全文获取类型
收费全文 | 6123篇 |
免费 | 150篇 |
国内免费 | 62篇 |
专业分类
测绘学 | 129篇 |
大气科学 | 506篇 |
地球物理 | 1406篇 |
地质学 | 2025篇 |
海洋学 | 610篇 |
天文学 | 989篇 |
综合类 | 14篇 |
自然地理 | 656篇 |
出版年
2021年 | 47篇 |
2020年 | 65篇 |
2019年 | 74篇 |
2018年 | 112篇 |
2017年 | 117篇 |
2016年 | 135篇 |
2015年 | 105篇 |
2014年 | 129篇 |
2013年 | 323篇 |
2012年 | 180篇 |
2011年 | 265篇 |
2010年 | 246篇 |
2009年 | 238篇 |
2008年 | 251篇 |
2007年 | 214篇 |
2006年 | 236篇 |
2005年 | 189篇 |
2004年 | 188篇 |
2003年 | 178篇 |
2002年 | 165篇 |
2001年 | 124篇 |
2000年 | 110篇 |
1999年 | 103篇 |
1998年 | 96篇 |
1997年 | 86篇 |
1996年 | 88篇 |
1995年 | 94篇 |
1994年 | 90篇 |
1993年 | 80篇 |
1992年 | 87篇 |
1991年 | 72篇 |
1990年 | 99篇 |
1989年 | 88篇 |
1988年 | 77篇 |
1987年 | 102篇 |
1986年 | 76篇 |
1985年 | 98篇 |
1984年 | 133篇 |
1983年 | 111篇 |
1982年 | 101篇 |
1981年 | 105篇 |
1980年 | 90篇 |
1979年 | 103篇 |
1978年 | 72篇 |
1977年 | 88篇 |
1976年 | 73篇 |
1975年 | 70篇 |
1974年 | 56篇 |
1973年 | 63篇 |
1972年 | 37篇 |
排序方式: 共有6335条查询结果,搜索用时 15 毫秒
31.
Jeffrey Robert Thompson 《Geological Journal》2015,50(4):550-551
32.
33.
Some approaches for location of centroids of quartz grain outlines to increase homology between Fourier amplitude spectra 总被引:2,自引:0,他引:2
The ability to test for similarities and differences among families of shapes by closed-form Fourier expansion is greatly enhanced by the concept of homology. Underlying this concept is the assumption that each term of a Fourier series, when compared to the same term in another series, represents the same thing. A method that ensures homology is one which minimizes the centering error, as reflected in the first harmonic term of the Fourier expansion. The problem is to chose a set of edge points derived from a much larger, but variable, number of edge points such that a valid homologous Fourier series can be calculated. Methods are reviewed and criteria given to define a proper solution. An algorithm is presented which takes advantage of the fact that minimization of the error term can be accomplished by minimizing the distance between the origin of the polar coordinate system in the calculation of the Fourier series and the shape centroid. The use of this algorithm has produced higher quality solutions for quartz grain provenance studies. 相似文献
34.
35.
Mutual Potential of Homogeneous Polyhedra 总被引:2,自引:0,他引:2
Robert A. Werner Daniel J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2005,91(3-4):337-349
The mutual gravitational potential between a pair of homogeneous polyhedra is expressed using an infinite series. The nested
volume integrals are evaluated analytically and result in simple tensor expressions containing no special functions. However,
complexity increases as O(6
n
), where n is the term degree. An alternate formulation due to Liebenthal is also presented. 相似文献
36.
37.
38.
The US Minerals Management Service (MMS) is responsible for safe and environmentally sound management of offshore oil and gas resources. In recent years, there has been a tremendous increase in both activities and plans for deepwater development of these resources in the Gulf of Mexico (GOM). As the industry meets the enormous technical challenges involved, there is a concomitant effort to assure environmental protection of deep-ocean and coastal resources. This paper will outline the research planning and program currently underway to assess impacts, identify potential problems, and discover more about unknown resources of the deep ocean. 相似文献
39.
Bowser Lake, a fiord lake in the northern Coast Mountains of British Columbia, contains a thick Holocene fill consisting mainly of silt and clay varves. These sediments were carried into the lake by proglacial Bowser River which drains a high-energy, heavily glacierized basin. Sedimentation in the lake is controlled by seasonal snow and ice melt, by autumn rainstorms, and by rare, but very large jökulhlaups from glacier-dammed lakes in the upper Bowser River basin which complicate environmental inferences from the sedimentary record. Sediment is dispersed through the deep western part of the lake by energetic turbidity currents. The turbidity currents apparently do not overtop a sill that separates the western basin from much shallower areas to the east. Large amounts of silt and clay are deposited from suspension in the eastern part of the lake, but sediment accumulation rates there are much lower than to the west. Several strong acoustic reflectors punctuate the varved fill in the western basin; these may be thick or relatively coarse beds deposited during jökulhlaups or exceptionally large storms. The contemporary sediment yield to Bowser Lake, estimated from sediments in the lake, is about 360 t km-2a-1. This is a relatively high value, but it is less than yields insome other, similar montane basins with extensive snow and ice cover.The most likely explanation for the difference is that large amounts of sediment have been, and continue to be, stored on the Bowser delta andin small proglacial lakes. 相似文献
40.