全文获取类型
收费全文 | 3651篇 |
免费 | 341篇 |
国内免费 | 340篇 |
专业分类
电工技术 | 3篇 |
综合类 | 231篇 |
化学工业 | 2280篇 |
金属工艺 | 22篇 |
机械仪表 | 8篇 |
建筑科学 | 92篇 |
矿业工程 | 139篇 |
能源动力 | 100篇 |
轻工业 | 61篇 |
水利工程 | 25篇 |
石油天然气 | 996篇 |
武器工业 | 4篇 |
无线电 | 16篇 |
一般工业技术 | 270篇 |
冶金工业 | 38篇 |
原子能技术 | 30篇 |
自动化技术 | 17篇 |
出版年
2024年 | 8篇 |
2023年 | 40篇 |
2022年 | 91篇 |
2021年 | 130篇 |
2020年 | 126篇 |
2019年 | 102篇 |
2018年 | 141篇 |
2017年 | 110篇 |
2016年 | 165篇 |
2015年 | 129篇 |
2014年 | 187篇 |
2013年 | 208篇 |
2012年 | 255篇 |
2011年 | 216篇 |
2010年 | 167篇 |
2009年 | 226篇 |
2008年 | 187篇 |
2007年 | 245篇 |
2006年 | 207篇 |
2005年 | 193篇 |
2004年 | 146篇 |
2003年 | 134篇 |
2002年 | 116篇 |
2001年 | 121篇 |
2000年 | 111篇 |
1999年 | 118篇 |
1998年 | 89篇 |
1997年 | 50篇 |
1996年 | 67篇 |
1995年 | 61篇 |
1994年 | 48篇 |
1993年 | 52篇 |
1992年 | 25篇 |
1991年 | 21篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有4332条查询结果,搜索用时 15 毫秒
21.
Takaaki Wajima Tomoe Shimizu Yasuyuki Ikegami 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(6):921-927
BACKGROUND: This study aimed to investigate the synthesis of zeolites from paper sludge ash (PSA) with added diatomite to remove both NH4+ and PO43? for water purification. The PSA had low Si and significant Ca contents. Four types of diatomite: white (T‐W) and brown (T‐B) from deposits of marine origin in Takanosu, and white (S‐W) and gray (S‐G) from lacustrine deposits in Shonai, were added to NaOH solution to increase the Si content and thereby synthesize zeolites with high cation exchange capacity (CEC). RESULTS: The order of the amounts of Si extracted from the diatomite to the alkali solution was S‐W > T‐W = T‐B > S‐G, which correlates with the amorphous SiO2 content of diatomite. The original ash without addition of diatomite yielded hydroxysodalite with CEC of about 1.0 mmol g?1. For all samples, the addition of diatomite to the solution yielded zeolite‐P with a higher CEC, but the addition of excess Si inhibited the synthesis of zeolite‐P, and the CEC of the product was low. A product with high CEC including zeolite‐P was obtained in a solution with around 500 mmol L?1 of Si concentration, and had the ability to remove both NH4+ and PO43?. CONCLUSION: Diatomite has the potential for used as an additive for the synthesis of high CEC zeolite from PSA. The product with zeolite‐P exhibited relatively high CEC, capacity for NH4+ uptake, and the ability to remove PO43? by precipitation, which is preferable for water purification applications. Copyright © 2008 Society of Chemical Industry 相似文献
22.
ZhangBaoji WangXieqing 《中国炼油与石油化工》2003,(3):49-52
A Ti/Si complex zeolite has been prepared. X-ray diffraction and infrared spectrometry study has shown that two structures, namely the ZSM-5 and MCM-41, exist in the sample. BET tests have revealed that the complex zeolite contains regular mesopores of 2.6 nm. Ultraviolet spectrometry analysis has shown that the Ti species exist in the zeolite skeleton in the form of tetra-coordinate valence. The Ti/Si complex zeolite (TS-1/Ti-MCM-41) has apparently improved catalytic activity with respect to the macromolecular organic compound oxidation as compared to individual components of either Ti or Si containing zeolites (TS-1 and Ti-MCM-41). 相似文献
23.
24.
长链烯烃-苯烷基化反应的分子筛催化剂再生性能的研究 总被引:9,自引:0,他引:9
通过热重分析和活性稳定性评定考察催化剂的再生性能。研究结果表明,进行氯气吹扫以及苯抽提后进行氮气吹扫两种预处理,导致失活催化剂的起燃点和烧焦反应活化能均有所提高,有利于控制烧焦反应速度。按苯抽提、氮气吹扫、烧焦的顺序,分三个阶段进行催化剂再生,再生催化剂的活性稳定性得到更充分的恢复。 相似文献
25.
A new synthesis procedure for titanium-containing aluminosilicate zeolites has been obtained using a clear colloidal dispersion (sol) which was prepared with titanium isopropoxide, water, hydrochloric acid and colloidal silica, Ludox. When NaY, KL, offretite, mordenite and ZSM-5 zeolites were crystallized from the sol following conventional hydrothermal crystallization procedures, all the aluminosilicate zeolites showed the same X-ray absorption fine structure at the Ti K edge indicating framework Ti. The zeolites showed remarkable catalytic activity for the partial oxidation of cyclohexene using H2O2 as an oxidant and the photocatalytic decomposition of trichloroethene using water. 相似文献
26.
27.
Zakaria Chajar Michel Primet Hélène Praliaud Michèle Chevrier Catherine Gauthier Frédéric Mathis 《Catalysis Letters》1994,28(1):33-40
The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO2 and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C3H8 does not differ significantly from that of NO2. In the absence of oxygen, the reduction of NO2 by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO2 formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process. 相似文献
28.
29.
The activation of propane using zeolite H-Y and Ga3+ exchanged zeolite Y indicates that in the presence of Ga3+ the mechanism of propane activation is changed from a cracking pathway to a dehydrogenation pathway. The presence of both Ga3+ and H+ are required to achieve this effect. 相似文献
30.
FTIR spectra of CO adsorbed on Pt/KL catalysts show that the relative band intensities and the total dispersion markedly depend on the catalyst preparation method (ion exchange, incipient wetness impregnation or co-impregnation with KCl). The CO stretching frequency of the dominant band for linear CO is shifted to higher wavenumbers, parallel with the proton concentration in the reduced catalyst, which is derived independently from the intensity of the IR bands of the OH groups. The results are in accordance with the model that electron-deficient platinum particles are platinum-proton adducts.On leave from: N.D. Zelinsky Institute of Organic Chemistry, Academy of Sciences, Moscow, USSR. 相似文献