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   807篇
  免费   16篇
  国内免费   157篇
安全科学   44篇
废物处理   30篇
环保管理   160篇
综合类   373篇
基础理论   153篇
环境理论   1篇
污染及防治   141篇
评价与监测   38篇
社会与环境   40篇
  2024年   2篇
  2023年   21篇
  2022年   30篇
  2021年   14篇
  2020年   15篇
  2019年   28篇
  2018年   20篇
  2017年   30篇
  2016年   41篇
  2015年   53篇
  2014年   52篇
  2013年   52篇
  2012年   32篇
  2011年   103篇
  2010年   44篇
  2009年   75篇
  2008年   69篇
  2007年   76篇
  2006年   31篇
  2005年   30篇
  2004年   20篇
  2003年   19篇
  2002年   13篇
  2001年   18篇
  2000年   11篇
  1999年   8篇
  1998年   15篇
  1997年   13篇
  1996年   10篇
  1995年   6篇
  1994年   7篇
  1993年   4篇
  1992年   3篇
  1991年   4篇
  1990年   1篇
  1989年   3篇
  1985年   3篇
  1984年   1篇
  1978年   2篇
  1969年   1篇
排序方式: 共有980条查询结果,搜索用时 781 毫秒
81.
/ Costa Rica has recently established a program that provides funds for reforestation and forest protection on private lands, partly through the sale of carbon certificates to industrialized countries. Countries purchasing these carbon offsets hope one day to receive credit against their own commitments to limit emissions of greenhouse gases. Costa Rica has used the proceeds of the sale of carbon offsets to Norway to help finance this forest incentive program, called the Private Forestry Project, which pays thousands of participants to reforest or protect forest on their lands. The Private Forestry Project is accompanied by a monitoring program conducted by Costa Rican forest engineers that seeks to determine net carbon storage accomplished on these lands each year. The Private Forestry Project, which is officially registered as an Activity Implemented Jointly, is a possible model for bundled projects funded by the Clean Development Mechanism (CDM) established by the 1997 Kyoto Protocol to the UN Framework Convention on Climate Change. It also serves as an interesting example for the CDM because it was designed by a developing country host-not by an industrialized country investor. Accordingly, it reflects the particular "sustainable development" objectives of the host country or at least the host planners. Early experience in implementing the Private Forestry Project is evaluated in light of the main objectives of the CDM and its precursor-Activities Implemented Jointly. It is concluded that the project appears to meet the criteria of global cost-effectiveness and financing from non-ODA sources. The sustainable development implications of the project are specific to the region and would not necessarily match the ideals of all investing and developing countries. The project may be seen to achieve additional greenhouse gas abatement when compared against some (although not all) baselines.  相似文献   
82.
Commercial poly(lactide) degradation was studied in an inert solid medium simulating compost conditions, with the aim to achieve a complete carbon balance of the polymer degradation. The mineralisation rate at the end of the test was compared to those obtained for poly(lactide) degradation in compost. It was shown that the mineralisation rate after 45 days of degradation was quite lower in inert solid medium than in compost but the standard deviation of data was enhanced. A protocol for both extraction and quantification of the carbon included in the different degradation by-products was proposed and the carbon balance of the polymer degradation was followed during the test with a satisfactory accuracy. The non-degraded PLA material was recovered during the test, hence the evolution of the glass transition temperature and the molecular weight was followed. A two-step degradation mechanism was highlighted in inert solid medium, showing the fundamental role of abiotic reactions for PLA degradation in compost.  相似文献   
83.
The information presented in this paper is directed to air pollution engineers who are concerned with monitoring Carbon Monoxide. This paper evaluates systems for CO sampling under conditions where the receptor is located at intersections within 40 meters of the road edge. Non-Dispersive Infrared and electrochemical analysis techniques are used in conjunction with continuous recording, continuous bag sampling, and meter readings at 5 second intervals. The relative accuracy of each system is examined and the conditions for which each system is best suited are described.  相似文献   
84.
Abstract

This paper describes the development of apparatus suitable for direct supercritical fluid extraction of organics from water. Results are presented for the extraction of pentachlorophenol present in water at concentrations of the order of 0.1 ppm. The effect of changes in apparatus design and supercritical fluid flow rate on recovery are discussed.  相似文献   
85.
The study concerning carbon dioxide measurements taken during the 1997, 1998 and 1999 summer campaigns at two different altitude stations and biospheric conditions are presented. The higher station (Mt. Cimone, 2165 m a.s.l.) is characterised by 360° free horizon and is located on a rocky mountain while the lower (Ninfa lake, 1550 m a.s.l.) is located inside the red spruce and beech forest. The different behaviour of CO2 at the two mountain stations has been registered. It shows the strong effect of nighttime soil emission and vegetation respiration on CO2 mixing ratio increases and of diurnal vegetative activity on CO2 concentration decreases at the lower measurement site. The baseline character of the higher measurement site has been confirmed by comparison of CO2 diurnal amplitudes recorded at the two stations.  相似文献   
86.
Carbon monoxide (CO) in the surface sea waters is produced predominantly by photochemical processes, oxidized by micro-organisms and outgassed to the atmosphere. to assess carbon monoxide flux from the oceans to the atmosphere, the photochemical production and microbial oxidation of carbon monoxide in the oceanic mixed-layer was investigated during several oeanographic cruises and in the laboratory. the photoproduction rate of carbon monoxide was found to be well correlated to the concentration of dissolved organic carbon (DOC) in coastal and open ocean surface waters. Taking a global average carbon monoxide production rate of 10 ± 2 nmole litre-1 (mg DOC hr)-1 in the surface open ocean water, and 25 ± 7 nmole litre-1 (mg DOC hr)-1 in coastal sea water, at cloud-free summer solar noon, the photochemical production of carbon monoxide in the global oceans is estimated to be at a rate of 1200 ± 200 Tg CO y-1. the microbial carbon monoxide turnover time in the mixed-layer was observed to range from hours in a coastal estuary to 16 days in the Pacific along 1057deg; W in dark incubations. Natural sunlight can largely inhibit the microbial consumption of carbon monoxide in surface water. On a global scale, microbial consumption is responsible for the loss of less than 10% of photochemical produced carbon monoxide in the surface ocean. Field measurements have shown that the net transport of carbon monoxide from the euphotic zone to the underlying deeper ocean water is limited and that the overall life time in surface sea waters is less than 3-4 hours. When combined, these field measurements with the photoproduction and microbial consumption rates obtained, we estimate the oceanic flux to the atmosphere is about 1000 ± 200 Tg CO y-1, which represents the largest single source of atmospheric carbon monoxide.  相似文献   
87.
88.
Fairness is a relative concept with multiple, subjective and competing notions of what it is, how to achieve it, and for which beneficiaries. Fairtrade International's collaborative efforts to develop a standard to certify Fairtrade Carbon Credits (FCCs) brought together multiple stakeholders in a deliberative context. This paper uses Q methodology to empirically assess the notions of fairness this wider consultation group held. Three distinct ‘factors’ (or perspectives) are identified, and discussed in relation to a multi-dimensional framework for exploring fairness. The first factor prioritises development delivered through organisations, participation in decision-making and use of minimum prices to adjust trade imbalances. The second factor conceptualises a non-exclusive approach maximising generation and sales of FCCs, involving a commodity chain where everyone performs their optimum function with financial transparency and information-sharing to facilitate negotiations. The third factor involves minimising intervention, allowing carbon commodity chains and project set-ups to function efficiently, and make their own adjustments to enhance benefits access and quality received by beneficiaries. The three factors reflect debates within carbon and fair trade spheres about who should be playing which roles, who should be accessing which benefits, and how people should be supported to interact on an uneven playing field. Communicating findings to standards organisations enables a more open and inclusive policy process. Our research provides a critical reflection on these plural notions of fairness, identifying areas of (dis)agreement within the FCC dialogue, and provides a wider, yet manageable, set of inputs for supporting the FCC process during its inception and subsequent implementation. Clearer definitions of “fairness” are also useful for standards organisations in reviewing ex post whether “fairness” goals have been met.  相似文献   
89.
The nexus between human rights and the environment is a key issue for climate policymakers and Indigenous peoples around the world. We combine national spatial, social and biological datasets from Australia to describe where Indigenous carbon projects are happening, why Indigenous people are participating, and how effective these schemes might be at marrying Indigenous co-benefit, biodiversity and carbon emission mitigation goals. Our study shows that many Indigenous people engage in carbon offset schemes as part of their broader cultural responsibility for landscapes, and that they seek to grow the relationship between social and ecological benefits. It also highlights the challenges associated with designing carbon offset schemes that address the impacts of climate change and respond to Indigenous peoples’ world views about what is required to sustain cultural-social-ecological systems.  相似文献   
90.
Elevated CO2 can stimulate wetland carbon(C) and nitrogen(N) exports through gaseous and dissolved pathways, however, the consequent influences on the C and N pools are still not fully known. Therefore, we set up a free-air CO2 enrichment experiment in a paddy field in Eastern China. After five year fumigation, we studied C and N in the plant–water–soil system. The results showed:(1) elevated CO2 stimulated rice aboveground biomass and N accumulations by 19.1% and 12.5%, respectively.(2) Elevated CO2 significantly increased paddy soil TOC and TN contents by 12.5% and 15.5%, respectively in the 0–15 cm layer, and22.7% and 26.0% in the 15–30 cm soil layer.(3) Averaged across the rice growing period,elevated CO2 greatly increased TOC and TN contents in the surface water by 7.6% and 11.4%,respectively.(4) The TOC/TN ratio and natural δ15N value in the surface soil showed a decreasing trend under elevated CO2. The above results indicate that elevated CO2 can benefit C and N accumulation in paddy fields. Given the similarity between the paddies and natural wetlands, our results also suggest a great potential for long-term C and N accumulation in natural wetlands under future climate patterns.  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