全文获取类型
收费全文 | 1341篇 |
免费 | 103篇 |
国内免费 | 129篇 |
专业分类
测绘学 | 177篇 |
大气科学 | 141篇 |
地球物理 | 239篇 |
地质学 | 399篇 |
海洋学 | 105篇 |
天文学 | 304篇 |
综合类 | 56篇 |
自然地理 | 152篇 |
出版年
2023年 | 14篇 |
2022年 | 17篇 |
2021年 | 21篇 |
2020年 | 26篇 |
2019年 | 48篇 |
2018年 | 36篇 |
2017年 | 39篇 |
2016年 | 41篇 |
2015年 | 41篇 |
2014年 | 64篇 |
2013年 | 72篇 |
2012年 | 49篇 |
2011年 | 56篇 |
2010年 | 35篇 |
2009年 | 77篇 |
2008年 | 68篇 |
2007年 | 92篇 |
2006年 | 80篇 |
2005年 | 77篇 |
2004年 | 75篇 |
2003年 | 68篇 |
2002年 | 50篇 |
2001年 | 52篇 |
2000年 | 55篇 |
1999年 | 38篇 |
1998年 | 42篇 |
1997年 | 28篇 |
1996年 | 26篇 |
1995年 | 19篇 |
1994年 | 11篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1973年 | 4篇 |
1972年 | 10篇 |
1971年 | 7篇 |
排序方式: 共有1573条查询结果,搜索用时 15 毫秒
991.
992.
We report on the statistical analysis of a sample of AGNs (Seyferts and LINERs) selected from an RBSC-NVSS sample of the brightest X-ray sources. The sample is large enough and unbiased for a detailed study of multi-frequency (radio to X-ray) properties of AGN. There are no significant differences in X-ray, optical, far-infrared, and radio powers, core dominance, radio loudness, radio spectral index, and two-point radio-to-optical and optical-to-X-ray spectral indices of Seyfert types 1 and 2. These findings strongly support the unification model, and the observed differences between Sy1 and Sy2 are due to both the variable obscuration and different geometric orientation effects. The correlation between the X-ray and radio emission over many decades is primary and indicates the intrinsically similar origin of both radiations in Seyfert galaxies, powered mainly by AGN, rather than compact starbursts. For Seyfert galaxies we found that the slopes of the relations L
X - L
R and L
X - L
B are flat, which indicate the existence of components unrelated with X-ray. Perhaps only for LINERs is the observed L
X - L
R relation completely due to AGNs. The Sy1, Sy2, and LINER galaxies show different slopes in the relation L
X - L
1.4, and the relative contribution of extended radio components may be the cause of these differences. The possible effects of unresolved extended radio and X-ray components are quantitatively discussed. 相似文献
993.
The probabilistic nature of the IMF in stellar systems implies that clusters of the same mass and age do not present the same
unique values of their observed parameters. Instead they follow a distribution. We address the study of such distributions
in terms of their confidence limits that can be obtained by evolutionary synthesis models. These confidence limits can be
understood as the inherent uncertainties of synthesis models. We will compare such confidence limits arising from the discreteness
of the number of stars obtained with Monte Carlo simulations with the dispersion resulting from an analytical formalism. We
give some examples of the effects on the kinetic energy, V–K, EW(Hβ) and multiwavelength continuum.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
994.
995.
Darren J. Croton Glennys R. Farrar Peder Norberg Matthew Colless John A. Peacock I. K. Baldry C. M. Baugh J. Bland-Hawthorn T. Bridges R. Cannon S. Cole C. Collins W. Couch G. Dalton R. De Propris S. P. Driver G. Efstathiou R. S. Ellis C. S. Frenk K. Glazebrook C. Jackson O. Lahav I. Lewis S. Lumsden S. Maddox D. Madgwick B. A. Peterson W. Sutherland K. Taylor 《Monthly notices of the Royal Astronomical Society》2005,356(3):1155-1167
We use the 2dF Galaxy Redshift Survey to measure the dependence of the b J -band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8 h −1 Mpc , and on spectral type, determined from principal component analysis. We find that the galaxy populations at both extremes of density differ significantly from that at the mean density. The population in voids is dominated by late types and shows, relative to the mean, a deficit of galaxies that becomes increasingly pronounced at magnitudes brighter than M b J −5log10 h ≲−18.5 . In contrast, cluster regions have a relative excess of very bright early-type galaxies with M b J −5log10 h ≲−21 . Differences in the mid- to faint-end population between environments are significant: at M b J −5log10 h =−18 early- and late-type cluster galaxies show comparable abundances, whereas in voids the late types dominate by almost an order of magnitude. We find that the luminosity functions measured in all density environments, from voids to clusters, can be approximated by Schechter functions with parameters that vary smoothly with local density, but in a fashion that differs strikingly for early- and late-type galaxies. These observed variations, combined with our finding that the faint-end slope of the overall luminosity function depends at most weakly on density environment, may prove to be a significant challenge for models of galaxy formation. 相似文献
996.
Biswajit Pandey Somnath Bharadwaj 《Monthly notices of the Royal Astronomical Society》2005,357(3):1068-1076
We have used the largest cluster statistics and the average filamentarity to quantify respectively the connectivity and the shapes of the patterns seen in the galaxy distribution in two volume-limited subsamples extracted from the equatorial strips of the Sloan Digital Sky Survey (SDSS) Data Release One (DR1). The data was projected on to the equatorial plane and analysed in two dimensions (2D). Comparing the results with Poisson point distributions at various levels of smoothing we find evidence for a network-like topology with filaments being the dominant patterns in the galaxy distribution. With increasing smoothing, a transition from many individual filamentary structures to an interconnected network is found to occur at a filling factor of 0.5–0.6. We have tested the possibility that the connectivity and the morphology of the patterns in the galaxy distribution may be luminosity dependent and find significant evidence for a luminosity–morphology relation, the brighter galaxies exhibiting lower levels of connectivity and filamentarity compared to the fainter ones. Using a statistical technique, Shuffle, we show that the filamentarity in both the SDSS strips is statistically significant up to 80 h −1 Mpc but not beyond. Larger filaments, though identified, are not statistically significant. Our findings reaffirm earlier work establishing the filaments to be the largest known statistically significant coherent structures in the Universe. 相似文献
997.
姜佩芳 《中国科学院上海天文台年刊》2002,(1)
对我台天体物理研究室 1992 - 2 0 0 1年期间科学论文产出情况进行了定量统计和分析 ,对已发表的论文总数、国内外SCI论文数、学报及台刊 (包括会议集等 )文章、青年作者论文数及论文引用情况的变化 ,分类归纳并进行讨论。结果表明该研究室科学论文产出的数量和质量逐年提高 ,并已形成了一支以青年天文工作者为主的天体物理基础研究队伍 相似文献
998.
利用重庆 1951-1996 年间 46 年地面气温年极小值的记录,采用韦伯分布和耿贝尔分布分别进行拟合试验.通过统计推断和对比,找出重庆地面最低气温年极值遵循的最佳渐近分布--韦伯分布. 相似文献
999.
The 2dF Galaxy Redshift Survey: correlation functions, peculiar velocities and the matter density of the Universe 总被引:1,自引:0,他引:1
Ed Hawkins Steve Maddox Shaun Cole Ofer Lahav Darren S. Madgwick Peder Norberg John A. Peacock Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Bryn Jones Ian Lewis Stuart Lumsden Will Percival Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2003,346(1):78-96
1000.
整理汇集了迄今最完整的同时具备绝对自行与视向速度数据的 14 4个疏散星团样本 ,计算得出这些星团的 3维空间速度。对银河系疏散星团的空间分布 (采用了更多样本 )和运动学性质进行了若干统计分析 相似文献