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   255篇
  免费   9篇
  2023年   3篇
  2022年   1篇
  2021年   1篇
  2020年   5篇
  2019年   8篇
  2018年   18篇
  2017年   20篇
  2016年   14篇
  2015年   11篇
  2014年   10篇
  2013年   44篇
  2012年   9篇
  2011年   9篇
  2010年   8篇
  2009年   10篇
  2008年   4篇
  2007年   2篇
  2006年   3篇
  2005年   3篇
  2004年   1篇
  2002年   1篇
  2001年   2篇
  2000年   4篇
  1999年   1篇
  1998年   4篇
  1997年   5篇
  1996年   5篇
  1995年   5篇
  1994年   5篇
  1993年   4篇
  1992年   4篇
  1991年   3篇
  1990年   6篇
  1989年   5篇
  1988年   4篇
  1987年   5篇
  1986年   9篇
  1985年   1篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1975年   1篇
  1974年   1篇
排序方式: 共有264条查询结果,搜索用时 15 毫秒
21.
This article analyses a collection of 26 watercolour drawings which portray ethnographic types from the Americas, Asia, and Africa. These drawings, presently kept at the British Library, were made for John Locke by his servant Sylvester Brounower during Locke’s exile in the Netherlands in the 1680s.  相似文献   
22.
The territorial and spatial planning impacts of European Union (EU) economic and competition policies have remained under-researched in the field of European spatial planning, in contrast to other EU policy fields. This briefing explores how two elements of the EU competition policy, the regulation of “state aid” and the liberalization of “services of general interest (SGI)”, have significant implications for the pursuit of the objective of territorial cohesion through spatial planning and territorial development policies at different scales. The paper first reviews the development of the concept of territorial cohesion in the EU discourse and policy agenda since the mid-1990s, as well as the contribution of public services (Services of General Interest, or SGI in EU jargon) to it. It, then, reviews how the EU state aid rules and liberalization policies affect the state's ability to intervene (i) in support of sub-national territories which are lagging behind or suffering decline, and (ii) in the provision of public services across the national territory, specifically in peripheral regions or areas where the provision is not catered for by the market. The conclusion of the paper outlines the additional challenges to the pursuit of territorial cohesion in the EU posed by the post-2008 economic crisis and suggests avenues for future research.  相似文献   
23.
ABSTRACT We investigate how cross‐country differences in firms' fixed set‐up costs affect the trade‐off between global efficiency and spatial equity. Our analysis reveals that the standard assumption of symmetry in set‐up costs masks the existence of an interesting effect: the range of available varieties depends on the spatial distribution of firms. In such a setting, where the market outcome leads to excessive agglomeration in the symmetric case, a planner may opt for asymmetric set‐up costs and even more agglomeration. We show that the planner will always favor lower set‐up costs in the large country with more agglomeration when the consumer's marginal preference for variety is high, or with less agglomeration when the consumer's marginal preference for variety is low.  相似文献   
24.
25.
26.
Mineralised fruits and seeds are frequently found in archaeological sediments but their chemical nature has not been often examined. The nature and the origin of these archaeobotanical remains have to be investigated to understand their taphonomic history. Fruits or seeds can be mineralised not only by replacement mineralisation but also by biomineralisation during the plant life. The mineral components of three fossil fruits sampled on the Pleistocene site of Dmanisi were analysed and compared with their modern analogues. Analyses were carried out by means of an environmental scanning electron microscope, equipped with an energy dispersive X-ray device and by means of a Fourier transform infrared spectrometer. Biogenic carbonates and/or biogenic silica were identified in the fossil and modern fruits of some taxa. Comparison between fossil and modern specimens has shown that molecular reorganisation occurred in carbonate and in biogenic silica during fossilisation, through diagenetic processes. The resulting stable mineral structures confer an exceptional preservation to fruits in sediments. Taking into account these taphonomic specificities (transformation and differential preservation), the chronological and palaeoenvironmental aspects of the mineralised fruits are discussed.  相似文献   
27.
28.
29.
30.
Organic fertilizers have the capacity to alter the nitrogen isotopic composition of plants. Camelid dung and seabird guano are two potentially important fertilizers in the agricultural systems of western South America, particularly Peru and Chile. This paper presents isotopic data (δ13C and δ15N) from field grown plants (maize, Zea mays) fertilized with the following four treatments: CO (control, no fertilizer applied), AS (ammonium sulfate, a chemical fertilizer), DU (camelid dung), and SG (seabird guano). Plants were grown in experimental plots in the Virú Valley, northern Peru. Plants fertilized with the chemical fertilizer presented very similar isotopic compositions compared to the control. Conversely, the camelid dung fertilized plants were characterized by higher δ15N values compared to the control plants (by 1.8 to 4.2‰ depending on the plant part). The seabird guano fertilized plants were greatly enriched in 15N in comparison to the control plants (by 11.3 to 20.0‰). The results of this study have important implications for the reconstruction of human diet using isotopic data derived from bone collagen and related tissues, particularly in the prehispanic Andes, but also in Europe and North America during the 19th century, when Peruvian seabird guano was used extensively. Specifically, the interpretation of the relative contributions of plant and animal protein to the diet on the basis of bulk isotopic compositions of bone collagen (or similar tissues) may be confounded by camelid dung fertilization if the carbon isotopic compositions of the two sources are similar. Likewise, the interpretation of the relative contributions of maize and marine protein may be confounded by seabird guano fertilization.  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