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排序方式: 共有157条查询结果,搜索用时 218 毫秒
131.
Dey A Okamura TA Ueyama N Hedman B Hodgson KO Solomon EI 《Journal of the American Chemical Society》2005,127(34):12046-12053
Hydrogen bonding (H-bonding) is generally thought to play an important role in tuning the electronic structure and reactivity of metal-sulfur sites in proteins. To develop a quantitative understanding of this effect, S K-edge X-ray absorption spectroscopy (XAS) has been employed to directly probe ligand-metal bond covalency, where it has been found that protein active sites are significantly less covalent than their related model complexes. Sulfur K-edge XAS data are reported here on a series of P450 model complexes with increasing H-bonding to the ligated thiolate from its substituent. The XAS spectroscopic results show a dramatic decrease in preedge intensity. DFT calculations reproduce these effects and show that the observed changes are in fact solely due to H-bonding and not from the inductive effect of the substituent on the thiolate. These calculations also indicate that the H-bonding interaction in these systems is mainly dipolar in nature. The -2.5 kcal/mol energy of the H-bonding interaction was small relative to the large change in ligand-metal bond covalency (30%) observed in the data. A bond decomposition analysis of the total energy is developed to correlate the preedge intensity change to the change in Fe-S bonding interaction on H-bonding. This effect is greater for the reduced than the oxidized state, leading to a 260 mV increase in the redox potential. A simple model shows that E degrees should vary approximately linearly with the covalency of the Fe-S bond in the oxidized state, which can be determined directly from S K-edge XAS. 相似文献
132.
Naya A Kobayashi K Ishikawa M Ohwaki K Saeki T Noguchi K Ohtake N 《Chemical & pharmaceutical bulletin》2003,51(6):697-701
The structure activity relationships of novel selective CCR3 receptor antagonists, 2-(benzothiazolylthio)acetamimde derivatives were described. A lead structure (1a) was discovered from the screening of the focused library that was based on the structure of our dual antagonists for the human CCR1 and CCR3 receptors. Derivatization of 1a including incorporation of substituent(s) into each benzene ring of the benzothiazole and piperidine side chain resulted in the identification of potent and selective compounds (1b, r, s) exhibiting nano-molar binding affinity (IC(50)s: 1.5-3.0 nM) and greater than 800-fold selectivity for the CCR3 receptor over the CCR1 receptor. 相似文献
133.
Right-handed helical structure of expanded oligo(L-leucine) containing [Ru(terpyridine)2]2+ moieties
Okamura TA Iwamura T Seno S Yamamoto H Ueyama N 《Journal of the American Chemical Society》2004,126(49):15972-15973
Expanded oligo(l-leucine)s, containing an alternate arrangement of a bis(terpyridine)ruthenium(II) moiety and a l-leucine residue, were synthesized and characterized by 1H NMR, UV, CD, and electrochemical properties. The intensity of CD spectra per ruthenium unit increased with the elongation of the peptide chain. 1H NMR analysis of a tetramer indicated the right-handed helical structure in acetonitrile. 相似文献
134.
Dansyl derivatives of racemic phenylalanine and its analogs have been resolved by microcolumn liquid chromatography with γ-cyclodextrin as mobile phase additive. The enantioselectivity of the system was influenced by the concentrations of both γ-cyclodextrin and acetonitrile in the mobile phase. Enantiomers of phenylalanine, phenylglycine, and tyrosine were resolved by isocratic elution in a single chromatographic run. 相似文献
135.
Zhang ZH Okamura TA Hasegawa Y Kawaguchi H Kong LY Sun WY Ueyama N 《Inorganic chemistry》2005,44(18):6219-6227
Five novel lanthanide complexes with the formulas [Nd(bta)(H2O)2.4.35H2O]n(1), [Sm(bta)(H2O)2.4.5H2O]n (2), [Eu(bta)(H2O).1.48H2O]n (3), [Tb(bta)(H2O).1.31H2O]n (4), and [Yb(bta)(H2O).H2O]n (5) (H3bta = 1,3,5-benzenetriacetic acid) have been prepared by using the corresponding lanthanide salt and H3bta. The results of an X-ray crystallographic analysis revealed that all the complexes have three-dimensional channel-like structures, in which the bta3- ligands adopt different coordination modes: monodentate and mu2-eta2:eta1-bridging coordination modes in 1, 2, and 5 and mu2-eta1:eta1-bridging and mu2-eta2:eta1-bridging coordination modes in 3 and 4, respectively. Complexes 1 and 2, as well as 3 and 4, are isostructural, respectively, in which all the Ln(III) (Ln = Nd, Sm, Eu, and Tb) atoms are nine-coordinated, while the Yb(III) atoms in complex 5 are eight-coordinated. Both complexes 3 and 4 showed strong luminescence upon excitation, and their luminescence decay curves fit well with single exponential decays of which the lifetime is 0.45 ms for 3 and 1.0 ms for 4. The magnetic properties of the complexes were investigated in the temperature range of 1.8-300 K. 相似文献
136.
Haruki Niwa Takashi Hasegawa Norikazu Ban Kiyoyuki Yamada 《Tetrahedron letters》1984,25(26):2797-2800
The first total synthesis of (±)-hydroxy patchouli alcohol (3) and the corresponding (±)-carboxylic acid 4, the biooxidation products of patchouli alcohol (2) has been achieved. (±)-Norpatchoulenol (1) has also been synthesized by the biogenetic route via 3 and 4. 相似文献
137.
Fan J Zhu HF Okamura TA Sun WY Tang Dagger WX Ueyama N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(19):4724-4731
Complex [Ag(tpba)N(3)] (1) was obtained by reaction of novel tripodal ligand N,N',N"-tris(pyrid-3-ylmethyl)-1,3,5-benzenetricarboxamide (TPBA) with [Ag(NH(3))(2)]N(3). While the reactions between 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (TITMB) and silver(I) salts with different anions and solvent systems give six complexes: [Ag(3)(titmb)(2)](N(3))(3).CH(3)OH.4 H(2)O (2), [Ag(3)(titmb)(2)](CF(3)SO(3))(2)(OH).5 H(2)O (3), [Ag(3)(titmb)(2)][Ag(NO(3))(3)]NO(3).H(2)O (4), [Ag(3)(titmb)(2)(py)](NO(3))(3).H(2)O (py=pyridine) (5), [Ag(3)(titmb)(2)(py)](ClO(4))(3) (6), and [Ag(3)(titmb)(2)](ClO(4))(3).CHCl(3) (7). The structures of these complexes were determined by X-ray crystallography. The results of structural analysis of complexes 1 and 2, with the same azide anion but different ligands, revealed that 1 is a twofold interpenetrated 3D framework with interlocked cage-like moieties, while 2 is a M(3)L(2) type cage-like complex with a methanol molecule inside the cage. Entirely different structure and topology between 1 and 2 indicates that the nature of organic ligands affected the structures of assemblies greatly. While in the cases of complexes 2-7 with flexible tripodal ligand TITMB, they are all discrete M(3)L(2) type cages. The results indicate that the framework of these complexes is predominated by the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and solvents. It is interesting that there is a divalent anion [Ag(NO(3))(3)](2-) inside the cage 4 and an anion of ClO(4)(-) or NO(3)(-) spontaneously encapsulated within the cage of complexes 5, 6 and 7. 相似文献
138.
Onoda A Yamada Y Okamura TA Doi M Yamamoto H Ueyama N 《Journal of the American Chemical Society》2002,124(6):1052-1059
Three new polynuclear Ca(II)- and Na(I) phosphate complexes with two strategically oriented bulky amide groups, 2,6-(PhCONH)(2)C(6)H(3)OPO(3)H(2), were synthesized, including one with a zigzag-chain, [Ca(II)[O(3)POC(6)H(3)-2,6-(NHCOPh)(2)](H(2)O)(4)(EtOH)](n), a cyclic-octanuclear form, [Ca(II)(8)[O(3)POC(6)H(3)-2,6-(NHCOPh)(2)](8)(O=CHNMe(2))(8)(H(2)O)(12)], and a hexanuclear complex, (NHEt(3))[Na(3)[O(3)POC(6)H(3)-2,6-(NHCOPh)(2)](2)(H(2)O)(MeOH)(7)]. X-ray crystallography revealed that all have an unsymmetric ligand position due to the bulky amide groups. A dynamic transformation of the Ca(II) zigzag-chain structure to the cyclic-octanuclear complex was induced by changing coordination of DMF molecules, which caused a reorganization of the intermolecular/intramolecular hydrogen bond network. 相似文献
139.
140.
Norikazu Kubotera 《Journal of Number Theory》2005,111(1):81-85
In this paper, by using an analogue of theorems of Iwasawa (Kenkichi Iwasawa Collected Papers, vol. 2, Springer, Berlin, 2001, pp. 862-870) we give a sufficient condition for Leopoldt's conjecture (J. Reine Angew. Math. 209 (1962) 54) on the non-vanishing of the p-adic regulator of an algebraic number field. Using this sufficient condition we are able to prove Leopoldt's conjecture for several non-Galois extensions over the rational number field Q. 相似文献