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排序方式: 共有354条查询结果,搜索用时 31 毫秒
1.
Juzo Oyamada 《Tetrahedron》2006,62(29):6918-6925
Synthesis of coumarins from phenols and propiolic acids was examined by using a Pt catalyst such as PtCl2/AgOTf, K2PtCl4/AgOTf, and K2PtCl4/AgOAc. Propiolic acid reacted even with less reactive phenols in trifluoroacetic acid to give coumarins and dihydrocoumarins. In the case of substituted propiolic acids, phenylpropiolic acid and 2-octynoic acid, the reactions proceeded selectively to afford coumarins in good to high yields. 相似文献
2.
G.P. Romanelli D. Bennardi D.M. Ruiz G. Baronetti H.J. Thomas 《Tetrahedron letters》2004,45(48):8935-8939
Substituted coumarins are synthesized from phenols and β-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H6P2W18O62·24H2O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130 °C temperature and as little as 1 mol % of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples). 相似文献
3.
4.
表面活性剂增敏2.5次微分极谱测定香豆素 总被引:1,自引:0,他引:1
王福民 《理化检验(化学分册)》2003,39(3):138-141
拟定了表面活性剂增敏、2 .5次微分极谱测定香豆素的方法。在含 6.0× 10 -6 mol·L-13 氯 2 羟丙基 三甲基氯化铵的 0 .1mol·L-1KH2 PO4 Na2 HPO4 (pH 6.8)缓冲液中 ,香豆素还原波 [峰电位Ep=- 1.60V(vs .SCE) ]的 2 .5次微分极谱峰峰电流e″p 与其浓度在 4 .0× 10 -7~ 6.0× 10 -5mol·L-1范围内呈良好线性关系 (r =0 .9998,n =10 ) ,检出限为 1.2× 10 -7mol·L-1。 13次平行测量 8.0× 10 -6 mol·L-1香豆素的峰电流 ,RSD为 1.5 %。该方法可用于中药白芷中香豆素的直接测定 相似文献
5.
A spectrofluorimetrical selective method was designed for determination of paracetamol in tablets. This important technique can be characterized by its sensitivity, simplicity, celerity and cheaper cost than current official methods. The employed methodology involves coumarinic compound formation obtained by reaction between paracetamol and ethylacetoacetate (EAA) in the presence of sulphuric acid as catalyst. The reaction product is highly fluorescent at 478 nm, being excited at 446 nm.The linear concentration range of the application was 0.1-0.4 μg/ml of paracetamol and the detection limit was 57 ng/ml.The influence of different variables was studied and optimized through chemometric techniques. Applying the above-mentioned method good results were obtained with regard to pharmaceutical formulations containing paracetamol. Therefore, it is relevant to suggest this profitable technique for medicament control analysis. 相似文献
6.
Mao Xiang Wang Xiang Ming Meng Man Zhou Zhu Qing Xiang Guo 《中国化学快报》2007,18(11):1403-1406
A novel fluorescence enhancement Cu~(2 ) chemosensor derived from coumarin was prepared.Emission study found that it exhibits evident Cu~(2 )-amplified fluorescence prior to Co~(2 ),Pb~(2 ),Mg~(2 ),Mn~(2 ),Ni~(2 ),Zn~(2 ),Fe~(3 ),Ag~ and Cd~(2 ),and the largest emission enhancement factor is about 9 at a ratio of 2:1 (chemosensor 1/Cu~(2 )). 相似文献
7.
The ability of titanium(IV) chloride as a catalyst to promote the Pechmann condensation reaction with a range of phenols and β-keto esters is described.The reaction was carried out by addition of TiCl4 to a mixture of the phenol and the β-keto ester with thorough stirring in the absence of a solvent and represents an improvement on the classical Pechmann conditions. The yields of coumarins obtained via this novel protocol were significantly higher than those using the conventional method and the reaction duration was reduced to a few minutes or even a few seconds. 相似文献
8.
The high-yielding six-step synthesis of 7-hydroxy-2,6-dimethylchromeno[3,4-d]oxazol-4-one 17 from commercially available 2,4-dihydroxy-3-methylacetophenone is described. Coumarin 17 constitutes a useful synthon for coumarin antibiotic synthesis. A new methodology for oxazole formation applicable to 3-aminocoumarins has been developed, and a mechanistic rationalization is proposed. 相似文献
9.
Wolfgang Stadlbauer Rita Laschober Thomas Kappe 《Monatshefte für Chemie / Chemical Monthly》1991,122(10):853-861
Summary 4-Chloro-3-aryl-coumarins and quinolones2 a–e undergo thermolytic ring closure by reaction with sodium azide in refluxing dimethyl formamide to yield indolo[3,2-c]coumarins and indolo[3,2-c]quinolin-6(5H)-ones6 a–e. In the case of the coumarin2 a the azido coumarin5 can be isolated. The mono- and diazacoumestrol-dimethylethers6 a–c are converted into the coumestrol analogues7 a–c and their diacetyl derivatives8 a–c.
Potentielle nichtsteroidale Östrogene und Antiöstrogene, 4. Mitt.: Organische Azide in der Heterocyclensynthese, Teil 13: Synthese von Aza- und Diazacumöstrolen über Azidzwischenstufen
Zusammenfassung 4-Chlor-3-arylcumarine und-chinolone2 a–e reagieren thermolytisch mit Natriumazid in siedendem Dimethylfomamid unter Ringschluß zu Indolo[3,2-c]cumarinen und Indolo[3,2-c]chinolin-6(5H)-onen6 a–e. Nur aus dem Cumarinderivat2 a kann das zwischenzeitlich gebildete Azidocumarin5 isoliert werden. Die so erhaltenen Mono- und Diazacumöstroldimethylether6 a–c werden in die entsprechenden Cumöstrole7 a–c und ihre Diacetylderivate8 a–c umgewandelt.相似文献
10.
A scheme of time-dependent density functional theory (TDDFT) combined with single-excitation configuration interaction (CIS) approach was employed to make a detailed investigation of the emitting energy for fifteen well-known coumarin derivatives. The results showed that the predicted emitting energies as well as the absorption ones were dominated mainly by the exchange-correlation (XC) functional to be used. So long as a functional is properly chosen, the experimental emitting energy of most derivatives can be accurately reproduced within 0.16 eV by a calculation at the TDDFT/6-31G(d)//CIS/3-21G(d) theoretical level. It was found that, nevertheless, the hybrid functional, B3LYP, well predicted the absorption energies for all the fifteen coumarin derivatives but none of the functionals could work equally well for the emitting energy calculations. Two pure functionals, OLYP and BLYP, yield good emitting energies for the 7-aminocoumarins or derivatives with a N atom connected to 7-position, which exhibit inconspicuous charge transfer (CT) in their excited states, whereas the B3LYP hybrid functional, with 20% Hartree-Fock (HF) exchange energy, performs significantly better than OLYP and BLYP for those 3-substituted coumarins with larger CT in excited states. Thus, in comparison with the absorption energies, the selection of proper functionals for the emitting energy calculations becomes more complex. In all probability, it is effective and doable to choose an XC-functional with alterable fraction of HF exchange energy according to the composition and structure characteristics of molecule. 相似文献