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861.
Svetlana V. Kirpichenko Erich Kleinpeter Bagrat A. Shainyan 《Journal of Physical Organic Chemistry》2010,23(9):859-865
The first conformational analysis of 3‐silathiane and its C‐substituted derivatives, namely, 3,3‐dimethyl‐3‐silathiane 1 , 2,3,3‐trimethyl‐3‐silathiane 2 , and 2‐trimethylsilyl‐3,3‐dimethyl‐3‐silathiane 3 was performed by using dynamic NMR spectroscopy and B3LYP/6‐311G(d,p) quantum chemical calculations. From coalescence temperatures, ring inversion barriers ΔG≠ for 1 and 2 were estimated to be 6.3 and 6.8 kcal/mol, respectively. These values are considerably lower than that of thiacyclohexane (9.4 kcal/mol) but slightly higher than the one of 1,1‐dimethylsilacyclohexane (5.5 kcal/mol). The conformational free energy for the methyl group in 2 (?ΔG° = 0.35 kcal/mol) derived from low‐temperature 13C NMR data is fairly consistent with the calculated value. For compound 2 , theoretical calculations give ΔE value close to zero for the equilibrium between the 2 ‐Meax and 2 ‐Meeq conformers. The calculated equatorial preference of the trimethylsilyl group in 3 is much more pronounced (?ΔG° = 1.8 kcal/mol) and the predominance of the 3 ‐SiMe3 eq conformer at room temperature was confirmed by the simulated 1H NMR and 2D NOESY spectra. The effect of the 2‐substituent on the structural parameters of 2 and 3 is discussed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
862.
Simple method for determining of the isokinetic temperature value for the SNAr reactions in solution 下载免费PDF全文
The changes of the free energy of activation δ?G≠exp and the activation entropy δ?S≠ in the framework of the isokinetic relationship δ?G≠exp versus (Tiso ? Texp) δ?S≠ were explored quantitatively to predict the isokinetic temperature Tiso for the aromatic nucleophilic substitution reactions in solution. 相似文献
863.
Dallas D. Parker Anne Buyle Padias H. K. Hall 《Journal of polymer science. Part A, Polymer chemistry》2000,38(10):1866-1872
Formaldehyde oxime and three O‐alkyl derivatives were examined as potential imine monomers. Formaldehyde oxime spontaneously polymerized below 60 °C and did not polymerize above 60 °C (ceiling temperature), even in the presence of free‐radical or cationic initiators. The O‐benzoyl derivative was isolated as the cyclic trimer but could not be converted into the monomeric form. Formaldehyde O‐benzyloxime was synthesized and isolated. Attempted homopolymerizations in the presence of free‐radical initiators only led to oligomers, whereas with cationic initiators only cyclic trimer was obtained. Copolymerizations with appropriate vinyl monomers and free‐radical and anionic initiators yielded only low molecular weight polymers. Cationic copolymerizations gave higher molecular weights and polymer yields, but the polymers containing appreciable amounts of imine function had very low molecular weights. We conclude that the polymerizability of imines is extremely sensitive to the substitution pattern: imines with only a substituent on nitrogen are unstable and readily polymerize, whereas imines with more substituents generally do not polymerize. Electron‐withdrawing substituents are more favorable to polymerizability. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1866–1872, 2000 相似文献
864.
Johannes Müller Janina Buck Prof. Dr. Andreas Hirsch 《European journal of organic chemistry》2023,26(9):e202201310
Within the scope of this paper, nine π-expanded mono-substituted 5,8,11,14,17-pentakis-(tert-butyl)-hexa-peri-hexabenzocoronenes (HBC) are introduced. 2-Iodo-5,8,11,14,17-pentakis-(tert-butyl)-hexa-peri-hexabenzocoronene served as precursor and was reacted with ethynyltrimethylsilane in a Sonogashira coupling reaction. The acetylene unit is used as a linker and can undergo another Sonogashira coupling reaction combining different phenyl coupling partners with the HBC core. The electron-withdrawing groups such as nitrile, pyridine and carbonyl species (aldehyde, methylester, carboxylic acid) as well as the three quinoxaline based species (diphenylquinoxaline, dibenzo[a,c]phenazine, phenanthro[4’,5’-a,b,c]phenazine) serve as substitution moieties. Their influence on the optoelectronic properties were investigated by UV/Vis absorption spectroscopy demonstrating a maximum redshift of 7 nm compared to starting compound 2-Iodo-5,8,11,14,17-pentakis-(tert-butyl) HBC. As for the phenanthro[4’,5’-a,b,c]phenazine substituted HBC a dramatic decrease in the intensity of the absorption of the UV/Vis spectrum was observed. The fluorescence spectroscopy pointed out that the dibenzo[a,c]phenazine and phenanthro[4’,5’-a,b,c]phenazine substitution changed the spectra to one broad peak departing from the characteristic HBC-like emission pattern. 相似文献
865.
This work examines theoretically the problem of the migration of borane groups between the nitrogen atoms of pyrazolyl rings. We have studied as a model the BH2 pyrazol-1-yl derivatives to determine the effects of substituents on the pyrazole ring; also 1-(9-borabicyclo[3.3.1]nonan-9-yl)-1H-pyrazoles to compare the calculated barriers with the experimental ones as well as to determine steric effects, i. e., how the buttressing effect increases the rate. The interacting quantum atoms methodology has been used for partitioning the energy of the systems in their stationary points into the contribution of pyrazole and BH2 group and their mutual interaction. 相似文献
866.
Sven Mörsel René Kellner Prof. Dr. Andreas Hirsch 《European journal of organic chemistry》2023,26(20):e202300299
The synthesis of novel mono-, di-, tri-, tetra-, and hexafluorinated hexa-peri-hexabenzocoronenes (HBCs) and their conversion into their thioether-substituted analogs is reported. The substitution reaction with the corresponding thiolates was performed microwave-assisted to significantly reduce the reaction time. With increasing amount of fluorination or thioether-substituents, a decreasing extinction coefficient can be observed for the HBCs. Successive addition of thioether-moieties leads to a bathochromic shift of the absorption and emission bands, whereas the nature of the attached thioether does not affect the optoelectronical properties. To further tune the electronic environment of the HBC core, a successive oxidation to the corresponding sulfone as well as the formation of the sulfonium salts were performed. With that, the electron-donating thioethers were transformed into electron-withdrawing substituents, resulting in an inversed electron demand in the periphery of the core. The so obtained compounds showed decreased extinction coefficients and a broadening of the absorption and emission bands. 相似文献
867.
Wen-Yi Wei Zi-Rong Gong Xin-Yue Chai Prof. Dr. Yan-Jun Xu Prof. Dr. Lin Dong 《European journal of organic chemistry》2023,26(19):e202300294
Rhodium(III)-catalyzed cross-dehydrogenative coupling involves a highly efficient C−C bond formation from N-phenyl-7-azaindole frameworks, thiophenes. Various novel 7-azaindole derivatives have been successfully developed with good substrate applicability. 相似文献