全文获取类型
收费全文 | 928篇 |
免费 | 61篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 55篇 |
大气科学 | 66篇 |
地球物理 | 233篇 |
地质学 | 304篇 |
海洋学 | 88篇 |
天文学 | 155篇 |
综合类 | 6篇 |
自然地理 | 92篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 28篇 |
2020年 | 12篇 |
2019年 | 19篇 |
2018年 | 35篇 |
2017年 | 38篇 |
2016年 | 49篇 |
2015年 | 34篇 |
2014年 | 30篇 |
2013年 | 60篇 |
2012年 | 43篇 |
2011年 | 46篇 |
2010年 | 43篇 |
2009年 | 61篇 |
2008年 | 46篇 |
2007年 | 50篇 |
2006年 | 41篇 |
2005年 | 25篇 |
2004年 | 46篇 |
2003年 | 31篇 |
2002年 | 24篇 |
2001年 | 19篇 |
2000年 | 30篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1984年 | 8篇 |
1983年 | 15篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 2篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有999条查询结果,搜索用时 265 毫秒
901.
902.
Rates of accumulation of Fe and Mn, as well as Cu, Ni, Co, Pb, Zn, Hg, U and Th have been determined for five ferromanganese deposits from four localities in the South Pacific Ocean.Manganese is accumulating in nodules and crusts at a rate roughly equivalent to that found to be accumulating in sediments in the same area. Iron shows a deficiency in accumulation in nodules and crusts with respect to sediments, especially near the continents, but also in the central and south-central Pacific. Copper is accumulating in nodules and crusts at a rate one order of magnitude less than the surrounding sediments.This is interpreted as meaning that most of the Mn is supplied as an authigenic phase to both sediments and nodules while Fe is supplied mostly by ferromanganese micro-nodules and by detrital and adsorbed components of sediments; and Cu is enriched in sediments relative to nodules and crusts most probably through biological activity. 相似文献
903.
Tom Beer 《Planetary and Space Science》1978,26(2):185-188
The dominant response of the terminator is found to be due to the change in thermospheric absorption of solar radiation, and leads to two types of atmospheric waves: (i) a ducted acoustic wave at altitudes below 100 km and (ii) a boundary wave concentrated along the mesopause. 相似文献
904.
Abstract: The task of designing appropriate institutional arrangements for metropolitan government and planning has recently proved highly contestable politically. We interrogate how the role of the Auckland Regional Council (ARC) was zealously contested and hollowed-out during the 1990s. More recently, the impacts of the neo-liberal reforms in Auckland have been mediated by a further round of local government reforms inspired by a Third Way ideology and by the imperative to respond to the planning crisis resulting from infrastructure underinvestment. New regionally based governance arrangements and planning processes have been created. We argue that this new commitment to regionalism can realistically expect to be tested by deep-seated political cleavages within Auckland and by Auckland's relationship with central government. 相似文献
905.
906.
907.
Philippe Paillou Ake Rosenqvist Jean-Marie Malezieux Bruno Reynard Tom Farr Essam Heggy 《Comptes Rendus Geoscience》2003,335(15):1059-1069
Using orbital imaging radar, we detected a double circular structure, located in the southeastern part of the Libyan Desert, which is partially hidden under sandy sediments. Fieldwork confirmed it to be an unknown double impact crater, each crater having a diameter of about 10 km, younger than 140 Ma. Sampling on the site enabled the observation of quantities of shatter cone structures and impact breccias containing planar fractures. To cite this article: P. Paillou et al., C. R. Geoscience 335 (2003). 相似文献
908.
909.
Nahum Arav Tom A. Barlow Ari Laor Wallace L. W. Sargent & Roger D. Blandford 《Monthly notices of the Royal Astronomical Society》1998,297(4):990-998
We search for a direct signature of discrete 'clouds' in the broad-line region (BLR) of the Seyfert galaxy NGC 4151. For this purpose we apply cross-correlation (CC) analysis to a high-resolution Keck spectrum of the galaxy. No such signature is found in the data. In order for cloud models to be compatible with this result, there must be at least ∼3×107 emitting clouds in the BLR, where the limit is based on simulation of a homogeneous cloud population. More realistic distributions increase the lower limit to above 108 . These numbers are an order-of-magnitude improvement on our previous limit from Mrk 335, where the improvement comes from higher signal-to-noise ratio (S/N), broader lines and refined simulations. Combined with the predicted upper limit for the number of emitting clouds in NGC 4151 (106 –107 ), the derived lower limit puts a strong constraint on the cloud scenario in the BLR of this object. Similar constraints can be placed on models where the emission originates in streams and sheets. Thus, this investigation suggests that the broad emission lines (BELs) in NGC 4151, and by extension in all AGNs, are not made of an ensemble of discrete independent emitters. 相似文献
910.
Measurements of 10Be concentration in the Dye 3 ice core show that magnetic cycles persisted throughout the Maunder Minimum, although the Sun's overall activity was drastically reduced and sunspots virtually disappeared. Thus the dates of maxima and minima can now be reliably estimated. Similar behaviour is shown by a nonlinear dynamo model, which predicts that, after a grand minimum, the Sun's toroidal field may switch from being antisymmetric to being symmetric about the equator. The presence of cyclic activity during the Maunder Minimum limits estimates of the solar contribution to climatic change. 相似文献