全文获取类型
收费全文 | 6074篇 |
免费 | 93篇 |
国内免费 | 112篇 |
专业分类
航空 | 2873篇 |
航天技术 | 2247篇 |
综合类 | 41篇 |
航天 | 1118篇 |
出版年
2022年 | 41篇 |
2021年 | 83篇 |
2019年 | 56篇 |
2018年 | 139篇 |
2017年 | 104篇 |
2016年 | 85篇 |
2015年 | 47篇 |
2014年 | 144篇 |
2013年 | 181篇 |
2012年 | 177篇 |
2011年 | 244篇 |
2010年 | 177篇 |
2009年 | 288篇 |
2008年 | 334篇 |
2007年 | 184篇 |
2006年 | 166篇 |
2005年 | 191篇 |
2004年 | 196篇 |
2003年 | 212篇 |
2002年 | 136篇 |
2001年 | 189篇 |
2000年 | 138篇 |
1999年 | 154篇 |
1998年 | 180篇 |
1997年 | 134篇 |
1996年 | 161篇 |
1995年 | 200篇 |
1994年 | 181篇 |
1993年 | 100篇 |
1992年 | 148篇 |
1991年 | 53篇 |
1990年 | 57篇 |
1989年 | 130篇 |
1988年 | 44篇 |
1987年 | 42篇 |
1986年 | 58篇 |
1985年 | 173篇 |
1984年 | 133篇 |
1983年 | 106篇 |
1982年 | 132篇 |
1981年 | 156篇 |
1980年 | 45篇 |
1979年 | 31篇 |
1978年 | 37篇 |
1977年 | 36篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 34篇 |
1970年 | 28篇 |
1969年 | 25篇 |
排序方式: 共有6279条查询结果,搜索用时 109 毫秒
511.
512.
卫星导航接收机需要精确的估计信号的扩频码相位并进行跟踪,估计的精度直接影响 伪距的测量精度。卫星信号的多径传播使得传统的基于DLL的估计器存在较大误差,提 出了一种抗多径的估计算法,它基于最大似然参数估计方法,并给出了该算法的推导过程, 仿真的结果表明该算法比传统的DLL跟踪环在性能上有很大的改进。结合传统卫星导 航接收机的实现结构,给出了一种整合了该算法的实现方案。 相似文献
513.
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
514.
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
515.
516.
517.
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
518.
519.
520.
航空涡轮发动机燃烧室内流场的PIV测量 总被引:4,自引:2,他引:2
设计了一种基于旋风分离原理的高压粒子发生器,并成功应用于高压状态下的航空涡轮发动机燃烧室内流场的PIV(粒子图像测速法)测量.在氢氧燃烧加热来流温度为813K、燃烧室压力为2.78MPa条件下,应用PIV技术开展了航空涡轮发动机单头部燃烧室复杂内流场测量研究,实现了高温高压条件下强旋流、强扰流、宽速域流场的PIV测量,获得了接近燃烧室工作压力工况下的流场速度和流场精细结构.结果表明:该型燃烧室内流场存在多处旋涡结构,形成回流区;流场旋流作用强,横截面流场存在顺时针大涡;主燃孔射流和掺混孔射流作用明显,射流穿透深度较大,对流场结构影响显著;高温高压状态下,流场结构与常温中压状态类似. 相似文献