全文获取类型
收费全文 | 704篇 |
免费 | 53篇 |
国内免费 | 159篇 |
专业分类
安全科学 | 47篇 |
废物处理 | 2篇 |
环保管理 | 181篇 |
综合类 | 468篇 |
基础理论 | 54篇 |
污染及防治 | 14篇 |
评价与监测 | 44篇 |
社会与环境 | 73篇 |
灾害及防治 | 33篇 |
出版年
2023年 | 11篇 |
2022年 | 27篇 |
2021年 | 20篇 |
2020年 | 31篇 |
2019年 | 20篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 32篇 |
2015年 | 32篇 |
2014年 | 37篇 |
2013年 | 31篇 |
2012年 | 54篇 |
2011年 | 57篇 |
2010年 | 50篇 |
2009年 | 42篇 |
2008年 | 33篇 |
2007年 | 53篇 |
2006年 | 40篇 |
2005年 | 43篇 |
2004年 | 28篇 |
2003年 | 30篇 |
2002年 | 26篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有916条查询结果,搜索用时 31 毫秒
901.
Wen‐Cheng Huang Tung‐Hsin Chang Fu‐Ti Yang 《Journal of the American Water Resources Association》2001,37(5):1279-1289
ABSTRACT: The objective of this paper is to examine a deficit in water for the Hsinchu area, the location of Taiwan's “Silicon Valley.” The methods suggested in this paper to diagnose water shortage problems are simple and practical. The results show that Hsinchu is in an area without sufficient water to meet demand for domestic and industrial uses. Until the completion of the Baoshan II Reservoir in 2006, the most feasible options for the Taiwan Water Supply Corporation to offset the water deficiency in Hsinchu City over the next five years are: (a) to obtain water gratuitously from the southern Yungheshan Reservoir; (b) to import additional water at an extra charge from other sources such as the northern Shihmen Reservoir and the agricultural sector; and (c) to conduct a comprehensive water conservation program at the Hsinchu Science‐based Industrial Park. 相似文献
902.
Mahesh Kumar Sahu Ashim Das Gupta 《Journal of the American Water Resources Association》2001,37(3):675-684
ABSTRACT: Operation of a storage‐based reservoir modifies the downstream flow usually to a value higher than that of natural flow in dry season. This could be important for irrigation, water supply, or power production as it is like an additional downstream benefit without any additional investment. This study addresses the operation of two proposed reservoirs and the downstream flow augmentation at an irrigation project located at the outlet of the Gandaki River basin in Nepal. The optimal operating policies of the reservoirs were determined using a Stochastic Dynamic Programming (SDP) model considering the maximization of power production. The modified flows downstream of the reservoirs were simulated by a simulation model using the optimal operating policy (for power maximization) and a synthetic long‐term inflow series. Comparing the existing flow (flow in river without reservoir operation) and the modified flow (flow after reservoir operation) at the irrigation project, the additional amount of flow was calculated. The reliability analysis indicated that the supply of irrigation could be increased by 25 to 100 percent of the existing supply over the dry season (January to April) with a reliability of more than 80 percent. 相似文献
903.
904.
为了揭示悬浮泥沙(SSC)对水库水质的影响规律,对汾河水库进行样品收集和长期水质监测,采用水动力模型与泥沙转移和富营养化模型相结合的方法,将这三者关联耦合,并通过实测数据对模型进行参数率定和验证,分析含沙水和不含沙水中总氮(TN)、总磷(TP)、叶绿素a(Chla)、溶解氧(DO)四项指标,得出两者对水质造成的影响。结果表明:SSC对TN、TP的去除作用明显,对Chla、DO浓度分布影响较小,并计算了污染物的释放量以及贡献率,得出TP的负荷仅为16.47t,而贡献率高达25.25%。因此在汾河的污染控制方面应侧重削减磷,进而改善汾河地区的污染现状。 相似文献
905.
Kyle E. Juracek 《Journal of the American Water Resources Association》2000,36(3):633-645
ABSTRACT: The stability of the Neosho River channel downstream from John Redmond Dam, in southeast Kansas, was investigated using multiple‐date aerial photographs and stream‐gage information. Bankfull channel width was used as the primary indicator variable to assess pre‐ and post‐dam channel change. Five sin‐mile river reaches and four stream gages were used in the analysis. Results indicated that, aside from some localized channel widening, the overall channel change has been minor with little post‐dam change in bankfull channel width. The lack of a pronounced post‐dam channel change may be attributed to a substantial reduction in the magnitude of the post‐dam annual peak discharges in combination with the resistance to erosion of the bed and bank materials. Also, the channel may have been overwidened by a series of large floods that predated construction of the dam, including one with an estimated 500‐year recurrence interval. 相似文献
906.
为探究高温作用对泥岩盖层密封性的影响,从理论上剖析储气库盖层产生热应力的3种形式,在室内试验的基础上,分析泥岩在高温环境下力学损伤程度和盖层物性封闭评价指标随温度变化特征.结果表明:高温环境下泥岩整体结构性能降低,400℃左右是泥岩在周期热应力作用下损伤的阈值温度;高温作用会显著改变泥岩盖层物性封闭特征,400℃左右是... 相似文献
907.
贵州红枫湖地区冷暖两季土壤/大气界面间汞交换通量的对比 总被引:22,自引:7,他引:15
采用动力学通量箱(Dynamic Flux Chamber,DFC)与高时间分辨率自动大气测汞仪联用技术,于2002年7月和2003年3月对红枫湖地区土壤/大气界面上汞交换通量进行了测定.夏冬2季土壤-大气汞的交换通量分别为(27.4±40.1)ng·(m2·h)-1(n=255)和(5.6±19.4)ng·(m2·h)-1(n=192).夏季汞交换通量和光照、气温及土壤温度的相关系数分别为0.74、0.83和0.80,而冬季分别为0.88、0.56和0.59.对比研究表明:暖季土壤向大气的释汞通量远高于冷季;2个季节光照、温度等气象因素对土壤/大气界面间汞交换均有重要的影响. 相似文献
908.
Li Chen 《Journal of the American Water Resources Association》2003,39(5):1157-1165
ABSTRACT: An optimization and simulation model holds promise as an efficient and robust method for long term reservoir operation, an increasingly important facet of managing water resources. Recently, genetic algorithms have been demonstrated to be highly effective optimization methods. According to previous studies, a real coded genetic algorithm (RGA) has many advantages over a binary coded genetic algorithm. Accordingly, this work applies an RGA to obtain the 10‐day (the traditional period of reservoir operation in Taiwan) operating rule curves for the proposed reservoir system. The RGA is combined with an effective and flexible scheme for coding the reservoir rule curves and applied to an important reservoir in Taiwan, considering a water reservoir development scenario to the year 2021. Each rule curve is evaluated using a complex simulation model to determine a performance index for a given flow series. The process of generating and evaluating decision parameters is repeated until no further improvement in performance is obtained. Many experiments were performed to determine the suitable RGA components, including macro evolutionary (ME) selection and blend‐α crossover. Macro evolution (ME) can be applied to prevent the premature problem of the conventional selection scheme of genetic algorithm. The purpose of adjusting a of a crossover scheme is to determine the exploratory or exploitative degree of various subpopulations. The appropriate rule curve searched by an RGA can minimize the water deficit and maintain the high water level of the reservoir. The results also show that the most promising RGA for this problem consists of these revised operators significantly improves the performance of a system. It is also very efficient for optimizing other highly nonlinear systems. 相似文献
909.
910.
Tessa Artruc Desiree Tullos Ben Leshchinsky 《Journal of the American Water Resources Association》2023,59(1):86-106
The drawdown of reservoirs behind dams is an important management strategy (e.g., for removal of aging infrastructure, flushing of sediment), and an opportunity to study erosional processes. A numerical model was developed to examine retrogressive bank erosion across reservoir drawdown scenarios and to evaluate factors controlling the rate, volume, and mechanisms of lateral erosion. Modeled processes included dynamic drawdown of groundwater, sequential slope failures via limit equilibrium analysis, and retrogression considering stress interaction between failing blocks. Field measurements were coupled with Staged, Slow, and Rapid drawdown scenarios. Results highlight the importance of including retrogression as an avenue for lateral erosion, as sequential block failures were found to occur in all scenarios except Slow drawdown. This result indicates that bank stability models without some means of characterizing the evolution of slope failure during drawdown are likely underestimating bank failure rates and volumes. In contrast, dynamic groundwater was not found to be a dominant control for any drawdown scenario. Model results also demonstrate that the drawdown increment is a first-order control on slope instability via the development of drained or undrained conditions. A majority of failures occurred under undrained conditions. To maximize slope stability, using slow drawdown to activate internal friction under drained conditions is essential. The design of the drawdown rate created a tradeoff between the amount of impact created and when the impact is produced. The study also articulated the need for coupling models and field observations for rapidly changing systems. 相似文献