全文获取类型
收费全文 | 914篇 |
免费 | 277篇 |
国内免费 | 173篇 |
专业分类
航空 | 1077篇 |
航天技术 | 84篇 |
综合类 | 85篇 |
航天 | 118篇 |
出版年
2024年 | 3篇 |
2023年 | 12篇 |
2022年 | 45篇 |
2021年 | 54篇 |
2020年 | 61篇 |
2019年 | 35篇 |
2018年 | 44篇 |
2017年 | 57篇 |
2016年 | 37篇 |
2015年 | 47篇 |
2014年 | 63篇 |
2013年 | 49篇 |
2012年 | 77篇 |
2011年 | 96篇 |
2010年 | 75篇 |
2009年 | 80篇 |
2008年 | 82篇 |
2007年 | 76篇 |
2006年 | 73篇 |
2005年 | 55篇 |
2004年 | 37篇 |
2003年 | 28篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 17篇 |
1999年 | 23篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 17篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有1364条查询结果,搜索用时 28 毫秒
991.
With the increasing demand for electricity,an efficiency improvement and thereby reduced CO2 emissions of the coal-fired plants are expected in order to reach the goals set in the Kyoto protocol.It can be achieved by a rise of the process parameters.Currently,live steam pressures and temperatures up to 300 bars and 923 K are planned as the next step.Closed circuit steam cooling of blades and vanes in modern steam turbines is a promising technology in order to establish elevated live steam temperatures in future steam turbine cycles.In this paper,a steam-cooled test vane in a cascade with external hot steam flow is analyzed numerically with the in-house code CHTflow.A parametric analysis aiming to improve the cooling effectiveness is carried out by varying the cooling mass flow ratio.The results from two investigated cases show that the steam cooling technique has a good application potential in the steam turbine.The internal part of the vane is cooled homogeneously in both cases.With the increased cooling mass flow rate,there is a significant improvement of cooling efficiency at the leading edge.The results show that the increased cooling mass flow ratio can enhance the cooling effectiveness at the leading edge.With respect to trailing edge,there is no observable improvement of cooling effectiveness with the increased cooling mass flow.This implies that due to the limited dimension at the trailing edge,the thermal stress cannot be decreased by increasing the cooling mass flow rate.Therefore,impingement-cooling configuration at the trailing edge might be a solution to overcome the critical thermal stress there.It is also observed that the performance of the cooling effective differs on pressure side and suction side.It implicates that the equilibrium of the cooling effectiveness on two sides are influenced by a coupled relationship between cooling mass flow ratio and hole geometry.In future work,optimizing the hole geometry and cooling steam supply conditions might be the solutions for an equivalent cooling effectiveness along whole profile. 相似文献
992.
993.
Advanced gas turbine stages are designed to operate at increasingly higher inlet temperatures to increase thermal efficiency and specific power output.To maintain durability and reasonable life,film cooling is needed in addition to internal cooling,especially for the first stage.Film cooling lowers material temperature by forced convection inside film-cooling holes and by forming a layer of coolant about component surfaces to insulate them from the hot gases.Unfortunately,each cooling jet forms a pair of counter-rotating vortices that entrains hot gas and causes the film-cooling jet to lift off from the surface that it is intended to protect.This paper gives an overview of efforts to enhance the effectiveness of film-cooling.This paper also describes two new design concepts.One design concept seeks to minimize the entrainment of hot gases underneath of film-cooling jets by using flow-aligned blockers.The other design concept shifts the interaction between the approaching hot gas and the cooling jet to occur further above the surface by using an upstream ramp.For both design concepts,computational fluid dynamics results are presented to examine their usefulness in enhancing film-cooling effectiveness. 相似文献
994.
995.
996.
微型涡喷发动机结构设计研究 总被引:12,自引:0,他引:12
探讨了一种正在研制的推力为100 N,转速为105 r/min的微型涡喷发动机的结构设计特点.首先介绍了微型涡轮发动机的总体构造特点;其次,又对这台发动机独有的结构特点进行了分析;最后,对它的旋转部件进行了强度、振动分析.最终结果表明旋转部件的结构设计满足要求.这些设计经验对于发展高推重比微型涡喷发动机有参考价值. 相似文献
997.
998.
直通道和弯曲通道中超声速气膜冷却研究 总被引:4,自引:3,他引:1
对直通道和弯曲通道两种不同几何形状中的二维平行缝槽形式的超声速气膜冷却进行了数值模拟,分析了在有、无斜激波入射冷却层时的冷却效果.计算结果表明,斜激波的入射使壁面的冷却效率较无斜激波入射时要低.在该计算模型中,无斜激波入射时,弯曲通道壁面的冷却效果好于直通道壁面,而有斜激波入射时,弯曲通道壁面的冷却效果不如直通道壁面. 相似文献
999.
为研究粉末冶金多孔结构的渗透性和流阻,以空气和氢气为介质进行了实验.实验显示微孔内流雷诺数低于1时,介质流量与穿过多孔结构的压降呈线性关系;当内流雷诺数高于1时,其流量与压降呈非线性特征.分析表明:传统的堆积床经验关系式将低估氢气和空气在烧结材料微孔中的流阻;相反,高估烧结多孔结构的渗透性能.并用粉末烧结结构的氢气和空气渗透实验数据拟合了多孔结构渗透率及摩擦阻力关联式. 相似文献
1000.