全文获取类型
收费全文 | 5075篇 |
免费 | 8篇 |
国内免费 | 15篇 |
专业分类
航空 | 2353篇 |
航天技术 | 1602篇 |
综合类 | 13篇 |
航天 | 1130篇 |
出版年
2021年 | 36篇 |
2019年 | 21篇 |
2018年 | 195篇 |
2017年 | 160篇 |
2016年 | 104篇 |
2015年 | 53篇 |
2014年 | 113篇 |
2013年 | 133篇 |
2012年 | 146篇 |
2011年 | 259篇 |
2010年 | 215篇 |
2009年 | 295篇 |
2008年 | 333篇 |
2007年 | 230篇 |
2006年 | 95篇 |
2005年 | 150篇 |
2004年 | 139篇 |
2003年 | 160篇 |
2002年 | 89篇 |
2001年 | 177篇 |
2000年 | 74篇 |
1999年 | 115篇 |
1998年 | 121篇 |
1997年 | 89篇 |
1996年 | 103篇 |
1995年 | 126篇 |
1994年 | 125篇 |
1993年 | 58篇 |
1992年 | 91篇 |
1991年 | 29篇 |
1990年 | 39篇 |
1989年 | 87篇 |
1988年 | 33篇 |
1987年 | 51篇 |
1986年 | 36篇 |
1985年 | 129篇 |
1984年 | 74篇 |
1983年 | 69篇 |
1982年 | 87篇 |
1981年 | 128篇 |
1980年 | 40篇 |
1979年 | 30篇 |
1978年 | 29篇 |
1977年 | 30篇 |
1976年 | 24篇 |
1975年 | 32篇 |
1974年 | 26篇 |
1973年 | 16篇 |
1972年 | 19篇 |
1969年 | 15篇 |
排序方式: 共有5098条查询结果,搜索用时 15 毫秒
271.
272.
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
273.
274.
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
275.
Grasset O. Castillo-Rogez J. Guillot T. Fletcher L. N. Tosi F. 《Space Science Reviews》2017,212(1-2):835-875
Space Science Reviews - Space exploration and ground-based observations have provided outstanding evidence of the diversity and the complexity of the outer solar system. This work presents our... 相似文献
276.
The mass loss of spacecraft polyimide films under the action of atomic oxygen and vacuum ultraviolet radiation 总被引:1,自引:0,他引:1
The threshold values of the annual fluence of atomic oxygen (F AO ≈ 1020 cm?2), as well as the ratios of the energy-flux density of vacuum ultraviolet radiation of the solar spectrum to the flux density of atomic oxygen (Φ ν /Φ AO ≈ 8 × 10?15 mJ) were determined, which are characterized the influence of the synergistic effect on the mass loss of Kapton-H, PM-A, and PM-1E polyimide films, which are spacecraft materials. 相似文献
277.
278.
T. Hopf S. KumarW.J. Karl W.T. Pike 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
It is often necessary for space-borne instrumentation to cope with substantial levels of shock acceleration both in the initial launch phase, as well as during entry, descent and landing in the case of planetary exploration. Current plans for a new generation of penetrator-based space missions will subject the associated on-board instrumentation to far greater levels of shock, and ways must therefore be found to either ruggedize or else protect any sensitive components during the impact phase. In this paper, we present an innovative method of shock protection that is suited for use in a number of planetary environments, based upon the temporary encapsulation of said components within a waxy solid which may then be sublimated to return the instrument back to its normal operation. We have tested this method experimentally using micromachined silicon suspensions under applied shock loads of up to 15,000g, and found that these were able to survive without incurring damage. Furthermore, quality factor measurements undertaken on these suspensions indicate that their mechanical performance remains unaffected by the encapsulation and subsequent sublimation process. 相似文献
279.
S. Mühlbachler D. Langmayr A.T.Y. Lui N.V. Erkaev I.V. Alexeev P.W. Daly H.K. Biernat 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
This study presents several observations of the Cluster spacecraft on September 24, 2003 around 15:10 UT, which show necessary prerequisites and consequences for the formation of the so-called modified-two-stream instability (MTSI). Theoretical studies suggest that the plasma is MTSI unstable if (1) a relative drift of electrons and ions is present, which exceeds the Alfvèn speed, and (2) this relative drift or current is in the cross-field direction. As consequences of the formation of a MTSI one expects to observe (1) a field-aligned electron beam, (2) heating of the plasma, and (3) an enhancement in the B-wave spectrum at frequencies in the range of the lower-hybrid-frequency (LHF). In this study we use prime parameter data of the CIS and PEACE instruments onboard the Cluster spacecraft to verify the drift velocities of ions and electrons, FGM data to calculate the expected LHF and Alfvèn velocity, and the direction of the current. The B-wave spectrum is recorded by the STAFF instrument of Cluster. Finally, a field aligned beam of electrons is observed by 3D measurements of the IES instrument of the RAPID unit. Observations are verified using a theoretical model showing the build-up of a MTSI under the given circumstances. 相似文献
280.
J. Watermann P. Stauning H. Lühr P.T. Newell F. Christiansen K. Schlegel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
We examined some 75 observations from the low-altitude Earth orbiting DMSP, Ørsted and CHAMP satellites which were taken in the region of the nominal cusp. Our objective was to determine whether the actually observed cusp locations as inferred from magnetosheath-like particle precipitation (“particle cusp”) and intense small-scale magnetic field variations (“current cusp”), respectively, were identical and were consistent with the statistically expected latitude of the cusp derived from a huge number of charged particle spectrograms (“statistical cusp”). 相似文献