全文获取类型
收费全文 | 1393篇 |
免费 | 65篇 |
国内免费 | 116篇 |
专业分类
测绘学 | 64篇 |
大气科学 | 55篇 |
地球物理 | 100篇 |
地质学 | 141篇 |
海洋学 | 147篇 |
天文学 | 959篇 |
综合类 | 45篇 |
自然地理 | 63篇 |
出版年
2024年 | 5篇 |
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 23篇 |
2019年 | 28篇 |
2018年 | 20篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 43篇 |
2014年 | 41篇 |
2013年 | 62篇 |
2012年 | 37篇 |
2011年 | 30篇 |
2010年 | 41篇 |
2009年 | 85篇 |
2008年 | 56篇 |
2007年 | 97篇 |
2006年 | 91篇 |
2005年 | 110篇 |
2004年 | 102篇 |
2003年 | 94篇 |
2002年 | 89篇 |
2001年 | 70篇 |
2000年 | 68篇 |
1999年 | 70篇 |
1998年 | 93篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1574条查询结果,搜索用时 10 毫秒
461.
462.
Linda Schmidtobreick Claus Tappert Alessandro Ederoclite Ivo Saviane Elena Mason 《Astrophysics and Space Science》2006,304(1-4):303-305
We report preliminary results of an observing run at the 1--m telescope at CTIO during which we followed RR Pic over several nights in February 2005. The resulting light curves show no sign of an eclipse. Apart from the 3.48 h period, which is usually interpreted as the orbital one, we find an additional period at P=3.78 h, which we interpret as the superhump period of the system.We furthermore present high–resolution Doppler maps in Hα, Hβ and He II, which we derived from observations at the NTT, La Silla in February 2004. They show strong variations in the emission distribution from one day to the next. While Hα and Hβ emission clearly show the accretion disc with some additional isolated sources, the He II emission is confined to an elongated region at low velocities. 相似文献
463.
Alexey?V.?BorisovEmail author Ivan?S.?Mamaev 《Celestial Mechanics and Dynamical Astronomy》2005,92(4):371-380
We consider integrable spherical analog of the Darboux potential, which appear in the problem (and its generalizations) of
the planar motion of a particle in the field of two and four fixed Newtonian centers. The obtained results can be useful when
constructing a theory of motion of satellites in the field of an oblate spheroid in constant curvature spaces. 相似文献
464.
Ying-He Zhao Zong-Yun Li Xiao-An Wu Qiu-He Peng Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2005,5(6):601-609
We report on time-resolved spectroscopic observations of the SU Ursae Majoris dwarf nova, YZ Cnc for over 11 h on two nights during its 2002 January superoutburst. The spectra on the first day only showed absorption-line profiles, while on the second day the lines showed "W" profiles with blue and red troughs. The radial velocity curve of the absorption troughs and emission peaks of Hβ has an amplitude of 49±10 km s-1 and a phase offset of -0.07±0.04, which are very similar to those measured in quiescence. However, the γ velocity deviates strongly from the systemic velocity measured in quiescence, by some ±60 km s-1. Large shifts of -70 km s-1 in the orbital-averaged velocity and -0.09 in the phase are also found in our observations. All these features can be well explained by a precessing, eccentric disk. 相似文献
465.
466.
Gavin Ramsay Mark Cropper Kinwah Wu K. O. Mason Pasi Hakala 《Monthly notices of the Royal Astronomical Society》2000,311(1):75-84
We have detected the optical counterpart of the proposed double degenerate polar RX J1914+24. The I -band light curve is modulated on the 9.5-min period seen in X-rays. There is no evidence for any other periods. No significant modulation is seen in J . The infrared colours of RX J1914+24 are not consistent with a main-sequence dwarf secondary star. Our ASCA spectrum of RX J1914+24 is typical of a heavily absorbed polar and our ASCA light curve also shows only the 9.5-min period. We find that the folded I band and X-ray light curves are out of phase. We attribute the I -band flux to the irradiated face of the donor star. The long-term X-ray light curve shows a variation in the observed flux of up to an order of magnitude. These observations strengthen the view that RX J1914+24 is indeed the first double degenerate polar to be detected. In this light, we discuss the synchronizing mechanisms in such a close binary and other system parameters. 相似文献
467.
Joaquín Bohigas Mauricio Tapia María Teresa Ruiz † Miguel Roth 《Monthly notices of the Royal Astronomical Society》2000,312(2):295-300
Continuum-subtracted dereddened images in the light of several atomic lines show the presence of an extended bipolar nebula surrounding η Carinae with size ∼100×45 arcsec2 (1.3×0.5 pc2 ). This feature is best delineated in [O iii ] 5007. The geometrical disposition and mass of the shell suggest that it was formed by mass ejections from η Carinae. The dynamic age of the nebula is ∼13 000/ V 7 yr, where V 7 is the mean expansion velocity in 100 km s−1 , and its mass is between 5 and 10 M⊙ . The nebula is photoionized and composed of unprocessed material. The major axes of the nebula and of the Homunculus are nearly perpendicular. We also report the discovery of elongated emission knots prominent in [N ii ] located 64 to 100 arcsec away from η Carinae, which implies that they were ejected either centuries ago or at a more recent date but with extremely large velocities. 相似文献
468.
J. R. Murray † B. Warner D. T. Wickramasinghe 《Monthly notices of the Royal Astronomical Society》2000,315(4):707-712
We investigate the role of the eccentric disc resonance in systems with mass ratios q ≳1/4, and demonstrate the effects that changes in the mass flux from the secondary star have upon the disc radius and structure. The addition of material with low specific angular momentum to the outer edge of a disc restricts that disc radially. Should the mass flux from the secondary be reduced, it is possible for the disc in a system with mass ratio as large as 1/3 to expand to the 3:1 eccentric inner Lindblad resonance and for superhumps to be excited. 相似文献
469.
S. B. Potter † 《Monthly notices of the Royal Astronomical Society》2000,314(4):672-680
The Stokes imaging technique of Potter, Hakala & Cropper is applied to the polarized emission from the AM Her system ST LMi. For the first time, the cyclotron emission region on the surface of the white dwarf is mapped in terms of optical depth/density in an analytical and objective manner. The region is found to consist of a less dense region leading a higher density region in orbital phase. It is demonstrated that the emission region needs to have a multi-temperature structure in order to explain the spectral slope and the general morphology of the cyclotron humps observed in the IR during the bright phase in ST LMi.
Furthermore, it is shown that a secondary emission region, fed by the same magnetic field lines that feed the main emission region, could be responsible for the positive circular polarization in the IR, the position angle variation and the excess flux during the faint phase of the white light observations which cannot be accounted for with a single emission region. 相似文献
Furthermore, it is shown that a secondary emission region, fed by the same magnetic field lines that feed the main emission region, could be responsible for the positive circular polarization in the IR, the position angle variation and the excess flux during the faint phase of the white light observations which cannot be accounted for with a single emission region. 相似文献
470.
Patricia Whitelock Michael Feast 《Monthly notices of the Royal Astronomical Society》2000,319(3):759-770
This paper concerns the calibration of the K period–luminosity relation for Mira variables using Hipparcos parallaxes. K magnitudes are available for 255 Mira-like variables which were observed by Hipparcos . Period–luminosity zero-points are evaluated for various subgroups of data. The best solution for oxygen-rich Miras, which uses 180 stars, omitting the short-period red group (which had different kinematics from the short-period blue stars) and the low-amplitude variables, provides a zero-point of which implies a distance modulus for the Large Magellanic Cloud of or perhaps slightly greater if a metallicity correction is required, in good agreement with the value derived from Cepheids. The zero-point of the period–luminosity relation for carbon stars is briefly discussed.
Linear diameters are derived for red variables with measured angular diameters and parallaxes, and are used to examine the long-standing question of the pulsation mode(s) of these stars. Evidence is presented to suggest that most of them are pulsating in the same mode and, if published model atmospheres are correct, this is probably the first overtone. Some discussion is given of sequences in the period–luminosity and period–colour diagrams and their bearing on the pulsation mode problem. 相似文献
Linear diameters are derived for red variables with measured angular diameters and parallaxes, and are used to examine the long-standing question of the pulsation mode(s) of these stars. Evidence is presented to suggest that most of them are pulsating in the same mode and, if published model atmospheres are correct, this is probably the first overtone. Some discussion is given of sequences in the period–luminosity and period–colour diagrams and their bearing on the pulsation mode problem. 相似文献