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   443篇
  免费   28篇
  2023年   8篇
  2022年   2篇
  2020年   9篇
  2019年   20篇
  2018年   28篇
  2017年   34篇
  2016年   25篇
  2015年   17篇
  2014年   25篇
  2013年   99篇
  2012年   18篇
  2011年   22篇
  2010年   15篇
  2009年   12篇
  2008年   8篇
  2006年   8篇
  2005年   5篇
  2004年   5篇
  2003年   3篇
  2002年   10篇
  2001年   4篇
  2000年   3篇
  1999年   9篇
  1998年   4篇
  1997年   6篇
  1996年   3篇
  1995年   4篇
  1994年   5篇
  1993年   2篇
  1990年   2篇
  1988年   4篇
  1987年   2篇
  1986年   2篇
  1985年   4篇
  1984年   3篇
  1983年   3篇
  1982年   3篇
  1981年   3篇
  1980年   3篇
  1977年   5篇
  1976年   4篇
  1975年   4篇
  1974年   1篇
  1972年   1篇
  1968年   1篇
  1966年   1篇
  1964年   2篇
  1960年   3篇
  1959年   1篇
  1950年   1篇
排序方式: 共有471条查询结果,搜索用时 15 毫秒
441.
In the context of an archaeological survey of the southern Argolid, Greece, studies have been carried out to elucidate the evolution of the landscape since its earliest known human occupation about 50,000 years ago. One of these studies was a detailed geological mapping of the late Quaternary alluvium and soils in the area. Dated by means of thorium-uranium disequilibria, archaeological finds, and historical information, seven periods of alluviation were identified, each of short duration relative to long intervening periods of stability and soil formation. The three earliest alluvial phases, falling before and during the last glacial interval, range from about 330,000 to 32,000 years in age. No alluviation accompanied the last glacial maximum around 20,000 years ago. In fact, a stable landscape persisted until about 4500 years ago, when debris flows and widespread aggradation in the valleys resulted from major slope destabilization and soil erosion, probably as a result of extensive land clearance in the Early Bronze Age. A subsequent stable period lasted through the many upheavals of the later Bronze Age, the Dark Ages, and the early historical period. It came to an end with a brief phase of alluviation between about 300 and 50 BC. Stability returned through the late Roman period, notwithstanding considerable expansion of the settled area. Another period of destabilization, this one marked by debris flows and hence major soil erosion, is poorly fixed in time, but probably coincides with expanded maquis clearance accompanying the resettlement of the area around AD 1000. Subsequent events of soil erosion and aggradation vary in nature and timing from one drainage to the next and, in some areas, continue today.Nature and chronology of the soil forming and alluviation events show that simple correlations with climatic events do not suffice to explain them. For the latter ones, past about 2500 BC, human activity seems to be the dominant cause, but once again the relation between cause and effect is not straightforward. Land clearing, or neglect of soil conservation efforts during economic downturns, appear to have a more devastating effect upon the landscape than do intensive land use or total land abandonment.  相似文献   
442.
443.
Interspecific variation in the equid lineage is limited when compared with other large mammal lineages, while a considerable amount of intraspecific ecomorphological variation occurs. This has led to considerable debate regarding the taxonomic status of palaeontological and archaeological equid remains. The possible confounding impact of sex and age variation on analyses of archaeological equid remains has so far remained untested. This could be especially problematic when it is unknown whether an assemblage contains more than one equid species, breed or hybrid. Here, sex and age variation in modern equid species is examined and compared to variation in Pleistocene equid assemblages from northwest Europe. Sex variation in the longbones of modern equid species was found to be lower than variation over time. Similarly, age variation in dental elements of the same species is predominantly lower than diachronic variation, although caution needs to be taken when an archaeological assemblages consists mostly of elements at a similar wear stage. To assess whether late Middle Pleistocene caballoid horse fossils should be assigned to multiple species or be considered to form a monospecific group, the coefficients of variation for measurements on fossil horse remains were compared with those for modern equid specimens. Results indicate that the fossil assemblages are similarly variable to samples of modern material. Taken as a whole, the late Middle Pleistocene caballoid horse lineage is equally variable to an assemblage of modern ponies of a variety of different breeds. This implies that the variation observed between samples dating from different parts of the Middle Pleistocene can be characterised as intraspecific variation within a single species reflecting ecomorphological adaptations to the changeable Pleistocene climate. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   
444.
445.
Urban creative clusters are currently a major focus of attention, as their prominent position in both local political and academic circles makes evident. Many authors stress the importance of spatial concentration for creative industries. However, only a few studies have focused on the individual entrepreneur. As a result, empirical evidence of the meaning of urban place as a site for social networks and a space for inspiration is still scarce. This is of some consequence as entrepreneurs provide a crucial link between creative activities and economic change and development. This study contributes to the existing literature by investigating how different creative entrepreneurs choose and evaluate their location. Using qualitative interviews with entrepreneurs in two creative clusters in the Berlin neighbourhoods Prenzlauer Berg and Kreuzberg, this article shows the significance of the look and feel of specific places and explains how and for whom local networks are important.  相似文献   
446.
447.
448.
449.
450.
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