全文获取类型
收费全文 | 2394篇 |
免费 | 260篇 |
国内免费 | 252篇 |
专业分类
化学 | 2185篇 |
晶体学 | 40篇 |
力学 | 18篇 |
综合类 | 13篇 |
数学 | 4篇 |
物理学 | 646篇 |
出版年
2024年 | 3篇 |
2023年 | 24篇 |
2022年 | 39篇 |
2021年 | 59篇 |
2020年 | 100篇 |
2019年 | 72篇 |
2018年 | 64篇 |
2017年 | 64篇 |
2016年 | 104篇 |
2015年 | 97篇 |
2014年 | 116篇 |
2013年 | 221篇 |
2012年 | 131篇 |
2011年 | 137篇 |
2010年 | 102篇 |
2009年 | 150篇 |
2008年 | 145篇 |
2007年 | 149篇 |
2006年 | 181篇 |
2005年 | 128篇 |
2004年 | 124篇 |
2003年 | 125篇 |
2002年 | 89篇 |
2001年 | 58篇 |
2000年 | 72篇 |
1999年 | 63篇 |
1998年 | 52篇 |
1997年 | 43篇 |
1996年 | 39篇 |
1995年 | 40篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 23篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有2906条查询结果,搜索用时 15 毫秒
21.
22.
电化学超级电容器电极材料的研究进展 总被引:9,自引:0,他引:9
回顾了电化学超级电容器电极材料的研究进展,并对不同电极材料的储能原理和性能特点进行了简要的阐述。参考文献29篇。 相似文献
23.
24.
S. M. A. Shibli V. S. Dilimon V. S. Saji 《Journal of Solid State Electrochemistry》2007,11(2):201-208
It has been recently proved that RuO2 can act as an effective surface activator of aluminum alloy sacrificial anodes. TiO2 has the property of stabilizing RuO2 coating and resisting biofouling on metal surfaces. Hence, a mixed oxide catalytic coating of TiO2 and RuO2 can enhance the galvanic performance of aluminum alloy sacrificial anodes and resists biofouling on the anode surface. In the present work RuO2–TiO2 mixed oxide was coated on aluminum alloy sacrificial anodes. The large and uniform porous nature of the coating was found to facilitate efficient ion diffusion. The coating was found to persist on the anode even after 3 months of galvanic exposure. The anode having an optimum combination of the mixed oxide had 70% TiO2 as the major component in the coating. The catalytic coating significantly improved the performance of the anodes to a large extent. 相似文献
25.
Two mixed oxide systems La2-xSrxCuO4±
λ (0.0⩽x⩽1. 0) and La2-xThxCuO4±
λ (O. O⩽x⩽ 0.4) with K2NiF4 structure were prepared by varyingx values. Their crystal structures were studied by means of XRD and IR spectra. The average valence of Cu ion at B site, nonstoichiometric
oxygen (λ) and the chemical composition in the bulk and on the surface of the catalysts were measured by means of chemical
analysis and XPS. The catalytic behavior in reaction CO+NO was investigated under the regular change of average valence of
Cu ion at B site and nonstoichiometric oxygen (λ). Meanwhile, the adsorption and activation of the small molecules NO and
the mixture of NO+CO over the mixed oxide catalysts were studied by means of MS-TPD. The catalytic mechanism of reaction NO+CO
over these oxide catalysts were proposed; and it has been found that, at lower temperatures the activation of NO is the rate
determining step and the catalytic activity is related to the lower valent metallic ion and its concentration, while at higher
temperatures the adsorption of NO is the rate determining step and the catalytic activity is related to the oxygen vacancy
and its concentration.
Project supported by the National Natural Science Foundation of China. 相似文献
26.
采用共沉淀和水热法合成了不同阴离子粘土前驱型复合氧化物催化材料,样品经XRD,FTIR,TPR,TG-DSC,SEM进行表征.同时考察了铜含量在掺杂和不掺杂稀土时对甲烷催化燃烧的影响,结果发现随含铜量增加催化活性增加;未掺杂La的催化剂在高温下出现失活现象,而掺杂型催化剂稳定性良好.同时,制备方法对催化剂的性能有显著影响,在不同制备前驱物pH的条件下,使用共沉淀和水热法合成的阴离子粘土材料,合成时的pH均对催化剂的活性影响较大;同时焙烧温度对催化活性有不同程度的影响. 相似文献
27.
钙钛矿型La_((1 x)/2)Sr_((1-x)/2)Co_(1-x)Cu_xO_3催化CO氧化活性与表征 总被引:1,自引:0,他引:1
研究了钙钛矿型LaSrCoCu_xO_3催化剂对CO氧化反应的催化活性及其表面氧的催化作用.结果表明,x=0.4的催化剂对CO氧化具有最高催化活性,常压及本实验条件下CO完全氧化的最低温度为168℃;催化剂均为氧缺陷化合物,吸附于表面晶格氧缺陷上的吸附氧是CO氧化反应的活性氧物种;并发现催化剂中存在有非常价态的C04 ,认为CO氧化反应是通过吸附氧调变Co3 和Co4 价态而进行. 相似文献
28.
Himadri Paul Sumit Bhaduri Goutam Kumar Lahiri 《Journal of organometallic chemistry》2004,689(2):309-316
Fumed silica, silica gel, silica-alumina and cross-linked (5.5%) polystyrene have been functionalized with quaternary ammonium groups and the Chini cluster [Pt12(CO)24]2− has been anchored onto these functionalized materials by ion pairing. A catalyst has also been prepared by the adsorption of Na2[Pt12(CO)24] on unfunctionalized fumed silica. The catalytic activities of the resultant materials, and that of commercially purchased 5% platinum on alumina have been studied for the hydrogenation of a variety of unsaturated compounds. The substrates studied are: α-acetamidocinnamic acid, cyclohexanone, acetophenone, methyl pyruvate, ethyl acetoacetate, nitrobenzene and benzonitrile. Compared to the polystyrene supported catalyst, the inorganic oxide supported catalysts have higher surface areas and for most of the substrates have notably higher activities. The functionalized fumed silica-based catalyst gives higher conversions than functionalized silica gel and silica-alumina-based catalysts. In the hydrogenation of acetophenone and ethyl acetoacetate, the functionalized fumed silica-based catalyst show superior activity compared to the commercial platinum catalyst, and the catalyst made by conventional adsorption method. In benzonitrile hydrogenation with all the cluster-derived catalysts a hydrazine derivative is selectively formed, but when the commercial platinum catalyst is used benzyl amine is the main product. 相似文献
29.
A rapid access to carbocyclic nucleosides containing a fused isoxazoline ring is proposed starting from cyclopentadiene. The route involves an hetero Diels-Alder cycloaddition reaction of nitrosocarbonylbenzene followed by a 1,3-dipolar cycloaddition of nitrile oxides, cleavage of the N-O tether and elaboration of the heterocyclic aminols into nucleosides via linear construction of purine and pyrimidine heterocycles. 相似文献
30.
Suzdalev I. P. Buravtsev V. N. Maksimov Yu. V. Zharov A. A. Imshennik V. K. Novichikhin S. V. Matveev V. V. 《Russian Chemical Bulletin》2003,52(9):1950-1958
Magnetic phase transitions of the first and second order were revealed by Mössbauer spectroscopy in nanosystems of - and -ferric oxides and metallic europium subjected to shear stress (240°) under high pressure (20 kbar). For - and -ferric oxide nanoclusters, the Curie (Neel) points decreased to 300 K, whereas for nanostructured europium the Neel point increased from 90 to 100 K. The thermodynamic model of magnetic phase transitions predicting a change in the character of magnetic phase transitions and a decrease (increase) in the critical Neel (Curie) points in nanoclusters was developed. The type of magnetic phase transitions and the change in the critical points were caused by defects in nanoclusters, whose maximum concentration was observed for the clusters with the 20—50 nm size range. 相似文献