全文获取类型
收费全文 | 2250篇 |
免费 | 127篇 |
国内免费 | 257篇 |
专业分类
安全科学 | 79篇 |
废物处理 | 13篇 |
环保管理 | 630篇 |
综合类 | 879篇 |
基础理论 | 504篇 |
污染及防治 | 88篇 |
评价与监测 | 66篇 |
社会与环境 | 306篇 |
灾害及防治 | 69篇 |
出版年
2024年 | 7篇 |
2023年 | 24篇 |
2022年 | 43篇 |
2021年 | 61篇 |
2020年 | 62篇 |
2019年 | 48篇 |
2018年 | 41篇 |
2017年 | 68篇 |
2016年 | 71篇 |
2015年 | 74篇 |
2014年 | 85篇 |
2013年 | 134篇 |
2012年 | 108篇 |
2011年 | 148篇 |
2010年 | 133篇 |
2009年 | 135篇 |
2008年 | 116篇 |
2007年 | 138篇 |
2006年 | 144篇 |
2005年 | 128篇 |
2004年 | 106篇 |
2003年 | 108篇 |
2002年 | 89篇 |
2001年 | 85篇 |
2000年 | 87篇 |
1999年 | 58篇 |
1998年 | 41篇 |
1997年 | 37篇 |
1996年 | 37篇 |
1995年 | 42篇 |
1994年 | 23篇 |
1993年 | 32篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有2634条查询结果,搜索用时 15 毫秒
51.
Keith E. Schilling Robert D. Libra 《Journal of the American Water Resources Association》2003,39(4):851-860
ABSTRACT: Historical trends in annual discharge characteristics were evaluated for 11 gauging stations located throughout Iowa. Discharge records from nine eight‐digit hydrologic unit code (HUC‐8) watersheds were examined for the period 1940 to 2000, whereas data for two larger river systems (Cedar and Des Moines Rivers) were examined for a longer period of record (1903 to 2000). In nearly all watersheds evaluated, annual base flow, annual minimum flow, and the annual base flow percentage significantly increased over time. Some rivers also exhibited increasing trends in total annual discharge, whereas only the Maquoketa River had significantly decreased annual maximum flows. Regression of stream discharge versus precipitation indicated that more precipitation is being routed into streams as base flow than as storm flow in the second half of the 20th Century. Reasons for the observed stream flow trends are hypothesized to include improved conservation practices, greater artificial drainage, increasing row crop production, and channel incision. Each of these reasons is consistent with the observed trends, and all are likely responsible to some degree in most watersheds. 相似文献
52.
Gerard McMahon Jerad D. Bales James F. Coles Elise M. P. Giddings Humbert Zappia 《Journal of the American Water Resources Association》2003,39(6):1529-1546
ABSTRACT: This paper presents the results of a study on the use of continuous stage data to describe the relation between urban development and three aspects of hydrologic condition that are thought to influence stream ecosystems—overall stage variability, stream flashiness, and the duration of extreme‐stage conditions. This relation is examined using data from more than 70 watersheds in three contrasting environmental settings—the humid Northeast (the metropolitan Boston, Massachusetts, area); the very humid Southeast (the metropolitan Birmingham, Alabama, area); and the semiarid West (the metropolitan Salt Lake City, Utah, area). Results from the Birmingham and Boston studies provide evidence linking increased urbanization with stream flashiness. Fragmentation of developed land cover patches appears to ameliorate the effects of urbanization on overall variability and flashiness. There was less success in relating urbanization and streamflow conditions in the Salt Lake City study. A related investigation of six North Carolina sites with long term discharge and stage data indicated that hydrologic condition metrics developed using continuous stage data are comparable to flow based metrics, particularly for stream flashiness measures. 相似文献
53.
环境是动物生存的基础,人类的活动对环境所造成的影响,直接导致动物种群数量的变动。通过渭河咸阳段气候、水质、水域面积、植物等环境因素的改变对野鸭数量分布影响的调查,表明环境的恶化导致了动物的生存受到威胁,数量减少,分布区域缩小。随着环境保护意识的增强,渭河流域的水土流失,水质污染、退耕还草等环境问题逐渐得到解决,动物的生活环境不断得到改善,其种群数量、分布范围随之增加。 相似文献
54.
Jon E. Schoonover Karl W. J. Williard 《Journal of the American Water Resources Association》2003,39(2):347-354
ABSTRACT: Ground water contamination by excess nitrate leaching in row‐crop fields is an important issue in intensive agricultural areas of the United States and abroad. Giant cane and forest riparian buffer zones were monitored to determine each cover type's ability to reduce ground water nitrate concentrations. Ground water was sampled at varying distances from the field edge to determine an effective width for maximum nitrate attenuation. Ground water samples were analyzed for nitrate concentrations as well as chloride concentrations, which were used as a conservative ion to assess dilution or concentration effects within the riparian zone. Significant nitrate reductions occurred in both the cane and the forest riparian buffer zones within the first 3.3 m, a relatively narrow width. In this first 3.3 m, the cane and forest buffer reduced ground water nitrate levels by 90 percent and 61 percent, respectively. Approximately 40 percent of the observed 99 percent nitrate reduction over the 10 m cane buffer could be attributed to dilution by upwelling ground water. Neither ground water dilution nor concentration was observed in the forest buffer. The ground water nitrate attenuation capabilities of the cane and forest riparian zones were not statistically different. During the spring, both plant assimilation and denitrification were probably important nitrate loss mechanisms, while in the summer nitrate was more likely lost via denitrification since the water table dropped below the rooting zone. 相似文献
55.
本文主要介绍了刺参无公害养殖的基本要求和生态养殖方法。针对刺参养殖过程中面积的问题进行分析探讨,提出可持续发展建议。 相似文献
56.
Joseph Domagalski 《Journal of the American Water Resources Association》1996,32(5):953-964
ABSTRACT: Pesticides in stormwater runoff, within the Sacramento River Basin, California, were assessed during a storm that occurred in January 1994. Two organophosphate insecticides (diazinon and methidathion), two carbamate pesticides (molinate and carbofuran), and one triazine herbicide (simazine) were detected. Organophosphate pesticide concentrations increased with the rising stage of the hydrographs; peak concentrations were measured near peak discharge. Diazinon oxon, a toxic degradation product of diazinon, made up approximately 1 to 3 percent of the diazinon load. The Feather River was the principal source of organophosphate pesticides to the Sacramento River during this storm. The concentrations of molinate and carbofuran, pesticides applied to rice fields during May and June, were relatively constant during and after the storm. Their presence in surface water was attributed to the flooding and subsequent drainage, as a management practice to degrade rice stubble prior to the next planting. A photo-degradation product of molinate, 4-keto molinate, was in all samples where molinate was detected and made up approximately 50 percent of the total molinate load. Simazine, a herbicide used in orchards and to control weeds along the roadways, was detected in the storm runoff, but it was not possible to differentiate the two sources of that pesticide to the Sacramento River. 相似文献
57.
58.
59.
农业旱灾监测中土壤水分遥感反演研究进展 总被引:14,自引:0,他引:14
土壤水分是农业干旱监测最重要的指标之一。文章全面回顾了光学遥感和微波遥感土壤水分遥感反演进展,重点讨论了符种反演方法的优点和不足。光学遥感中,热惯量法和作物缺水指数法可分别较好地应用于裸露地和作物覆盖地的土壤水分监测;距平植被指数、植被条件指数采用了植被指数因子实现农业旱情监测,温度植被指数、植被供水指数和条件植被温度指数同时考虑了作物植被指数和地表温度。微波遥感被认为是当前土壤水分监测中最有效的方法。主动微波遥感空间分辨率较高,但对土壤粗糙度和植被敏感;被动微波遥感空间分辨率低,重访周期短,对大尺度农业旱灾监测具有较大潜力。为提高农业旱灾监测巾土壤水分遥感反演的精度和效率,采用光学遥感和微波遥感的结合可能是较为实际的方法。 相似文献
60.
土地开发整理是一项旨在提高土地生产力,改善农业生产条件和生态环境的活动,本文从目前黄河三角洲地区实际土地开发整理的情况分析,通过土地开发整理增加耕地面积,提高土地生产力,进一步呼吁对农业生态环境保护这一目标加强重视,形成一整套完整的土地开发整理生态绩效的评价体系和方法,以利于土地经济和土地生态的均衡发展。从生态学的角度对这一问题做出了比较全面的思考。 相似文献