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   440篇
  免费   11篇
  451篇
  2024年   5篇
  2023年   14篇
  2022年   1篇
  2021年   8篇
  2020年   15篇
  2019年   36篇
  2018年   36篇
  2017年   36篇
  2016年   32篇
  2015年   18篇
  2014年   23篇
  2013年   66篇
  2012年   24篇
  2011年   21篇
  2010年   18篇
  2009年   20篇
  2008年   17篇
  2007年   4篇
  2006年   3篇
  2005年   14篇
  2004年   8篇
  2003年   2篇
  2002年   7篇
  2001年   7篇
  2000年   1篇
  1999年   4篇
  1997年   2篇
  1996年   1篇
  1995年   3篇
  1993年   1篇
  1985年   1篇
  1979年   1篇
  1974年   2篇
排序方式: 共有451条查询结果,搜索用时 0 毫秒
21.
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   
22.
Middle Egypt provides a unique insight into the organization of power, politics, economy, and culture at the turn of the third millennium BC. The apparently easy integration of this region into the reunified monarchy of king Mentuhotep II (2055–2004 BC) was possible because the interests and the local lineages of potentates were preserved. Trade and access and/or control of international exchange networks were important sources of wealth and power then. And Middle Egypt appears as a crossroads of diverse populations, as a hub of political and economic power, as a crucial node of exchanges through the Nile Valley, and as a power center whose rulers provided support to the monarchy in exchange of local autonomy and considerable political influence at the Court. In the new conditions of early second millennium, potentates from Middle Egypt succeeded in occupying a unique advantageous position, not matched elsewhere in Egypt, because of the concentration of wealth, trade routes, new technologies, political power, and autonomy in the territories they ruled.  相似文献   
23.
24.
The paper presents the analysis of organic and mineral sediments filling the depression, which developed over the landslide located at the slope (767–773 m a.s.l.) of Lubań ridge decscending to the Ochotnica river valley in the Polish Flysch Carpathians. The landslide formed in an early stage of the Subatlantic Phase (2490 ± 35 BP). The top of peat is dated at 1360 ± 50 years BP and is covered by 72 cm of clayey silts with some sandy intercalations, which indicate slopewash after deforestation. The pollen of ruderal plants and Cerealia (undiff.) reflect agricultural activity in the surroundings. The fragments of charcoal indicate the age of the forest clearance to the first half of the 17th century. The late forest clearance at the elevated north exposed slopes followed 200–300 years later in relation to the foundation of the village at the valley floor.  相似文献   
25.
26.
The place of propaganda in a democratic society has been discussed long before the age of fake news, as the heated debate on this issue that took place in the UK and other democracies from around 1914 to 1950 clearly shows. Drawing upon a variety of published and archival sources, the article examines the changing views of British political elites, intellectuals, publicity experts and the public on the proper role of government in the public sphere, while discussing their influence on government policies and exploring the light they shed on British—and, more broadly, liberal democratic—culture and identity.  相似文献   
27.
28.
    
In this paper, we present an analysis of the exploitation of medium‐sized deer in the lower Paraná wetland by pre‐Columbian hunter‐gatherers. To achieve this goal, we developed an osteometric frame of reference for the proper identification of hunted medium‐sized deer, and the sex and age of captured individuals. An analysis of 13 archaeofaunal assemblages showed that Ozotoceros bezoarticus (“pampas deer”) was the medium‐sized deer that was hunted with exclusivity. The presence of Mazama gouazoubira (“brown brocket deer”; “gray brocket deer”), which could have been another potentially hunted medium‐sized deer, is absent from the record, although this area is indicated as being its southernmost distribution range in South America. These results restrict the distribution of this species to a more northern sector of this large wetland. The hunted individuals of O. bezoarticus are all older than 2 years of age, and preferentially males, although some methodological bias could be influencing these results. Issues related to sex‐age selectivity in capturing these animals are discussed according to the development of conservation strategies for local resources.  相似文献   
29.
30.
    
In the great civilisations of the past, shapeshifting promised a restoration of order in turbulent times in return for the deference of loyal subjects. It was a strategy of the powerful to maintain advantage and could also be used to bind opponents to an undesired form. This study finds its resonance in the contemporary shapeshifting that is the supposed transition from the fossil fuel economy. With reference to the fusion of oil, grain and sugar companies in Brazil's ethanol sector, it explores how amidst economic, environmental and political insecurity these “old villains” of the carbon economy have fused and emerged as the “new heroes” of the green economy. Accounts of dissenting rural subjects, however, unveil the mythical nature of avowed social gains from this shapeshifting. Amidst rural conflict and a successive weakening of regulation, it becomes evident how their petrification, in a metaphorical and increasingly literal sense is required.  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