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   2756篇
  免费   78篇
  国内免费   26篇
安全科学   185篇
废物处理   153篇
环保管理   565篇
综合类   310篇
基础理论   679篇
环境理论   3篇
污染及防治   640篇
评价与监测   190篇
社会与环境   100篇
灾害及防治   35篇
  2023年   15篇
  2022年   19篇
  2021年   30篇
  2020年   27篇
  2019年   29篇
  2018年   62篇
  2017年   60篇
  2016年   83篇
  2015年   74篇
  2014年   72篇
  2013年   249篇
  2012年   111篇
  2011年   159篇
  2010年   123篇
  2009年   136篇
  2008年   133篇
  2007年   150篇
  2006年   140篇
  2005年   102篇
  2004年   90篇
  2003年   113篇
  2002年   75篇
  2001年   65篇
  2000年   61篇
  1999年   44篇
  1998年   42篇
  1997年   40篇
  1996年   37篇
  1995年   30篇
  1994年   40篇
  1993年   32篇
  1992年   24篇
  1991年   26篇
  1990年   15篇
  1989年   11篇
  1988年   18篇
  1987年   25篇
  1986年   17篇
  1985年   25篇
  1984年   16篇
  1983年   23篇
  1982年   22篇
  1981年   25篇
  1980年   16篇
  1979年   11篇
  1978年   8篇
  1977年   14篇
  1974年   8篇
  1971年   7篇
  1955年   5篇
排序方式: 共有2860条查询结果,搜索用时 15 毫秒
911.
This paper discusses methodologies that have been employed to give insights into business performance in relation to sustainable development, both at a sectoral and corporate level. From consideration of different sectoral sustainable development methodologies, some key issues and good practice related to their derivation are elaborated. These issues are then further illustrated by a detailed comparison between three sustainable development methodologies that have been used in the UK offshore oil and gas industry. The methodologies chiefly differ in terms of how they address the problem of comparing different impacts across potentially non-commensurable dimensions, one proceeding through explicit monetary valuation, another through implicit valuation of different options and another through presentation of an unaggregated framework of indicators. The paper concludes by identifying the different situations in which use of these different methodologies is appropriate.  相似文献   
912.
Abstract: Spatio‐temporal linkages between hydrologic and ecologic dimensions of watersheds play a critical role in conservation policies. Habitat potential is influenced by variation along longitudinal and lateral gradients and land use disturbance. An assessment of these influences provides critical information for protecting watershed ecosystems and in making spatially explicit, conservation decisions. We use an ecohydrologic approach that focuses on interface between hydrological and ecological processes. This study focuses on changes in watershed habitat potentials along lateral (riparian), and longitudinal (stream order) dimensions and disturbance (land use). The habitat potentials were evaluated for amphibians, reptiles, mammals, and birds in the Westfield River Watershed of Massachusetts using geographic information systems and multivariate analysis. We use a polynomial model to study nonlinear effects using robust regression. Various spatial policies were modeled and evaluated for influence on species diversity. All habitat potentials showed a strong influence along spatial dimensions and disturbance. The habitat potential for all vertebrate groups studied decreased as the distance from the riparian zone increased. Headwaters and lower order subwatersheds had higher levels of species diversity compared to higher order subwatersheds. It was observed that locations with the least disturbance also had higher habitat potential. The study identifies three policy criteria that could be used to identify critical areas within a watershed to conserve habitat suitable for various species through management and restoration activities. A spatially variable policy that is based on stream order, riparian distance, and land use can be used to maximize watershed ecological benefits. Wider riparian zones with variable widths, protection of headwaters and lower order subwatersheds, and minimizing disturbance in riparian and headwater areas can be used in watershed policy. These management objectives could be achieved using targeted economic incentives, best management practices, zoning laws, and educational programs using a watershed perspective.  相似文献   
913.
The analysis of PCBs in fish tissues by immunoassay methods was evaluated using fish collected from a US monitoring program, the National Contaminant Biomonitoring Program of the US Department of Interior, Fish and Wildlife Service. Selected composite whole fish samples, which represented widely varying concentrations and sources of PCBs, were extracted and subjected to congener PCB analysis by gas chromatography (GC) and total PCB analysis using an ELISA (ePCBs) calibrated against technical Aroclor 1248. PCB congener patterns in these fishes were different from the patterns found in commercial Aroclors or their combinations as demonstrated by principal component analysis of normalized GC congener data. The sum of the PCB congeners measured by GC (total-PCBs) ranged from 37 to 4600 ng/g (wet weight). Concentrations of PCBs as determined by the ELISA method were positively correlated with total-PCBs and the ePCBs/total-PCBs ratios for individual samples ranged from 1 to 6. Ratios of ePCBs/total-PCBs for dilutions of Aroclors 1242, 1254, and 1260 and for matrix spikes range from 0.6 for 1242 to 2.5 for 1254 and 1260. These results suggest that higher chlorinated PCB congeners have higher affinity for the anti-PCB antibodies. Partial least squares with latent variable analysis of GC and ELISA data of selected Aroclors and fish samples also support the conclusion that ELISA derived PCB concentrations are dependent on the degree of chlorination.  相似文献   
914.
915.
England is one of the few industrialised countries where water metering is not compulsory. Most households instead pay a fixed charge regardless of use. Yet water consumption is already at the limit of resources and beyond them in some regions. Despite the need to control demand, compulsory water metering has not been implemented largely because of concerns about the regressive impact on poorer households. This research analysed new data from Anglian Water on household water consumption and income to examine the distributional impacts of ten different hypothetical tariff designs. It was found that it was possible to design revenue-neutral metered tariffs that would cause only a small percentage of low-income households to lose and most to gain. With sensitive design, the social concerns about compulsory water metering can be dealt with.  相似文献   
916.
ABSTRACT: Under the Clean Water Act (CWA) program, the Texas Commission on Environmental Quality (TCEQ) listed 110 stream segments in the year 2000 with pathogenic bacteria impairment. A study was conducted to evaluate the probable sources of pollution and characterize the watersheds associated with these impaired water bodies. The primary aim of the study was to group the water bodies into clusters having similar watershed characteristics and to examine the possibility of studying them as a group by choosing models for total maximum daily load (TMDL) development based on their characteristics. This approach will help to identify possible sources and determine appropriate models and hence reduce the number of required TMDL studies. This in turn will help in reducing the effort required to restore the health of the impaired water bodies in Texas. The main characteristics considered for the classification of water bodies were land use distribution within the watershed, density of stream network, average distance of land of a particular use to the closest stream, household population, density of on‐site sewage facilities (OSSFs), bacterial loading from different types of farm animals and wildlife, and average climatic conditions. The climatic data and observed instream fecal coliform bacteria concentrations were analyzed to evaluate seasonal variability of instream water quality. The grouping of water bodies was carried out using the multivariate statistical techniques of factor analysis/principal component analysis, cluster analysis, and discriminant analysis. The multivariate statistical analysis resulted in six clusters of water bodies. The main factors that differentiated the clusters were found to be bacterial contribution from farm animals and wildlife, density of OSSFs, density of households connected to public sewers, and land use distribution.  相似文献   
917.
918.
919.
The Environmental Protection Agency and others have opposed gasoline price decontrol, alleging a wider posted price differential between leaded and unleaded grades would result, inducing more motorists to switch illegally to leaded gasoline fouling catalytic converters and hence increasing air pollution. EPA's model must assume that only the unleaded price ceiling is binding. It is shown that the resulting excess demand is shifted to a close substitute: leaded gasoline. Hence, controls cause more consumption of leaded fuel in new cars (switching) and more pollution. Thus, decontrol would have a palliative effect, contrary to EPA's claim.  相似文献   
920.
The role that genetic and environmental factors play in triggering neural tube defects in the mouse mutant curly-tail (ct) were investigated by transplanting curly-tail blastocysts into the uterus of either curly-tail females or females of an unrelated A strain with a low natural incidence of abnormalities of the neural tube. The percentages of fetuses with neural tube defects were found to be similar in both groups. These results show that in curly-tail mice exencephaly and spina bifida are manifested independently of the maternal environment.  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