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   840篇
  免费   26篇
  国内免费   7篇
测绘学   12篇
大气科学   80篇
地球物理   129篇
地质学   261篇
海洋学   79篇
天文学   212篇
综合类   6篇
自然地理   94篇
  2021年   8篇
  2020年   7篇
  2019年   15篇
  2018年   12篇
  2017年   18篇
  2016年   18篇
  2015年   24篇
  2014年   13篇
  2013年   31篇
  2012年   15篇
  2011年   26篇
  2010年   27篇
  2009年   48篇
  2008年   36篇
  2007年   26篇
  2006年   30篇
  2005年   39篇
  2004年   20篇
  2003年   23篇
  2002年   21篇
  2001年   17篇
  2000年   24篇
  1999年   12篇
  1998年   17篇
  1997年   10篇
  1996年   6篇
  1995年   12篇
  1994年   11篇
  1993年   8篇
  1992年   14篇
  1990年   15篇
  1989年   15篇
  1988年   9篇
  1987年   13篇
  1986年   6篇
  1985年   18篇
  1984年   16篇
  1983年   12篇
  1982年   12篇
  1981年   13篇
  1980年   15篇
  1979年   21篇
  1978年   15篇
  1977年   12篇
  1976年   10篇
  1975年   10篇
  1974年   7篇
  1973年   14篇
  1972年   6篇
  1971年   6篇
排序方式: 共有873条查询结果,搜索用时 31 毫秒
871.
Seismic detection of faults, dykes, potholes and iron-rich ultramafic pegmatitic bodies is of great importance to the platinum mining industry, as these structures affect safety and efficiency. The application of conventional seismic attributes (such as instantaneous amplitude, phase and frequency) in the hard-rock environment is more challenging than in soft-rock settings because the geology is often complex, reflections disrupted and the seismic energy strongly scattered. We have developed new seismic attributes that sharpen seismic reflections, enabling additional structural information to be extracted from hard-rock seismic data. The symmetry attribute is based on the invariance of an object with respect to transformations such as rotation and reflection; it is independent of the trace reflection amplitude, and hence a better indicator of the lateral continuity of thin and weak reflections. The reflection-continuity detector attribute is based on the Hilbert transform; it enhances the visibility of the peaks and troughs of the seismic traces, and hence the continuity of weak reflections. We demonstrate the effectiveness of these new seismic attributes by applying them to a legacy 3D seismic data set from the Bushveld Complex in South Africa. These seismic attributes show good detection of deep-seated thin (∼1.5 m thick) platinum ore bodies and their associated complex geological structures (faults, dykes, potholes and iron-rich ultramafic pegmatites). They provide a fast, cost-effective and efficient interpretation tool that, when coupled with horizon-based seismic attributes, can reveal structures not seen in conventional interpretations.  相似文献   
872.
873.
The development of specialized and commercial fishing activity in the island archipelago of Lofoten and Vesterålen in northern Norway is a critical foundation from which to understand the subsequent spread of commercial fishing across the north Atlantic region during the medieval and early modern period. One little understood aspect of this development is the relationship between medieval commercial fishing stations (fiskevaer) and earlier fishing activity. In this article, cultural sediment deposits at Langenesværet, Vesterålen, Northern Norway provide an opportunity to examine this relationship and its implications for current historical models of fishing development in northern Norway and the north Atlantic region. Conventional and AMS radiocarbon dating techniques are used to establish a chronology for the deposits, while activities associated with the sediments are characterized using thin‐section micromorphology supported by proton induced X‐ray emission spectrometry (PIXE). The results suggest that the site commenced formation as early as ca. 3000 B.C. and that the site was first used for specialized fishing activity from the early centuries A.D. The medieval commercial fiskevaer settlement at Langenesværet was introduced to an area that had a longstanding tradition of specialised fishing activity. © 2000 John Wiley & Sons, Inc.  相似文献   
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