全文获取类型
收费全文 | 562篇 |
免费 | 60篇 |
国内免费 | 182篇 |
专业分类
安全科学 | 94篇 |
废物处理 | 28篇 |
环保管理 | 90篇 |
综合类 | 349篇 |
基础理论 | 118篇 |
污染及防治 | 60篇 |
评价与监测 | 16篇 |
社会与环境 | 34篇 |
灾害及防治 | 15篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 26篇 |
2019年 | 26篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 33篇 |
2015年 | 37篇 |
2014年 | 27篇 |
2013年 | 62篇 |
2012年 | 48篇 |
2011年 | 25篇 |
2010年 | 31篇 |
2009年 | 39篇 |
2008年 | 28篇 |
2007年 | 48篇 |
2006年 | 41篇 |
2005年 | 33篇 |
2004年 | 22篇 |
2003年 | 28篇 |
2002年 | 19篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有804条查询结果,搜索用时 31 毫秒
1.
In this laboratory study different combinations of bed (sand, pebble gravel [gravel], and a mix of sand and gravel) and flow (typical and overtopping) were experimented with to investigate the impact of porous deflectors in flow diversity, water quality, and fish performance in prismatic open channels. Deflectors changed the gradually varied flow to a rapidly varied flow, as a sudden change in the water depth was observed at the deflectors, and this change was large for smooth beds. With the presence of gravel, the scouring near the downstream deflector was almost twice that of the sand bed, and with the scouring at its own upstream deflector, irrespective of whether the flow was typical or overtopping. This behavior was a result of sand mobilization due to shear stress and sand mobilization aided gravel transport. The mixed bed showed less gravel movement compared to the gravel-only bed. The percentage of sediment washed out was minor for all bed scenarios, indicating that sediment transport was local. Relative to the sand bed without deflectors (representing a typical urban canal), deflectors resulted in reduced and improved water quality (in terms of sediment load) for sand, and mixed bed, respectively. The fishes found refuge and were comfortable in the pool areas created by deflectors unlike in channels without deflectors where they showed exhaustion. 相似文献
2.
为研究氟橡胶O形圈在集输油环境中的老化行为特征,以长庆油田使用的氟橡胶O形圈(位于非金属复合管连接接头处)为研究对象,采用宏观与微观相结合的方法,通过挂片实验分析氟橡胶O形圈在不同介质(采出油,采出水)、温度(25,50 ℃)、压力条件(0.1,4,6 MPa)下老化后的形貌、质量、拉伸性能及硬度。结果表明:采出油、采出水均能引起O形圈发生溶胀,从而降低O形圈的强度、韧性、硬度;采出水引起的溶胀显著高于采出油更易导致O形圈表面产生坑洞缺陷;渗透速率随温度升高而急剧增加,压力对渗透速率的影响不明显;硬度降低较小,最大降幅为4.17%。结合现场服役813 d的密封圈SEM形貌,证实集输介质渗透会引起氟橡胶圈溶胀、导致表面产生坑洞等缺陷。 相似文献
3.
染料废水处理技术现状与发展 总被引:2,自引:0,他引:2
文章介绍了染料废水的物理、化学和生物处理技术,并分析了其去除原理和工艺优缺点,目的在于为染料废水处理工作提供理论基础和现实指导,并提出未来染料废水处理技术的发展走向———高效、经济、适应性强、清洁性的废水处理技术。 相似文献
4.
5.
6.
Introduction: Using connected vehicle technologies, pedestrian to vehicle (P2V) communication applications can be installed on smart devices allowing pedestrians to communicate with drivers by broadcasting discrete safety messages, received by drivers in-vehicle, as an alternative to expensive fixed-location physical safety infrastructure. Method: This study consists of designing, developing, and deploying an entirely cyber-physical P2V communication system within the cellular vehicle to everything (C-V2X) environment at a mid-block crosswalk to analyze drivers’ reactions to in-vehicle advanced warning messages, the impacts of the advanced warning messages on driver awareness, and drivers’ acceptance of this technology. Results: In testing human subjects with, and without, advanced warning messages upon approaching a mid-block crosswalk, driver reaction, acceptance, speed, eye tracking data, and demographic data were collected. Through an odds ratio comparison, it was found that drivers were at least 2.44 times more likely to stop for the pedestrian with the warning than without during the day, and at least 1.79 times more likely during the night. Furthermore, through binary logistic regression analysis, it was found that driver age, time of the day, and the presence of the advanced warning message all had strong, significant impacts with a confidence value of at least 98% (p < 0.02) on the rate at which drivers stopped for the pedestrian. Conclusions: The results from this study indicate that the advanced warning message sent within the C-V2X had a strong, positive impact on driver behavior and understanding of pedestrian intent. Practical Applications: Pedestrian crashes and fatality rates at mid-block crossings continue to increase over the years. Connected vehicle technology utilizing smart devices can be used as a means for communications between pedestrians and drivers to deliver safety messages. State and local city planners should consider geofencing designated mid-block crossings at which this technology operates to increase pedestrian safety and driver awareness. 相似文献
7.
为提高油气管道安全风险评估的准确性,以含内表面缺陷管道为研究对象,利用ABAQUS软件线弹性及弹塑性分析不同尺寸缺陷对裂纹萌生特征的影响;采用扩展有限元法,建立管道3点弯曲模型与全尺寸静载物理试验,并非线性拟合裂纹扩展尺寸,研究内表面缺陷处裂纹扩展情况。研究结果表明:内表面缺陷中心处极易萌生裂纹,随着缺陷尺寸的增大,裂纹萌生所需外力在缺陷相对长度为0.08、相对深度为0.4时的增长趋势变化较大,且缺陷深度对裂纹萌生的影响更大;对比数值模拟与全尺寸物理试验,发现在小于70 mm位移载荷或147.25 kN外力下裂纹尺寸快速扩展,之后呈变缓的趋势;非线性拟合裂纹尺寸,得到较为准确的裂纹扩展尺寸的预测结果。 相似文献
8.
两种基因型菜心根系形态和生理特性差异对其吸收累积DEHP影响的初步研究 总被引:1,自引:0,他引:1
在前期筛选出油青60天菜心和特青60天菜心分别为PAEs高/低吸收累积基因型菜心的基础上,进行邻苯二甲酸二(2-乙基己基)酯(DEHP)不同污染水平的溶液培养试验,对比研究两种基因型菜心的根系形态和生理特性的差异,初步探讨其与菜心吸收累积DEHP的关系.结果表明,随着培养液中DEHP浓度的增加,在根系形态方面,两种基因型菜心根系生物量、总根长和根表面积均下降,油青60天菜心根直径变粗,而特青60天菜心根直径变细;在根系生理特性方面,油青60天菜心除了根系活力下降外,总吸收面积、活跃吸收面积、比表面积和根系脂肪含量均增加,而特青60天菜心除了根系活跃吸收面积增加外,其余指标均下降.因此,两种基因型菜心的根系形态和生理特性对DEHP胁迫响应存在差异.除根直径外,油青60天菜心根系形态和生理指标总体上均高于特青60天菜心,更有利于其根系对DEHP的捕获和吸收. 相似文献
9.
微生物絮凝剂的絮凝性能及其絮凝形态研究 总被引:2,自引:0,他引:2
利用本实验室分离、筛选的微生物絮凝剂菌株G15,对其进行发酵培养,研究了絮凝剂投加量、絮凝反应体系pH值等对其絮凝性能的影响;对反应体系的ζ电位进行了测定,并且对所形成絮体的微观形态进行了观察。研究结果表明:该微生物絮凝剂在碱性条件下有较强的絮凝活性,当pH=10时最佳投加量为2.5mL;絮凝剂具有较强的热稳定性;加入菌株G15的发酵液后,高岭土悬浊液的ζ电位从-36.27mV显著上升至-12.97mV;并且该微生物絮凝剂产生的絮体颗粒大且结构密实,形态上有明显的分形特征。 相似文献
10.