全文获取类型
收费全文 | 5783篇 |
免费 | 960篇 |
国内免费 | 1062篇 |
专业分类
测绘学 | 45篇 |
大气科学 | 217篇 |
地球物理 | 632篇 |
地质学 | 3706篇 |
海洋学 | 281篇 |
天文学 | 2298篇 |
综合类 | 241篇 |
自然地理 | 385篇 |
出版年
2024年 | 16篇 |
2023年 | 47篇 |
2022年 | 120篇 |
2021年 | 132篇 |
2020年 | 142篇 |
2019年 | 165篇 |
2018年 | 150篇 |
2017年 | 154篇 |
2016年 | 177篇 |
2015年 | 192篇 |
2014年 | 257篇 |
2013年 | 261篇 |
2012年 | 281篇 |
2011年 | 304篇 |
2010年 | 261篇 |
2009年 | 479篇 |
2008年 | 389篇 |
2007年 | 505篇 |
2006年 | 471篇 |
2005年 | 453篇 |
2004年 | 411篇 |
2003年 | 388篇 |
2002年 | 344篇 |
2001年 | 269篇 |
2000年 | 261篇 |
1999年 | 219篇 |
1998年 | 230篇 |
1997年 | 123篇 |
1996年 | 80篇 |
1995年 | 96篇 |
1994年 | 95篇 |
1993年 | 66篇 |
1992年 | 71篇 |
1991年 | 43篇 |
1990年 | 38篇 |
1989年 | 44篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有7805条查询结果,搜索用时 15 毫秒
51.
陈刘组为新建立的岩石地层单位,代表广西早三叠世盆地滨岸相带沉积类型。层型剖面位于贵港市陈刘村附近。层型定义指位于龙潭组与板纳组之间的沉积序列,岩性为灰绿、紫红色泥岩、粉砂细砂岩夹少量火山岩及碳酸盐岩,含菊石、双壳类、牙形石等化石,厚359m。 相似文献
52.
熊耳群为玄武粗安岩-英安流纹岩组合,大红口组为粗面岩组合,属B类的过渡型拉斑玄武岩浆系列,具以太华群为岩浆房的壳幔混染型成因;秦岭群和宽坪群为变拉斑玄武岩建造,属A类拉斑玄武岩浆系列,具幔源型成因;二郎坪群和丹凤群属细碧岩-石英角斑岩建造,C类石英角斑岩浆系列与A类拉斑玄武岩浆系列共存,具壳幔双层混合型成因。 相似文献
53.
54.
M. A. Smith 《第四纪科学杂志》2009,24(7):747-760
Puritjarra rock shelter provides a long record of late Quaternary vegetation in the Australian arid zone. Analysis of the sedimentary history of this rock shelter is combined with reanalysis of charcoal and phytolith records to provide a first‐order picture of changing landscapes in western Central Australia. These show a landscape responding to increasing aridity from 45 ka with deflation of clay‐rich red palaeosols (<45 ka) and sharp declines in grassland and other vegetation at 40–36 ka, and at the beginning of the Last Glacial Maximum (LGM) (24 ka). Vegetation in the catchment of the rock shelter recovered after 15 ka with expansion of both acacia woodland and spinifex grasslands, registering stronger summer rainfall in the interior of the continent. By 8.3 ka re‐vegetation of local palaeosols and dunes had choked off sediment supply to the rock shelter and the character of the sediments changed abruptly. Poaceae values peaked at 5.8 ka, suggesting the early–mid Holocene climatic optimum in Central Australia is bracketed between 8.3 and 5.8 ka. Local vegetation was disrupted in the late Holocene with a sharp decline in Poaceae at 3.8 ka, coinciding with an abrupt intensification of ENSO. Local grasslands recovered over the next two millennia and by 1.5 ka the modern vegetation appears to have become established. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
55.
56.
57.
58.
M. R. Bate S. H. Lubow G. I. Ogilvie K. A. Miller 《Monthly notices of the Royal Astronomical Society》2003,341(1):213-229
We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M⊕ ) to 1 Jupiter mass (1 MJ ) by using the zeus hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses M p ≳ 0.1 MJ produce significant perturbations in the surface density of the disc. The flow within the Roche lobe of the planet is fully three-dimensional. Gas streams generally enter the Roche lobe close to the disc mid-plane, but produce much weaker shocks than the streams in two-dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the orbit of the planet. Much of the mass supply to the circumplanetary disc comes from non-coplanar flow. The accretion rate peaks with a planet mass of approximately 0.1 MJ and is highly efficient, occurring at the local viscous rate. The migration time-scales for planets of mass less than 0.1 MJ , based on torques from disc material outside the Roche lobes of the planets, are in excellent agreement with the linear theory of type I (non-gap) migration for three-dimensional discs. The transition from type I to type II (gap) migration is smooth, with changes in migration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few MJ with little migration. Planets with final masses of the order of 10 MJ would undergo large migration, which makes formation and survival difficult. 相似文献
59.
60.
S. Viti 《Astrophysics and Space Science》2003,285(3-4):791-800
In this article, some aspects of the clumpy nature of molecular clouds are reviewed. In particular the observational evidence
for small-scale structures both in low and high mass star forming regions will be discussed. I will review some examples of
`clumpiness' such as: i) the molecular clumps ahead of HH objects and how the study of the physical and chemical nature of
these clumps is important for the understanding of the clumpiness of the Interstellar Medium; and ii)hot cores and their use
as a tool to study the early phases of massive star formation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献