全文获取类型
收费全文 | 4374篇 |
免费 | 944篇 |
国内免费 | 448篇 |
专业分类
测绘学 | 1249篇 |
大气科学 | 113篇 |
地球物理 | 728篇 |
地质学 | 2468篇 |
海洋学 | 557篇 |
天文学 | 86篇 |
综合类 | 294篇 |
自然地理 | 271篇 |
出版年
2024年 | 8篇 |
2023年 | 47篇 |
2022年 | 207篇 |
2021年 | 285篇 |
2020年 | 246篇 |
2019年 | 212篇 |
2018年 | 111篇 |
2017年 | 182篇 |
2016年 | 164篇 |
2015年 | 202篇 |
2014年 | 340篇 |
2013年 | 253篇 |
2012年 | 301篇 |
2011年 | 318篇 |
2010年 | 223篇 |
2009年 | 233篇 |
2008年 | 255篇 |
2007年 | 310篇 |
2006年 | 268篇 |
2005年 | 204篇 |
2004年 | 215篇 |
2003年 | 191篇 |
2002年 | 157篇 |
2001年 | 105篇 |
2000年 | 102篇 |
1999年 | 102篇 |
1998年 | 90篇 |
1997年 | 85篇 |
1996年 | 87篇 |
1995年 | 72篇 |
1994年 | 40篇 |
1993年 | 28篇 |
1992年 | 31篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有5766条查询结果,搜索用时 15 毫秒
21.
A. Winter K.O. Coyle G. Swartzman 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2869
Cohort abundance of walleye pollock (Theragra chalcogramma) is subject to strong interannual variation in the eastern Bering Sea, and this variation is known to be determined largely at the age-0 stage. We estimated the spatial distributions and densities of age-0 walleye pollock in five nursery areas around the eastern Bering shelf in three successive years (1997–1999) from acoustic survey data. Concurrently, we calculated estimates of the spatial distribution of euphausiids, a major prey of age-0 walleye pollock, and estimates of spatial overlap of groundfish predators with the age-0 walleye pollock. The analyses showed that all nursery areas had low densities of age-0 walleye pollock in 1997, which ultimately produced the weakest adult year-class. In the intermediate year of 1998, age-0 densities were low to medium, and in 1999, which produced the strongest of the three adult year-classes, all nursery areas had medium to high age-0 walleye pollock densities. Euphausiid distributions had a consistently positive spatial relationship with age-0 walleye pollock. Groundfish predator density ratios were positively related to age-0 walleye pollock density when age-0 walleye pollock were displaced relatively northward. Our results suggest that abundance of age-0 walleye pollock, and hence of adult cohorts in the eastern Bering Sea, can be predictable from a concise set of indicators: the densities of age-0 walleye pollock at nursery areas in mid- to late-summer, their spatial relationship to euphausiids and groundfish predators, and the latitudinal trend of their distributions. The 3 years 1997–1999 had significant differences of physical conditions in the eastern Bering Sea, and represent an advantageous framework for testing these hypotheses. 相似文献
22.
23.
海底勘查技术的最新发展 总被引:4,自引:0,他引:4
本文将介绍用于探测海底三维地质特征的海底勘查的最新发展。它主要包括海底地形测绘技术,海底形貌观测技术、海底地层声学探测技术等。 相似文献
24.
针对《城镇地籍调查规程》和《城市测量规范》对光电测距(EDM)导线技术参数规定的不同,对低等光电测距导线的合理等级及各等级导线的技术标准进行了研究,并通过精度估算证明了各级导线精度的可靠性。 相似文献
25.
ICES baseline survey of trace metals in European shelf waters 总被引:1,自引:0,他引:1
Balls P.; Cofino W.; Schmidt D.; Topping G.; Wilson S.; Yeats P. 《ICES Journal of Marine Science》1993,50(4):435-444
26.
27.
The seismic expression of a salt-filled channel which cuts across the Mid North Sea High in Quadrant 37 is described, with features interpreted as being produced by salt-edge dissolution forming both eastern and western margins of the channel. The apparent half-graben nature of the channel is shown to be only superficial, and due to complex faulting associated with, but not defining, its western margin. The shallower faulting here is a Mesozoic to early Tertiary growth fault related to local dissolution of Zechstein salt. The dissolution effect appears in turn to have been localized by the presence of a deeper fault that was already downthrown to the east in Zechstein times, when it seems to have limited the eastward progradation of Zechstein shelf carbonates and anhydrites, and had probably ceased to move significantly before the onset of the Late Cimmerian erosional phase. The origin of this arcuate fault is tentatively ascribed to subsidence around a granite batholith. Zechstein salt originally spread some distance to the east and west of the channel; it was dissolved from the edges inwards, mainly before the Late Cretaceous, giving rise to a thicker Mesozoic sequence on parts of the flanks of the channel than in the middle. Besides providing an interesting structural case history, the features described have implications regarding Zechstein sedimentation, reservoir potential, the tectonic history of the North Sea, and the nature of the Mid North Sea High itself. 相似文献
28.
29.
底部浮泥表层推移速度分布的ADCP—GPS估测方法 总被引:3,自引:0,他引:3
ADCP对底跟踪走航观测的流速数据中包含水体底部浮泥、底沙运动信息,对比GPS定位方法算出的水体流速数据可以分离出浮泥相对于GPS定位的运动信号,从而达到对底质推移观测的目的。 相似文献
30.