全文获取类型
收费全文 | 108篇 |
免费 | 10篇 |
国内免费 | 18篇 |
专业分类
航空 | 57篇 |
航天技术 | 27篇 |
综合类 | 22篇 |
航天 | 30篇 |
出版年
2023年 | 4篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 2篇 |
2012年 | 7篇 |
2011年 | 7篇 |
2010年 | 3篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 5篇 |
2006年 | 13篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 296 毫秒
21.
在CAGD中,构造光滑曲线通过给定的二维或三维点集是非常重要的问题。广泛釆用的方法是Hermite技术,但是依照这种方法,插值曲线的形状过多地依赖于切矢的模长,且形状的修改不能依几何的方式交互完成。本文提出了一种结合交互技术和插值技术于一体的曲线插值方法,插值基函数为有理函数,在此基础上讨论了形状参数在几何修形中的作用, 相似文献
22.
《中国航空学报》2021,34(12):39-50
Aircrafts damages caused by lightning strikes have been known since the early days of aviation. However, the physical effects on the aircraft structure are still being investigated. This work seeks to evaluate the lightning strike effects in the aluminum alloy 7075-T6. Samples were submitted to lightning strike simulation in laboratory and the damages evaluated through characterization techniques. Ultrasound and profilometry tests have shown material loss to 0.272 mm depth in the damaged region. In addition, it was detected the material accumulation occurrence in the damage vicinity of the region. Below the damage, it was found a region where metallurgical changes were identified. The tensile and microhardness tests results have shown reduction in the percentage elongation and hardness increasing in the material affected by lightning. These results are corroborated by the X-Ray Diffraction (XRD) and Rietveld Method (red line) that indicated an increasing in dislocation density and micro-deformation in the material matrix. Optical microscopy results have shown the presence of microcracks on the normal and cross-section surface of the samples damaged. The Energy Dispersive X-Ray Spectroscopy (EDXS) and Electron Backscattered Diffraction Test (EBSD) found coarse intermetallic phases and precipitates compounds with dimensions greater than 1 μm in length. They were responsible for nucleation of the microcracks that propagate along the material grain boundaries. 相似文献
23.
《Acta Astronautica》2014,93(2):547-552
The possibility of interstellar migration has been theorized during the past thirty years in the form of “Dysonships” that, using non-relativistic propulsion systems, are able to colonize the Galaxy in a relatively short time compared to the age of the Galaxy and consequently penetrate inside our solar system too. Observational evidence of this can be potentially obtained using the present state of the art of telescopes and related sensors, by following aimed searches and an expanded SETI protocol. Some transient and unrepeated radio signals recorded during standard SETI observations might be due to the transit of high-proper motion artificial sources of extraterrestrial origin, which are expected to show a very weak optical emission, a strong infrared excess and occasional high-energy bursts in the X and Gamma-ray wavelength ranges. Such artificial sources might show an interest to Earth by sending probes to visit it: such a possibility can be investigated scientifically as well. 相似文献
24.
Ivan Milić Olga Atanacković 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
State-of-the-art methods in multidimensional NLTE radiative transfer are based on the use of local approximate lambda operator within either Jacobi or Gauss–Seidel iterative schemes. Here we propose another approach to the solution of 2D NLTE RT problems, Forth-and-Back Implicit Lambda Iteration (FBILI), developed earlier for 1D geometry. In order to present the method and examine its convergence properties we use the well-known instance of the two-level atom line formation with complete frequency redistribution. In the formal solution of the RT equation we employ short characteristics with two-point algorithm. Using an implicit representation of the source function in the computation of the specific intensities, we compute and store the coefficients of the linear relations J=a+bS between the mean intensity J and the corresponding source function S. The use of iteration factors in the ‘local’ coefficients of these implicit relations in two ‘inward’ sweeps of 2D grid, along with the update of the source function in other two ‘outward’ sweeps leads to four times faster solution than the Jacobi’s one. Moreover, the update made in all four consecutive sweeps of the grid leads to an acceleration by a factor of 6–7 compared to the Jacobi iterative scheme. 相似文献
25.
Wang Xiaoying Dai Ziqiang Zhang Enhong K.E. Fuyang Cao Yunchang Song Lianchun 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Algebraic reconstruction techniques (ART) have been successfully used to reconstruct the total electron content (TEC) of the ionosphere and in recent years be tentatively used in tropospheric wet refractivity and water vapor tomography in the ground-based GNSS technology. The previous research on ART used in tropospheric water vapor tomography focused on the convergence and relaxation parameters for various algebraic reconstruction techniques and rarely discussed the impact of Gaussian constraints and initial field on the iteration results. The existing accuracy evaluation parameters calculated from slant wet delay can only evaluate the resultant precision of the voxels penetrated by slant paths and cannot evaluate that of the voxels not penetrated by any slant path. The paper proposes two new statistical parameters Bias and RMS, calculated from wet refractivity of the total voxels, to improve the deficiencies of existing evaluation parameters and then discusses the effect of the Gaussian constraints and initial field on the convergence and tomography results in multiplicative algebraic reconstruction technique (MART) to reconstruct the 4D tropospheric wet refractivity field using simulation method. 相似文献
26.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(6):2759-2769
In this study, predictions of the E-CHAIM ionospheric model are compared with measurements by the incoherent scatter radars RISR at Resolute Bay, Canada, in the northern polar cap. Reasonable coverage was available for all seasons except winter for which no conclusions were drawn. It is shown that ratios of the model-to measured electron densities are close to unity in the central part of the F layer, around its peak. This is particularly evident for summer daytime. Distributions of the ratios are wider for other seasons indicating larger number of cases when the model underestimates or overestimates. E-CHAIM underestimates the electron density at ionospheric topside and bottomside by ~ 10–20 %. At the bottomside, the underestimations are strongest in summer and equinoctial nighttime. At the topside, the underestimations are strongest in autumn nighttime. Model overestimations are noticeable in the middle part of the F layer during dawn hours in autumn. Overall, the model tends to not predict highest-observed peak electron densities and the largest-observed heights of the peak. 相似文献
27.
为提高飞机大修效率,缩短大修时间,对其中航炮冷校靶流程进行了分析,运用网络计划技术原理并根据逻辑关系绘制了航炮冷校靶网络图,采用关键线路法对关键工序进行优化,调整关键线路进而有效缩短航炮冷校靶时间,对于飞机大修其他工作流程也可应用网络计划技术,从而能有效地提高飞机大修效率。 相似文献
28.
变分原理的自适应网格技术被应用到运动激波问题的求解上,在解的大梯度区自动加密网格,从而非常成功地算出了激波。通过分析发现权函数选择和取值对自适应网格技术至关重要 相似文献
29.
技术性贸易壁垒一方面严重制约了河北省对外贸易的正常发展,同时也给河北省的对外贸易带来难得的发展机遇.对于一个个市场主体而言,技术进步是突破技术性贸易壁垒制约的关键,市场多元化是突破技术性贸易壁垒制约的重要方法. 相似文献
30.
王荪馨 《航空精密制造技术》2008,44(5)
为降低CSP调度算法的计算复杂度和减少搜索过程中回溯发生概率,采用一致性预处理技术来预先修剪和过滤搜索空间。仿真实验证明:两种方法的综合运用可以显著提高CSP调度算法的搜索效率,从而为CSP调度算法求解大规模作业车间调度问题提供可能。 相似文献