全文获取类型
收费全文 | 11264篇 |
免费 | 880篇 |
国内免费 | 515篇 |
专业分类
电工技术 | 144篇 |
综合类 | 591篇 |
化学工业 | 6130篇 |
金属工艺 | 239篇 |
机械仪表 | 51篇 |
建筑科学 | 96篇 |
矿业工程 | 89篇 |
能源动力 | 466篇 |
轻工业 | 268篇 |
水利工程 | 18篇 |
石油天然气 | 3385篇 |
武器工业 | 49篇 |
无线电 | 98篇 |
一般工业技术 | 499篇 |
冶金工业 | 384篇 |
原子能技术 | 45篇 |
自动化技术 | 107篇 |
出版年
2024年 | 29篇 |
2023年 | 131篇 |
2022年 | 277篇 |
2021年 | 301篇 |
2020年 | 339篇 |
2019年 | 344篇 |
2018年 | 302篇 |
2017年 | 299篇 |
2016年 | 389篇 |
2015年 | 348篇 |
2014年 | 552篇 |
2013年 | 584篇 |
2012年 | 767篇 |
2011年 | 742篇 |
2010年 | 626篇 |
2009年 | 635篇 |
2008年 | 606篇 |
2007年 | 685篇 |
2006年 | 663篇 |
2005年 | 571篇 |
2004年 | 551篇 |
2003年 | 569篇 |
2002年 | 414篇 |
2001年 | 406篇 |
2000年 | 348篇 |
1999年 | 265篇 |
1998年 | 219篇 |
1997年 | 177篇 |
1996年 | 150篇 |
1995年 | 87篇 |
1994年 | 57篇 |
1993年 | 54篇 |
1992年 | 58篇 |
1991年 | 31篇 |
1990年 | 22篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
F. Figueras J. L. Flores G. Delahay A. Bourane J.-M. Clacens A. Desmartin-Chomel B. Coq A. Giroir-Fendler 《Topics in Catalysis》2006,39(1-2):59-64
Titanias of different surface areas have been sulfated and used as supports of Rh oxide for the selective catalytic reduction
of nitrogen oxides. Only the sulfation of TiO2 of large surface areas gives strong Br?nsted acid sites, retaining pyridine up to 773 K. Low surface area anatase is unable
to retain sulfates. The catalytic activities measured at 523 K, increase with the number of acid sites, and then reach a plateau,
showing the intervention of acidity in the SCR. This is true only for Rh but not for Pt. The investigation of the elemental
steps on Rh/sulfated TiO2 by in situ diffuse reflectance spectroscopy permits to clarify a few points: the oxidation of propene, presumably to acetaldehyde, occurs
by the reaction with nitrates adsorbed on the support. The further oxidation of this intermediate by NO2 yields an isocyanate, which can be hydrolysed to ammonia. 相似文献
72.
Ion exchange of HZSM-5 samples with alkali metal cations, using metal chloride solutions, results in partially exchanged zeolites, MHZSM-5, M = Li, Na, K or Cs. The degree of exchange is found to increase with increasing ionic radius of the cations. The catalytic properties of the alkalized zeolites were evaluated using the reaction conditions under which the catalytic activity of the HZSM-5 samples in terms of n-hexane cracking is proportional to the aluminium content. From the residual catalytic activity exhibited by the Na-, K- and CsHZSM-5 samples it is concluded that each of the larger Na+, K+ and Cs+ ions is influencing more than one AlO
4
–
tetrahedron, implying that the aluminium sites in ZSM-5 are not isolated. The ion-exchange results are then interpreted in terms of non-isolated aluminium sites. The ion-exchange and catalytic properties of the zeolites as a function of aluminium content are also discussed. 相似文献
73.
Simona Caudo Gabriele Centi Chiara Genovese Siglinda Perathoner 《Topics in Catalysis》2006,40(1-4):207-219
Homogeneous (Cu2+ ions) and heterogeneous (Cu2+-pillared clay) Fenton-like catalysts have been compared in the conversion of p-coumaric acid. The performances of the two classes of catalysts are similar for an analogous amount of copper, but there are
some relevant differences in terms of (i) the presence of an induction time, (ii) the turnover frequency, (iii) the efficiency
in the use of H2O2, (iv) the initial attack of p-coumaric acid (hydroxylation on the aromatic ring or oxidative attack on the double bond of the lateral chain), and (v) the
effect of dissolved oxygen on the removal of total organic carbon (TOC). These differences were interpreted in terms of reaction
network of generation of radical oxygen species and of organics conversion. The possible formation of a surface peroxo adduct
coordinated to a copper binulcear site was also evidenced for the solid heterogeneous catalyst. 相似文献
74.
A systematic reactivity study of N2O, NO, and NO2 on highly dispersed CuO phases over modified silica supports (SiO2–Al2O3, SiO2–TiO2, and SiO2–ZrO2) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N2O) to selective reductions by hydrocarbons (N2O, NO, and NO2) and oxidation (NO to NO2). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO2–Al2O3 and SiO2–ZrO2, led to a better activity and selectivity of CuO for the reactions of N2O, NO, and NO2 reductions and N2O decomposition than SiO2–TiO2. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values. 相似文献
75.
Yury V. Kissin 《Catalysis Letters》1993,19(2-3):181-187
An experimental technique is discussed for measuring relative reactivities of alkanes in the catalytic cracking of multi-component hydrocarbon mixtures over a heterogeneous, Y-zeolitebased catalyst at 250–350 °C. With the technique, ca. 0.1 l of an alkane mixture is evaporated and contacted with a catalyst, after which the mixture of reaction products and the unreacted feed enters the chromatographic column and is immediately analyzed. The technique is used to measure relative reactivities of 21 alkanes in a single experiment. The principal results of these experiments are similar to the results of single-component cracking: alkane reactivity rapidly increases with the increase of the carbon number, and methyl-branched alkanes are more reactive than linear alkanes. However, the variations in alkane reactivities as a function of their molecular weight and skeleton structure differ very significantly between single- and multicomponent experiments. 相似文献
76.
77.
Ruthenium tetroxide selectively oxidizes activated aromatic compounds under mild conditions and has been used for the catalytic oxidation of several different coals. The quantities of the volatile monocarboxylic acids with 2–6 carbon atoms have been determined by an isotope dilution technique. The amount of ethanoic acid ranges from 1 to 3mol/100C and the quantities of propanoic acid, and butanoic acid exceed 0.1 mol/100C. Methylpropanoic, pentanoic, 2-methylbutanoic, 3-methylbutanoicand hexanoic acid are formed in lesser amounts. The outcome of the experiment depends upon whether or not the coal has been extracted prior to oxidation. The results for Illinois No. 6 coal expressed in moles of ethanoic acid produced/l00C illustrate this feature: raw whole coal, 1.9; coal extracted by the method of Hayatsu and co-workers, 1.0. Dehydrogenation with benzoquinone prior to oxidation increases the yield of ethanoic acid to The amounts of ethanoic acid obtained from the other extracted coals are 1.0 for Texas lignite, 1.2 for Rawhide subbituminous, 3.4 for Pittsburgh No. 8, 3.3 for a higher ranking bituminous coal (PSOC 726) and 0.7 for an anthracite (PSOC872). The results obtained in this study are compared with related information concerning the distribution of alkyl groups within coal by other methods. 相似文献
78.
用玻璃球负载纳米级SO42-/TiO2固体超强酸催化合成乙酸正丁酯,对催化剂的制备条件和乙酸正丁酯的合成条件进行了研究。在最佳反应条件下,乙酸的转化率为99.3%,催化剂重复使用8次后乙酸的转化率仍高达92.3%。该催化剂选择性好,未发现有副产物生成,看来具有较好的应用前景。 相似文献
79.
根据煤催化气化原理及熔融盐特性,设计了一套小型熔融盐催化煤气化实验装置。针对无烟煤燃烧特性差的特点,在实验中研究了温度和二氧化碳流量对气化结果的影响,并对影响机理进行分析。 相似文献
80.
乙烯催化二聚制丁-1技术是当今聚烯烃工业中具有重要意义的工业过程。介绍了4种竞争发展的新工艺及催化剂研究的进展,并对各新工艺的经济性进行了评价。 相似文献