全文获取类型
收费全文 | 3709篇 |
免费 | 60篇 |
国内免费 | 42篇 |
专业分类
航空 | 1760篇 |
航天技术 | 1343篇 |
综合类 | 71篇 |
航天 | 637篇 |
出版年
2022年 | 21篇 |
2021年 | 39篇 |
2018年 | 55篇 |
2017年 | 62篇 |
2016年 | 41篇 |
2015年 | 35篇 |
2014年 | 77篇 |
2013年 | 102篇 |
2012年 | 86篇 |
2011年 | 165篇 |
2010年 | 115篇 |
2009年 | 141篇 |
2008年 | 207篇 |
2007年 | 115篇 |
2006年 | 109篇 |
2005年 | 117篇 |
2004年 | 81篇 |
2003年 | 116篇 |
2002年 | 90篇 |
2001年 | 105篇 |
2000年 | 88篇 |
1999年 | 102篇 |
1998年 | 107篇 |
1997年 | 101篇 |
1996年 | 88篇 |
1995年 | 104篇 |
1994年 | 107篇 |
1993年 | 64篇 |
1992年 | 75篇 |
1991年 | 39篇 |
1990年 | 44篇 |
1989年 | 74篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 34篇 |
1985年 | 114篇 |
1984年 | 79篇 |
1983年 | 79篇 |
1982年 | 60篇 |
1981年 | 103篇 |
1980年 | 25篇 |
1979年 | 27篇 |
1978年 | 33篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1975年 | 39篇 |
1972年 | 33篇 |
1971年 | 25篇 |
1969年 | 22篇 |
1967年 | 23篇 |
排序方式: 共有3811条查询结果,搜索用时 15 毫秒
151.
RCS分析中多次反射的计算及程序实现技术 总被引:2,自引:0,他引:2
介绍目标RCS分析计算中多次散射的计算方法,计算多次散射时主要考虑面元-面元之间的相互作用,计算过程采用几何光学法(GO)、物理光学法(PO),在总后向RCS计算中还运用了等效电磁流法.同时,文中讨论计算多次散射的程序实现技术.最后,给出计算例子,考虑多次散射时总的后向RCS计算结果与前人发表的实验结果相吻合. 相似文献
152.
电铸成型是采用离子沉积的方法制造复制件,具有很好的复制精度,因此电铸技术得到了广泛的应用。但由于受极限电流密度等多方面因素的影响,电铸速率一直是制约电铸技术发展的一个瓶颈,许多学者为此做了大量的理论和试验研究,但对如何提高极限电流密度还没有提供一个比较满意的答案,为提高电铸局部电沉积速率,本文在前人工作的基础上,讨论了影响电铸速率的因素,提出了一种新型的电铸方法-喷射式电铸,并通过两组试验分析了局部电沉积速率怀电铸液流量的关系以及局部铸速率与喷嘴口径的关系,试验结果表明,采用喷射式电铸可以大大提高局部极限电流密度,从而使电铸局部电沉积速率有一个较大范围的提高,为将电铸与快速成型结合奠定了试验基础。 相似文献
153.
The vortical mixing concept in the ramjet channel is analyzed. The results of simulating the gasodynamic scheme permit the concept of increasing efficiency for ramjet operation to be substantiated. 相似文献
154.
The present paper discusses a need to develop a methodology of predicting the reliability of small thrust liquid rocket engines with a flow section made of composite materials under actual operating conditions for their successful practical use in the propulsion systems. 相似文献
155.
L. J. Lanzerotti K. Rinnert G. Dehmel F. O. Gliem E. P. Krider M. A. Uman G. Umlauft J. Bach 《Space Science Reviews》1992,60(1-4):91-109
The Lightning and Radio Emission Detector (LRD) instrument will be carried by the Galileo Probe into Jupiter's atmosphere. The LRD will verify the existence of lightning in the atmosphere and will determine the details of many of its basic characteristics. The instrument, operated in its magnetospheric mode at distances of about 5, 4, 3, and 2 planetary radii from Jupiter's center, will also measure the radio frequency (RF) noise spectrum in Jupiter's magnetosphere. The LRD instrument is composed of a ferritecore radio frequency antenna ( 100 Hz to 100 kHz) and two photodiodes mounted behind individual fisheye lenses. The output of the RF antenna is analyzed both separately and in coincidence with the optical signals from the photodiodes. The RF antenna provides data both in the frequency domain (with three narrow-band channels, primarily for deducing the physical properties of distant lightning) and in the time domain with a priority scheme (primarily for determining from individual RF waveforms the physical properties of closeby-lightning). 相似文献
156.
E. E. Russell F. G. Brown R. A. Chandos W. C. Fincher L. F. Kubel A. A. Lacis L. D. Travis 《Space Science Reviews》1992,60(1-4):531-563
The Photopolarimeter/Radiometer (PPR) is a remote sensing instrument on the Galileo Orbiter designed to measure the degree of linear polarization and the intensity of reflected sunlight in ten spectral channels between 410 and 945 nm to determine the physical properties of Jovian clouds and aerosols, and to characterize the texture and microstructure of satellite surfaces. The PPR also measures thermal radiation in five spectral bands between 15 and 100 m to sense the upper tropospheric temperature structure. Two additional channels which measure spectrally integrated solar and solar plus thermal radiation are used to determine the planetary radiation budget components. The PPR photopolarimetric measurements utilize previously flown technology for high-precision polarimetry using a calcite Wollaston prism and two silicon photodiodes to enable simultaneous detection of the two orthogonal polarization components. The PPR radiometry measurements are made with a lithium tantalate pyroelectric detector utilizing a unique arrangement of radiometric stops and a scene/space chopper blade to enable a warm instrument to sense accurately the much colder scene temperatures. 相似文献
157.
Halpin S.M. Grigsby L.L. 《IEEE transactions on aerospace and electronic systems》1992,28(4):1033-1041
Alternative methods for power flow and fault analysis of single-phase distribution systems are presented. The algorithms for both power flow and fault analysis utilize a generalized approach to network modeling. The generalized admittance matrix, formed using elements of linear graph theory, is an accurate network model for all possible single-phase network configurations. Unlike the standard nodal admittance matrix formulation algorithms, the generalized approach uses generalized component models for the transmission line and transformer. The standard assumption of a common node voltage reference point is not required to construct the generalized admittance matrix. Therefore, truly accurate simulation results can be obtained for networks that cannot be modeled using traditional techniques 相似文献
158.
In a nonstationary and/or nonhomogeneous interference environment, an adaptive system for target detection may suffer a severe performance degradation due to the lack of a sufficient amount of data from which the system can learn (estimate) the statistics of the environment. The detection performance of an adaptive system, which employs a frequency diversity (multiband) signaling waveform and a multiband sample matrix inversion algorithm (SMI), is analyzed. By comparison with the corresponding single-band system under the chosen system constraint, it is shown that the multiband system can significantly outperform the single band when the amount of data available from a single frequency band is severely limited by the environment 相似文献
159.
160.
J. L. Phillips S. J. Bame S. P. Gary J. T. Gosling E. E. Scime R. J. Forsyth 《Space Science Reviews》1995,72(1-2):109-112
Ulysses plasma measurement from 1.15 to 5.31 AU and from S6.4° to S48.3° solar latitude are used to assess the trends in the solar wind thermal electron temperature and anisotropy. Improved spacecraft potential corrections and data products have been incorporated. The radial temperature gradient is steeper than in previous determinations, but flatter than adiabatic. When normalized to 1 AU, temperature decrease with increasing latitude. Little change in the average thermal anisotropy has been seen during the mission. 相似文献