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A revision to Chemical Markup Language (CML) is presented as a XML Schema compliant form, modularized into nonchemical and chemical components. STMML contains generic concepts for numeric data and scientific units, while CMLCore retains most of the chemical functionality of the original CML 1.0 and extends it by adding handlers for chemical substances, extended bonding models and names. We propose extension via new namespaced components for chemical queries, reactions, spectra, and computational chemistry. The conformance with XML schemas allows much greater control over datatyping, document validation, and structure. 相似文献
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MNDO calculations of heats of formation, dipole moments, ionization potentials, and structures are reported for a wide range of compounds containing chlorine in its characteristic valence state (ClI) and one or more of the elements H, B, Be, C, N, O, and F. The calculated errors in the heats of formation and the dipole moments are not significantly greater than those previously reported for compounds containing no chlorine. First vertical ionization potentials were on average 0.95 eV too high. The ordering of higher cationic states was found to be correct, even for species such as Cl2O, Cl2, and HOCl, where ab initio–Koopmans' theorem calculations predict the incorrect ordering. The calculated energies and geometries of compounds such as CIF3 are qualitatively incorrect, probably because of the lack of 3d atomic orbitals in the orbital basis set. 相似文献
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Rzepa HS 《Organic letters》2005,7(21):4637-4639
[structure: see text] B3LYP and KMLYP/6-31G(d) calculations predict a double-helical and chiral conformation of [14]annulene with the topological properties of a double-twist M?bius band as highly aromatic; its energy with respect to the known Hückel-aromatic conformation is predicted to be stabilized by suitable ring substitution. 相似文献
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Abbotto A Bradamante S Capri N Rzepa H Williams DJ White A 《The Journal of organic chemistry》1996,61(5):1770-1778
Enamines and enol ethers substituted in the beta position by the 2-benzoxazolyl and 2-benzothiazolyl group have been obtained by condensing dimethylformamide dimethyl acetal and ethyl orthoformate, respectively, with bis(2-benzoxazolyl)methane and bis(2-benzothiazolyl)methane. A dynamic NMR and semiempirical (PM3) investigation on rotational energy barriers has been carried out in order to rank the electron-withdrawing capacity of the heterocyclic rings. The NMR-based evaluation of the energy barriers corresponding to the rotation along the enaminic double bond has shown that the pi-electron-withdrawing power of benzothiazole is larger than that of benzoxazole, in full accord with previously obtained charge demand values based on (13)C and (15)N pi-charge/shift relationships. The NMR and the computational approaches have led to consistent results. The X-ray crystal structure of alpha,alpha-bis(2-benzothiazolyl)-beta-(dimethylamino)ethene shows that only one heteroaryl ring is coplanar with the enaminic double bond, while the second one is twisted by 73 degrees relative to such a plane. Moreover, in this case calculations closely reproduce the experimental results. In the calculated transition states corresponding to the rotational process along the enamine double bond, the two heteroaryl groups become coplanar and conjugation develops between the enaminic nitrogen electron pool and both heterocycles. The lower rotational barrier observed in the case of the 2-benzothiazolyl derivatives, with respect to the 2-benzoxazolyl derivatives, is therefore a direct consequence of the higher electron-withdrawing power of the former group. Furthermore, a stabilizing intramolecular nonbonded S.S interaction in the rotational transition state of the benzothiazolyl derivatives is evidenced by the calculations. An unprecedented isolation of the NH-enamine tautomer involving the benzoxazolyl and benzothiazolyl ring in alpha,alpha-diheteroacetaldehydes has been performed, confirming these heterocycles as strong electron-withdrawing substituents. 相似文献
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Cem B. Yildiz Kinga I. Leszczyska Sandra Gonzlez‐Gallardo Michael Zimmer Akin Azizoglu Till Biskup Christopher W. M. Kay Volker Huch Henry S. Rzepa David Scheschkewitz 《Angewandte Chemie (International ed. in English)》2020,59(35):15087-15092
Main group analogues of cyclobutane‐1,3‐diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all‐silicon 1,3‐cyclobutanediyls as stable closed‐shell singlet species from the reversible reactions of cyclotrisilene c‐Si3Tip4 (Tip=2,4,6‐triisopropylphenyl) with the N‐heterocyclic silylenes c‐[(CR2CH2)(NtBu)2]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N‐heterocyclic silylene c‐(CH)2(NtBu)2Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3‐cyclobutanediyl intermediate. 相似文献
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