全文获取类型
收费全文 | 459篇 |
免费 | 27篇 |
国内免费 | 35篇 |
专业分类
航空 | 141篇 |
航天技术 | 283篇 |
综合类 | 37篇 |
航天 | 60篇 |
出版年
2024年 | 1篇 |
2023年 | 18篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 42篇 |
2013年 | 30篇 |
2012年 | 37篇 |
2011年 | 37篇 |
2010年 | 35篇 |
2009年 | 33篇 |
2008年 | 38篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 22篇 |
2004年 | 16篇 |
2003年 | 12篇 |
2002年 | 11篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 18篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
排序方式: 共有521条查询结果,搜索用时 46 毫秒
211.
212.
L. Golub 《Space Science Reviews》2006,124(1-4):23-33
We provide a brief overview of present-day studies of inner corona dynamics, with examples of mass ejections (CME), flares
and active region dynamics. While the names of the topics have not changed in several decades, the internal details and the
language used to express the nature of the problem have changed considerably. We conclude with a short discussion of the contribution
to studies of coronal dynamics to be expected from the Atmospheric Imager Assembly (AIA) on the Solar Dynamics Observatory. 相似文献
213.
Energetic proton precipitation occurring during solar events can increase the production of odd nitrogen in the upper stratosphere
and mesosphere. A very intense solar proton event (SPE) occurred on 28 October 2003. Its impact on the composition of the
middle atmosphere was observed in details due to the availability of several space instruments. Here we present GOMOS observations
of a strong NO2increase and a related ozone decrease in the upper stratosphere at north polar latitude. The perturbation of the chemical
composition of the stratosphere was observed until the middle of December 2003. A strong NO2 increase was also observed in the south polar vortex in June-July 2003. It is tentatively attributed to the effect of an
SPE with protons of moderate energy occurring on 29 May 2003. If this hypothesis is confirmed, it will imply that the global
effect of SPEs on the composition of the stratosphere is underestimated when only strong energy SPEs are considered. 相似文献
214.
飞机翼面结构布局综合设计方法研究 总被引:3,自引:0,他引:3
为了探讨飞机翼面结构主要纵横骨架的最佳布局问题,并提供符合工程实际的、用于概念设计阶段的飞机结构设计方法,本文采用分级优化与集成的策略,该策略分为3个层次。第一个层次为拓扑优化,并由此确定纵向骨架的个数与位置的最优布局;第二个层次为尺寸优化,它用来确定翼面的中间参数;第三个层次为稳定性准则优化,它确定横向骨架的个数与位置的最优布局。在分级优化的3个层次中,拓扑优化是独立的,尺寸优化与稳定性准则优化是相互耦合的。以国外某飞机机翼为例,结果表明本文提出分级优化的思路与所采用的集成方法是可行的,并且具有很好的数值效果。作者认为:它对从事飞机结构设计的人员有一定的指导性和参考价值,值得在飞机设计部门推广应用。最后,总结给出5点结论供参考。 相似文献
215.
边界弹性支撑板固有振动分析的一种解析方法 总被引:4,自引:0,他引:4
板的挠曲面微分方程与振型函数方程在数学上具有相同的形式,在力学上又具有相同的意义。这种可比拟性使得利用贝蒂功互等定理对板的固有振动进行研究成为可能。该文给出了求解矩形板的通用基本解,并对对边简支矩形板分别具有均匀的一般弹性边界支撑和弹性嵌固支撑时的固有振动进行了讨论,得到了解析形式的频率方程。 相似文献
216.
太阳活动区R9077引起的强烈吸收事件 总被引:1,自引:0,他引:1
利用南极中山站的观测数据分析了太阳活动区R9077所引起的强烈吸收事件,其中2000年7月14日的太阳质子事件引起了持续3天多强烈的极盖吸收,同时,激烈的太阳活动使磁层处于极度扰动状态,磁层高能粒子沉降使许多持续时间较短的吸收峰叠加在极盖吸收背景之上,最突出的是7月1日的吸收增强事件,其最大值达26dB。这是自1997年2月中山站安装成像式宇宙噪声接收机以来观测到的最强的吸收,另一个较突出的吸收峰发生在14日1753UT前后,本文还讨论了产生这些吸收的原由。 相似文献
217.
Jan Laštovička 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):2-8
The problem of optimum solar proxy is important for long-term and/or climatological studies of ionospheric parameters. Here we focus on possibly different optimum solar proxies for different ionospheric parameters, as they are affected by partly different spectral ranges of solar ionizing radiation. We use yearly average values of foF2 and foE of four European stations with long (1976–2014) and high-quality data (Juliusruh, Pruhonice, Rome, Slough/Chilton), and the global total electron content (G-TEC). Four solar proxies are used: F10.7, Mg II, solar Lymna-alpha flux Fα and sunspot numbers. The most important finding is that the optimum solar proxies are different for different ionospheric parameters. The most suitable solar proxy for foF2 is found to be Mg II, whereas for foE F10.7 evidently outperforms Mg II. Fα and sunspot numbers perform slightly worse but none of four solar proxies performs poorly. F10.7 is favored for G-TEC, to some extent surprisingly, as previous results favored rather Mg II. 相似文献
218.
A.M. El-Taher A.A. Thabet 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3213-3227
In this article, we investigate the interconnection and phase asynchrony between the periodicities of geomagnetic activity indices Kp, Ap, aa, and Dst according to the interplanetary magnetic field (IMF) polarities, toward (T) or away (A), during the time interval 1967–2018. For this purpose, the daily data of Kp, Ap, aa, and Dst indices during the considered period have been sorted into two groups (T and A) according to the IMF polarities. The wavelet transform (WT), the cross-wavelet transform (XWT), and the wavelet coherence (WTC) have been applied on the monthly averages of T and A groups for each geomagnetic index. Moreover, the correlation analyses (linear and running correlations) between the annual averages of T and A groups of each geomagnetic index have been investigated. The results of XWT and WTC revealed the existence of a long-term periodicity in the frequency range 8–16 yr for the monthly averages of T and A groups for aa, Kp, and Ap indices existed during the entire period. In contrast, the Dst index revealed this periodicity during the period 1980–2018. In addition, during this frequency band, both T and A groups of each geomagnetic index revealed a highly positive correlation and nearly in-phase relationship behavior. Furthermore, during the frequency band 4–8 yr, the XWT displayed a prominent periodicity that occurred for the monthly averages of T and A groups of each geomagnetic index, revealing a phase change during some time intervals. Periodicity in the range 2–4 yr for the monthly averages of T and A groups of aa, Kp, Ap, and Dst occurred in the intervals; 1967–2009 for aa and Kp, 1967–2007 for Ap, and 1976–1995 for Dst. The annual periodicity is also identified for all considered indices. Both T and A groups of Dst shared a semiannual periodicity (~187 days) during different intervals in the entire period. On the other hand, a periodicity around 0.25-yr (~90 days) appeared only near the times of solar activity maxima in the case of the T and A groups of aa, Kp, and Ap indices. 相似文献
219.
J.M. Vaquero S. Gutiérrez-López A. Szelecka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We have studied the relationship between three different versions of the sunspot number (Group, International and American Sunspot Number) and the number of active days (i.e., the number of days with spots on the solar disk). We have detected an approximately linear relationship for low solar activity conditions. However, this relationship for the International Sunspot Number is very different to the ones obtained with the other versions of the sunspot number. The discordant values correspond to older observations. 相似文献
220.
E.I. Astafyeva E.L. Afraimovich A.V. Oinats Yu.V. Yasukevich I.V. Zhivetiev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We analyzed the dynamics of global electron content (GEC) for the period 1998–2005 and compared the estimated GEC with variations of the 10.7-cm solar radio emission and with and with GEC values obtained with IRI-2001. We found a strong resemblance between the curves’ shapes for the experimental and modeled GEC: strong semiannual variations are discernible in these series and both curves tend to increase the absolute GEC value during the period of maximum of solar activity. However, there are some significant distinctions, such as absence of 27-day fluctuations in the series of GEC computed by the IRI-2001. On the contrary, observational GEC reflects well dynamics of solar activity: 27-day variations of GEC are very similar to the ones of the index F10.7, but GEC undergoes a lagging of about of 30–60 h as compared to value of the F10.7 index. The relative amplitude of 27-day variations decreases from 8% at the rising and falling solar activity to 2% at the period of its maximum. 相似文献