全文获取类型
收费全文 | 755篇 |
免费 | 77篇 |
国内免费 | 117篇 |
专业分类
安全科学 | 225篇 |
废物处理 | 26篇 |
环保管理 | 146篇 |
综合类 | 438篇 |
基础理论 | 22篇 |
污染及防治 | 64篇 |
评价与监测 | 8篇 |
社会与环境 | 12篇 |
灾害及防治 | 8篇 |
出版年
2023年 | 9篇 |
2022年 | 4篇 |
2021年 | 34篇 |
2020年 | 30篇 |
2019年 | 27篇 |
2018年 | 10篇 |
2017年 | 29篇 |
2016年 | 20篇 |
2015年 | 45篇 |
2014年 | 42篇 |
2013年 | 33篇 |
2012年 | 69篇 |
2011年 | 58篇 |
2010年 | 36篇 |
2009年 | 56篇 |
2008年 | 27篇 |
2007年 | 46篇 |
2006年 | 49篇 |
2005年 | 44篇 |
2004年 | 42篇 |
2003年 | 54篇 |
2002年 | 32篇 |
2001年 | 22篇 |
2000年 | 25篇 |
1999年 | 8篇 |
1998年 | 23篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有949条查询结果,搜索用时 15 毫秒
941.
采用高效混凝沉降—超滤工艺对循环冷却水排水进行预处理后,考察了NF-A、NF-B和NF-C型纳滤膜的运行情况和处理效果.实验结果表明:NF-A膜对COD、Ca2+和Mg2+的去除率均较低,对Clˉ没有去除效果;NF-C膜对COD、Ca2+、Mg2+和SO42-的去除率均较高,对Clˉ去除率为83.1%,但运行压力较高;NF-B膜运行压力居中,对COD去除率为95.9%,对Ca2+去除率为98.3%,对Mg2+去除率为93.4%,对SO42-去除率为98.2%,对Clˉ去除率为67.4%,处理后出水达到循环回用的要求. 相似文献
942.
Tessa Artruc Desiree Tullos Ben Leshchinsky 《Journal of the American Water Resources Association》2023,59(1):86-106
The drawdown of reservoirs behind dams is an important management strategy (e.g., for removal of aging infrastructure, flushing of sediment), and an opportunity to study erosional processes. A numerical model was developed to examine retrogressive bank erosion across reservoir drawdown scenarios and to evaluate factors controlling the rate, volume, and mechanisms of lateral erosion. Modeled processes included dynamic drawdown of groundwater, sequential slope failures via limit equilibrium analysis, and retrogression considering stress interaction between failing blocks. Field measurements were coupled with Staged, Slow, and Rapid drawdown scenarios. Results highlight the importance of including retrogression as an avenue for lateral erosion, as sequential block failures were found to occur in all scenarios except Slow drawdown. This result indicates that bank stability models without some means of characterizing the evolution of slope failure during drawdown are likely underestimating bank failure rates and volumes. In contrast, dynamic groundwater was not found to be a dominant control for any drawdown scenario. Model results also demonstrate that the drawdown increment is a first-order control on slope instability via the development of drained or undrained conditions. A majority of failures occurred under undrained conditions. To maximize slope stability, using slow drawdown to activate internal friction under drained conditions is essential. The design of the drawdown rate created a tradeoff between the amount of impact created and when the impact is produced. The study also articulated the need for coupling models and field observations for rapidly changing systems. 相似文献
943.
944.
采用有限元方法 ,考虑在静载和动载共同作用下 ,对常压立式拱顶储油罐的地震应力进行了计算分析 ,给出了轴向应力的分布状态 ;并与相关抗震设计规范中的验算公式得出的结果进行了比较。结果表明 :由于地震的动力作用 ,储油罐的受力状态不是均匀分布 ,出现了峰值和谷值 ,而这些应力峰值大于工业设备抗震鉴定标准和石油化工设备抗震鉴定标准中公式的计算应力值 ,这应引起足够的注意。 相似文献
945.
地下储液罐抗爆炸地冲击作用的流固耦合有限元分析 总被引:1,自引:0,他引:1
储液罐的抗震性能虽然得到了较为深入的研究,但对其抗爆炸产生的地冲击作用的研究还十分罕见。本文通过建立流固耦合的数值分析模型,研究爆炸地冲击作用下地下立式储液罐的动力特性,包括储液晃动波高、罐壁的应力和应变、底板的提离和浮放储液罐的"象足"变形产生原因及破坏机理等。研究结果表明,储液罐在爆炸地冲击荷载和地震荷载作用下的动力响应有明显区别,地震荷载作用下的储液罐抗震验算方法不适用于爆炸地冲击荷载。 相似文献
946.
目的 带坞舱船舶尾部具有与外界连通的自由液面,由于船舶运动会在坞舱内产生波浪,形成有害的波浪砰击,影响舱内装备的正常作业。针对这一问题,系统地对带坞舱船舶尾舱内的消浪方案进行模拟与优化,提出一套具有良好消浪性能的消浪装置方案。方法 以荷兰皇家海军两栖运输船为目标进行三维建模,使用CFD方法对其进行不同波浪下船舶响应模拟和分析,监测船舶的运动响应和舱内多个监测点的波高情况,使用多孔挡板为基础,给出一套消浪装置,并进行带有消浪装置方案的船舶响应模拟,评估该消浪装置方案的消浪性能。结果 对舱内首端和侧壁布置多孔板消浪装置,消浪效果可达40%~50%,验证了该消浪装置的可行性。结论 采用多孔介质区域模型对带有多孔介质消浪装置的整船进行数值模拟,在计算效率远高于对实际物理模型建模的同时,可以得到较好的消浪效果。 相似文献
947.
化工储罐爆炸产生的抛射碎片击中并破坏相邻罐体后,将引发多米诺效应。N guyen破坏概率模型认为,当罐壳受撞击后,残余壁厚小于某个临界值时就会被破坏,并假设该临界残余壁厚为定值,存在不合理之处。本文基于储罐壳体损失面积安全评价方法AP I 579,把撞击形成的复杂凹坑简化为圆锥形,分别针对圆柱储罐、球罐推导出圆锥形凹坑剩余强度系数的求解方法,并根据塑性失效理论确定了罐壳的临界剩余强度系数,由此建立了新的破坏准则。在此基础上,采用蒙特卡罗法进行模拟,建立了新的爆炸碎片对目标储罐的破坏概率模型,与N guyen模型相比,得出的破坏概率偏大,结果更为安全保守。通过对剩余强度系数与无量纲撞击深度和凹坑锥角的变化关系进行分析,证明N guyen模型中临界残余壁厚为定值的假设并不合理,而新的基于剩余强度系数计算的破坏概率更为准确合理。 相似文献
948.
Growing interest in the dynamics of floodplain evolution and the important role of overbank sedimentation on river floodplains as a sediment sink has focused attention on the need to document contemporary and recent rates of overbank sedimentation. The potential for using the fallout radionuclides 137Cs and excess 210Pb to estimate medium-term (10-102 years) sedimentation rates on river floodplains has attracted increasing attention. Most studies that have successfully used fallout radionuclides for this purpose have focused on the use of 137Cs. However, the use of excess 210Pb potentially offers a number of advantages over 137Cs measurements. Most existing investigations that have used excess 210Pb measurements to document sedimentation rates have, however, focused on lakes rather than floodplains and the transfer of the approach, and particularly the models used to estimate the sedimentation rate, to river floodplains involves a number of uncertainties, which require further attention. This contribution reports the results of an investigation of overbank sedimentation rates on the floodplains of several UK rivers. Sediment cores were collected from seven floodplain sites representative of different environmental conditions and located in different areas of England and Wales. Measurements of excess 210Pb and 137Cs were made on these cores. The 210Pb measurements have been used to estimate sedimentation rates and the results obtained by using different models have been compared. The 137Cs measurements have also been used to provide an essentially independent time marker for validation purposes. In using the 210Pb measurements, particular attention was directed to the problem of obtaining reliable estimates of the supported and excess or unsupported components of the total 210Pb activity of sediment samples. Although there was a reasonable degree of consistency between the estimates of sedimentation rate provided by the 137Cs and excess 210Pb measurements, some differences existed and the various models used to interpret excess 210Pb measurements could produce different results. By using the 137Cs measurements to provide independent validation of the estimates of sedimentation rate provided by the different models used with the excess 210Pb measurement it was shown that the CICCS and Composite CRS models appeared to generally provide the best results. 相似文献
949.