全文获取类型
收费全文 | 3524篇 |
免费 | 1898篇 |
国内免费 | 323篇 |
专业分类
航空 | 3939篇 |
航天技术 | 231篇 |
综合类 | 190篇 |
航天 | 1385篇 |
出版年
2024年 | 26篇 |
2023年 | 38篇 |
2022年 | 168篇 |
2021年 | 187篇 |
2020年 | 160篇 |
2019年 | 129篇 |
2018年 | 94篇 |
2017年 | 166篇 |
2016年 | 193篇 |
2015年 | 170篇 |
2014年 | 201篇 |
2013年 | 209篇 |
2012年 | 238篇 |
2011年 | 277篇 |
2010年 | 236篇 |
2009年 | 254篇 |
2008年 | 227篇 |
2007年 | 242篇 |
2006年 | 240篇 |
2005年 | 256篇 |
2004年 | 200篇 |
2003年 | 223篇 |
2002年 | 179篇 |
2001年 | 160篇 |
2000年 | 136篇 |
1999年 | 160篇 |
1998年 | 134篇 |
1997年 | 140篇 |
1996年 | 114篇 |
1995年 | 90篇 |
1994年 | 86篇 |
1993年 | 86篇 |
1992年 | 80篇 |
1991年 | 54篇 |
1990年 | 52篇 |
1989年 | 62篇 |
1988年 | 57篇 |
1987年 | 19篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有5745条查询结果,搜索用时 171 毫秒
151.
半浮区液桥自由面振荡特征 总被引:1,自引:0,他引:1
使用一套双路同步显微放大录像及图像处理系统,研究了夹角为90°的两个竖直剖面沿轴向不同高度液桥自由表面的位移振荡,得到轴向不同高度上的环向相位差,观测到在振荡周期内液桥表面轮廓线在不同时刻均不相交的特点。实验结果表明,液桥自由面振荡除具有径向扰动及轴向振荡变化外,还存在环向波动变化。根据实验结果,讨论了环向波动基本变化规律以及本实验在测量精度和测量误差方面存在的问题。 相似文献
152.
153.
154.
针对某型发动机自动调节器自动检测异常的故障现象,对产生发动机自动调节器自动检测异常的原因进行了深入地研究分析,并提出了针对性的预防措施。 相似文献
155.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2507-2514
The effect of the rocket exhaust products on the D-region of the ionosphere is investigated with the help of Very low frequency (VLF) electromagnetic wave propagation characteristics within the Earth-ionosphere waveguide. The changes in the electron density profile are computed from the observed VLF signal amplitude perturbations about 3 dB during the rocket launch. We find a localized electron depletion in the lower ionosphere at an altitude of around 58 km, that is thought to be originated by the attachment of ionospheric ion and molecular hydrogen along with water molecule in the exhaust product of first stage burn of Geosynchronous Launch Vehicle (GSLV) rocket at the time of GSLV launched from Sriharikota, India, on 27 August 2015 at 11:22 UT (16:52 IST). The ionospheric depletion perturbed the navigational VLF signal (VTX = 17 kHz) 134 s after the launch of the GSLV rocket. 相似文献
156.
通过对深圳航空公司CFM56-7B发动机水洗方法改进前后的发动机进厂大修数据进行比较,主要分析HPT导向器报废率的变化,说明改进的发动机水洗方式对于延长发动机在翼时间、降低HPT导向器报废率、节约大修成本起到良好促进作用。 相似文献
157.
《中国航空学报》2020,33(4):1181-1191
This paper presents the combustion characteristics in hybrid rocket motors with multi-segmented grain through three-dimensional numerical simulations. Multi-segmented grain is composed of several thin grains with two or more ports. The numerical model consists of Navier-Stokes equations with turbulence, solid fuel pyrolysis, chemical reactions, a fluid–solid coupling model and a regression rate model. The simulations adopt 90% Hydrogen Peroxide (HP) and PolyEthylene (PE) as the propellant combination. The effects of the rotation, port number, fuel grain segment number and mid-chamber length on the flow field and combustion performances are analyzed. The results indicate that the multi-segmented grain configuration can strengthen the flow field, and the regression rate and combustion efficiency are enhanced. Take the cases with two grain segments and three ports for example, the regression rate is increased by 32.4%−45.1% and the combustion efficiency increases by 6%−8.6% in different rotation angles. 相似文献
158.
Aiming at the high fuel consumption and use-cost of truck-mounted concrete pump , an energy-saving matching strategy of pumping system is presented and the experimental study is conducted.Since pumping system occupies most resources of engine , the matching strategy between engine and main pump is analyzed to meet the load demand and reduce the engine rational speed drop.The testing method is established to measure the fuel consumption of engine under various working conditions , and the experimental data are analyzed to find the law of the fuel consumption of engine.The system performance can be improved by adjusting the system input value.Finally , the energy-saving matching strategy is established to reduce the fuel consumption of truck for unit workload , which provides a new approach for the energy-saving of truck-mounted concrete pump. 相似文献
159.
针对某新型靶机出现的发动机空中停车故障,对测控站记录数据进行分析,发现了转速采集系统和ECU控制系统存在的缺陷,并提出了解决措施。 相似文献
160.