全文获取类型
收费全文 | 8538篇 |
免费 | 831篇 |
国内免费 | 190篇 |
专业分类
电工技术 | 635篇 |
技术理论 | 1篇 |
综合类 | 783篇 |
化学工业 | 3141篇 |
金属工艺 | 136篇 |
机械仪表 | 108篇 |
建筑科学 | 1632篇 |
矿业工程 | 754篇 |
能源动力 | 545篇 |
轻工业 | 255篇 |
水利工程 | 239篇 |
石油天然气 | 117篇 |
武器工业 | 6篇 |
无线电 | 57篇 |
一般工业技术 | 597篇 |
冶金工业 | 368篇 |
原子能技术 | 35篇 |
自动化技术 | 150篇 |
出版年
2024年 | 13篇 |
2023年 | 87篇 |
2022年 | 213篇 |
2021年 | 269篇 |
2020年 | 244篇 |
2019年 | 199篇 |
2018年 | 203篇 |
2017年 | 248篇 |
2016年 | 295篇 |
2015年 | 320篇 |
2014年 | 522篇 |
2013年 | 405篇 |
2012年 | 601篇 |
2011年 | 631篇 |
2010年 | 470篇 |
2009年 | 585篇 |
2008年 | 432篇 |
2007年 | 629篇 |
2006年 | 547篇 |
2005年 | 458篇 |
2004年 | 395篇 |
2003年 | 361篇 |
2002年 | 317篇 |
2001年 | 211篇 |
2000年 | 193篇 |
1999年 | 163篇 |
1998年 | 105篇 |
1997年 | 99篇 |
1996年 | 60篇 |
1995年 | 46篇 |
1994年 | 35篇 |
1993年 | 30篇 |
1992年 | 23篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 19篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有9559条查询结果,搜索用时 187 毫秒
91.
Kwangryul Hwang Takafumi Noguchi Fuminiro Tomosawa 《Cement and Concrete Research》2004,34(12):697-2276
Based on experimental results concerning the compressive strength development of concrete containing fly ash, the authors derived an estimation equation for compressive strength development. The equation can express coefficient , which indicates the activity of fly ash as a binder, in the form of a function of age, fly-ash content, and Blaine specific surface area of fly ash.
This equation is capable of explaining the increases in the early strength due to fly ash in place of part of fine aggregate, the decreases in the early strength due to fly ash in place of part of cement, the increases in the long-term strength due to pozzolanic reaction, the relationship between the fly-ash replacement ratio and the ratio of strength increase/decrease, and the effect of fly ash's Blaine specific surface area on the strength. 相似文献
92.
93.
在全球范围内,纯碱生产和进出口贸易主要是由中国、欧洲SOLVAY公司和美国主导和控制,中国已经成为世界上生产量和消费量最大的国家,美国则是世界上最大的纯碱出口国,SOLVAY公司不断采取各种措施,调整策略,收购美国和中国的纯碱企业,积极参与国际市场竞争。分析了我国及世界纯碱工业的生产、进出口等现状及发展趋势。 相似文献
94.
Pozzolanic properties of reject fly ash in blended cement pastes 总被引:2,自引:0,他引:2
Low-grade fly ash (reject fly ash, r-FA), a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process, has remained unused due to its high carbon content and large particle size. But it may be used in certain areas, such as in solidification and stabilization processes of hazardous waste and materials for road base or subbase construction, which require relatively lower strength and reactivity. It is therefore necessary to extend research on the properties of r-FA and explore its possible applications. This paper presents experimental results of a study on the mechanical and hydration properties of cementitious materials prepared by blending r-FA with ordinary Portland cement (OPC). Parallel mixes were also prepared with the good ash [i.e., classified fine fly ash (f-FA)] for comparison. Selective chemical activators were added to the mix to study the effects of the activators on the properties of the blend system. The results show that r-FA generally has a lower rate of hydration than f-FA particularly at the early stage of hydration. Adding Ca(OH)2 alone almost had no effect on accelerating the hydration of r-FA. But adding a small quantity of Na2SO4 or K2SO4 together with Ca(OH)2 significantly accelerated the hydration reaction. The results of the compressive strength measurement correlated nicely with the degree of hydration results. It was also found that water-to-binder ratio (w/b) was an important factor in affecting the strength development and the hydration degree of r-FA pastes. 相似文献
95.
Zeolite Formation in Class F Fly Ash Blended Cement Pastes 总被引:5,自引:0,他引:5
Judith L. LaRosa Stephen Kwan Michael W. Grutzeck 《Journal of the American Ceramic Society》1992,75(6):1574-1580
Zeolite formation in Class F fly ash blended cement pastes is under investigation. A Na–P type zeolite and Zeolite Y were synthesized from Class F fly ash and NaOH solution after 2 days of aging at room temperature and 6 days of curing at 80°C. However, no zeolites formed when KOH was used. In additional experiments, a Na–P type zeolite, Zeolite Y, and chabazite developed in cement pastes blended with Class F fly ash and NaOH solution which had been aged 2 days at room temperature and then cured 6 days at temperatures ranging from room temperature to 90°C. Seeding the pastes with natural zeolites was also investigated. 相似文献
96.
本文选用废渣制成的粉煤灰纤维棉(FAF)和聚氯乙烯(PVC)树脂作为原料,成功制备了FAF/PVC复合材料,研究了FAF的表面处理及其加入量对复合材料力学性能、热性能和硬度的影响,并用SEM对复合材料的界面进行了表征。实验结果表明,相对于纯PVC树脂而言,复合材料含经KH550处理的FAF40phr时,拉伸强度提高约12%;含经软化剂处理的FAF10phr时,冲击强度提高约110%;含经偶联剂和软化剂联合处理的FAF10phr时,冲击强度提高约70%,拉伸强度提高约11%,维卡软化温度随FAF添加量的增加呈上升趋势。研究结果证明,KH550和软化剂联合使用会对复合材料起到有效的增强增韧效果,因此能提高复合材料中FAF的填充量。制成的环保型FAF/PVC复合材料不仅性能全面高于纯PVC,而且材料成本显著降低,为综合利用废渣FAF开拓了新方向。 相似文献
97.
98.
分析了影响热媒炉热效率的主要因素 ,介绍了通过对热媒炉盘管干冰除灰和改进风油比控制方式来提高热效率的方法 ,指出提高热媒炉热效率的主要途径是 :降低排烟温度和空气过剩系数。 相似文献
99.
Batch leaching tests have been performed on fly ashes collected from four Australian power stations fuelled by chemically different coals. Two acidic and two alkaline fly ashes were subjected to long-term (144 h) leaching tests, and the behaviour of As, B, Mo and Se was investigated to obtain data on their potential for mobilisation during fly ash-water interactions. All four elements are mobile under different conditions and over different leaching times. The concentrations of these elements released in leaching solutions with initial pH values of 4, 7 and 10 were used to assess the influence of pH conditions on element mobility from the acidic and alkaline fly ashes. The most mobile of the four elements leached were Mo from alkaline fly ashes and B from acidic fly ashes. Arsenic concentration increased with time in leachate solutions from acidic and alkaline fly ashes; however, in solutions in contact with alkaline fly ashes the As concentration, after reaching a maximum, later decreased with time. Selenium mobility shows a similar pattern to that of As, with similar leaching concentrations. Boron has the highest relative mobility of all four elements. A process possibly responsible for the decrease in concentration of B, As and Se in alkaline leaching solutions is the formation of ettringite. Equilibrium between the solid phase (ash) and the leaching solution was not reached in any of the leaching experiments. The pH of the leaching solution is the key factor affecting the mobility of these trace elements in these fly ashes. 相似文献
100.
介绍了粉煤灰对掺有M17塑化剂的混凝土拌合物泵送性能和混凝土强度的影响,通过扫描电镜对粉煤灰颗粒形貌进行了观察,初步探讨了粉煤灰的作用机理。试验说明在接有M17塑化剂的泵送混凝土中加入粉煤灰,可增加坍落度,降低泌水率,泵逆性能可得到改善。 相似文献