全文获取类型
收费全文 | 3484篇 |
免费 | 8篇 |
国内免费 | 6篇 |
专业分类
航空 | 1549篇 |
航天技术 | 1253篇 |
综合类 | 181篇 |
航天 | 515篇 |
出版年
2021年 | 21篇 |
2019年 | 23篇 |
2018年 | 63篇 |
2017年 | 36篇 |
2016年 | 39篇 |
2015年 | 21篇 |
2014年 | 77篇 |
2013年 | 92篇 |
2012年 | 79篇 |
2011年 | 128篇 |
2010年 | 75篇 |
2009年 | 144篇 |
2008年 | 175篇 |
2007年 | 95篇 |
2006年 | 87篇 |
2005年 | 91篇 |
2004年 | 97篇 |
2003年 | 100篇 |
2002年 | 164篇 |
2001年 | 165篇 |
2000年 | 53篇 |
1999年 | 86篇 |
1998年 | 101篇 |
1997年 | 80篇 |
1996年 | 102篇 |
1995年 | 120篇 |
1994年 | 85篇 |
1993年 | 52篇 |
1992年 | 78篇 |
1991年 | 32篇 |
1990年 | 27篇 |
1989年 | 67篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1985年 | 113篇 |
1984年 | 99篇 |
1983年 | 62篇 |
1982年 | 85篇 |
1981年 | 107篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1978年 | 24篇 |
1977年 | 23篇 |
1975年 | 19篇 |
1974年 | 25篇 |
1972年 | 20篇 |
1971年 | 21篇 |
1970年 | 20篇 |
1969年 | 24篇 |
排序方式: 共有3498条查询结果,搜索用时 0 毫秒
881.
In the design of an aircraft at the stage of selecting its geometrical parameters, a method is proposed for evaluating the performance capabilities of manual control to ensure the quality of a given flight stabilization mode. The attainability of the given aircraft-pilot dynamic properties is evaluated by a frequency-domain method for permissible values of the aircraft and the pilot model parameters. The quality of the manual control for the longitudinal motion of the aircraft is evaluated. 相似文献
882.
883.
An indirect method of estimating the visible flame propagation speed of the methane–hydrogen–air mixture with account of carbon content in the fuel mixture and the ion current amplitude is proposed by the experimental results. By comparing the calculated and experimental values, it has been shown that an approach using the methane–hydrogen mixture is advisable at the stage of the internal combustion engine design and development. 相似文献
884.
Yu. V. Klochkov A. P. Nikolaev O. V. Vakhnina T. A. Kiseleva 《Russian Aeronautics (Iz VUZ)》2016,59(3):316-323
We developed a triangular discretization element of the fuselage fragment in the form of a thin shell compatible with the adjacent elements based on Lagrange multipliers. Solution of several test problems showed a high efficiency of using the modification of a triangular finite element being proposed. 相似文献
885.
The Mi-2 helicopter was taken as an example for modeling the main and tail rotors operation with account for the interference at low speed sliding flight. Aerodynamic characteristics were calculated. The form of nonlinear vortical wake was obtained. 相似文献
886.
887.
B. Williams P. Antreasian E. Carranza C. Jackman J. Leonard D. Nelson B. Page D. Stanbridge D. Wibben K. Williams M. Moreau K. Berry K. Getzandanner A. Liounis A. Mashiku D. Highsmith B. Sutter D. S. Lauretta 《Space Science Reviews》2018,214(4):69
OSIRIS-REx is the first NASA mission to return a sample of an asteroid to Earth. Navigation and flight dynamics for the mission to acquire and return a sample of asteroid 101955 Bennu establish many firsts for space exploration. These include relatively small orbital maneuvers that are precise to ~1 mm/s, close-up operations in a captured orbit about an asteroid that is small in size and mass, and planning and orbit phasing to revisit the same spot on Bennu in similar lighting conditions. After preliminary surveys and close approach flyovers of Bennu, the sample site will be scientifically characterized and selected. A robotic shock-absorbing arm with an attached sample collection head mounted on the main spacecraft bus acquires the sample, requiring navigation to Bennu’s surface. A touch-and-go sample acquisition maneuver will result in the retrieval of at least 60 grams of regolith, and up to several kilograms. The flight activity concludes with a return cruise to Earth and delivery of the sample return capsule (SRC) for landing and sample recovery at the Utah Test and Training Range (UTTR). 相似文献
888.
Features of fuel atomization and propagation in the flow behind a gas-dynamic stabilizer are considered. Estimations of the influence of transverse jets impulse magnitude on characteristics of mixing behind the stabilizer are obtained by numerical and experimental methods. 相似文献
889.
Øieroset Marit Mitchell David L. Phan Tai D. Lin Robert P. Crider Dana H. Acuña Mario H. 《Space Science Reviews》2004,111(1-2):185-202
Using magnetometer and electron observations from the Mars Global Surveyor (MGS) and the Wind spacecraft we show that the region of magnetic field pile-up and density decrease located between the Martian ionosphere and bow shock exhibit strong similarities with the plasma depletion layer (PDL) observed upstream of the Earth's magnetopause in the absence of magnetic reconnection when the magnetopause is a solid obstacle in the solar wind. A PDL is formed upstream of the terrestrial magnetopause when the magnetic field piles up against the obstacle and particles in the pile-up region are squeezed away from the high magnetic pressure region along the field lines as the flux tubes convect toward the magnetopause. We here discuss the possibility that at least part of the region of magnetic field pile-up and density depletion upstream of Mars may be formed by the same physical processes which generate the PDL upstream of the Earth's magnetopause. More complete ion, electron, and neutral measurements are needed to conclusively determine the relative importance of the plasma depletion process versus exospheric processes. 相似文献
890.
A. B. Agul’nik I. V. Kravchenko A. A. Gorbunov A. A. Novoselova A. P. Sklyarova 《Russian Aeronautics (Iz VUZ)》2018,61(3):441-444
This paper considers double bypass aircraft engine with controlled air bleed to the second bypass duct. Its performance is evaluated by mathematical modeling techniques. The second bypass air bleed amount is determined to provide the best engine efficiency at various operating modes. 相似文献