全文获取类型
收费全文 | 655篇 |
免费 | 65篇 |
国内免费 | 20篇 |
专业分类
航空 | 422篇 |
航天技术 | 84篇 |
综合类 | 105篇 |
航天 | 129篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 16篇 |
2016年 | 29篇 |
2015年 | 18篇 |
2014年 | 64篇 |
2013年 | 45篇 |
2012年 | 49篇 |
2011年 | 38篇 |
2010年 | 40篇 |
2009年 | 35篇 |
2008年 | 40篇 |
2007年 | 34篇 |
2006年 | 34篇 |
2005年 | 42篇 |
2004年 | 30篇 |
2003年 | 24篇 |
2002年 | 40篇 |
2001年 | 17篇 |
2000年 | 23篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1984年 | 2篇 |
排序方式: 共有740条查询结果,搜索用时 468 毫秒
431.
在一种基于虚拟仪器的多功能快速可重组测控实验环境中,为了实现快速可重组思想,需要实现模块之间布线系统的设计。本文讨论了在Visual C++开发平台下布线系统中线类的设计思想和实现过程,并对其中设计的主要函数和算法进行详细描述。 相似文献
432.
提出了一种新型的投影栅和相位法视觉检测系统,该系统由投射器将具有正弦分布的条纹投射到被测物体表面,利用不同方位投射条纹的相位来确定双目立体视觉中的对应匹配点。文中对该视觉检测系统进行了标定,建立了双目视觉传感器的三维测量数学模型,标定结果的平均误差为0.039 6mm,均方差为0.023 1mm,角度相对误差为0.2%。最后不仅给出了V型体表面测量的结果,角度相对误差为0.22%,同时还给出了V型体的三维重建图。 相似文献
433.
434.
435.
Ti-15V-3Cr-3Sn-3Al合金是一种在航空航天工业领域具有广泛应用前景的亚稳定β型钛合金。本文用恒应变速率法进行实验,测试Ti-15-3板材的超塑性,为超塑成形提供参考依据。 相似文献
436.
437.
N.C. Patel S.P. Karia K.N. Pathak 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(6):1860-1881
This paper investigated the performance of the latest International Reference Ionosphere model (IRI-2016) over that of IRI-2012 in predicting total electron content (TEC) at three different stations in the Indian region. The data used were Global Positioning System (GPS) data collected during the ascending phase of solar cycle 24 over three low-latitude stations in India namely; Bangalore (13.02°N Geographic latitude, 77.57°E Geographic longitude), Hyderabad (17.25°N Geographic latitude, 78.30°E Geographic longitude) and Surat (21.16°N Geographic latitude, 72.78°E Geographic longitude). Monthly, the seasonal and annual variability of GPS-TEC have been compared with those derived from International Reference Ionosphere IRI-2016 and IRI-2012 with two different options of topside electron density: NeQuick and IRI01-corr. It is observed that both versions of IRI (i.e., IRI-2012 and IRI-2016) predict the GPS-TEC with some deviations, the latest version of IRI (IRI-2016) predicted the TEC similar to those predicted by IRI-2012 for all the seasons at all stations except for morning hours (0500 LT to 1000?LT). This shows that the effect of the updated version is seen only during morning hours and also that there is no change in TEC values by IRI-2016 from those predicted by IRI-2012 for the rest of the time of the day in the Indian low latitude region. The semiannual variations in the daytime maximum values of TEC are clearly observed from both GPS and model-derived TEC values with two peaks around March-April and September-October months of each year. Further, the Correlation of TEC derived by IRI-2016 and IRI-2012 with EUV and F10.7 shows similar results. This shows that the solar input to the IRI-2016 is similar to IRI 2012. There is no significant difference observed in TEC, bottom-side thickness (B0) and shape (B1) parameter predictions by both the versions of the IRI model. However, a clear improvement is visible in hmF2 and NmF2 predictions by IRI-2016 to that by IRI-2012. The SHU-2015 option of the IRI-2016 gives a better prediction of NmF2 for all the months at low latitude station Ahmedabad compare to AMTB 2013. 相似文献
438.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(1):95-106
To understand global variability and triggering mechanisms of ionospheric nighttime equatorial spread F (ESF), we analyzed measurements from satellite and a ground-based GPS station for the years between 2010 and 2017. In this study we present seasonal-longitudinal as well as monthly variability of ESF occurrence for solar minimum and yearly variations of ESF occurrence for solar maximum and minimum periods. One of the long standing open questions in the study of ESF is what exactly initiates the Rayleigh-Taylor (RT) plasma instability growth. This question is the focus of the present work. Zonal background eastward electric field and E × B upward plasma drift speed patterns are found to be critically important in understanding plasma irregularity formation. In addition to particular patterns observed on these parameters, the background plasma density in the local evening hours just before the onset of ESF occurrence is very important. Stronger plasma densities just before the onset of irregularities resulted in stronger plasma irregularities, while relatively less dense plasma just before the onset of irregularities resulted in relatively lower plasma irregularities. Seasonal variations in ESF activity between March and September equinox seasons with comparable plasma densities can be defined in terms of the rate of change of solar flux F10.7 (dF10.7/day) index. Strongest ESF occurrence and strongest dF10.7/day are measured in the same month out of all other months in 2016 and 2017. Longitudinal variations of ESF activity in our measurements are related to longitudinal variations of plasma densities. We also found that ESF occurrence is better correlated with rate of change of F10.7 index for months in equinox seasons than for months in solstice seasons for the years between 2013 and 2016. 相似文献
439.
Yi Zhang Bo Xu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):662-677
A kinetic impact occurs when an asteroid is moving. The impact may be caused by other small celestial body or an artificial object. Ejecta is produced from an impact. Dynamics of ejecta near a binary system which contains an ellipsoid and a sphere is analyzed. A phase diagram which comes from numerical simulation is shown in this work. The phase diagram shows a clear structure. Some special trajectories are also shown, which indicates a potential source of asteroid orbiting objects. 相似文献
440.
Liqiang Hou Shufan Wu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(11):3638-3653
A new method is proposed for multi-objective optimal control of satellite formation reconfiguration. First, necessary optimality conditions of single-objective fuel-optimal reconfiguration are studied. Problem of initial guess of the costate and control discontinuity are addressed by using a new developed stochastic based method. Terminal conditions of Two Point Boundary Value Problem (TPBVP) of the optimal control equations are relaxed using augmented Gaussian. Variances or bandwidths of the terminal conditions are set to decision variables to be optimized. Responses of varied initial costate are modeled and propagated using Riccati equation. Using quadratic convolution of relaxed terminal conditions, objective function of the fuel-optimal problem is reformulated into a quadratic equation, and a gradient based optimizer is used to search the optimal initial guess. In the second part of the paper, optimal control of format flying reconfiguration with two competitive objectives:fuel and time of flight (ToF) is studied. With Pascoletti-Serafini scalarization, the Multi-objective Optimal Control Problem (MOCP) is scalarized into a set of weighted Single-objective Optimal Control Problems (SOCP). Hamiltonian and switch function for the weighted SOCP are developed and constructed. New developed stochastic based approach is then used to search the optimal Pareto solutions. Verification and performances of proposed algorithms are demonstrated through numerical simulations of single-objective and multi-objective optimal control of low-thrust elliptical orbit formation reconfiguration. Potential applications of the algorithms to some other preliminary space mission designs are also discussed. 相似文献