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   118篇
  免费   4篇
  2024年   1篇
  2023年   4篇
  2021年   3篇
  2020年   3篇
  2019年   2篇
  2018年   13篇
  2017年   9篇
  2016年   4篇
  2015年   4篇
  2014年   6篇
  2013年   30篇
  2012年   3篇
  2011年   9篇
  2010年   5篇
  2009年   3篇
  2008年   5篇
  2007年   3篇
  2006年   1篇
  2004年   1篇
  2003年   2篇
  2002年   1篇
  2001年   2篇
  2000年   3篇
  1999年   1篇
  1998年   1篇
  1997年   2篇
  1995年   1篇
排序方式: 共有122条查询结果,搜索用时 15 毫秒
91.
The fruit (pods) of Prosopis (Fabaceae) are frequently recovered from pre-Hispanic Argentinian archaeological sites, suggesting that this genus was of importance in ancient economies in this region. Yet it is only recently that archaeobotanists have begun to carry out systematic research into this genus. Therefore many questions remain to be addressed concerning the food value of Prosopis fruit, and its potential contribution. This paper examines starch from the pods of two species, Prosopis flexuosa and Prosopis chilensis, for the purposes of describing and classifying their morphological features and biometrical parameters. Pods of both species were gathered from two extremes (northern and southern) of the Hualfín Valley, Catamarca, Argentina. Starch abundance is estimated and compared with that of Zea mays, an economically important plant with high concentrations of starch. This paper reveals that Prosopis pods contain very low amounts of starch compared to starch-rich edible species. Despite this, the recovery of Prosopis starch grains can be successfully used to assess archaeological tool uses. Prosopis starch grains were found to be highly variable in shape. Grain size ranged between 10 and 20 μm. Granule irregularity and the high birefringence under polarized light are two of the most important diagnostic features. No significant statistical differences were found in the structure (morphology, size and hilum) of the starch of the same species from both localities. Finally, the implications for the role of this plant in past societies are discussed.  相似文献   
92.
93.
94.
In the course of an archaeological project in the southern Chad Basin of Nigeria, excavations were conducted at several deeply stratified mound sites that date from the Late Neolithic to the Late Iron Age. As a way to complement the ceramic sequence obtained so far and to link it with today's pottery tradition, a small excavation was conducted at a site that dates to the turn of the nineteenth to the twentieth century A.D. A pottery assemblage was discovered that shows obvious links to today's tradition but notable breaks with those of the nineteenth century and earlier. This break in decoration style and technique is interpreted as an archaeologically visible expression of changing ethnic identity. This ethnic change and the associated spread of the ceramic tradition can be linked with the expansion of the sphere of power of the Kanem-Borno Empire into the area south of Lake Chad after the sixteenth century A.D.  相似文献   
95.
Raptor pellets from Cerro Casa de Piedra archaeological sites, Patagonia, have yielded consistent evidence of parasitism and possible zoonoses in ancient times. Pellet samples analyzed were dated at 2740 ± 100 and 3.990 ± 80 years before present and have produced evidence of three intestinal parasite genera. Eggs of two nematodes Trichuris and Calodium, and one cestode, taeniid, were found. Its significance for rock shelters paleoepidemiology of the Holocene is discussed. This study increases the evidences that raptor pellets can be used as source of paleoparasitological information in archaeological sites.  相似文献   
96.
Interaction between hominins and carnivores has been common and constant through human evolution and generated mutual pressures similar to those present in worldwide modern human-carnivore conflicts. This current interaction is sometimes violent and can be reflected in permanent skeletal pathologies and other bone modifications. In the present paper, we carry out a survey of 124 forensic cases of dangerous human-carnivore encounters. The objective is to infer direct hominin-carnivore confrontation during the Pleistocene, which is important to understand behavioral changes during human evolution. In addition, the case of Neanderthals is analyzed in order to find evidence of past attacks using forensic observations. The results obtained pose that Neanderthals could potentially have been involved in dangerous encounters during the Pleistocene, validating our methodology to approach past attacks from a forensic perspective.  相似文献   
97.
This paper seeks to contribute to the development and improvement of displacement-based design procedures, proposing improved ductility-equivalent viscous damping relationships for steel moment-resisting framed structures with dissipative beam-to-column partial-strength joints. These relationships can be used directly in procedures like the Direct Displacement-Based Seismic Design (DDBD) that uses effective stiffness, ductility-equivalent viscous damping relationships, and period-displacement relationships in a performance-based design approach. To this end, a finite element model of a steel beam-to-column sub-assemblage, characterized by an extended end-plate, is developed in ABAQUS. The model, which is validated against monotonic and cyclic experimental data obtained in previous research, is employed to carry out non-linear time-history (NLTH) analyses, using real records scaled to target several levels of ductility demand. A procedure is then proposed and applied to determine the ductility-equivalent viscous damping relationships of the sub-assemblages. The equivalent linearization technique is applied to the non-linear responses obtained in the NLTH analyses, using an elastic single degree of freedom structure and the elastic displacement spectra. The influence of joints mechanisms and of the dynamic characteristics of the structure in the equivalent viscous damping is investigated, and an expression for ductility-equivalent viscous damping is proposed. The proposed expression represents a clear improvement in relation to the existing expressions available in literature.  相似文献   
98.
As social constructions, heritage properties require the participation of all their stakeholders, especially in the case of UNESCO World Heritage Sites. The Atapuerca (Burgos, Spain) World Heritage Site is used as a test case for assessing the fulfilment of the local community’s development expectations, perceptions, and values. This paper is the first formal attempt to ascertain the opinions of residents in the surrounding villages — Ibeas de Juarros and Atapuerca — regarding the initiatives taken by the authorities, and the changes produced, since the site was included in the World Heritage List. The results show that many improvements can be made with the aim of democratizing the decision-making process, ensuring the involvement of the local community and improving their quality of life, in order to fulfil the spirit and recommendations of UNESCO.  相似文献   
99.
A new microdomatid gastropod, Eopagodea sevillana gen. and sp. nov., is described from the Late Ordovician (pre-Hirnantian Ashgill) limestones of Seville, Ossa Morena Zone, Spain. Palaeozoic microdomatids lived in shallow-water environments and were restricted to warm-water regions. Occurrence of microdomatid gastropods in the pre-Hirnantian Ashgill limestones of the Cerrón del Hornillo syncline (Ossa Morena Zone, Spain) is interpreted as an example of an influx of warm-water faunal elements into the otherwise cool to cold climate of the Mediterranean region during a short-termed, pre-Hirnantian increase of palaeotemperatures. The Late Ordovician microdomatid genus Daidia Wilson, 1951, is revised and two new Late Ordovician (Ashgill) subspecies of Daidia cerithioides (Salter, 1859) are described: Daidia cerithioides sewardensis n. subsp. from the Don River area of the York Mountains, Seward Peninsula, western Alaska, and Daidia cerithioides wilsonae n. subsp. from the Little East Lake Formation of northwestern Maine.  相似文献   
100.
The seismic vulnerability of housing stock in El Salvador was demonstrated during the recent 2001 earthquakes. Relative to other types of common residential construction, confined masonry dwellings performed well. A coordinated pilot study was conducted with the objective of improving the seismic resistance of this form of construction while reducing associated costs and greenhouse gas emissions. Laboratory tests examined brick strength in relation to firing temperature and duration. Analytical studies examined the potential for voided bricks to improve seismic performance, the reduction in demands associated with stiffening the roof diaphragm, and demands imposed on the roof bracing system. This pilot study identifies the potential for voided bricks to reduce construction costs and greenhouse gas emissions with negligible effects on performance. The addition of end-bay diagonal bracing at the roof level resulted in significant performance enhancements.  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