全文获取类型
收费全文 | 2474篇 |
免费 | 64篇 |
国内免费 | 166篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 3篇 |
地球物理 | 81篇 |
地质学 | 458篇 |
海洋学 | 32篇 |
天文学 | 2068篇 |
综合类 | 18篇 |
自然地理 | 38篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 37篇 |
2021年 | 9篇 |
2020年 | 26篇 |
2019年 | 27篇 |
2018年 | 23篇 |
2017年 | 23篇 |
2016年 | 33篇 |
2015年 | 66篇 |
2014年 | 60篇 |
2013年 | 44篇 |
2012年 | 55篇 |
2011年 | 54篇 |
2010年 | 69篇 |
2009年 | 181篇 |
2008年 | 139篇 |
2007年 | 219篇 |
2006年 | 234篇 |
2005年 | 250篇 |
2004年 | 203篇 |
2003年 | 164篇 |
2002年 | 163篇 |
2001年 | 122篇 |
2000年 | 92篇 |
1999年 | 97篇 |
1998年 | 125篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有2704条查询结果,搜索用时 15 毫秒
31.
D. Falceta-Gonçalves Z. Abraham 《Monthly notices of the Royal Astronomical Society》2009,399(3):1441-1446
During the past decade, several observational and theoretical works have provided evidence of the binary nature of η Carinae. Nevertheless, there is still no direct determination of the orbital parameters, and the different current models give contradictory results. The orbit is, in general, assumed to coincide with the Homunculus equator although the observations are not conclusive. Among all systems, η Car has the advantage that it is possible to observe both the direct emission of line transitions in the central source and its reflection by the Homunculus, which is dependent on the orbital inclination. In this work, we studied the orbital phase-dependent hydrogen Paschen spectra reflected by the south-east lobe of the Homunculus to constrain the orbital parameters of η Car and determine its inclination with respect to the Homunculus axis. Assuming that the emission excess originates in the wind–wind shock region, we were able to model the latitude dependence of the spectral line profiles. For the first time, we were able to estimate the orbital inclination of η Car with respect to the observer and to the Homunculus axis. The best fit occurs for an orbital inclination to the line of sight of i ∼ 60°± 10° , and i *∼ 35°± 10° with respect to the Homunculus axis, indicating that the angular momenta of the central object and the orbit are not aligned. We were also able to fix the phase angle of conjunction as ∼−40° , showing that periastron passage occurs shortly after conjunction. 相似文献
32.
1 .IntroductionThe lifting systemis composed of pipes andtheir connectors .It is not onlythe lifting channel formanganese nodule betweenthe miningship andintermediate bin,but alsothe supporting massfor deepsea miningequipment and cables .Sothe reliability… 相似文献
33.
34.
35.
36.
37.
38.
Peter J. Wheatley Christopher W. Mauche Janet A. Mattei 《Monthly notices of the Royal Astronomical Society》2003,345(1):49-61
We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer and Rossi X-ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high-energy outburst begins in the X-ray waveband 0.9–1.4 d after the beginning of the optical rise and 0.6 d before the extreme-ultraviolet rise. The X-ray flux drops suddenly, immediately before the extreme-ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X-ray flux shows that the propagation time of the outburst heating wave may have been previously overestimated.
The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve.
X-ray and extreme-ultraviolet luminosities imply accretion rates of 3 × 1015 g s−1 in quiescence, 1 × 1016 g s−1 when the boundary layer becomes optically thick, and ∼1018 g s−1 at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state. 相似文献
The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve.
X-ray and extreme-ultraviolet luminosities imply accretion rates of 3 × 10
39.
40.