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   56篇
  免费   3篇
  2023年   1篇
  2021年   1篇
  2020年   2篇
  2019年   3篇
  2017年   4篇
  2015年   1篇
  2014年   4篇
  2013年   7篇
  2012年   2篇
  2011年   6篇
  2010年   5篇
  2009年   5篇
  2008年   4篇
  2007年   3篇
  2006年   2篇
  2005年   1篇
  2004年   1篇
  2003年   3篇
  2001年   1篇
  1999年   1篇
  1996年   1篇
  1994年   1篇
排序方式: 共有59条查询结果,搜索用时 0 毫秒
21.
22.
The Upper Palaeolithic site of the Abri Pataud (Dordogne, France) has been the subject of numerous14C age determinations which cover the period from 20,400±450 years (OXA-373) to 34,250±675 years (Grn-4507). The racemization ratios of aspartic acid have been determined in 26 fossil bones. The bones are present in two different sedimentary surroundings: levels (fine deposits with numerous artefacts and fossil bones) and “éboulis” (coarse deposits derived from the neighbouring limestone cliff). Racemization ratios for total aspartic acid have a poor correlation with14C ages (respectivelyr2=0·59 and 0·82 for the two environments) but apparent racemization rates are clearly dependent on the type of deposits (levels: K=4·4×10−6year−1; éboulis: K=9×10−6year−1).Racemization ratios of aspartic acid in a high molecular weight protein fraction (>10,000 Da) correlate much better with14C ages (r2=0·999) for the samples from the levels (k=2·1×10−5year−1). From this regression line we estimate ages for two Aurignacian levels: level 6≈29,560 years and level 9≈30,440 years .It is noteworthy that none of the regression lines intercepts the origin. Racemization of aspartic acid appears to occur only after a delay of many thousands of years. This phenomenon could be the result of a coupling between the degradation of proteins and the racemization of amino acids.  相似文献   
23.
24.
25.
26.
Metasequoia glyptostroboides is considered to be a species highly resistant to harmful environmental factors. For this reason it has been introduced to the cities. The climate of Krakow differs from that in its natural range in China. The research was focused on 40-year-old trees, planted in Kraków on fertile alluvial soils with a low level of ground water, in the vicinity of the steelworks. During the period of the highest level of air pollution in the 1970s and 1980s, the radial increment of investigated trees showed an increasing trend. At the end of the 1980s, when the emissions were reduced, a decreasing trend in radial growth was recorded. Throughout the entire period of their life the investi-gated trees have shown high homogeneity of short-term growth reactions. The sensitivity chronology of the trees was characterized by a high representativeness and a strong high-frequency signal. This may indicate that the investigated trees have shown a large sensitivity to climatic factors. The positive effect on the radial growth of Metasequoia had a cold September in the previous year, and also a cold January, April and May in the year of ring formation. Positive impact on the growth of trees had also the high precipitation occurring in April and August, as well as high air humidity in the spring of the year of ring formation. In the period 1974–2011 fifteen signature years were found. The analysis of the climatic conditions in these years confirms the results of the statistical analyses.  相似文献   
27.
ABSTRACT Regional differences in real wages have been shown to be both large and persistent in the United States and the U.K., as well as in the economies of other countries. Empirical evidence suggests that wage differentials adjusted for the cost of living cannot only be explained by the unequal spatial distribution of characteristics determining earnings. Rather, average wage gap decomposition reveals the important contribution made by regional heterogeneity in the price assigned to these characteristics. This paper proposes a method for assessing regional disparities in the entire wage distribution and for decomposing the effect of differences across regions in the endowments and prices of the characteristics. The hypothesis forwarded is that the results from previous studies obtained by comparing average regional wages may be partial and nonrobust. Empirical evidence from a matched employer–employee dataset for Spain confirms marked differences in wage distributions between regions, which do not result from worker and firm characteristics but from the increasing role of regional differences in the return to human capital.  相似文献   
28.
‘Value has always been the reason underlying heritage conservation. It is self‐evident that no society makes an effort to conserve what it does not value.’ 1 1. de la Torre and Mason, Assessing the Values of Cultural Heritage, 3–4. However, assessing the value of a cultural heritage asset as a representative sample of our tangible and intangible heritage for present and future generations is a difficult concept to deal with. It is, therefore, the aim of the researchers to help the conservation decision process by attempting to make an assessment of the values attributed to the cultural heritage assets of one of the most notable heritage sites in Egypt: the Valley of the Kings in Luxor.  相似文献   
29.
30.
In the 1970s, the discoveries of Palaeolithic human remains in the caves of Dar es Soltane 2, El Harhoura 1 and Les Contrebandiers reinforced interest in the sites of the Témara region. These sites, often cited, have been the object of numerous investigations which have produced a major contribution to the prehistory of Morocco. Over the past 15 years, research at two key sites, El Mnasra and El Harhoura 2, have considerably enhanced the available data for this region. Preliminary results obtained from excavations since 2001, allow us to present the palaeoenvironmental framework and describe the technological behaviour of prehistoric groups within a re-evaluated stratigraphic context. The microfaunal and macrofaunal assemblages are analysed according to systematics, taphonomy and palaeoecology. The lithic and bone industries document patterns of raw material acquisition and transformation. Within the context of the history of more than 60 years of research in the region of Témara, this contribution allows us to approach the question of Palaeolithic population on the basis of recent, and for the most part new, data and evidence.  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