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   688篇
  免费   55篇
  2024年   1篇
  2023年   23篇
  2022年   3篇
  2021年   9篇
  2020年   35篇
  2019年   35篇
  2018年   104篇
  2017年   75篇
  2016年   69篇
  2015年   48篇
  2014年   39篇
  2013年   146篇
  2012年   32篇
  2011年   25篇
  2010年   12篇
  2009年   14篇
  2008年   13篇
  2007年   11篇
  2006年   2篇
  2005年   2篇
  2004年   1篇
  2003年   3篇
  2002年   4篇
  2001年   9篇
  2000年   4篇
  1999年   1篇
  1998年   1篇
  1997年   4篇
  1996年   2篇
  1995年   7篇
  1994年   2篇
  1993年   2篇
  1992年   3篇
  1982年   1篇
  1979年   1篇
排序方式: 共有743条查询结果,搜索用时 15 毫秒
71.
72.
73.
A polyphasic tectonic‐fluid system of a fault that involves crystalline and carbonate rocks (Hospital fault, Barcelona Plain) has been inferred from regional to thin section scale observations combined with geochemical analyses. Cathodoluminescence, microprobe analyses and stable isotopy in fracture‐related cements record the circulation of successive alternations of hydrothermal and low‐temperature meteoric fluids linked with three main regional tectonic events. The first event corresponds to the Mesozoic extension, which had two rifting stages, and it is characterized by the independent tectonic activity of two fault segments, namely southern and northern Hospital fault segments. During the Late Permian‐Middle Jurassic rifting, these segments controlled the thickness and distribution of the Triassic sediments. Also, dolomitization was produced in an early stage by Triassic seawater at shallow conditions. During increasing burial, formation of fractures and their dolomite‐related cements took place. Fault activity during the Middle Jurassic–Late Cretaceous rifting was localized in the southern segment, and it was characterized by hydrothermal brines, with temperatures over 180°C, which ascended through this fault segment precipitating quartz, chlorite, and calcite. The second event corresponds to the Paleogene compression (Chattian), which produced exhumation, folding and erosion, favouring the percolation of low‐temperature meteoric fluids which produced the calcitization of the dolostones and of the dolomite cements. The third event is linked with the Neogene extension, where three stages have been identified. During the syn‐rift stage, the southern segment of the Hospital fault grew by tip propagation. In the relay zone, hydrothermal brines with temperature around 140°C upflowed. During the late postrift, the Hospital fault acted as a unique segment and deformation occurred at shallow conditions and under a low‐temperature meteoric regime. Finally, and possibly during the Messinian compression, NW‐SE strike‐slip faults offset the Hospital fault to its current configuration.  相似文献   
74.
This paper continues the characterization of the lead isotopic fingerprint of ancient copper mines in the north‐west of Spain. In this work, the lead isotopic compositions found in copper ores from the La Profunda mine are presented. Azurites and malachites sampled from this deposit were subjected to lead isotope analysis by multicollector ICP–MS. The results showed a clear radiogenic lead signature compatible with the presence of uranium‐rich minerals (such as zeunerite) in the same mining complex. Moreover, a rare copper artefact, found in the galleries of the mine during its modern exploitation, was also analysed and showed that local mineral was used for its manufacturing.  相似文献   
75.
Relying on stochastic frontier analysis we propose a methodology to study the technological characteristics and cost efficiency levels related to the provision of public infrastructure for basic utilities. The methodology assumes a cost minimizing behaviour on the part of public officials when planning the construction of local infrastructure, which is represented by way of a flexible translog cost function. Introducing relevant definitions of scale economies, associated with larger numbers of inhabitants and dwellings, as well as economies of density, brought about by reductions in urban dispersion, we analytically determine the optimal population densities for which average cost is minimized. We illustrate our model with the water cycle sector, including water distribution, sewage collection and cleansing of wastewater, and considering data at the municipality level for the Spanish region of Castilla y León. The obtained results indicate potential cost savings in the form of decreasing average costs, as relevant scale and density economies are present, along with large inefficiency levels. Relevant policy guidelines favouring larger and denser urban sizes are drawn, as the observed cost excess is the result of a general suboptimal urban size in terms of population density, and the negative effects of dispersed settlement patterns.  相似文献   
76.
77.
78.
This paper discusses the impact of the conference ‘Las Olvidadas: Gender and Women's History in Post‐Revolutionary Mexico’ that took place at Yale University in May 2001, into my own work on women's political mobilisations. It points out from where I departed and how it changed my perspective from women's history to gender history by focusing on women workers in the tortilla industry, a union cacicazgo (political bossism), civic culture, narratives, cultural memory and female political trajectories after the granting of women's suffrage in 1953 in Jalisco.  相似文献   
79.
This study analyzes the faunal assemblages corresponding to the Middle and Upper Paleolithic and the Early Epipaleolithic for the central Spanish Mediterranean Region dated from between 135,000 and 9,000 B.P. To interpret these data, we employ a zooarchaeological and paleoeconomic perspective. Human large and small game hunting systems are analyzed through the identification of the origins of faunal assemblages, bone breackage patterns, and prey selection patterns. Our study shows that hunting systems changed significantly through time, which may be related to the characteristics of the Mediterranean ecosystem and, above all, to cultural changes.  相似文献   
80.
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