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   7356篇
  免费   248篇
  2020年   81篇
  2019年   138篇
  2018年   252篇
  2017年   248篇
  2016年   255篇
  2015年   136篇
  2014年   142篇
  2013年   2138篇
  2012年   195篇
  2011年   253篇
  2010年   251篇
  2009年   200篇
  2008年   152篇
  2007年   218篇
  2006年   132篇
  2005年   89篇
  2004年   79篇
  2003年   74篇
  2002年   87篇
  2001年   92篇
  2000年   91篇
  1999年   98篇
  1998年   86篇
  1997年   73篇
  1996年   84篇
  1995年   73篇
  1994年   63篇
  1993年   62篇
  1992年   59篇
  1991年   61篇
  1990年   40篇
  1989年   69篇
  1988年   59篇
  1987年   72篇
  1986年   66篇
  1985年   76篇
  1984年   76篇
  1983年   75篇
  1982年   54篇
  1981年   74篇
  1980年   85篇
  1979年   77篇
  1978年   60篇
  1977年   73篇
  1976年   64篇
  1975年   59篇
  1974年   42篇
  1973年   45篇
  1972年   46篇
  1969年   44篇
排序方式: 共有7604条查询结果,搜索用时 15 毫秒
91.
92.
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   
93.
94.
95.
Isolation effects on the distributions of plant species in fragmented forests appear to be weak over tens to hundreds of years and strong over geological eras. The 250 km wide, 6.5 millennia old Bass Strait, and other millennium-scale disjunctions in the range of Eucalyptus regnans forests, were used to determine the effects of intermediate periods of isolation on plant species occurrence and composition. Three of six floristic communities were found on both sides of Bass Strait. The residuals from multiple regression models using climatic variables on the latitude vector were not explained by latitude, indicating negligible isolation effects from Bass Strait. However, there was a lesser compositional effect of disjunctions within land masses than between land masses, suggesting some effect of the larger barrier. No species that commonly occurred with E. regnans and were largely confined to wet forest exhibited absences from any region where the climate and soils were within their range. If areas isolated from each other for millennia can maintain their vascular plant biota, the expenditure of conservation funds on creating corridors to connect large areas separated by anthropogenic landscape modification might require more justification than it is currently afforded.  相似文献   
96.
97.
98.
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   
99.
100.
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