全文获取类型
收费全文 | 6989篇 |
免费 | 172篇 |
国内免费 | 189篇 |
专业分类
电工技术 | 134篇 |
综合类 | 130篇 |
化学工业 | 1468篇 |
金属工艺 | 1147篇 |
机械仪表 | 532篇 |
建筑科学 | 195篇 |
矿业工程 | 223篇 |
能源动力 | 1068篇 |
轻工业 | 254篇 |
水利工程 | 19篇 |
石油天然气 | 134篇 |
武器工业 | 27篇 |
无线电 | 332篇 |
一般工业技术 | 1237篇 |
冶金工业 | 234篇 |
原子能技术 | 86篇 |
自动化技术 | 130篇 |
出版年
2024年 | 10篇 |
2023年 | 85篇 |
2022年 | 182篇 |
2021年 | 226篇 |
2020年 | 213篇 |
2019年 | 187篇 |
2018年 | 166篇 |
2017年 | 176篇 |
2016年 | 136篇 |
2015年 | 151篇 |
2014年 | 338篇 |
2013年 | 435篇 |
2012年 | 364篇 |
2011年 | 548篇 |
2010年 | 370篇 |
2009年 | 438篇 |
2008年 | 438篇 |
2007年 | 404篇 |
2006年 | 354篇 |
2005年 | 293篇 |
2004年 | 252篇 |
2003年 | 271篇 |
2002年 | 173篇 |
2001年 | 162篇 |
2000年 | 159篇 |
1999年 | 159篇 |
1998年 | 128篇 |
1997年 | 87篇 |
1996年 | 124篇 |
1995年 | 79篇 |
1994年 | 62篇 |
1993年 | 53篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有7350条查询结果,搜索用时 15 毫秒
991.
装甲防护材料的新葩——陶瓷-金属功能梯度复合材料 总被引:5,自引:0,他引:5
本文重点说明了在陶瓷增强的金属基复合材料的基础上,发展起来的陶瓷增强颗粒连续分布的陶瓷-金属功能梯度复合材料用作防护装甲的优点,介绍了陶瓷-金属功能梯度复合装甲材料的研究现状,并对其未来发展做了阐述。 相似文献
992.
防治金属腐蚀的五大对策 总被引:3,自引:0,他引:3
本文从理论和应用上概括介绍了防治金属腐蚀的五大对策,即隔离法,增大电极电势法,阴极保护法,改善腐蚀环境和介质(缓蚀剂法),以及研制开发新的耐腐蚀材料等。 相似文献
993.
Mark A. Keane 《Catalysis Letters》1993,19(2-3):197-209
Enantioselective Ni/SiO2 catalysts have been prepared by modification with aqueous solutions of (R)-(+)-tartaric acid (TA) and used in the asymmetric hydrogenation of a prochiral -keto ester (methylacetoacetate) to a -hydroxy ester ((R)-(-)-methyl-3-hydroxybutyrate). The simultaneous adsorption of TA and corrosive leaching of surface nickel metal are graphically illustrated and the progress of TA buildup on the catalyst surface with the duration of modification is presented. Variations of modifier pH were found to strongly affect the modification process and influence the ultimate hydrogenation rate and enantioselectivity. The surface coverage by TA is correlated to the asymmetric activity and an optimum fractional coverage of 0.2 is identified; at higher coverages modification with basic TA solutions yielded superior enantioselectivities. While TA treatment in basic media was less corrosive, a proportion of the surface enantioselective nickel sites was leached into solution during the hydrogenation step. The difference in the response of nickel precursors, prepared by impregnation and homogeneous precipitation/deposition, to TA treatment is compared and discussed in terms of metal/support interaction. 相似文献
994.
邻二氮菲分光光度法测定金属锑中铁含量 总被引:1,自引:0,他引:1
用王水溶解金属锑 ,以酒石酸钾钠为络合剂 ,盐酸羟胺为还原剂 ,在波长 5 1 0nm处以邻二氮菲分光光度法测定铁的含量。此方法准确度较高 相似文献
995.
996.
We report a simple method to synthesize Ag, Au, and Pt nanoparticles with a reasonable size dispersity using water-dispersible conducting polymer colloids composed of polyaniline (PANI) and conventional polyelectrolyte. This facile synthesis results in single crystalline metal nanoparticles that are stable in an aqueous solution for at least several weeks. The process involves incrementally adding a metal ion solution to aqueous conducting polymer colloids and does not require reducing agents such as NaBH4. In addition, the complete synthetic and purification procedure is carried out in an aqueous solution; therefore, it is environmentally benign and potentially suitable for large-scale production. We have also demonstrated synthesis of larger nanoparticles and nanosheets by varying the experimental parameters. With the tunable oxidation states of conducting polymers, we expect this synthetic platform can synthesize a wide range of nanostructured metals with specific size, shape and properties. Finally, the nanoparticles embedded in the conducting polymer matrix, the metal-polyaniline nanocomposite itself may be interesting since it represents a type of materials where metallic nanoislands are embedded in a semiconducting matrix. 相似文献
997.
998.
Guido Busca 《Catalysis Today》1996,27(3-4):457-496
The use of IR spectroscopic techniques to provide information on the mechanisms of catalytic oxidation over metal oxide catalysts is briefly discussed. The data published on studies of the catalytic oxidation of methanol, of linear C4 hydrocarbons and of methylaromatics over different metal oxide surfaces are reviewed and discussed. Lattice oxygen appears to act as the active oxygen species in both selective and total oxidation. Generalized mechanisms of these complex oxidation reactions are proposed and the catalyst features affecting selectivities in these reactions are discussed. The reaction network is apparently essentially governed by the organic chemistry of the reacting molecule (thus being substantially the same over the different oxide catalysts). However, the catalyst surface governs the rate of the different steps, favoring some paths over others. Thus, selectivity is determined by the catalyst chemical behavior and by the reaction variables (contact time, temperature, gas-phase composition, presence of steam, etc.). IR studies, if performed under conditions where some intermediates are actually detectable and jointly with other techniques, can give valuable information on the catalysis mechanisms. On the other hand, it has been concluded that in situ studies frequently do not give reliable information on reaction mechanisms, because under reaction conditions spectators rather than intermediates are detected. 相似文献
999.
《Ceramics International》2022,48(10):13748-13753
Thermal management requires an understanding of the relations among the thermal energy transfer, electronic properties, and structures of thermoconductive materials. Here, we enhanced the metal–insulator transition (MIT)-induced effect on the thermal conductivities of microstructure-controlled Ti2O3 composites containing W as a thermal conductive filler at approximately 450 K. To change the electronic and thermal transport properties, we varied the particle radii of the conductive phases in the raw material. The change in the calculated electronic thermal conductivity relative to the electrical conductivity of the Wx(Ti2O3)1?x composite was enhanced by compounding the material. When x was reduced from 50 vol% to 20 vol% and the W particle diameter was reduced from 150 μm to 5 μm, the variation in the estimated electronic thermal conductivity of the Wx(Ti2O3)1?x composite was increased by a factor of 2.01. The total thermal conductivity was also changed by the MIT. At x = 50 vol% and a W particle diameter of 5 μm, the maximum thermal conductivity change was 6.34 times larger than that of pure Ti2O3. The detailed relation between the MIT-induced changes in thermal transport and the microstructure were elucidated in classical effective medium approximations. 相似文献
1000.
Shigeyoshi Maeda 《Progress in Organic Coatings》1996,28(4):227-238
A review is presented on the recent development of surface treatment technologies for hot-dip galvanized steels relevant to adhesion of organic coatings. Applications of surface analytical techniques have elucidated that the surface layers of the nanometer scale dramatically govern the adhesion performance of painting or adhesive bonding. Surface enrichment of aluminium in the zinc layer deteriorates paint adhesion due to the reduction in phosphatability on the galvanized steel sheets and decreases the adhesive strength of the epoxy/dicyandiamide-bonded sheets due to the loss of acid-base interaction at the adhesive-substrate interface. In addition, the co-segregation of Al and Pb into the surface layer is responsible for the intergranular corrosion of zinc and facilitates the formation of a weak boundary layer, resulting in poor bond durability in a wet atmosphere. Improved adhesion performance has been established by developing new technologies that reduce the surface enrichment of minor elements or impurities in the zinc layer on the galvanizing line or that adopt a surface conditioning process prior to pretreatment in subsequent coil coating lines. 相似文献