全文获取类型
收费全文 | 97543篇 |
免费 | 1253篇 |
国内免费 | 1127篇 |
专业分类
安全科学 | 3855篇 |
废物处理 | 3616篇 |
环保管理 | 14706篇 |
综合类 | 21648篇 |
基础理论 | 27437篇 |
环境理论 | 79篇 |
污染及防治 | 17975篇 |
评价与监测 | 5912篇 |
社会与环境 | 4099篇 |
灾害及防治 | 596篇 |
出版年
2022年 | 901篇 |
2021年 | 913篇 |
2020年 | 695篇 |
2019年 | 919篇 |
2018年 | 1323篇 |
2017年 | 1348篇 |
2016年 | 2362篇 |
2015年 | 1919篇 |
2014年 | 2724篇 |
2013年 | 9490篇 |
2012年 | 2561篇 |
2011年 | 3035篇 |
2010年 | 3424篇 |
2009年 | 3562篇 |
2008年 | 2600篇 |
2007年 | 2488篇 |
2006年 | 2707篇 |
2005年 | 2568篇 |
2004年 | 2868篇 |
2003年 | 2684篇 |
2002年 | 2273篇 |
2001年 | 2647篇 |
2000年 | 2185篇 |
1999年 | 1590篇 |
1998年 | 1407篇 |
1997年 | 1401篇 |
1996年 | 1526篇 |
1995年 | 1622篇 |
1994年 | 1511篇 |
1993年 | 1357篇 |
1992年 | 1347篇 |
1991年 | 1320篇 |
1990年 | 1261篇 |
1989年 | 1241篇 |
1988年 | 1084篇 |
1987年 | 1002篇 |
1986年 | 1005篇 |
1985年 | 1082篇 |
1984年 | 1171篇 |
1983年 | 1185篇 |
1982年 | 1183篇 |
1981年 | 1104篇 |
1980年 | 952篇 |
1979年 | 937篇 |
1978年 | 833篇 |
1977年 | 730篇 |
1976年 | 659篇 |
1974年 | 630篇 |
1973年 | 656篇 |
1972年 | 671篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
831.
832.
Abedalrazq F. Khalil Mac McKee Mariush Kemblowski Tirusew Asefa 《Journal of the American Water Resources Association》2005,41(1):195-208
ABSTRACT: Water scarcity in the Sevier River Basin in south‐central Utah has led water managers to seek advanced techniques for identifying optimal forecasting and management measures. To more efficiently use the limited quantity of water in the basin, better methods for control and forecasting are imperative. Basin scale management requires advanced forecasts of the availability of water. Information about long term water availability is important for decision making in terms of how much land to plant and what crops to grow; advanced daily predictions of streamflows and hydraulic characteristics of irrigation canals are of importance for managing water delivery and reservoir releases; and hourly forecasts of flows in tributary streams to account for diurnal fluctuations are vital to more precisely meet the day‐to‐day expectations of downstream farmers. A priori streamflow information and exogenous climate data have been used to predict future streamflows and required reservoir releases at different timescales. Data on snow water equivalent, sea surface temperatures, temperature, total solar radiation, and precipitation are fused by applying artificial neural networks to enhance long term and real time basin scale water management information. This approach has not previously been used in water resources management at the basin‐scale and could be valuable to water users in semi‐arid areas to more efficiently utilize and manage scarce water resources. 相似文献
833.
Jerry R. Miller Mark Lord Steven Yurkovich Gail Mackin Lawrence Kolenbrander 《Journal of the American Water Resources Association》2005,41(5):1053-1075
Sedimentation rates and sediment provenance were examined for lacustrine sediments deposited in Fairfield Lake, western North Carolina, during the past 111 years. Stratigraphic, radionuclide, and cartographic data indicate that sedimentation rates have increased several fold during the past three decades in response to localized development. The magnitude of increased sedimentation was surprising given limited development within the basin: 0.12 to 0.68 buildings/ha in 2000 in those parts directly delivering sediment to the dated cores. Thus, the analysis illustrates the potential sensitivity of watersheds in the southern Appalachians to changes in land cover. An approach that combined geochemical fingerprinting with sediment mixing models was subsequently evaluated to determine its ability to accurately estimate the contribution of sediment from (1) major bedrock formations that underlie the watershed and (2) potential sources associated with four land cover categories. Sediment sources in both analyses proved difficult to geochemically fingerprint to greater than 90 percent accuracy using data on acid‐soluble metals and selected isotopes of lead (Pb). The relative contributions of sediment from delineated sources, estimated by the mixing models, generally corresponded with known temporal and spatial patterns of land cover. However, the models were plagued by two significant problems — the chemical alteration of sediments as they were transported through upland streams to depositional sites within the lake and the loss of elemental mass. Thus, future investigations using the fingerprinting approach in this area of intense weathering, and presumably others, will need to modify the existing methods to more accurately elucidate changes in sediment provenance related to development. 相似文献
834.
David Brandes Gregory J. Cavallo Michael L. Nilson 《Journal of the American Water Resources Association》2005,41(6):1377-1391
Rapid land development is raising concern regarding the ability of urbanizing watersheds to sustain adequate base flow during periods of drought. Long term streamflow records from unregulated watersheds of the lower to middle Delaware River basin are examined to evaluate the impact of urbanization and imperviousness on base flow. Trends in annual base flow volumes, seven‐day low flows, and runoff ratios are determined for six urbanizing watersheds and four reference watersheds across three distinct physiographic regions. Hydrograph separation is used to determine annual base flow and stormflow volumes, and nonparametric trend tests are conducted on the resulting time series. Of the watersheds examined, the expected effects of declining base flow volumes and seven‐day low flows and increasing stormflows are seen in only one watershed that is approximately 20 percent impervious and has been subject to a net water export over the past 15 years. Both interbasin transfers and hydrologic mechanisms are invoked to explain these results. The results show that increases in impervious area may not result in measurable reductions in base flow at the watershed scale. 相似文献
835.
836.
This paper examines the optimal tax to achieve maximum economic yield (MEY) exploitation in a rational expectations model of a competitive open-access fishery. To analyze the dynamic evolution of resource use a structural model which explains the relationship between the firm and the industry is presented. The unregulated equilibrium is contrasted with the potential MEY. Conditions under which the unregulated equilibrium will be MEY are explored. In addition, a tax is devised which will cause non-MEY competitive exploitation to become MEY when the tax is implemented. 相似文献
837.
Biodiversity and Ecological Redundancy 总被引:53,自引:0,他引:53
BRIAN H. WALKER 《Conservation biology》1992,6(1):18-23
838.
DENNIS D. COX LAWRENCE H. COX KATHERINE B. ENSOR 《Environmental and Ecological Statistics》1997,4(3):219-233
In this paper we summarize research issues for spatial environmental sampling stemming from a NISS/USEPA workshop held on 21-22 September 1994 at Chapel Hill, NC. 相似文献
839.
Do Habitat Corridors Provide Connectivity? 总被引:33,自引:1,他引:33
840.
The Ria Formosa lagoon, Portugal, receives organic matter from many natural and anthropogenic sources. This paper presents an overview of the contribution these sources made through the use of lipid biomarkers. Sixty-one surface sediment samples were collected and analysed for a range of lipids. Sewage materials were confined to regions within 2 km of discharge points; phytoplankton biomarkers (sterols and fatty acids) suggest production was greatest in the inner parts of the lagoon that also have greatest inorganic nutrient enrichment; terrestrial organic matter was present in relatively low concentrations as shown by both sterol and fatty alcohols; bacteria were widespread although the Sulphate Reducing Bacteria (SRBs, shown by the presence of 3-OH fatty acids) were located near but not adjacent to sewage discharge points. 相似文献