全文获取类型
收费全文 | 3016篇 |
免费 | 42篇 |
国内免费 | 25篇 |
专业分类
安全科学 | 163篇 |
废物处理 | 154篇 |
环保管理 | 612篇 |
综合类 | 335篇 |
基础理论 | 725篇 |
环境理论 | 5篇 |
污染及防治 | 753篇 |
评价与监测 | 212篇 |
社会与环境 | 106篇 |
灾害及防治 | 18篇 |
出版年
2023年 | 21篇 |
2022年 | 37篇 |
2021年 | 26篇 |
2020年 | 21篇 |
2019年 | 31篇 |
2018年 | 66篇 |
2017年 | 67篇 |
2016年 | 89篇 |
2015年 | 58篇 |
2014年 | 84篇 |
2013年 | 280篇 |
2012年 | 143篇 |
2011年 | 177篇 |
2010年 | 120篇 |
2009年 | 123篇 |
2008年 | 154篇 |
2007年 | 187篇 |
2006年 | 153篇 |
2005年 | 105篇 |
2004年 | 104篇 |
2003年 | 116篇 |
2002年 | 89篇 |
2001年 | 67篇 |
2000年 | 46篇 |
1999年 | 51篇 |
1998年 | 38篇 |
1997年 | 43篇 |
1996年 | 43篇 |
1995年 | 40篇 |
1994年 | 41篇 |
1993年 | 34篇 |
1992年 | 37篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 20篇 |
1986年 | 25篇 |
1985年 | 17篇 |
1984年 | 18篇 |
1983年 | 28篇 |
1982年 | 28篇 |
1981年 | 25篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1971年 | 11篇 |
排序方式: 共有3083条查询结果,搜索用时 312 毫秒
801.
The hyporheic zone, the transition region between groundwater and surface water, represents an important interface between terrestrial and aquatic ecosystems. When groundwater combines with surface water in this zone, the characteristics of each are blended and new gradients are established, especially for contaminants. Therefore, the hyporheic zone is important in considering the “big ecological picture” as the hydrologic continuum connecting groundwater and surface water. The importance is reflected by the current focus of this zone in ecological risk assessments conducted under the Resource Conservation and Recovery Act (RCRA), Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), and Clean Water Act (CWA) programs. A variety of tools can be used to measure, analyze, and predict the physical, chemical, and biological processes that occur within the hyporheic zone. Directly measuring the flux of water across the interface between groundwater and surface water determines whether surface water enters the streambed at downwelling zones or groundwater discharges from the streambed in upwelling zones. In addition to direct measurements of the flux of water, several states have developed models to characterize the interaction of groundwater and surface water. The variability in physical and chemical characteristics between upwelling and downwelling zones influences the local ecology within the zone. The study of the species within the hyporheic zone includes ecological surveys and ecotoxicological investigations. The evolving study of the hyporheic zone will necessitate an increase in basic research into hydraulic considerations, an identification of regional representative sites with contaminated hyporheic zones, and a better understanding of the ecology of the species within the zone. © 2001 John Wiley & Sons, Inc. 相似文献
802.
803.
Masum A. Patwary William Thomas O’Hare Graham Street K. Maudood Elahi Syed Shahadat Hossain Mosharraf H. Sarker 《Waste management (New York, N.Y.)》2009,29(8):2392-2397
There is a concern that mismanagement of medical waste in developing countries may be a significant risk factor for disease transmission. Quantitative estimation of medical waste generation is needed to estimate the potential risk and as a basis for any waste management plan. Dhaka City, the capital of Bangladesh, is an example of a major city in a developing country where there has been no rigorous estimation of medical waste generation based upon a thorough scientific study. These estimates were obtained by stringent weighing of waste in a carefully chosen, representative, sample of HCEs, including non-residential diagnostic centres. This study used a statistically designed sampling of waste generation in a broad range of Health Care Establishments (HCEs) to indicate that the amount of waste produced in Dhaka can be estimated to be 37 ± 5 ton per day. The proportion of this waste that would be classified as hazardous waste by World Health Organisation (WHO) guidelines was found to be approximately 21%. The amount of waste, and the proportion of hazardous waste, was found to vary significantly with the size and type of HCE. 相似文献
804.
Objectives: In this study, we aimed to determine whether three minimum legal drinking age 21 (MLDA-21) laws—dram shop liability, responsible beverage service (RBS) training, and state control of alcohol sales—have had an impact on underage drinking and driving fatal crashes using annual state-level data, and compared states with strong laws to those with weak laws to examine their effect on beer consumption and fatal crash ratios.Methods: Using the Fatality Analysis Reporting System, we calculated the ratio of drinking to nondrinking drivers under age 21 involved in fatal crashes as our key outcome measure. We used structural equation modeling to evaluate the three MLDA-21 laws. We controlled for covariates known to impact fatal crashes including: 17 additional MLDA-21 laws; administrative license revocation; blood alcohol concentration limits of.08 and.10 for driving; seat belt laws; sobriety checkpoint frequency; unemployment rates; and vehicle miles traveled. Outcome variables, in addition to the fatal crash ratios of drinking to nondrinking drivers under age 21 included state per capita beer consumption.Results: Dram shop liability laws were associated with a 2.4% total effect decrease (direct effects: β =.019, p =.018). Similarly, RBS training laws were associated with a 3.6% total effect decrease (direct effect: β =.048, p =.001) in the ratio of drinking to nondrinking drivers under age 21 involved in fatal crashes. There was a significant relationship between dram shop liability law strength and per capita beer consumption, F (4, 1528) = 24.32, p <.001, partial η2 =.016, showing states with strong dram shop liability laws (Mean (M) = 1.276) averaging significantly lower per capita beer consumption than states with weak laws (M = 1.340).Conclusions: Dram shop liability laws and RBS laws were both associated with significantly reduced per capita beer consumption and fatal crash ratios. In practical terms, this means that dram shop liability laws are currently associated with saving an estimated 64 lives in the 45 jurisdictions that currently have the law. If the remaining 6 states adopted the dram shop law, an additional 9 lives could potentially be saved annually. Similarly, RBS training laws are associated with saving an estimated 83 lives in the 37 jurisdictions that currently have the laws. If the remaining 14 states adopted these RBS training laws, we estimate that an additional 28 lives could potentially be saved. 相似文献
805.
Accuracy Assessment of NOAA Gridded Daily Reference Evapotranspiration for the Texas High Plains 下载免费PDF全文
Jerry Moorhead Prasanna Gowda Mike Hobbins Gabriel Senay George Paul Thomas Marek Dana Porter 《Journal of the American Water Resources Association》2015,51(5):1262-1271
The National Oceanic and Atmospheric Administration (NOAA) provides daily reference evapotranspiration (ETref) maps for the contiguous United States using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large‐scale spatial representation of ETref, which is essential for regional scale water resources management. Data used in the development of NOAA daily ETref maps are derived from observations over surfaces that are different from short (grass — ETos) or tall (alfalfa — ETrs) reference crops, often in nonagricultural settings, which carries an unknown discrepancy between assumed and actual conditions. In this study, NOAA daily ETos and ETrs maps were evaluated for accuracy, using observed data from the Texas High Plains Evapotranspiration (TXHPET) network. Daily ETos, ETrs and the climatic data (air temperature, wind speed, and solar radiation) used for calculating ETref were extracted from the NOAA maps for TXHPET locations and compared against ground measurements on reference grass surfaces. NOAA ETref maps generally overestimated the TXHPET observations (1.4 and 2.2 mm/day ETos and ETrs, respectively), which may be attributed to errors in the NLDAS modeled air temperature and wind speed, to which reference ETref is most sensitive. Therefore, a bias correction to NLDAS modeled air temperature and wind speed data, or adjustment to the resulting NOAA ETref, may be needed to improve the accuracy of NOAA ETref maps. 相似文献
806.
Identifying and Evaluating a Suitable Index for Agricultural Drought Monitoring in the Texas High Plains 下载免费PDF全文
Jerry E. Moorhead Prasanna H. Gowda Vijay P. Singh Dana O. Porter Thomas H. Marek Terry A. Howell B.A. Stewart 《Journal of the American Water Resources Association》2015,51(3):807-820
Drought is a complex and highly destructive natural phenomenon that affects portions of the United States almost every year, and severe water deficiencies can often become catastrophic for agricultural production. Evapotranspiration (ET) by crops is an important component in the agricultural water budget; thus, it is advantageous to include ET in agricultural drought monitoring. The main objectives of this study were to (1) conduct a literature review of drought indices with a focus to identify a simple but simultaneously adequate drought index for monitoring agricultural drought in a semiarid region and (2) using the identified drought index method, develop and evaluate time series of that drought index for the Texas High Plains. Based on the literature review, the Standardized Precipitation‐Evapotranspiration Index (SPEI) was found to satisfy identified constraints for assessing agricultural drought. However, the SPEI was revised by replacing reference ET with potential crop ET to better represent actual water demand. Data from the Texas High Plains Evapotranspiration network was used to calculate SPEIs for the major irrigated crops. Trends and magnitudes of crop‐specific, time‐series SPEIs followed crop water demand patterns for summer crops. Such an observation suggests that a modified SPEI is an appropriate index to monitor agricultural drought for summer crops, but it was found to not account for soil water stored during the summer fallow period for winter wheat. 相似文献
807.
Can Rapid Assessment Protocols Be Used to Judge Sediment Impairment in Gravel‐Bed Streams? A Commentary 下载免费PDF全文
Thomas E. Lisle John M. Buffington Peter R. Wilcock Kristin Bunte 《Journal of the American Water Resources Association》2015,51(2):373-387
Land management agencies commonly use rapid assessments to evaluate the impairment of gravel‐bed streams by sediment inputs from anthropogenic sources. We question whether rapid assessment can be used to reliably judge sediment impairment at a site or in a region. Beyond the challenges of repeatable and accurate sampling, we argue that a single metric or protocol is unlikely to reveal causative relations because channel condition can result from multiple pathways, processes, and background controls. To address these concerns, a contextual analysis is needed to link affected resources, causal factors, and site history to reliably identify human influences. Contextual analysis is equivalent in principle to cumulative effects and watershed analyses and has a rich history, but has gradually been replaced by rapid assessment methods. Although the approaches differ, rapid assessment and contextual analysis are complementary and can be implemented in a two‐tiered approach in which rapid assessment provides a coarse (first‐tier) analysis to identify sites that deserve deeper contextual assessment (second‐tier). Contextual analysis is particularly appropriate for site‐specific studies that should be tailored to local conditions. A balance between rapid assessment and contextual analysis is needed to provide the most effective information for management decisions. 相似文献
808.
809.
810.
Danz NP Niemi GJ Regal RR Hollenhorst T Johnson LB Hanowski JM Axler RP Ciborowski JJ Hrabik T Brady VJ Kelly JR Morrice JA Brazner JC Howe RW Johnston CA Host GE 《Environmental management》2007,39(5):631-647
Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be valuable tools in environmental research and management. Despite the fundamental appeal of a regional approach, development of regional stress measures remains one of the most important current challenges in environmental science. Using publicly available, pre-existing spatial datasets, we developed a geographic information system database of 86 variables related to five classes of anthropogenic stress in the U.S. Great Lakes basin: agriculture, atmospheric deposition, human population, land cover, and point source pollution. The original variables were quantified by a variety of data types over a broad range of spatial and classification resolutions. We summarized the original data for 762 watershed-based units that comprise the U.S. portion of the basin and then used principal components analysis to develop overall stress measures within each stress category. We developed a cumulative stress index by combining the first principal component from each of the five stress categories. Maps of the stress measures illustrate strong spatial patterns across the basin, with the greatest amount of stress occurring on the western shore of Lake Michigan, southwest Lake Erie, and southeastern Lake Ontario. We found strong relationships between the stress measures and characteristics of bird communities, fish communities, and water chemistry measurements from the coastal region. The stress measures are taken to represent the major threats to coastal ecosystems in the U.S. Great Lakes. Such regional-scale efforts are critical for understanding relationships between human disturbance and ecosystem response, and can be used to guide environmental decision-making at both regional and local scales. 相似文献