全文获取类型
收费全文 | 1266篇 |
免费 | 46篇 |
国内免费 | 123篇 |
专业分类
电工技术 | 15篇 |
综合类 | 85篇 |
化学工业 | 660篇 |
金属工艺 | 29篇 |
机械仪表 | 16篇 |
建筑科学 | 79篇 |
矿业工程 | 2篇 |
能源动力 | 72篇 |
轻工业 | 36篇 |
水利工程 | 10篇 |
石油天然气 | 186篇 |
武器工业 | 1篇 |
无线电 | 16篇 |
一般工业技术 | 138篇 |
冶金工业 | 17篇 |
原子能技术 | 12篇 |
自动化技术 | 61篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 23篇 |
2020年 | 12篇 |
2019年 | 26篇 |
2018年 | 25篇 |
2017年 | 24篇 |
2016年 | 30篇 |
2015年 | 35篇 |
2014年 | 35篇 |
2013年 | 60篇 |
2012年 | 85篇 |
2011年 | 95篇 |
2010年 | 68篇 |
2009年 | 122篇 |
2008年 | 118篇 |
2007年 | 107篇 |
2006年 | 106篇 |
2005年 | 76篇 |
2004年 | 61篇 |
2003年 | 61篇 |
2002年 | 55篇 |
2001年 | 41篇 |
2000年 | 53篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 9篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1435条查询结果,搜索用时 15 毫秒
101.
以六甲基亚胺为模板剂,静态水热晶化法合成了MCM-56分子筛,通过X-射线衍射、N2等温吸附等方法对样品进行表征.当硅铝比低于20时易生成MCM-49和丝光沸石,加入少量碱能提高分子筛的相对结晶度,最佳合成温度为135~150 ℃,时间分别为3天.考察了MCM-56对苯和长链烯烃烷基化反应的催化活性,并与MCM-22进行了对比.实验表明,在最佳反应温度120 ℃时,烯烃的转化率为29.35%,烷基苯(LAB)的选择性为98.22%,MCM-56的催化活性明显低于MCM-22. 相似文献
102.
Ru incorporated Ni-MCM-41 mesoporous catalysts for dry reforming of methane: Effects of Mg addition, feed composition and temperature 总被引:1,自引:0,他引:1
S. Yasyerli S. FilizgokH. Arbag N. YasyerliG. Dogu 《International Journal of Hydrogen Energy》2011,36(8):4863-4874
Nickel incorporated MCM-41-like mesoporous materials, which were synthesized following a one-pot hydrothermal route, were promoted by Ru and Mg in order to improve their catalytic performances for dry reforming of methane. In this study, Ni-MCM-41 based catalysts (with a Ni/Si molar ratio of 0.2), containing different amounts of Ru (0.5-3.0 wt%) and Mg (1 and 5 wt%) were prepared by using sequential impregnation of Ru and Mg into Ni-MCM-41. Dry reforming of methane was studied in a tubular flow reactor in the temperature range of 500-600 °C with different CH4/CO2 ratios in the feed stream. Quite high hydrogen yield values and improved stability of these catalysts indicated the promoting effects of Ru for the Ni-MCM-41 type catalysts. Ru incorporation (1.0% Ru) was shown to improve H2 yields. Mg impregnation into 1.0Ru@Ni-MCM-41 improved catalytic performance by increasing CH4 conversion and decreasing the contribution of reverse water gas shift reaction, especially at initial times (first 60 min). Coke formation by decomposition of CH4 contributed to the hydrogen selectivity, but did not cause significant change in catalytic performance, especially at longer reaction times. 相似文献
103.
Alumina-based macro-porous ceramic foams were successfully coated with MCM-41 meso-porous materials using an in-situ one step hydrothermal synthesis. Low H2O/NaOH ratio in the starting mixture leads to a not uniform deposition of the meso-porous materials. Using higher H2O/NaOH ratio and two cycles of deposition, a CF with a continuous and thick layer of well-ordered MCM-41 material coating was produced. 相似文献
104.
In his response to Closure in Cole's Reformulated Leontief Model (Jackson et al. 1997) Cole presents the mechanics of his solution. His spreadsheet demonstration of the model, however, fails
to fully address the conceptual issues and model specification concerns raised in our critique. His demonstration does enable
us to provide a sorely needed formalization that pinpoints the inconsistencies in his model. While we join with Cole in urging
modellers to strive for clarity, transparency, and utility, we caution against allowing these goals to cause us to lose sight
of internal consistency requirements.
Received: 9 September 1998 / Accepted: 1 March 1999 相似文献
105.
MCM—41中孔分子筛的研究和开发 总被引:3,自引:0,他引:3
介绍了近期国内外中孔分子筛MCM-41的研究情况,阐述了其合成机理并简述了其性能和应用。 相似文献
106.
Muthuraj Esther Leena Preethi Thiripuranthagan Sivakumar Muthiahpillai Palanichami 《Catalysis communications》2010,11(10):876-879
Fe/Al-MCM-41 (Si/Al = 25, 50, 75 and 100) were synthesized. Their catalytic activity was evaluated towards benzylation of benzene with benzyl chloride in liquid phase. The catalytic activity of Fe/Al-MCM-41(25) was higher than the other catalysts. Diphenylmethane(DPM) was obtained as the major product with 100% selectivity and with 100% conversion of benzyl chloride under optimum condition. The effect of temperature and the feed ratio, on the activity of Fe/Al-MCM-41(25) and selectivity towards DPM was studied and a possible reaction mechanism was proposed. 相似文献
107.
Isabel Daz Federico Mohino Teresa Blasco Enrique Sastre Joaqun Prez-Pariente 《Microporous and mesoporous materials》2005,80(1-3):33-42
Ordered mesoporous materials functionalized with alkyl sulfonic acid groups have been proved to be efficient catalysts for esterification. In this paper we report on the synthesis and characterization of new materials containing simultaneously alkyl groups (vinyl, chloromethyl), that have been sulfonated in a post-synthesis step, and methyl groups. Different techniques have been used to characterize the obtained materials: XRD, TEM, elemental analysis, nitrogen adsorption, TGA, 29Si and 13C MAS NMR. Finally, the influence of the different synthesis parameters and functional groups on the behavior of the catalysts in the reaction of esterification of glycerol with lauric and oleic acids has been studied. The catalytic performance of the resulting HSO3-ethyl-MCM-41, HSO3-ethyl/methyl-MCM-41 and HSO3-methyl-MCM-41 new materials is also compared to those of HSO3-phenyl/methyl-MCM-41 and HSO3-propyl/methyl-MCM-41 synthesized previously. It has been demonstrated that an optimum balance among parameters such as nature of the organic group which support the sulfonic acid, distance between the sulfonic group and the silica surface, average pore size of the material, etc., allows to obtain catalysts with improved activity and selectivity for these reactions. 相似文献
108.
MgAPO-5/MCM-41分子筛的表征及催化性能 总被引:1,自引:0,他引:1
采用微波水热法合成了MgAPO-5/MCM-41分子筛。考察了晶化温度对分子筛合成和性质的影响,并通过XRD、NH3-TPD、TEM、NMR等分析手段对合成的样品进行了表征。结果表明,当晶化温度为90℃时,合成的样品具有微孔结构和MCM-41特有的六方排列的孔道结构,P原子和Al原子都进入了分子筛的骨架,并且具有较高的有序度、比表面积、孔容和平均孔径。Mg的掺入能显著提高分子筛的酸性。用MgAPO-5/MCM-41分子筛催化苯与α-十二烯的烷基化反应时,α-十二烯的转化率可达到99%以上,2-苯基十二烷的选择性达到20%以上,但该分子筛稳定性不高。 相似文献
109.
共缩聚法制备功能化P(St-MPS)/MCM-41核壳复合微球 总被引:1,自引:0,他引:1
以聚(苯乙烯-γ-甲基丙烯酰氧基丙基三甲氧基硅烷)(P(St-MPS))微球为核模版,十六烷基三甲基溴化铵为壳模版,以P(St-MPS)微球、正硅酸乙酯与MPS的混合物为硅源,直接在无皂乳液中通过共缩聚方法合成表面链有碳-碳双键功能基的P(St-MPS)/MCM-41核壳复合微球;采用TEM,XRD和FT-IR对产物进行了表征.结果表明,表面功能化的P(St-MPS)/MCM-41核壳复合微球可以直接在无皂乳液中一步合成,所制备的核壳复合微球粒径约为260 nm,壳层约为10 nm. 相似文献
110.
A series of supported catalysts has been obtained by grafting of chemically generated palladium nanoparticles onto basic, Cs+ ion-exchanged molecular sieves (Al)MCM-41 and onto the non-basic, parent material MCM-41. Catalytic activity of the catalysts has been investigated in the Heck reaction between bromobenzene and butyl acrylate under microwave irradiation. The activity of the bifunctional catalysts (Pd@Cs+-(Al)MCM-41) and the activity of Pd@MCM-41 combined with sodium acetate as an external base were considerably higher under microwave irradiation than activities observed for the same catalytic systems under the conventional heating. The Pd@MCM-41/NaOAc system showed higher conversions than the bifunctional catalysts presumably due to a different nature and accessible amount of the base. On the other hand, microwave irradiation seems to increase the rate of aggregation of the metallic particles and thus also catalyst deactivation as compared with the usual heating. 相似文献