全文获取类型
收费全文 | 808篇 |
免费 | 76篇 |
国内免费 | 81篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 14篇 |
地球物理 | 63篇 |
地质学 | 210篇 |
海洋学 | 74篇 |
天文学 | 423篇 |
综合类 | 33篇 |
自然地理 | 59篇 |
出版年
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 26篇 |
2019年 | 14篇 |
2018年 | 24篇 |
2017年 | 25篇 |
2016年 | 22篇 |
2015年 | 28篇 |
2014年 | 38篇 |
2013年 | 42篇 |
2012年 | 31篇 |
2011年 | 32篇 |
2010年 | 22篇 |
2009年 | 50篇 |
2008年 | 54篇 |
2007年 | 58篇 |
2006年 | 65篇 |
2005年 | 63篇 |
2004年 | 61篇 |
2003年 | 52篇 |
2002年 | 30篇 |
2001年 | 31篇 |
2000年 | 30篇 |
1999年 | 23篇 |
1998年 | 36篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有965条查询结果,搜索用时 829 毫秒
101.
We present our numerical simulations of the dynamical evolution of the Hyades open cluster. The simulations were performed usinga modified NBODY6 algorithm that included tidal forces and a realistic orbit of the cluster in a gravitational field described by the Miyamoto-Nagai potential. Our goal was to study the nature of movingclu sters. We show that the stars that were earlier cluster members could be later identified within a sphere of 50 pc in diameter around the Sun. The number of such stars for the chosen initial mass and virial radius of the cluster does not exceed ten. The maximum space velocity of these stars relative to the core of the current cluster does not exceed 3 km s?1. Our numerical simulations confirm the assumption that some of the moving clusters near the Sun could consist of stars that have escaped from open clusters in the course of their dynamical evolution. 相似文献
102.
103.
D. Koester 《Astronomy and Astrophysics Review》2002,11(1):33-66
Summary. During the last decade white dwarfs have become important as tools in many areas beyond traditional stellar physics: from
the age determination of the stars in the solar neighborhood to the dating of open clusters and the distance determination
of globular clusters. They are primary candidates for the MACHO microlensing events, possibly for a stellar component of the
dark halo, and for the supernova Ia progenitors. The recent developments in these areas are reviewed, but some highlights
from more “mature” areas such as stellar parameters, mass distributions, magnetic, and pulsating white dwarfs are also summarized
briefly.
Received 5 October 2001 / Published online 11 January 2002 相似文献
104.
S. L. Casewell R. F. Jameson P. D. Dobbie 《Monthly notices of the Royal Astronomical Society》2006,365(2):447-453
We present the results of a survey of the Coma Berenices open star cluster (Melotte 111), undertaken using proper motions from the USNO-B1.0 (United States Naval Observatory) and photometry from the Two-Micron All-Sky Survey (2MASS) Point Source catalogues. We have identified 60 new candidate members with masses in the range 1.007 < M < 0.269 M⊙ . For each we have estimated a membership probability by extracting control clusters from the proper motion vector diagram. All 60 are found to have greater than 60 per cent probability of being members, more than doubling the number of known cluster members. The new luminosity function for the cluster peaks at bright magnitudes, but is rising at K ≈ 12 , indicating that it is likely that lower mass members may exist. The mass function also supports this hypothesis. 相似文献
105.
Hongqi Zhang 《Monthly notices of the Royal Astronomical Society》2001,326(1):57-66
We present the results of a photometric study of X-ray-active weak-lined T Tauri (WTT) stars in the η Chamaeleontis star cluster. Multi-epoch V -band photometric monitoring during 1999 and 2000 of the 10 X-ray-active WTT stars found that all were variable in one or both years, with periods ascribed to rotational modulation of starspots. Comparison between the rotational and X-ray properties of these objects indicates the saturation level, observed in other studies of X-ray-active pre-main-sequence stars, persists in the η Cha stars from the slow- to the fast-rotator regimes. Cousins VRI photometry of the WTT stars has enabled us to investigate further the photometric properties of these stars. The stars appear sufficiently coeval to distinguish near-equal-mass binaries within the sample. A new Hertzsprung–Russell diagram for these objects suggests ages of 4–9 Myr for M-type RECX primaries using the tracks of D'Antona & Mazzitelli. 相似文献
106.
Yu Xin Xiao-Bin Zhang Li-Cai DengNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,2(6)
We present a snapshot of our recent results of a variable star survey in 1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A total number of 39 variable stars are newly discovered, including 22 W UMa stars, 10 EA (Algol) type binaries, one RR-lyr and one RRd pulsator, and five unclassified variables. 相似文献
107.
108.
109.
110.