全文获取类型
收费全文 | 6489篇 |
免费 | 719篇 |
国内免费 | 263篇 |
专业分类
电工技术 | 83篇 |
综合类 | 356篇 |
化学工业 | 3505篇 |
金属工艺 | 269篇 |
机械仪表 | 85篇 |
建筑科学 | 314篇 |
矿业工程 | 138篇 |
能源动力 | 152篇 |
轻工业 | 267篇 |
水利工程 | 51篇 |
石油天然气 | 272篇 |
武器工业 | 10篇 |
无线电 | 352篇 |
一般工业技术 | 1237篇 |
冶金工业 | 292篇 |
原子能技术 | 55篇 |
自动化技术 | 33篇 |
出版年
2024年 | 10篇 |
2023年 | 85篇 |
2022年 | 154篇 |
2021年 | 200篇 |
2020年 | 211篇 |
2019年 | 175篇 |
2018年 | 203篇 |
2017年 | 245篇 |
2016年 | 237篇 |
2015年 | 262篇 |
2014年 | 402篇 |
2013年 | 414篇 |
2012年 | 487篇 |
2011年 | 468篇 |
2010年 | 347篇 |
2009年 | 410篇 |
2008年 | 340篇 |
2007年 | 388篇 |
2006年 | 365篇 |
2005年 | 345篇 |
2004年 | 278篇 |
2003年 | 269篇 |
2002年 | 235篇 |
2001年 | 177篇 |
2000年 | 144篇 |
1999年 | 116篇 |
1998年 | 77篇 |
1997年 | 59篇 |
1996年 | 59篇 |
1995年 | 47篇 |
1994年 | 40篇 |
1993年 | 28篇 |
1992年 | 40篇 |
1991年 | 38篇 |
1990年 | 44篇 |
1989年 | 30篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1959年 | 2篇 |
1951年 | 4篇 |
排序方式: 共有7471条查询结果,搜索用时 31 毫秒
71.
This paper presents results of an experimental program conducted to investigate the capacity of hydration products of different cementing materials to retain “bound” alkalis when the alkalinity of the surrounding solution drops. The study covered paste samples containing high-alkali Portland cement and various levels of silica fume and/or fly ash. The results showed that the ability of the hydration products of cement-fly ash systems to bind alkalis is a function of the CaO content of the fly ash, the binding increasing as the calcium content decreases. High-alkali fly ashes (Na2Oe > 5.0% and CaO in the range of 15% to 20%) showed considerable amounts of alkali contributed to the test solutions. Silica fume does not have a high capacity to retain alkalis in its hydration products; however, ternary blends containing silica fume and fly ash have excellent capacity to bind and retain alkalis. 相似文献
72.
Ni–W catalysts were prepared by impregnation of commercial -alumina and silica supports. The sulfidation, performed directly after drying at 100°C, yielded fully sulfided Ni–W species on both supports (SEM-EDAX, XPS, XRD). At optimal metals loading (50 wt% NiO + WO3, Ni/W = 2), the sulfided catalysts had similar texture (N2 adsorption) and displayed similar activity in dibenzothiophene hydrodesulfurization (DBT HDS), while the activity of the Ni–W/SiO2 catalyst in toluene hydrogenation (HYD) was six times higher than that of Ni–W/Al2O3. This is due to the more than two times higher WS2 slabs stacking number in Ni–W/SiO2 compared with Ni–W/Al2O3 (XRD, HR-TEM), yielding stronger adsorption of toluene (TPD). 相似文献
73.
In this work, ethylene was polymerized by using Cp2ZrCl2 supported on silica pretreated with methylaluminoxane (MAO) as the catalyst system. The influence of the conditions for the preparation of the heterogeneous catalyst, such as temperature, washing method of the catalytic solid, MAO and metallocene concentration in the support treatment, time of MAO, and metallocene immobilization on the support, type of alkylaluminum used in the support pretreatment, and calcination temperature of the support were investigated. Aluminum and zirconium content fixed on the silica surface were determined by inductively coupled plasma emission spectroscopy. Polymer characteristics were determined by gel permeation chromatography and differential scanning calorimetry. According to the results, the activity of some supported catalysts were far higher than with the homogeneous system. Moreover, polyethylene with very high molecular weights were also obtained and with molecular weight distribution larger than those produced with the homogeneous precursor. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2054–2061, 2002 相似文献
75.
76.
77.
合成二氧化硅对硅橡胶性能的影响 总被引:5,自引:0,他引:5
介绍了合成二氧化硅及硅橡胶的结构性质,探究了二氧化硅的结构性质对硅橡胶补强性能的影响,指出了二氧化硅颗粒的大小、形态、聚结状态、表面性质和与高分子硅氧烷之间的相互作用是影响二氧化硅对硅橡胶补强性能的最主要的因素,并用实验对硅橡胶的硬度、拉伸强度、300%定伸应力、扯断伸长率、撕裂强度、压缩永久变形等物理性能进行测定,结果表明:BET比表面积180~200m^2/g,孔隙度(吸油量)为3.0~3.2mL/g,平均粒径为8~10岬的沉淀法白炭黑对硅橡胶具有很好的补强效果。 相似文献
79.
Paul W. Angel Chandra S. Ray Delbert E. Day 《Journal of the American Ceramic Society》1990,73(10):2965-2969
The glass-formation region of the calcia-gallia-silica system was determined. The glasses within this region were measured to have a density of 3 to 4 g/cm3 , a refractive index of 1.6 to 1.73, an Abbe number between 35 and 58, a thermal expansion coefficient of 6.5 × 10−7 /°C to 11.5 × 10−7 /°C, softening temperatures between 730° and 790°C, and a Vickers microhardness of 5.2 to 7.3 GPa. Crystalline phases were identified along the glass-formation boundary. Infrared transmission spectra were used to explain glass structures and their effect on glass properties. The results suggest that the role of calcia in the glass structure is similar to that for calcia in calcium aluminosilicate glasses. 相似文献
80.
纳米材料及其在有机硅材料中的应用 总被引:2,自引:0,他引:2
简要介绍了纳米技术和纳米材料如粒径为10-30nm的石英粉、TiO2、ZnO、Fe2O3、CaCO3、气相法白炭黑等在有机硅材料中的应用。 相似文献