全文获取类型
收费全文 | 895篇 |
免费 | 39篇 |
国内免费 | 347篇 |
专业分类
安全科学 | 62篇 |
废物处理 | 48篇 |
环保管理 | 71篇 |
综合类 | 472篇 |
基础理论 | 178篇 |
污染及防治 | 317篇 |
评价与监测 | 35篇 |
社会与环境 | 34篇 |
灾害及防治 | 64篇 |
出版年
2023年 | 27篇 |
2022年 | 55篇 |
2021年 | 38篇 |
2020年 | 29篇 |
2019年 | 26篇 |
2018年 | 34篇 |
2017年 | 44篇 |
2016年 | 42篇 |
2015年 | 60篇 |
2014年 | 67篇 |
2013年 | 93篇 |
2012年 | 76篇 |
2011年 | 102篇 |
2010年 | 81篇 |
2009年 | 50篇 |
2008年 | 70篇 |
2007年 | 50篇 |
2006年 | 49篇 |
2005年 | 49篇 |
2004年 | 32篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 26篇 |
1998年 | 20篇 |
1997年 | 12篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有1281条查询结果,搜索用时 5 毫秒
841.
1概况 加拿大Enbridge公司(以下简称E公司)是北美地区最大的输油(含原油、成品油、人工合成油等)、气(液化气、天然气等)的管道运营公司.拥有管线7×104 km,公司职工4000余名.管道管径41~122 cm,采取不加热顺序输送75种液体,中间不设隔离球,日输量达27.4×104t.管道途经4个国家,即加拿大、美国、哥伦比亚和西班牙.该公司所辖的技术公司遍布世界各地,主要从事技术转让、咨询服务及天然气分配等.现在已与中国多家石油公司进行了合作,如与中石油签订了Gate way石油管道运输项目,2006年动工,2009年投产. 相似文献
842.
本文在省域层面上测度了科技投入效率、产学合作研发与全要素碳排放绩效三者之间的关系。结果表明,无论在绩效层面还是在技术层面,2000-2009年间我国科技投入效率和产学合作研发都显著影响全要素碳排放绩效,而市场发育程度、企业联盟研发和企业研发投入三者则不太显著。值得一提的是,经济发展程度与全要素碳排放绩效之间存在显著的正向关系。原因是,一方面我国加大科技投入力度,鼓励、支持、引导产学研合作研发创新,明显地提高了全要素碳排放绩效;另一方面我国市场发育不太完善,企业研发投入不够,企业联盟研发进展缓慢,降低了我国全要素碳排放绩效。我国应加大企业科技经费投入幅度,合理安排科技经费投入结构,实现节能减排的科技经费投入多元化、立体化和动态化,继续发挥产学研的互补优势,建立健全产学研合作的体制机制,营造良好的政策环境和服务氛围,地区间应在要素、技术、监管等层面扩展合作范围,实现不同区域、产业和企业间空间联动。 相似文献
843.
利用Mettler-Toledo同步热分析仪对市场上利用率比较高的四种木质地板在不同程序控制升温,和不同气氛流量条件下的热解特性进行了研究.同时,为了更好地对地板材料的热解特性进行深入了解,以实木地板为例,验证了升温速率对热分解过程的影响.通过研究发现,四种地板样品的热解过程分为三个阶段,但每个阶段的峰值大小和峰面积各不相同.同时,气氛流量中氧气的参与使热解机理发生改变,反应时间提前,温度升高,热解速度加快.通过对比受热期间的TG、DTG和DSC曲线,确定失重范围,以及各成分的残炭百分比,可以得出四种地板材料试验成分的火灾危险性,即,实木地板的火灾危险性低于其它三种地板材料. 相似文献
844.
Assessment of water quality and identification of pollution sources of plateau lakes in Yunnan (China) 总被引:1,自引:0,他引:1
The plateau lakes of Yunnan are important both ecologically and economically in China. Nevertheless, the human impact on water quality in these lakes has become increasingly highlighted. The water quality of 10 plateau lakes was monitored regularly over the period of 2000 through 2004 for 24 parameters. Multivariate statistical techniques, including cluster analysis (CA), factor analysis (FA), and principal component analysis (PCA), were employed to better interpret information about the water quality and its pollution sources. No obvious data reduction from CA/FA was found because three principal components (PCs) needed 14 variables to explain 85.01% of the total variance. However, three latent factors accounted for pollution mainly from the following sources: agricultural activities, residential activities and anthropogenic-toxic pollution from industrial effluents, or other special activities. Box-whiskers plots were employed to visually interpret the spatiotemporal variations of water quality variables, which were highly correlated with three PCs. Three types of water quality (i.e., low-, medium-, and high-polluted lakes) were determined through CA based on the similarity of water quality variables. Our results may provide helpful information for the authorities to effectively manage the water quality and make sound policies. 相似文献
845.
846.
847.
To explore the sediment interception capacity of plants and its relationship with the surface morphological traits of plants, we used laboratory simulations and off-site flume experiments to study the ability for sediment retention of six familiar species: Leucaena leucocephala (LL), Melia azedarach (MA), Dodonaea viscosa (DV), Coriaria sinica (CS), Heteropogon contortus (HC), and Eulaliopsis binata (EB) aver two growth periods in the dry-hot river valley of the Jinsha River. We analyzed the relationship between near-surface morphological traits of individuals of six species and their ability for sediment retention. Our study resulted in three main observations. (1) In the flume experiment, three-month seedlings and one-year old seedlings of the six species showed different abilities for sediment retention. In the three-month seedlings, the ability for sediment retention of CS was the highest, followed by MA and LL, whereas it was the lowest in HC and EB. However, in one-year old seedlings, the ability for sediment retention of CS was the highest, but the ability for sediment retention of HC and EB was better than those of MA and LL. Hence, the ability for sediment retention of the six species fluctuated between different growth periods. (2) The three-month old and one-year old seedlings of all six species showed different near-surface morphological traits. (3) The sediment mass was significantly and positively correlated with near-surface leaf areas, crown lengths, crown widths, stem dry matter densities at the intersection volume, and above-ground biomass, but significantly and negatively correlated with the angle between stem and ground, indicating that these latter are the main near-surface morphological traits able to affect sediment retention. In addition, the sediment mass was also correlated (positively and negatively) with the stem epidermal crack number, stem dry matter content, leaf dry matter content at the intersection volume, and dry mass per unit volume of the intersection volume, which could also reflect the ability of sediment retention. We conclude that in the areas where plant measures are used to control soil erosion and intercept sediment, the key, above-mentioned plant morphological factors should be taken into account in order to select the optimal plant species. © 2018 Science Press. All rights reserved. 相似文献
848.
849.
分析了某化工厂一起反应釜爆炸事故的可能原因,认为事故发生的原因主要是氮气置换失效及提前对反应釜进行加热,提出了预防措施. 相似文献
850.
In this paper, we present a three-step methodological framework, including location identification, bias modification, and out-of-sample validation, so as to promote human mobility analysis with social media data. More specifically, we propose ways of identifying personal activity-specific places and commuting patterns in Beijing, China, based on Weibo (China’s Twitter) check-in records, as well as modifying sample bias of check-in data with population synthesis technique. An independent citywide travel logistic survey is used as the benchmark for validating the results. Obvious differences are discerned from Weibo users’ and survey respondents’ activity-mobility patterns, while there is a large variation of population representativeness between data from the two sources. After bias modification, the similarity coefficient between commuting distance distributions of Weibo data and survey observations increases substantially from 23% to 63%. Synthetic data proves to be a satisfactory cost-effective alternative source of mobility information. The proposed framework can inform many applications related to human mobility, ranging from transportation, through urban planning to transport emission modeling. 相似文献