全文获取类型
收费全文 | 6863篇 |
免费 | 564篇 |
国内免费 | 664篇 |
专业分类
化学 | 1328篇 |
晶体学 | 110篇 |
力学 | 320篇 |
综合类 | 57篇 |
数学 | 663篇 |
物理学 | 737篇 |
综合类 | 4876篇 |
出版年
2024年 | 32篇 |
2023年 | 65篇 |
2022年 | 140篇 |
2021年 | 179篇 |
2020年 | 158篇 |
2019年 | 129篇 |
2018年 | 133篇 |
2017年 | 205篇 |
2016年 | 255篇 |
2015年 | 221篇 |
2014年 | 424篇 |
2013年 | 347篇 |
2012年 | 466篇 |
2011年 | 504篇 |
2010年 | 338篇 |
2009年 | 436篇 |
2008年 | 419篇 |
2007年 | 527篇 |
2006年 | 472篇 |
2005年 | 410篇 |
2004年 | 338篇 |
2003年 | 304篇 |
2002年 | 259篇 |
2001年 | 160篇 |
2000年 | 160篇 |
1999年 | 155篇 |
1998年 | 107篇 |
1997年 | 141篇 |
1996年 | 104篇 |
1995年 | 107篇 |
1994年 | 102篇 |
1993年 | 50篇 |
1992年 | 44篇 |
1991年 | 39篇 |
1990年 | 48篇 |
1989年 | 34篇 |
1988年 | 23篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1979年 | 6篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有8091条查询结果,搜索用时 218 毫秒
61.
IntroductionInthepastseveralyears ,considerableprogresshasbeenachievedincontrollingtheassemblyofindividualbuildingblocksintostructureswithspecifictopologiesandinterestingpropertiessuchasmolecularrecognition ,ionexchangeandselectiveguestinclusion .1 3 Itis… 相似文献
62.
63.
64.
氧化共沉淀法制备纳米级掺锑α—Fe2O3气敏陶瓷粉料 总被引:1,自引:0,他引:1
氧化共沉淀法制备纳米级掺锑α┐Fe2O3气敏陶瓷粉料王忠春**刘尔生陈耐生*黄金陵(福州大学化学系福州350002)关键词α-Fe2O3陶瓷,锑掺杂气敏材料,纳米材料1996-10-05收稿,1997-04-22修回福建省科委资助项目**现在上海硅酸... 相似文献
65.
CO2部分氧化乙烷制乙烯Pd—Cu/MoO3—SiO2催化剂的研究 总被引:7,自引:0,他引:7
用化学吸附-红外光谱、化学吸附-程序升温脱附(TPD)和微型反应技术研究了Pd-Cu/MoO3-SiO2(MoSO)催化剂对CO2和乙烷的吸附活化和部分氧化反应性能.结果表明,乙烷以C—H键中的H吸附于MoSO载体表面MoO键的端基氧上;Pd-Cu/MoSO催化剂对CO2有良好的化学吸附活化性能,CO2的吸附除有线式吸附态和剪式吸附态外,还有一种新的卧式吸附态;Pd-Cu/MoSO催化剂的晶格氧参与了化学反应.探讨了在Pd-Cu/MoSO催化剂上CO2的部分氧化乙烷反应机理 相似文献
66.
C. Guizard C. Mouchet R. Vacassy A. Julbe A. Larbot 《Journal of Sol-Gel Science and Technology》1994,2(1-3):483-487
Basic principles involved in sol-gel processing of ceramic membranes are described. This process has been applied to ceramic ultrafiltration membranes and is now investigated to prepare ceramic nanofilters. In this paper special emphasis is put on new developments concerning microporous zirconia membranes obtained by the polymeric route. A zirconium alkoxide precursor modified with an acetylacetone ligand has been used in order to control particle growth in the sols and pore size distribution in the membranes. N2 adsorption and X-ray diffraction analysis have been performed on membrane materials showing the influence of process parameters (molar ratio r = acacH/Zr and sintering temperature T) on membrane structural evolution. 相似文献
67.
Yoichi M.A Yamada 《Tetrahedron》2004,60(18):4087-4096
A novel catalyst PWAA, an assembled complex of phosphotungstic acid (H3PW12O40) and a non-cross-linked copolymer of N-isopropylacrylamide with an ammonium, was developed. It is an amphiphilic, cross-linked, and supramolecular insoluble complex and showed catalytic activity on oxidation with aqueous hydrogen peroxide. PWAA, used in 2.7×10−5-2.0×10−3 mol equiv., catalyzed oxidation of allylic alcohols, amines, and sulfides efficiently. The turnover number (TON) of PWAA reached up to 35,000. PWAA showed a good stability in organic/aqueous media and was reused three to five times. 相似文献
68.
D-72 resin supported nickel-copper catalysts prepared by solvated metal atom impreg-nation (SMAI) were studied by magnetic measurements and X-ray photoelectron spectro-scopy (XPS). The Ni particles on the catalysts are very highly dispersed and displaysuperparamagnetic behaviour. Ni-Cu alloy clusters were found to be formed. The sur-face compositions are different from the bulk concentrations. In contrast with the surfaceenrichment in copper generally observed on conventional Ni-Cu catalysts, the surfaces ofthese catalysts are enriched in nickel. The nickel is in both zero and valent states, whilecopper is mainly in metallic state. Catalytic data show that the formation of Ni-Cu alloyclusters has a profound effect on the catalytic activities of the catalysts in the hydrogena-tion of furfural. The activity of the Ni:Cu ratio of one bimetallic catalysts is much higherthan that of the Ni or Cu monometallic catalyst. 相似文献
69.
CHEN Shuixia LIU Jinrong ZHANG Xiaoping ZENG Hanmin Materials Science Institute Zhongshan University Guangzhou Department of Environmental Science Engineering South China University of Technology Guangzhou P. R. China 《Chinese Journal of Reactive Polymers》2002,(2)
1. INTRODUCTION Microbial pollution will bring about various problems in industry and other vital fields, such as causing decomposing of materials, harming people抯 health. In order to reduce these problems, new antibacterial materials have been demanded. Recently, much attention has been paid to inorganic materials including zinc oxide [1~4]. These inorganic antibacterial materials are now substituting for organic materials to avoid releasing noxious organic molecules harmful to humans;… 相似文献
70.
The nano-ZnFe2O4/TiO2 films possess the functions of desulfurization and degradation for organic pollutants. The sols of ZnFe2O4/TiO2 were prepared by sol-gel method and coated on glass and porous ceramic by vertical coating and dipping-lift processes, respectively, and the samples were obtained after drying and sintering. The composition, appearance, absorption spectrum of the films, and the influence of the film on porous ceramic performances were analyzed using SEM, AFM, UV-Vis spectrometer, and mercury porosimeter, respectively, to determine the operation parameters of the multifunction porous ceramic elements for gas-purification. 相似文献