全文获取类型
收费全文 | 683篇 |
免费 | 86篇 |
国内免费 | 83篇 |
专业分类
安全科学 | 183篇 |
废物处理 | 5篇 |
环保管理 | 239篇 |
综合类 | 231篇 |
基础理论 | 73篇 |
污染及防治 | 17篇 |
评价与监测 | 25篇 |
社会与环境 | 53篇 |
灾害及防治 | 26篇 |
出版年
2024年 | 3篇 |
2023年 | 23篇 |
2022年 | 28篇 |
2021年 | 34篇 |
2020年 | 37篇 |
2019年 | 41篇 |
2018年 | 27篇 |
2017年 | 39篇 |
2016年 | 47篇 |
2015年 | 40篇 |
2014年 | 29篇 |
2013年 | 36篇 |
2012年 | 55篇 |
2011年 | 49篇 |
2010年 | 31篇 |
2009年 | 29篇 |
2008年 | 17篇 |
2007年 | 28篇 |
2006年 | 35篇 |
2005年 | 21篇 |
2004年 | 18篇 |
2003年 | 21篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1977年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 4篇 |
1970年 | 1篇 |
排序方式: 共有852条查询结果,搜索用时 15 毫秒
71.
Thomas J. Jackson Richard H. McCuen 《Journal of the American Water Resources Association》1979,15(2):436-446
ABSTRACT: Remote sensing offers an attractive alternative to conventional data collection employed in the estimation of certain hydrologic model parameters. In this investigation, the standard error of parameters estimated from Landsat data are examined. Relationships between the standard error and the size of the spatial-modeling units are developed that allow extending results to larger areas. Based upon the investigations conducted, a generalized model of the error relationships could not be developed. 相似文献
72.
E. C. Dickey J. K. Mitchell J. N. Scarborough 《Journal of the American Water Resources Association》1979,15(6):1753-1769
ABSTRACT: The application of hydrologic models to small watersheds of mild topography is not well documented. This study evaluates the applicability of hydrologic models described by Huggins and the Soil Conservation Service to small watersheds by comparing the simulated and actual hydrograph for both gaged and ungaged situations. The annual maximum rainfall events plus storms exceeding 2.5 inches from 25 years of rainfall and runoff data for two small watersheds were selected for the model evaluations. These storms had a variety of patterns and occurred on many different watershed conditions. Simulated and actual hydrographs were compared using a parameter which contained volume, peak, and shape factors. One-half of the selected storms were used to calibrate the models. For both models, there were no significant differences between the simulated and actual runoff volumes and peak runoff rates. Parameters obtained during the calibration process and relationships developed to estimate antecedent moisture and to modify tabulated runoff curve numbers were used to simulate the runoff hydrograph from the remaining storms. These remaining storms or test storms were simulated only once in order to imitate an ungaged situation. In general, both the Huggins and SCS model performed similarly on the test storms, but the level of model performance was lower than that for the calibration storms. For both models, the two-day antecedent rainfall was more important than the five-day in determining antecedent moisture and modifying tabulated curve numbers. The time of concentration which resulted in good hydrograph simulations was about three times larger than that estimated using published empirical relationships. 相似文献
73.
Michael L. Shrader Richard H. McCuen Walter J. Rawls 《Journal of the American Water Resources Association》1980,16(1):49-55
ABSTRACT: With the increased use of models in hydrologic design, there is an immediate need for a comprehensive comparison of hydrologic models, especially those intended for use at ungaged locations (i.e., where measured data are either not available or inadequate for model calibration). But some past comparisons of hydrologic models have used the same data base for both calibration and testing of the different models or implied that the results of model calibration are indicative of the accuracy at ungaged locations. This practice was examined using both the regression equation approach to peak discharge estimation and a unit hydrograph model that was intended for use in urban areas. The results suggested that the lack of data independence in the calibration and testing of regression equations may lead to both biased results and misleading statements about prediction accuracy. Additionally, although split-sample testing is recognized as desirable, the split-samples should be selected using a systematic-random sampling scheme, rather than random sampling, because random sampling with small samples may lead to a testing sample that is not representative of the population. A systematic-random sampling technique should lead to more valid conclusions about model reliability. For models like a unit hydrograph model, which are more complex and for which calibration is a more involved process, data independence is not as critical because the data fitting error variation is not as dominant as the error variation due to the calibration process and the inability of the model structure to conform with data variability. 相似文献
74.
Marvin V. Damm 《Journal of the American Water Resources Association》1980,16(5):907-913
ABSTRACT: Simulation of a large stream-aquifer system in Nebraska has been accomplished for the period from 1975 to 2020 to determine effects of controls on ground water pumpage. Three scenarios tested consisted of average annual withdrawals of 15.2 ac-in/ac (FUTURE 1), 14.8 ac-in/ac (FUTURE 2), and 9.8 ac-in/ac (FUTURE 3). The highest quantity represents the historical tendency; while the 14.8 in. figure represents a slight reduction and also represents an equalization of irrigation application efficiencies throughout the area. The lowest figure represents a substantial increase in application efficiency. Comparisons between simulated ground water elevations indicate maximum savings of FUTURE 2 over FUTURE 1 of less than 8 ft. FUTURE 3 ft. FUTURE 3 levels are projected to be a maximum of approximately 13 ft. higher than FUTURE 1's. The relatively small savings from reductions in pumpage result primarily from recirculation effects. Differences between ground water contributions to stream flow are small for all scenarios. These contributions decrease with time and increasing pumpage amounts. Base flow rates at the end of the simulation are approximately 25 percent of those at the beginning. 相似文献
75.
Zia Qureshi 《Journal of the American Water Resources Association》1977,13(1):117-123
ABSTRACT: The Fort Walton Beach area is presently faced with an excessive drawdown of the potentiometric level in the upper Floridan aquifer. Based on available data, the potentiometric level in the Floridan aquifer has dropped 162 feet since 1936. This declining potentiometric level can lead to problems and possible loss of the natural resource on a long-term basis. However, if corrective measures or programs for proper management of groundwater resources are undertaken at this time, the potential problems may be averted. 相似文献
76.
Gary D. Tasker 《Journal of the American Water Resources Association》1982,18(6):965-970
ABSTRACT: Data splitting is used to compare methods of determining “homogeneous” hydrologic regions. The methods compared use cluster analysis based on similarity of hydrologic characteristics or similarity of characteristics of a stream's drainage basin. Data for 221 stations in Arizona are used to show that the methods, which are a modification of DeCoursey's scheme for defining regions, improve the fit of estimation data to the model, but that is is necessary to have an independent measure of predictive accuracy, such as that provided by data splitting, to demonstrate improved predictive accuracy. The methods used the complete linkage algorithm for cluster analysis and computed weighted average estimates of hydrologic characteristics at ungaged sites. 相似文献
77.
Ashok N. Shahane 《Journal of the American Water Resources Association》1982,18(2):231-237
ABSTRACT: A simple procedure for estimating pre- and post-development water quality loadings from residential communities is discussed. The procedure deals with: (a) gathering basic water quality loading numbers observed by others at several watersheds with various land uses; (b) obtaining the breakdown of proposed land uses at various phases of the community development; and (c) estimating pre- and post-development water quality loading numbers by taking the weighted average of the basic loading numbers in terms of areal coverages of different land uses at various phases of development. Results of this simplified procedure have been verified indirectly by comparing them with the estimates derived independently through a more fundamental but time-consuming approach. The procedure was used to evaluate the anticipated water quality impact of two future residential communities in South Florida by analyzing four water quality parameters: Suspended Soils (SS), Total Nitrogen (TN), Total Phosphorus (TP), and Biochemical Oxygen Demand (BOD5). Although computation of loading numbers with mixed land uses is not an exact science at the present time, the recommended approach appears to be the best available technique to analyze quantitatively the water quality-quantity-land use interactions. 相似文献
78.
针对细水雾灭火技术在载人航天器安全中应用的可行性,通过理论分析研究了微重力环境下液滴滞止距离与初始速度、粒径的关系,并利用Fluent模拟研究了水雾喷嘴雾场结构.理论分析结果表明,初始速度一定,水雾粒径越小,其滞止距离也越短;初始速度越大,其滞止距离越长.粒径小于50μm时,初始速度对滞止距离影响不大.数值模拟结果表明,微重力下的雾场分布与常重力下有明显差异,水雾主要集中在喷嘴附近,而且水雾蒸发速率较慢,液滴存活时间长.对比理论分析和模拟结果,模拟的迁移距离要小于理论值,这是因为理论分析中忽略了液滴的蒸发.为解决液滴滞止的问题,建议微重力环境下采取气体载运水雾的方式. 相似文献
79.
模糊综合评价法的改进及其在水库水质评价中的应用 总被引:1,自引:0,他引:1
为了克服传统模糊综合评价法中权重赋值的片面性及最大隶属度原则导致评价结果不合理的弊端,提出了基于层次分析法和熵权法的主客观组合权重,并结合相乘相加算子及加权平均原则,建立了改进的模糊综合评价法.选取TP、TN、DO、NH3-N、CODMn和BOD5为评价指标,用改进的模糊综合评价法对重庆某水库2012年7-12月的水质进行了综合评价.结果表明:TN为主要的污染物;水质最差时段为8月,评价结果为2.655,水质属于Ⅱ级,略偏于Ⅲ级.评价结果与人工神经网络模型所得结果基本一致. 相似文献
80.
A Modeling System to Assess Land Cover Land Use Change Effects on SAV Habitat in the Mobile Bay Estuary
下载免费PDF全文
![点击此处可从《Journal of the American Water Resources Association》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Maurice G. Estes Jr. Mohammad Z. Al‐Hamdan Jean T. Ellis Chaeli Judd Dana Woodruff Ronald M. Thom Dale Quattrochi Brian Watson Hugo Rodriguez Hoyt Johnson III Tom Herder 《Journal of the American Water Resources Association》2015,51(2):513-536
Estuarine ecosystems are largely influenced by watersheds directly connected to them. In the Mobile Bay, Alabama watersheds we examined the effect of land cover and land use (LCLU) changes on discharge rate, water properties, and submerged aquatic vegetation, including freshwater macrophytes and seagrasses, throughout the estuary. LCLU scenarios from 1948, 1992, 2001, and 2030 were used to influence watershed and hydrodynamic models and evaluate the impact of LCLU change on shallow aquatic ecosystems. Overall, our modeling results found that LCLU changes increased freshwater flows into Mobile Bay altering temperature, salinity, and total suspended sediments (TSS). Increased urban land uses coupled with decreased agricultural/pasture lands reduced TSS in the water column. However, increased urbanization or agricultural/pasture land coupled with decreased forest land resulted in higher TSS concentrations. Higher sediment loads were usually strongly correlated with higher TSS levels, except in areas where a large extent of wetlands retained sediment discharged during rainfall events. The modeling results indicated improved water clarity in the shallow aquatic regions of Mississippi Sound and degraded water clarity in the Wolf Bay estuary. This integrated modeling approach will provide new knowledge and tools for coastal resource managers to manage shallow aquatic habitats that provide critical ecosystem services. 相似文献