全文获取类型
收费全文 | 527篇 |
免费 | 21篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 40篇 |
地球物理 | 104篇 |
地质学 | 221篇 |
海洋学 | 47篇 |
天文学 | 61篇 |
综合类 | 3篇 |
自然地理 | 63篇 |
出版年
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 18篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 19篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 27篇 |
2012年 | 15篇 |
2011年 | 25篇 |
2010年 | 15篇 |
2009年 | 23篇 |
2008年 | 19篇 |
2007年 | 26篇 |
2006年 | 23篇 |
2005年 | 14篇 |
2004年 | 25篇 |
2003年 | 22篇 |
2002年 | 14篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1967年 | 2篇 |
排序方式: 共有554条查询结果,搜索用时 0 毫秒
551.
We compare the results from the application of four different methods to determine the speed of meteoroids from single station
radar data. The methods used are the pre-t
0 amplitude, post-t
0 amplitude, pre-t
0 phase and the Fresnel transform (FT) methods. Speeds from the first three methods are compared to the FT method since, requiring
the use of the entire records of both the amplitude and phase data, this method is the most accurate of the four. 相似文献
552.
553.
The Fulani of West Africa have increasingly migrated to humid West Africa since the Sahelian droughts of the 1970s, drawing opposition from indigenous groups that are concerned about the deprivation of their livelihood and monopolization of resources for herders’ livestock. This research, which involved farmers, shepherds, and Fulani herders, addressed three issues: the nature of indigenous grazing and watering regimes, shepherd–herder relations, and herders’ impact on resource access for indigenes’ livestock. The research indicates that in-community and off-community platforms for resource access exist. The former has not been impacted by the herders; the latter has experienced changes insufficient to constitute an overhaul of resource access at the expense of indigenes’ livestock. Instead, a “shepherd–herder” category of resource access has emerged that is characterized by negotiation for resource space, opening avenues for addressing broader resource access issues, and typically tense indigene–herder relationships. 相似文献
554.
Surface water on the mainly dry, upland interfluves of the Upper Coastal Plain of South Carolina occurs currently as a sporadic distribution of shallow ponds held within Carolina bays and other small, isolated basins. At seven bays on the U.S. Department of Energy's Savannah River Site on the Upper Coastal Plain of South Carolina, we investigated Holocene changes in bay morphology, ecology, and prehistoric human activity. At Flamingo Bay, we employed archaeological survey and testing, shovel and auger testing, sediment analysis, and ground-penetrating radar to document stratigraphy and chronology of the sand rim on the eastern side of the bay. Artifact assemblage indicate changes in intensity of human use of the bay. Radiocarbon dates from a sediment core establish time scales for depositional processes at the center of the basin. Ground-penetrating radar data from the other bays indicate that the stratigraphy of all seven bays is broadly similar. We conclude that: (1) Significant modification of the bays, including rim development and basin infilling, occurred during the Holocene; (2) ponds on the early Holocene landscape were larger and more permanent than at present; (3) early Holocene climate, as indicated by both depositional processes and human activity, was not characterized by prolonged periods of extremely dry conditions; and (4) fluvial-centric models of terminal Pleistocene—early Holocene human adaptations require revision to include intensive use of isolated upland ponds. © 1996 John Wiley & Sons, Inc. 相似文献