全文获取类型
收费全文 | 167篇 |
免费 | 34篇 |
国内免费 | 107篇 |
专业分类
化学 | 301篇 |
综合类 | 1篇 |
物理学 | 6篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 3篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 11篇 |
2017年 | 7篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 14篇 |
2012年 | 17篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 17篇 |
2008年 | 13篇 |
2007年 | 28篇 |
2006年 | 17篇 |
2005年 | 26篇 |
2004年 | 10篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有308条查询结果,搜索用时 15 毫秒
31.
Jan Henk Marsman Berthold B. Breman Antonie A. C. M. Beenackers 《Journal of separation science》1993,16(3):141-147
The main problems with complete analysis of the components of fuel methanol, or in Fischer-Tropsch studies, are the several classes of compound present in the sample (permanent gases, water, alcohols, hydrocarbons), its wide range of components, its boiling point range, and the wide range of component concentrations. A flexible on-line GC method has been developed for kinetic study of catalyzed chemical reactions of hydrogen and oxides of carbon. The single capillary column, temperature programmed method was designed for complete analysis of reactants and products (hydrogen, carbon monoxide, carbon dioxide, water, C1-C10 hydrocarbons, and C1-C6 alcohols): a sample selection valve is used to switch between either the heated line used for input of the synthesis gases or the heated line used to transport reaction products from the reactor. Sample is introduced to the capillary column by means of a 10-port heated gas sampling valve with two external injection loops (0.07 and 1.95 cm3); this results in the determination of components over a wide range of concentrations in the sample (ppm to percentage levels). Helium from a pressure-controlled supply is used as carrier gas and detection of the components is performed by serial connection of thermal conductivity and flame ionization detectors. Peak identification is performed by mass spectrometry and by comparison of component retention times. The automated analytical equipment is integrated with a process control computer and delivers repeatable analytical results for the individual components (RSDs varying between 0.3 and 10% depending strongly on the concentration of the component and the accuracy of the determination of its peak area). 相似文献
32.
SHEN Wen-Jie YAN Shi-Run ZHOU Jing-Lai ZHANG Bi-JiangInstitute of Coal Chemistry Academia Sinica Taiyuan Shanxi 《天然气化学杂志》1995,(3)
The kinetics of the Fischer-Tropsch Synthesis reaction is studied in an internally recycled reactor (CSTR) over a commercial, precipitated Fe/Mn/K catalyst. Kinetic data are obtained with 1 47-4.04 H2/CO feed gas over a temperature range of 265-320℃, a pressure range of 1.0-2.6 MPa, and a space velocity range of 300-800 h-1 . The kinetic model which fits the experimental data well is the same as that of the intrinsic kinetics, i.e. -RH2 CO=kPH2PCO/(PCO bPH2O, where k is the kinetic constant for the rate-determining step and b is a function of temperature only. This model may be derived by assuming that the rate-determining step is the hydrogenation of adsorbed CO according to the enol mechanism. It is found that the CO usage ratio is probably independent of synthesis gas conversion and total pressure, and the catalyst shows high water-gas-shift activity. 相似文献
33.
IntroductionCatal}ticrcactionsaffcctcdb}'diffosionaIlimitationincatal}'stporcshavcbccnextensive1}dcaltx`ithinlit.rat.rcll~5I.Scvcraltcchniqucsonthcspccialcase0fFischcr-Tropschs}'nthcsis(FTS)t\crcapplicdtocxplorcthebchaviorofthiscatal}ticrcactionundercxpcrimcntalandopcrationaIconditionsI3~5l.It`"ouldbeofvaluctoindicatchcrcthatthcseinvcstigationsx"ercmainl}'bascdonthesimplcstkineticsofthcfirstordcrinH2proposedbyAndersonl6]attheearIystages.However-thesetboents,striCtlyspeaking,areinvalidfor… 相似文献
34.
Zhichao Tao Yong fang Chenghua Zhang Tingzhen Li Mingyue Ding Hongwei Xiang Yongwang Li 《天然气化学杂志》2007,16(3):278-285
The effects of Manganese(Mn)incorporation on a precipitated iron-based Fischer-Tropsch synthesis(FTS)catalyst were investigated using N_2 physical adsorption,air differential thermal analysis (DTA),H_2 temperature-programmed reduction(TPR),and M(?)ssbauer spectroscopy.The FTS perfor- mances of the catalysts were tested in a slurry phase reactor.The characterization results indicated that Mn increased the surface area of the catalyst,and improved the dispersion ofα-Fe_2O_3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction.The Fe-Mn inter- action also suppressed the reduction ofα-Fe_2O_3 to Fe_3O_4,stabilized the FeO phase,and(or)decreased the carburization degree of the catalysts in the H_2 and syngas reduction processes.In addition,incorporated Mn decreased the initial catalyst activity,but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe_3O_4,and improved further carburization of the catalysts.Manganese suppressed the formation of CH_4 and increased the selectivity to light olefins(C_(2-4)~=),but it had little effect on the selectivities to heavy(C_(5 )) hydrocarbons.All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter,to some extent,in the precipitated iron-manganese catalyst system. 相似文献
35.
采用连续共沉淀与喷雾干燥成型技术相结合的方法制备了微球状Fe/Cu/K/Al2O3催化剂, 结合TG、N2物理吸附、XRD、H2-TPR、CO-TPR、Mossbauer谱等表征手段, 研究焙烧温度对Fischer-Tropshc (F-T)合成铁基催化剂的结构性质、还原行为和碳化行为的影响. 结果表明, 较高的焙烧温度有利于碳酸盐的分解和结晶水的脱除, 促进了催化剂的还原. 随着焙烧温度的进一步升高, 催化剂的比表面积减小, 平均孔径增大, α-Fe2O3晶粒的粒径增大, 催化剂中金属与载体的相互作用增强, 从而削弱了CuO、K2O助剂的作用, 严重抑制了催化剂的还原和碳化. 相似文献
36.
采用脉冲D2反应研究了CeO2在Co-CeO2/SiO2费托合成催化剂中的作用机理. 通过比较在Co-CeO2/SiO2和Co/SiO2催化剂上的脉冲D2反应实验结果发现, CeO2可以提高载体表面 Si-OH 的H-D同位素交换活性和 Si-OH 中H参与CO加氢反应的活性; CeO2不仅增加了催化剂表面活性碳物种的总量,而且活性碳物种以链增长单体-CH2-为主,因而有利于增加费托合成反应速率和链增长几率; CeO2的加入明显提高了催化剂表面碳原子的加氢反应速率,从而减少了碳沉积. 相似文献
37.
Tingzhen Li Yong Yang Zhichao Tao Haijun Wan Xia An Chenghua Zhang Hongwei Xiang Yongwang Li 《天然气化学杂志》2007,16(4):354-362
The effect of sulfate on Fischer-Tropsch synthesis performance was investigated in a slurry- phase continuously stirred tank reactor(CSTR)over a Fe-Mn catalyst.The physiochemical properties of the catalyst impregnated with different levels of sulfate were characterized by N_2 physisorption,X-ray photoelectron spectroscopy(XPS),H_2(or CO)temperature-programmed reduction(TPR),Mφssbauer spectroscopy,and CO_2 temperature-programmed desorption(TPD).The characterization results indicated that the impregnated sulfate slightly decreased the BET surface area and pore volume of the catalyst, suppressed the catalyst reduction and carburization in CO and syngas,and decreased the catalyst surface basicity.At the same time,the addition of small amounts of sulfate improved the activities of Fischer- Tropseh synthesis(FTS)and water gas shift(WGS),shifted the product to light hydrocarbons(C_1-C_(11)) and suppressed the formation of heavy products(C_(12 )).Addition of SO_4~(2-)to the catalyst improved the FTS activity at a sulfur loading of 0.05-0.80 g per 100 g Fe,and S-05 catalyst gave the highest CO conversion(62.3%),and beyond this sulfur level the activity of the catalyst decreased. 相似文献
38.
考虑了烯烃、醇与酸的再吸附及其非本征效应(烯烃、醇与酸在催化剂孔道中的扩散作用、物理吸附及溶解度效应)对产物分布的影响,推导了基于详细反应机理的亚甲基插入的烷基机理F-T合成校正综合动力学模型.利用文献数据对动力学模型进行了回归,获得了与文献报道结果相一致的动力学参数.由校正动力学模型计算的烷烃、烯烃、醇与酸产物分布及烯烃比、醇烃比及酸烃比与实验数据较好地吻合.动力学计算结果表明,在铁锰催化剂上,烷烃、烯烃、醇与酸生成的反应是平行竞争反应,烯烃、醇与酸在催化剂表面的再吸附及二次反应导致产物分布偏离了ASF分布.动力学研究还表明,相同碳数的醇与酸产物在催化剂表面上再吸附及二次反应的机会比相同碳数的烯烃大.通过比较相同碳数的烯烃、醇与酸的分子体积及沸点,指出了在铁锰催化剂上,低碳数的烯烃、醇与酸的再吸附及二次反应对产物分布影响的非本征效应中,烯烃、醇与酸的扩散阻力不是主导效应. 相似文献
39.
助剂Cu、K对F-T合成铁基催化剂作用的表征研究 总被引:3,自引:3,他引:3
采用连续共沉淀和喷雾干燥技术相结合的方法制备了一组Cu、K助剂单独或同时加入的微球状Fischer-Tropsch(F-T)合成铁基催化剂,借助低温N2吸附、MES、XRD、H2-TPR、CO-TPR研究了Cu和K助剂对催化剂织构、还原性能以及还原和炭化过程中的物相变化的影响。结果表明,K助剂的加入能明显提高催化剂的比表面积和铁物相在催化剂中的分散程度,增加了Fe2O3与SiO2间的相互作用;当催化剂在H2和合成气中还原时,Cu助剂的加入有利于催化剂的还原和Fe3O4的生成,在CO中还原时,Cu助剂的加入则有利于α-Fe的生成和稳定化。在H2和合成气中,单独K助剂的加入会抑制催化剂的还原或炭化,而Cu和K助剂的同时加入在H2、CO和合成气下均可使催化剂的还原或炭化能力明显提高,表明Cu和K助剂间存在一定的协同作用。 相似文献
40.
Effect of epitaxial growth on the formation of the cobalt catalysts of the Fischer-Tropsch synthesis
Ya. V. Mikhailova S. A. Sviderskii M. N. Mikhailov I. V. Mishin V. Z. Mordkovich 《Russian Chemical Bulletin》2007,56(9):1922-1926
Mixed oxides CoxAlyO4 with different Al/Co ratios applied as supports for the catalysts of the Fischer-Tropsch synthesis were prepared using the
solid-state chemical reaction. The CoxAlyO4 supports were prepared by modifying gibbsite with various cobalt salts (acetate, nitrate, and basic carbonate). The use of
basic cobalt carbonate gives the Co(20%)/CoxAlyO4 catalyst, which provides an increased yield of hydrocarbons C5+ and a decreased methane content compared to the impregnation catalyst Co(30%)/Al2O3. The introduction of small amounts of rhenium additives makes it possible to enhance the yield of hydrocarbons C5+ (179 g m−3) and also to increase the selectivity with respect to the C5–C18 fraction. The introduction of basic cobalt carbonate into the support, most likely, creates favorable conditions for the
epitaxial growth of the precursor of the active phase.
Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1856–1860, September, 2007. 相似文献