全文获取类型
收费全文 | 3471篇 |
免费 | 4篇 |
国内免费 | 6篇 |
专业分类
航空 | 1766篇 |
航天技术 | 913篇 |
综合类 | 9篇 |
航天 | 793篇 |
出版年
2021年 | 18篇 |
2019年 | 16篇 |
2018年 | 180篇 |
2017年 | 149篇 |
2016年 | 73篇 |
2015年 | 37篇 |
2014年 | 56篇 |
2013年 | 90篇 |
2012年 | 91篇 |
2011年 | 204篇 |
2010年 | 181篇 |
2009年 | 231篇 |
2008年 | 214篇 |
2007年 | 182篇 |
2006年 | 64篇 |
2005年 | 113篇 |
2004年 | 77篇 |
2003年 | 85篇 |
2002年 | 43篇 |
2001年 | 94篇 |
2000年 | 48篇 |
1999年 | 65篇 |
1998年 | 69篇 |
1997年 | 66篇 |
1996年 | 64篇 |
1995年 | 87篇 |
1994年 | 86篇 |
1993年 | 46篇 |
1992年 | 51篇 |
1991年 | 15篇 |
1990年 | 24篇 |
1989年 | 51篇 |
1988年 | 32篇 |
1987年 | 20篇 |
1986年 | 28篇 |
1985年 | 73篇 |
1984年 | 70篇 |
1983年 | 42篇 |
1982年 | 69篇 |
1981年 | 67篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 31篇 |
1977年 | 12篇 |
1975年 | 24篇 |
1974年 | 16篇 |
1973年 | 16篇 |
1972年 | 16篇 |
1970年 | 9篇 |
1969年 | 12篇 |
排序方式: 共有3481条查询结果,搜索用时 31 毫秒
211.
212.
本文描述的是研究爆炸成型发射弹(EFP)模型的流场及超高速空气动力特性所用的弹道试验设备;简要报导了记录全尺寸干涉图形的技术;对径向密度分布再现的方法进行了讨论;在零攻角实验时不同模型的空气动力阻力是采用简化方法来计算的;对各种不同EFP型式的气动稳定性提出了定性估计的方法;并阐述了用于组合体超高速飞行特性研究的数值计算技术的基本原理 相似文献
213.
The present paper discusses a need to develop a methodology of predicting the reliability of small thrust liquid rocket engines with a flow section made of composite materials under actual operating conditions for their successful practical use in the propulsion systems. 相似文献
214.
215.
Paul Morgan Suzanne E. Smrekar Ralph Lorenz Matthias Grott Olaf Kroemer Nils Müller 《Space Science Reviews》2017,211(1-4):277-313
The HP3 instrument on the InSight lander mission will measure subsurface temperatures and thermal conductivities from which heat flow in the upper few meters of the regolith at the landing site will be calculated. The parameter to be determined is steady-state conductive heat flow, but temperatures may have transient perturbations resulting from surface temperature changes and there could be a component of thermal convection associated with heat transport by vertical flow of atmospheric gases over the depth interval of measurement. The experiment is designed so that it should penetrate to a depth below which surface temperature perturbations are smaller than the required measurement precision by the time the measurements are made. However, if the measurements are delayed after landing, and/or the probe does not penetrate to the desired depth, corrections may be necessary for the transient perturbations. Thermal convection is calculated to be negligible, but these calculations are based on unknown physical properties of the Mars regolith. The effects of thermal convection should be apparent at shallow depths where transient thermal perturbations would be observed to deviate from conductive theory. These calculations were required during proposal review and their probability of predicting a successful measurement a prerequisite for mission approval. However, their uncertainties lies in unmeasured physical parameters of the Mars regolith. 相似文献
216.
217.
M. Ayub S. Iqbal M.A. Ameen B.W. Reinisch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The monthly hourly medians of maximum electron density, NmF2, at two Pakistani ionospheric stations, Karachi and Islamabad, have been determined for solar minimum (1996) and solar maximum (2000) and compared with IRI predictions using the URSI coefficients. At night and pre-noon period the NmF2 values at both stations are almost equal during the 2 years. However, at post-noon the values at Karachi are considerably larger than those at Islamabad due to the equatorial or geomagnetic anomaly. Karachi (geomag. coord. 16.44°N, 139.08°E) lies near the region of the equatorial anomaly (+20 and −20 geomagnetic latitude), so most of the NmF2 values at Karachi are larger than those at Islamabad (geomag. coord. 24.46°N, 145.67°E). The maximum monthly values of NmF2 show a semi-annual variation at Karachi and Islamabad both during 1996 and 2000 as predicted by IRI. 相似文献
218.
W.D. Apel J.C. Arteaga-Velázquez K. Bekk M. Bertaina J. Blümer H. Bozdog I.M. Brancus E. Cantoni A. Chiavassa F. Cossavella K. Daumiller V. de Souza F. Di Pierro P. Doll R. Engel J. Engler M. Finger B. Fuchs D. Fuhrmann H.J. Gils R. Glasstetter C. Grupen A. Haungs D. Heck J.R. Hörandel D. Huber T. Huege K.-H. Kampert D. Kang H.O. Klages K. Link P. Łuczak M. Ludwig H.J. Mathes H.J. Mayer M. Melissas J. Milke B. Mitrica C. Morello J. Oehlschläger S. Ostapchenko N. Palmieri M. Petcu T. Pierog H. Rebel M. Roth H. Schieler S. Schoo F.G. Schröder O. Sima 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
219.
S. Narendranath P.S. Athiray P. Sreekumar V. Radhakrishna A. Tyagi B.J. Kellett the CLASS team 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS. 相似文献
220.
B. Sylwester J. Sylwester K.J.H. Phillips E. Landi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We present the observations of He-like Ar triplet lines obtained by RESIK spectrometer aboard CORONAS-F. Interpretation of intensity ratios between triplet lines of lower Z elements is known to provide useful diagnostics of plasma conditions within the emitting source. Here, we investigate whether triplet line ratios are useful for interpretation of higher Z element spectra. A high sensitivity, low background and precise absolute calibration of RESIK allow to consider in addition also the continuum contribution. This provides a way to determine the Ar absolute abundance from the observed triplet component ratios. The method is presented and the results are shown for two selected flares. Derived values of Ar absolute abundance for these flares are found to be similar: 2.6 × 10−6 and 2.9 × 10−6. They fall in the range between presently accepted Ar photospheric and coronal abundances. 相似文献