全文获取类型
收费全文 | 707篇 |
免费 | 126篇 |
国内免费 | 203篇 |
专业分类
安全科学 | 170篇 |
废物处理 | 24篇 |
环保管理 | 113篇 |
综合类 | 491篇 |
基础理论 | 59篇 |
污染及防治 | 70篇 |
评价与监测 | 35篇 |
社会与环境 | 24篇 |
灾害及防治 | 50篇 |
出版年
2023年 | 15篇 |
2022年 | 18篇 |
2021年 | 42篇 |
2020年 | 37篇 |
2019年 | 32篇 |
2018年 | 23篇 |
2017年 | 30篇 |
2016年 | 44篇 |
2015年 | 56篇 |
2014年 | 47篇 |
2013年 | 77篇 |
2012年 | 69篇 |
2011年 | 62篇 |
2010年 | 56篇 |
2009年 | 59篇 |
2008年 | 38篇 |
2007年 | 60篇 |
2006年 | 42篇 |
2005年 | 33篇 |
2004年 | 23篇 |
2003年 | 28篇 |
2002年 | 20篇 |
2001年 | 21篇 |
2000年 | 12篇 |
1999年 | 21篇 |
1998年 | 8篇 |
1997年 | 17篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1036条查询结果,搜索用时 640 毫秒
41.
42.
43.
西安市城市主干道路面径流初期冲刷效应 总被引:3,自引:0,他引:3
以西安市城市主干道南二环太白路高架桥为路面径流采样区域,采用人工等时间间隔采样方法,在桥梁排水立管对2010年9—11月的3场径流事件进行全程采样,测试径流过程SS、COD、溶解性COD、NH3-N、Pb、溶解性Pb、Zn和溶解性Zn的浓度变化,研究路面径流的初期冲刷效应及其影响因素。结果表明,西安市城市主干道路面径流污染严重,降雨数小时后的末期径流仍具有较高的污染水平;径流过程污染物浓度变化规律与其赋存形态有关,SS、COD、Pb等以颗粒态为主的污染物的浓度随雨强变化剧烈波动,NH3-N、溶解态COD、溶解态Zn等以溶解态为主的污染物浓度变化受雨强影响较小,随径流过程呈逐渐减小趋势;路面径流初期冲刷现象并非普遍存在,与污染物的赋存状态和场次降雨特征密切相关,溶解态污染物易于出现初期冲刷现象,颗粒态污染物是否出现初期冲刷与场次降雨特征有关;测试的3场径流事件初期30%的径流携带的SS、COD、溶解性COD、NH3-N、Pb、Zn和溶解性Zn的负荷占场次径流总负荷的比例分别为21.8%~50.0%、25.5%~49.3%、36.3%~52.6%、52.6%~66.7%、26.8%~45.0%、27.2%~63.4%和36.2%~62.6%,表明仅对初期径流进行治理无法实现对西安市路面径流污染的有效控制。 相似文献
44.
We report observations of disappearance of Erica tetralix in wet heathland, which is unlikely to be caused by competition, as E. tetralix is dying before its place is taken up by other species. To investigate the causes, we used both old and new data. Results showed that presence of Molinia caerulea and Calluna vulgaris were substantial in the former E. tetralix dominated areas. Measurements of the C/N ratio in the morlayer were between 21 and 26 under the E. tetralix stands. As the expected C/N ratio in a healthy nutrient poor ecosystem like the E. tetralix wet heathland is around 30, this indicates that the ratio is probably decreasing and, correspondingly, the probability of nitrogen leaching from the ecosystem is increasing. The morlayer pH was extremely low—between 3.03 and 3.78. This represents a pH decline since the 1960s, where pH values generally were above 4. This supports the hypothesis that the decrease in morlayer pH is the major factor explaining the disappearance of E. tetralix and that measures to increase pH should be considered as part of the recommendations for relevant future management.
Electronic supplementary material
The online version of this article (doi:10.1007/s13280-012-0251-z) contains supplementary material, which is available to authorized users. 相似文献45.
武钢三烧区域改建了二台大连三洋蒸汽型双效溴化锂吸收式制冷机。叙述了该改建项目的主机选型、参数选定、设计特点等。 相似文献
46.
Steven G. McNulty Johnny L. Boggs 《Environmental pollution (Barking, Essex : 1987)》2010,158(6):2053-2058
Federal agencies of several nations have or are currently developing guidelines for critical forest soil acid loads. These guidelines are used to establish regulations designed to maintain atmospheric acid inputs below levels shown to damage forests and streams. Traditionally, when the critical soil acid load exceeds the amount of acid that the ecosystem can absorb, it is believed to potentially impair forest health. The excess over the critical soil acid load is termed the exceedance, and the larger the exceedance, the greater the risk of ecosystem damage. This definition of critical soil acid load applies to exposure of the soil to a single, long-term pollutant (i.e., acidic deposition). However, ecosystems can be simultaneously under multiple ecosystem stresses and a single critical soil acid load level may not accurately reflect ecosystem health risk when subjected to multiple, episodic environmental stress. For example, the Appalachian Mountains of western North Carolina receive some of the highest rates of acidic deposition in the eastern United States, but these levels are considered to be below the critical acid load (CAL) that would cause forest damage. However, the area experienced a moderate three-year drought from 1999 to 2002, and in 2001 red spruce (Picea rubens Sarg.) trees in the area began to die in large numbers. The initial survey indicated that the affected trees were killed by the southern pine beetle (Dendroctonus frontalis Zimm.). This insect is not normally successful at colonizing these tree species because the trees produce large amounts of oleoresin that exclude the boring beetles. Subsequent investigations revealed that long-term acid deposition may have altered red spruce forest structure and function. There is some evidence that elevated acid deposition (particularly nitrogen) reduced tree water uptake potential, oleoresin production, and caused the trees to become more susceptible to insect colonization during the drought period. While the ecosystem was not in exceedance of the CAL, long-term nitrogen deposition pre-disposed the forest to other ecological stress. In combination, insects, drought, and nitrogen ultimately combined to cause the observed forest mortality. If any one of these factors were not present, the trees would likely not have died. This paper presents a conceptual framework of the ecosystem consequences of these interactions as well as limited plot level data to support this concept. Future assessments of the use of CAL studies need to account for multiple stress impacts to better understand ecosystem response. 相似文献
47.
Uncertainty plays an important role in water quality management problems. The major sources of uncertainty in a water quality management problem are the random nature of hydrologic variables and imprecision (fuzziness) associated with goals of the dischargers and pollution control agencies (PCA). Many Waste Load Allocation (WLA) problems are solved by considering these two sources of uncertainty. Apart from randomness and fuzziness, missing data in the time series of a hydrologic variable may result in additional uncertainty due to partial ignorance. These uncertainties render the input parameters as imprecise parameters in water quality decision making. In this paper an Imprecise Fuzzy Waste Load Allocation Model (IFWLAM) is developed for water quality management of a river system subject to uncertainty arising from partial ignorance. In a WLA problem, both randomness and imprecision can be addressed simultaneously by fuzzy risk of low water quality. A methodology is developed for the computation of imprecise fuzzy risk of low water quality, when the parameters are characterized by uncertainty due to partial ignorance. A Monte-Carlo simulation is performed to evaluate the imprecise fuzzy risk of low water quality by considering the input variables as imprecise. Fuzzy multiobjective optimization is used to formulate the multiobjective model. The model developed is based on a fuzzy multiobjective optimization problem with max–min as the operator. This usually does not result in a unique solution but gives multiple solutions. Two optimization models are developed to capture all the decision alternatives or multiple solutions. The objective of the two optimization models is to obtain a range of fractional removal levels for the dischargers, such that the resultant fuzzy risk will be within acceptable limits. Specification of a range for fractional removal levels enhances flexibility in decision making. The methodology is demonstrated with a case study of the Tunga–Bhadra river system in India. 相似文献
48.
近49年中国夏季制冷度日数的变化 总被引:1,自引:0,他引:1
利用全国531个气象站1960~2008年逐日平均气温资料,分析了近49 a来我国夏季制冷度日数的变化趋势,并以浙江省为例分析了制冷度日数与夏季空调降温电力负荷的关系。主要结论如下:我国日平均温度等于或高于26℃的日数(1971~2000年平均)大于10 d,夏季有制冷需求的站点主要分布在新疆、四川盆地和太行山 巫山 雪峰山一线以东地区,以及云南干热河谷地区。1960~2008年我国黄河以北地区夏季有制冷需求的站点6~9月平均气温从20世纪90年代中期开始呈现出较明显的上升趋势,使得制冷日数和度日数都相应增加;黄河以南、南岭以北地区近49 a来6~9月平均气温线性趋势不明显,制冷度日数变化不大;南岭以南地区6~9月气温持续上升,夏季制冷度日数的增加最为显著。以浙江省为例的分析显示,制冷度日数与夏季空调降温电力负荷有很好的线性相关关系,可以用来预测降温耗电量。
相似文献
相似文献
49.
50.