全文获取类型
收费全文 | 2306篇 |
免费 | 243篇 |
国内免费 | 822篇 |
专业分类
安全科学 | 229篇 |
废物处理 | 112篇 |
环保管理 | 354篇 |
综合类 | 1620篇 |
基础理论 | 358篇 |
环境理论 | 1篇 |
污染及防治 | 428篇 |
评价与监测 | 67篇 |
社会与环境 | 187篇 |
灾害及防治 | 15篇 |
出版年
2024年 | 9篇 |
2023年 | 44篇 |
2022年 | 88篇 |
2021年 | 108篇 |
2020年 | 123篇 |
2019年 | 120篇 |
2018年 | 96篇 |
2017年 | 138篇 |
2016年 | 166篇 |
2015年 | 155篇 |
2014年 | 160篇 |
2013年 | 200篇 |
2012年 | 248篇 |
2011年 | 233篇 |
2010年 | 158篇 |
2009年 | 166篇 |
2008年 | 131篇 |
2007年 | 175篇 |
2006年 | 161篇 |
2005年 | 98篇 |
2004年 | 89篇 |
2003年 | 106篇 |
2002年 | 83篇 |
2001年 | 59篇 |
2000年 | 62篇 |
1999年 | 45篇 |
1998年 | 27篇 |
1997年 | 22篇 |
1996年 | 12篇 |
1995年 | 19篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有3371条查询结果,搜索用时 15 毫秒
971.
Akhter U. Ahmed Rajan K. Sampath 《Journal of the American Water Resources Association》1988,24(5):1057-1063
ABSTRACT: This paper investigates and estimates the welfare loss due to monopoly in tubewell irrigation water market in Bangladesh. In this context, an attempt has been made to evaluate the efficacy of the landless irrigation groups. Using cross-sectional data and regression analysis, cost and demand functions for irrigation water are estimated. The study demonstrates the relatively superior performance of the landless groups in terms of economic efficiency in shallow tubewell irrigation operation, in comparison to irrigation operation by the landowners. 相似文献
972.
Douglas R. Franklin Rangesan Narayanan 《Journal of the American Water Resources Association》1988,24(6):1289-1294
ABSTRACT: From 1940 to 1978, irrigated acreage in the Western United States increased by over 150 percent, irrigated acres per farm increased by 204 percent, and the number of irrigation organizations grew by 31 percent. Understanding the factors affecting these trends (in the structure of irrigated agriculture) is the key to formulating policies for efficient allocation and transfer of water in the west. Four variables that impact the composition of irrigation organizations are farm size changes, organizational efficiency, intersectoral competition for water, and governmental policies. The conclusions show that from 1940 to 1978, the total number of irrigated farms and organizations declined, and the average farm size increased, and larger management oriented organizations such as districts and U.S. Bureau of Reclamation have become more prevalent. With respect to total quantities of water delivered, districts have increased over 50 percent since the 1959 Census and over 100 percent since the 1950 Census, while unincorporated mutuals have declined by approximately 20 percent. Future organizational structure tends to be moving in the direction of more management control as opposed to user control. Changes in water use, delivery, investment, transfers, and laws will continue to change the structure of irrigation organizations and institutions in the west. 相似文献
973.
Hudak PF 《Environmental monitoring and assessment》2002,75(2):215-221
Effects of distance lags between landfills and monitoring wells on contaminant detection capability were quantified in several groundwater velocity settings. Detection efficiency calculations were made with and without imposing a time limit on contaminant travel. In general, longer distance lags yieldedhigher detection efficiencies. However, detection efficienciesdecreased as monitoring wells approached a buffer zone boundaryimposing a maximum permissible contaminant transport distance.Imposing a time limit on contaminant travel substantially reduced detection efficiency in low velocity settings, especiallyat longer distance lags. Time limits were less significant in high velocity settings where contaminants more quickly reachedmonitoring wells. Detection efficiencies also decreased as velocity increased, but decreases were minor once the velocityreached a threshold value. 相似文献
974.
Hoenicke R Davis JA Gunther A Mumley TE Abu-Saba K Taberski K 《Environmental monitoring and assessment》2003,81(1-3):15-25
The San Francisco Estuary Regional Monitoring Program (RMP) for Trace Substances is an innovative partnership among a regulatory agency, more than 70 regulated entities, and an independent scientific organization. The institutional arrangement behind the RMP has made the regulatory system increasingly responsive to emerging management needs, particularly with regard to the development of total maximum daily loads and ecosystem impairment assessment. Through multi-agency partnerships within and outside the RMP institutional structure, major information gaps for several pollutants of concern have been narrowed, resulting in a successful consensus-based regulatory approach to managing copper and nickel mass inputs into the Estuary. Short-term research efforts, based upon monitoring results, helped identify the most cost-effective control and remediation options for various bioaccumulative substances. Additionally, adaptive changes to the monitoring program documented the existence of widespread aquatic toxicity in the Estuary that is apparently due to pesticide runoff from agricultural and urban areas. One of the most important contributions of this collaborative monitoring program is the deliberate and systematic adjustment of management and research questions that serve to influence and add relevance to the overall research agenda related to San Francisco Estuary ecosystem assessment. 相似文献
975.
Chevalier LR 《Environmental monitoring and assessment》2003,84(1-2):19-33
Improper disposal, accidental spills and leaks of non-aqueousphase liquids (NAPL) such as gasoline, fuel oil and creosote result in long-term persistent sources of groundwater pollution.Column and 2-D tanks experiments were conducted to evaluate the use of surfactant-enhanced recovery of light non-aqueous phase liquids (LNAPL) in groundwater aquifers. These experiments focused on the use of surfactants to promote dissolution and mobilization in addition to evaluating the increase of aqueous phase permeability as residual NAPL is recovered. Further experiments are presented that show the innovative use of surfactants during primary pumping to recover free product canpotentially increase the amount of free product recovered, canpotentially reduce the amount of residual NAPL remaining afterprimary pumping and performs better than the use of surfactantsto mobilize trapped residual NAPL. 相似文献
976.
利用自养煤矸石砖技术治理铬渣初步研究 总被引:7,自引:1,他引:7
本研究通过焙烧试验 ,对利用自养煤矸石砖技术治理铬渣进行了初步研究。结果表明 ,在自养煤矸石砖的焙烧过程中 ,其中炭和自身热量能将铬渣中六价铬还原成 (三价铬 )。本研究确定了该铬渣治理方法工艺简单、成本低、解毒彻底、稳定性强 ,具有广泛的应用前景。 相似文献
977.
Leaf area development, dry weight accumulation and solar energy conversion efficiencies of Phaseolus vulgaris L. cv GLP-2 under two soil moisture levels in two contrasting seasons near Nairobi, Kenya were investigated. The experiment confirms that dry weights and yields of Phaseolus vulgaris are limited by a drought induced decrease in leaf area, leading to less radiation interception as a source for assimilation. However, photosynthetic efficiency in Phaseolus vulgaris also appears to decrease and to contribute to these effects. Finally, an even larger decreases of economic efficiency as obtained in the second season, where stress lasted much later into the season, reveals that such a drought also limits considerably the partitioning and translocation of assimilates to the seeds of Phaseolus vulgaris. The efficiencies obtained are in line with the better literature data for other crops. 相似文献
978.
979.
声波反吹清灰对除尘效率的影响 总被引:2,自引:0,他引:2
声波反吹清灰会使除尘效率略有降低,已被实验和统计资料所证实。为减小其对除尘效率的影响,又要达到降低除尘器运行阻力的目的,必须选择合适的鸣喇叭次数。对于较难脱落的粉尘应选较多的鸣喇叭次数,而对较易脱落的粉尘则不需每次清灰都鸣喇叭,仅需偶而启动一次。本文通过实验证明,对本实验所用的除尘系统,每四次反吹清灰后鸣喇叭一次是合适的。 相似文献
980.
试论执行力文化的构建与政府行政效率的提高 总被引:1,自引:0,他引:1
首先论述了执行力文化的提出及内涵,随后说明了导致政府行政效率低下的3个原因,由此引出了在政府中倡导构建执行力文化是提高政府效率的有效手段,最后以秦皇岛市为例,说明了在政府中如何构建执行力文化的几个方面内容. 相似文献