全文获取类型
收费全文 | 1560篇 |
免费 | 145篇 |
国内免费 | 250篇 |
专业分类
安全科学 | 191篇 |
废物处理 | 20篇 |
环保管理 | 409篇 |
综合类 | 741篇 |
基础理论 | 244篇 |
污染及防治 | 54篇 |
评价与监测 | 92篇 |
社会与环境 | 139篇 |
灾害及防治 | 65篇 |
出版年
2024年 | 4篇 |
2023年 | 31篇 |
2022年 | 54篇 |
2021年 | 63篇 |
2020年 | 54篇 |
2019年 | 57篇 |
2018年 | 51篇 |
2017年 | 67篇 |
2016年 | 59篇 |
2015年 | 72篇 |
2014年 | 68篇 |
2013年 | 77篇 |
2012年 | 89篇 |
2011年 | 122篇 |
2010年 | 75篇 |
2009年 | 111篇 |
2008年 | 70篇 |
2007年 | 94篇 |
2006年 | 102篇 |
2005年 | 65篇 |
2004年 | 73篇 |
2003年 | 69篇 |
2002年 | 57篇 |
2001年 | 59篇 |
2000年 | 46篇 |
1999年 | 31篇 |
1998年 | 30篇 |
1997年 | 35篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有1955条查询结果,搜索用时 31 毫秒
971.
Water, Air, &; Soil Pollution: Focus - The mountain ecosystems of the Hindu Kush Himalayas are generally considered to be pristine despite little available data to confirm it. Is there any... 相似文献
972.
David W. Crowder Panayiotis Diplas 《Journal of the American Water Resources Association》2002,38(2):397-408
ABSTRACT: Urbanization, farming, and other watershed activities can significantly alter storm hydrographs and sediment erosion rates within a watershed. These changes routinely cause severe economic and ecological problems manifested in the form of increased flooding and significant changes in channel morphology. As the activities within a watershed influence the hydrologic, hydraulic, and ecological conditions within a river, interdisciplinary approaches to predict and assess the impacts that different land uses have on streams need to be developed. An important component of this process is ascertaining how hydrologic changes induced by specific watershed activities will affect hydraulic conditions and the accompanying flood levels, sediment transport rates, and habitat conditions within a stream. A conceptual model for using spatially explicit (two‐dimensional) hydraulic models to help evaluate the impacts that changes in flow regime might have on a river is presented. This framework proposes that reproducing and quantifying flow complexity allows one to compare the hydraulic conditions within urban, urbanizing, and non‐urban streams in a more biologically and economically meaningful way. The justification, advantage, and need for such a method is argued through the results of one‐ and two‐dimensional hydraulic model studies. The implementation of this methodology in watershed urbanization studies is described. 相似文献
973.
Kristine F. Stepenuck Ronald L. Crunkilton Lizhu Wang 《Journal of the American Water Resources Association》2002,38(4):1041-1051
ABSTRACT: Macroinvertebrates were used to assess the impact of urbanization on stream quality across a gradient of watershed imperviousness in 43 southeastern Wisconsin streams. The percentage of watershed connected imperviousness was chosen as the urbanization indicator to examine impact of urban land uses on macroinvertebrate communities. Most urban land uses were negatively correlated with the Shannon diversity index, percent of pollution intolerant Ephemeroptera, Plecoptera, and Trichoptera individuals, and generic richness. Nonurban land uses were positively correlated with these same metrics. The Hilsenhoff biotic index indicated that stream quality declined with increased urbanization. Functional feeding group metrics varied across a gradient of urbanization, suggesting changes in stream quality. Proportions of collectors and gatherers increased, while proportions of filterers, scrapers, and shredders decreased with increased watershed imperviousness. This study demonstrated that urbanization severely degraded stream macroinvertebrate communities, hence stream quality. Good stream quality existed where imperviousness was less than 8 percent, but less favorable assessments were inevitable where imperviousness exceeded 12 to 20 percent. Levels of imperviousness between 8 and 12 percent represented a threshold where minor increases in urbanization were associated with sharp declines in stream quality. 相似文献
974.
笔者阐述了企业安技人员的工作职能已发生转变的背景和原因 ,由原来“直接实施安全”转变为“间接实施安全” ;而负有为企业培养安技人员职责的高等院校 ,其安全工程本科专业的知识结构须作相应改革 ,从“系统安全”型的“拼盘式”知识结构转变到“安全系统”型的“有机”知识结构 ;通过深入研讨和分析后 ,笔者认为 ,推动和加速安技人员在企业安全生产管理工作中的职能及其转变 ,并实现安全工程本科专业知识结构的改革 ,对提高我国企业整体安全生产管理水平有着重要意义 相似文献
975.
地震应急指挥模式探讨 总被引:10,自引:1,他引:10
通过对地震应急指挥系统业务范畴、工作特点、所起作用及特定结构的较为系统的分析,确定了实现地震应急指挥功能的必备条件和实施地震应急指挥的各个关键环节.在总结了近几年地震应急工作经验的基础上,就有关地震应急指挥模式的问题进行了初步研究,认为目前我国地震应急指挥模式的核心是"提醒"功能,所有指挥事项均应围绕"提醒"进行深化与展开. 相似文献
976.
海南野生仙人掌资源的开发利用 总被引:1,自引:0,他引:1
介绍了海南野生仙人掌的成分、药理作用及其开发利用状况,以期为进一步开发利用提供借鉴. 相似文献
977.
The distribution of coarse woody debris (CWD) was analyzed in three Appalachian watersheds in eastern Kentucky, eighteen years after harvest. The three watersheds included an unharvested control (Control), a second watershed with best management practices (BMPs) applied that included a 15.2 m unharvested zone near the stream (BMP watershed), and a third watershed that was harvested without strict BMPs with harvesting occurring up to the stream edge and slash left within the stream and riparian zones (No BMP watershed). We assessed the CWD occurring both within the riparian zone and stream in the three watersheds. Within both stream and riparian zones, the BMP and No BMP watersheds contained more CWD biomass than in the Control, however, the No BMP watershed CWD was in a more advanced state of decay than in either the BMP or Control watersheds. Nitrogen content in CWD was also greater in the No BMP watershed because of the more advanced state of the decay. The CWD present in the Control is the result of natural forest processes such as death and self-pruning. The CWD in the No BMP watershed is a result of the slash left behind after the harvest since little opportunity exists for new recruitment of CWD from the surrounding area. From our decay class data, it is apparent that at least some of the CWD in the BMP watershed has occurred since harvest, and, based on our biomass data, at a much greater rate of recruitment than in the Control watershed. We hypothesize that the harvest outside of the riparian zone in the BMP watershed may have led to greater windthrow and/or slumping than in the Control watershed. As such, our data suggest that riparian zones of 15.2 m may not be effective in maintaining the short-term integrity of the CWD pool within steep gradient Appalachian systems. 相似文献
978.
979.
Dan Binkley George G. Ice Jason Kaye Christopher A. Williams 《Journal of the American Water Resources Association》2004,40(5):1277-1291
ABSTRACT: Seventy to eighty percent of the water flowing in rivers in the United States originates as precipitation in forests. This project developed a synoptic picture of the patterns in water chemistry for over 300 streams in small, forested watersheds across the United States. Nitrate (NO3?) concentrations averaged 0.31 mg N/L, with some streams averaging ten times this level. Nitrate concentrations tended to be higher in the northeastern United States in watersheds dominated by hardwood forests (especially hardwoods other than oaks) and in recently harvested watersheds. Concentrations of dissolved organic N (mean 0.32 mg N/L) were similar to those of NO3~, whereas ammonium (NH4+) concentrations were much lower (mean 0.05 mg N/L). Nitrate dominated the N loads of streams draining hardwood forests, whereas dissolved organic N dominated the streams in coniferous forests. Concentrations of inorganic phosphate were typically much lower (mean 12 mg P/L) than dissolved organic phosphate (mean 84 mg P/L). The frequencies of chemical concentrations in streams in small, forested watersheds showed more streams with higher NO3? concentrations than the streams used in national monitoring programs of larger, mostly forested watersheds. At a local scale, no trend in nitrate concentration with stream order or basin size was consistent across studies. 相似文献
980.
Anf H. Ziadat Bruce W. Berdanier 《Journal of the American Water Resources Association》2004,40(3):631-638
ABSTRACT: Ninety‐one sediment oxygen demand (SOD) samples from six designated sites along the stretch of Lower Rapid Creek, South Dakota, were conducted using an in‐situ SOD chamber. Inside the chamber, readings of dissolved oxygen (DO), water temperature, pH, and specific conductance were recorded every minute for more than one hour using the Datasonde 3 Hydrolab. Initial readings of such parameters were recorded for the overlaying water before the deployment of the SOD chamber. Characteristics of the stream conditions, air temperature, barometric pressure, average flow velocity of the stream, depth of the stream, and the flow velocity by the chamber were recorded. Single and multiple linear regression analyses on all parameters indicated that the velocity of the stream is the least critical parameter for SOD in shallow streams. 相似文献