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51.
PMB ethers of alcohols are obtained in good yields and under mild conditions using the 4-methoxybenzyl N-allyl thiocarbamate and N-bromosuccinimide (NBS)/TfOH as the catalyst. The present method is very fast, simple, and efficient. 相似文献
52.
Complete (1)H and (13)C NMR signal assignments of two lactucin-type sesquiterpene lactone glycosides, derivatives of 11β,13-dihydrolactucin, isolated from roots of Picris conyzoides, were achieved by one- and two-dimensional NMR experiments, allowing the correction of previously published data for cichorioside B and the structure elucidation of its new ester with 3-hydroxy-2-methylpropanoic acid. In addition, seven known sesquiterpene lactones and three phenolic compounds were isolated from the plant material. 相似文献
53.
Katarzyna HeliosRafa? Wysokiński Adam PietraszkoDanuta Michalska 《Vibrational Spectroscopy》2011,55(2):207-215
The crystal and molecular structure of a polymeric Cu(II)-orotate complex, [Cu(μ-HOr)(H2O)2]n, has been reinvestigated by single crystal X-ray diffraction. It is shown that several synergistic interactions: two axial Cu-O interactions; intramolecular and intermolecular hydrogen bonds; and π-π stacking between the uracil rings contribute to the stability of the crystal structure. The Raman and FT-IR spectra of the title complex are reported for the first time. Comprehensive theoretical studies have been performed by using three unrestricted DFT methods: B3LYP; and the recently developed M06, and M05-2X density functionals. Clear-cut assignments of all the bands in the vibrational spectra have been made on the basis of the calculated potential energy distribution, PED. The very strong Raman band at 1219 cm−1 is diagnostic for the N1-deprotonation of the uracil ring and formation of the copper-nitrogen bond, in this complex. The Cu-O (carboxylate) stretching vibration is observed at 287 cm−1 in the IR spectrum, while the Cu-N (U ring) stretching vibration is assigned to the strong Raman band at 263 cm−1. The molecular structure and vibrational spectra (frequencies and intensities) calculated by the M06 functional method are very similar to the results obtained by the B3LYP method, but M06 performs better than B3LYP in calculations of the geometrical parameters and vibrational frequencies of the interligand O-H?O hydrogen bonding. Unfortunately, the M05-2X method seriously overestimates the strength of interligand hydrogen bond. 相似文献
54.
Maślanka A Krzek J Stolarczyk M Walczak M Głogowska A 《Journal of AOAC International》2011,94(6):1791-1799
Stability of clonazepam, diazepam, haloperidol, and doxepin was determined in acidic solutions. In addition, determination of the kinetic and thermodynamic properties of this stability was carried out. Reaction rate constants (k), half-life times (t(0.1) and t(0.5)), and activation energy (Ea) were estimated for the drugs, which differed in polarity expressed with log P values. It was observed that estimated Ea values increased from 42.13 to 125.03 kJ/mol with an increase of lipophilicity (log P) beginning from the most hydrophilic drug (clonazepam, 2.70 log P) to the most lipophilic drug (doxepin, 4.10 log P). All degradation products were studied using an HPLC/electrospray ionization-MS technique in the positive ionization mode. 相似文献
55.
Agata Górniak Alina Wojakowska Bożena Karolewicz Janusz Pluta 《Journal of Thermal Analysis and Calorimetry》2011,104(3):1195-1200
Enhancement of the dissolution rate of poorly soluble compounds through the formation of drug–drug eutectics was investigated
using fenofibrate and acetylsalicylic acid. Solid–liquid equilibria in the system under study were investigated by differential
scanning calorimetry (DSC). The phase diagram for the whole range of compositions was constructed. In addition, existence
of a metastable polymorph of fenofibrate has been confirmed. The investigation has revealed that acetylsalicylic acid and
fenofibrate form a simple eutectic mixture containing 0.958 mol fraction of fenofibrate at the eutectic point. Dissolution
rate improvement of fenofibrate correlated with the phase diagram. The amount of fenofibrate released from the solid dispersions
that contained fenofibrate as the eutectic mixture with acetylsalicylic acid was at least threefold higher compared to untreated
fenofibrate. 相似文献
56.
Katarzyna Betlejewska-Kielak Elbieta Bednarek Armand Budzianowski Katarzyna Michalska Jan K. Maurin 《Molecules (Basel, Switzerland)》2021,26(13)
Racemic ketoprofen (KP) and β-cyclodextrin (β-CD) powder samples from co-precipitation (1), evaporation (2), and heating-under-reflux (3) were analysed using X-ray techniques and nuclear magnetic resonance (NMR) spectroscopy. On the basis of NMR studies carried out in an aqueous solution, it was found that in the samples obtained by methods 1 and 2, there were large excesses of β-CD in relation to KP, 10 and 75 times, respectively, while the sample obtained by method 3 contained equimolar amounts of β-CD and KP. NMR results indicated that KP/β-CD inclusion complexes were formed and the estimated binding constants were approximately 2400 M−1, showing that KP is quite strongly associated with β-CD. On the other hand, the X-ray single-crystal technique in the solid state revealed that the (S)-KP/β-CD inclusion complex with a stoichiometry of 2:2 was obtained as a result of heating-under-reflux, for which the crystal and molecular structure were examined. Among the methods used for the preparation of the KP/β-CD complex, only method 3 is suitable. 相似文献
57.
The structure of tetraaqua-bis(nitrato-O,O′)-(1,10-phenanthroline-N,N′)-lanthanum(III) 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane nitrate dihydrate, [La(NO3)2 · phen · (H2O)4]+ · hmt · NO
3
−
· 2H2O, is presented. The lanthanum ion exhibits tenfold coordination and the polyhedron can be described as tetradecahedron. The
complex cations, nitrate ions, water and hexamethylenetetramine molecules are assembled via hydrogen bonds, H–π rings and π–π stacking interactions into 3D supramolecular network. The bond strength of coordination sphere was calculated by means of
the bond-valence method. The influence of La:phen stoichiometry and additional ligand on the changes of lanthanum(III) coordination
sphere geometry in ten-coordinated complexes with 1,10-phenanthroline was discussed. The infrared spectrum of structure optimised
by means of quantum mechanical calculations was analysed and compared with measured one. The obtained compound was characterised
by thermogravimetric analysis in conjunction with evolved gases in the air atmosphere. 相似文献
58.
Ambident anions derived from phosphorus monothio acids have been glycosylated by 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl-, 2,3,4,6-tetra-O-acetyl-α-D-galactopyranosyl- and 2,3,4-tri-acetyl-α-D-xylopyranosyl bromides, yielding β-S-glycosyl- and /gb-O-glycosylthioates. The S/O ratio of the glycosylated phosphorothioates depends markedly on the salt used. Ammonium salts favour the formation of S-derivatives, whereas silver salts give mainly O-derivatives. O-Glucosyl phosphorothioate undergoes thermal isomerisation to S-glucosyl phosphorothioate, with retention of configuration at the glycosylic centre. The implications of this stereochemical result are briefly discussed. 相似文献
59.
Zofia M. Michalska 《Transition Metal Chemistry》1980,5(1):125-129
Summary The catalytic activity of homogeneous and silica-supported rhodium(I) complexes has been investigated for the reaction of tertiary silanols with a series of mono-, di- and triorganosubstituted hydridosilanes. The reaction is very sensitive to the electronic effects of substituents attached to silicon in the hydridosilane. The nature of the catalyst ligands and the structure of organosilanols seem to have little effect on the reaction rate. A mechanism involving rapid activation of the organosilicon hydride in the oxidative addition step followed by nucleophilic attack of the silanol on silicon complexed to rhodium is proposed. The system investigated has also been found to efficiently catalyse the reaction of oligomeric ,(1)-dihydriclopolyeiimethylsiloxane with polydimethylsiloxane-,(1)-diols giving cyclic compounds. Silica-supported complexes showed lower activity than their homogeneous counterparts. 相似文献
60.
Ambident anions derived from phosphorus thioselcnoacids were glycosylated with 2,3,4,6 - tetra - O - acetyl - α - d - glucopyranosyl bromide, 2,3,4,6 - tetra - O - acetyl - α - d - galactopyranosyl bromide and 2,3,4 - tri- O - acetyl - α - d - xylopyranosyl bromide. The products were β-Se-glucosyl- and β-S-glucosylthioselenoates. The Se/S ratio of the glycosylated phosphorothioselenoates depends on the reaction conditions. At higher temperatures an equilibrium was observed. As a result of this equilibrium the Se/S ratio of the linkages formed in the glycosylated products was different from that observed under kinetic control. The structures of the glycosylated phosphorothioselenoates were confirmed by spectroscopy, independent synthesis and selective oxidation. 相似文献