全文获取类型
收费全文 | 55188篇 |
免费 | 5285篇 |
国内免费 | 6566篇 |
专业分类
测绘学 | 1756篇 |
大气科学 | 7606篇 |
地球物理 | 12272篇 |
地质学 | 24080篇 |
海洋学 | 5758篇 |
天文学 | 8168篇 |
综合类 | 3105篇 |
自然地理 | 4294篇 |
出版年
2023年 | 437篇 |
2022年 | 1384篇 |
2021年 | 1683篇 |
2020年 | 1524篇 |
2019年 | 1701篇 |
2018年 | 2540篇 |
2017年 | 2342篇 |
2016年 | 2688篇 |
2015年 | 1777篇 |
2014年 | 2588篇 |
2013年 | 3146篇 |
2012年 | 2496篇 |
2011年 | 2810篇 |
2010年 | 2759篇 |
2009年 | 2999篇 |
2008年 | 2639篇 |
2007年 | 2655篇 |
2006年 | 2311篇 |
2005年 | 1630篇 |
2004年 | 1464篇 |
2003年 | 1444篇 |
2002年 | 1403篇 |
2001年 | 1306篇 |
2000年 | 1482篇 |
1999年 | 1845篇 |
1998年 | 1591篇 |
1997年 | 1561篇 |
1996年 | 1389篇 |
1995年 | 1219篇 |
1994年 | 1194篇 |
1993年 | 986篇 |
1992年 | 836篇 |
1991年 | 716篇 |
1990年 | 641篇 |
1989年 | 514篇 |
1988年 | 492篇 |
1987年 | 439篇 |
1986年 | 352篇 |
1985年 | 420篇 |
1984年 | 342篇 |
1983年 | 313篇 |
1982年 | 343篇 |
1981年 | 257篇 |
1980年 | 270篇 |
1979年 | 222篇 |
1978年 | 221篇 |
1977年 | 169篇 |
1976年 | 170篇 |
1975年 | 174篇 |
1974年 | 168篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
151.
152.
Type II radio bursts are produced by material moving outwards in the solar atmosphere. Their drift in frequency allows the calculation of the radial speed with which the shock is moving- very basic information in assessing the likelihood that the shock will reach the Earth and its time of arrival. This paper compares the shock speeds derived from radio bursts observed by the Swept Frequency Interferometric Radiometer (SFIR) equipment at the US Air Force Radio Solar Telescope Network (RSTN) of observatories with those measured with the Culgoora radiospectrograph operated by IPS Radio and Space Services. The SFIR shock speeds are found to be 1.5–3.0 times larger than the Culgoora values which are consistent with earlier results. This difference appears to originate from the incorrect interpretation of events as a result of the smaller frequency range of the SFIR equipment. 相似文献
153.
本文对第22太阳周(1987年1月至1992年12月)中发生过M级以上的X射线耀斑(Hα耀斑级别≥M级,并伴有X射线的耀斑)对应的395个活动区资料进行了耀斑指数的统计,得到的结果:1.22太阳周M级以上X射线耀斑级别综合指数表,2.22太阳周M级以上X射线耀斑总指数表,3.第22太阳周M级以上X射线耀斑总指数随时间的变化曲线,4.第22太阳周M级以上X射线濯斑总指数直方图,该图表明第22太阳周活动的极大年分别是1989和1991年,为第23周太阳活动预报提供了可用参数。 相似文献
154.
155.
156.
N. Yoshida J. Colberg S.D.M. White A.E. Evrard T.J. MacFarland † H.M.P. Couchman A. Jenkins C.S. Frenk F.R. Pearce G. Efstathiou J.A. Peacock P.A. Thomas 《Monthly notices of the Royal Astronomical Society》2001,325(2):803-816
We create mock pencil-beam redshift surveys from very large cosmological N -body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model ( τ CDM) and a flat model with Ω0 =0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation particles are tagged as 'galaxies' so as to reproduce observed present-day correlations. They are then identified along the past light-cones of hypothetical observers to create mock catalogues with the geometry and the distance distribution of the Broadhurst et al. data. We produce 1936 (2625) quasi-independent catalogues from our τ CDM (ΛCDM) simulation. A couple of large clumps in a catalogue can produce a high peak at low wavenumbers in the corresponding one-dimensional power spectrum, without any apparent large-scale periodicity in the original redshift histogram. Although the simulated redshift histograms frequently display regularly spaced clumps, the spacing of these clumps varies between catalogues and there is no 'preferred' period over our many realizations. We find only a 0.72 (0.49) per cent chance that the highest peak in the power spectrum of a τ CDM (ΛCDM) catalogue has a peak-to-noise ratio higher than that in the Broadhurst et al. data. None of the simulated catalogues with such high peaks shows coherently spaced clumps with a significance as high as that of the real data. We conclude that in CDM universes, the regularity on a scale of ∼130 h −1 Mpc observed by Broadhurst et al. has a priori probability well below 10−3 . 相似文献
157.
1 INTRODUCTIONCompact Symmetric Objects (CSOs) are powerful and compact sources (overall size <1 bpc) with lobe emission on both sides of the central engine. The small size of these sourcesis almost certainly to be attributed to the youth of the sources themselves (ages < 104 yr) andnot due to a dense coallning medium (Readhead 1996). The unification scenario assumes thatCSOs evolve into compact steep spectrum (CSS) sotirces and then into Fanaroff-Riley type 11objects (Fanti 1995). … 相似文献
158.
159.
N. S. Chauhan 《Astrophysics and Space Science》1985,112(1):185-192
The treatment followed by Coxet al. (1973) for the estimation of the effects of thermal imbalance on the pulsational stability of stars is applied to Roche and point source (Chandrika Prashad) model. The calculations suggest that the eigenvalues obtained for the above model are correct to 0(t
ff/ts). The expressions for stability coefficients and corresponding eigenfunctions for the stars in thermal imbalance for the above models have also been derived. 相似文献
160.
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