全文获取类型
收费全文 | 683篇 |
免费 | 95篇 |
国内免费 | 231篇 |
专业分类
安全科学 | 7篇 |
废物处理 | 5篇 |
环保管理 | 372篇 |
综合类 | 374篇 |
基础理论 | 118篇 |
污染及防治 | 42篇 |
评价与监测 | 52篇 |
社会与环境 | 35篇 |
灾害及防治 | 4篇 |
出版年
2024年 | 9篇 |
2023年 | 16篇 |
2022年 | 21篇 |
2021年 | 24篇 |
2020年 | 30篇 |
2019年 | 35篇 |
2018年 | 31篇 |
2017年 | 36篇 |
2016年 | 47篇 |
2015年 | 51篇 |
2014年 | 49篇 |
2013年 | 66篇 |
2012年 | 62篇 |
2011年 | 64篇 |
2010年 | 58篇 |
2009年 | 50篇 |
2008年 | 33篇 |
2007年 | 47篇 |
2006年 | 43篇 |
2005年 | 33篇 |
2004年 | 21篇 |
2003年 | 17篇 |
2002年 | 20篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 12篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有1009条查询结果,搜索用时 15 毫秒
231.
Bioassessment of nonwadeable streams in the United States is increasing, but methods for these systems are not as well-developed as for wadeable streams. In this study, we compared six macroinvertebrate field sampling methods for nonwadeable streams adapted from those used by three major programs: the U.S. Environmental Protection Agencys Environmental Monitoring and Assessment Program-Surface Waters, the U.S. Geological Surveys National Water Quality Assessment Program, and the Ohio Environmental Protection Agency, Division of Surface Water Biocriteria Program. We performed all six methods at 60 sites across four rivers and measured water chemistry and physical habitat at each site to assess abiotic conditon. Sites were divided into two groups: those influenced by navigational lock and dam structures (restricted flow, or RF) and those free-flowing or with lowhead dams (run-of-the-river, or ROR). Metrics based on passive Hester-Dendy artificial substrate samplers differed greatly from active sampling methods (i.e., using nets) but represented abiotic conditions well in both ROR and RF sites. Although metric values were similar across certain sampling methods, the metrics significantly correlated with abiotic variables varied among methods and between ROR and RF sites. These results emphasize that methods are not interchangeable, and the ability to detect certain stressors depends on sampling method.The U.S. Governments right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
232.
颗粒态重金属通过河流与大气向海洋输送 总被引:8,自引:2,他引:8
本文综述了河流与大气向海洋输送颗态重金属的过程、特点及输送通量、参考文献83篇。 相似文献
233.
云南省国际河流水质状况及其保护 总被引:2,自引:0,他引:2
介绍了云南省红河,澜沧江,怒江和伊洛瓦底江4大国际河流水系2000年的水质状况,对其1991-2000年的水质变化趋势及其主要污染因素进行了分析。据此提出了“十五”期间和以后较长一段时间内水环境治理的综合对策和措施。 相似文献
234.
Utility of semivariogram for spatial variation of soil nutrients and the robust analysis of semivariogram 总被引:1,自引:0,他引:1
IntroductionGeostatisticshasprovenusefulforcharacterizingandmappingthespatialvariationofsoilproperties (Webster,1985;Trangmar,1985;Goovaerts ,1999) .Mostpreviousgeostatisticalstudiesfocusedonthedataofarelativelysmallspatialscale(Chien ,1997) .Theapplicationofgeostat… 相似文献
235.
John S. Richardson Robert J. Naiman Frederick J. Swanson David E. Hibbs 《Journal of the American Water Resources Association》2005,41(4):935-947
Riparian areas of large streams provide important habitat to many species and control many instream processes — but is the same true for the margins of small streams? This review considers riparian areas alongside small streams in forested, mountainous areas of the Pacific Northwest and asks if there are fundamental ecological differences from larger streams and from other regions and if there are consequences for management from any differences. In the moist forests along many small streams of the Pacific Northwest, the contrast between the streamside and upslope forest is not as strong as that found in drier regions. Small streams typically lack floodplains, and the riparian area is often constrained by the hillslope. Nevertheless, riparian‐associated organisms, some unique to headwater areas, are found along small streams. Disturbance of hillslopes and stream channels and microclimatic effects of streams on the riparian area provide great heterogeneity in processes and diversity of habitats. The tight coupling of the terrestrial riparian area with the aquatic system results from the closed canopy and high edge‐to‐area ratio for small streams. Riparian areas of the temperate, conifer dominated forests of the Pacific Northwest provide a unique environment. Forest management guidelines for small streams vary widely, and there has been little evaluation of the local or downstream consequences of forest practices along small streams. 相似文献
236.
Keith A. Cherkauer Stephen J. Burges Rebecca N. Handcock Jennifer E. Kay Stephanie K. Kampf Alan R. Gillespie 《Journal of the American Water Resources Association》2005,41(5):1149-1159
One central issue affecting the health of native fish species in the Pacific Northwest is water temperature. In situ observation methods monitor point temperatures, while thermal infrared (TIR) remote sensing captures spatial variations. Satellite‐based TIR sensors have the ability to view large regions in an instant. Four Pacific Northwest river reaches were selected to test the ability of both satellite‐based and moderate resolution aircraft‐based TIR remote sensing products to measure river temperatures. Images with resolutions of 5, 15, and 90 meters were compared with instream temperature observations to assess how along stream radiant temperatures are affected by resolution, reach width, and sensor platform. Where the stream reach can be resolved by the sensor, all sensors obtain water temperatures within ±2°C of instream observations. Along stream temperature variations of up to ±5°C were also observed. Trends were similar between two sets of TIR images taken several hours apart, indicating that the sensors are observing actual temperature patterns from the river surface. If sensor resolution is sufficient to obtain fully resolved water pixels in the river reach, accurate temperatures and spatial patterns can be observed. The current generation of satellite‐based TIR sensors is, however, only able to resolve about 6 percent of all Washington reaches listed as thermally impaired. 相似文献
237.
An understanding of temporal trends in total stream‐flow (TSF), base flow (BF), and storm runoff (RO) can help in the development of water management plans for watersheds and local communities. In this study, 47 streams across Pennsylvania that were unregulated and unaffected by karst environments or coal mining were studied for flow trends and their relationships to selected climate parameters for the period 1971 to 2001. LOWESS curves for annual flow showed that almost all of the selected streams in Pennsylvania had downward trends in total TSF, BF, and RO. Using a seasonal Mann‐Kendall analysis, downward trends were significant at an α= 0.05 level for 68, percent 70 percent, and 62 percent of the streams and at an α= 0.10 level for another 19, 17, and 13 percent of the streams for TSF, BF, and RO, respectively. The ratio of BF to TSF (RBS) had significant upward trends for 34 percent of the streams at an α= 0.05 level and for another 9 percent of the streams at an α= 0.10 level, indicating that TSF decreased relative to BF for more than 40 percent of the streams during the previous 30 years. Downward trends in TSF, BF, and RO were most common for the months of June, July, and December. Trend analyses using monthly and annual total precipitation and mean temperature showed some association between climate and the streamflow trends, but Spearman's correlation and partial Mann‐Kendall analyses revealed that the trends in TSF, BF, and RO could not be explained by trends in precipitation and temperature alone, and thus urbanization and development may have played a role. 相似文献
238.
Uta Krogmann Hai‐Ning C. Chiang 《Journal of the American Water Resources Association》2002,38(3):681-691
ABSTRACT: In order to determine appropriate application rates and to ensure low pollutant levels in sewage sludge, knowing the chemical composition of sewage sludge is of great importance in a land application program. The objective of this study is to evaluate the variability of selected chemical characteristics of sewage sludge from New Jersey publicly owned treatment works (POTWs). Measurements of total Kjeldahl nitrogen (TKN), NH4+‐N, P, K+, Cd, Cu, Pb, and Zn reported by 98 facilities in the 1996 and 1997 New Jersey Sludge Quality Assurance Regulations (SQAR) reports were statistically analyzed. Sewage sludge from Category 5 POTWs (greater than 10 percent industrial input) showed higher Cd, Cu, and Pb concentrations than Category 3 and Category 4 facilities (less than 10 percent industrial input). Even though only two years of data were analyzed, there was an indication that Cd and Pb concentrations in sewage sludge are decreasing with time. The yearly mean of only a few facilities exceeded the federal pollution concentration limits (40 CFR Part 503, Table 3). Phosphorus and Cd values showed the highest variability within facilities based on the coefficient of variation. Due to the variability of sewage sludge constituents, the use of the yearly rolling mean of nutrient concentrations to determine application rates was considered inadequate. An actual analysis of the sewage sludge to be applied is more appropriate to determine application rates than historical data. 相似文献
239.
Clayton W. Ogg Gary A. Keith 《Journal of the American Water Resources Association》2002,38(2):577-586
ABSTRACT: In the past five years, USDA and EPA programs became major players in implementing watershed programs. The 1996 Farm Bill for the first time required that USDA assistance for farmers address priority environmental needs on a site‐specific, or watershed, basis. USDA involves farmers and other players in locally run watershed programs and focuses cost share and incentive payments on nutrient planning, riparian protection, and other practices prioritized to most efficiently achieve watershed goals. As a result, USDA has become a funding source for environmental initiatives targeted to watersheds, as well as a technical resource that attempts to support more efficient use of federal and state environmental expenditures. Analysis identifies institutional and technical barriers to targeting the very limited, new assistance and suggests how those barriers are being addressed by some innovative programs. Since Total Maximum Daily Load (TMDL) and other state run programs face many of the same challenges of ranking watersheds, setting goals, and finding cost effective remedies, this paper identifies a very close fit between the new federal programs and other watershed programs. 相似文献
240.
建立网络生态水库系统实现城市河流的可持续发展 总被引:2,自引:0,他引:2
城市河流在城市及周边地区经济发展和生态保护中地位十分重要。网络生态水库系统可以克服我国水资源时空分配不均的弊端,优化水资源配置,满足各城市生产生活需要,实现可持续发展。 相似文献