全文获取类型
收费全文 | 3274篇 |
免费 | 23篇 |
国内免费 | 13篇 |
专业分类
航空 | 1586篇 |
航天技术 | 1148篇 |
综合类 | 4篇 |
航天 | 572篇 |
出版年
2021年 | 27篇 |
2019年 | 23篇 |
2018年 | 54篇 |
2017年 | 51篇 |
2016年 | 45篇 |
2015年 | 26篇 |
2014年 | 71篇 |
2013年 | 91篇 |
2012年 | 84篇 |
2011年 | 120篇 |
2010年 | 79篇 |
2009年 | 137篇 |
2008年 | 153篇 |
2007年 | 99篇 |
2006年 | 72篇 |
2005年 | 93篇 |
2004年 | 92篇 |
2003年 | 99篇 |
2002年 | 72篇 |
2001年 | 116篇 |
2000年 | 65篇 |
1999年 | 69篇 |
1998年 | 88篇 |
1997年 | 58篇 |
1996年 | 93篇 |
1995年 | 113篇 |
1994年 | 112篇 |
1993年 | 48篇 |
1992年 | 72篇 |
1991年 | 34篇 |
1990年 | 34篇 |
1989年 | 76篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 33篇 |
1985年 | 91篇 |
1984年 | 91篇 |
1983年 | 65篇 |
1982年 | 66篇 |
1981年 | 99篇 |
1979年 | 25篇 |
1978年 | 29篇 |
1977年 | 27篇 |
1975年 | 29篇 |
1974年 | 24篇 |
1973年 | 21篇 |
1972年 | 20篇 |
1971年 | 19篇 |
1969年 | 20篇 |
1968年 | 19篇 |
排序方式: 共有3310条查询结果,搜索用时 31 毫秒
991.
The Cluster mission is aimed at the study of small-scale structures that are believed to be fundamental in determining the behaviour of key interactive processes of cosmic plasma. The mission will be controlled from the European Space Operations Centre (ESOC). ESOC is also in charge of the commanding of the scientific payloads on-board the four Cluster spacecraft after negotiation with the Cluster Principal Investigators (PIs) and of collecting and distributing the mission's scientific results to the Cluster community. This paper describes the process of translating the scientific requirements of the Cluster mission into a data-processing system supporting the mission via the definition of an appropriate operational scenario. In particular, the process of negotiation between the PIs and ESOC to command the spacecraft is mediated by the Joint Science Operations Centre (JSOC) and finalised by the Cluster Mission Planning System (CMPS) while the return of the data to the Cluster community is actuated by the Cluster Data Disposition System (CDDS). The Cluster Mission Control System (CMCS) provides the interface between these two systems and the spacecraft. These elements constitute the Cluster Data-Processing System (CDPS). 相似文献
992.
993.
Taylor H.P. Haroules G.G. Brown W.E. 《IEEE transactions on aerospace and electronic systems》1969,(4):581-588
In angle tracking antenna applications, the angle sensing boresight accuracy capabilities are important. The ability of an antenna to precisely determine the bearing angle to a point source is determined by the slope of the control function pattern at boresight. In the presence of extraneous interference, the magnitudes of the sidelobe and backlobe responses are important. Control pattern slope (angular sensitivity) is primarily a function of aperture illumination. It can be described by a current distribution in intensity and phase at every point. Once distribution is defined, lobe structure is defined by the associated transform. When more than one feed is used, the distribution will be a vector sum of the individual feed distributions. The resulting secondary pattern can be defined in terms of the amplitude distribution and the phase center locations of the contributing feeds. With a four-horn monopulse configuration, the feed phase centers are displaced from the boresight axis. Placing the phase centers on the boresight axis by rotating the feeds through 45 degrees results in a different set of intensity and phase values. A quite different secondary pattern results. The control function obtained by the subtraction of the powers from a paired set of on-axis feeds results in a lower sidelobe level than that obtained with a conventional monopulse combiner for a given feed taper. 相似文献
994.
If accurate first-order corrections for ionospheric delay are applied to VHF ranging signals, the second-order terms become dominant. Only with abnormally large values of ionospheric electron content do the second-order terms lead to serious errors, however. Since these terms can be estimated to within 10 percent, further correction can lead to very small position errors. 相似文献
995.
An inverse filter, contained in a recently published paper by Senmoto and Childers, is improved by the application of a shaping function derived by Turin in an earlier paper. 相似文献
996.
We present the resuIts of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the role of functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g. 相似文献
997.
A distribution-free detection procedure for a multiplerange-bin radar is described. This procedure is based on the ranks of observations, but does not require elaborate equipment for rapidly ranking large amounts of data. Proposed equipment is described and analysis and results are given comparing this new procedure with certain practical (nondistribution-free) procedures. Comparisons with some "best" theoretical procedures are also given. 相似文献
998.
999.
1000.
Mirmak E.V. Blumgold R.M. Grimes G. 《IEEE transactions on aerospace and electronic systems》1977,(5):546-548
An analysis of the saturation and quantization noise generated by analog-to-digital (A/D) conversion of radar returns from targets with log-normal radar cross sections is presented. The results of the analysis show that the high-cross-section tails of the log-normal distribution require higher saturation levels to be set in the A/D converter. The setting of the higher saturation level in the converter results in an increase in quantization noise. Thus the minimum achievable distortion in the output of the A/D converter signal is considerably higher than that for radar targets if their radar cross section had an exponential power distribution. 相似文献