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   294篇
  免费   1篇
  国内免费   4篇
安全科学   15篇
废物处理   22篇
环保管理   22篇
综合类   47篇
基础理论   58篇
环境理论   5篇
污染及防治   94篇
评价与监测   17篇
社会与环境   17篇
灾害及防治   2篇
  2023年   3篇
  2022年   3篇
  2021年   7篇
  2020年   7篇
  2019年   13篇
  2018年   7篇
  2017年   5篇
  2016年   19篇
  2015年   5篇
  2014年   12篇
  2013年   18篇
  2012年   14篇
  2011年   19篇
  2010年   12篇
  2009年   11篇
  2008年   7篇
  2007年   19篇
  2006年   12篇
  2005年   18篇
  2004年   9篇
  2003年   17篇
  2002年   9篇
  2001年   7篇
  2000年   2篇
  1999年   3篇
  1998年   7篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1994年   4篇
  1993年   2篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1986年   1篇
  1984年   1篇
  1982年   2篇
  1981年   1篇
  1979年   1篇
  1977年   1篇
  1974年   2篇
  1968年   1篇
  1967年   1篇
  1965年   1篇
  1962年   1篇
  1955年   1篇
  1954年   1篇
排序方式: 共有299条查询结果,搜索用时 15 毫秒
261.
Carbon (C) conservation and sequestration in many developing countries needs to be accompanied by socio-economic improvements. Tree crop plantations can be a potential path for coupling climate change mitigation and economic development by providing C sequestration and supplying wood and non-wood products to meet domestic and international market requirements at the same time. Financial compensation for such plantations could potentially be covered by the Clean Development Mechanism under the United Nations Framework Convention on Climate Change (FCCC) Kyoto Protocol, but its suitability has also been suggested for integration into REDD?+?(reducing emissions from deforestation, forest degradation and enhancement of forest C stocks) currently being negotiated under the United Nations FCCC. We assess the aboveground C sequestration potential of four major plantation crops – cocoa (Theobroma cacao), oil palm (Elaeis guineensis), rubber (Hevea brasiliensis), and orange (Citrus sinesis) – cultivated in the tropics. Measurements were conducted in Ghana and allometric equations were applied to estimate biomass. The largest C potential was found in the rubber plantations (214 tC/ha). Cocoa (65 tC/ha) and orange (76 tC/ha) plantations have a much lower C content, and oil palm (45 tC/ha) has the lowest C potential, assuming that the yield is not used as biofuel. There is considerable C sequestration potential in plantations if they are established on land with modest C content such as degraded forest or agricultural land, and not on land with old-growth forest. We also show that simple C assessment methods can give reliable results, which makes it easier for developing countries to partake in REDD?+ or other payment schemes.  相似文献   
262.

This paper analyses the outcome of an actor game aimed at finding ways to institutionalise farmer co-operation in a water catchment threatened by eutrophication from heavy use of fertilisers. Although offered several advantageous options for collective action, acting farmers stuck to their preference for individual management in spite of very draconian measures from central authorities. Theories on collective action developed by Mancur Olson and Elinor Ostrom cover some ground in explaining this puzzling outcome, as do Fritz Scharpf's models of games played out under the 'shadow of hierarchy'. However, the most decisive factor for the farmers' choice of strategy seems to stand Mancur Olson's theory on its head, and adds to the importance of trust and reciprocity emphasised by Elinor Ostrom. Because the farmers knew each other well, and because of the transparency of farmers' action in the geographically limited catchment, they turned down options of co-operation; too few farmers were considered trustworthy enough to make it worthwhile to engage in collective action. Theories of 'collective memories of the history of play' in an area or on an issue should thus be given more concern in future efforts to bring about collective action towards common pool resources. Este documento analiza el resultado de juego de actor dirigido a encontrar formas de institucionalizar la cooperación entre agricultores en la captación de agua amenazada por eutroficación de fuerte uso de fertilizantes. Aunque ofrecieron varias opciones ventajosas para la acción colectiva, los agricultores participantes se quedan apegados a sus preferencias de manejo individual a pesar de las medidas bastante draconianas de las autoridades centrales. Las teorias de acción colectiva desarrolladas por Mancur Olson y Elinor Ostrom cubren algún terreno en explicar este curioso resultado, al igual que los modelos de juego de Fritz Scharpf jugados bajo la "sombra de jerarquia". Sin embargo, el factor mas decisivo para la estrategia de decisión de los agricultores parece poner la teoria de Mancur Olson de revéz y se suma a la importancia de la confianza y reciprocidad enfatizada por Elinor Ostrom. Debido a que los agricultores se conocian bien y a la transparencia de la accion de agricultores en la captacion limitada geograficamente, ellos rechazaron opciones de cooperación; muy pocos agricultores fueron considerados de suficiente confianza para que merecieran participar en acción colectiva. Las teorias de "memorias colectivas de la historia del juego" en una área o sobre un asunto deben de esta manera estar mostrando mayor interes en esfuerzos futuros para atraer la acción colectiva hacia recursos de fondo común.  相似文献   
263.
The aim of the present study was to estimate spillover effects between the work and the family sphere in a sample of nurses (N = 2058). Hierarchical regression analyses investigated whether shift work schedules were associated with negative or positive spillover, both from family to work and vice versa, controlling for demographic factors, job demands and decision latitude. With daytime work as a reference group, all types of shift work (day and evening shift, night shift only and rotating 3 shift) were associated with higher negative work-to-family spillover. Night work was associated with significantly less negative family-to-work spillover. None of the different shift work schedules were related to any type of positive spillover. The results indicate that working outside of daytime hours is less compatible with workers’ family lives, compared to working ordinary day shifts. On the other hand, working night shifts only was associated with reduced negative family-to-work spillover.  相似文献   
264.
A natural treatment system for the treatment of leachate was studied at Moskogen landfill in southern Sweden. This facility consists of three consecutive ponds and a soil-plant (SP)-system. A test area, receiving water from the third pond with the same hydraulic load as the SP-system, was used for estimation of the latter system. Quality parameters including biochemical oxygen demand, total organic carbon, ammonium, nitrate, orthophosphate, and total suspended solids along the treatment line were determined as well as soluble metals (Cu, Cd, Zn, Cr, Ni, and Pb). In addition a thorough investigation along the treatment line has also been performed concerning volatile organic compounds and semi-volatile organic compounds. Non-polar organic compounds were investigated using gas chromatography-mass spectrometry. Quantification was based on the assumption of equal response for the compounds found in comparison with the chosen marker substances. For polar, water-soluble compounds the measurements were restricted to phenolic compounds using high-performance liquid chromatography. Several different types of organic compounds were found in the raw leachate including aromatics, benzene-sulfonamides, biphenyls, naphthalene, organic phosphates, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, phenols and phthalates. The treatment system efficiently reduced organic pollutants, heavy metals, and nitrogen/phosphorous compounds. Most metals and organic compounds in the leachate were already significantly reduced to a low level in the treatment ponds and ammonium-N was efficiently transformed to nitrate-N in the SP-system.  相似文献   
265.
This paper presents a methodological approach for the study of volatile organic compounds (VOCs) in air, emitted during storage of municipal solid waste in bales. Determination of VOCs was based on sampling with adsorbent tubes followed by automated analysis using on-line work-up with a thermal desorption unit directly connected to a gas chromatograph-mass spectrometer. Using calculation algorithms and multidimensional statistical analysis of large amounts of data collected, the information was compressed and visualized. The approach was applied to initial measurements of emissions of VOCs from 24 bales composed of municipal solid waste, each bale stored in a wooden box. These bales were produced using the two types of baling equipment available, resulting in cylindrical or rectangular bales, with different densities. Hundreds of different VOCs emitted from these bales sorted out into groups with different chemical structure. Differences in VOC concentrations in air were found between wastes stored in cylindrical or rectangular bales. For instance, it was found that the concentration of VOCs (relative to the concentration of toluene), in the first experiment after storing, for cylindrical bales with six layers of LDPE was 115 +/- 10 microg m(-3), while for rectangular bales it was only 64 +/- 8 microg m(-3). The procedure used for data interpretation suggested different degradation mechanisms in different types of bales. The use of multiple data interfaces, multidimensional statistics and automated chemical analysis methods are likely to be more and more common for waste companies and waste research in the near future. This is due to the interdisciplinary nature of the subject that relies heavily on various areas of science and information technology.  相似文献   
266.
The estuary Byfjord (Sweden) is characterized by high primary production, a well developed meiofauna compared to the macrofauna, high epifaunal biomass, a low number of herbivorous copepods and a small fish stock. A simplified energy flow model of the ecosystem of the fjord is given. The energy transfer is approximated to 15%. About one-fourth-300 (metric) tons of carbon — of the annual primary production is suggested to be directly consumed and to produce 5 tons of zooplankton carbon and 40 tons of epifaunal (mainly Mytilus edulis) carbon. About 500 tons of carbon from the detritus pool are probably utilized in animal production. This amount will produce 5 tons of zooplankton carbon, 6 tons of meiofaunal carbon, and 3 tons of carbon from the benthic macrofauna. Production of fish is estimated at 0.3 ton carbon per year. M. edulis seems to be the only food resource in the fjord worth harvesting by man.  相似文献   
267.
Critical load calculations in the Czech part of 'the Black Triangle' show exceedance of critical load in 75% of the forest area. A comparison with forest damage data shows an insignificant tendency toward more forest damage in areas with high exceedance. We conclude that high exceedance of critical load is a probable contributing factor to forest damage in the area.  相似文献   
268.
An investigation of the influence of excess heat discharge from a nuclear power plant on the residual levels of the sDOT and PCB in roach and perch has been made during a period of one year. A seasonal variation of the residual concentrations was observed, with the highest levels during spring and early summer and lower more stable levels in the autumn. Significantly higher levels of the sDDT and PCB was observed in perch from the cooling water recipient as compared to values in perch from the intake area. No significant differences could however be verified for roach. The result stress the importance that, in a monitoring program, a sampling period with stable ecological conditions is selected.  相似文献   
269.
In environmental monitoring, it is important that the monitoring system should emit early warnings when undesired events occur. These events may be sudden or of a more subtle nature. In the design of such monitoring systems, a proper balance between cost and risk must be achieved. There are 2 classic types of risk connected with early warning systems, namely the risk of not detecting significant changes and the risk of false alarms. The purpose of this paper is to describe a method for comparing the performance of different monitoring systems, considering the classic types of risk and cost. The method is applied to the monitoring of the lichen cover as a test case. The expected utility has been used as a measure of performance. When estimating the probabilities of the events, spatial microsimulation and Monte-Carlo simulation techniques have been used. The monitoring programs studied are based on satellite images, aerial photos, field samples, and land-cover maps. The major conclusions of this study are that standardized quality measures are extremely useful for evaluating the usability of environmental monitoring methods. In addition, when estimating gains and costs, spatial microsimulation techniques are useful. To improve the method, however, macroconstraints should also be used for aligning the simulation model.  相似文献   
270.
The Swedish coastal zone is a scene of conflicting interests about various goods and services provided by nature. Open-access conditions and the public nature of many services increase the difficulty in resolving these conflicts. "Sustainability" is a vague but widely accepted guideline for finding reasonable trade-offs between different interests. The UN view of sustainable development suggests that coastal zone management should aim at a sustainable ecological, economic, and social-cultural development. Looking closer at economic sustainability, it is observed that economic analyses about whether changes in society imply a gain or a loss should take into account the economic value of the environment. Methods used for making such economic valuation in the context of the Swedish coastal zone are briefly reviewed. It is noted that the property rights context matters for the results of a valuation study. This general background is followed by a concise presentation of the design and results of four valuation studies on Swedish coastal zone issues. One study is on the economic value of an improved bathing water quality in the Stockholm archipelago. The other studies are a travel cost study about the economic value of improved recreational fisheries in the Stockholm archipelago, a replacement cost study on the value of restoring habitats for sea trout, and a choice experiment study on the economic value of improved water quality along the Swedish westcoast.  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