全文获取类型
收费全文 | 2015篇 |
免费 | 161篇 |
国内免费 | 292篇 |
专业分类
安全科学 | 315篇 |
废物处理 | 143篇 |
环保管理 | 417篇 |
综合类 | 1047篇 |
基础理论 | 181篇 |
环境理论 | 4篇 |
污染及防治 | 217篇 |
评价与监测 | 67篇 |
社会与环境 | 57篇 |
灾害及防治 | 20篇 |
出版年
2024年 | 2篇 |
2023年 | 15篇 |
2022年 | 25篇 |
2021年 | 45篇 |
2020年 | 67篇 |
2019年 | 60篇 |
2018年 | 40篇 |
2017年 | 59篇 |
2016年 | 85篇 |
2015年 | 74篇 |
2014年 | 89篇 |
2013年 | 168篇 |
2012年 | 181篇 |
2011年 | 168篇 |
2010年 | 110篇 |
2009年 | 149篇 |
2008年 | 86篇 |
2007年 | 125篇 |
2006年 | 120篇 |
2005年 | 102篇 |
2004年 | 93篇 |
2003年 | 102篇 |
2002年 | 103篇 |
2001年 | 71篇 |
2000年 | 71篇 |
1999年 | 55篇 |
1998年 | 46篇 |
1997年 | 57篇 |
1996年 | 33篇 |
1995年 | 32篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有2468条查询结果,搜索用时 453 毫秒
711.
Russian olive (Elaeagnus angustifolia L.) was introduced in 1950 onto one site on the Milk River floodplain, northern Montana, 10 km downstream from the Canada/United States border. To analyze dispersal of Russian olive from the point source between 1950 and 1999, we compared distribution, numbers, size structure, and mortality of Russian olive and plains cottonwood (Populus deltoides Marsh:) on an unregulated reach of the Milk River floodplain in southeastern Alberta and north-central Montana. Within 50 years, Russian olive in this reach has moved upriver into Alberta and downriver to the Fresno Reservoir. It is now present on 69 of the 74 meander lobes sampled, comprising 34%, 62%, and 61% of all Russian olive and plains cottonwood seedlings, saplings, and trees, respectively. On some meander lobes, Russian olive has colonized similar elevations on the floodplain as plains cottonwood and is oriented in rows paralleling the river channel, suggesting that recruitment may be related to river processes. Breakup ice had killed 400 Russian olive saplings and trees and damaged >1000 others on 30 of the meander lobes in 1996. Nevertheless, Russian olive now outnumbers cottonwood on many sites on the Milk River floodplain because its seeds can be dispersed by wildlife (particularly birds) and probably by flood water and ice rafts; seeds are viable for up to 3 years and germination can take place on bare and well-vegetated soils; and saplings and trees are less palatable to livestock and beaver than plains cottonwood. Without control, Russian olive could be locally dominant on the Milk River floodplain in all age classes within 10 years and replace plains cottonwood within this century. 相似文献
712.
石油短缺与中国经济安全 总被引:6,自引:0,他引:6
石油短缺已经成为引起中国能源危机最核心的问题,本文分析了中国石油短缺的背景及其影响因素,在实证分析的基础上,提出了“对石油依赖程度”这一概念。本文还把石油短缺与经济安全问题联系了起来,并提出了确保我国经济安全的具体对策。 相似文献
713.
714.
Effect of the water–oil ratio on brine/surfactant/alcohol/oil systems optimized for soil remediation
The optimum middle-phase microemulsion used for remediation of oily contaminated soils is often obtained by mixing a certain
amount of a surfactant/alcohol mixture with oil and adjusting the salinity concentrations at a constant water–oil ratio. Upon
introduction to the subsurface, however, the system may not be in the optimum state throughout the remediation process owing
to the change in the water–oil ratio. This research has attempted to investigate the effect of the water–oil ratio on the
phase behavior of systems containing brine, anionic surfactant, alcohols, and different oils. By systematically changing the
water–oil ratio, while keeping the others variables constant, the systems exhibited different phase behavior. The results
revealed that the effect of the water–oil ratio on system behavior was significant, and analogous to that of salinity. Increasing
the water–oil ratio led the system change from winsor I → winsor III → winsor II. The greater the water–oil ratio the lower
the salinity required to produce the middle-phase microemulsion, but the narrower the salinity range of the three-phase region.
An empirical correlation has been developed in order to predict the changes in phase behavior with the changes in water–oil
ratio. This provides a useful tool for designing optimum formulations suitable for soil remediation.
Received: October 5, 1999 / Accepted: March 27, 2000 相似文献
715.
716.
解脂耶氏酵母菌处理含油废水的研究 总被引:9,自引:2,他引:7
利用解脂耶氏酵母菌在最佳降解条件下分别处理色拉油、餐饮油等油脂类废水和柴油、机油等石油类废水50 h.结果表明:该菌株能快速降解油脂,在油质量浓度≤2 000 mg/L时生化反应属于一级反应,对色拉油、餐饮油中油脂的降解率分别为93.30%和85.08%,同时菌体细胞大量生长,其生物量分别为1 652.7和1 940.0 mg/L,废水处理过程中pH稳定在3~4之间;但该菌对石油的降解率低,生成的生物量少,处理后废水pH维持在6~7之间.解脂耶氏酵母菌对油的降解与自身生物量的生成有关,该菌株降解油脂类和石油类物质的途径不同,产生的脂酶系统不同,使得废水的pH变化规律不相同. 相似文献
717.
718.
为了实现油(气)田(特别是环境敏感地区)开发的可持续发展,在原有基础上,针对水网地区油田开发环境的特点,就现在环境保护技术工作中存在的重点难点问题进行进一步的研究和探讨,完善和发展了整套污染防治工艺、处理技术及处理装备。 相似文献
719.
新疆油气田开发对环境的影响及其对策 总被引:4,自引:0,他引:4
该文论述了新疆油气田开发对大气环境,土壤,地下水以及生态环境的不同程度的影响,重点论述了对生态环境的影响,并提出了一些对策和建议,这些对新疆乃至对全国的油气田环境保护工作都具有一定的参考和借鉴作用。 相似文献
720.