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   7246篇
  免费   281篇
  2020年   97篇
  2019年   139篇
  2018年   157篇
  2017年   185篇
  2016年   228篇
  2015年   158篇
  2014年   153篇
  2013年   2092篇
  2012年   208篇
  2011年   220篇
  2010年   246篇
  2009年   218篇
  2008年   195篇
  2007年   197篇
  2006年   191篇
  2005年   101篇
  2004年   92篇
  2003年   90篇
  2002年   97篇
  2001年   110篇
  2000年   78篇
  1999年   95篇
  1998年   63篇
  1997年   56篇
  1996年   70篇
  1995年   73篇
  1994年   72篇
  1993年   80篇
  1992年   71篇
  1991年   59篇
  1990年   52篇
  1989年   66篇
  1988年   56篇
  1987年   65篇
  1986年   65篇
  1985年   76篇
  1984年   66篇
  1983年   94篇
  1982年   70篇
  1981年   72篇
  1980年   68篇
  1979年   67篇
  1978年   71篇
  1977年   63篇
  1976年   73篇
  1975年   67篇
  1974年   53篇
  1973年   54篇
  1972年   55篇
  1970年   44篇
排序方式: 共有7527条查询结果,搜索用时 31 毫秒
991.
992.
993.
994.
995.
This paper investigates evidence for subsistence and settlement activities in the Levantine Middle Epipalaeolithic through the application of stable isotope analysis to human and non-human remains from the site of 'Uyun al-Hammam, northern Jordan. In general, bone from the site suffers a high degree of diagenesis and collagen could not be extracted for analysis here. Carbon and oxygen isotopic values from human tooth enamel samples were variable, but within expected values for the Middle Epipalaeolithic, whereas animal carbon and oxygen isotopic values varied widely, most likely due to hydrological and climatological factors. Carbon and isotopic values for the human samples indicated a predominantly C3 plant dietary input, while animal samples appeared to have varying amounts of C4 inputs into their diet. This is the first isotopic analysis conducted on material from the Middle Epipalaeolithic of the southern Levant and, as such, even results constrained by temporal and climatological variants within the region contribute to the overall knowledge of settlement and subsistence strategies during this cultural period.  相似文献   
996.
A landscape-scale conception of the circa 1688–1715 CE Seneca occupation at the White Springs Site (NYSM 1952; RMSC Plp-018), located in Geneva, NY, is important for understanding their built environment during a period of residential upheaval. This paper reports on approximately five hectares of high-resolution, multi-instrument archaeogeophysical surveys. These surveys allowed engagement with layered, temporal contexts and the gathering of otherwise inaccessible information. In combination with excavation, surface survey, and historic research, archaeogeophysical techniques provided expanded access to the site, a settlement size estimate of 1.42–2.75 ha, and tentative evidence for a palisade at the White Springs Site. The interplay between archaeogeophysics and other techniques was critical to this undertaking.  相似文献   
997.
Results of analyses of the photoperiod response gene (PPD-H1) and simple sequence repeats (SSRs) in modern landraces of cultivated barley were used as evidence for the mechanism of agricultural spread in Neolithic Europe. In particular, we explored the usefulness of considering adaptive genes as indicators of past selective pressures acting on crops, during their spread through Europe. In some areas, such as the Alpine region, Britain and Scandinavia, we have evidence to suggest that the adaptation of crops to certain climatic conditions may have contributed to the timing of agricultural spread. At the northern fringes of Europe, and in higher altitude locations in central Europe, the introduction of more suitably adapted cereals may have facilitated successful agriculture to trigger agricultural expansion. This research opens up the possibility of investigating other genetic adaptations to climate, which would permit a fuller evaluation of the relative contributions of climate/crop and forager/farmer interactions in the process of agricultural spread.  相似文献   
998.
The archaeological transition from Clovis to Folsom and Midland in the North American Great Plains coincides with the end of the Pleistocene and onset of the Younger Dryas. Comparisons exploring the adaptive changes that took place during this period frequently employ regional-scale approaches. The focus on regional-scale analyses largely results from the dearth of sites repeatedly visited by multiple early Paleoindian groups. However, regional-scale comparisons have the potential to overlook smaller-scale differences. The Debra L. Friedkin site, Texas offers an opportunity to study Midland, Folsom, and Clovis technology and site-use at a single site. This paper presents the context and chronology of the Midland, Folsom, and Clovis assemblages and a site-scale analysis of lithics from the Friedkin site. It is argued that point production and late-stage reduction were primary activities, and the use of bifacial cores for flake tools was important throughout these occupation periods. Site use at Friedkin differs from early Paleoindian occupation at the nearby Gault site and expands our understanding of settlement and technological organization in the region.  相似文献   
999.
Excavations at Cladh Hallan, a Bronze Age-Iron Age settlement on South Uist in the Outer Hebrides off the west coast of Scotland, revealed the skeletons of two adults, a sub-adult and a child buried beneath the foundations of three roundhouses. Osteological and isotopic evidence has shown that the male adult skeleton is a composite made up of parts of at least three different individuals. To test the hypothesis that the female skeleton was also a composite we examined ancient DNA from four of its components: the skull, mandible, right humerus and right femur. Seven polymerase chain reactions (PCRs) were attempted, these covering positions 15,996–16,420, 16–132 and 232–368 of the mitochondrial DNA hypervariable I and II regions. Three PCRs were successful for each sample and a total of 55 sequences were obtained from the cloned products. After exclusion of possible contaminating sequences, the remaining 34 were compared. It was concluded that the mandible, humerus and femur come from different individuals. Insufficient data were obtained to draw conclusions regarding the origin of the skull. The presence of two composite skeletons at Cladh Hallan indicates that the merging of identities may have been a deliberate act, perhaps designed to amalgamate different ancestries into a single lineage.  相似文献   
1000.
The stability characteristics of 16th century ships are not known with certainty, but safety issues related to floatability, stability and overloading were a cause of concern at the time. The aim of the paper is to advance knowledge in this field by developing a set of loading conditions for a typical Portuguese ship of this epoch, for both the voyage from Lisbon to India and the return voyage. This allows testing the reconstruction of the presumable Nossa Senhora dos Mártires as well as to use this reconstruction to bring a better understanding of safety and loading issues on the Portuguese East India route. Given the uncertainties about the loading conditions, several hypotheses are tested, varying the amount of ballast, the degree of overloading and the distribution of weights on board, and allowing the development of a range of plausible loading arrangements. The stability of the ship is then assessed using modern tools to develop the limit KG curve for compliance with a modern stability criterion applicable to large sailing vessels. The case study ship is a plausible reconstruction based on the analysis of nautical archaeological remains, contemporary documents and the use of modern naval architecture methods.  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