全文获取类型
收费全文 | 6943篇 |
免费 | 277篇 |
国内免费 | 290篇 |
专业分类
航空 | 3408篇 |
航天技术 | 2495篇 |
综合类 | 238篇 |
航天 | 1369篇 |
出版年
2022年 | 42篇 |
2021年 | 82篇 |
2020年 | 28篇 |
2019年 | 55篇 |
2018年 | 132篇 |
2017年 | 103篇 |
2016年 | 92篇 |
2015年 | 77篇 |
2014年 | 195篇 |
2013年 | 244篇 |
2012年 | 238篇 |
2011年 | 321篇 |
2010年 | 268篇 |
2009年 | 334篇 |
2008年 | 399篇 |
2007年 | 249篇 |
2006年 | 192篇 |
2005年 | 230篇 |
2004年 | 209篇 |
2003年 | 250篇 |
2002年 | 168篇 |
2001年 | 229篇 |
2000年 | 184篇 |
1999年 | 206篇 |
1998年 | 221篇 |
1997年 | 178篇 |
1996年 | 201篇 |
1995年 | 247篇 |
1994年 | 219篇 |
1993年 | 141篇 |
1992年 | 174篇 |
1991年 | 81篇 |
1990年 | 81篇 |
1989年 | 144篇 |
1988年 | 60篇 |
1987年 | 47篇 |
1986年 | 68篇 |
1985年 | 178篇 |
1984年 | 133篇 |
1983年 | 106篇 |
1982年 | 133篇 |
1981年 | 159篇 |
1980年 | 45篇 |
1979年 | 30篇 |
1978年 | 37篇 |
1977年 | 36篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 34篇 |
1970年 | 27篇 |
排序方式: 共有7510条查询结果,搜索用时 765 毫秒
661.
662.
SSME实时振动监测系统在先进发动机健康管理中的应用 总被引:1,自引:0,他引:1
介绍了由马歇尔太空飞行中心(MSFC)开发的实时振动监测系统(RTVMS)的工作能力,该系统用于航天飞机主发动机(SSME)高速涡轮泵振动分析和减轻破坏。在斯坦尼斯太空中心(SSC)的 SSME 静态试车中正在使用 RTVMS 系统,表明已具有了在发动机工作过程中进行实时振动分析和健康监测的能力。由这些数据可评估高速运转的涡轮泵主要健康指标的离散谱信号,以减缓潜在的灾难性破坏。监测潜在故障的指标可使 SSME 项目能够开发一种基于振动分析的数字化发动机健康监测系统,从而在航天飞机飞行计划历史上首次实现了一种发动机高压涡轮泵振动飞行红线预警。 相似文献
663.
664.
665.
民航无线电陆空通话语言是以英语为载体的一种空地交流的特殊语言。本文在应用语言学的研究成果之上,提出了该语言的交际能力模型,该模型包括语言能力、策略能力、背景知识和心理生理机制四个部分。笔者结合民航陆空通话实际,对模型各个部分进行了分析,重点解析了策略能力在模型中的核心功能。 相似文献
666.
本文通过计算机模拟研究,利用气体温度场的先验知识,考查了将Radon变换迭代法用于光束偏转层析技术重建三维温度场的重建精度。作为一个应用实例,测试了电弧某截面上的温度分布。 相似文献
667.
In the paper, the problem of designing interplanetary trajectories with several swing-bys and deep-space maneuvers is solved using the method of virtual trajectories developed by the authors. The algorithms for the calculation of both heliocentric and planetocentric trajectory arcs are presented, including the case of resonant trajectories. The results of applying the method of virtual trajectories to the problem of designing an interplanetary transfer to Jupiter are given and compared with the baseline trajectories for the Juno, Europa Clipper, and Laplace missions. 相似文献
668.
669.
A.?I.?EfimovEmail author L.?A.?Lukanina I.?V.?Chashei S.?F.?Kolomiets M.?K.?Bird M.?P?tzold 《Cosmic Research》2018,56(1):1-10
In 2013 and 2015, investigations of the internal solar wind were carried out using the method of two-frequency radio sounding by signals from the Mars Express European spacecraft. The values of the S- and X-bands’ frequency and the differential frequency were registered with a sampling rate of 1s at the American and European networks of ground-based tracking stations. The spatial distribution of the frequency fluctuation’s level has been studied. It has been shown that the intensity of frequency fluctuation considerably decreases at high heliolatitudes. In some radio sounding sessions, quasiperiodic oscillations of sub-mHz band have been observed in the temporal spectra of frequency fluctuations; they are supposed to be associated with the density inhomogeneities, the sizes of which are close to the turbulence outer scale. 相似文献
670.
M.?Yu.?Belyaev T.?V.?Matveeva M.?I.?Monakhov D.?N.?Rulev V.?V.?SazonovEmail author 《Cosmic Research》2018,56(1):54-67
We have reconstructed the uncontrolled rotational motion of the Progress M-29M transport cargo spacecraft in the single-axis solar orientation mode (the so-called sunward spin) and in the mode of the gravitational orientation of a rotating satellite. The modes were implemented on April 3–7, 2016 as a part of preparation for experiments with the DAKON convection sensor onboard the Progress spacecraft. The reconstruction was performed by integral statistical techniques using the measurements of the spacecraft’s angular velocity and electric current from its solar arrays. The measurement data obtained in a certain time interval have been jointly processed using the least-squares method by integrating the equations of the spacecraft’s motion relative to the center of mass. As a result of processing, the initial conditions of motion and parameters of the mathematical model have been estimated. The motion in the sunward spin mode is the rotation of the spacecraft with an angular velocity of 2.2 deg/s about the normal to the plane of solar arrays; the normal is oriented toward the Sun or forms a small angle with this direction. The duration of the mode is several orbit passes. The reconstruction has been performed over time intervals of up to 1 h. As a result, the actual rotational motion of the spacecraft relative to the Earth–Sun direction was obtained. In the gravitational orientation mode, the spacecraft was rotated about its longitudinal axis with an angular velocity of 0.1–0.2 deg/s; the longitudinal axis executed small oscillated relative to the local vertical. The reconstruction of motion relative to the orbital coordinate system was performed in time intervals of up to 7 h using only the angularvelocity measurements. The measurements of the electric current from solar arrays were used for verification. 相似文献