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   4336篇
  免费   175篇
  2020年   62篇
  2019年   68篇
  2018年   104篇
  2017年   114篇
  2016年   109篇
  2015年   98篇
  2014年   91篇
  2013年   1105篇
  2012年   136篇
  2011年   121篇
  2010年   110篇
  2009年   144篇
  2008年   168篇
  2007年   116篇
  2006年   93篇
  2005年   60篇
  2004年   69篇
  2003年   64篇
  2002年   57篇
  2001年   93篇
  2000年   66篇
  1999年   61篇
  1998年   43篇
  1997年   35篇
  1996年   48篇
  1995年   48篇
  1994年   39篇
  1993年   48篇
  1992年   36篇
  1991年   39篇
  1990年   30篇
  1989年   41篇
  1988年   39篇
  1987年   42篇
  1986年   38篇
  1985年   42篇
  1984年   51篇
  1983年   61篇
  1982年   45篇
  1981年   44篇
  1980年   48篇
  1979年   41篇
  1978年   52篇
  1977年   49篇
  1976年   53篇
  1975年   32篇
  1974年   30篇
  1973年   31篇
  1972年   34篇
  1971年   31篇
排序方式: 共有4511条查询结果,搜索用时 15 毫秒
61.
62.
The upper Mersey Valley was glaciated on three occasions during the Pleistocene. The youngest, Rowallan Claciation, probably commenced after 28000 years B.P. The maximum ice limit was attained before 13500 years B.P., and retreat occurred before 10000years B.P. Deposits associated with Rowallan Glaciation are weakly weathered chemically. They overlie moderately weathered deposits that were formed during the Arm Glaciation, which is inferred from relative dating data to have occurred before the Last Interglacial Stage. North of the deposits and ice limits of the Arm Glaciation extremely weathered tills and rhythmites occur. They were formed by ice of the Croesus Glaciation which is inferred to be of Early Pleistocene age or older.  相似文献   
63.
Tin mining, based largely on alluvial tin deposited along the line of the ancestral Ringarooma, began in 1875 and reached a peak in the period 1905-9. Output declined thereafter and, following a brief recovery during the Second World War, had virtually ceased by 1981. Neither the methods, location nor level of production remained constant during the mining era. The widespread use of hydraulic sluicing and the proximity of many mines to the main river were major factors contributing to the high rate of sediment supply, with the Briseis mine at Derby being the dominant source. Based on data from published and unpublished papers, and mine records, the variable nature of that supply was estimated using a procedure which takes account of the effects of storage and changing practices. Many input points supplied material but the overall pattern is one in which downstream reaches made later starts and reached later peaks, suggesting that they will continue to experience the effects of an increased sediment load for some time.  相似文献   
64.
65.
The advent of new techniques of dental ageing has permitted inferences about the age-structures of ancient animal populations on the basis of faunal remains. Unfortunately, inference from archaeological populations of faunal elements to the age-structure of ancient herds is fraught with both sampling problems and logical difficulties. The relationship between a living herd—a dynamic system characterized by growth—and a static archaeological population is more complex than that assumed by current models based on kill-off patterns and survivorship curves. Using a computer simulation, these logical relationships are explored, and the effects of herd growth on the composition of live and death populations are evaluated. By employing the simulation within a deductive framework, constrained by ethnographically derived criteria for reproduction, mortality, and economic viability in the Near East, it is possible to determine whether certain archaeological kill-off patterns could represent viable herding systems. Examples were found to vary widely in terms of both demographic plausibility and economic viability. Some implications for the possible course of ova-caprine domestication in the Near East are discussed.  相似文献   
66.
67.
68.
69.
70.
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