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 15 毫秒
101.
本文介绍粉煤灰经电除尘器分离后所得分电场灰密度沿电场方向的变化规律及影响因素,并阐述了粉煤灰密度与成份之间的关系。 相似文献
102.
脱硫石膏粉煤灰胶结材水化硬化机理及耐水性研究 总被引:13,自引:0,他引:13
以火电厂的两种废渣即脱硫石膏和粉煤灰为主要原料制得的胶结材,其强度明显高于普通石膏制品,软化系数大于0.85。采用水化热测定、XRD和pH值测定及SEM/EDXA分析,并结合宏观试验结果,分析了这种胶结材的水化硬化机理和微结构特点,并对其耐水性提高的原因进行了讨论。 相似文献
103.
An experimental investigation on the effects of incorporating large volumes of fly ash on the early engineering properties and long-term strength of masonry mortars is reported. The effect of fly ash and its mean particle size (PD) on the variation of workability and strength has been studied. It was found that fly ash and its mean particle size play a very significant role on the strength of masonry mortars. It has been observed that the early-term strength, except the mortars incorporating coarse fly ash (CFA), was slightly influenced by the replacement with fly ash. The long-term strength (both the bond strength and the compressive strength) will significantly increase, especially for the bond strength of mortars incorporating coarse fly ash. It was also found that the bond strength significantly increased as the mean particle size of fly ash decreases after 28 days curing. However, the 7-day strength was little influenced by fly ash particle size. The fluidity of composite mortar enhanced due to replace cement and lime with fly ash, and the mean PD of fly ash significantly influenced the workability. 相似文献
104.
Isidoro Izquierdo Cubero Maria T. Plaza López-Espinosa Rafael Acuña Castillo 《Journal of chemical ecology》1991,17(8):1529-1541
The synthesis of the title compound13 has been carried out through the preparation of its precursor, (3R,4R,5S,6R)-3,4,5-trihydroxy-1,7-dioxaspiro[5.5]undecane (6), obtained fromd-fructose using Wittig's methodology, reduction, and spiroketalation. Compound6 was transformed into13 by a Barton deoxygenation at C-5 followed by a Corey dideoxygenation at C-3,4 of the appropriately protected derivatives.Enantiospecific synthesis of spiroacetals. Part II. For Part I, see Izquierdo and Plaza (1990). 相似文献
105.
本文试图论述现有合成氨厂改变产品结构,采取以生产化肥为主,联产化工产品。通过对钾芒硝法工艺及联碱工艺技术路线的选择,技术经济分析,以期提高化肥厂的经济效益。 相似文献
106.
107.
以粉煤灰、活化剂、硫酸为主要原料经活化、陈化、浸泡、焙烧等处理制得的固体酸催化剂,应用于草酸二乙酯的合成中取得了良好的催化效果。实验发现,当醇酸摩尔比为3.5、催化剂用量为草酸的5%、反应时间在4h时,酯产率可达81.8%,该催化剂具有贮存稳定性高、可重复使用、制备工艺简单、原料成本低廉等特点,是一种易于工业化应用的环境友好固体酸催化剂。 相似文献
108.
Mari Paz Lorenzo Sara Goñi Ana Guerrero 《Journal of the American Ceramic Society》2002,85(12):3071-3075
The activation of the pozzolanic reaction of fly ash in portland cement paste immersed in sulfate solution has been studied. Mixtures of two Spanish fly ashes (ASTM class F) with 0%, 15%, and 35% replacement of portland cement by fly ash were immersed in Na2 SO4 solution, of 2880 ppm SO4 2− concentration, for a period of 90 days. The resistance of the different mixtures to the sulfate attack was evaluated using the Koch-Steinegger test. The results showed that all of the mixtures were sulfate resistant, despite the high Al2 O3 content of the fly ash. The diffusion of SO4 2− and Na+ ions through the pore solution activated the pozzolanic reactivity of the fly ashes, causing microstructural changes, which were characterized by X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). As a result, the flexural strength of the mixtures increased, principally for the fly ash of a lower particle size and 35% of addition. 相似文献
109.
A. Proctor C. Adhikari G. D. Blyholder 《Journal of the American Oil Chemists' Society》1995,72(3):331-335
Fourier transform infrared spectroscopy was used to investigate the adsorption of oleic acid (OA) onto dry rice hull ash (RHA)
silica. Adsorption partially occurred by surface hydrogen bonding of the carboxylic acid. There was also formation of carboxylate
ions by reaction of OA with residual potassium oxide. These ions were strongly bound by the ash. Isopropanol inhibited OA
adsorption by H-bonding and encouraged desorption of H-bonded OA, but without itself being significantly bound. RHA with 40%
moisture also adsorbed a small amount of OA by H-bonding and reacted with OA to form and adsorb carboxylate ions. 相似文献
110.
针对火电厂输灰系统在线化学清洗工艺,研制出一种新型溶垢缓蚀剂。在清洗中,这种溶垢缓蚀剂既能促进灰垢的溶解,又能防止电厂输灰系统及其它有关设备的腐蚀。现场应用结果表明,溶垢缓蚀效果良好。 相似文献