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   602篇
  免费   35篇
  2021年   2篇
  2020年   11篇
  2019年   24篇
  2018年   23篇
  2017年   26篇
  2016年   31篇
  2015年   17篇
  2014年   18篇
  2013年   192篇
  2012年   21篇
  2011年   15篇
  2010年   15篇
  2009年   17篇
  2008年   11篇
  2007年   12篇
  2006年   8篇
  2005年   7篇
  2004年   12篇
  2003年   8篇
  2002年   8篇
  2001年   4篇
  2000年   9篇
  1999年   6篇
  1998年   7篇
  1997年   6篇
  1996年   2篇
  1995年   9篇
  1994年   4篇
  1993年   5篇
  1991年   6篇
  1990年   2篇
  1989年   5篇
  1988年   2篇
  1986年   4篇
  1985年   7篇
  1984年   8篇
  1983年   6篇
  1982年   8篇
  1981年   4篇
  1980年   10篇
  1979年   4篇
  1978年   7篇
  1977年   3篇
  1976年   5篇
  1975年   5篇
  1973年   3篇
  1972年   2篇
  1971年   2篇
  1969年   4篇
  1948年   2篇
排序方式: 共有637条查询结果,搜索用时 15 毫秒
11.
Book reviews     
City and Village in Iran: Settlement and Economy in the Kirman Basin. By Paul W. English. Madison, Wisc.: The University of Wisconsin Press, 1966. 204 pp. $6.75.

The Conflict of Traditionalism and Modernism in the Muslim Middle East. Edited with an Introduction by Carl Leiden. Austin: The University of Texas, 1966. 160 pp. $4.95.  相似文献   

12.
13.
14.
15.
The need for experiments to study physical aspects of craft of the past is stated, as well as the necessity for them to have clear aims and to follow the established principles of scientific enquiry. These principles are discussed in this joint paper by ten maritime archaeologists and others, together with methods and some points of management critical to their application in this field.  相似文献   
16.
17.
We review evidence from human biology—paleopathological and isotopic paleodietary studies on ancient Maya skeletons—to assess the validity of ecological models of the Classic Maya collapse, in which elevated disease and deteriorating diet are commonly assumed. To be upheld, the health arguments of ecological models require that the Maya disease burden (1) was greater than that for many other societies and (2) increased over the span of occupation. The dietary argument requires (1) consistent change in diet from Preclassic and Early Classic Periods to the Terminal Classic and (2) increasing social divergence in diet. A correlation between diet and disease is necessary to link these arguments. Neither pathology nor isotopic data consistently support these criteria. Instead, it appears that local environmental and political factors created diversity in both disease burden and diet. In view of the human biological data, we are skeptical of ecological models as generalized explanations for the abandonment of Classic Maya sites in the southern lowlands.  相似文献   
18.
Farmer adaptation to climatic variability is explored via an analysis of corn hybrid selection in southern Ontario. Corn hybrid varieties are available for a wide range of conditions, including accumulated heat, measured as Corn Heat Units (chus). Hybrids with higher chu ratings generally have higher yields, so long as there is sufficient heat for them to mature. Farmers choose their hybrid varieties prior to the growing season, in the face of uncertainty about the chus that will accumulate at their location. Farmers in the sample counties showed a consistent tendency to adjust their hybrid selection on the basis of the previous year's growing conditions. After the high chu year of 1991, farmers chose significantly more longer-maturing and potentially higher-yielding, but riskier varieties. After the lower chu years of 1992 and 1993, farmers' hybrid selections became markedly more conservative. L'étude de I'adaptation des fermiers aux changements climatiques se fait par une analyse de /'hybridation du maïs au sud de l'Ontario. Les variétés de maïs hybrides conviennent à différentes conditions climatiques in-cluant la chaleur accumulée, mesurée en Unitées de Chaleur de Maïs (ucms). Les hybrides ayant une valeur ucm plus élevée donnent généralement un rendement plus élevéà condition qu'ils bénéficient d'assez de chaleur pour mûrir. Les fermiers des comtés sélectionnés ont démontré une tendance persistante à baser leurs sélections d'hybrides en fonction des conditions de crois-sance de I'année précédente. Depuis 1991, année ayant connu un taux élevé d'UCM, les fermiers ont opté pour un type d'hybride à croissance prolongée, au potentiel de rendement plus élevé mats également plus risqué. Les années 1992 et 1993 ayant connu un niveau ucm moins élevé, les fermiers ont alors sélectionné des hybrides plus traditionnels.  相似文献   
19.
The sophistication of regional economic models has been demonstrated in numerous ways, most recently in the form of linking several modeling systems or in the expansion in the number of equations that can be manipulated successfully to produce impact analyses or forecasts. In this paper, an alternative perspective is employed. What do regional macro-level forecasts indicate about the process of structural change? A new methodology is illustrated that enables analysts to make forecasts of detailed structural change in the interindustry relations in an economy. Using a regional econometric input-output model developed for the Chicago metropolitan region, derived input-output tables are extracted for the period 1975–2016. These tables are then analyzed to determine the forecasted direction of structural changes for the region. The innovation illustrated here is based on a model that exploits the general equilibrium spirit of computable general equilibrium models through the adjustment of input coefficients to clear markets.  相似文献   
20.
This paper summarizes results of a research project funded by the Overseas Development Administration of the UK Government. Its aims were to explore the nature and extent of foreign direct investment in Poland, and to assess the extent of integration of such investment with the indigenous economy. The research involved interviews with Polish government ministries, banks, development agencies, inward investors and indigenous firms. It concludes that there are numerous financial and technical obstacles to indigenous business development. The majority of inward investors aim to serve the Polish and other Central and Eastern European markets rather than simply selling cheaply produced products to the West. Moreover, most have already developed significant local sourcing from Polish suppliers.  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