全文获取类型
收费全文 | 594篇 |
免费 | 95篇 |
国内免费 | 199篇 |
专业分类
航空 | 437篇 |
航天技术 | 168篇 |
综合类 | 48篇 |
航天 | 235篇 |
出版年
2024年 | 4篇 |
2023年 | 16篇 |
2022年 | 11篇 |
2021年 | 30篇 |
2020年 | 38篇 |
2019年 | 27篇 |
2018年 | 35篇 |
2017年 | 37篇 |
2016年 | 50篇 |
2015年 | 43篇 |
2014年 | 56篇 |
2013年 | 42篇 |
2012年 | 45篇 |
2011年 | 35篇 |
2010年 | 35篇 |
2009年 | 22篇 |
2008年 | 28篇 |
2007年 | 37篇 |
2006年 | 70篇 |
2005年 | 35篇 |
2004年 | 15篇 |
2003年 | 26篇 |
2002年 | 19篇 |
2001年 | 4篇 |
2000年 | 15篇 |
1999年 | 27篇 |
1998年 | 17篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
排序方式: 共有888条查询结果,搜索用时 218 毫秒
361.
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
362.
翼型—扰流片的分离气动特性计算 总被引:1,自引:0,他引:1
本文介绍了用涡面元法模拟带扰流片的翼型低速无粘分离绕流。在翼型和扰流片的面元上分布线性变化涡。在扰流片后的上下分离流线的面元上分布等强度的涡。上分离流线始自扰流片的梢部,下分离流线自翼型的后缘引出。分离所泡由两离散涡结尾。气泡内总压为常值,它与涡强大小一同求解。分离气泡的形状在迭代求解过程中确定。压强分布和升力系数的计算值与现存文献的数值结果和实验数据是一致的。 相似文献
363.
本文通过两类带有对接桁条加劲板应力强度因子的求解,说明推广的铆钉力法及其应用,侧重地讨论了用Pars位移公式确定不规则含裂纹构件位移场的具体步骤。文中给出了两个实际算例的计算曲线,这一结果趋势合理,精度满足工程要求,可直接为工程应用服务。 相似文献
364.
Thomas H. Zurbuchen 《Space Science Reviews》2006,124(1-4):77-90
Research into the heliospheric structure and its relation to the solar boundary is at an impasse. After successful predictions
by Parker about the zeroth-order behavior of the heliospheric magnetic field and the solar wind, the heliospheric community
struggles to make substantive progress toward a predictive model describing the connections between the Sun and its space
environment, between the closed corona and the open corona extending to the planets. This is caused by our lack of understanding
of the basic processes heating the corona and transporting open magnetic field. We detail the models used to describe this
connectivity, from potential field source surface models to full MHD techniques. We discuss the current limitations of both
approaches. Finally, we address a recent attempt to advance our understanding beyond these limitations. At this point in time
the proposed theory remains controversial in the community, but it addresses important shortcomings of current approaches
outlined above. 相似文献
365.
如何提高面元法的求解效率是面元法应用研究的一个重要课题。本文利用面元法积分核的变量分离技术及网格组合的网片串技术,对飞机气动力计算方面应用颇广的求解技术做了一定的改进,提出了一种面元法的快速算法,从在DEC7620机上运行的一个实例来看,其结果是令人满意的。 相似文献
366.
367.
We discuss the recent progress in studying the absolute and convective instabilities of circularly polarized Alfvén waves
(pump waves) propagating along an ambient magnetic field in the approximation of ideal magnetohydrodynamics (MHD). We present
analytical results obtained for pump waves with small dimensionless amplitude a, and compare them with numerical results valid for arbitrary a. The type of instability, absolute or convective, depends on the velocity U of the reference frame where the pump wave is observed with respect to the rest plasma. One of the main results of our analysis
is that the instability is absolute when U
l < U < U
r and convective otherwise. We study the dependences of U
l and U
r on a and the ratio of the sound speed to the Alfvén speed b. We also present the results of calculation of the increment of the absolute instability on U for different values of a and b. When the instability is convective (U < U
l or U > U
r) we consider the signalling problem, and show that spatially amplifying waves exist only when the signalling frequency is
in two symmetric frequency bands. Then, we write down the analytical expressions determining the boundaries of these frequency
bands and discuss how they agree with numerically calculated values. We also present the dependences of the maximum spatial
amplification rate on U calculated both analytically and numerically. The implication of the obtained results on the interpretation of observational
data from space missions is discussed. In particular, it is shown that circularly polarized Alfvén waves propagating in the
solar wind are convectively unstable in a reference frame of any realistic spacecraft. 相似文献
368.
20世纪上海航天器电源技术的进展 总被引:7,自引:2,他引:7
较为系统地介绍了作为航天器电源的锌银电池组和硅太阳电池阵/镉镍蓄电池组联合供电系统的组成、主要性能参数及其技术特点。阐述了近半个世纪以来,上海航天技术研究院在航天器电源研制技术方面所取得的成就及其在国内卫星、飞船和国外卫星领域的应用情况。指出了航天器电源技术今后的发展方向。 相似文献
369.
370.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(7):1831-1842
The present paper has investigated the associations of solar activity (SA), represented by total solar irradiance (TSI), galactic cosmic rays (GCR) and terrestrial climate parameters in particular the global cloudiness and global surface temperature. To that end, we have analysed thirty five years (1983–2018) data of these parameters and have applied the Granger-causality test in order to assess whether there is any potential predictability power of one indicator to the other. The correlations among the involved parameters are tested using Vector Auto Regression (VAR) model and variance decomposition method. As a result of the above analysis, we have found that the TSI is an important factor and has contributed about 8.77 ± 0.42% in the cosmic ray intensity variations. In case of cloud cover variations, the other three parameters (TSI, cosmic ray and global surface temperature) have played a significant role. Further, the TSI changes have contributed 1.68 ± 0.03% fluctuations in the variance of the cloud cover while the cosmic ray intensity and global surface temperature have contributed about 4.89 ± 0.08% and 10.87 ± 1.41% respectively. In case of the global surface temperature anomaly both TSI and cloud covers have contributed about 5.07 ± 0.47% and 14.42 ± 2.13% fluctuations respectively. Additionally, we have also assessed the impact of internal climate oscillations like multivariate ENSO index (MEI), north Atlantic oscillations (NAO) and quasi biennial oscillations (QBO) on cloud cover variations. The contribution of these internal oscillations e.g. ENSO, NAO and QBO in cloud cover variation were reported as 7.48 ± 1.02%, 5.51 ± 0.16% and 1.36 ± 0.43% respectively. 相似文献