全文获取类型
收费全文 | 1464篇 |
免费 | 142篇 |
国内免费 | 52篇 |
专业分类
财政金融 | 17篇 |
工业经济 | 21篇 |
计划管理 | 112篇 |
经济学 | 136篇 |
综合类 | 51篇 |
运输经济 | 6篇 |
旅游经济 | 27篇 |
贸易经济 | 51篇 |
农业经济 | 250篇 |
经济概况 | 44篇 |
水利工程 | 943篇 |
出版年
2024年 | 14篇 |
2023年 | 26篇 |
2022年 | 60篇 |
2021年 | 59篇 |
2020年 | 81篇 |
2019年 | 66篇 |
2018年 | 55篇 |
2017年 | 58篇 |
2016年 | 65篇 |
2015年 | 54篇 |
2014年 | 85篇 |
2013年 | 83篇 |
2012年 | 114篇 |
2011年 | 124篇 |
2010年 | 88篇 |
2009年 | 100篇 |
2008年 | 102篇 |
2007年 | 100篇 |
2006年 | 90篇 |
2005年 | 52篇 |
2004年 | 48篇 |
2003年 | 37篇 |
2002年 | 29篇 |
2001年 | 19篇 |
2000年 | 14篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有1658条查询结果,搜索用时 15 毫秒
51.
生态需水量的核算是湿地水文生态恢复的关键步骤。通过分析计算,评估天津滨海新区湿地生态系统各类生态需水的3个特征值:最低生态需水量(即湿地生态系统丧失生态功能的临界需水量)、最适生态需水量(即维持湿地生态功能最佳状态的需水量)、最高生态需水量(即湿地生态系统所能承受的最大水量),得出如下结论:天津滨海地区湿地的生态需水主要包括蒸发蒸散需水量、湿地土壤需水量、补给地下水、湿地生物栖息地需水量4个部分;湿地的最低生态需水量为177.68×106~276.85×106 m3,最适生态需水量539.23×106~807.81×106 m3,最高生态需水量1 206.55×106~1 409.02×106 m3。 相似文献
52.
近一个时期,我国高等学校普遍开始重视办学定位和战略规划,这是好事,但重视不能仅仅停留在口头,更要落实在行动上。那么,不论是口头还是行动之前,都要做好充足的功课。笔者在高校工作多年,关于高校定位和战略规划借此发表自己的拙见,与读者分享,敬请批评指正。 相似文献
53.
Estimation of ecosystem service values is a hot area of research in ecological conservation and economics. However, the costs of these outputs are largely unknown. In this paper, we estimated the opportunity cost of water allocated to afforestation projects through mathematical modeling based on statistical data for all of China to provide support for restoration planning based on a fuller consideration of the true costs. To guide future ecological conservation and environmental policy development, we illustrate a neglected concept (ecosystem service costs) and use this concept to compare the ecological services provided by ecological restoration based on afforestation with those of restoration based on the conservation of natural vegetation using data obtained since 1949 in China. The results showed that afforestation and natural vegetation create annual costs related to use of the available water resources equal to 4800 and 3700 RMB ha−1, respectively, representing a water opportunity cost of 1100 RMB ha−1 for afforestation. This illustrates the rule that “there is no free lunch” for any service, including ecosystem services. Therefore, to support the development of more effective and sustainable environmental restoration policy, it will be necessary to evaluate the associated opportunity costs. 相似文献
54.
North America has few cultural agricultural landscapes, and often commensurately poor governance arrangements for managing change in such settings. This research uses the Acadian dykelands of Nova Scotia, Canada, as an opportunity to explore the social and governance limits to coastal climate adaptation in ‘new world’ cultural agricultural landscapes, as well as inform local decision-making. Approximately half of Nova Scotia’s coastal wetlands were converted to dykeland in the 1600s, lowering local resilience to the increased frequency and storm severity anticipated with climate change. Today, dykelands protect a diversity of public and private interests, meanings and values, yet are controlled by the agricultural sector, which can no longer afford to maintain them all to 2050 climate projections. We report here on a representative online Q-methodology survey of 183 adult Nova Scotians in the spring of 2015. Respondents sorted 34 statements along a normal distribution about whether they prefer dykeland maintenance or wetland restoration, and under what governance arrangements. Four factors were derived: the dominant discourse was local, female and strongly pro-dykeland, indicating the likelihood for local resistance to dykeland removal on for cultural, recreational and farming reasons. The second factor was supportive of wetland restoration for reasons of efficiency, not wetland affinity, but characterized by those in positions of management power. The two minority viewpoints were less informed about dykelands, characteristic of outsiders, and concerned more with governance. More education is needed about the challenges facing dykelands, the benefits of coastal wetlands, and the management options, but this research shows proposals to change landscape should emphasize flood mitigation over cost-saving. Cultural values and status quo bias are clearly barriers to adaptation planning, even when discussing the removal of man-made structures. The factors were surprisingly polarized, suggesting the forced-normal distribution affects the space available to convey nuanced perspectives. Large p-set Q-method of this kind is likely most useful for characterizing the emergent discourses demographically, and understanding their prevalence; the same discourses had emerged within a much smaller pilot study. 相似文献
55.
56.
Coupled Hydrological/Hydraulic Modelling of River Restoration Impacts and Floodplain Hydrodynamics 下载免费PDF全文
H. M. Clilverd J. R. Thompson C. M. Heppell C. D. Sayer J. C. Axmacher 《河流研究与利用》2016,32(9):1927-1948
Channelization and embankment of rivers has led to major ecological degradation of aquatic habitats worldwide. River restoration can be used to restore favourable hydrological conditions for target species or processes. However, the effects of river restoration on hydraulic and hydrological processes are complex and are often difficult to determine because of the long‐term monitoring required before and after restoration works. Our study is based on rarely available, detailed pre‐restoration and post‐restoration hydrological data collected from a wet grassland meadow in Norfolk, UK, and provides important insights into the hydrological effects of river restoration. Groundwater hydrology and climate were monitored from 2007 to 2010. Based on our data, we developed coupled hydrological/hydraulic models of pre‐embankment and post‐embankment conditions using the MIKE‐SHE/MIKE 11 system. Simulated groundwater levels compared well with observed groundwater. Removal of the river embankments resulted in widespread floodplain inundation at high river flows (>1.7 m3 s?1) and frequent localized flooding at the river edge during smaller events (>0.6 m3 s?1). Subsequently, groundwater levels were higher and subsurface storage was greater. The restoration had a moderate effect on flood peak attenuation and improved free drainage to the river. Our results suggest that embankment removal can increase river–floodplain hydrological connectivity to form a more natural wetland ecotone, driven by frequent localized flood disturbance. This has important implications for the planning and management of river restoration projects that aim to enhance floodwater storage, floodplain species composition and biogeochemical cycling of nutrients. © 2016 The Authors. River Research and Applications Published by John Wiley & Sons Ltd. 相似文献
57.
本文在分析永安市开展职业教育工作优势和劣势的基础上,就山区城市如何打造区域职业教育中心提出了合理化建议。 相似文献
58.
With international food price shocks in 2008 and 2011, food security became a political priority in many countries. In addition, some politicians have recently adopted a more nationalistic stance. Against that background, this paper critically investigates the prospects of increased food production within a national context. We use a small, high-income country, Norway, as an empirical case. In 2012, the government set a goal of increasing agricultural food production by 20% by 2030. We ask: 1) How has food production in Norway developed before and after the goal was set? 2) What plans do farmers have, and what do they regard as the main obstacles to increased production? We apply a mixed method combining public statistics, a survey, and interviews. We analyze four production systems: a) milk; b) grass-based meat; c) combined pig and grain; and d) grain. These systems represent around 80% of the domestically consumed food produced on farms in Norway. Since 2000, aggregate food production has had a slight downward trend with periodic fluctuations. Based on a political economy approach, we identify land and labor as the most limiting factors. Capital is less of a hindrance and offers a potential for increased production. Farmers have modest expectations of increased production, though. This outlook resonates with the strong integration of agriculture into the wider economy, at both micro and macro levels, making it challenging to implement new policies and change farm practices on a broad basis. Increases in some specific products, however, are realistic. 相似文献
59.
The forest and landscape restoration (FLR) targets set as part of the Bonn Challenge draw attention to the governance arrangements required to translate national FLR targets into local action. To achieve the targets, actors at multiple levels of the governance scale aim to influence relevant processes on the ecological scale. In this article, we focus on the scale challenges relating to the implementation of Ecuador’s restoration targets, by analysing the implementation of the 2014–2017 National Forest Restoration Plan in the montane Chocó Andino and Bosque Seco landscapes. From 54 semi-structured interviews, a document review, and geographical data analysis, we identified two temporal (i, ii) and three spatial scale challenges (iii, iv, v): i) Political cycles mismatch with FLR timelines; ii) Planning horizons mismatch with FLR timelines; iii) National restoration objectives mismatch with decentralised land use planning realities; iv) The governance level of existing FLR efforts mismatches with the level receiving restoration funds; and v) Tensions exist between the spatial dimensions of biodiversity and water-related restoration efforts. The findings highlight that more attention must be given to scale-sensitive governance to make the process in which national FLR targets are translated into local action more effective. 相似文献
60.
Isabel‐María García‐Snchez Lzaro Rodríguez‐Ariza Beatriz Aibar‐Guzmn Cristina Aibar‐Guzmn 《Business Strategy and the Environment》2020,29(5):2019-2036
Institutional investors show increasing interest in how companies align their corporate social responsibility strategies with the sustainable development goals (SDGs) proposed by the United Nations (UN). The information disclosed in this regard is essential to know and monitor business contribution to the 2030 Agenda. In this paper, we analyze the influence that institutional investors have on the adoption of the disclosure strategy established by UN and the Global Reporting Initiative (GRI)—GRI‐SDG Compass. The results obtained for a sample of 989 international companies, which prepare their sustainability reports following the GRI guidelines, show that ownership by foreign investors, pension funds, and “other” investors boosts the relevance of the information disclosed in relation to the 2030 Agenda. On the contrary, government, financial institutions, and cross holdings have no impact on the information systems developed. 相似文献