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   248篇
  免费   7篇
  国内免费   17篇
安全科学   13篇
废物处理   7篇
环保管理   44篇
综合类   62篇
基础理论   73篇
环境理论   1篇
污染及防治   48篇
评价与监测   13篇
社会与环境   5篇
灾害及防治   6篇
  2023年   7篇
  2022年   5篇
  2021年   8篇
  2020年   5篇
  2019年   8篇
  2018年   6篇
  2017年   13篇
  2016年   12篇
  2015年   8篇
  2014年   11篇
  2013年   17篇
  2012年   16篇
  2011年   19篇
  2010年   15篇
  2009年   20篇
  2008年   13篇
  2007年   5篇
  2006年   17篇
  2005年   8篇
  2004年   12篇
  2003年   7篇
  2002年   5篇
  2001年   8篇
  2000年   1篇
  1998年   1篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1991年   2篇
  1990年   1篇
  1988年   3篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1979年   1篇
  1961年   3篇
  1959年   1篇
排序方式: 共有272条查询结果,搜索用时 31 毫秒
181.
The analysis of mitochondrial DNA in loggerhead sea turtles (Caretta caretta) from eight foraging grounds in the Mediterranean and the adjoining Atlantic revealed deep genetic structuring within the western Mediterranean. As a consequence, the foraging grounds off the North-African coast and the Gimnesies Islands are shown to be inhabited mainly by turtles of the Atlantic stocks, whereas the foraging grounds off the European shore of the western Mediterranean are shown to be inhabited mainly by turtles from the eastern Mediterranean rookeries. This structuring is explained by the pattern of sea surface currents and water masses and suggests that immature loggerhead sea turtles entering the western Mediterranean from the Atlantic and the eastern Mediterranean remain linked to particular water masses, with a limited exchange of turtles between water masses. As the north of the western Mediterranean comprises mostly individuals from the highly endangered eastern Mediterranean rookeries, conservation plans should make it a priority to reduce the mortality caused by incidental by-catch in these areas.  相似文献   
182.
Like many modular organisms, genetically distinct colonies of the hydrozoan Hydractinia symbiolongicarpus naturally fuse to produce chimeras. One of the principal cooperative benefits of fusion arises from the increased size of the resulting chimeric individual, which may enhance survivorship. However, fusion also promotes conflict through competition between cell lineages for representation in reproductive tissues. Previous studies on H. symbiologicarpus show that, consistent with kin selection theory, a highly polymorphic self/non-self recognition system limits fusion to close kin. However, these recognition systems are intrinsically subject to error. Conspecific acceptance threshold theory predicts that as the costs and benefits of making recognition errors change, or the frequencies of encounters between acceptable and unacceptable kin vary, the recognition system should respond. Specifically, as the benefits of acceptance decline or the frequency of encounters with unacceptable individuals increases, the acceptance threshold should become more restrictive. We tested this hypothesis by monitoring changes in the expression of fusion/rejection behaviors of H. symbiolongicarpus during colony establishment, a period of high mortality when the size-dependent benefits of fusion may be changing most rapidly, and the frequency of encounters with close kin declines. Across seven full-sib families, fusion frequencies between pairs of sibling colonies declined from 73% for 3-day-old colonies to 58% by day 12. This decline is consistent with optimal acceptance threshold theory. However, the period of maximum decline also corresponds to an interval during which the recognition effector mechanism becomes fully functional, suggesting that the shift to a more restrictive conspecific acceptance threshold may reflect an intrinsic constraint on recognition system maturation.Communicated by T. Czeschlik  相似文献   
183.
The determination of methane emissions on a regional scale is needed in order to reduce some of the uncertainties in the global methane budget. Our measurements of the concentration and the Carbon-13 isotope composition (13C) of atmospheric methane are, combined with trajectories, used to get insight in the type and size of the methane emissions of a large area.  相似文献   
184.
Surface barriers for waste disposal sites should preventwaste water and gas emission into the environment. It isnecessary to assess their proper operation by monitoring thewater regime of the containment. A set of three new water contentmeasuring devices has been developed that provide an economicalsolution for monitoring the moisture distribution and waterdynamic. They will give an early warning service if the barriersystem is at risk of being damaged. The cryo soil moisture sensor`LUMBRICUS' is an in situ self-calibrating absolute water contentmeasuring device. It measures moisture profiles at spot locationsdown to 2.5 m depth with an accuracy of better than 1.5% and adepth resolution of 0.03 m. The sensor inherently measuresdensity changes and initial cracks of shrinking materials likeclay minerals. The large area soil moisture sensor `TAUPE' is amoisture sensitive electric cable network to be buried in themineral barrier material of the cover. A report will be givenwith results and experiences on an exemplary installation at theWaste Disposal Facility Karlsruhe-West. 800 m2 of the barrierconstruction have been continuously monitored since December1997. Volumetric water content differences of 1.5% have beendetected and localised within 4 m. This device is alreadyinstalled in two other waste disposal sites. A modified `TAUPE'was constructed for the control of tunnels and river dams aswell. Thin sheet moisture sensor `FORMI' is specifically designedfor moisture measurements in liners like bentonite, textile andplastic. Due to its flexibility it follows the curvature of theliner. The sensor measures independently from neighbouringmaterials and can be matched to a wide range of differentthickness of the material. The sensors are patented in several countries.  相似文献   
185.
The objective of this study was to determine the concentrations of trace elements in sediment samples taken from impermeable urban areas of a city with predominantly agroindustrial development characteristics. For this, samples were taken every month from paved streets in the city of Toledo, Paraná State (PR), Brazil. Thus, trace element levels were obtained through analysis performed by optical emission spectrometry with inductively coupled plasma. Levels of total organic carbon were also obtained through the dry combustion method. When compared to local background levels, the trace element levels were shown to be enriched in the following percentage proportions: barium (Ba) (45.4%), copper (Cu) (48.6%), chromium (Cr) (37.2%), manganese (Mn) (81.6%), nickel (Ni) (0%), lead (Pb) (40%), zinc (Zn) (283.7%), magnesium (Mg) (34.3%), and sodium (Na) (250.2%), whereas the carbon (C) percentages were around 1%. The most significant enrichment factors occurred for Ba, Cr, Pb, Zn, Mg, and Na. The highest rates occurred in geoaccumulation where the sediments were enriched by zinc. According to the principal guidelines, the concentrations obtained for cadmium (Cd), Cr, Cu, Ni, and Zn can cause adverse environmental impacts.  相似文献   
186.
Urban water scarcity from ongoing drought and an increasing population are driving a range of water saving options to be explored in Melbourne (Australia). This paper assesses the cost effectiveness of five water treatment and industrial reuse options in the Fishermans Bend industrial area at Port Melbourne. In consultation with industrial stakeholders and the local water utility, the study design began by identifying potential water sources and sinks in the area. Treatment technologies for each option - using a combination of membrane bioreactors (MBR) and in some cases reverse osmosis (RO) technologies - were developed. In evaluating the potential for future implementation, the cost effectiveness ($/kiloLitre) was assessed relative to water supply augmentation and water demand management options available in Melbourne. Additionally, the opportunities and barriers for option implementation in Port Melbourne were contrasted with the Kwinana Industrial Area, Western Australia where many regional synergy projects have been undertaken. This research identifies that the future implementation of industrial ecology opportunities requires strong and ongoing stakeholder involvement as described in this paper.  相似文献   
187.
水资源短缺是困扰当今世界各国政府的主要问题之一.澳大利亚政府在水资源的分配方面进行了深入有益的探索和改革,取得了不少成功的经验.本文着重介绍了澳大利亚水资源分配的法律原则,希望对水资源短缺的国家和地区在立法上有一定的借鉴意义.  相似文献   
188.
多模式模拟评估奥运赛事期间可吸入颗粒物减排效果   总被引:12,自引:5,他引:7  
以空气质量多模式系统为工具,分析奥运赛事期间可吸入颗粒物(PM10)浓度大幅减小特征,从气象场和排放源两方面研究PM10浓度大幅减小的主要原因.多模式系统由嵌套网格空气质量模式(NAQPMS)、通用空气质量多尺度模式(CMAQ)和复杂大气空气质量三维模式(CAMx)3个空气质量复合模型组成,并以中尺度气象模式(MM5)和稀疏矩阵排放处理模型(SMOKE)提供统一气象场及排放源.研究对比2006年8月、2008年8月两组气象条件下北京PM10浓度水平及模拟效果,结果表明奥运赛事期间PM10浓度大幅减小的主要原因不是气象因素,而是由于额外措施引起的PM10排放减少.同时采用多模式系统数值模拟反向评估,获得北京奥运赛事期间奥运控制及额外减排措施引起的PM10减排量,结果表明,奥运赛事期间所有额外控制措施对颗粒物浓度效果相当于在2008年8月气象条件下,削减大约200t.d-1的无组织PM10排放,相当于北京正常时期PM10排放的50%.  相似文献   
189.
The suitability of two common and ubiquitously distributed and exotic ornamental plant species in Nigeria-Delonix regia and Casuarina equisetifolia as biomonitors and as effective bioaccumulators of atmospheric trace metals(Cd,Pb,Zn and Cu) has been evaluated.Bark and leaf samples from these plant species were collected in June and July 2006 at five locations in Benin City.Four of the sampling sites were in areas of high traffic density and commercial activities,the fifth site is a remote site,selected to act as a control and also to provide background information for the metals.The plant samples were collected and processed using standard procedures and trace metals were determined using atomic absorption spectrometer.The bark of the plants was able to bioaccumulate the trace metals,especially Pb which originates from anthropogenic contributions in the city.The Pb range of 20.00-70.00 μg/g measured for the bark samples of D.regia,exceeded the normal plant Pb concentration of 0.2-20.0 μg/g and most Pb data available in literature.The bark of the plants was observed to accumulate more metals compared to the leave,while D.regia was found to be slightly better than C.equisetifolia in trace metal uptake efficiency.Spatial variations in the distributions of Pb and Zn were significant(p 0.05),and the continuous use of leaded fuel in Nigeria was identified as the predominant source of Pb in the atmosphere.  相似文献   
190.
反应器理论在复合垂直流构建湿地水流流态研究中的应用   总被引:6,自引:0,他引:6  
运用反应器理论研究了一种新型的复合垂直流构建湿地系统(IVCW)的水流流态,由示踪剂试验得到水流停留时间分布(RTD),从而确定了IVCW在水力负荷为200~800mm/d时,停留时间为19~35h,并由RTD曲线的特征值确定IVCW的水流流态介于理想推流与完全混合流之间,同时应用离散流模型,不仅较好地模拟了IVCW的实际水流流态,还得到了水流的Peclect准数在11~19之间.通过有植物与无植物系统的对照发现植物根系有利于IVCW的水流流态接近理想推流状态.  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