全文获取类型
收费全文 | 19843篇 |
免费 | 10408篇 |
国内免费 | 3241篇 |
专业分类
航空 | 22420篇 |
航天技术 | 3953篇 |
综合类 | 2039篇 |
航天 | 5080篇 |
出版年
2024年 | 111篇 |
2023年 | 222篇 |
2022年 | 435篇 |
2021年 | 497篇 |
2020年 | 721篇 |
2019年 | 1261篇 |
2018年 | 1444篇 |
2017年 | 1368篇 |
2016年 | 1402篇 |
2015年 | 1522篇 |
2014年 | 1594篇 |
2013年 | 1592篇 |
2012年 | 1603篇 |
2011年 | 1651篇 |
2010年 | 1743篇 |
2009年 | 1772篇 |
2008年 | 1592篇 |
2007年 | 1412篇 |
2006年 | 1116篇 |
2005年 | 914篇 |
2004年 | 787篇 |
2003年 | 732篇 |
2002年 | 740篇 |
2001年 | 781篇 |
2000年 | 654篇 |
1999年 | 712篇 |
1998年 | 652篇 |
1997年 | 549篇 |
1996年 | 451篇 |
1995年 | 379篇 |
1994年 | 397篇 |
1993年 | 431篇 |
1992年 | 355篇 |
1991年 | 497篇 |
1990年 | 390篇 |
1989年 | 413篇 |
1988年 | 273篇 |
1987年 | 148篇 |
1986年 | 72篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 2篇 |
1975年 | 2篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1962年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
31.
The authors present a new scientific space mission consisting of a satellite carrying a receiving- only SAR which receives the signal transmitted by the ENVISAT-1 SAR. The integration of ENVISAT-1 SAR and bistatic radar data offers an improved potentiality of surface classification, three-dimensional observation, and the opportunity of advanced scientific experiments in the field of bistatic scattering. The small satellite nominal orbit and the attitude manoeuvres are designed in order to maintain an adequate overlap between the two radar swaths along the whole orbit, taking into account the ENVISAT-1 attitude and pointing. A preliminary satellite design (2-year lifetime) is then performed to evaluate the orbit decay and to determine the appropriate orbit manoeuvres (every 4 days) to control the satellites relative phase. The numerical simulation shows that a spacecraft of about 584kg is able to meet the mission requirements. 相似文献
32.
With the increase of information capacity of an airborne system, high speed driving of laser diodes have been of interest. In order to match the low resistive LD, proposed in this paper is an exponential transmission line, which is used as preshaping to compensate the pattern effect in gain switching of laser diodes. It also will be used to overcome the effect of parasitic elements in high speed driving to improve the rise and trail edges of the output waveform. An accurate circuit model of the exponential line for the PSPICE program has been developed and simulations are conveniently carried out by employing PSPICE 相似文献
33.
介绍一种高压快开阀装置。它可产生370MPa上升时间小于20μs的阶跃压力,用于对高压传感器进行动态校准。 相似文献
34.
本文利用弹性力学和断裂力学方法对纤维增强复合材料的横向拉伸强度进行了分析,其中考虑了90度开裂层厚度和开裂邻层的约束效应的影响,推导出正交各向异性对称铺层中昨合就位横向拉伸强度的数学表达式,得出开裂层的厚度和约束邻层铺设角对就位横向拉伸强度都有影响的结论,理论计算与Flaggs实验结果吻合较好。 相似文献
35.
In extension to common applications such as groundtrack displays and antenna steering, the SGP4 orbit model is proposed for operational orbit determination in small satellite missions. SGP4 is an analytical orbit model for Low-Earth orbiting satellites that is widely used for the propagation of NORAD twoline elements. Twoline elements may hence be generated completely independent of NORAD. Their use as exclusive source of orbital information simplifies the operations concept and reduces mission costs through the extensive use of existing low-cost mission support software. Due to small computer resource requirements of 8–10kByte, the SGP4 model may also be applied for onboard orbit computations making use of e.g. a 80186 processor, thus ensuring full compatibility of ground-based and onboard operations. The proposed approach is particularly suited in combination with a space-borne GPS receiver, were the C/A-code navigation solutions are treated as measurements that are adjusted in a least-squares sense using the SGP4 model. As consequence, inherent drawbacks of the pure navigation solutions such as data gaps and scatter as well as limited velocity accuracy are avoided, while the operational navigation activities are kept at a minimum. The feasibility of the concept is illustrated based on real GPS navigation data from the TOPEX/Poseidon and the MIR space station with an inherent data quality of 50–100 m. It is shown that 3 hours of data within a 4 day period are sufficient to keep the position error within 4 km, that is considered sufficient for most applications. 相似文献
36.
依据美机实用手册介绍的疲劳寿命S-N方程,对超差结构疲劳寿命推导出了一个量化评定方程。并应用该方程对一些典型结构超差形式具体地进行了疲劳寿命量化评定。实践证明,用本文介绍的方法对超差结构疲劳寿命进行定量评定,不仅简捷明快,而且结果可靠。 相似文献
37.
介绍了光敏元件与光传感器技术的发展及在国民经济和军事领域中的重要怍用;分析了国内外光电子产业的市场动态与发展趋势;论述了我国光电子产业面临的机遇和挑战。 相似文献
38.
叙述和分析了外差激光干涉光电信号处理主其特点,指出了它们各自的应用范围,同时介绍了一处新型的光电信号处理方法,它不仅使外差干涉仪用于动态测量,而且可以同时实现高分辩率测量 。 相似文献
39.
马凤贤 《中国民航学院学报》1989,(3)
本文为拓宽创新设计机构的思路,扼要地介绍了一种利用空间周转轮系,实观机械手臂的公转与自转动作要求的机构运动分析、设计方案及结构参考图。 相似文献
40.