全文获取类型
收费全文 | 2850篇 |
免费 | 98篇 |
国内免费 | 228篇 |
专业分类
安全科学 | 233篇 |
废物处理 | 89篇 |
环保管理 | 1137篇 |
综合类 | 837篇 |
基础理论 | 218篇 |
环境理论 | 1篇 |
污染及防治 | 91篇 |
评价与监测 | 197篇 |
社会与环境 | 145篇 |
灾害及防治 | 228篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 18篇 |
2021年 | 21篇 |
2020年 | 34篇 |
2019年 | 14篇 |
2018年 | 19篇 |
2017年 | 44篇 |
2016年 | 49篇 |
2015年 | 45篇 |
2014年 | 52篇 |
2013年 | 80篇 |
2012年 | 77篇 |
2011年 | 129篇 |
2010年 | 118篇 |
2009年 | 131篇 |
2008年 | 140篇 |
2007年 | 146篇 |
2006年 | 123篇 |
2005年 | 125篇 |
2004年 | 120篇 |
2003年 | 155篇 |
2002年 | 218篇 |
2001年 | 182篇 |
2000年 | 210篇 |
1999年 | 169篇 |
1998年 | 134篇 |
1997年 | 102篇 |
1996年 | 226篇 |
1995年 | 71篇 |
1994年 | 30篇 |
1993年 | 19篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 2篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 22篇 |
1984年 | 38篇 |
1983年 | 35篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 7篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1971年 | 14篇 |
1967年 | 1篇 |
排序方式: 共有3176条查询结果,搜索用时 78 毫秒
231.
Land-cover change in upper Barataria Basin estuary,Louisiana, 1972-1992: increases in Wetland area 总被引:1,自引:0,他引:1
The Barataria Basin, Louisiana, USA, is an extensive wetland and coastal estuary system of great economic and intrinsic value.
Although high rates of wetland loss along the coastal margin of the Barataria Basin have been well documented, little information
exists on whether freshwater wetlands in the upper basin have changed. Our objectives were to quantify land-cover change in
the upper basin over 20 years from 1972–1992 and to determine land-cover transition rates among land-cover types. Using 80-m
resolution Landsat MSS data from the North American Landscape Characterization (NALC) data archive, we classified images from
three time steps (1972, 1985, 1992) into six land-cover types: agriculture, urban, bottomland hardwood forest, swamp forest,
freshwater marsh, and open water. Significant changes in land cover occurred within the upper Barataria Basin over the study
period. Urban land increased from 8% to 17% of the total upper basin area, primarily due to conversions from agricultural
land, and to a lesser degree, bottomland forest. Swamp forest increased from 30% to 41%, associated with conversions from
bottomland hardwood forest and freshwater marsh. Overall, bottomland forest decreased 38% and total wetland area increased
21%. Within the upper Barataria, increases in total wetland area may be due to land subsidence. Based on our results, if present
trends in the reduction of bottomland forest land cover were to continue, the upper Barataria Basin may have no bottomland
hardwood forests left by the year 2025, as it is subjected to multiple stressors both in the higher elevations (from urbanization)
and lower elevations (most likely from land subsidence). These results suggest that changes in the upper freshwater portions
of coastal estuaries can be large and quite different from patterns observed in the more saline coastal margins. 相似文献
232.
Modeling the spatial dynamics of regional land use: the CLUE-S model 总被引:95,自引:3,他引:92
Verburg PH Soepboer W Veldkamp A Limpiada R Espaldon V Mastura SS 《Environmental management》2002,30(3):391-405
Land-use change models are important tools for integrated environmental management. Through scenario analysis they can help
to identify near-future critical locations in the face of environmental change. A dynamic, spatially explicit, land-use change
model is presented for the regional scale: CLUE-S. The model is specifically developed for the analysis of land use in small
regions (e.g., a watershed or province) at a fine spatial resolution. The model structure is based on systems theory to allow
the integrated analysis of land-use change in relation to socio-economic and biophysical driving factors. The model explicitly
addresses the hierarchical organization of land use systems, spatial connectivity between locations and stability. Stability
is incorporated by a set of variables that define the relative elasticity of the actual land-use type to conversion. The user
can specify these settings based on expert knowledge or survey data. Two applications of the model in the Philippines and
Malaysia are used to illustrate the functioning of the model and its validation. 相似文献
233.
Kennett SA 《Environmental management》2002,30(5):0595-0608
Biosphere greenhouse gas (GHG) management consists of preserving and enhancing terrestrial carbon pools and producing biomass
as a fossil fuel substitute. The discussion of this topic has focused primarily on carbon-accounting and project-level issues,
particularly relating to carbon sequestration as a source of emissions credits under the Kyoto Protocol. While international
consensus on these matters is needed, this paper argues that an important domestic policy agenda also deserves attention.
National policies for biosphere GHG management are necessary to bring about large-scale changes in land-use, forestry, and
agricultural practices and can address some of the technical and policy issues that have proven to be particularly problematic
from carbon-accounting and project-level perspectives. These policies should minimize land-use and resource-management conflicts,
account for collateral benefits, and ensure institutional compatibility with existing resource-management regimes. Issues
relating to project permanence, leakage, and transaction costs should also be addressed. A range of policy instruments should
be used and biosphere GHG management should be one component of an integrated approach to environmental and resource management.
Countries promoting biosphere GHG management as an important element of their climate change strategies should be developing
these domestic policies to complement international negotiations and to demonstrate that carbon sequestration and biomass
production can make an effective contribution to the stabilization of atmospheric GHG concentrations. 相似文献
234.
Ziegler CK 《Environmental management》2002,29(3):409-427
The stability of cohesive sediment deposits during a rare storm is a critical component in the evaluation of remedial options
at a contaminated sediment site. Estimating scour depths during a rare storm, and the resulting contaminant concentrations
in the surficial layer of the bed, is necessary for comparing the efficacy of various remedial alternatives. Evaluation of
sediment stability is accomplished using sediment transport analyses that employ quantitative procedures. Qualitative analyses
or conceptual models can be useful for developing and validating quantitative analysis tools; however, qualitative techniques
alone generally are insufficient for conducting defensible remedial alternative evaluations. The level of analysis used for
a specific site depends on data availability, required level of accuracy, and time and budget constraints. A tier 1 analysis
involves the use of approximate equations to produce order-of-magnitude estimates of scour depths during a rare storm. The
second tier of this analysis scheme employs the development and application of a sediment transport model to evaluate bed
stability. State-of-the-science sediment transport models have been effectively used as management tools for evaluating remedial
options at several contaminated sediment sites. It should not be presumed that rare storm events cause catastrophic impacts
at the site under review. Two case studies demonstrate that a rare storm is not necessarily catastrophic; significant increases
in surficial bed concentrations caused by reexposure of elevated concentrations buried at depth in the bed will not necessarily
occur during a rare storm. However, it is important to note that sediment stability is site-specific. 相似文献
235.
Under the United States Clean Air Act Amendments of 1977, a class I designation safeguards wilderness areas from the negative
effects of new sources of air pollution. We monitored streamwater chemistry in the class I Lye Brook Wilderness in southwestern
Vermont from May 1994 through August 1995. Stream samples were collected biweekly at nine sampling locations throughout the
wilderness and were analyzed for major cations and anions, dissolved organic carbon, pH, and acid-neutralizing capacity. Eight
of nine sites sampled had mean annual acid neutralizing capacity values below zero. During the study period, decreases in
streamwater acid neutralizing capacity values were caused primarily by SO4
2−. At some sites, however, NO3
− and naturally occurring, weak organic acids were seasonally important. During high discharge, the low pH and high concentrations
of inorganic monomeric Al were at levels that are toxic to acid-sensitive aquatic species. Watershed mass balances were calculated
to determine annual gains or losses for measured ions. These budgets indicate that S inputs and outputs were nearly equal,
there was a net loss of base cations, and a net gain in N. How long these watersheds can continue to assimilate additional
N inputs is unknown. 相似文献
236.
Fertilizer Management in Watersheds of Two Ramsar Wetlands and Effects on Quality of Inflowing Water
Two field experiments were carried out in the watersheds of two Ramsar wetland areas, Lakes Koronia and Volvi (area A) and
Lakes Mikri and Megali Prespa (area B), to study the effect of application of N fertilizer on wheat yields, the quality of
runoff water, and the quality of stream water. The treatments were a combination of two methods of fertilizer application
(total amount in fall, and 2/3 in fall + 1/3 in spring) at three rates (0, 100, and 200 kg N/ha) with four replications. Concentrations
of NH4
+, NO3
−, NO2
−, P, and Cl− and pH were determined in all water samples. Runoff water quality was not influenced by fertilizer application in either
area. Chemical parameters for water did not differ along the selected watercourses in area B, while in area A they were higher
in the samples taken near Lake Koronia than in the samples taken upstream, indicating that the watercourses are polluted downstream
by nonagricultural sources. The differences in wheat yields between the 100 and 200 kg N/ha application rates were not high.
These results call for better fertilizer management in order to achieve better yields and to diminish the possibility to have
negative effects to the environment. 相似文献
237.
Preparation and implementation of seven ecological compensation plans for Dutch highways 总被引:5,自引:0,他引:5
First-generation compensation plans (CPs) for Dutch highway projects have been evaluated with respect to implementation of
the compensation principle (1993), which aims to counterbalance the adverse ecological impacts of large-scale development
projects. Decision-making on the seven projects took place between 1993 and 1995. Specifically, we considered: (a) the processes
employed to prepare and implement the compensation plans; (b) the methods used to identify, plan, and execute the compensation
measures; and (c) the results yielded by these methods. We conclude that the CPs were prepared fairly uniformly, particularly
in terms of the processes and methodologies used to derive compensation measures. Five of the seven CPs had become operational
by 2001 and initial experience is now being gained on land acquisition and transfer of compensation sites to nature conservation
trusts. Further progress of CPs is likely to be seriously hampered by growing demand for land for development in general and
associated increases in real estate prices. Several problems are addressed and recommendations made with respect to: (a) developing
a legal basis for the compensation principle; (b) the relationship with re-allotment projects; (c) estimation of compensation
costs; (d) an annual bias of CP budgets to account for rising costs; (e) contingency measures; and (f) criteria for CP (ex-post)
evaluation. 相似文献
238.
239.
Francisco Olivera Milver Valenzuela R. Srinivasan Janghwoan Choi Hiudae Cho Srikanth Koka Ashish Agrawal 《Journal of the American Water Resources Association》2006,42(2):295-309
This paper presents ArcGIS‐SWAT, a geodata model and geographic information system (GIS) interface for the Soil and Water Assessment Tool (SWAT). The ArcGIS‐SWAT data model is a system of geodatabases that store SWAT geographic, numeric, and text input data and results in an organized fashion. Thus, it is proposed that a single and comprehensive geodatabase be used as the repository of a SWAT simulation. The ArcGIS‐SWAT interface uses programming objects that conform to the Component Object Model (COM) design standard, which facilitate the use of functionality of other Windows‐based applications within ArcGIS‐SWAT. In particular, the use of MS Excel and MATLAB functionality for data analysis and visualization of results is demonstrated. Likewise, it is proposed to conduct hydrologic model integration through the sharing of information with a not‐model‐specific hub data model where information common to different models can be stored and from which it can be retrieved. As an example, it is demonstrated how the Hydrologic Modeling System (HMS) ‐ a computer application for flood analysis ‐ can use information originally developed by ArcGIS‐SWAT for SWAT. The application of ArcGIS‐SWAT to the Seco Creek watershed in Texas is presented. 相似文献
240.
Jason W. Oberg Assefa M. Melesss 《Journal of the American Water Resources Association》2006,42(3):565-582
ABSTRACT: Little work is reported where spatial methods are employed to monitor evapotranspiration (ET) changes as a result of vegetation and wetland restoration. A remote sensing approach with the Surface Energy Balance Algorithm for Land (SEBAL) for estimating ET at The Nature Conservancy's Glacial Ridge prairie‐wetland restoration site in northwestern Minnesota is presented. The calibrated 24‐hour ET from SEBAL was estimated with an average error of prediction of ?4.3 percent. Monthly, interseasonal, and seasonal ET for the period of June to September (2000 to 2003) from three adjacent land‐uses: a hydrologic control preserved wetland; a treated or restored site; and a nontreated or impacted wetland, were used in the study. Results from comparing ET behavior to the preserve suggest restoration efforts have affected monthly and seasonal ET within the treated site. Spatial average standard deviations of the seasonal ET within the preserve, treated, and nontreated sites give 47.3, 75.7, and 109.9 mm, respectively, suggesting hydrologic stabilization within the treated site. Monthly and interseasonal comparisons show similar behavior to that of the seasonal data, where monthly correlations suggest increasing agreement within the treated site, approaching those within the preserve. 相似文献