全文获取类型
收费全文 | 2921篇 |
免费 | 6篇 |
国内免费 | 7篇 |
专业分类
航空 | 1067篇 |
航天技术 | 1045篇 |
综合类 | 10篇 |
航天 | 812篇 |
出版年
2022年 | 11篇 |
2021年 | 38篇 |
2019年 | 14篇 |
2018年 | 92篇 |
2017年 | 66篇 |
2016年 | 63篇 |
2015年 | 28篇 |
2014年 | 95篇 |
2013年 | 105篇 |
2012年 | 99篇 |
2011年 | 138篇 |
2010年 | 108篇 |
2009年 | 168篇 |
2008年 | 188篇 |
2007年 | 95篇 |
2006年 | 65篇 |
2005年 | 90篇 |
2004年 | 87篇 |
2003年 | 102篇 |
2002年 | 70篇 |
2001年 | 118篇 |
2000年 | 56篇 |
1999年 | 50篇 |
1998年 | 65篇 |
1997年 | 42篇 |
1996年 | 67篇 |
1995年 | 56篇 |
1994年 | 58篇 |
1993年 | 31篇 |
1992年 | 48篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 48篇 |
1988年 | 18篇 |
1987年 | 26篇 |
1986年 | 23篇 |
1985年 | 91篇 |
1984年 | 50篇 |
1983年 | 34篇 |
1982年 | 44篇 |
1981年 | 79篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 20篇 |
1974年 | 23篇 |
1973年 | 10篇 |
1972年 | 10篇 |
排序方式: 共有2934条查询结果,搜索用时 15 毫秒
1.
2.
L O Bjorn S Widell T Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(6):1557-1562
Plants have evolved under the influence of UV-B radiation and have acquired systems for monitoring it and investing appropriate resources for protection against it, i.e., filters, quenchers of radicals and reactive oxygen species, and repair systems. An hypothesis for how plants monitor radiation has been presented. 相似文献
3.
This study introduces a field oriented controlled (FOC) induction machine based flywheel energy storage (FES) system fed from a 20 kHz high frequency (HF) ac link and pulse density modulated (PDM) Converter. The feasibility of FES system is investigated both in software and hardware and is demonstrated successfully in both cases. The investigated system offers a good potential as a temporary energy storage system for various applications from automobile industry to aerospace applications. 相似文献
4.
5.
S I Bartsev V V Mezhevikin V A Okhonin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(1-2):201-204
Any attempt to create LSS for practical applications must take into account the possibility of castastrophic consequences if the problem of LSS reliability and stability is not solved. An integrated conception of CELSS studies development as a possible way to increase its reliability is considered. The BIOS-4 facility project is developed in the context of the conception. Three principles of highly effective experimental CELSS facility design are proposed. Some details of BIOS-4 design and its exploitation features are presented. 相似文献
6.
P.L. Israelevich A.I. Ershkovich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(12):99-103
Plasma and magnetic field disturbances accompanying dust particle impacts are explained by means of creation of a secondary cloud around the spacecraft. Cold cometary ions impinging upon the cloud are scattered by atoms of the cloud. This scattering changes initial angular distribution of cometary ions. Magnetic field perturbation is created by the friction between the electron component of the cometary plasma flow and the cloud. 相似文献
7.
The motion of a spacecraft with small asymmetry relative to its center of mass is considered. The restoring aerodynamic moment of the spacecraft is described by the Fourier series in terms of the angle of attack with the two first sinusoidal and the first cosinusoidal terms. A solution for the angle of attack in the undisturbed rotational motion is found. The analytical expression is obtained for the integral of action taken along the separatrices that separate the rotational and oscillatory regions of the phase portrait of a system. The transition of the spacecraft's motion from planar rotational to oscillatory is investigated. This transition is caused by a slow variation of moment characteristic coefficients, as well as by the presence of small asymmetry and damping and slow variation of their coefficients. Analytical formulas are obtained for determining the times of transition from rotational to oscillatory motion, as well as for the critical angular velocity of beyond-the-atmosphere rotation. When this critical velocity is exceeded, body rotation proceeds for a long time interval (planar autorotation arises). 相似文献
8.
The problem of target motion analysis (TMA) has been the subject of an important literature. However, present methods use data estimated by a short time analysis (azimuths, Dopplers, etc.). For far sources, the nonstationarities of the array processing outputs, induced by the sources motion, may be simply modeled. This model leads one to consider directly a spatio-temporal TMA. Then new (spatio-temporal) data can be estimated. These estimates correspond to a long time analysis. Further, note that they are estimated independently of the (classical) bearings. In this general framework, the concept of source trajectory replaces the classical instantaneous bearings. Corresponding TMA algorithms are then studied. Then the study of statistical performance is carefully studied 相似文献
9.
The results of the experimental studies of damping characteristics of a composite torsion bar in the helicopter main rotor
hingeless hub are presented. A variant of their improvement is considered. 相似文献
10.
I. S. Akhmed’yanov 《Russian Aeronautics (Iz VUZ)》2009,52(4):383-389
The application of the quadrature method [1] to analyzing the shells of revolution under symmetrical loading relative to the
zero meridian is considered. The method can be treated as a generalization of the method presented in [2] to solve the Volterra
integral equation of the second kind. 相似文献