全文获取类型
收费全文 | 2187篇 |
免费 | 273篇 |
国内免费 | 762篇 |
专业分类
安全科学 | 227篇 |
废物处理 | 92篇 |
环保管理 | 781篇 |
综合类 | 1184篇 |
基础理论 | 342篇 |
污染及防治 | 292篇 |
评价与监测 | 229篇 |
社会与环境 | 45篇 |
灾害及防治 | 30篇 |
出版年
2024年 | 5篇 |
2023年 | 98篇 |
2022年 | 127篇 |
2021年 | 148篇 |
2020年 | 136篇 |
2019年 | 123篇 |
2018年 | 76篇 |
2017年 | 132篇 |
2016年 | 93篇 |
2015年 | 114篇 |
2014年 | 119篇 |
2013年 | 149篇 |
2012年 | 134篇 |
2011年 | 156篇 |
2010年 | 100篇 |
2009年 | 166篇 |
2008年 | 101篇 |
2007年 | 128篇 |
2006年 | 123篇 |
2005年 | 114篇 |
2004年 | 80篇 |
2003年 | 100篇 |
2002年 | 83篇 |
2001年 | 74篇 |
2000年 | 92篇 |
1999年 | 72篇 |
1998年 | 48篇 |
1997年 | 31篇 |
1996年 | 48篇 |
1995年 | 35篇 |
1994年 | 26篇 |
1993年 | 19篇 |
1992年 | 16篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 4篇 |
1974年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有3222条查询结果,搜索用时 31 毫秒
991.
Scott V. Harder Devendra M. Amatya Timothy J. Callahan Carl C. Trettin Jon Hakkila 《Journal of the American Water Resources Association》2007,43(3):563-575
Abstract: Increases in timber demand and urban development in the Atlantic Coastal Plain over the past decade have motivated studies on the hydrology, water quality, and sustainable management of coastal plain watersheds. However, studies on baseline water budgets are limited for the low‐lying, forested watersheds of the Atlantic Coastal Plain. The purpose of this study was to document the hydrology and a method to quantify the water budget of a first‐order forested watershed, WS80, located within the USDA Forest Service Santee Experimental Forest northeast of Charleston, South Carolina. Annual Rainfall for the 2003 and 2004 periods were 1,671 mm (300 mm above normal) and 962 mm (over 400 mm below normal), respectively. Runoff coefficients (outflow as a fraction of total rainfall) for the 2003 and 2004 periods were 0.47 and 0.08, respectively, indicating a wide variability of outflows as affected by antecedent conditions. A spreadsheet‐based Thornthwaite monthly water balance model was tested on WS80 using three different potential evapotranspiration estimators [Hamon, Thornthwaite, and Penman‐Monteith (P‐M)]. The Hamon and P‐M‐based methods performed reasonably well with average absolute monthly deviations of 12.6 and 13.9 mm, respectively, between the measured and predicted outflows. Estimated closure errors were all within 9% for the 2003, 2004, and seasonal water budgets. These results may have implications on forest management practices and provide necessary baseline or reference information for Atlantic Coastal Plain watersheds. 相似文献
992.
Henry N.N. Bulley James W. Merchant David B. Marx John C. Holz Aris A. Holz 《Journal of the American Water Resources Association》2007,43(3):605-621
Abstract: The U.S. Environmental Protection Agency is charged with establishing standards and criteria for assessing lake water quality. It is, however, increasingly evident that a single set of national water quality standards that do not take into account regional hydrogeologic and ecological differences will not be viable as lakes clearly have different inherent capacities to meet such standards. We demonstrate a GIS‐based watershed classification strategy for identifying groups of Nebraska reservoirs that have similar potential capacity to attain a certain level of water quality standard. A preliminary cluster analysis of 78 reservoirs was performed to determine the potential number of Nebraska reservoir groups. Subsequently, a Classification Trees method was used to refine number of classes, describe the structure of reservoir watershed classes, and to develop a predictive model that relates watershed conditions to reservoir classes. Results suggest that Nebraska reservoirs can be represented by nine classes and that soil organic matter content in the watershed is the most important single variable for segregating the reservoirs. The cross‐validation prediction error rate of the Classification Tree model was 26.3%. Because all geospatial data used in this work are available nationally, the method could be adopted throughout the U.S. Hence, this GIS‐based watershed classification approach could provide water resources managers an effective decision‐support tool in managing reservoir water quality. 相似文献
993.
环境空气中大气颗粒物源解析的研究进展 总被引:25,自引:0,他引:25
介绍了国内外用于大气颗粒物源解析研究的受体模型的进展情况,对受体模型的研究体系,测量分析技术、研究方法作了详细阐述,并对源解析近期的研究热点及发展趋势作了评述。 相似文献
994.
995.
The experimental plants were grown in open-top chamber and exposed to 0.26 ppm of ozone for six hrs. per day from seedling stage till ripening. The results showed that the height of plants, rates of earing, flowering, grain forming, ripening and the weight/1000 kernels all declined in fumigated plants in comparison with the controls. The yield lost 76.7%. The actual actions of ozone were that it caused foliar injury and chlorophyll destruction accelerating leaf senescence, reduction of assimilation products. O3 was unfavorable injurious to transport and accumulation of substances to the grains after flowering. 相似文献
996.
Muezzinoglu Aysen Elbir Tolga Bayram Abdurrahman 《Water, Air, & Soil Pollution: Focus》2003,3(5-6):307-316
Future (24 h later) daily ground level SO2 concentration in Istanbul was modeled and predicted using a new and powerful technique, Artificial Neural Networks (ANN) in the case of meteorological parameters as input variables. Results show that the trend of SO2 from higher values in winter to lower values in spring and summer, and again to higher values towards winter can be correctly represented by the neural networks. The model better predicted the lower SO2 values in spring and summer seasons when compared to higher values in winter season because of the pattern distribution in training data sets. Beside the amount of the database, the more the variation of the values of the parameters in their own ranges, the more the network learns the database. As a result of this study, considerably successful results were obtained when considering the complex and nonlineer structure of the atmosphere, which is the source of the database. 相似文献
997.
A system dynamics model to facilitate public understanding of water management options in Las Vegas,Nevada 总被引:12,自引:0,他引:12
Stave KA 《Journal of environmental management》2003,67(4):303-313
Water managers increasingly are faced with the challenge of building public or stakeholder support for resource management strategies. Building support requires raising stakeholder awareness of resource problems and understanding about the consequences of different policy options. One approach that can help managers communicate with stakeholders is system dynamics modeling. Used interactively in a public forum, a system dynamics model can be used to explain the resource system and illustrate the effects of strategies proposed by managers or suggested by forum participants. This article illustrates the process of building a strategic-level system dynamics model using the case of water management in Las Vegas, Nevada. The purpose of the model was to increase public understanding of the value of water conservation in Las Vegas. The effects of policies on water supply and demand in the system are not straightforward because of the structure of the system. Multiple feedback relationships lead to the somewhat counterintuitive result that reducing residential outdoor water use has a much greater effect on water demand than reducing indoor water use by the same amount. The model output shows this effect clearly. This paper describes the use of the model in research workshops and discusses the potential of this kind of interactive model to stimulate stakeholder interest in the structure of the system, engage participant interest more deeply, and build stakeholder understanding of the basis for management decisions. 相似文献
998.
Prioritizing Abandoned Coal Mine Reclamation Projects Within the Contiguous United States Using Geographic Information System Extrapolation 总被引:4,自引:0,他引:4
Coal mine reclamation projects are very expensive and require coordination of local and federal agencies to identify resources for the most economic way of reclaiming mined land. Location of resources for mine reclamation is a spatial problem. This article presents a methodology that allows the combination of spatial data on resources for the coal mine reclamation and uses GIS analysis to develop a priority list of potential mine reclamation sites within contiguous United States using the method of extrapolation. The extrapolation method in this study was based on the Bark Camp reclamation project. The mine reclamation project at Bark Camp, Pennsylvania, USA, provided an example of the beneficial use of fly ash and dredged material to reclaim 402,600 sq mi of a mine abandoned in the 1980s. Railroads provided transportation of dredged material and fly ash to the site. Therefore, four spatial elements contributed to the reclamation project at Bark Camp: dredged material, abandoned mines, fly ash sources, and railroads. Using spatial distribution of these data in the contiguous United States, it was possible to utilize GIS analysis to prioritize areas where reclamation projects similar to Bark Camp are feasible. GIS analysis identified unique occurrences of all four spatial elements used in the Bark Camp case for each 1 km of the United States territory within 20, 40, 60, 80, and 100 km radii from abandoned mines. The results showed the number of abandoned mines for each state and identified their locations. The federal or state governments can use these results in mine reclamation planning. 相似文献
999.
We studied the effects of spatial and temporal timber harvesting constraints on competing objectives of sustaining wildlife habitat supply and meeting timber harvest objectives in a boreal mixedwood forest. A hierarchical modeling approach was taken, where strategic and tactical level models were used to project blocking and scheduling of harvest blocks. Harvest block size and proximity, together with short- and long-term temporal constraints, were adjusted in a factorial manner to allow creation of response–surface models. A new measure of the habitat mosaic was defined to describe the emergent pattern of habitat across the landscape. These models, together with multiple linear regression, were used to provide insight on convergence or divergence between spatial objectives. For example, green-up delay (defined as time required before a harvest block adjacent to a previously logged block can be scheduled for harvest) had an adverse effect on the amount of annual harvest area that could be allocated and blocked spatially, and habitat supply responded in an opposite direction to that of wood supply, where caribou, moose wintering, and marten habitat supply increased when harvest blocks were further apart, maximum block size smaller, and both a green-up delay and mesoscale stratification were applied. Although there was no solution space free of conflicts, the analysis suggests that application of the mesoscale stratification, together with a diversity of harvest block sizes and a between-harvest block proximity of 250 m, will perform relatively well with respect to wood supply objectives, and at the same time create a less fragmented landscape that better reflects natural forest patterns. 相似文献
1000.
Stocki TJ Blanchard X D'Amours R Ungar RK Fontaine JP Sohier M Bean M Taffary T Racine J Tracy BL Brachet G Jean M Meyerhof D 《Journal of environmental radioactivity》2005,80(3):305-326
In preparation for verification of the Comprehensive Nuclear-Test-Ban-Treaty, automated radioxenon monitoring is performed in two distinctive environments: Ottawa and Tahiti. These sites are monitored with SPALAX (Systeme de Prelevement d'air Automatique en Ligne avec l'Analyse des radioXenons) technology, which automatically extracts radioxenon from the atmosphere and measures the activity concentrations of (131m,133m,133,135)Xe. The resulting isotopic concentrations can be useful to discern nuclear explosions from nuclear industry xenon emissions. Ambient radon background, which may adversely impact analyser sensitivity, is discussed. Upper concentration limits are reported for the apparently radioxenon free Tahiti environment. Ottawa has a complex radioxenon background due to proximity to nuclear reactors and medical isotope facilities. Meteorological models suggest that, depending on the wind direction, the radioxenon detected in Ottawa can be characteristic of the normal radioxenon background in the Eastern United States, Europe, and Japan or distinctive due to medical isotope production. 相似文献