全文获取类型
收费全文 | 5350篇 |
免费 | 213篇 |
出版年
2020年 | 67篇 |
2019年 | 126篇 |
2018年 | 143篇 |
2017年 | 168篇 |
2016年 | 160篇 |
2015年 | 130篇 |
2014年 | 109篇 |
2013年 | 1513篇 |
2012年 | 157篇 |
2011年 | 159篇 |
2010年 | 186篇 |
2009年 | 173篇 |
2008年 | 129篇 |
2007年 | 135篇 |
2006年 | 117篇 |
2005年 | 74篇 |
2004年 | 70篇 |
2003年 | 71篇 |
2002年 | 89篇 |
2001年 | 88篇 |
2000年 | 74篇 |
1999年 | 75篇 |
1998年 | 85篇 |
1997年 | 63篇 |
1996年 | 63篇 |
1995年 | 52篇 |
1994年 | 56篇 |
1993年 | 53篇 |
1992年 | 48篇 |
1991年 | 41篇 |
1990年 | 34篇 |
1989年 | 46篇 |
1988年 | 47篇 |
1987年 | 59篇 |
1986年 | 43篇 |
1985年 | 50篇 |
1984年 | 55篇 |
1983年 | 53篇 |
1982年 | 41篇 |
1981年 | 46篇 |
1980年 | 60篇 |
1979年 | 52篇 |
1978年 | 33篇 |
1977年 | 54篇 |
1976年 | 37篇 |
1975年 | 42篇 |
1974年 | 26篇 |
1972年 | 27篇 |
1970年 | 25篇 |
1969年 | 22篇 |
排序方式: 共有5563条查询结果,搜索用时 31 毫秒
61.
62.
Tervamaki E 《Fennia》1987,165(1):1-88
A systems approach is applied to the study of migration trends in Finland for the period 1971-1981, with particular attention to the period 1971-1978. The results indicate the existence of six permanent migration regions linked by a multilevel system. "The organization of this system varies from one part of the country to another, the most common modes being hierarchical tree flow networks belonging to a nodal system and polar and dendritic networks associated with a highly polarized system. The nodal system mode is seen to be increasing in currency." 相似文献
63.
64.
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
65.
This paper is concerned with the reciprocal relationship between migration and development in Third World settings. Using individual-level data for Venezuela, migration behavior is related to a person's age, educational attainment, gender, and characteristics of his/her place(s) of residence as an out-migrant, in-migrant, or stayer. Place characteristics are in terms of four groups based on employment patterns: the core, regional centers, resource frontiers, and traditional rural areas. Four questions are of concern. First, does development influence migration? All analyses indicate this is so. Second, does migration influence development? Findings are ambiguous in that places experiencing improvement in their mix of human capital lagged in the net number of persons obtained through migration whereas a gain in numbers was accompanied by deterioriation in human capital profiles. Third, was incipient polarization reversal occurring in Venezuela in the late 1960s, early 1970s? This paper departs from the usual approach by addressing this question in terms of human capital attributes instead of population aggregates. On this basis, polarization reversal is in evidence, particularly in regional centers. Finally, this study answers in the affirmative that places with different development characteristics generate migration streams differing in type, magnitude, explanation, and impact. 相似文献
66.
David M. Mark 《Geographical analysis》1987,19(3):264-272
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
67.
68.
Two contexts from the Colombian sites, Yotoco Ferry and Moralba, had been linked by archaeological similarities in pottery style, and dated by association with ware from other sites at circaa.d. 1000. However, radiocarbon dating of those contexts set Moralba at circa 800 b.c. , some 2000 yr older than Yotoco Ferry. Thermoluminescent dating of pottery from Yotoco Ferry dated it at circaa.d. 900, and pottery from Moralba was dated at circaa.d. 870. In addition a metal-smelting pottery crucible, thought to be prehispanic, was studied by thermoluminescence and dated, on the contrary, at less than 120 yr old. 相似文献
69.
70.