全文获取类型
收费全文 | 1141篇 |
免费 | 255篇 |
国内免费 | 399篇 |
专业分类
航空 | 1208篇 |
航天技术 | 264篇 |
综合类 | 167篇 |
航天 | 156篇 |
出版年
2024年 | 4篇 |
2023年 | 22篇 |
2022年 | 39篇 |
2021年 | 67篇 |
2020年 | 44篇 |
2019年 | 53篇 |
2018年 | 64篇 |
2017年 | 65篇 |
2016年 | 75篇 |
2015年 | 51篇 |
2014年 | 88篇 |
2013年 | 72篇 |
2012年 | 96篇 |
2011年 | 92篇 |
2010年 | 71篇 |
2009年 | 65篇 |
2008年 | 83篇 |
2007年 | 86篇 |
2006年 | 55篇 |
2005年 | 55篇 |
2004年 | 38篇 |
2003年 | 47篇 |
2002年 | 38篇 |
2001年 | 37篇 |
2000年 | 45篇 |
1999年 | 43篇 |
1998年 | 32篇 |
1997年 | 29篇 |
1996年 | 40篇 |
1995年 | 34篇 |
1994年 | 37篇 |
1993年 | 30篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 2篇 |
排序方式: 共有1795条查询结果,搜索用时 31 毫秒
361.
K. Scherer H. Fichtner B. Heber S.E.S. Ferreira M.S. Potgieter 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1171-1176
In recent years the variability of the cosmic ray flux has become one of the main issues not only for the interpretation of the abundances of cosmogenic isotopes in cosmochronic archives like, e.g., ice cores, but also for its potential impact on the terrestrial climate. It has been re-emphasized that the cosmic ray flux is not only varying due to the solar activity-induced changes of the solar wind but also in response to the changing state of the interstellar medium surrounding the heliosphere. We demonstrate the significance of these external boundary condition changes along the galactic orbit of the Sun for the flux as well as spectra of cosmic rays. Such interstellar–terrestrial relations are a major topic of the International Heliophysical Year 2007. 相似文献
362.
Once in the hands of end users, such durable equipment as spacecraft, aircraft, ships,automobiles, computers, etc. are in a state of debugging, working or storage. In either state, availability, reliability and super-efficiency are the ultimate goals, which have been achieved through constant monitoring as well as regular, preventive, routine and corrective maintenance. Although some advanced instruments can visualize certain invisible malfunctioning phenomena into visible ones, deeply hidden troubles cannot be found unless monitoring and testing data are addressed using tools that process the data statistically, analytically and mathematically. Some state-of-theart trouble-shooting and life-predicting techniques and approaches are introduced in this paper. 相似文献
363.
研究了固体火箭发动机装药硬度和HTPB推进剂方坯硬度、强度及延伸率在贮试期内的变化规律,建立了装药硬度-强度、延伸率-贮存期相关联的数学模型和回归方程组。用其预估固体发动机装药寿命。 相似文献
364.
介绍单元肼为推进剂的卫星推进系统,该系统已成功用于我国地球同步轨道通信卫星,高可靠,长寿命。叙述了系统及各部件的主要性能,关键部件的特性与可靠性试验,材料相容性试验,微粒控制及系统热试车。根据多年的飞行试验及地验对系统进行了可靠性计算。 相似文献
365.
The K field parameters of K1, KI, and *ox at the crack tip associated with crack high-velocity curving of epoxy resin specimen under impact tension are determined. The parameters obtained are used to construct the theoretical isochromatic fringe patterns fitting the experimental data. The curves of dynamic relation between stress intensity factor and crack length is also given. 相似文献
366.
In this paper, the stress strength factor of fuselage stiffened panels of transport airplanes has been obtained by using two-dimensional, analytical solution, curvature correc tion and nonuniform stress correction. Based on the Kc criterion critical crack length has been obtained. By using the fast integral technic the residual strength and residual life under random spectra for skin circumferential crack at the typical broken stringer and for longitudinal crack at the typical broken frame were obtained and analysed. Then by analyzing the above numerical results, the basic information for determining the life of the transport airplane has been provided. The above calculation is conducted on a IBM236 microcomputer.Due to the use of analytical and fast integral approaches the method used in this paper is convenient and economic.It can be used for crack tolerance analysis of other airplane structures. 相似文献
367.
DISTRIBUTIONMODELOFFATIGUELIFEANDITSGOODNESS-OF-FITTESTDongCong;RongHaiwu;XiaRenwei(DepartmentofAircraftEngineering,BeijingUn... 相似文献
368.
369.
370.
研究大迎角飞行稳定性一般需用高阶非线性模型。目前广泛采用分歧和突变理论算出飞机运动的平衡面和分歧面,判断平衡面上各点的稳定性质,然后利用飞行参数的时间历程来判断飞机的运动性质。该方法是行之有效的,但它对飞机受扰后的动态响应中每一时 相似文献