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   41866篇
  免费   1643篇
  2020年   530篇
  2019年   823篇
  2018年   929篇
  2017年   1134篇
  2016年   1238篇
  2015年   938篇
  2014年   911篇
  2013年   14084篇
  2012年   1058篇
  2011年   1086篇
  2010年   1095篇
  2009年   1076篇
  2008年   1021篇
  2007年   919篇
  2006年   827篇
  2005年   579篇
  2004年   574篇
  2003年   534篇
  2002年   510篇
  2001年   515篇
  2000年   462篇
  1999年   534篇
  1998年   467篇
  1997年   420篇
  1996年   402篇
  1995年   418篇
  1994年   364篇
  1993年   416篇
  1992年   392篇
  1991年   297篇
  1990年   295篇
  1989年   306篇
  1988年   310篇
  1987年   328篇
  1986年   307篇
  1985年   425篇
  1984年   452篇
  1983年   456篇
  1982年   391篇
  1981年   394篇
  1980年   431篇
  1979年   423篇
  1978年   401篇
  1977年   430篇
  1976年   382篇
  1975年   383篇
  1974年   300篇
  1973年   270篇
  1972年   248篇
  1970年   225篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
221.
222.
223.
224.
225.
Discrete-choice theory and logit models are evaluated for their usefulness in analyzing migration patterns in a zonal system. The authors "argue that spatial effects and more specifically the relative location of zones are not taken into account in such analyses. We, therefore, introduce a measure of spatial structure and advocate its usage as a predictor of migration in such models. In an example of intrametropolitan migration in Toronto [Canada], we demonstrate that this variable is not only significant but also it improves the performance of all the other variables with the greatest impact on the distance between zones. In addition, inclusion of this variable improves the overall performance of the model in terms of residuals."  相似文献   
226.
The spatial structuring of “classical” central place systems is the primary concern of this research. Emphasizing the development of such systems from basic spatial relations between centers and hinterland locations (rather than as a result of an underlying geometry of regions), this paper takes an optimization approach to the siting of central places in a single-good system. The objective function is shown to be one that maximizes both market coverage of demand and market overlap. Access to this objective is given through the natural slack covering model.  相似文献   
227.
Eastern North America in late Pleistocene times was characterized by two major environmental regions: a periglacial tundra or open spruce parkland and an extensive complex boreal/deciduous forest in the unglaciated, lower latitudes. These environments selected for different adaptive strategies on the part of human foraging groups—known archaeologically as Paleoindians. Those in the tundra and tundra-forest region were highly mobile, possibly specialized hunters, exploiting caribou; those in the forest were generalists, exploiting a variety of subsistence resources with a less mobile settlement system. There is little evidence in either area for hunting of Pleistocene megafauna. These differences in adaptive strategies are reflected in the record of sites and isolated fluted points scattered throughout the region, as well as aspects of tool technology, function, and patterns of stone use.  相似文献   
228.
The decisions of seventy household members during a residential search for a new home for owner-occupancy were measured in a search simulation game. Their decisions both to inquire about homes during the search, and to select a new home at the termination of the search, were more accurately predicted by a heuristic decision-making model than by a rational model.  相似文献   
229.
230.
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