全文获取类型
收费全文 | 29915篇 |
免费 | 543篇 |
国内免费 | 3730篇 |
专业分类
安全科学 | 1263篇 |
废物处理 | 1622篇 |
环保管理 | 3257篇 |
综合类 | 7711篇 |
基础理论 | 6893篇 |
环境理论 | 6篇 |
污染及防治 | 9112篇 |
评价与监测 | 2040篇 |
社会与环境 | 1766篇 |
灾害及防治 | 518篇 |
出版年
2023年 | 237篇 |
2022年 | 691篇 |
2021年 | 603篇 |
2020年 | 419篇 |
2019年 | 437篇 |
2018年 | 669篇 |
2017年 | 773篇 |
2016年 | 924篇 |
2015年 | 907篇 |
2014年 | 1372篇 |
2013年 | 2773篇 |
2012年 | 1563篇 |
2011年 | 1736篇 |
2010年 | 1482篇 |
2009年 | 1428篇 |
2008年 | 1615篇 |
2007年 | 1547篇 |
2006年 | 1353篇 |
2005年 | 1072篇 |
2004年 | 996篇 |
2003年 | 1045篇 |
2002年 | 970篇 |
2001年 | 1142篇 |
2000年 | 883篇 |
1999年 | 636篇 |
1998年 | 521篇 |
1997年 | 485篇 |
1996年 | 513篇 |
1995年 | 443篇 |
1994年 | 368篇 |
1993年 | 355篇 |
1992年 | 342篇 |
1991年 | 284篇 |
1990年 | 267篇 |
1989年 | 245篇 |
1988年 | 222篇 |
1987年 | 168篇 |
1986年 | 142篇 |
1985年 | 149篇 |
1984年 | 180篇 |
1983年 | 161篇 |
1982年 | 202篇 |
1981年 | 142篇 |
1980年 | 119篇 |
1979年 | 152篇 |
1978年 | 118篇 |
1977年 | 107篇 |
1976年 | 101篇 |
1975年 | 84篇 |
1974年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
961.
监测结果表明室外的机动车流量对于室外的苯系物浓度起到较大的贡献作用,并且室外苯系物浓度的变化曲线和机动车流量变化结果呈现出一致性;同时,通过监测还表明室内的三苯浓度变化中,开窗情况下室内的污染物浓度的变化和室外浓度变化是一致,而在关窗情况下室内的三苯浓度变化较为的复杂,这可能是在交通主干道旁和对照点的建筑室内存在三苯污染源。 相似文献
962.
963.
采用UV-Fenton体系处理活性黑KNB染料废水.研究了pH值、H2O2和FeSO4用量、反应温度和反应时间等对染料废水脱色率的影响.实验结果表明,当KNB的初始浓度为50mg/L时,在t=25℃、pH =5.4、[H2O2]=0.2ml/L,[FeSO4]=0.7mmol/L,使用30W的紫外灯光照射条件,反应1小时后,KNB染料废水脱色率几乎可达100%.通过比较反应前后染料废水的UV-Vis吸收光谱,初步探讨了KNB的降解机理.研究表明,UV-Fenton体系可以有效地处理活性黑KNB染料废水,为该工艺处理实际染料废水提供基础数据. 相似文献
964.
965.
本研究以水中总氮空白值为研究对象,不同厂家的过硫酸钾和不同试验用水条件下的总氮空白的变化规律。研究结果表明:无氨水和二次水蒸出来的总氮空白明显低于一次水蒸出来的总氮空白;这跟蒸馏水纯度有关系,一次水含有氨,所以消解时蒸馏水中的氨会被氧化,从而导致空白值偏高。同样有的厂家的过硫酸钾纯度不高,所以导致空白值高。 相似文献
966.
967.
New lightweight sandwich materials challenge existing forming processes as well as following process steps. As such the manufacturing potential of shear cutting has to be evaluated. Two cutting methods are compared. Method commonly used is shear-cutting within one stroke engaged, the other one is known as counter-shear cutting, which uses two strokes.The challenges of cutting sandwich materials are variation of hole diameter within the different layers, fraying of the textiles, deformation of the hole contour and burr formation. These effects occur in conventional shear cutting as the intermediate layer and the lower sheet metal are cut by the scrap of the upper sheet instead of the cutting punch.The following methodology included shear cutting with closed cutting edge i.e. cutting of holes into five different sandwich materials. The sandwiches exemplarily represent multiple kinds of possible material designs. For instance, aluminum and steel face sheets, different thicknesses of intermediate layers and different intermediate layers materials such as integrated textile fibers have been used. Adequate cutting parameters such as die clearance and the use of a blank holder have been determined. To achieve good results a stiff machine design with good guidance and precise control of punch position was crucial.Observations of conventional shear cutting revealed the need of small cutting clearance of 4%. High burnish area is possible for the upper face sheet due to the superimposed force by the lower face sheet. The major conclusion depicted that high cutting quality of sandwich materials requires counter shear cutting. Hence, the roll-over of the lower sheet facing the intermediate layer, the burnish area at the lower sheet, good cutting quality of the fibers improve significantly and burr formation is avoided completely. Summarized this paper provides cutting parameters for sandwich materials based on experimental work. 相似文献
968.
The automotive industry is developing designs and manufacturing processes for a new generation of electric motors intended for use in hybrid and electric vehicles. This paper is focused on using solid-state welding to join rectangular wires in the fabrication of motor stators. Resistance welding has not typically been applied to copper due to its very high electrical conductivity; however through optimization of the current and pressure profiles, excellent quality copper-to-copper joints have been demonstrated with a technique known as resistance mash welding. A better understanding of resistance mash welding characteristics will help advancements in its application for stators. The limitations of this application will be discussed. 相似文献
969.
F. Khodabakhshi M. Abbaszadeh H. Eskandari S.R. Mohebpour 《Journal of Manufacturing Processes》2013,15(4):533-541
A modified method of severe plastic deformation (SPD) entitled constrained groove pressing-cross route (CGP-CR) was introduced for imposing a high magnitude of equivalent strain of about 2.32 per pass on the sheet form samples. The major benefit of this improved route compared to previous common route was the more homogeneity of strain in the rolling (RD) and transverse (TD) directions of sheets. In this study, low carbon steel samples were used for examination of evolutions in microstructure and mechanical properties during SPD via CGP-CR process. Mechanical properties improvement were measured by tensile and macro hardness tests. The results indicate that CGP-CR process can effectively improve tensile strength; and also, yield stress and hardness of as-received low carbon steel samples were improved up to about 100% after two deformation passes. Also, high magnitude of inhomogeneity can be observed in hardness distribution through first pass of the process which diminishes in the subsequent passes. Microstructural evolutions during process were monitored by optical microscopy observations and X-ray diffraction analysis. The results demonstrate that initial ferritic microstructure with grain size of about 30 μm was refined to a 225 nm cell structure after two passes of CGP-CR process. 相似文献
970.
城市生态环境保护是生态文明建设的重要组成部分之一,而餐厨垃圾是影响城市生态环境的一种主要污染源,因此,有效处理餐厨垃圾也是当前城市生态环境保护的重要内容。本文以重庆市为例,针对其特殊的餐厨垃圾组成成分,调查分析了其主城区餐厨垃圾污染状况及处理难点,提出了3种主要处理方案情景并进行综合效益评价。结果表明建立餐厨垃圾小型处理站是最优方案,其成本效益核算结果说明当政府基金和垃圾产量有限时,也可采用缩小处理站规模以达到最高的组合效益。 相似文献