全文获取类型
收费全文 | 3238篇 |
免费 | 645篇 |
国内免费 | 478篇 |
专业分类
航空 | 1962篇 |
航天技术 | 769篇 |
综合类 | 427篇 |
航天 | 1203篇 |
出版年
2024年 | 15篇 |
2023年 | 47篇 |
2022年 | 105篇 |
2021年 | 148篇 |
2020年 | 129篇 |
2019年 | 106篇 |
2018年 | 122篇 |
2017年 | 136篇 |
2016年 | 125篇 |
2015年 | 155篇 |
2014年 | 184篇 |
2013年 | 180篇 |
2012年 | 204篇 |
2011年 | 219篇 |
2010年 | 266篇 |
2009年 | 271篇 |
2008年 | 196篇 |
2007年 | 188篇 |
2006年 | 153篇 |
2005年 | 148篇 |
2004年 | 88篇 |
2003年 | 114篇 |
2002年 | 156篇 |
2001年 | 104篇 |
2000年 | 104篇 |
1999年 | 99篇 |
1998年 | 68篇 |
1997年 | 77篇 |
1996年 | 65篇 |
1995年 | 71篇 |
1994年 | 53篇 |
1993年 | 36篇 |
1992年 | 46篇 |
1991年 | 35篇 |
1990年 | 26篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 19篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1965年 | 1篇 |
排序方式: 共有4361条查询结果,搜索用时 31 毫秒
811.
Chunliang Xia Qi Wang Tao Yu Guirong Xu Shaomin Yang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We investigate the ionospheric total electron content (TEC) anomalies occurred in the Qinghai-Tibet region before three large earthquakes (M > 7.0). The temporal and spatial TEC variations were used to detect the ionospheric possible precursors of these earthquakes. We identified two TEC enhancements in the afternoon local time 9 days and 2–3 days before each earthquake, between which a TEC decrement occurred 3–6 days before earthquakes. These anomalies happened in the area of about 30° in latitude and the maximum is localized equatorward from the epicenters. These TEC anomalies can be found in all three earthquakes regardless the geomagnetic conditions. The features of these anomalies have something in common and may have differences from those caused by geomagnetic storms. Our results suggest that these ionospheric TEC perturbations may be precursors of the large earthquakes. 相似文献
812.
Katsuyuki Noguchi Andreas Richter Heinrich Bovensmann Andreas Hilboll John P. Burrows Hitoshi Irie Sachiko Hayashida Yu Morino 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We have conducted a feasibility study for the geostationary monitoring of the diurnal variation of tropospheric NO2 over Tokyo. Using NO2 fields from a chemical transport model, synthetic spectra were created by a radiative transfer model, SCIATRAN, for summer and winter cases. We then performed a Differential Optical Absorption Spectroscopy (DOAS) analysis to retrieve NO2 slant column densities (SCDs), and after converting SCDs into vertical column densities (VCDs), we estimated the precision of the retrieved VCDs. The simulation showed that signal-to-noise ratio (SNR) ? 500 is needed to detect the diurnal variation and that SNR ? 1000 is needed to observe the local minimum occurring in the early afternoon (LT13–14) in summer. In winter, the detection of the diurnal variation during LT08–15 needs SNR ? 500, and SNR ? 1000 is needed if early morning (LT07) and early evening (LT16) are included. The currently discussed sensor specification for the Japanese geostationary satellite project, GMAP-Asia, which has a horizontal resolution of 10 km and a temporal resolution of 1hr, has demonstrated the performance of a precision of several percent, which is approximately corresponding to SNR = 1000–2000 during daytime and SNR ? 500 in the morning and evening. We also discuss possible biases caused by the temperature dependence of the absorption cross section utilized in the DOAS retrieval, and the effect of uncertainties of surface albedo and clouds on the estimation of precisions. 相似文献
813.
814.
815.
816.
817.
刘宇 《中国民航飞行学院学报》2011,22(3):48-49
在分析了九寨机场的气象特点以及环境因素对航空器造成的影响的基础上,就如何做好九寨机场的航务代理工作提出了合理建议和措施,这对提高航班正常率非常重要. 相似文献
818.
819.
为了研究脉冲爆震发动机的部分填充效应,建立了不依赖于实验数据的通用理论分析模型。将该理论模型得到的计算结果与实验数据进行对比,误差在15%以内。并应用该模型进行了一些算例计算,计算结果表明:部分填充能显著增加比冲,理论比冲最高能接近600s;比冲增益随填充系数的减小而增大,最后趋于某一上限值,计算中,该上限值最高达到4;采用氧气作氧化剂时不仅比采用空气作氧化剂时的比冲更高,而且比冲增益也更大;不可燃气体密度越大,部分填充产生的比冲增益越大;背压降低,部分填充产生的比冲增益也随之减小。 相似文献
820.
Uncertainties are taken into account in reentry trajectory optimization and a robust trajectory optimization model is constructed based on the robust optimization theory. There are computational difficulties in solving this robust trajectory optimization problem due to the random variables associated with the uncertainties. To overcome these difficulties, the covariance analysis describing function technique (CADET) is employed to convert the robust trajectory optimization model into an equivalent deterministic trajectory optimization formulation, which is then solvable by using the existing pseudo spectral method. In the case study, a robust reentry trajectory optimization problem considering the uncertainties of aerodynamic parameters is solved to obtain the robust optimal trajectories. By comparing with the traditional deterministic optimal trajectories, the robust optimal trajectories are significantly less sensitive to the uncertainties of aerodynamic parameters, showing the effectiveness of the presented method. 相似文献