全文获取类型
收费全文 | 252683篇 |
免费 | 2375篇 |
国内免费 | 883篇 |
专业分类
化学 | 115012篇 |
晶体学 | 3917篇 |
力学 | 13878篇 |
综合类 | 3篇 |
数学 | 52032篇 |
物理学 | 71099篇 |
出版年
2020年 | 1510篇 |
2019年 | 1715篇 |
2018年 | 12296篇 |
2017年 | 12218篇 |
2016年 | 9427篇 |
2015年 | 2983篇 |
2014年 | 3729篇 |
2013年 | 8583篇 |
2012年 | 9699篇 |
2011年 | 17343篇 |
2010年 | 10684篇 |
2009年 | 11069篇 |
2008年 | 13273篇 |
2007年 | 15235篇 |
2006年 | 6560篇 |
2005年 | 6952篇 |
2004年 | 6752篇 |
2003年 | 6623篇 |
2002年 | 5540篇 |
2001年 | 5524篇 |
2000年 | 4223篇 |
1999年 | 3154篇 |
1998年 | 2716篇 |
1997年 | 2559篇 |
1996年 | 2476篇 |
1995年 | 2270篇 |
1994年 | 2201篇 |
1993年 | 2117篇 |
1992年 | 2394篇 |
1991年 | 2357篇 |
1990年 | 2282篇 |
1989年 | 2227篇 |
1988年 | 2223篇 |
1987年 | 2227篇 |
1986年 | 2119篇 |
1985年 | 2770篇 |
1984年 | 2815篇 |
1983年 | 2478篇 |
1982年 | 2588篇 |
1981年 | 2404篇 |
1980年 | 2388篇 |
1979年 | 2518篇 |
1978年 | 2526篇 |
1977年 | 2433篇 |
1976年 | 2488篇 |
1975年 | 2406篇 |
1974年 | 2367篇 |
1973年 | 2551篇 |
1972年 | 1652篇 |
1971年 | 1353篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
81.
82.
83.
Following a thermal reduction method, platinum nanoparticles were synthesized and stabilized by polyvinylpyrrolidone. The colloidal platinum nanoparticles were stable for more than 3 months. The micrograph analysis unveiled that the colloidal platinum nanoparticles were well dispersed with an average size of 2.53 nm. The sol–gel‐based inverse micelle strategy was applied to synthesize mesoporous iron oxide material. The colloidal platinum nanoparticles were deposited on mesoporous iron oxide through the capillary inclusion method. The small‐angle X‐ray scattering analysis indicated that the dimension of platinum nanoparticles deposited on mesoporous iron oxide (Pt‐Fe2O3) was 2.64 nm. X‐ray photoelectron spectroscopy (XPS) data showed that the binding energy on Pt‐Fe2O3 surface decreased owing to mesoporous support–nanoparticle interaction. Both colloidal and deposited platinum nanocatalysts improved the degradation of methyl orange under reduction conditions. The activation energy on the deposited platinum nanocatalyst interface (2.66 kJ mol?1) was significantly lowered compared with the one on the colloidal platinum nanocatalyst interface (40.63 ± 0.53 kJ mol?1). 相似文献
84.
Zenon Moszner 《Aequationes Mathematicae》2018,92(4):617-625
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form. 相似文献
85.
86.
87.
Prof. Piotr Bałczewski Dr. Emilia Kowalska Dr. Ewa Różycka-Sokołowska Dr. Joanna Skalik Dr. Krzysztof Owsianik Dr. Marek Koprowski Dr. Bernard Marciniak Dr. Dariusz Guziejewski Prof. Witold Ciesielski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14148-14161
The highly substituted mono-aryl/alkylthio-(hetero)acenes prepared in this study have been found to be thermally more stable (Tdecomp.=331–354 °C) than the known di-aryl/alkylthio-substituted acenes by an average of 25 °C. They are also much more photostable at 254 and 365 nm (in both argon and air) than the parent anthracene and other reported anthracenes. The most photostable aryl/alkylthio-anthracenes at 254 nm were found to be 60–70 (in air) and 130 (in argon) times more stable in solution than the unsubstituted anthracene, and much more stable than known EDG/EWG-substituted anthracenes (EDG=electron-donating group, EWG=electron-withdrawing group) with an extended aromatic core. Furthermore, the acenes showed significantly higher photostability at 365 nm in both air and argon. The anthracenes were obtained by the novel thio-Friedel–Crafts/Bradsher cyclization reaction of hitherto unknown [o-(1,3-dithian-2-yl)aryl](aryl)methyl thioethers. The developed approach provides a general access to mono-aryl/alkylthio-substituted (hetero)acene frameworks containing at least three fused (hetero)aromatic rings. The characteristic feature of this approach, which leads to highly substituted acenes, is that the substituents, unlike in other methods, may be introduced at an early stage of the synthesis. DFT and TD-DFT calculations confirmed the stabilizing role of the aryl/alkylthio substituent in the mono-aryl/alkylthio-substituted anthracenes, which are the most stable anthracenes prepared to date. Their high photostability is mainly due to the quenching of singlet oxygen by the acene and the quenching of the acene S1 state by molecular oxygen. 相似文献
88.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
89.
Plasma Chemistry and Plasma Processing - The hydrocarbons present in diesel exhaust, although treated as minor pollutants, are equivalent to some of the major pollutants in terms of toxicity,... 相似文献
90.
Gas-phase 21Ne nuclear magnetic resonance spectra were measured at the natural abundance of 21Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B0 = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the 21Ne nuclear magnetic moment, μ(21Ne) = 0.6617774(10) μN. The present value of μ(21Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(21Ne). 相似文献