全文获取类型
收费全文 | 1826篇 |
免费 | 891篇 |
国内免费 | 359篇 |
专业分类
航空 | 1630篇 |
航天技术 | 570篇 |
综合类 | 226篇 |
航天 | 650篇 |
出版年
2025年 | 27篇 |
2024年 | 62篇 |
2023年 | 87篇 |
2022年 | 117篇 |
2021年 | 130篇 |
2020年 | 134篇 |
2019年 | 145篇 |
2018年 | 137篇 |
2017年 | 120篇 |
2016年 | 132篇 |
2015年 | 128篇 |
2014年 | 148篇 |
2013年 | 132篇 |
2012年 | 130篇 |
2011年 | 183篇 |
2010年 | 126篇 |
2009年 | 132篇 |
2008年 | 112篇 |
2007年 | 127篇 |
2006年 | 106篇 |
2005年 | 102篇 |
2004年 | 80篇 |
2003年 | 67篇 |
2002年 | 49篇 |
2001年 | 53篇 |
2000年 | 45篇 |
1999年 | 28篇 |
1998年 | 30篇 |
1997年 | 27篇 |
1996年 | 27篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 26篇 |
1992年 | 21篇 |
1991年 | 25篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 2篇 |
排序方式: 共有3076条查询结果,搜索用时 15 毫秒
951.
V.M. Dvornikov M.V. KravtsovaA.A. Lukovnikova V.E. Sdobnov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Dynamic processes in the interplanetary space have been investigated using time variations in time parameters of the cosmic-ray rigidity spectrum. Change of heliosphere electromagnetic characteristics has been found out to precede sporadic phenomena on the Sun. In particular, it is shown that sporadic phenomena are followed by generation of local polarization electric fields, decrease of the magnetic-field strength in small-scale heliospheric structures, and increase of the potential difference between the pole and the plane of the ecliptic. These features allow prediction of solar proton events in advance (from several hours to several tens of hours) with a high degree of confirmation. 相似文献
952.
953.
An experimental method and a theoretical analysis based on continuum damage mechan- ics are applied for the defects tolerance of fixed plate. The defects type studied in this article is scratch, which is considered a typical defect on fixed plate according to the engineering practice. The general approach to the defects tolerance analysis of scratched fixed plate is presented. The method of fatigue life prediction for standard notched specimens has been established on the basis of continuum damage mechanics. For the purpose of obtaining the influence law of fatigue life in consequence of scratches, fatigue experiments of standard notched specimens and scratched specimens have been done. Evalu- ation of the fatigue life of scratched fixed plate has been carried out. And the value of scratch defects permissible to the condition of safety service life has been worked out. According to the results of the- oretical calculations, the fatigue experiment of scratched fixed plate has been performed. The outcome shows that the theoretical prediction tallies with the experimental results. 相似文献
954.
提出了超音速混合层着火距离的一种理论预测方法。基于超音速混合层来流热力学参数和考虑粘性加热及可压缩性效应的修正温度,定义了密闭容器反应系统。耦合详细化学反应机理获得该系统的着火延迟时间,并基于超音速混合层的平均流动速度获得了着火距离。其预测结果与高精度数值模拟结果相符,同时该理论预测方法能够从物理上很清晰地解释已有研究中所观察到的着火距离随相关影响因素的变化规律。同时,该预测方法为定性认识超音速着火距离及其变化规律提供了简易可行的途径,为耦合有限试验和数值模拟结果实现着火距离的定量预测提供了理论支撑。 相似文献
955.
日益繁重和复杂的靶场试验对靶场安全控制能力要求不断提高,保护航区周围重要目标的安全成为靶场地面安全控制系统的重要使命.针对这一现实需求提出了安全控制决策自动化问题.在分析影响安全控制决策依据的安全控制信息的基础上,构建基于一体化体系结构的靶场安全控制辅助决策系统,建立专家系统模型;探讨了基于模糊推理的导弹工作状态判定问题的推理规则,设计了安全控制辅助决策系统各模块功能;总结了系统须解决的关键技术问题及实现的技术途径.为靶场安全控制辅助决策系统建设提供了科学依据. 相似文献
956.
An experimental method and a theoretical analysis based on continuum damage mechan-ics are applied for the defects tolerance of fixed plate. The defects type studied in this article is scratch, which i... 相似文献
957.
文章提出一种新的动目标检测(MTD)滤波器组设计方法,即信号处理系统分为目标处理通道和气象处理通道;目标通道采用自适应动目标检测(AMTD)处理方式,实时检测杂波的存在,判定杂波强度(如强、中、弱),根据杂波的强度自动产生或选择滤波器加权因子,以期保证对地杂波高度抑制的前提下,尽量减少信噪比损失,提高对弱小目标的检测能力。该方法可提高雷达在杂波环境中的自适应性能,具有一定的实用价值。 相似文献
958.
以高压压气机为例,确定效率和流量损失作为性能衰退分析的主要因素。得到叶片粗糙度引起的效率和流量损失变化规律,利用神经网络建立并验证其对应关系。提出运用主成分分析将两个中间变量转化成单一变量,通过引入性能衰退综合指数,建立飞行循环数与叶片粗糙度的函数关系。利用时间序列三次指数平滑方法对性能衰退进行预测,效果较好。将高压压... 相似文献
959.
《中国航空学报》2021,34(4):32-41
Obtaining accurate development cost estimation results of general aviation aircraft is crucial for companies to adopt the best strategy in the development process. To address this problem, this paper proposes a combination of three commonly used single prediction methods. The optimal weight values of the three single prediction methods are determined by utilizing the shortest ideal point method. Ten cost datasets collected from literature are utilized for fitting and testing the combined prediction method, and the weight coefficients of the three individual prediction methods are calculated as 0.6859, 0.0035 and 0.3106, respectively. The results of this study indicate that the developed method has better fitting and estimation accuracy than that of the three individual methods, with average fitting and predicting error values of 2.60% and 6.43%, respectively. Additionally, the cost data of military and civil aircraft development from literature are collected for verification. The results further confirm that the proposed method is not only superior to the single prediction methods in terms of high precision but has wider applications. More importantly, this research can provide important reference for general aviation aircraft companies in term of product cost planning and corporate sales strategies. 相似文献
960.
GPS/惯性导航组合系统目前正得到越来越广泛的应用,但GPS接收机载波环失锁时,码环的速率辅助信息来自惯导系统,由于惯性速度的不精确性及伪距测量误差和它之间的相关性,将可能导致组合系统工作的不稳定,本文根据码环的工作特性,在组合卡尔曼滤波器中考虑了码环的跟踪误差,利用GPS/捷联惯导组合系统的导航性能,结果表明,GPS/捷联惯导组合系统中,若消除了伪距测量误差与惯性速度误差之间的相关性,将可较显著 相似文献