全文获取类型
收费全文 | 575篇 |
免费 | 34篇 |
国内免费 | 203篇 |
专业分类
安全科学 | 17篇 |
废物处理 | 1篇 |
环保管理 | 283篇 |
综合类 | 332篇 |
基础理论 | 68篇 |
污染及防治 | 58篇 |
评价与监测 | 26篇 |
社会与环境 | 19篇 |
灾害及防治 | 8篇 |
出版年
2023年 | 11篇 |
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 28篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 24篇 |
2015年 | 28篇 |
2014年 | 27篇 |
2013年 | 41篇 |
2012年 | 49篇 |
2011年 | 31篇 |
2010年 | 27篇 |
2009年 | 25篇 |
2008年 | 34篇 |
2007年 | 36篇 |
2006年 | 49篇 |
2005年 | 34篇 |
2004年 | 21篇 |
2003年 | 28篇 |
2002年 | 20篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 3篇 |
排序方式: 共有812条查询结果,搜索用时 15 毫秒
711.
亚铁对水平潜流人工湿地反硝化作用的影响 总被引:6,自引:0,他引:6
亚铁离子可以作为电子供体参与反硝化作用,某些微生物可以通过氧化亚铁离子还原硝酸盐,从而去除污水中的硝态氮.本研究通过在潜流人工湿地中添加Fe2+,分析不同初始Fe2+浓度对反硝化过程的强化效果及不同C/N对Fe2+参与反硝化作用的影响.结果表明,Fe2+的添加可以显著提高人工湿地反硝化能力,进水NO-3-N为30 mg·L-1、C/N为2、水力停留时间为1 d,添加45 mg·L-1Fe2+的人工湿地中硝氮去除率可以提高24%;硝氮去除率随初始Fe2+浓度的增加而增加.C/N与初始Fe2+浓度对反硝化作用都具有显著影响且两者具有交互作用,碳源的存在可以促进Fe2+参与的反硝化作用. 相似文献
712.
为解决城镇污水二级生物处理厂脱磷不达标的问题,设计了潜流碎石床湿地,通过其填料的吸附、沉淀和植物摄取作用,对二级生化处理后的城镇污水进行脱磷试验。结果表明碎石床湿地有较高的脱磷效果,当进水TP为1.74mg/L时,出水为0.25mg/L,去除率为85.63%,同时对BOD5、COD、SS、NH3-N等也有一定去除作用。出水不仅能满足《污水综合排放标准》(GB8978-96)一级,而且满足《城市污水再生利用景观环境用水水质标准》(GB/T18921-2002),污水可以回用。潜流碎石床湿地深度脱磷技术运行费用低、管理方便、环境景观好、有推广应用价值。 相似文献
713.
Griffith JF Aumand LA Lee IM McGee CD Othman LL Ritter KJ Walker KO Weisberg SB 《Environmental monitoring and assessment》2006,117(1-3):335-344
During the summers of 2002 and 2004, in-stream integrated flow and concentration measurements for the total dissolved solids
in the Cheyenne River, South Dakota, USA was conducted in order to compare the obtained actual field measurements with the
predictions values made by the Bureau of Reclamation in the Environmental Impact Statement. In comparison to the actual field
measurements conducted in this study, The Bureau of Reclamation extension of a small database used in the analysis for the
impact of operations at the Angostura Unit over the past 50 years and into the future to predict the annual total dissolved
solid loadings doesn't represent the actual loading values and various conditions in the study area. Additional integrated
flow and concentration sampling is required to characterize the impact of the current Angostura Dam operations and Angostura
Irrigation District return flows on the Cheyenne River in different seasons of the year. 相似文献
714.
南方海涂海水灌溉库拉索芦荟的试验研究 总被引:20,自引:0,他引:20
在海南海涂沙滩(非耕地资源)对药用植物库拉索芦荟进行海水灌溉试验,设6种处理,淡、海水配比分别为A1(CK):100∶0;A2:90∶10;A3:75∶25;A4:50∶50;A5:25∶75;A6:0∶100。结果表明:①用一定浓度范围的海水灌溉时,库拉索芦荟苗期返青系数、根的综合生长量等植物生态指标为处理A3>A2>A1,超过一定海水浓度后则递减;连续3年的田间试验表明,芦荟叶片鲜重、干重A1、A2、A3三种处理间没有显著差异,而根干重A3显著高于A1,A4比A1处理叶片鲜重、干重减产均在20%以内,表明海水灌溉库拉索芦荟是可行的。②海水灌溉明显推迟芦荟从营养生长向生殖生长的转化时期,随着海水比例的增加,抽苔期明显推迟。③各种处理海水灌溉的沙滩深度在0~10cm范围内,盐分含量随深度迅速下降,10cm以下下降幅度变缓;经3年的海水灌溉试验,海涂沙滩在未作任何人为调控措施下,0~50cm沙滩含盐量仍在0.3%范围内。 相似文献
715.
Sam H. Johnson W. Doral Kemper Max K. Lowdermilk 《Journal of the American Water Resources Association》1979,15(2):473-495
ABSTRACT: Over half of the water delivered from the canal system to the watercourses managed by the farmers is not made available to the farmers' crops in Pakistan. Most of this water loss is due to loss of water through the banks of the watercourses. Lack of maintaining these banks and lack of cleaning the watercourse is a result of inadequate organization of the 10 to 150 farmers who use the watercourse, and a deficiency of knowledge concerning the amount of their water which is being lost. Various methods of watercourse improvement have been evaluated including concrete and masonry linings and simple earthen improvements of the ditches with concrete control structures, junctions, and turnouts. With the cost of labor low in Pakistan, the earthen improvements with concrete structures appear to be the best investment. Farm water management improvement programs have been implemented in most of the provinces which include this type of watercourse improvement, land leveling and advice to the farmers on how and when to irrigate his crops to optimize his production. The rate at which personnel can be trained to help the farmers implement these improved water management practices is limiting the rate of implementation. 相似文献
716.
Enrique V. Palacios John C. Day 《Journal of the American Water Resources Association》1977,13(4):709-720
ABSTRACT: In this paper a new methodology for estimating conveyance efficiency within irrigation systems is presented. Based on statistical analysis of daily water releases from the source of supply and deliveries to the farmers in an irrigation district in Mexico, a linear model is obtained for estimating conveyance efficiency and two component factors. One of these factors points out the relative importance of the operational losses (i.e., losses due to water management), and the second shows the importance of the fixed losses which can be attributed to the average flow through the canal network without variations. In the last part of this paper, an analysis of the expected benefits and costs accruing from system improvement permits derivation of a decision rule which may be used for analyzing the economic feasibility of lining in-place canals. 相似文献
717.
渍害田地下排水技术与江汉平原农业综合开发 总被引:7,自引:2,他引:5
江汉平原是全国重点开发区域之一。本文由分析江汉平原的资源优势及其主要后备资源渍害中低产田入手,以科学试验资料为依据,从理论与实践的结合上,阐述了地下排水技术是改造渍害中低产田的治本措施,进而说明了该项技术的推广应用是江汉平原农业综合开发的主体和关键。 相似文献
718.
D. J. Bernardo N. K. Whittlesey K. E. Saxton D. L. Bassett 《Journal of the American Water Resources Association》1988,24(1):149-157
ABSTRACT: A two-stage simulation/mathematical programming model was developed to derive irrigation water values that reflect efficient response to reduced water supplies. The failure of many previous water valuation studies to represent the dynamic dimension of irrigation was shown to result in overestimation of derived water values. Water values are also shown to be dramatically influenced by both application system characteristics, as well as the relative costs of irrigation inputs. Finally, the marginal value of irrigation water was shown to vary considerably over the irrigation season, reaching its maximum when atmospheric demand is highest and crops are most susceptible to water stress. Results presented should be of interest to policymakers investigating the viability of alternative water reallocation mechanisms. 相似文献
719.
George A. Whetstone Ernst W. Kiesling 《Journal of the American Water Resources Association》1971,7(4):684-688
ABSTRACT .The major purpose of existing and proposed diversions of water to the Prairies is for irrigation. Being flat lands adaptable to mechanized agriculture and possessing a good network of rail and highway access, they are well suited for such use. Wheat surpluses, currently a serious problem in Canada, can be expected to melt under world population pressures and conversion of wheat lands to other crops with the advent of irrigation. The water sources envisaged are in the Canadian Arctic watershed with the United States purchasing Canadian water at the boundary. There is an increasing interest in the Canadian Prairie Provinces in regarding water as a commodity and selling some of it to pay for the development required to put the portion retained in Canada to use. 相似文献
720.
J. H. Krishna G. F. Arkin J. R. Martin 《Journal of the American Water Resources Association》1987,23(6):1057-1061
ABSTRACT: The current increase in the demand for water by municipal, industrial, and other users is likely to result in approximately one-third less water being available for agricultural use in Texas by the year 2000. As water supplies diminish, the rainfall excess needs to be used more efficiently. Large amounts of runoff occur in the eastern part of Texas that could be collected in small impoundments and utilized for crop production. Farmers in water-surplus basins or subbasins can apply for a permit to divert surface water into small on-farm impoundments to be used for supplemental irrigation. The costs for runoff collection and two supplemental irrigations, which amount to a total of 4 in./yr., are estimated to be approximately $60/acre/year. Depending upon the crop produced, the estimated increase in gross income from supplemental irrigation ranges from about $80 to more than $100 per acre annually. 相似文献