全文获取类型
收费全文 | 1425篇 |
免费 | 286篇 |
国内免费 | 705篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 11篇 |
地球物理 | 150篇 |
地质学 | 2009篇 |
海洋学 | 23篇 |
天文学 | 96篇 |
综合类 | 94篇 |
自然地理 | 27篇 |
出版年
2024年 | 5篇 |
2023年 | 34篇 |
2022年 | 43篇 |
2021年 | 54篇 |
2020年 | 51篇 |
2019年 | 69篇 |
2018年 | 67篇 |
2017年 | 81篇 |
2016年 | 84篇 |
2015年 | 72篇 |
2014年 | 99篇 |
2013年 | 150篇 |
2012年 | 120篇 |
2011年 | 97篇 |
2010年 | 66篇 |
2009年 | 116篇 |
2008年 | 93篇 |
2007年 | 102篇 |
2006年 | 107篇 |
2005年 | 87篇 |
2004年 | 82篇 |
2003年 | 87篇 |
2002年 | 74篇 |
2001年 | 68篇 |
2000年 | 58篇 |
1999年 | 58篇 |
1998年 | 45篇 |
1997年 | 59篇 |
1996年 | 51篇 |
1995年 | 47篇 |
1994年 | 35篇 |
1993年 | 39篇 |
1992年 | 30篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有2416条查询结果,搜索用时 15 毫秒
991.
992.
993.
东昆仑西段托库孜达坂群中组火山岩岩石地球化学特征及构造环境分析 总被引:1,自引:0,他引:1
托库孜达坂群中组火山岩厚度大、分布广,由下而上包括3个火山活动旋回,下部为溢流相-次火山岩相-沉积相;中部为爆发相-溢流相-次火山岩相-沉积相;上部为溢流相-沉积相。中、上部旋回火山作用最强,形成时代为早石炭世早期。通过岩石学、岩石地球化学等综合研究,其岩石主要为英安质火山角砾岩、火山角砾凝灰岩、安山玢岩、安山岩、流纹英安质凝灰熔岩等;SiO2一般大于70%,Na2O-2相似文献
994.
995.
Yuejun CHEN Chunlin SUN Yuewu SUN Research Center of Palaeontology & Stratigraphy Jilin University Changchun China 《东北亚地学研究》2008,11(3):145-149
Jianshanzi volcanic rocks at Qinghe valley in the northern Liaoning were considered belonging to Early Proterozoie Gaojiayu Formation of Liaohe Group, or to Early Cambrian Beidagou Formation of Qinghezhen Group, or Middle-Late Proterozoic Shenjiapu Formation-Complex of Kaiyuan Group-complex. Dating the zircons from the dacite with schistosity is 2 506 Ma in method of U-Pb (SHRIMP). This evidence indicates the rocks may be referred to Late Permian in age. Discovery of the rocks is significant to re-recognize stratigraphic property of "Liaohe Group", regional geoteetonie location and revolution of orogenic zone in Qinghe valley of the northern Liaoning. 相似文献
996.
997.
998.
熊耳群火山岩中产出各种类型的金矿床,碲化物型(构造蚀变岩型)是金矿主要类型,该类型余矿以出现大量碲化物或富碲、硒为特征.硫化物δ ̄(34)S以较大的负值为特征,本文通过综合研究及与国内外行关矿床对比,认为该碲化物型金矿δ ̄(34)S负值的主要原因是地表水的渗透参与导致成矿热液物理化学条件改变,fo_2升高、pH值降低,从而引起硫同位素强烈分馏形成的。有关铅同位素组成具深源壳幔混合(染)特征,显示成矿物质来源于熊耳群富钾火山岩系。该类型金矿床成矿作用为上升岩浆与下渗地表水共同作用形成浅成热液系统,在剪切带内氧化环境下液体的稀释和冷却是金沉淀的主要原因。其成因类型应属浅成低温热液富碲化物型金矿。 相似文献
999.
Daniel J. Rolfe Carole A. Haswell Joseph Patterson 《Monthly notices of the Royal Astronomical Society》2001,324(3):529-536
We present two simple dynamical models for Sagittarius based on N -body simulations of the progressive disruption of a satellite galaxy orbiting for 12.5 Gyr within a realistic Galactic potential. In both models the satellite initially has observable properties similar to those of current outlying dwarfs; in one case it is purely stellar while in the other it is embedded in an extended massive halo. The purely stellar progenitor is a King model with a total velocity dispersion of 18.9 km s−1 , a core radius of 0.44 kpc and a tidal radius of 3 kpc. The initial stellar distribution in the other case follows a King profile with the same core radius, a slightly larger total velocity dispersion and similar extent. Both these models are consistent with all published data on the current Sagittarius system, they match not only the observed properties of the main body of Sagittarius, but also those reported for unbound debris at larger distances. 相似文献
1000.
Halton Arp 《Journal of Astrophysics and Astronomy》1987,8(3):241-255
Galaxies of redshiftz ≲ 1000 km s−1 are investigated. In the South Galactic Hemisphere there are two large concentrations of these galaxies. One is in the direction
of the centre of the Local Group, roughly aligned with M 31 and M 33. The other concentration is centred almost 80 degrees
away on the sky and involves the next nearest galaxies to the Local Group, NGC 55, NGC 300 and NGC 253.
The large scale and isolation of these concentrations, and the continuity of their redshifts require that they are all galaxies
at the same, relatively close distance of the brightest group members. The fainter members of the group have higher redshifts,
mimicking to some extent a Hubble relation. But if they are all at the same average distance the higher redshifts must be
due to a cause other than velocity.
The redshifts of the galaxies in the central areas of these groups all obey a quantization interval of δcz0 = 72.4 kms−1. This is the same quantization found by William Tifft, and later by others, in all physical groups and pairs which have been
tested. The quantization discovered here, however, extends over a larger interval in redshift than heretofore encountered.
The majority of redshifts used in the present analysis are accurate to ± 8 km s−1. The deviation of those redshifts from multiples of 72.4 km s-1 averages ±8.2 km s−1. The astonishing result, however, is that for those redshifts which are known more accurately, the deviation from modulo
72.4 drops to a value between 3 and 4 km s−1! The amount of relative velocity allowed these galaxies is therefore implied to be less than this extremely small value. 相似文献