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191.
Zora?Popovi?Email author Gordana?Pavlovi? Vibor?Roje Nadja?Do?li? Dubravka?Matkovi?-?alogovi? Ivan?Leban 《Structural chemistry》2004,15(6):587-598
Three Schiff-bases of the Ar—CH—N—Ar type were synthesized from 2-hydroxy-1-naphthaldehyde and o- (1), m- (2), and p-nitroaniline (3) in order to investigate the shift of the keto-amine/enol-imine tautomeric equilibrium that arises by the introduction of the electron-withdrawal nitro group. The compounds have been investigated experimentally, in the solid state and in the solution, by IR, NMR, UV spectroscopy, and X-ray single crystal analysis, and theoretically by using density functional theory (DFT). The tautomeric equilibrium is strongly shifted towards the keto-amine form despite of the nitro group position at N-phenyl ring in the solid state of molecular structures of 1, 2, and 3 (especially indicated by C—O and C—N bond distances). The keto-amine tautomeric form of the compounds is characterized by a strong, resonance assisted hydrogen bond (RAHB) of the N—H O type (the N O distances are 2.530(8), 2.554(2) and 2.555(5) Å in 1, 2, and 3, respectively). The molecules are assembled in the crystalline state into a 3D HB network (1), centrosymmetrical dimers (2) or infinite chains (3) by the C—H O intermolecular hydrogen bonds. In contrast, UV/VIS spectra of the chloroform solution of the title compounds reveal predominance of the enol-imine form. The molecular geometries and relative stabilities of the compounds determined by using DFT find good agreement with the experimental data. 相似文献
192.
Felicíssimo VC Cesar A Luo Y Gel'mukhanov F Agren H 《The journal of physical chemistry. A》2005,109(33):7385-7395
Carbon and oxygen near-edge X-ray absorption fine structure (NEXAFS) spectra of 1,4-cyclohexadiene, p-benzoquinone, norbornadiene, norbornadienone, and cis-cis-[4,4,2]propella-3,8-diene-11,12-dione were calculated by means of Hartree-Fock and hybrid density functional theory using the static-exchange (STEX) approximation. The NEXAFS spectra are used as a probe to identify weak molecular interactions between the two non-conjugated ethylenic pi* orbitals present in these molecules. We show that the X-ray absorption spectrum of 1,4-cyclohexadiene exhibits some particular spectral structures in the discrete energy region that evidence diene through-bond orbital interaction, whereas absorption peaks are identified in the norbornadiene and norbornadienone spectra that indicate effective through-space orbital interactions. The molecular structure of the cis-cis-[4,4,2]propella-3,8-diene-11,12-dione isomer is such that the indirect through-bond or through-space diene orbital interactions are too weak to be assigned by its C1s NEXAFS spectrum. 相似文献
193.
Simple and reliable thin-layer chromatography-densitometry methods for determination of antimycotics (bifonazole, clotrimazole, and miconazole) and preservatives (benzyl alcohol and benzoic acid) were developed. The pairs bifonazole/benzyl alcohol, clotrimazole/benzyl alcohol, and miconazole/benzoic acid were determined simultaneously. The following mobile phases were used: ethyl acetate-n-heptane-methanoldiethylamine (3 + 4.5 + 1 + 0.2, v/v/v/v) for bifonazole and benzyl alcohol; n-butyl acetate-n-heptane-methanol-dietylamine (3 + 4.5 + 1 + 0.2, v/v/v/v) for clotrimazole and benzyl alcohol; and n-butyl acetate-carbon tetrachloride-methanol-diethylamine (3 + 6 + 2.5 + 0.5, v/v/v/v) for miconazole and benzoic acid. The chromatographic zones on silica gel plates were scanned in the reflectance/absorbance mode at 230 nm (bifonazole, benzyl alcohol, miconazole, and benzoic acid) and 210 nm (clotrimazole and benzyl alcohol). The recovery for all substances ranged from 98.7 to 100.7%. The limits of detection and quantitation were 0.03 to 0.2 microg and 0.1 to 0.5 microg/spot, respectively. The proposed methods were applied for determination of antimycotics and preservatives in commercially available pharmaceuticals. 相似文献
194.
A kinetic method is proposed for the determination of propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid, based on its inhibitory effect on the acetonitrile-catalysed oxidation of Pyrocatechol Violet by hydrogen peroxide. The concentrations of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid determined ranged from 5.0 × 10?7 to 4.0 × 10?6 M with a relative standard deviation of up to 3.3%. The same indicator reaction can be applied to the determination of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid and ethylenediaminetetra-acetic acid in mixtures. Mixtures of these acids in molar ratios from 1 ∶ 4.5 to 10 ∶ 1 have been analysed. Concentrations of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid from 2.0 × 10?7 to 1.0 × 10?6 M and ethylenediaminetetra-acetic acid from 1.0 × 10?7 to 9.0 × 10?7 M were determined with relative standard deviations of up to 4.3 and 5.7%, respectively. The effect of foreign ions on the accuracy of these determinations was also investigated. 相似文献
195.
Gordana Todorov 《Milan Journal of Mathematics》2008,76(1):201-228
Cluster categories were introduced in the paper “Tilting theory and cluster combinatorics” [8] in order to better understand
the combinatorics of cluster algebras, by giving new, module theoretic and categorical meanings to the combinatorics of the
well known cluster algebras [20]. Subsequently, correspondences between the many notions in these two areas were given, e.g.
[5, 6, 11, 9] and others.
This proved to be quite useful and productive approach with even further connections to semi-invariants of quivers [26]. However,
in order to get this connection, one needs to define and study virtual representation spaces for vectors having both positive
and negative dimensions at the vertices of a quiver without oriented cycles. Then, the virtual semi-invariants satisfy the
three basic theorems: the First Fundamental Theorem (determinantal), the Saturation theorem and the Canonical Decomposition
theorem.
From the above theorems it follows that in the case of Dynkin quivers there is a nice relationship between supports of the
semi-invariants and the tilting triangulation of the (n – 1)-sphere.
Lecture held in the Seminario Matematico e Fisico on September 26, 2007.
Received: September 2008 相似文献
196.
Aslak Bakke Buan Robert J. Marsh Idun Reiten Gordana Todorov with an Appendix coauthored in addition by P. Caldero B. Keller 《Proceedings of the American Mathematical Society》2007,135(10):3049-3060
Cluster algebras are commutative algebras that were introduced by Fomin and Zelevinsky in order to model the dual canonical basis of a quantum group and total positivity in algebraic groups. Cluster categories were introduced as a representation-theoretic model for cluster algebras. In this article we use this representation-theoretic approach to prove a conjecture of Fomin and Zelevinsky, that for cluster algebras with no coefficients associated to quivers with no oriented cycles, a seed is determined by its cluster. We also obtain an interpretation of the monomial in the denominator of a non-polynomial cluster variable in terms of the composition factors of an indecomposable exceptional module over an associated hereditary algebra.
197.
Daohua Song Feng Wang Gordana Dukovic Ming Zheng E. D. Semke Louis E. Brus Tony F. Heinz 《Applied Physics A: Materials Science & Processing》2009,96(2):283-287
A strong optical Stark effect has been observed in (6,5) semiconducting single-walled carbon nanotubes by femtosecond pump-probe
spectroscopy. The response is characterized by an instantaneous blueshift of the excitonic resonance upon application of pump
radiation at photon energy well below the band gap. The large Stark effect is attributed to the enhanced Coulomb interactions
present in these one-dimensional materials. 相似文献
198.
Ivana Jarak Grace Karminski‐Zamola Gordana Pavlovi Zora Popovi 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(2):o98-o100
The title compound, C10H16N·Cl−·C2H6O, is an important intermediate in the convergent synthesis of amidine‐substituted polycyclic heterocycles, a class of compounds that shows significant anticancer activity. The molecule of (I) is not planar, having a dihedral angle of 25.00 (7)° between the aniline and amidine (–C—NH=C=NH2) groups. The protonation of the amidine molecular fragment is accompanied by delocalized C—N bond distances of 1.320 (2) and 1.317 (2) Å. The cations and chloride anions are involved in a network of hydrogen bonds, resulting in the formation of infinite chains propagating along the b direction. The chains are further grouped within the ab plane, in such a way that the structure is segregated into layers dominated by hydrophobic interactions involving N‐isopropyl residues and layers dominated by N—H⋯Cl [N⋯Cl = 3.275 (2)–3.596 (2) Å], O—H⋯Cl [O⋯Cl = 3.229 (3) Å] and N—H⋯O [N⋯O = 2.965 (3) Å] hydrogen bonds. 相似文献
199.
Velimir Popsavin Sanja Grabe? Ivana Krsti? Gordana Bogdanovi? 《Tetrahedron letters》2004,45(51):9409-9413
A new approach to the dephenyl goniofufurone analogue 2 and the corresponding (3S,4R)-stereoisomer 3 is reported. The resulting furanolactones 2 and 3 have shown a potent and selective in vitro cytotoxicity against certain human tumour cell lines. 相似文献
200.
Dukovic G White BE Zhou Z Wang F Jockusch S Steigerwald ML Heinz TF Friesner RA Turro NJ Brus LE 《Journal of the American Chemical Society》2004,126(46):15269-15276
We have investigated reversible single-wall carbon nanotube (SWNT) oxidation by quantitative analysis of the oxide-induced absorption bleaching and luminescence quenching at low pH. These data, in combination with DFT structure calculations, suggest that the nanotube oxide is a 1,4-endoperoxide. At low pH, the endoperoxide protonates to create a hydroperoxide carbocation, introducing a hole in the SWNT valence band. Nanotube luminescence is extremely sensitive to quenching by hole-doping, while the absorption is relatively robust. 相似文献