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   939篇
  免费   84篇
  国内免费   118篇
安全科学   35篇
废物处理   5篇
环保管理   235篇
综合类   400篇
基础理论   229篇
污染及防治   40篇
评价与监测   45篇
社会与环境   124篇
灾害及防治   28篇
  2024年   4篇
  2023年   14篇
  2022年   38篇
  2021年   61篇
  2020年   40篇
  2019年   42篇
  2018年   25篇
  2017年   39篇
  2016年   49篇
  2015年   37篇
  2014年   59篇
  2013年   71篇
  2012年   61篇
  2011年   67篇
  2010年   71篇
  2009年   56篇
  2008年   54篇
  2007年   61篇
  2006年   44篇
  2005年   45篇
  2004年   32篇
  2003年   31篇
  2002年   19篇
  2001年   14篇
  2000年   20篇
  1999年   7篇
  1998年   14篇
  1997年   9篇
  1996年   12篇
  1995年   4篇
  1994年   13篇
  1993年   6篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   4篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1978年   2篇
  1977年   2篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
排序方式: 共有1141条查询结果,搜索用时 31 毫秒
961.
Information about the net benefits of land degradation treatment is required at the relevant management level, such as regional, local or site-specific, to assist decision makers in the allocation of funds to soil conservation. In this paper, estimates of regional opportunity costs of erosion and costs of treatment are used to derive benefit-cost ratios to assess the profitability of gully erosion treatment for localities in the wheat-sheep zone of New South Wales. These results are then used to develop site-specific models which predict benefit-cost ratios of treatment from land attributes including gully length, slope, soil type and land use. These predictive models form the basis of a rapid appraisal method to aid soil conservation decisions.  相似文献   
962.
通过对集成式污水处理装置工艺和运行参数进行优化,选择水力停留时间为32 h、回流比为100%、好氧区D0 2 mg/L为最佳运行工况.并在此基础上,研制出一体化处理设施——净化槽,在北京市大兴区庞各庄镇梨花村对其进行了示范应用,结果表明净化槽具有一定的耐冲击负荷的能力,出水水质稳定,对于推动北京平原地区农村生活污水达标排放具有重要意义.  相似文献   
963.
针对新疆“十三五”期间温室气体减排领域潜力分析及预测,依据京都议定书的规定及新疆的具体情况,分析了新疆温室气体排放现状及预测,探讨了新疆温室气体主要减排领域减排潜力,介绍了提高工业能源效率领域、建筑节能领域和煤田灭火等领域,提出了新疆九大行业温室气体减排潜力,利用统计年鉴数据及相关资料,估计在“十三五”期间的新疆总的温室气体减排潜力为35 100.39万吨C02.同时,本文对“十三五”期间新疆碳减排项目开发前景进行了分析和预测,并探讨了减排项目的优先开发领域.  相似文献   
964.
To elucidate the air pollution characteristics of northern China, airborne PM_10(atmospheric dynamic equivalent diameter ≤ 10 μm) and PM_(2.5)(atmospheric dynamic equivalent diameter ≤ 2.5 μm) were sampled in three different functional areas(Yuzhong County,Xigu District and Chengguan District) of Lanzhou, and their chemical composition(elements, ions, carbonaceous species) was analyzed. The results demonstrated that the highest seasonal mean concentrations of PM_10(369.48 μg/m~3) and PM_(2.5)(295.42 μg/m~3) were detected in Xigu District in the winter, the lowest concentration of PM_(2.5)(53.15 μg/m~3) was observed in Yuzhong District in the fall and PM_10(89.60 μg/m~3) in Xigu District in the fall.The overall average OC/EC(organic carbon/elemental carbon) value was close to the representative OC/EC ratio for coal consumption, implying that the pollution of Lanzhou could be attributed to the burning of coal. The content of SNA(the sum of sulfate, nitrate,ammonium, SNA) in PM_(2.5)in Yuzhong County was generally lower than that at other sites in all seasons. The content of SNA in PM_(2.5)and PM_10 in Yuzhong County was generally lower than that at other sites in all seasons(0.24–0.38), indicating that the conversion ratios from precursors to secondary aerosols in the low concentration area was slower than in the area with high and intense pollutants. Six primary particulate matter sources were chosen based on positive matrix factorization(PMF) analysis, and emissions from dust, secondary aerosols, and coal burning were identified to be the primary sources responsible for the particle pollution in Lanzhou.  相似文献   
965.
选取我国东、中、西部3个地区6个典型村镇的生活垃圾,设计了两种淋滤强度:低强度(10 mm·d~(-1))和高强度(20 mm·d~(-1)),采用室内降雨模拟实验,研究了生活垃圾污染物如CODCr、BOD5、TN和NH3-N等的动态淋滤释放特征.结果显示,两种淋滤强度下,3个地区淋滤液pH值整体随时间的增加呈现小幅的上升,变化范围分别在6.5~8.0(10 mm·d~(-1))和5.5~8.0(20 mm·d~(-1))之间;CODCr呈现显著下降(1~2周)、缓慢下降(2~7周)和相对平稳(7~10周)3个阶段.淋滤液BOD5在前6周降低明显,在第7和第8周基本达到了溶出的平衡点.淋滤液TN分别在第8周(10 mm·d~(-1))和第7周(20 mm·d~(-1))基本达到了溶出平衡,NH3-N分别在第8周(10 mm·d~(-1))和第6周(20 mm·d~(-1))基本达到了溶出平衡.整个淋溶周期内(10周),淋滤液CODCr、BOD5、TN和NH3-N浓度变化规律整体呈现:高强度(20 mm·d~(-1))淋滤条件下浓度降低率高于低强度(10 mm·d~(-1)).  相似文献   
966.
Traditionally, the criteria used to measure conservation success or failure are based on biological factors. Biological factors include changes in the amount of targeted conserved species, biodiversity, and total area conserved. However, conservation efforts are not simply a matter of biological concern; environmental, political, social, and conflict pressures on different scales (ranging from local to global) also have strong influences on the outcome of conservation. These other factors can either pose threats to or enhance conservation, but are not addressed by current criteria. Using a proposed holistic rubric that includes interdisciplinary fields, this paper examines a set of conservation factors on different scales – ranging from local to global – to determine their importance in conservation. The paper analyses positive factor influences with more successful conservation and negative factor influences with less successful, or failed, conservation attempts. Neutral and non‐applicable factor influences are also identified, defined, and ranked as a standardization mechanism. The determination of success changed when the holistic rubric was applied to conservation projects in Costa Rica, Mekong Valley, and Cameroon. In the Costa Rica case study, conservation success for Guanacaste and Talamanca national parks is rated ‘moderately low’. In the case of Mekong Valley, conservation success is rated ‘low’ for Lower Mekong, ‘moderately low’ for Greater Annamites, and ‘low’ for Phong Nha‐Ke Bang national parks. Cameroon's Congo Basin and Sangha Tri‐National conservation efforts are both rated ‘low’, while Dja Faunal is rated ‘very low’. We conclude that if conservation efforts are to attain a high level of success, the strategy for global conservation must move away from the traditional biological approach, which focuses mainly on biological concerns, and embrace a holistic approach, which in addition to biological concerns, addresses environmental, political, social, and conflict pressures, which have strong influences on the outcomes of conservation.  相似文献   
967.
海门沿江地区开发适宜性分区研究   总被引:2,自引:0,他引:2  
区域不合理开发将会引发大量的生态环境问题。要建立开发与保护兼容的空间秩序,区域开发适宜性分区具有十分重要的意义。以海门沿江地区作为研究案例区,借助GIS空间分析技术,通过确定符合区域要求的格网评价单元,利用约束型和引导型指标叠合判断的方法,将案例区划分为鼓励开发、适度开发、适度保护和优先保护区域。结果表明,鼓励开发区域主要集中在城区、港区这类自然基础较好、发展潜力较大而生态约束较低的地区;适度开发区域主要分布在重点中心镇以及一般镇的镇区;适度保护区域主要分布在生态敏感性较高、发展基础和条件一般的地区;优先保护区域则主要为具有重要生态服务功能的地区。并依据开发适宜性分区提出开发建设强度和时序的建议,可为合理布局沿江城镇和产业发展提供科学引导。  相似文献   
968.
重庆市主城区属于典型的城市生态系统,是三峡库区的重要组成部分,其生态环境质量的好坏不仅影响着重庆经济、社会的发展,还影响着整个三峡库区生态功能的稳定及可持续发展。为了准确评价重庆市主城区生态环境质量,根据区域生态环境特点,从空间格局、环境特性、生物特征、服务功能等4大方面(准则层)构建出城市生态环境质量评价体系,并通过层次分析法进行系统评价,剖析区域存在的主要生态环境问题及其根源,提出相应的保护对策及建议。评价结果为:重庆主城区总体生态环境质量得分为65.68,对应评价等级为一般;空间格局、环境特性、生物特征、服务功能得分分别为66.02、74.82、50.34和66.81,对应评价等级分别为良、良、较差及一般。综合分析表明,重庆市主城区生态环境问题在水环境、大气环境、生物特征等方面较为突出,因此必须着重加强相关的环境保护与生态建设工作。  相似文献   
969.
Biodiversity conservation strategies are increasingly focused on regions outside national protected areas, where animals face numerous anthropogenic threats and must coexist with human settlements, livestock, and agriculture. The effects of these potential threats are not always clear, but they could have profound implications for population viability. We used savannah elephants (Loxodonta africana) as a case study to assess the physiological stress associated with living in a human‐livestock‐dominated landscape. We collected samples over two 3‐month periods in 2007 and 2008. We used fecal DNA to identify 96 individual elephants in a community conservation area (CCA) and measured fecal glucocorticoid metabolite (FGM) concentrations as a proxy for stress. The CCA is community Maasai land managed for livestock and wildlife. We compared the FGM concentrations from the CCA to FGM concentrations of 40 elephants in Amboseli National Park and 32 elephants in the Maasai Mara National Reserve, where human settlements and intense livestock grazing were absent. In the CCA, we found no significant individual differences in FGM concentrations among the elephants in 2007 (p = 0.312) or 2008 (p = 0.412) and no difference between years (p = 0.616). The elephants in the CCA had similar FGM concentrations to the Maasai Mara population, but Amboseli elephants had significantly lower FGM concentrations than those in either Maasai Mara or the CCA (Tukey pairwise test, p < 0.001), due primarily to females excreting significantly lower FGM relative to males (p = 0.025). In the CCA, there was no relation among female group size, average pairwise group relatedness, and average group FGM concentration. We found no clear evidence of chronic stress in elephants living on CCA communal land, which is encouraging for conservation strategies promoting the protection of animals living outside protected areas. Conservación Fuera de Áreas Protegidas y el Efecto de Paisajes Dominados por Humanos sobre Hormonas del Estrés en Elefantes Africanos  相似文献   
970.
Abstract: Declining rural security and pressures to reduce public‐sector expenditures in the late 1990s spurred efforts to develop alternative funding models for Uganda's Kibale National Park (KNP). The Wild Coffee Project, established in 1999 with support from the U.S. Agency for International Development, the World Bank, and the Ford Foundation, sought to develop a market for wild coffee that had been harvested traditionally from areas within today's KNP. The Kibale Forest Foundation, a U.S.‐based nonprofit organization, was created to legalize harvests, obtain third‐party wild and organic certification, and coordinate management between KNP, the coffee industry, and local communities. Although the project was successful in legalizing, harvesting, and processing the world's first certified wild and organic coffee, efforts to gain entry into the international marketplace failed. Chief among the lessons learned from this project is that for many wild‐grown products, the value of “the story”—in both human and conservation terms—is likely to far exceed actual product values. This value differential should be captured through high‐value niche markets to avoid low commodity pricing and subsequent pressures to improve financial returns through over harvesting. In addition, local producers should hold significant assets in whatever brands are developed, creating a shared‐equity approach that serves social responsibility goals, fosters project sustainability, and ensures a steady stream of positive stories for use in marketing to build brand value. Shared equity—in this case ownership interest in the intellectual property embodied in the brand—provides a second incentive beyond transactional profits that can only be realized if resource conservation is maintained.  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