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   2339篇
  免费   54篇
财政金融   359篇
工业经济   134篇
计划管理   331篇
经济学   614篇
综合类   55篇
运输经济   16篇
旅游经济   22篇
贸易经济   392篇
农业经济   161篇
经济概况   308篇
邮电经济   1篇
  2021年   17篇
  2020年   35篇
  2019年   44篇
  2018年   68篇
  2017年   80篇
  2016年   66篇
  2015年   32篇
  2014年   65篇
  2013年   241篇
  2012年   80篇
  2011年   104篇
  2010年   81篇
  2009年   82篇
  2008年   82篇
  2007年   62篇
  2006年   54篇
  2005年   45篇
  2004年   45篇
  2003年   30篇
  2002年   38篇
  2001年   30篇
  2000年   43篇
  1999年   30篇
  1998年   32篇
  1997年   33篇
  1996年   30篇
  1995年   19篇
  1994年   30篇
  1993年   33篇
  1992年   40篇
  1991年   30篇
  1990年   31篇
  1989年   22篇
  1988年   29篇
  1987年   23篇
  1986年   19篇
  1985年   35篇
  1984年   36篇
  1983年   43篇
  1982年   31篇
  1981年   33篇
  1980年   28篇
  1979年   30篇
  1978年   26篇
  1977年   16篇
  1976年   22篇
  1975年   23篇
  1974年   16篇
  1973年   26篇
  1972年   17篇
排序方式: 共有2393条查询结果,搜索用时 0 毫秒
41.
At the European level there is an increasing focus on how freight transport can be moved from trucks on roads to more environmentally friendly modes such as rail and ship. A large proportion of the transport services between OD pairs, however, cannot be substituted since there is only one alternative available. The paper investigates the magnitude of this “structural inelasticity” of modal substitution in freight transport due to a sparser layout of rail and ship-based freight networks compared to road. In the analysis we use a recent Scandinavian freight demand model covering more than 800 zones. We find that the structural inelasticity is very significant - in particular for transportation over less than 500 km. Moreover, the inelasticity varies greatly with commodity groups and between OD pairs, and it depends strongly on the port and rail infrastructure. The results suggest that pure charging instruments (road pricing for trucks) in many regions will have limited mode substitution impacts. However, if combined with structural changes in terms of improved infrastructure for rail and ship, impacts may be greater.  相似文献   
42.
This article assembles the results of three multicountry surveys on variety performance and adoption patterns to measure the impacts of maize research in West and Central Africa from 1981 to 2005, and uses cost data since 1971 to compute social rates of return on public investments in maize research in the region. Adoption of modern varieties increased from less than 5% of the maize area in the 1970s to about 60% in 2005, yielding an aggregate rate of return on research and development (R&D) investment of 43%. The estimated number of people moved out of poverty through adoption of new maize varieties rose gradually in the 1980s to more than one million people per year since the mid 1990s. Over half of these impacts can be attributed to international maize research at IITA and CIMMYT. The article concludes with a discussion of strategic options to enhance the impacts of maize research in the region.  相似文献   
43.
Patterns in property values provide strong signals about the future and sustainability of land use. This paper analyzes the determinants of land value in an Amazonian frontier settlement. We estimate hedonic price functions to identify factors that affect the value of farm properties in the western Brazilian Amazon. Distance to market explains nearly one-third of the variation in farm value, as predicted by the von Thünen model. After controlling for location relative to the central market and for municipality, we find that investment in the farms (as reflected in the stocking rate of pastures and the establishment of home gardens) has the next largest impact on land value. The value per hectare of land is negatively related to total lot size, suggesting that any economies of scale are outweighed by the cost of accessing remote corners of large properties. We do not find that land values are related to available measures of biophysical factors or to historic or current land use. Our results do not identify any premium for forest cover or for land uses considered to be more sustainable than pasture on the property itself. However, farm values are affected by neighboring land cover, specifically, the extent of barren land. Thus, local knowledge of factors contributing to future productivity, as summarized in land values, confirms that soil exhaustion can lead to a general decline in property values, while investments in a property both as a homestead and as a farm can help sustain frontier settlements.  相似文献   
44.
In Sub-Saharan Africa, fish ponds are often an integral part of farming systems but have suffered from a lack of viability and sustainability. The present study aims to understand the strategies used by fish farmers to overcome economic and environmental constraints. In 2008 and 2009, fish farmers were surveyed in Central and Western Cameroon, and the fish production systems were classified by cluster analysis. Four broad types were identified according to the complexity of household operations. The development of extensive systems (large-scale and low-input) in rural areas of central Cameroon is induced mainly by abundant available land. For semi-intensive systems in both regions (small-scale and high-input in the Western Region, large-scale and high-input in peri-urban areas of the Central Region), horizontal integration is not sufficient to make fish production profitable and sustainable. More intensive fish farms tend towards vertical integration, in which farmers establish close links with input suppliers. Main causes of low productivity of semi-intensive systems (1–2?t/ha/yr) are both lack of knowledge of fish farming principles by farmers and lack of technical improvement by extension agents and researchers which need to consider the local complexity of farming systems to develop and intensify fish production. The adaptation of development strategies to socio-economic and environmental contexts is a necessity to hope for an increase in fish pond aquaculture production in Africa.  相似文献   
45.
This article revisits a conventional wisdom that inorganic fertiliser use across sub‐Saharan Africa is too low. This expectation that more farmers should be using inorganic fertiliser, and at higher rates, implies it is profitable to use rates higher than observed if farmers are rational expected profit maximisers. We obtain consistent estimates of the effects of applied nitrogen on rice production. We find the yield response to applied nitrogen to be low in the main rice growing farming system. Farmer behaviour is not inconsistent with expected profitability which is limited by a low yield response to applied fertiliser, high transportation costs, and low selling prices for rice in rural areas. In particular, we do not find any farmers for whom applied nitrogen is profitable that are not using fertiliser in the study sample for each of our survey years (2010 and 2012).  相似文献   
46.
This study examines both accruals based earnings management (AEM) and real earnings management (REM) in U.S. agribusinesses. In particular, the focus is on agribusinesses that report low earnings quality, defined as firms with extreme level of accruals compared to their peers. The cross‐sectional modified Jones model (Jones 1991; Dechow et al 1995) is used to test for AEM. To capture REM practices, we implement the discretionary expenses model by Roychowdhury (2006). We find evidence of AEM and find no evidence of REM in agribusinesses. In addition, our results show that managers might be managing earnings through specific accruals doubtful accounts receivable provisions and special items.  相似文献   
47.
In 2015, the Federal Communications Commission (FCC) imposed common carriage regulation—so-called Title II requirements—on previously unregulated broadband Internet service providers. The regime shift was premised on the FCC’s findings that such rules had demonstrably yielded economic gains. This paper evaluates the FCC’s empirical arguments and finds them uncompelling. Adjustments for inflation or general economic trends eliminate the effects cited by the FCC. Moreover, contrary to the Commission’s assessment, mobile services and broadband markets have shown notable growth in response to deregulatory events that reduce Title II requirements.  相似文献   
48.
49.
We identify the impact of emergency food aid programs after the 2002 drought in rural Ethiopia on future welfare. Based on a difference-in-differences matching estimator, participation in food-for-work increases growth in total consumption and food consumption eighteen months after the drought. Separately, receiving free food raises growth in food consumption, but, surprisingly, negatively impacts food security. Food-for-work benefited households in the middle and upper tail of the consumption distribution, while the better-targeted free food program benefited the poorest. Evidence suggests these impacts demonstrate accumulated and persistent effects of food aid received in the first twelve months after the drought.  相似文献   
50.
Achieving the Sustainable Development Goals (SDGs) in African agriculture requires a better understanding why high levels of poverty and resource degradation persist in African agriculture despite decades of policy interventions and development projects. In this article, we hypothesize that policies need to account for the key features of the semi‐subsistence crop–livestock systems (CLS) in the region to become effective. The semi‐subsistence CLS are characterized by a high degree of biophysical and economic heterogeneity and a complex, diversified production system involving a combination of subsistence and cash crops with livestock. We investigated the potential for interventions proposed by the Government of Kenya to meet the SDGs by 2030. The analysis uses an integrated modeling approach designed to deal with the key features of these systems. A strategy that stimulates rural development, increases farm size to a sustainable level, and reduces distortions and inefficiencies in input and output markets could lead to a sustainable development pathway and achieve the SDGs for rural households dependent on CLS.  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