全文获取类型
收费全文 | 172篇 |
免费 | 42篇 |
国内免费 | 25篇 |
专业分类
航空 | 127篇 |
航天技术 | 50篇 |
综合类 | 14篇 |
航天 | 48篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 18篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 15篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 17篇 |
2013年 | 14篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 11篇 |
2009年 | 18篇 |
2008年 | 17篇 |
2007年 | 8篇 |
2006年 | 13篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有239条查询结果,搜索用时 15 毫秒
11.
航空公司因市场定位、品牌建设、拟飞航线和所选设备不同,导致客户对不同架次或批次商用飞机的 客户化需求存在较大差异,因此灵活高效的客户化管理是实现客户飞机有效构型配置的第一个关键步骤,也是 飞机采购合同签署的基础。提出一种基于产品结构的需求管理方案,构建三层数据管理结构和各种表单对客 户需求进行全流程管控,对某型号飞机信息系统开发的案例进行分析。该管理方案能够支撑不同航空公司客 户化构型的定义,保证客户需求传递的便捷性和实现的准确性,符合产品全寿命周期管理的发展需求。 相似文献
12.
13.
G.J. Nagy D.N. Severov V.A. Pshennikov M. De los Santos J.J. Lagomarsino K. Sans E.G. Morozov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(11):1876-1881
This paper deals with the application of SeaWIFS images to characterize spatial and temporal variability of fronts in the Rio de la Plata estuarine system over the period 2000–2003. We aim to depict the relationship between river outflow and variability of fronts’ loci on monthly to ENSO-related timescales and the influence of the winds along Rio de la Plata (axial winds) on the abrupt changes in frontal dynamics over synoptic timescales. During the studied period both La Niña (July 1999–June 2000) and El Niño (April 2002–May 2003) events induced significant displacements of fronts. Three distinct fronts were analyzed between river, estuarine, coastal and marine waters of the Rio de la Plata: Main Turbidity Front, Main Marine Front, and Secondary Marine Front. Their number, location and separation seem to be mainly related to river outflow and second, to fresh (>8 m/s) axial winds. During low discharge periods (i.e. summer time and/or La Niña events) these winds induce abrupt changes in the location of fronts (100–200 km) and greater separation between them over synoptic timescale, whereas during high river discharge or ENSO years some of the variability of fronts location is explained by the river’s outflow fluctuations, especially by the high variability of the River Uruguay discharge. 相似文献
14.
S.P. Teng Y.K. Chen K.S. Cheng H.C. Lo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(11):1744-1754
Remote sensing images and technologies have been widely applied to environmental monitoring, in particular landuse/landcover classification and change detection. However, the uncertainties involved in such applications have not been fully addressed. In this paper two hypothesis-test-based change detection methods, namely the bivariate joint distribution method and the conditional distribution method, are proposed to tackle the uncertainties in change detection by making decisions based on the desired level of significance. Both methods require a data set of class-dependent no-change pixels to form the basis for class-dependent hypothesis test. Using an exemplar study area in central Taiwan, performance of the proposed methods are shown to be significantly superior to two other commonly applied methods (the post-classification comparison and the image differencing methods) in terms of the overall change detection accuracies. The conditional distribution method takes into consideration the correlation between digital numbers of the pre- and post-images and the effect of the known pre-image digital number on the range of the post-image digital number, and therefore yields the highest change detection accuracy. It is also demonstrated that the class-dependent change detection is crucial for accurate landuse/landcover change detection. 相似文献
15.
数据采集器是飞行试验关键的测试设备,它的性能与现代飞机飞行试验有很大的关系.为满足现代飞机设计定型的需求,新一代数据采集器设计大量采用了FPGA和DSP器件,大大提高了采集器测量参数的采样率、通道数、测量参数类型和使用的灵活性.本文介绍的新一代采集器模拟量采集卡设计技术,用数字信号处理技术来实现信号的放大、滤波及偏置修正,并提供了对采集卡各个部分进行设计的理论依据. 相似文献
16.
运用Malmquist生产率指数方法,对中美15个航空公司2000~2006年期间的全要素生产率的变化作了测算与对比。分析结果显示,2000—2006年这些公司的生产效率总体上都有所提高,中国航空公司的全要素生产率的平均增长率为4.3%,美国的平均增长率为6.1%;综合效率改善与技术进步对中美两国航空公司生产率的影响程度并不相同,美国航空公司的主要驱动因素为技术变革与创新,中国航空公司的发展动力主要为对已有技术的运用以及组织管理效率的提升。中国航空公司全要素生产率水平的提高,除继续强调综合效率的重要性之外,也要进一步加强对技术进步的重视。 相似文献
17.
18.
19.
P.S. Sawyer H. Stephen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Recent variations in normal meteorological conditions indicate the earth’s climate is changing in ways that may impact delicate ecological balances in sensitive regions. Identifying how those changes are affecting the biosphere is essential if we are going to be able to adapt to those changes and to potentially mitigate their harmful consequences. This paper presents a time series study of an alpine ecosystem in the Big Pine Creek watershed in California’s Eastern Sierra Nevada Mountain’s. Raw Landsat data covering the years 1984 through 2011 is converted to observed surface reflectance and analyzed for trends that would indicate a change in the ecosystem. We found that over the time period of the study, observed surface reflectance shows a general decline across the spectrum while our analysis of environmental data demonstrates statistically significant increases in temperatures. While declining reflectance in the visible and short wave bands are indicators of increased surface cover, the fact that the IR band also shows declines is consistent with a decline in tree density. This study provides a useful insight into the ecological response of the Big Pine Creek watershed to recent climate change. These findings suggest that alpine ecosystems are particularly sensitive to increasing temperatures. If these results are replicated in other alpine watersheds it will demonstrate that the biosphere is already showing the effects of a warmer environment. 相似文献
20.