全文获取类型
收费全文 | 681篇 |
免费 | 65篇 |
国内免费 | 54篇 |
专业分类
安全科学 | 30篇 |
废物处理 | 12篇 |
环保管理 | 268篇 |
综合类 | 251篇 |
基础理论 | 93篇 |
污染及防治 | 14篇 |
评价与监测 | 20篇 |
社会与环境 | 66篇 |
灾害及防治 | 46篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 15篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2017年 | 27篇 |
2016年 | 27篇 |
2015年 | 16篇 |
2014年 | 13篇 |
2013年 | 27篇 |
2012年 | 25篇 |
2011年 | 31篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 38篇 |
2007年 | 34篇 |
2006年 | 48篇 |
2005年 | 27篇 |
2004年 | 44篇 |
2003年 | 23篇 |
2002年 | 42篇 |
2001年 | 29篇 |
2000年 | 21篇 |
1999年 | 30篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 2篇 |
排序方式: 共有800条查询结果,搜索用时 15 毫秒
41.
V Hrissanthou 《Journal of the American Water Resources Association》1990,26(5):801-810
ABSTRACT: A simulation model that computes sediment yield due to sheet and rill erosion at the outlet of a large watershed requires daily precipitation and the soil, topographic, and vegetative characteristics of the watershed. An important problem, particularly in a large watershed, is the transport of sediment produced in the sub-watersheds to the outlet of the whole watershed. This problem is approached mathematically by a sediment routing model that is used as a component of the total model. 相似文献
42.
Marc O. Ribaudo C. Edwin Young 《Journal of the American Water Resources Association》1989,25(1):71-78
ABSTRACT: A framework for estimating the water quality benefits from soil erosion was developed. The framework is based on the linkages between soil erosion and offsite damages. The linkages are: erosion on the field, movement of eroded materials to waterways, impact of discharged material on water quality parameters, impact of water quality changes on ability of water to provide economic services, and the economic value of the changes in water use. These linkages need to be modeled in order to estimate the water quality benefits from reductions in soil erosion. Methods for modeling each link on a geographic level, which enables the analyses of national soil conservation, were examined. Areas where data or models were found to be lacking include transport of sediment and nutrients to water systems, impact of discharged materials on water quality parameters, and impact of water quality on ability of water to provide economic services. An economic evaluation of 1983 soil conservation programs was presented as an example of how the framework could be used. A number of simplifying assumptions were made to represent links that could not be modeled with available data. 相似文献
43.
F B. Pierson W. H. Blackburn S. S. Van Vactor J. C. Wood 《Journal of the American Water Resources Association》1994,30(6):1081-1089
ABSTRACT: Most hydrologic models require input parameters which represent the variability found across an entire landscape. The estimation of such parameters is very difficult, particularly on rangeland. Improved model parameter estimation procedures are needed which incorporate the small-scale and temporal variability found on rangeland. This study investigates the use of a surface soil classification scheme to partition the spatial variability in hydrologic and interrill erosion processes in a sagebrush plant community. Four distinct microsites were found to exist within the sagebrush coppice-dune dune-interspace complex. The microsites explained the majority of variation in hydrologic and interrill erosion response found on the site and were discernable based on readily available soil and vegetation information. The variability within each microsite was quite low and was not well correlated with soil and vegetation properties. The surface soil classification scheme defined in this study can be quite useful for defining sampling procedures, for understanding hydrologic and erosion processes, and for parameterizing hydrologic models for use on sagebrush range-land. 相似文献
44.
Analysis of bank erosion on the Merced River,Yosemite Valley,Yosemite National Park,California, USA 总被引:1,自引:0,他引:1
Channel changes from 1919 to 1989 were documented in two study reaches of the Merced River in Yosemite National Park through
a review of historical photographs and documents and a comparison of survey data. Bank erosion was prevalent and channel width
increased an average of 27% in the upstream reach, where human use was concentrated. Here, trampling of the banks and riparian
vegetation was common, and banks eroded on straight stretches as frequently as on meander bends. Six bridges in the upper
reach constrict the channel by an average of 38% of the original width, causing severe erosion. In the downstream control
reach, where human use was minimal, channel widths both decreased and increased, with a mean increase of only 4% since 1919.
Bank erosion in the control reach occurred primarily on meander bends. The control reach also had denser stands of riparian
vegetation and a higher frequency of large woody debris in channels. There is only one bridge in the lower reach, located
at the downstream end. Since 1919, bank erosion in the impacted upstream reach contributed a significant amount of sediment
(74,800 tonnes, equivalent to 2.0 t/km2/yr) to the river. An analysis of 75 years of precipitation and hydrologic records showed no trends responsible for bank erosion
in the upper reach. Sediment input to the upper reach has not changed significantly during the study period. Floodplain soils
are sandy, with low cohesion and are easily detached by lateral erosion. The degree of channel widening was positively correlated
with the percentage of bare ground on the streambanks and low bank stability ratings. Low bank stability ratings were, in
turn, strongly associated with high human use areas. Channel widening and bank erosion in the upper reach were due primarily
to destruction of riparian vegetation by human trampling and the effect of bridge constrictions on high flow, and secondarily
to poorly installed channel revetments. Several specific recommendations for river restoration were provided to park management. 相似文献
45.
M. Reza Savabi Gerald F. Giffor 《Journal of the American Water Resources Association》1987,23(4):709-716
ABSTRACT: Soil loss prediction equations (Universal Soil Loss Equation, Modified Universal Soil Loss Equation, and Onstad-Foster Method) were modified to reflect the impact of trampling on soil erosion. The erosion control practice factor, P, was replaced by a trampling ratio, Tr, which is a function of the change in soil erosion due to animal trampling. Trampling impact on soil erosion varied With soil type. The data are a preliminary attempt to account for the impact of trampling on soil erosion. 相似文献
46.
47.
本文介绍了黄土地区土壤侵蚀信息系统的建造原理与方法。分析探讨了土壤侵蚀各因子计算机自动提取的算法,以及土壤侵蚀预测模型的构造方法,并用灰色控制系统的原理确定了模型的参数。并以山西省离石县王家沟流域羊道沟为例进行了试验研究。 相似文献
48.
Ensuring that new buildings do not interfere with the recreational and protective functions of the natural system and that the buildings will be useful long enough to protect the investment are among long-term solutions to coastal erosion. We propose that coastal cliff management districts be established for management of eroding high relief shorelines. Such districts would include an imminent failure zone, in which bluff retreat is possible at any time; a migration zone, which allows for long-term shoreline retreat; and a stability control zone in which activities affecting bluff erosion are restricted. Procedures are described for delineating these zones based on geomorphic criteria. If these land use controls are implemented, some shorefront development can be accommodated while retaining valuable characteristics of the natural system. 相似文献
49.
Peter F. Korsching Peter J. Nowak 《Journal of the American Water Resources Association》1983,19(3):459-462
Water pollution through loss of topsoil from farmland continues to be a major problem, despite nearly 50 years of providing farmers technical and financial assistance for soil and water conservation. The technology for controlling erosion and water pollution is available, but farmers have been slow in implementing control practices. Past research has shown that farmers tend to be unaware of the seriousness of the erosion problem on their own operations. Using a random sample of farmers from central Iowa, the relationship is examined between awareness of a soil erosion problem and the use of conservation tillage. Results indicate that awareness of a soil erosion problem effects the use of conservation tillage, and that awareness can be enhanced by experiential educational strategies such as the development and implementation of a soil and water conservation plan. 相似文献
50.
Understanding how hydraulic factors control alluvial river meander migration can help resource managers evaluate the long-term
effects of floodplain management and bank stabilization measures. Using a numerical model based on the mechanics of flow and
sediment transport in curved river channels, we predict 50 years of channel migration and suggest the planning and ecological
implications of that migration for a 6.4-km reach (river miles 218–222) of the Sacramento River near the Woodson Bridge State
Recreation Area, California, USA.
Using four different channel management scenarios, our channel migration simulations suggest that: (1) channel stabilization
alters the future channel planform locally and downstream from the stabilization; (2) rock revetment currently on the bank
upstream from the Woodson Bridge recreation area causes more erosion of the channel bank at the recreation area than if the
revetment were not present; (3) relocating the channel to the west and allowing subsequent unconstrained river migration relieves
the erosion pressure in the Woodson Bridge area; (4) the subsequent migration reworks (erodes along one river bank and replaces
new floodplain along the other) 26.5 ha of land; and (5) the river will rework between 8.5 and 48.5 ha of land in the study
reach (over the course of 50 years), depending on the bank stabilization plan used. The reworking of floodplain lands is an
important riparian ecosystem function that maintains habitat heterogeneity, an essential factor for the long-term survival
of several threatened and endangered animal species in the Sacramento River area. 相似文献