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   1263篇
  免费   74篇
  国内免费   176篇
安全科学   123篇
废物处理   22篇
环保管理   265篇
综合类   509篇
基础理论   204篇
环境理论   3篇
污染及防治   149篇
评价与监测   20篇
社会与环境   133篇
灾害及防治   85篇
  2024年   1篇
  2023年   15篇
  2022年   47篇
  2021年   46篇
  2020年   59篇
  2019年   49篇
  2018年   39篇
  2017年   70篇
  2016年   72篇
  2015年   53篇
  2014年   67篇
  2013年   137篇
  2012年   73篇
  2011年   90篇
  2010年   48篇
  2009年   60篇
  2008年   68篇
  2007年   87篇
  2006年   65篇
  2005年   45篇
  2004年   33篇
  2003年   56篇
  2002年   46篇
  2001年   29篇
  2000年   32篇
  1999年   11篇
  1998年   14篇
  1997年   10篇
  1996年   11篇
  1995年   11篇
  1994年   10篇
  1993年   15篇
  1992年   8篇
  1991年   12篇
  1990年   9篇
  1989年   5篇
  1988年   5篇
  1982年   1篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1973年   1篇
排序方式: 共有1513条查询结果,搜索用时 140 毫秒
951.
The number of urban food initiatives in many regions of the world, notably Europe and the USA, has burgeoned in recent years, and analyses of the impacts of these activities on people and environments are the focus of an increasing academic literature. The impacts documented include enhanced food security, cohesive neighbourhoods, sustainability, and food justice. Yet, another literature presents opposing analyses and focuses on exclusionary aspects of projects and their enabling of a continued neo-liberal reduction in state welfare provision. As a result, there has been an impasse in debates over the potential of urban food projects to reduce inequalities. This paper proposes that the benchmark of the UK allotment system provides a means to examine these opposing positions. It uses the conceptual frameworks of diverse economies and the capital assets framework to attain clarity in the analysis of the many kinds of food-related activities seen in (peri-)urban areas. Drawing on empirical work in Plymouth, UK, it focuses on the potential of the different food ventures to reduce inequalities, given certain contingent economic and political factors. It also presents evidence that the allotment movement despite its initially radical roots can be seen as largely apolitical in the present day and has no leverage over allocation of land to allotment sites. Even so, evidence is growing that both allotments and the newer forms of urban food activities contribute to meeting national and city-level policy objectives, with the potential to enhance food justice and reduce inequalities.  相似文献   
952.
In a previous paper (Nahman et al., 2012), the authors estimated the costs of household food waste in South Africa, based on the market value of the wasted food (edible portion only), as well as the costs of disposal to landfill. In this paper, we extend the analysis by assessing the costs of edible food waste throughout the entire food value chain, from agricultural production through to consumption at the household level. First, food waste at each stage of the value chain was quantified in physical units (tonnes) for various food commodity groups. Then, weighted average representative prices (per tonne) were estimated for each commodity group at each stage of the value chain. Finally, prices were multiplied by quantities, and the resulting values were aggregated across the value chain for all commodity groups. In this way, the total cost of food waste across the food value chain in South Africa was estimated at R61.5 billion per annum (approximately US$7.7 billion); equivalent to 2.1% of South Africa’s annual gross domestic product. The bulk of this cost arises from the processing and distribution stages of the fruit and vegetable value chain, as well as the agricultural production and distribution stages of the meat value chain. These results therefore provide an indication of where interventions aimed at reducing food waste should be targeted.  相似文献   
953.
A new series of 1, 3-Benzoxazines were synthesized, characterized (1H NMR and 13C NMR) and evaluated for their pesticidal activity. Six new 3-alkyl-3, 4-dihydro-4-methyl-2H-1, 3-benzoxazines (1-6) were prepared by hydroxymethylation of secondary amines with formaldehyde in 65–68% yields. These compounds were screened for there IGR activity against Spodoptera litura and for antifungal fungal activity in vitro against Sclerotium rolfsii ITCC 6181 by poisoned food technique. Insect Growth Regulatory (IGR) activity against Spodoptera litura showed that compound 3-Nonyl-3,4-dihydro-4-methyl-2H-1,3-benzoxazines was most effective as IGR with larval GI50 of 1.863 μ g/Insect. Compounds 3-Octyl-3,4-dihydro-4-methyl-2H-1,3-benzoxazines and 3-Decyl-3,4-dihydro-4-methyl-2H-1,3-benzoxazines were effective IGRs. Antifungal screening revealed that compound 3-Dodecyl-3, 4-dihydro-4-methyl-2H-1,3-benzoxazines, was highly effective against Sclerotium rolfsii with LC50 value 31.7 mg L?1 comparable with commercial fungicide Hexaconazole (LC50 1.27 mg L?1). Also compounds 3-Nonyl-3, 4-dihydro-4-methyl-2H-1,3-benzoxazines and 3-Decyl-3,4-dihydro-4-methyl-2H-1,3-benzoxazines displayed promising fungitoxicity. The results described in this paper are promising and provides new array of synthetic chemicals to be utilized as pesticides.  相似文献   
954.
Competition between several cladoceran species has been studied with the use of simulation. The results have demonstrated that, in most cases, one or two species survive. Under conditions of the minimum food supply, the most competitive species have the selective advantage. With an increase in food supply, the survival of low-competitive species was observed more often. The mean body size of surviving species increases with an increase in food reproduction.  相似文献   
955.
乡村振兴与新型城镇化耦合协调的动态演进及其驱动机制   总被引:11,自引:0,他引:11  
重构乡村振兴与新型城镇化的指标体系,采用耦合协调度模型、空间马尔可夫链以及地理加权回归模型,分析了2005—2017年中国30个省(市、自治区)乡村振兴与新型城镇化的耦合协调水平、时空分异格局、空间动态演进以及驱动机制。研究发现:(1)乡村振兴与新型城镇化的耦合协调度呈现“东部高、西南低”的分布特征,中级协调区域逐步向中部扩散,高级协调区域数量不断增加;高级协调类型省(市、自治区)中“乡村振兴滞后型”占大多数,初级协调和濒临失调类型省(市、自治区)中“新型城镇化发展滞后型”居多。(2)耦合协调度的动态演进呈现维持原有状态稳定性的特征,较难实现跨越式转移,处于高级协调阶段的省(市、自治区)存在“俱乐部趋同”现象。向上转移的省(市、自治区)主要集中在中部,向下调整的以北方省(市、自治区)居多;耦合协调较高的省(市、自治区)对邻近省(市、自治区)具有正向溢出效应,而耦合协调度低的省(市、自治区)对周围产生负向效应,且这种影响是不对称的。(3)影响乡村振兴与新型城镇化耦合协调度变化的驱动力空间差异显著,表现出层级带状分布的发展态势。政府驱动、投资驱动、人口驱动呈现南北层级带状分布。消费驱动、收入驱动、产业驱动呈现东西层级带状分布。  相似文献   
956.
As nations develop policies for low-carbon transitions, conflicts with existing policies and planning tools are leading to competing demands for land and other resources. This raises fundamental questions over how multiple demands can best be managed. Taking the UK as an empirical example, this paper critiques current policies and practices to explore the interdependencies at the water-energy-food nexus. It considers how current land uses and related policies affect the UK’s resilience to climate change, setting out an agenda for research and practice relevant to stakeholders in land-use management, policy and modelling. Despite recent progress in recognising such nexus challenges, most UK land-related policies and associated science continue to be compartmentalised by both scale and sector and seldom acknowledge nexus interconnections. On a temporal level, the absence of an over-arching strategy leaves inter-generational trade-offs poorly considered. Given the system lock-in and the lengthy policy-making process, it is essential to develop alternative ways of providing dynamic, flexible, practical and scientifically robust decision support for policy-makers. A range of ecosystem services need to be valued and integrated into a resilient land-use strategy, including the introduction of non-monetary, physical-unit constraints on the use of particular services.  相似文献   
957.
The diet of juvenile trout and the state of their food resources in autumn (September–November) were studied in two typical small rivers tributary to Lake Onega (Karelia) in 2003. The relationship between the composition of food objects among benthic and drifting invertebrates and the food spectrum of trout was analyzed. The results show that before freeze-up, despite the disappearance of aerial and terrestrial insects, juveniles trout continue active feeding. However, their feeding priorities change: they begin to take food objects directly from the bottom, as well as from the water surface and within the water column.  相似文献   
958.
Green supply chain management has emerged as an important organizational philosophy to reduce environmental risks. We develop a model of the drivers affecting the implementation of green supply chain management using an Interpretive Structural Modeling (ISM) framework. The various drivers of green supply chain management (GSCM) are identified based on the GSM literature and on consultations with experts in the industry. The model developed is validated on a case study involving a manufacturing firm in southern India.  相似文献   
959.
Abstract

This study demonstrates that the growth of S. typhimurium in Luria Bertani broth supplemented with acetate, propionate, butyrate, or a mixture of the three SCFA, affected cell‐association and the ability to invade cultured HEp‐2 cells. Cell‐association and invasion was determined after growth for 4 h of growth in the presence of the SCFA at pH 6 and 7. The results suggest that the growth rate of the culture may have affected cell‐association and invasion since accompanying the significant decrease in growth rate in the presence of SCFA at pH 6 was a decrease in cell‐association and invasion. However, the results also suggest that the individual SCFA may play a role in modulating cell‐association and the invasion phenotype and the regulation of cell‐association and invasion by the SCFA was dependent on the concentration and the pH of the medium. Although the growth rates were similar for S. typhimurium in the SCFA mixture, butyrate (100 mM) and propionate (50 mM) at pH 6, differences in cell‐association and invasion were observed among these cultures. Also, at pH 7, differences were observed among the SCFA treatments even though the growth rates were similar.  相似文献   
960.
The increasing generation of municipal solid waste (MSW) is a major problem particularly for large urban areas with insufficient landfill capacities and inefficient waste management systems. Several options associated to the supply chain for implementing a MSW management system are available, however to determine the optimal solution several technical, economic, environmental and social aspects must be considered. Therefore, this paper proposes a mathematical programming model for the optimal planning of the supply chain associated to the MSW management system to maximize the economic benefit while accounting for technical and environmental issues. The optimization model simultaneously selects the processing technologies and their location, the distribution of wastes from cities as well as the distribution of products to markets. The problem was formulated as a multi-objective mixed-integer linear programing problem to maximize the profit of the supply chain and the amount of recycled wastes, where the results are showed through Pareto curves that tradeoff economic and environmental aspects. The proposed approach is applied to a case study for the west-central part of Mexico to consider the integration of MSW from several cities to yield useful products. The results show that an integrated utilization of MSW can provide economic, environmental and social benefits.  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