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61.
A highly enantioselective Michael addition of malonates to β,γ-unsaturated α-ketoesters was achieved using cinchona alkaloid-derived thioureas as the bifunctional catalyst. The corresponding Michael addition products were obtained in excellent yields (90–99%) and ee values (up to >99% ee) using a quinidine-derived thiourea as the catalyst under neat conditions. The opposite enantiomer may be obtained using a quinine- or cinchonidine-derived thiourea as the catalyst. 相似文献
62.
63.
Xian Li Lijun Wu Zhizong Ji Yoshihiro Harigaya Yaeko Konda Mieko Iguchi Hiroshi Takahashi Masayuki Onda 《Journal of heterocyclic chemistry》1988,25(5):1403-1406
The absolute stereochemistry of curcumol ( 1 ) is confirmed on the basis of the spectroscopic data. The existence of two conformations in curdione ( 4 ) is revealed by nOe experiments at ambient temperature. One-step conversion of 4 into 1 stereospecifically proceeds via the ene-reaction without epimerization at any asymmetric center in 4 . 相似文献
64.
Konda Ashok Prashant V. Kamat Manapurathu V. George 《Research on Chemical Intermediates》1990,13(3):203-220
The results of our studies on potassium-induced transformations of several bridgehead-substituted dibenzobarrelenes are presented.
The dibenzobarrelenes 1b,c,e,f having methyl, hydroxymethyl, methoxy and phenyl groups, respectively, at the bridgehead position and the bridgehead-dimethyl
derivative 1g give, on treatment with potassium in THF, the corresponding anthracenes 8b,c,e-g, dihydrodibenzobarreneses 6b,c,e-g and benzoic acid (5). The dibenzobarrelenes 1b,g give, in addition to 8b,g, 6b,g and 5, the corresponding mono-debenzoylated products 7b,g, whereas the methoxy derivative 1e gives both anthraquinone (9) and an enol derivaiive 11, besides 8e, 6e and 5. In contrast, the reaction of the hydroxy derivative 1d with potassium in THF gives a mixture of 5, anthracene (8a), the anthrone 10 and the anthrol 12. To assess the role of oxygen in these reactions, if any, the reactions of some representative substrates such as 1b,d,e with potassium in THF, saturated with oxygen and with potassium superoxide have been studied. Cyclic voltammetric studies
have been carried out to measuee the reduction potentials for both one electron and two electron processes, leading to the
generation of the corresponding radical anions and dianion intermediates. The radical anions of 1b-g have also been generated pulse radiolytically in methanol and their spectra show absorption maxima in the regions 310-390
and 400-450 nm. 相似文献
65.
Cross-sections for the reactions with product nuclei24Na,22Na,68Ga and67Ga were investigated over the energy range of 30 to 75 MeV for alpha particle induced reactions on natural aluminium and copper,
using stacked-foil activation technique. The measured excitation functions were analysed with special reference to their suitability
for monitoring beam energy and intensity. The experimental results were compared with the predictions of hybrid model of Blann.
The assumption of initial exciton numbern
0=4(4p0h) best satisfies the measured excitation functions in the present work. 相似文献
66.
Heterocyclic base adducts of salicylaldehyde N(4)- cyclohexylthiosemicarbazone(H2L) copper(II) complexes have been synthesized
and characterized. I.r., electronic and e.s.r. spectra of the complexes, as well as i.r., electronic and 1H- and 13C-n.m.r.
spectra of the thiosemicarbazone have been obtained. Based on e.s.r. studies, all possible parameters have been calculated.
The g values, calculated for all the complexes in frozen solution, indicate the presence of the unpaired electron in the dx2−y2
orbital. The metal–ligand bonding parameters evaluated showed strong in-plane σ- and in-plane π-bonding. The magnetic and
spectroscopic data indicate a square-planar geometry for the four-coordinate and a distorted square-pyramidal structure for
the five-coordinate complexes. From cyclic voltammetric data quasireversible copper(II)/copper(I) couples are observed for
the complexes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
67.
T 1 andT m for nitridochromium(V) tetratolylporphyrin and nitridochromium(V) octaethylporphyrin were measured by saturation recovery and electron spin echo EPR, respectively, between 10 and 130 K. The temperature dependence of 1/T 1 was similar to that observed previously for chromium(V) complexes of hydroxycarboxylic acids. The spin lattice relaxation rate was faster in the perpendicular plane (the porphyrin plane) than normal to this plane. 1/T m was orientation dependent with the fastest rates observed for orientations intermediate between the principal axes. The orientation dependence of 1/T m increased with increasing temperature and decreasing rigidity of the matrix, and is attributed to molecular motion. 相似文献
68.
Arima S Yamada Konda Y Takeda K Takayanagi H Harigaya Y 《Chemical & pharmaceutical bulletin》2001,49(10):1340-1342
Cis- and trans-5,8-dihydroxy-5,6,7,8-tetrahydro-1,4-naphthoquinone (1a, 1b) were for the first time synthesized from 5,8-dihydroxy-1,4-naphthoquinone (naphthazazine) (6) as a starting material and racemic triol (3) was first synthesized from 7. The configuration of 1a was determined by X-ray analysis. 相似文献
69.
The unique properties of N-heterocyclic carbenes (NHCs) have attracted much attention, mainly from theorists and organometallic chemists, the latter using them impressively as ligands for metals. Less well known, however, has been their suitability as excellent catalysts and nucleophilic reagents. Transesterification, nucleophilic aromatic substitution, and cycloaddition reactions are examples in which NHCs can play an important role. Asymmetric reactions using catalytic amounts of chiral NHCs are an efficient approach to optically active compounds. This minireview focuses on this aspect of the chemistry of NHCs. 相似文献
70.
The thermal rearrangement of 2,4-di(N-aryl)amino-1,3,5-triazin-6yl-prop-2-ynyl ethers yield a mixture of 6-methyleneimidazo(1,2-a)-1,3,5-triazine-4-one and 6-methylimidazo(1,2-a)-1,3,5-triazine-4-one , whereas under the influence of mercuric trifluroacetate the ethers yield only , at room temperature. Mechanisms invoking [3,3] sigmatropic rearrangement of ethers were proposed to account for the product formation. 相似文献