全文获取类型
收费全文 | 20493篇 |
免费 | 1713篇 |
国内免费 | 794篇 |
专业分类
电工技术 | 402篇 |
综合类 | 1194篇 |
化学工业 | 5971篇 |
金属工艺 | 2446篇 |
机械仪表 | 649篇 |
建筑科学 | 1476篇 |
矿业工程 | 710篇 |
能源动力 | 317篇 |
轻工业 | 3034篇 |
水利工程 | 165篇 |
石油天然气 | 213篇 |
武器工业 | 271篇 |
无线电 | 443篇 |
一般工业技术 | 2716篇 |
冶金工业 | 2779篇 |
原子能技术 | 86篇 |
自动化技术 | 128篇 |
出版年
2024年 | 85篇 |
2023年 | 335篇 |
2022年 | 518篇 |
2021年 | 663篇 |
2020年 | 637篇 |
2019年 | 538篇 |
2018年 | 537篇 |
2017年 | 667篇 |
2016年 | 649篇 |
2015年 | 654篇 |
2014年 | 1017篇 |
2013年 | 1147篇 |
2012年 | 1218篇 |
2011年 | 1357篇 |
2010年 | 1061篇 |
2009年 | 998篇 |
2008年 | 878篇 |
2007年 | 1349篇 |
2006年 | 1334篇 |
2005年 | 1203篇 |
2004年 | 1041篇 |
2003年 | 874篇 |
2002年 | 789篇 |
2001年 | 638篇 |
2000年 | 558篇 |
1999年 | 433篇 |
1998年 | 403篇 |
1997年 | 305篇 |
1996年 | 248篇 |
1995年 | 202篇 |
1994年 | 212篇 |
1993年 | 140篇 |
1992年 | 100篇 |
1991年 | 47篇 |
1990年 | 40篇 |
1989年 | 35篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
在已经得到的描述鱼雷罐喷粉处理基本参数具体表达式的基础上,运用多目标非线性优化方法,对工艺操作参数进行优化。 相似文献
72.
撞击流管式反应制备超细氧化锆粉体 总被引:6,自引:0,他引:6
我国氧化锆粉体产业目前基本上“精进粗出”,迫切需要开发氧化锆粉体备新工艺,特别是具有高附加值的纳米氧化锆粉体制备技术,液相反应沉淀法具有成本低,易于工业化等优点而成为研究的热点。本文采用撞击流管式反应新工艺,撞击流接触反应强化了过程的微观混合。实现了均匀成核,使得成核过程易于控制,而管式反应器的独特设计克服了返混,因而使得反应沉淀过程易于控制,粒子分布窄。用该工艺结合醇热处理表面改性制备的超细氧化锆粉体。平均粒径约为14nm,粒度分布窄并无硬团聚发生。该方法过程简单,易于工业化大生产。 相似文献
73.
74.
评述了国内外粉末冶金铁基烧结炉的发展动向和具体改进装备。即功能带设计、脱蜡装置,烧结带气氛控制,淬火带的设想,加热元件配置及新型可塑性耐火材料。 相似文献
75.
76.
Large woody debris (LWD) can increase stream habitat heterogeneity by providing structure, altering flow patterns, enhancing sediment deposition, forming pools and retaining organic matter. In North America, the role of LWD has been studied extensively in streams of mature forests (e.g. Pacific Northwest), but few studies have assessed LWD in streams of younger forests (e.g. Midwestern USA). Our objectives were to: (1) quantify the volume and abundance of LWD in a set of Midwestern streams; (2) evaluate possible factors influencing LWD quantity; (3) identify the functional roles of LWD; and (4) compare LWD levels in the upper Midwest to those elsewhere in North America. In 2002 and 2003, we measured LWD and geomorphological variables in 15 low‐gradient streams draining previously logged watersheds in the Upper Peninsula of Michigan. Mean (±SE) LWD volume (0.77 ± 0.12 m3 100 m−2) and abundance (33 ± 3 pieces 100 m−1) were 71% and 10% lesser, respectively, than in streams of similar gradient elsewhere in North America. Channel shape (width:depth ratio) explained 30% of the variation in LWD volume (multiple stepwise regression, P = 0.015) while LWD length and length:channel width combined, explained 72% of the variation in LWD density (multiple stepwise regression, P < 0.0001). About 50% of the LWD either stored sediment or stabilized banks and 14% of the LWD formed pools, although pool density was not significantly related to LWD volume or density. LWD levels, overall, were low in upper Midwestern streams, but the relative importance of that LWD to ecosystem function may be magnified in these wood‐poor systems. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
77.
N. F. Kuschevskaya A. E. Kushchevskii A. I. Oleshko 《Powder Metallurgy and Metal Ceramics》2006,45(3-4):202-206
The possibility of utilizing nanopowders of iron and Fe-Co-Ni produced bu a thermochemical method in the fabrication of sealing
composition materials is investigated. It is established that such hermetic sealing composition materials function reliably
under extremal conditions and guarantee elevated strength of adhesion to the surface of the metal and high corrosion and temperature
stability.
__________
Translated from Poroshkaya Metallurgiya, Nos. 3–4(448), pp. 112–117, March–April, 2006. 相似文献
78.
79.
Woodceramics Prepared from Wood Powder/Phenolated Wood Composite 总被引:2,自引:0,他引:2
B.Y. Zhao T. Hirose T. Okabe D. Zhang T.X. Fan K.A. Hu 《Journal of Porous Materials》2002,9(3):195-201
In this paper, composites were made from wood powder and its phenolated product, and then were carbonized into woodceramics. The effects of the content of the phenolated wood in the composites on the forming ability, size, density, compressive strength, volume electrical resistivity, and specific surface area of the woodceramics were investigated. It is suggested that in the preparation of woodceramics, phenolic resin can possibly be substituted totally by phenolated wood that is the main constituent of liquefied wood. 相似文献
80.
S. B. Hanna F. F. Abdel-Mohsen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(6):285-290
A beta-silicon carbide powder with a surface area of 30m2g?l and a mean particle size of < 1μm was produced from the thermal conversion of silicon resin in an atmosphere of hydrogen. The amount of product increased with increasing iron content (0–2.1 wt%) and firing temperature (1200–1500°C). Chemical analysis, X-ray diffraction and i.r. absorption spectrometry were used to follow the conversion reaction. 相似文献