全文获取类型
收费全文 | 224篇 |
免费 | 11篇 |
国内免费 | 5篇 |
专业分类
化学 | 205篇 |
晶体学 | 3篇 |
力学 | 4篇 |
数学 | 4篇 |
物理学 | 24篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 11篇 |
2012年 | 17篇 |
2011年 | 16篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 16篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有240条查询结果,搜索用时 0 毫秒
101.
The time-resolved fluorescence Stokes shift of α-naphthylamine in polar solvents has been measured at room temperature using a mode-locked Nd: YAG laser and a streak camera. Fluorescence spectra show a red-shift with an exponential rise time of 52 ps in isopropanol at 295 K. The rate of the relaxation process involved in the Stokes shift appears to be dependent on the extent of the change in dipole moment of the solute upon excitation. 相似文献
102.
103.
A convenient synthesis of immunosuppressive agent FTY720 (1) using the Petasis reaction was developed. 4-Octylbenzaldehyde (9) was converted into 1-ethenyl-4-octylbenzene (11) by two-step synthesis. Hydroboration of 11 using catecholborane and hydrolysis gave (E)-2-(4-octylphenyl)vinylboronic acid (4). The Petasis reaction of 4, dihydroxyacetone (3), and benzylamine following catalytic hydrogenation afforded FTY720 (1). 相似文献
104.
Sadao Nishigaki Misuzu Ichiba Kiyoko Fukami Keitaro Senga 《Journal of heterocyclic chemistry》1982,19(4):769-773
Reaction of 5-arylazo-6-arylidenehydrazino-1,3-dimethyluracils (II), prepared by the treatment of 6-aryl-idenehydrazino-1,3-dimethyluracils (I) with diazotized arylamines, with dimethylformamide dimethylacetal resulted in the formation of pyrimido[5,4-e]-as-triazine (V) system, while the thermolysis of II resulted in the formation of purine (X), v-triazolo[4,5-d]pyrimidine (XII), and pyrazolo[3,4-d]pyrimidine (XIV, XIX) systems in lieu of the expected V. Reasonable mechanisms have been proposed for the formation of the various ring systems in these reactions. 相似文献
105.
Tanaka M Imai M Yamamoto Y Tanaka K Shimowatari M Nagumo S Kawahara N Suemune H 《Organic letters》2003,5(8):1365-1367
[reaction: see text] Rh-Catalyzed intermolecular hydroacylation between salicylaldehydes and 1,5-hexadienes proceeded under remarkably mild reaction conditions to afford a mixture of iso- and normal-hydroacylated products in good yields. The experiments using deuterated salicylaldehyde-d revealed that "double chelation" of salicylaldehyde and 1,5-hexadiene to Rh-complex played vital roles in the catalytic cycle of intermolecular hydroacylation. 相似文献
106.
Keitaro Senga Yukako Kanamori Hashime Kanazawa Sadao Nishigaki 《Journal of heterocyclic chemistry》1978,15(3):359-363
Treatment of 1,3-dimethyl-6-hydrazinouracil with the appropriate dimethylformamide dialkylacetal afforded the, corresponding 2-alkyl-5,7-dimethylpyrazolo[3,4-d]pyrimidine-4,6-(5H,7H)diones. The reaction of 1,3-dimethyl-6-(α-methylbenzylidenehydrazino)uracils with dimethylformamide dimethylacetal or triethyl orthoformate gave the corresponding 5,7-dimethyl-2-vinylpyrazolo[3,4-d]pyrimidine-4,6(5H,7H)diones, respectively. Similarly, treatment of 1,3-dimethyl-6-(α-methylbenzylidenehydrazino)uraeils with triethyl orthopropionate yielded the corresponding 5,7-dimethyl-3-ethyl-2-vinylpyrazolo[3,4-d]pyrimidine-4,6(5H,7H)diones. 相似文献
107.
The changes in the conformation and molecular mobility accompanied by a phase transition in the crystalline domain were analyzed for ethylene (E) and tetrafluoroethylene (TFE) copolymer, ETFE, using variable-temperature (VT) solid-state 19F magic angle spinning (MAS) and 1H --> 19F cross-polarization (CP)/MAS NMR spectroscopy. The shifts of the signals for fluorines in TFE units to higher frequency and the continuing decrease and increase in the T1rho(F) values suggest that conformational exchange motions exist in the crystalline domain between 42 and 145 degrees C. Quantum chemical calculations of magnetic shielding constants showed that the high-frequency shift of TFE units should be induced by trans to gauche conformational changes at the CH2-CF2 linkage in the E-TFE unit. Although the 19F signals of the crystalline domain are substantially overlapped with those of the amorphous domain at ambient probe temperature (68 degrees C), they were successfully distinguished by using the dipolar filter and spin-lock pulse sequences at 145 degrees C. The dipolar coupling constants for the crystalline domain, which can be estimated by fitting the dipolar oscillation behaviors in the 1H --> 19F CP curve, showed a significant decrease with increasing temperature from 42 to 145 degrees C. This is due to the averaging of 1H-19F dipolar interactions originating from the molecular motion in the crystalline domain. The increase in molecular mobility in the crystalline domain was clearly shown by VT T1rho(F) and 1H --> 19F CP measurements in the phase transition temperature range. 相似文献
108.
Keitaro Ishii Peter Mathies Takehiko Nishio Hans Richard Wolf Bruno Frei Oskar Jeger 《Helvetica chimica acta》1984,67(5):1175-1183
The title compounds (E/Z)- 7 were prepared in 66% overall yield by reaction of β-ionone ((E)-( 1 ) with lithium dimethylcuprate, trapping of the intermediate enolate with benzeneselenenyl bromide and oxidation with H2O2. Analogously, (E/Z)-7-methyl-α-inone ((E/Z)- 12 ) was obtained in 65% yield from α-ionone ((E)- 11 ). 1n, π*- Excitation (λ > 347 nm, pentane) of (E)-7 causes rapid (E/Z)-isomerization and subsequent reaction of (Z)- 7 to 15 (66%). The formation of 15 is explained by twisting of the dienone chromophore due to repulsive interaction of the 7-CH3-group with the CH3-groups of the cyclohexene ring. On the other hand, irradiation λ > 347 nm, Et2O) of (E)- 7 in the presence of acid leads to (Z)- 7 (5%) and to the novel compound 16 (88%). 相似文献
109.
Giant Amplification of Photoswitching by a Few Photons in Fluorescent Photochromic Organic Nanoparticles 下载免费PDF全文
Dr. Jia Su Prof. Tuyoshi Fukaminato Dr. Jean‐Pierre Placial Dr. Tsunenobu Onodera Ryuju Suzuki Prof. Hidetoshi Oikawa Arnaud Brosseau Dr. François Brisset Dr. Robert Pansu Prof. Keitaro Nakatani Dr. Rémi Métivier 《Angewandte Chemie (International ed. in English)》2016,55(11):3662-3666
Controlling or switching the optical signal from a large collection of molecules with the minimum of photons represents an extremely attractive concept. Promising fundamental and practical applications may be derived from such a photon‐saving principle. With this aim in mind, we have prepared fluorescent photochromic organic nanoparticles (NPs), showing bright red emission, complete ON–OFF contrast with full reversibility, and excellent fatigue resistance. Most interestingly, upon successive UV and visible light irradiation, the NPs exhibit a complete fluorescence quenching and recovery at very low photochromic conversion levels (<5 %), leading to the fluorescence photoswitching of 420±20 molecules for only one converted photochromic molecule. This “giant amplification of fluorescence photoswitching” originates from efficient intermolecular energy‐transfer processes within the NPs. 相似文献
110.
Michel Sliwa Arnaud Spangenberg Rémi Métivier Sylvie Létard Keitaro Nakatani Pei Yu 《Research on Chemical Intermediates》2008,34(2-3):181-190
In photochromic materials, we demonstrated that non-linear optical (NLO) properties such as second harmonic generation (SHG) can be switched reversibly by alternate UV and visible irradiations. We report here on the design of materials fulfilling the prerequisites for SHG activity (push-pull and acentric space group) and photochromic properties. Photochromic and NLO properties of a series of anils are presented, along with the ability of some of them to switch SHG. 相似文献