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   94篇
  免费   10篇
  2024年   1篇
  2023年   4篇
  2022年   1篇
  2021年   1篇
  2020年   2篇
  2019年   6篇
  2018年   8篇
  2017年   11篇
  2016年   12篇
  2015年   3篇
  2014年   8篇
  2013年   16篇
  2012年   7篇
  2011年   2篇
  2010年   3篇
  2009年   2篇
  2008年   5篇
  2007年   2篇
  2006年   1篇
  2005年   2篇
  2004年   1篇
  2002年   1篇
  2000年   1篇
  1998年   2篇
  1993年   1篇
  1990年   1篇
排序方式: 共有104条查询结果,搜索用时 171 毫秒
11.
Over the last decade, a long-running archaeological project in the Guadalquivir Basin (Spain) has identified the emergence (c. 3000 BC) and collapse (between c. 2500 and c. 2300 BC) of a regional inter-settlement hierarchical system centred on the south-western Pyrite Belt and the Lower Guadalquivir Basin.  相似文献   
12.
In this paper, we explore regional innovation in the use of varieties of algae as inputs to industrial processes. It is important to understand that algae are one of nature's most bountiful products, with an almost infinite variety of applications. Algae have received prominence in the research literature because of the strong evidence that they can make a major contribution to the production and—importantly—storage of renewable energy. Following the introduction to this paper, Section 2 reviews the nature and application of algae in two main aspects of clean energy production: first as biogasolene or biodiesel; second as large-scale storage batteries for electricity. The latter is particularly important as one classic deficiency of electricity is the difficulty in storing it for lengthy periods other than in short-life batteries. However (Section 3), there are other uses for algae, ranging from aquaculture to medicine and the production of cosmetics. In the southwest corner of the Iberian Peninsula, between Faro in Portugal through Huelva to Cadiz in Spain, is a significant research and commercial algae production zone. The paper describes the key system elements in play in this trans-border innovation network and considers prospects for new path creation towards biofuels, the main research and application centres for which are in the San Francisco Bay Area in California. Conclusions and recommendations for policy action are then drawn.  相似文献   
13.
14.
15.
The first Miocene records of silicified fossil woods from the Mariño Formation, Potrerillos area, Andes Precordillera, Mendoza province, Argentina are described. Rhaphithamnoxylon artabeae gen. et sp. nov. is described as the first fossil wood referable to Verbenaceae from Argentina. This new fossil species is related to extant Rhaphithamnus Miers, sharing the following anatomical features: diffuse porosity, distinct growth ring boundaries, numerous small to very small vessels, commonly in radial multiples, 1–3 seriate rays, and heterocellular and scarce paratracheal axial parenchyma. Rhaphithamnus contains only two extant species: R. spinosus (A.L. Juss.) Moldenke, which occurs in the Valdivian forests of Chile and Argentina, and R. venustus (Philippi) Robinson, which is endemic to the Juan Fernández Islands. Representatives of Verbenaceae are distributed predominantly in the Americas from Patagonia (Argentina) to Canada, and they are inferred to have originated in South America. The fossil wood described herein provides new age and geographical constraints on the raphithanoid lineage within Verbenaceae. Other fossil woods recorded from the Mariño level are retained under open nomenclature, as they possess a combination of mostly solitary broad vessels, and smaller vessels in radial multiples or in clusters, with numerous, vasicentric to confluent axial parenchyma, and heterocellular, high rays. Thus, they have features akin to dicotyledonous lianas or vine-like or small shrub species.  相似文献   
16.
The paleopathological record of neoplastic conditions in the past is considered scarce. The detection of tumours in ancient populations is hindered by the quality and quantity of signs visible on the skeleton, the methodological approach, the preservation of remains, and by difficulties of differential diagnosis. The aims of this paper are to report the extensive and multiple osteolytic lesions observed in an adult male and to discuss the possible etiology of these lesions. The individual, a 71‐year‐old male who died in 1932, is part of the Coimbra Identified Skeletal Collection. Records indicate that he died of a ‘heart lesion’. The present study used macroscopic, radiological, and computerized tomography examinations to analyse the skeletal remains of the individual number 439. The type and pattern of the lesions detected, which were most prominent on the skull, were compared with both clinical and paleopathological diagnostic criteria for different nosologic groups. The differential diagnosis addresses problems expressed both in clinical and in paleopathological literature with regard to the difficulties in distinguishing metastatic tumours from multiple myeloma. The nature of the lesions represented by this individual precludes an exact diagnosis. Therefore, we employed a broader category, neoplastic condition, instead of choosing a more specific diagnosis that would likely have resulted in a misdiagnosis due to overlapping features on this individual's condition. Further investigations are necessary to establish more replicable indicators and to improve confidence in retrospective diagnosis of these types of conditions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
17.
18.
19.
20.
Archaeomagnetic dating based on the full geomagnetic field vector was carried out on a limekiln excavated at Pinilla del Valle archaeological site (Madrid, Spain). The limekiln tradition in this area is largely documented by historical sources for recent centuries but the date of the studied kiln's last use was unknown. The combination of mean archaeomagnetic directional and absolute archaeointensity results shows that the kiln was last used between ad 1296 and 1413, in good agreement with two independent radiocarbon dates. This study provides the first archaeomagnetic evidence that the local limekiln tradition dates back to at least late medieval times. Furthermore, the inclusion of these data in the Iberian secular variation curve and geomagnetic field models will help to improve the archaeomagnetic dating technique.  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