全文获取类型
收费全文 | 10189篇 |
免费 | 993篇 |
国内免费 | 329篇 |
专业分类
电工技术 | 651篇 |
技术理论 | 1篇 |
综合类 | 904篇 |
化学工业 | 3609篇 |
金属工艺 | 364篇 |
机械仪表 | 141篇 |
建筑科学 | 1675篇 |
矿业工程 | 882篇 |
能源动力 | 553篇 |
轻工业 | 400篇 |
水利工程 | 244篇 |
石油天然气 | 153篇 |
武器工业 | 36篇 |
无线电 | 107篇 |
一般工业技术 | 1016篇 |
冶金工业 | 582篇 |
原子能技术 | 39篇 |
自动化技术 | 154篇 |
出版年
2024年 | 24篇 |
2023年 | 106篇 |
2022年 | 243篇 |
2021年 | 318篇 |
2020年 | 298篇 |
2019年 | 240篇 |
2018年 | 253篇 |
2017年 | 305篇 |
2016年 | 337篇 |
2015年 | 354篇 |
2014年 | 579篇 |
2013年 | 466篇 |
2012年 | 679篇 |
2011年 | 722篇 |
2010年 | 539篇 |
2009年 | 658篇 |
2008年 | 481篇 |
2007年 | 735篇 |
2006年 | 638篇 |
2005年 | 542篇 |
2004年 | 494篇 |
2003年 | 445篇 |
2002年 | 386篇 |
2001年 | 292篇 |
2000年 | 283篇 |
1999年 | 223篇 |
1998年 | 156篇 |
1997年 | 149篇 |
1996年 | 107篇 |
1995年 | 84篇 |
1994年 | 76篇 |
1993年 | 66篇 |
1992年 | 53篇 |
1991年 | 31篇 |
1990年 | 31篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 20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 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
1.
Abdulrahman S. Albidah 《Ceramics International》2021,47(11):14923-14943
The growth of demand for concrete raises concerns about the consumption of natural resources and ordinary Portland cement. Geopolymer composites show promise as a sustainable alternative for conventional cement concrete. Considering the wide range of potential geopolymer composites applications (including suitability for transportation infrastructure, underwater applications, repair and rehabilitation of structures as well as recent developments in 3D printing), the desired fresh and mechanical properties of the geopolymer composite may vary between applications: for example, rapid setting can be a merit for certain applications and a demerit for others. Therefore, the desired fresh and mechanical properties (e.g., workability, setting time, compressive strength, etc.) can be controlled for a given geopolymer source material through its partial substitution by natural or by-product materials. Recognizing the critical role of various replacement materials in enhancing the potential applications of geopolymer composites, the present review was undertaken to quantify and understand the effect of partial replacement by fly ash, metakaolin, kaolin, red mud, slag, ordinary Portland cement, and silica fume on the setting time, workability, compressive strength and flexural strength of various source materials addressed in the literature. The review also provides insights into research gaps in the field to promote future research. 相似文献
2.
This paper reports an assessment of the performance of concrete based on a calcium sulfoaluminate–anhydrite–fly ash cement combination. Concretes were prepared at three different w/c ratios and the properties were compared to those of Portland cement and blast-furnace cement concretes. The assessment involved determination of mechanical and durability properties. The results suggest that an advantageous synergistic effect between and ettringite and fly ash (Ioannou et al., 2014) was reflected in the concrete’s low water absorption rates, high sulfate resistance, and low chloride diffusion coefficients. However, carbonation depths, considering the dense ettringite-rich microstructure developed, were higher than those observed in Portland cement concretes at a given w/c ratio. It was concluded that the amount of alkali hydroxides present in the pore solution is as important factor as the w/c ratio when performance of this type of concrete is addressed. 相似文献
3.
Chaoxin Li Yi Zhou Yuming Tian Yuanyuan Zhao Kaiyue Wang Guomin Li Yuesheng Chai 《Ceramics International》2019,45(5):5613-5616
Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF3, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources. 相似文献
4.
在内径120 mm的半圆柱形内循环流化床中,以平均粒径387 nm的Ti O2为原料,考察了单独通入流化气、射流气和同时通入流化气和射流气三种流化方式下超细粉的流化特性以及射流气速对超细粉聚团尺寸的影响。结果表明:同时通入流化气和射流气时,流化气能促进粉体循环,消除环隙死区;高速射流能有效破碎聚团,显著减小聚团尺寸,从而使超细粉在环隙区与导流管之间形成稳定循环,小聚团在环隙区实现平稳流态化。随着射流气速的增大,聚团尺寸减小,粒度分布变窄,在射流气速分别为60,90,120,150 m/s的条件下,聚团平均直径分别为194,158,147,135μm。 相似文献
5.
6.
Using the SiO2 and Al2O3 components of the amorphous phase in coal fly ash (Fa), Fa was converted to Na-X zeolites in NaOH-NaAlO2 solutions by stirring at 35°C for 72 hr and then aging at 85°C for a given period. The molar ratio SiO2/Al2O3 of the starting materials was controlled from 2.0 to 13.2. The resulting materials were characterized by various means. Increasing the SiO2/Al2O3 ratio of the starting material increased the degree of crystallinity of faujasite, exhibiting a maximum at SiO2/Al2O3 = 8.0. The faujasite formed was identified as Na-X zeolite with Si/Al = 1.20. The amorphous phase in Fa was dissolved during the stirring to form a precursor of zeolite, such as amorphous aluminosilicate. The Na-X zeolite was formed by aging for 24 hr, and the degree of crystallinity of this material was increased with the increasing aging period. The cation exchange capacity and specific surface area were increased with the increasing degree of crystallinity of the Na-X zeolites. 相似文献
7.
8.
用化学还原法合成了FeBP非晶态合金超细微粒,用电感耦合等离子体光谱(ICP)、X射线粉末衍射(XRD)、透射电子显微镜(TEM)和差热分析(DSC)等手段对其进行了物性表征,并用微型催化反应装置考察了其对PH3分解的催化作用,结果表明,非晶态合金FeBP对PH3的分解具有良好的催化作用,能使PH3的分解温度从800℃以上降到500℃左右。490℃时分解率超过90%,540℃时达100%。 相似文献
9.
Chun Yang Yin Sharifah Aishah Syed Abdul KadirYing Pei Lim Sharifah Nawirah Syed-AriffinZurinawati Zamzuri 《Fuel Processing Technology》2008
Ash derived from combustion of Malaysian oil palm biomass (empty fruit bunches consisting of fibers) was physically and chemically characterized in order to provide a comprehensive understanding of its specific properties in terms of toxicity, compositions and reusability. Principal analyses conducted include particle size distribution, scanning electron microscopy, elemental dispersive X-ray, elemental analysis, toxicity characteristic leaching procedure (TCLP) as well as thermogravimetric, X-ray diffractometry and Fourier-transform infrared analyses. TCLP result indicated that the oil palm ash (OPA) should not be classified as toxic wastes in terms of heavy metal leachability since leachable copper, cadmium, lead and nickel concentrations were detected below the stipulated leachability limits. It was determined that the OPA contained high amount of potassium as well as presence of silica which implied its suitability to be reused as crude fertilizer or cement replacement material. 相似文献
10.