全文获取类型
收费全文 | 729篇 |
免费 | 41篇 |
国内免费 | 4篇 |
专业分类
化学 | 612篇 |
晶体学 | 6篇 |
力学 | 2篇 |
数学 | 44篇 |
物理学 | 110篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 20篇 |
2015年 | 25篇 |
2014年 | 24篇 |
2013年 | 23篇 |
2012年 | 62篇 |
2011年 | 65篇 |
2010年 | 18篇 |
2009年 | 27篇 |
2008年 | 50篇 |
2007年 | 45篇 |
2006年 | 47篇 |
2005年 | 44篇 |
2004年 | 34篇 |
2003年 | 30篇 |
2002年 | 24篇 |
2001年 | 21篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1985年 | 7篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1968年 | 3篇 |
1963年 | 2篇 |
1961年 | 3篇 |
1959年 | 2篇 |
排序方式: 共有774条查询结果,搜索用时 359 毫秒
91.
Fukushima M Mizutani Y Maeno S Zhu Q Kuramitz H Nagao S 《Molecules (Basel, Switzerland)》2011,17(1):48-60
The influence of halogen substituents on the catalytic oxidation of 2,4,6-trihalogenated phenols (TrXPs) by iron(III)-porphyrin/KHSO? catalytic systems was investigated. Iron(III)-5,10,15,20-tetrakis(p-hydroxyphenyl)porphyrin (FeTHP) and its supported variants were employed, where the supported catalysts were synthesized by introducing FeTHP into hydroquinone-derived humic acids via formaldehyde poly-condensation. F (TrFP), Cl (TrCP), Br (TrBP) and I (TrIP) were examined as halogen substituents for TrXPs. Although the supported catalysts significantly enhanced the degradation and dehalogenation of TrFP and TrCP, the oxidation of TrBP and TrIP was not enhanced, compared to the FeTHP catalytic system. These results indicate that the degree of oxidation of TrXPs is strongly dependent on the types of halogen substituent. The order of dehalogenation levels for halogen substituents in TrXPs was F > Cl > Br > I, consistent with their order of electronegativity. The electronegativity of a halogen substituent affects the nucleophilicity of the carbon to which it is attached. The levels of oxidation products in the reaction mixtures were analyzed by GC/MS after extraction with n-hexane. The most abundant dimer product from TrFP via 2,6-difluoroquinone is consistent with a scenario where TrXP, with a more electronegative halogen substituent, is readily oxidized, while less electronegative halogen substituents are oxidized less readily by iron(III)-porphyrin/KHSO? catalytic systems. 相似文献
92.
93.
Dr. Hua Lu Dr. Soji Shimizu Dr. John Mack Prof. Zhen Shen Prof. Nagao Kobayashi 《化学:亚洲杂志》2011,6(4):1026-1037
A series of fused‐ring‐expanded aza‐boradiazaindacene (aza‐BODIPY) dyes have been synthesized by reacting arylmagnesium bromides with phthalonitriles or naphthalenedicarbonitriles. An analysis of the structure–property relationships has been carried out based on X‐ray crystallography, optical spectroscopy, and theoretical calculations. Benzo and 1,2‐naphtho‐fused 3,5‐diaryl aza‐BODIPY dyes display markedly red shifted absorption and emission bands in the near‐IR region (>700 nm) due to changes in the energies of the frontier MOs relative to those of 1,3,5,7‐tetraaryl aza‐BODIPYs. Only one 1,2‐naphtho‐fused aza‐BODIPY of the three possible isomers is formed due to steric effects, and 2,3‐naphtho‐fused compounds could not be characterized because the final BF2 complexes are unstable in solution. The incorporation of a N(CH3)2 group at the para‐positions of a benzo‐fused 3,5‐diaryl aza‐BODIPY quenches the fluorescence in polar solvents and results in a ratiometric pH response, which could be used in future practical applications as an NIR “turn‐on” fluorescence sensor. 相似文献
94.
A series of nitrogen‐tethered allenynes (‘5‐aza‐1,2‐dien‐7‐ynes’) 1 were transformed to the corresponding 3‐acyl‐4‐alkenylpyrrolidines 3 when treated with a catalytic amount of PtCl2 in MeOH at 70°. Initial Pt‐promoted cyclization forms a nonclassical carbocationic intermediate. In contrast to the cycloisomerization in toluene, which produced the bicyclic cyclobutenes 2 , the intermediate is intercepted by addition of an oxygen nucleophile to achieve the formal hydrative cyclization. 相似文献
95.
96.
97.
Masahito Ochiai Munetaka Kunishima Kenzo Sumi Yoshimitsu Nagao Eiichi Fujita Masao Arimoto Hideo Yamaguchi 《Tetrahedron letters》1985,26(37):4501-4504
New general methods for the synthesis of alkynyl(phenyl)iodonium tetrafluoroborate 2 from alkynyltrimethylsilanes 1 utilizing the combination of iodosylbenzene and triethyloxonium tetrafluoroborate or boron trifluoride etherate were developed. The medium effect observed in the reaction was also discussed. 相似文献
98.
99.
Sho Suzuki 《Colloid and polymer science》1959,167(1):23-25
Zusammenfassung Mittels Elektronenbeugung wurden Versuche durchgeführt, die Hydratationsf?higkeit einiger Metallhalide festzustellen.
Bei den Cd-Haliden nimmt die Hydratationsf?higkeit nach folgender Reihe ab: CdCl2>CdBr2>CdJ2 und bei Metallchloriden nach folgender Reihe ZnCl2>CdCl2>PbCl2>HgCl2>Hg2Cl2 ab.
Diese Ergebnisse entsprechen dem Anionen- oder Kationendurchmesser. Für 80% rel. Feuchtigkeit zeigen Hg2Cl2 und PbCl2 Platzwechsel der Atome. 相似文献
100.