全文获取类型
收费全文 | 240篇 |
免费 | 77篇 |
国内免费 | 23篇 |
专业分类
航空 | 198篇 |
航天技术 | 62篇 |
综合类 | 37篇 |
航天 | 43篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 14篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 14篇 |
2012年 | 12篇 |
2011年 | 16篇 |
2010年 | 15篇 |
2009年 | 5篇 |
2008年 | 21篇 |
2007年 | 7篇 |
2006年 | 10篇 |
2004年 | 2篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 9篇 |
1992年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有340条查询结果,搜索用时 531 毫秒
241.
脉冲等离子体推力器的设计评估仿真 总被引:1,自引:0,他引:1
运用磁流体动力学(Magnetohydrodynamic,MHD)的方法,对脉冲等离子体推力器推力室工作过程开展三维双温MHD数值仿真,并对推力室的工作机理进行了分析研究。通过该模型计算得到的推进剂烧蚀质量和原冲量与实验结果相符,同时对不同初始电压、电容、电极长度及推进剂高宽比下的情况进行了评估,为推力器设计提供指导依据。结果显示,高放电能量、长电极长度及大高宽比对推力器的性能都有一定提升,但这种提升是有限的,在进行推力器设计时,这些因素应进行综合考虑。 相似文献
242.
将DSMC(Direct Simulation Monte-Carlo)/PIC(Particle in Cell)流体混合算法与一维MHD双温放电模型相结合,一体化模拟NASA Glenn PPT羽流。对不同出口偏转角的羽流场进行模拟,给出了不同偏转角度下离子、电势、温度的变化情况,并与实验结果进行了比较。结果显示,该模型具有一体化(从工作过程到羽流)预测脉冲等离子体推力器羽流的能力。人工偏转角的加入,增强了羽流的扩散,使得羽流径向扩散、轴向收缩、回流减弱,同时对放电模型带来的不足有一定改善作用。 相似文献
243.
已有的研究证实,在均匀各向同性湍流中速度梯度张量(VGT)演化的无量纲时间是当地Kolmogorov时间。本文使用大涡模拟的方法,计算了一个雷诺数7 000的槽道流场,以到壁面的无量纲距离的大小将流场分为不同区间,使用当地Kolmogorov时间对不同区间的应变率张量的拉格朗日时间自相关函数进行无量纲化。发现不同区间自相关函数的下降曲线不完全重合:在对数区中不同区间自相关函数的下降曲线基本重合,但在靠近壁面的黏性底层和过渡层中则无此现象。因此,当地Kolmogorov时间不是槽道中速度梯度张量演化的普适无量纲时间。 相似文献
244.
245.
Aymeric Spiga Don Banfield Nicholas A. Teanby François Forget Antoine Lucas Balthasar Kenda Jose Antonio Rodriguez Manfredi Rudolf Widmer-Schnidrig Naomi Murdoch Mark T. Lemmon Raphaël F. Garcia Léo Martire Özgür Karatekin Sébastien Le Maistre Bart Van Hove Véronique Dehant Philippe Lognonné Nils Mueller Ralph Lorenz David Mimoun Sébastien Rodriguez Éric Beucler Ingrid Daubar Matthew P. Golombek Tanguy Bertrand Yasuhiro Nishikawa Ehouarn Millour Lucie Rolland Quentin Brissaud Taichi Kawamura Antoine Mocquet Roland Martin John Clinton Éléonore Stutzmann Tilman Spohn Suzanne Smrekar William B. Banerdt 《Space Science Reviews》2018,214(7):109
In November 2018, for the first time a dedicated geophysical station, the InSight lander, will be deployed on the surface of Mars. Along with the two main geophysical packages, the Seismic Experiment for Interior Structure (SEIS) and the Heat-Flow and Physical Properties Package (HP3), the InSight lander holds a highly sensitive pressure sensor (PS) and the Temperature and Winds for InSight (TWINS) instrument, both of which (along with the InSight FluxGate (IFG) Magnetometer) form the Auxiliary Sensor Payload Suite (APSS). Associated with the RADiometer (RAD) instrument which will measure the surface brightness temperature, and the Instrument Deployment Camera (IDC) which will be used to quantify atmospheric opacity, this will make InSight capable to act as a meteorological station at the surface of Mars. While probing the internal structure of Mars is the primary scientific goal of the mission, atmospheric science remains a key science objective for InSight. InSight has the potential to provide a more continuous and higher-frequency record of pressure, air temperature and winds at the surface of Mars than previous in situ missions. In the paper, key results from multiscale meteorological modeling, from Global Climate Models to Large-Eddy Simulations, are described as a reference for future studies based on the InSight measurements during operations. We summarize the capabilities of InSight for atmospheric observations, from profiling during Entry, Descent and Landing to surface measurements (pressure, temperature, winds, angular momentum), and the plans for how InSight’s sensors will be used during operations, as well as possible synergies with orbital observations. In a dedicated section, we describe the seismic impact of atmospheric phenomena (from the point of view of both “noise” to be decorrelated from the seismic signal and “signal” to provide information on atmospheric processes). We discuss in this framework Planetary Boundary Layer turbulence, with a focus on convective vortices and dust devils, gravity waves (with idealized modeling), and large-scale circulations. Our paper also presents possible new, exploratory, studies with the InSight instrumentation: surface layer scaling and exploration of the Monin-Obukhov model, aeolian surface changes and saltation / lifing studies, and monitoring of secular pressure changes. The InSight mission will be instrumental in broadening the knowledge of the Martian atmosphere, with a unique set of measurements from the surface of Mars. 相似文献
246.
高速球轴承的生热分析 总被引:11,自引:8,他引:3
在结合球轴承的拟静力学和生热分析的基础上, 对球轴承各热源分别进行生热计算, 得到了高速球轴承各个单元间的局部生热和轴承总生热, 分析了输入转速、载荷等多种参数对轴承各单元间的局部生热和总生热的影响, 结果显示球轴承的生热绝大部分来自球与内圈滚道的自旋生热, 并且转速、轴向载荷和内圈沟曲率系数对生热的影响最大.同时将球轴承作为一个整体用现有经验公式计算轴承生热, 其结果严重偏离台架功耗试验结果, 而从局部热源出发计算轴承总生热更为准确, 为轴承的三维温度场计算、润滑油油量选择等奠定了良好的基础. 相似文献
247.
Le Cadre J.-P. Souris G. 《IEEE transactions on aerospace and electronic systems》2000,36(4):1149-1166
Search theory is the discipline that studies the problem of how best to search for an object when the amount of searching efforts is limited and only probabilities of the possible position of the object are given. Then, the problem is to find the optimal distribution of this total effort that maximizes the probability of detection. Although the general formalism of search theory will be used subsequently, we consider now a radically different problem. The problem is to detect target tracks. In the "classical" search theory, the target is said detected if a detection occurs during any time of the time frame. Here, on the contrary, the target track will be said to be detected if elementary detections occur at various times. That means that there is a test for acceptance (or detection) of a target track and that the problem is to optimize the allocation of the search effort for track detection. So, specific optimization problems are solved by means of the primal-dual formalism, in an original setup. Other aspects concern Markovian targets and two-sided search for which simple and efficient algorithms are derived. 相似文献
248.
Pfiffner SM Onstott TC Ruskeeniemi T Talikka M Bakermans C McGown D Chan E Johnson A Phelps TJ Le Puil M Difurio SA Pratt LM Stotler R Frape S Telling J Lollar BS Neill I Zerbin B 《Astrobiology》2008,8(3):623-638
A scientific drilling expedition to the High Lake region of Nunavut, Canada, was recently completed with the goals of collecting samples and delineating gradients in salinity, gas composition, pH, pe, and microbial abundance in a 400 m thick permafrost zone and accessing the underlying pristine subpermafrost brine. With a triple-barrel wireline tool and the use of stringent quality assurance and quality control (QA/QC) protocols, 200 m of frozen, Archean, mafic volcanic rock was collected from the lower boundary that separates the permafrost layer and subpermafrost saline water. Hot water was used to remove cuttings and prevent the drill rods from freezing in place. No cryopegs were detected during penetration through the permafrost. Coring stopped at the 535 m depth, and the drill water was bailed from the hole while saline water replaced it. Within 24 hours, the borehole iced closed at 125 m depth due to vapor condensation from atmospheric moisture and, initially, warm water leaking through the casing, which blocked further access. Preliminary data suggest that the recovered cores contain viable anaerobic microorganisms that are not contaminants even though isotopic analyses of the saline borehole water suggests that it is a residue of the drilling brine used to remove the ice from the upper, older portion of the borehole. Any proposed coring mission to Mars that seeks to access subpermafrost brine will not only require borehole stability but also a means by which to generate substantial heating along the borehole string to prevent closure of the borehole from condensation of water vapor generated by drilling. 相似文献
249.
采用间断有限元方法对非定常欠膨胀射流进行了数值模拟,将二维守恒方程的间断有限元方法发展到轴对称Euler方程,对欠膨胀射流问题进行了数值计算。计算结果表明,采用间断有限元方法能够有效地捕捉到包括激波、滑移线、涡环和多级马赫盘等复杂流场结构,与实验照片反映的流动特征吻合较好。此外,两个马赫盘的位置与其他数值结果和实验测量结果吻合很好,表明该方法具有很好的鲁棒性,对非定常欠膨胀燃气射流的数值模拟是有效的。 相似文献
250.