全文获取类型
收费全文 | 8447篇 |
免费 | 681篇 |
国内免费 | 510篇 |
专业分类
测绘学 | 87篇 |
大气科学 | 24篇 |
地球物理 | 737篇 |
地质学 | 2617篇 |
海洋学 | 242篇 |
天文学 | 5670篇 |
综合类 | 199篇 |
自然地理 | 62篇 |
出版年
2024年 | 11篇 |
2023年 | 26篇 |
2022年 | 58篇 |
2021年 | 89篇 |
2020年 | 97篇 |
2019年 | 115篇 |
2018年 | 78篇 |
2017年 | 84篇 |
2016年 | 104篇 |
2015年 | 148篇 |
2014年 | 165篇 |
2013年 | 178篇 |
2012年 | 212篇 |
2011年 | 248篇 |
2010年 | 267篇 |
2009年 | 600篇 |
2008年 | 529篇 |
2007年 | 701篇 |
2006年 | 673篇 |
2005年 | 757篇 |
2004年 | 623篇 |
2003年 | 614篇 |
2002年 | 580篇 |
2001年 | 485篇 |
2000年 | 453篇 |
1999年 | 415篇 |
1998年 | 470篇 |
1997年 | 157篇 |
1996年 | 159篇 |
1995年 | 164篇 |
1994年 | 117篇 |
1993年 | 54篇 |
1992年 | 37篇 |
1991年 | 31篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 24篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 1篇 |
排序方式: 共有9638条查询结果,搜索用时 0 毫秒
101.
102.
103.
Sunetra Giridhar N. Kameswara Rao David L. Lambert 《Journal of Astrophysics and Astronomy》1996,17(1-2):23-40
Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines
show a radial velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission components to some CII lines present
in 1989 are almost entirely absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII] appear unchanged from 1989 to
1992 相似文献
104.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献
105.
Da-Ming Chen 《中国天文和天体物理学报》2001,1(4):287-290
1 INTRODUCTIONObservations of the most famous starburst galaxy M82 with the High-Resolution Cameraon board the Chandra X-Ray Observatory, showed that there are nine sources in the celltral11 x 11 region, but no son-roe was detected at the galactic center (Matsumoto et al. 2001).Comparing the observations on 1999 October 28 and those on 2000 January 20, the authorsfound an extremely large time variability of the source CXO M82 J095550.2 694047, which islocated gll away from the galact… 相似文献
106.
The proper motions of stars in the main sequence and of luminosity class III giants are analyzed kinematically. A new method has been used for reliably separating all the parameters of the Ogorodnikov-Milne model based on representing the proper motions of the stars in coordinate systems whose poles lie on each of the three principal axes of the galactic trihedron. Solutions for stars in different spectral classes are obtained. The main sequence is found to subdivide into two zones (near and far stars) with a fairly sharp boundary at B-V=0.5. It is shown that the Parenago effect may be related to the different distances from the sun of the main sequence stars. 相似文献
107.
108.
109.
110.
K. S. Stankevich A. M. Aslanyan V. P. Ivanov R. M. Martirosyan Ye. Terzian 《Astrophysics》2003,46(4):429-433
Radio emission of the historical supernovae remnants Tycho (SNR1572) and Kepler (SNR1604) and evolution of their luminosity are considered. Measurement data of secular luminosity decrease rate, obtained earlier by the authors, were corrected with account of variation in time of the flux density of the reference sources. As a result, it is found that the SNR1604 luminosity at 1667 MHz is weakening with an annual mean rate equal to (0.2 ± 0.07)%. The corresponding rate for SNR1572 is (0.47 ± 0.05)%. Since the radio luminosity evolution, as well as energy densities of magnetic field and relativistic electrons inside SNR1604 and SNR1572 are essentially different, these remnants should be considered as different types of supernovae. Bandiera classified SN1604 as type SNIb or SNII. 相似文献