全文获取类型
收费全文 | 471篇 |
免费 | 121篇 |
国内免费 | 111篇 |
专业分类
航空 | 341篇 |
航天技术 | 153篇 |
综合类 | 76篇 |
航天 | 133篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 3篇 |
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 33篇 |
2013年 | 35篇 |
2012年 | 29篇 |
2011年 | 36篇 |
2010年 | 41篇 |
2009年 | 31篇 |
2008年 | 21篇 |
2007年 | 19篇 |
2006年 | 18篇 |
2005年 | 26篇 |
2004年 | 9篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 16篇 |
2000年 | 30篇 |
1999年 | 43篇 |
1998年 | 35篇 |
1997年 | 33篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 16篇 |
1993年 | 19篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有703条查询结果,搜索用时 15 毫秒
621.
A type of 2D magnetic equivalent circuit framework of permanent magnet for magnetic system in AEMR 总被引:1,自引:1,他引:0
Modeling of permanent magnet(PM) is very important in the process of electromagnetic system calculation of aerospace electromagnetic relay(AEMR). In traditional analytical calculation, PM is often equivalent to a lumped parameter model of one magnetic resistance and one magnetic potential, but great error is often caused for the inner differences of PM; based on the conception of flux tube, a type of 2D magnetic equivalent circuit framework of permanent magnet model(2D MECF) is established; the element is defined, the relationship between elements is deduced, and solution procedure as well as verification condition of this model is given; by a case study of the electromagnetic system of a certain type of AEMR, the electromagnetic system calculation model is established based on 2D MECF and the attractive force at different rotation angles is calculated; the proposed method is compared with the traditional lumped parameter model and finite element method(FEM); for some types of electromagnetic systems with symmetrical structure, 2D MECF proves to be of acceptable accuracy and high calculation speed which fit the requirement of robust design for AEMR. 相似文献
622.
2010年,John Wiley & Sons出版了陈乃兴先生的著作《Aerothermodynamics of Turbomachinery:Analysis and Design》。这本长达445页的英文版专著凝聚着他半个世纪以来从事叶轮机械气动热力学研究的心血与经验。我如饥似渴地连读了两遍,感受很深,故特写此书评推荐给大家, 相似文献
623.
风机叶片用缝编织物渗透性能评估 总被引:1,自引:1,他引:0
在渗透性能测试方法归纳介绍的基础上,开展了试验及比较,初步确定了相应的测试试验规范.结合风机叶片的具体工艺和使用部位等,初步选定了缝编织物的渗透性能评估参数和测试方法,以对风机叶片用缝编织物渗透性能测试评估方法的统一规范确定提供一些思路. 相似文献
624.
625.
626.
本文中对固体火箭喷管颗粒尺寸分级的两相跨音速流场作了计算.气相控制方程采用隐式近似因子分解法求解,尺寸分级的颗粒控制方程采用特征线求解,然后,二者进行充分的耦合,可以获得固体火箭发动机含有任意颗粒质量分数和不同颗粒尺寸时轴对称喷管跨音速流场的参数分布.文中讨论了不同颗粒半径和质量分数对流场的影响,对单一颗粒尺寸和颗粒尺寸分级的参数进行了比较.两相耦合计算的迭代收敛速度取决于气相,本文中气相方程求解的格式除部分边界外是隐式的,CFL数可取至6左右,收敛速度快.特别是对颗粒尺寸分级的计算,得益更大,其得益的倍数为颗粒的分级数. 相似文献
627.
Plume aerodynamic effects of cushion engine in lunar landing 总被引:1,自引:0,他引:1
During the second period of China "Tanyue" Project, the explorer will softland on the moon. The cushion engines are used to decelerate the explorer and reduce the impact on the lunar ground. It is necessary to study its plume effects on the explorer component. The self-developed PWS (Plume WorkStation) software based on direct simulation Monte Carlo (DSMC) method is used to simulate the plume effects of two 150 N engines. Due to the complex structure of the explorer, PWS uses a decoupling method to treat the boundary mesh, which mainly interacts with simulation particles, and has no relation with the computational grids. After the analytical expressions of plane surfaces and curved surfaces of each boundary block are given, the particle position within or without the boundary blocks can be easily determined. Finally the 3D plume field of two 150 N engines is simulated. The pressure, temperature and velocity distributions of plume field are clearly presented by three characteristic slices. The aerodynamic effects on the explorer bottom, the landfall legs and antenna are separately shown. The compression influence on the plume flow of four landfall legs can be observed. 相似文献
628.
A new method to predict fatigue crack growth rate of materials based on average cyclic plasticity strain damage accumulation 总被引:3,自引:3,他引:0
By introducing a fatigue blunting factor, the cyclic elasto-plastic Hutchinson-Rice-Rosengren (HRR) field near the crack tip under the cyclic loading is modified. And, an average damage per loading-cycle in the cyclic plastic deformation region is defined due to Manson-Coffin law. Then, according to the linear damage accumulation theory-Miner law, a new model for predicting the fatigue crack growth (FCG) of the opening mode crack based on the low cycle fatigue (LCF) damage is set up. The step length of crack propagation is assumed to be the size of cyclic plastic zone. It is clear that every parameter of the new model has clearly physical meaning which does not need any human debugging. Based on the LCF test data, the FCG predictions given by the new model are consistent with the FCG test results of Cr2Ni2MoV and X12CrMoWVNbN 10-1-1. What’s more, referring to the relative researches, the good predictability of the new model is also proved on six kinds of materials. 相似文献
629.
Design and analysis of spiral bevel gears with seventh-order function of transmission error 总被引:2,自引:0,他引:2
This paper proposes a new approach to mial function of transmission error (TE) for spiral design and implement a seventh-order polyno- bevel gears with an aim to reduce the running vibration and noise of gear drive and improve the loaded distribution of the tooth. Based on the constraint conditions of predesigned seventh-order polynomial function curve and the theory of linear algebra, the polynomial coefficients of the seventh-order polynomial function of transmission error can be obtained. By applying a method named reverse tooth contact analysis, the modified roll coefficients as well as parts of machine-tool settings for the face-milling of spiral bevel gears can be individually determined. Therefore, a predesigned seventh-order polynomial function of transmission error for spiral bevel gears can be obtained by the modified roll with high-order coef- ficients, and comparisons of the seventh-order polynomial and parabolic functions of transmission error are also performed. The achievement of spiral bevel gears with the seventh-order function of transmission error can be accomplished on a universal Cartesian-type hypoid gear generator or a numerically controlled cradle-style hypoid gear generator due to its simple generating motion of axes of the cradle and the work piece. The results of a numerical example show that the bending stresses of the tooth of seventh-order are less than those of a parabolic one, while the contact stresses remain almost eouivalent. 相似文献
630.