全文获取类型
收费全文 | 2135篇 |
免费 | 269篇 |
国内免费 | 285篇 |
专业分类
安全科学 | 760篇 |
废物处理 | 42篇 |
环保管理 | 379篇 |
综合类 | 938篇 |
基础理论 | 145篇 |
污染及防治 | 96篇 |
评价与监测 | 90篇 |
社会与环境 | 121篇 |
灾害及防治 | 118篇 |
出版年
2024年 | 5篇 |
2023年 | 38篇 |
2022年 | 41篇 |
2021年 | 91篇 |
2020年 | 81篇 |
2019年 | 77篇 |
2018年 | 49篇 |
2017年 | 103篇 |
2016年 | 141篇 |
2015年 | 140篇 |
2014年 | 114篇 |
2013年 | 159篇 |
2012年 | 226篇 |
2011年 | 199篇 |
2010年 | 164篇 |
2009年 | 133篇 |
2008年 | 77篇 |
2007年 | 146篇 |
2006年 | 130篇 |
2005年 | 89篇 |
2004年 | 64篇 |
2003年 | 64篇 |
2002年 | 44篇 |
2001年 | 54篇 |
2000年 | 28篇 |
1999年 | 28篇 |
1998年 | 19篇 |
1997年 | 12篇 |
1996年 | 21篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 6篇 |
1971年 | 11篇 |
1970年 | 4篇 |
排序方式: 共有2689条查询结果,搜索用时 250 毫秒
181.
182.
水环境质量评价3种方法的应用对比 总被引:6,自引:0,他引:6
从众多水质评价方法中选取单项指数法、加权均值型指数法、模糊数学法进行介绍,并通过运用这3种方法对大汶河某年监测数据的平均值进行评价.经对比分析发现,加权均值型指数法是一种比较实用的水质评价方法,模糊数学法可以作为必要的补充. 相似文献
183.
184.
Richard L. Skaggs Larry W. Mays Lance W. Vail 《Journal of the American Water Resources Association》2001,37(4):867-875
ABSTRACT: A methodology for ground water remediation design has been developed that interfaces ground water simulation models with an enhanced annealing optimizer. The ground water flow and transport simulators provide the ability to consider site‐specific contamination and geohydrologic conditions directly in the assessment of alternative remediation system designs. The optimizer facilitates analysis of tradeoffs between technical, environmental, regulatory, and financial risks for alternative design and operation scenarios. A ground water management model using an optimization method referred to as “enhanced annealing” (simulated annealing enhanced to include “directional search” and “memory” mechanisms) has been developed and successfully applied to an actual restoration problem. The demonstration site is the contaminated unconfined aquifer referred to as N‐Springs located at Han‐ford, Washington. Results of the demonstration show the potential for improving groundwater restoration system performance while reducing overall system cost. 相似文献
185.
Dragan A. Savic Donald H. Burn Zolt Zrinji 《Journal of the American Water Resources Association》1989,25(5):977-983
ABSTRACT: An analysis of four streamflow generation schemes for the use in the estimation of the required conservation storage for a single reservoir is presented. The comparison of the generating schemes should aid in the selection of an appropriate model type for the reservoir sizing problem. The streamflow generation models are compared using two criteria. The first comparison is between the statistics of the generated streamflow sequences and the corresponding statistics from the historical record. The second evaluation compares the median reservoir size determined by each model with the required storage based on the historical flow sequence. The results of a comparative analysis for monthly streamflow data for the Rzav River in Yugoslavia are presented and discussed. The results indicate that both evaluation criteria are required to discriminate between the various options. 相似文献
186.
187.
Nageshwar Rao Bhaskar E. Earl Whitlatch 《Journal of the American Water Resources Association》1987,23(6):1027-1036
ABSTRACT: Mathematical optimization techniques are used to study the operation and design of a single, multi-purpose reservoir system. Optimal monthly release policies are derived for Hoover Reservoir, located in Central Ohio, using chance-constrained linear programming and dynamic programming-regression methodologies. Important characteristics of the former approach are derived, discussed, and graphically illustrated using Hoover Reservoir as a case example. Simulation procedures are used to examine and compare the overall performance of the optimal monthly reservoir release policies derived under the two approaches. Results indicate that, for the mean detention time and the corresponding safe yield target water supply release under existing design of Hoover Reservoir, the dynamic programming policies produce lower average annual losses (as defined by a two-sided quadratic loss function) while achieving at least as high reliability levels when compared to policies derived under the chance-constrained linear programming method. In making this comparison, the reservoir release policies, although not identical, are assumed to be linear. This restricted form of the release policy is necessary to make the chance-constrained programming method mathematically tractable. 相似文献
188.
M. Hossein Sabet James Q. Coe 《Journal of the American Water Resources Association》1986,22(4):587-596
ABSTRACT: A large-scale simulation/optimization model provides schedules for operation of water and power for the California State Water Project (SWP). The SWP consists of a series of reservoirs linked by rivers, pumping plants, canals, tunnels, and generating plants and is operated by the California Department of Water Resources. The Department provides water to municipal and agricultural users, and manages its electrical loads and resources. The model, therefore, performs hydraulic and electrical computations leading to optimal operation of the entire system. It consists of hydraulic network programming components to meet the storage objectives at all the reservoirs, a linear programming component to determine the schedules at pumping and generating plants, an electrical network programming component to balance electrical loads and resources, and a number of other simulation components. It operates on yearly, weekly, and daily bases. It is primarily used for real-time operation of the SWP and can provide hourly detail schedules which are implemented by the SWP staff via a computerized system. 相似文献
189.
Ernest T. Smerdon John A. Gronouski Judith M. Clarkson 《Journal of the American Water Resources Association》1988,24(6):1257-1262
ABSTRACT: Texas is one of the states in which limitations in water supplies could severely constrain economic growth in certain areas. The traditional planning approach for addressing this problem has involved devising schemes for large water development projects, which for many years included the importation of water from other states. Now the attitude towards water resource management is changing, and it is generally agreed that better management of existing supplies is the preferred approach. In this paper we review some of the changes that have recently occurred in Texas, including attempts to streamline the water institutions in such a way that they might be more responsive to the need for more comprehensive management of water resources statewide, with greater emphasis on social and environmental concerns. 相似文献
190.
Thanakorn Uan-On Otto J. Helweg 《Journal of the American Water Resources Association》1988,24(2):261-268
ABSTRACT: The Nonlinear Risk-Benefit (NRB) Algorithm includes risk as one of the objectives in a multiple-objective optimization problem. The NRB Algorithm is derived by extending the Surrogate Worth Trade-Off method to quadratic programming. This category of problem is common in water resources planning and design, especially multipurpose reservoir systems. Consequently, an example is given using the algorithm for optimally operating a multipurpose reservoir. 相似文献