全文获取类型
收费全文 | 10026篇 |
免费 | 363篇 |
出版年
2020年 | 130篇 |
2019年 | 178篇 |
2018年 | 199篇 |
2017年 | 237篇 |
2016年 | 325篇 |
2015年 | 219篇 |
2014年 | 194篇 |
2013年 | 2754篇 |
2012年 | 265篇 |
2011年 | 302篇 |
2010年 | 297篇 |
2009年 | 260篇 |
2008年 | 225篇 |
2007年 | 242篇 |
2006年 | 223篇 |
2005年 | 130篇 |
2004年 | 140篇 |
2003年 | 122篇 |
2002年 | 127篇 |
2001年 | 140篇 |
2000年 | 144篇 |
1999年 | 184篇 |
1998年 | 125篇 |
1997年 | 80篇 |
1996年 | 92篇 |
1995年 | 110篇 |
1994年 | 97篇 |
1993年 | 101篇 |
1992年 | 107篇 |
1991年 | 84篇 |
1990年 | 82篇 |
1989年 | 89篇 |
1988年 | 96篇 |
1987年 | 105篇 |
1986年 | 93篇 |
1985年 | 135篇 |
1984年 | 129篇 |
1983年 | 134篇 |
1982年 | 107篇 |
1981年 | 113篇 |
1980年 | 119篇 |
1979年 | 108篇 |
1978年 | 101篇 |
1977年 | 112篇 |
1976年 | 91篇 |
1975年 | 103篇 |
1974年 | 85篇 |
1973年 | 82篇 |
1972年 | 71篇 |
1971年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
81.
Young JH 《Indiana magazine of history》1992,88(4):303-319
82.
This paper is concerned with the products of a number of Neolithic quarries in highland Britain. It investigates the claim that the scale of axe distribution was partly the result of social factors which resulted in these artefacts gaining an added value in areas remote from their sources. One case study considers the sequence of production in Cumbria, in relation to the tensile strength of the rock quarried in different parts of the region. It shows that these considerations had only a limited influence over the choice of stone source and the scale on which it was worked. A second study compares the tensile strength of the main raw materials used for making non-flint axes with the extent to which these sources were actually exploited. Again there is only a limited relationship between the two, suggesting that social factors may indeed have been important. 相似文献
83.
84.
An attempt has been made to relate steatite artifacts to the source of rock from which they were manufactured, using the distribution patterns of rare earth elements. Radiochemical- and instrumental-neutron activation analyses of Shetland steatites suggest that the use of rare earth elements in artifact provenancing may be unreliable. Concentrations of rare earth elements in many Shetland steatites are too low to be measured reliably by a cost effective method. The relative importance of primary igneous and secondary metasomatic processes in controlling steatite rare earth element geochemistry is discussed and geological arguments against the existence of unique rare earth ‘fingerprints’ for steatite are presented. 相似文献
85.
86.
87.
88.
89.
90.
Digital analysis of Landsat data is applied to up-dating land cover maps for the Goondiwindi district of southern, inland Queensland. The imagery was paired with climax cover maps obtained from land systems reports with analysis conducted separately for each of three climax cover types (open forest, woodland and open woodland). Computer classification using this approach produced readily interpreted and reliable results. This work demonstrates that Landsat can be used in conjunction with existing, land systems derived maps to produce data that combine the advantages of two approaches to environmental survey, the former being based on current land cover/land use and the latter on the original environment and its land use potential. 相似文献