全文获取类型
收费全文 | 1540篇 |
免费 | 188篇 |
国内免费 | 761篇 |
专业分类
安全科学 | 191篇 |
废物处理 | 66篇 |
环保管理 | 243篇 |
综合类 | 1375篇 |
基础理论 | 216篇 |
污染及防治 | 188篇 |
评价与监测 | 89篇 |
社会与环境 | 75篇 |
灾害及防治 | 46篇 |
出版年
2024年 | 22篇 |
2023年 | 87篇 |
2022年 | 129篇 |
2021年 | 132篇 |
2020年 | 129篇 |
2019年 | 106篇 |
2018年 | 89篇 |
2017年 | 117篇 |
2016年 | 91篇 |
2015年 | 104篇 |
2014年 | 137篇 |
2013年 | 149篇 |
2012年 | 125篇 |
2011年 | 145篇 |
2010年 | 106篇 |
2009年 | 94篇 |
2008年 | 82篇 |
2007年 | 114篇 |
2006年 | 105篇 |
2005年 | 58篇 |
2004年 | 54篇 |
2003年 | 51篇 |
2002年 | 40篇 |
2001年 | 35篇 |
2000年 | 34篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 15篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有2489条查询结果,搜索用时 0 毫秒
951.
考虑“水—土—能—碳”关联,本文将水土资源要素纳入投入变量,构建了我国工农业碳排放效率投入产出测度指标,运用考虑非期望产出的SBM-undesirable模型计算我国29个省份2004—2017年农业、工业部门碳排放效率,利用乘法逆转法计算碳减排潜力并对影响碳排放的投入产出因素进行分析。结果表明:研究期内我国整体农业、工业碳排放效率均呈波动下降趋势,各年的农业碳排放效率均高于工业碳排放效率,江苏、山东等7省份农业碳排放效率以及北京、天津工业碳排放效率最优;各省份农业、工业减排潜力和规模具有显著差异,山西、甘肃的农业、工业碳减排均具有较大潜力;我国绝大多数省份均存在农业、工业的资源能源投入冗余和非期望产出冗余,土地资源投入过剩是影响农业碳排放效率的最重要因素,水资源投入过剩是影响工业碳排放效率的最重要因素。碳排放效率较低省份应积极开展技术创新,发展低碳技术,提高水土资源和能源利用效率,减少碳排放。 相似文献
952.
In this study, an interval type-2 fuzzy stochastic linear programming method (IT2FSLP) is developed to support regional-scale electric power system (REM) planning. The IT2FSLP-REM model is based on an integration of interval type-2 fuzzy sets boundary programming and stochastic linear programming techniques enable it to have robust abilities to the deal with uncertainties expressed as type-2 fuzzy intervals and probabilistic distributions within a general optimization framework. Moreover, it can reflect dynamic decisions for energy supply and energy conversion processes, as well as provide capacity expansion options with multiple periods. The developed model is applied to a case of planning regional-scale energy and environmental systems to demonstrate its applicability. Based on a two-step solution algorithm, reasonable solutions have been obtained, which reflect tradeoffs among economic cost, environmental requirements, and energy-supply security. Thus, the lower and upper solutions of IT2FSLP-REM would then help energy authorities adjust or justify allocation patterns of regional energy resources and services. 相似文献
953.
复合绝缘子的积污特性与瓷绝缘子和玻璃绝缘子有所不同,研究其积污规律对防止污闪有着重要意义。为此,以3支实际运行后的±500kV直流复合绝缘子为研究对象,系统测量其沿串不同位置的污秽度,用等值盐密(ESDD)和灰密(NSDD)表征。试验发现绝缘子不同伞上下表面的等值盐密和灰密大多呈现出U形的分布规律,尤其以等值盐密的U形分布更为明显,而且不同伞上下表面污秽U形分布规律性的强弱有一定差异。讨论了积污过程中电场对污秽沉积的作用以及自清洗过程中雨水冲洗的随机作用,更好地解释了直流复合绝缘子的沿串积污规律。 相似文献
954.
955.
Pamela MacQuarrie Lawrence C. Nkemdirim 《Journal of the American Water Resources Association》1991,27(1):73-82
ABSTRACT: This paper examines the relationship between both potential (E*) and nonpotential evapotranspiration and equilibrium evapotranspiration (EQ) in an irrigated wheat field in southcentral Alberta, Canada. The control exercised by surface wetness and root reservoir moisture content in determining the value of the Priestley-Taylor constant a is explored. Also investigated is the relationship between a and the vapor flux fraction ET/(R-G) where ET is the actual evapotranspiration, R the net radiation, and G the soil heat flux. It is shown that evapotranspiration occurred at the potential rate (E*) when the available soil moisture (ASM) within the root zone was ≥3 percent. a varied from 0.84 for a dry soil to 1.49 for a saturated soil. The mean a for E* was 1.24. Surface wetness sustained evapotranspiration at the potential rate when such wetting exceeded 2mm d?1 following a period of prolonged drawdown of soil moisture, α and ET/(R-G) were positively correlated and this correlation strengthened with increasing soil moisture for constant values of the energy partitioning factor s+γ/s where s is the slope of the saturation humidity-temperature curve and γ is the psychrometric constant. ET=EQ when ETI(R-G) lay within the range of 0.59 to 0.82 corresponding to Bowen ratio (β) values of 0.22 and 0.69, respectively. 相似文献
956.
低碳经济下的智能用电技术与环境安全 总被引:1,自引:0,他引:1
智能用电作为建设坚强智能电网的重要组成部分,具有高度的自动化水平和很强的自愈能力。采用智能用电技术可以将各种分布式再生能源迅速接入电网,对环境安全具有重要的促进作用。通过介绍智能用电这一新技术的发展现状和及其关键技术,从能源防御体系、土地利用和电力生产等方面对智能用电与环境安全之间的关系进行了分析。采用智能用电技术可以减少碳排放,提高用电系统的抗击灾害能力,保护环境、集约利用土地,是环境安全体系中非常重要的组成环节。 相似文献
957.
958.
Temporal Changes in Streamflow and Attribution of Changes to Climate and Landuse in Wisconsin Watersheds 下载免费PDF全文
Rabi Gyawali Steve Greb Paul Block 《Journal of the American Water Resources Association》2015,51(4):1138-1152
Previous historic trends analyses on 21st Century hydrologic data in the United States generally focus on annual flow statistics and have continued to use USGS hydro‐climatic data network (HCDN) stations, although post‐1988 diversions and runoff regulations are not reflected in the HCDN. Using a more recent dataset, Geospatial Attributes of Gages for Evaluating Streamflow, version II (GAGES II), compiled by Falcone (2012), which includes more watersheds with reference conditions, a comprehensive analysis of changes in seasonal, and annual streamflow in Wisconsin watersheds is demonstrated. Given the pronounced influence of seasonal hydrology in Wisconsin watersheds, the objective of this study is to elucidate the nature of temporal (annual, seasonal, and monthly) changes in runoff. Considerable temporal and regional variability was found in annual and seasonal streamflow changes between the two historic periods 1951‐1980 and 1981‐2010 considered in the study. For example, the northern watersheds show relatively small changes in streamflow discharge ranging from ?6.0 to 4.2%, while the southern watersheds show relatively large increases in streamflow discharge ranging from 13.1 to 18.2%. To apportion streamflow changes to climate and nonclimatic factors, a method based on potential evapotranspiration changes is demonstrated. Results show that nonclimatic factors account for more than 60% of changes in annual runoff in Wisconsin watersheds considered in the study. 相似文献
959.
解析电除尘烟温与粉尘特性的最佳结合点 总被引:2,自引:0,他引:2
分析了电除尘烟温对粉尘特性的影响,以及烟温对电除尘器效率的影响,从中找出烟温调节与粉尘特性的最佳结合点。利用烟温调节的理念,应用余热利用节能电除尘技术对电除尘器进行提效改造,通过实例证明,这既可扩大电除尘器适应性和提高电除尘效率、满足低排放要求,又可节省电煤消耗和降低电耗,具有环保与经济的双重效益。 相似文献
960.