbonates discovered to date do not clearly indicate the past presence of a dense Noachian atmosphere, but instead suggest localized hydrothermal aqueous environments with limited water availability that existed primarily in the early to mid-Noachian followed by low levels of carbonate formation from thin films of transient water from the late Noachian to the present. The prevalence of carbonate along with evidence for active carbonate precipitation suggests that a global acidic chemistry is unlikely and a more complex relationship between acidity and carbonate formation is present. 相似文献
996.
V.V. Paznukhov V.G. Galushko B.W. Reinisch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
A technique for studying ionospheric wavelike phenomena, primarily AGW/TID events, is developed based on the solution of the problem of radio wave propagation in ionospheric plasma disturbed by wavelike processes. A perfectly reflecting surface model is used for representing TIDs propagating at ionospheric heights. This technique is a generalization of the Frequency-and-Angular Sounding (FAS) method developed earlier for oblique TID diagnostics using transmitters of opportunity. Trial measurements were made in November 2003 with two DPS-4 systems at Millstone Hill Observatory, providing experimental validation of the developed method by comparing the results of disturbance diagnostics to those simultaneously obtained with the original (oblique) FAS method. The TID parameters recovered during the November 2003 campaign suggest that the observed disturbances predominately propagated equatorward which likely indicates their sources to be in the auroral region. The equatorward propagating AGW/TIDs are typical for disturbed geomagnetic conditions which were observed during the campaign. Implementation of the generalized FAS technique in the DPS sounder allowed development of a dedicated data acquisition system for ionospheric disturbance diagnostics. Routine measurements with the developed technique using the existing world-wide network of Digisondes (GIRO) will make it possible to conduct large-scale studies of the AGW/TID phenomena. 相似文献
997.
Performance of 10- and 20-target MSE classifiers 总被引:2,自引:0,他引:2
Novak L.M. Owirka G.J. Brower W.S. 《IEEE transactions on aerospace and electronic systems》2000,36(4):1279-1289
MIT Lincoln Laboratory is responsible for developing the ATR (automatic target recognition) system for the DARPA-sponsored SAIP program; the baseline ATR system recognizes 10 GOB (ground order of battle) targets; the enhanced version of SAIP requires the ATR system to recognize 20 GOB targets. This paper presents ATR performance results for 10- and 20-target mean square error (MSE) classifiers using high-resolution SAR (synthetic aperture radar) imagery. 相似文献
998.
O.A. Maltseva N.S. MozhaevaT.V. Nikitenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Modern use and study of the auroral region needs to attract a wider class of models for describing conditions of radio wave propagation in the ionosphere. In this paper the possibilities of the International Reference Ionosphere model, well-proven and widespread in the mid-latitudes, are investigated in the high latitude zone. Model and measured values of the critical frequency foF2 for two mid-latitude stations (Juliusruh and Goosebay) and four high-latitude ones (Loparskaya, Sodankyla, Sondrestrom, Thule) are compared. Deviations of medians, variations from day to day and solar activity trends seemed to be similar for both areas. This similarity is irrespective of the RZ12 index. Special attention is paid to the TEC parameter and its determination using 6 versions of models, a new version of the model IRI2010 (IRI-Plas) among them. It is shown that the IRI-Plas model significantly improves the definition of TEC in contrast to the versions of IRI2007 and the new model NeQuick. The use of the median of the experimental equivalent slab thickness, together with the current values of the TEC, increases by a factor of two the agreement between calculated and measured foF2 values as compared with the variations from day to day. This allows foF2 to be defined in near-real time. 相似文献
999.
D Leugner T Streibel H Rocher G Reitz W Heinrich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(4):511-515
Stacks of CR-39 plastic nuclear track detectors were mounted inside the MIR-station during the EUROMIR-94-mission. We present LET-spectra determined separately for long range cosmic ray heavy ions and for short range target fragments produced in nuclear interactions of cosmic rays and measured charge distributions for relativistic and stopping particles. 相似文献