首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   17997篇
  免费   2732篇
  国内免费   4408篇
测绘学   362篇
大气科学   738篇
地球物理   2123篇
地质学   12983篇
海洋学   1603篇
天文学   5099篇
综合类   719篇
自然地理   1510篇
  2024年   76篇
  2023年   192篇
  2022年   468篇
  2021年   554篇
  2020年   576篇
  2019年   669篇
  2018年   569篇
  2017年   574篇
  2016年   631篇
  2015年   662篇
  2014年   996篇
  2013年   1138篇
  2012年   1122篇
  2011年   1311篇
  2010年   1225篇
  2009年   1609篇
  2008年   1508篇
  2007年   1456篇
  2006年   1429篇
  2005年   1215篇
  2004年   1080篇
  2003年   938篇
  2002年   813篇
  2001年   739篇
  2000年   704篇
  1999年   599篇
  1998年   447篇
  1997年   343篇
  1996年   291篇
  1995年   260篇
  1994年   198篇
  1993年   184篇
  1992年   102篇
  1991年   85篇
  1990年   72篇
  1989年   54篇
  1988年   51篇
  1987年   31篇
  1986年   32篇
  1985年   27篇
  1984年   20篇
  1983年   17篇
  1982年   16篇
  1981年   7篇
  1980年   12篇
  1979年   4篇
  1978年   8篇
  1977年   16篇
  1877年   1篇
  1875年   1篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
101.
In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
102.
103.
104.
105.
106.
107.
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   
108.
109.
110.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号