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   4081篇
  免费   227篇
  2020年   54篇
  2019年   96篇
  2018年   139篇
  2017年   133篇
  2016年   182篇
  2015年   111篇
  2014年   104篇
  2013年   973篇
  2012年   116篇
  2011年   152篇
  2010年   122篇
  2009年   131篇
  2008年   108篇
  2007年   108篇
  2006年   101篇
  2005年   59篇
  2004年   61篇
  2003年   67篇
  2002年   62篇
  2001年   81篇
  2000年   64篇
  1999年   66篇
  1998年   62篇
  1997年   53篇
  1996年   43篇
  1995年   37篇
  1994年   26篇
  1993年   56篇
  1992年   39篇
  1991年   26篇
  1990年   41篇
  1989年   40篇
  1988年   37篇
  1987年   43篇
  1986年   31篇
  1985年   41篇
  1984年   30篇
  1983年   56篇
  1982年   44篇
  1981年   36篇
  1980年   40篇
  1979年   33篇
  1978年   39篇
  1977年   42篇
  1976年   33篇
  1975年   34篇
  1974年   29篇
  1973年   26篇
  1972年   30篇
  1971年   25篇
排序方式: 共有4308条查询结果,搜索用时 15 毫秒
41.
42.
Nested multinomial logit models are used to investigate migration behavior during the 1971–74 period for a large sample of the population of Ecuador. The nested form of the model makes it possible to test hypotheses about the importance of destination characteristics in conditioning the odds for out-migration. Our empirical results indicate that the odds for migration from each origin are conditioned by the expected utilities of the available set of destinations, as well as characteristics of the origins and the personal characteristics of potential migrants. The association between destination characteristics and the frequency of out-migration allows the total volumes of migration to be adjusted to interregional differences in place-specific utilities.  相似文献   
43.
A new and recursive algorithm for determining proximal polygons is based on quadtree concepts. The algorithm can use any distance metric, and produces a quadtree of the image of the proximal polygons. This can be converted to vector form, or be incorporated directly into a quadtree-based geographic information system, in order to solve a number of closest-point problems. The algorithm can also produce the Delaunay triangulation, which is the dual of the proximal polygons. Empirically, the running time of the algorithm is proportional to the number of centers raised to the 1.6 power.  相似文献   
44.
45.
The beginning of the Late Bronze Age in the Aegean has usually been thought to coincide with the start of the Eighteenth Dynasty in Egypt, and radiocarbon dates (which consistently suggest an earlier chronology) have been rejected by Aegean specialists because they do not agree with this view. Evidence from pottery is used to re-examine the links between the Aegean and Egypt, with the conclusion that the Aegean Late Bronze Age began during the Hyksos period.  相似文献   
46.
47.
In September 1968, one of the authors (P. Mayes), having been appointed Head of Mission by the British Ministry of Overseas Development to act as advisor to the Jamaica National Trust Commission, made recommendations which formed the basis for the establishment of the Port Royal Project. The Project is concerned with the excavation, conservation and presentation of 17th century Port Royal, which was founded in 1655 and destroyed by an earthquake in 1692 (see Fig. 1). For the purposes of archaeology the area was divided into three: the Archaeological-Historical Reserve, encompassing the protected underwater area and lands currently occupied by government facilities at the west end of Port Royal; the area in the centre of Port Royal which is protected archaeologically by modern housing and the area at the east end of Port Royal in which it was proposed that commercial expansion should be allowed on land held on lease from the Jamaican government. Work began early in 1969 in a section of this last area, which was threatened, at that time, by the construction of an hotel. This area was part of the shoal water section of sunken Port Royal (see below and Fig. 2). Since that date excavation headquarters and conservation laboratories have been established in the old naval hospital and the construction of a major museum, the first phase of the presentation programme, has begun.  相似文献   
48.
This paper is a statistical and geological study of the results of analysis of flint from British and West European flint mines, carried out by emission and atomic absorption spectroscopy. Groups of flint specimens were studied from each geographically separate flint mining area. Flints were analysed for a group of easily measured trace elements shown by previous work to be generally present. The ratios between the trace elements form a consistent pattern for each flint mine and statistically valid differences of pattern can be recognized between different flint mines. A geological investigation shows that the measured trace elements may be derived from clay minerals and explains geographical and statistical variation in the composition of flint in terms of its mode of origin in the chalk. An advanced statistical technique allows individual flint specimens of unknown origin to be attributed by their composition to one or other of the identified flint sources. The archaeological implications of this study are discussed.  相似文献   
49.
50.
A method is described for the identification of the origin of flint artefacts. The method is based on the variation in the trace element concentrations for different origins. The trace element concentrations were determined by non-destructive neutron activation analysis. The identification was obtained from a pattern recognition analysis.  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