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81.
Kazutoshi Kobayashi Gerhard Wenz Wolfgang Knoll 《Journal of inclusion phenomena and macrocyclic chemistry》1997,28(4):349-358
Lipophilic cyclodextrin (CD) derivatives were prepared to extract alkali metal cations from a water phase into an organic phase. The extraction equilibrium constant, K ex, was determined by the solvent extraction method using UV absorption spectroscopy. Hydroxyl groups at the carbons in the 2,6-positions of CD molecules were dipropylated to add the hydrophobicity for dissolving into organic solvents, and furthermore hydroxyl groups at the carbons in the 3-position of these derivatives were acylated as complexing sites with the alkali metal cations. These CD derivatives formed a 1 : 1 complex with alkali metal cations, except for the case of Li+, and transported the alkali metal cations from a water phase into a benzene phase. The initial concentrations of alkali metal cation and picrate anion in the water phase and that of the CD derivatives in the organic phase strongly influenced the extraction equilibrium. Extraction of the alkali metal cation by the derivative without acyl groups was not detected. K ex values of these CD derivatives are of the same order of magnitude as or larger than those of crown ethers. The order of the K ex values in all cases is Li+ < Na+ < K+ Rb+ Cs+, although these CD derivatives have no special selectivity for the alkali metal cations. The cation extraction mechanism was interpreted by an induced-fit mechanism. 相似文献
82.
Takashima H Yamada S Obara S Kitamura K Inabata S Miyakawa N Tanabe K Nagashima U 《Journal of computational chemistry》2002,23(14):1337-1346
We developed a novel parallel algorithm for large-scale Fock matrix calculation with small locally distributed memory architectures, and named it the "RT parallel algorithm." The RT parallel algorithm actively involves the concept of integral screening, which is indispensable for reduction of computing times with large-scale biological molecules. The primary characteristic of this algorithm is parallel efficiency, which is achieved by well-balanced reduction of both communicating and computing volume. Only the density matrix data necessary for Fock matrix calculations are communicated, and the data once communicated are reutilized for calculations as many times as possible. The RT parallel algorithm is a scalable method because required memory volume does not depend on the number of basis functions. This algorithm automatically includes a partial summing technique that is indispensable for maintaining computing accuracy, and can also include some conventional methods to reduce calculation times. In our analysis, the RT parallel algorithm had better performance than other methods for massively parallel processors. The RT parallel algorithm is most suitable for massively parallel and distributed Fock matrix calculations for large-scale biological molecules with more than thousands of basis functions. 相似文献
83.
Norihiko Misawa Ryoko Nakamura Yukiko Kagiyama Hiroshi Ikenaga Kensuke Furukawa Kazutoshi Shindo 《Tetrahedron》2005,61(1):195-204
Various aromatic molecules, in which heterocycles are linked with a phenyl or benzyl group, were converted to their respective 2,3-diols (catechols) in the benzene ring by growing cell reactions using recombinant Escherichia coli, which expressed the evolved biphenyl dioxygenase [bphA (2072)] genes and the subsequent bacterial dihydrodiol dehydrogenase (bphB) gene. These vicinal diol products showed strong in vitro inhibitory activity against the lipid peroxidation induced by free radicals and strong scavenging activity towards DPPH radicals. The vicinal diols were also synthesized from ionized monocyclic aromatics incorporating an amino or carboxyl group. 相似文献
84.
Ming-Rong Zhang Masanao Ogawa Kenji Furutsuka Yuichiro Yoshida Kazutoshi Suzuki 《Journal of fluorine chemistry》2004,125(12):1879-1886
In this study, we report the synthesis and reactivity of [18F]fluoromethyl iodide ([18F]FCH2I) with various nucleophilic substrates and the stabilities of [18F]fluoromethylated compounds. [18F]FCH2I was prepared by reacting diiodomethane (CH2I2) with [18F]KF, and purified by distillation in radiochemical yields of 14-31% (n = 25). [18F]FCH2I was stable in organic solvents commonly used for labeling and aqueous solution with pH 1-7, but was unstable in basic solutions. [18F]FCH2I displayed a high reactivity with various nucleophilic substrates such as phenol, thiophenol, amide and amine. The [18F]fluoromethylated compounds synthesized by the reactions of phenol, thiophenol and tertiary amine with [18F]FCH2I were stable for purification, formulation and storage. In contrast, the [18F]fluoromethylated compounds synthesized by the reactions of primary or secondary amines, and amide with [18F]FCH2I were too unstable to be detected or purified from the reaction mixtures. Defluorination of these [18F]fluoromethyl compounds was a main decomposition route. 相似文献
85.
Kazutoshi Shindo Tomohisa Hasunuma Aya Sano Noriko Minemura Takashi Maoka 《Tetrahedron letters》2008,49(20):3294-3296
Higher plants do not ordinarily possess ketocarotenoids due to the absence of a carotenoid ketolase enzyme. We expressed genes coding for marine-bacterial enzymes β-carotene ketolase (CrtW) and β-carotene hydroxylase (CrtZ) in tobacco plants (Nicotiana tabacum) by transplastomic engineering. A novel carotenoid, 4-ketoantheraxanthin, was isolated from the leaves of the tobacco transformants. The structure of 4-ketoantheraxanthin was determined to be (3S,3′S,5′R,6′S)-5′,6′-epoxy-3,3′-dihydroxy-β,β-caroten-4-one by analysis of the MS, NMR, and CD data. This carotenoid was considered to be synthesized by a 4-ketolation reaction by CrtW of antheraxanthin that had been synthesized by the endogenous carotenoid biosynthetic enzymes present in higher plants and CrtZ. 4-Ketoantheraxanthin was also shown to have potent antioxidative activity against a 1O2 suppression model. 相似文献
86.
Katayama H Nagao M Nishimura T Matsui Y Umeda K Akamatsu K Tsuruoka T Nawafune H Ozawa F 《Journal of the American Chemical Society》2005,127(12):4350-4353
Geometrically pure, all-cis poly(phenylene vinylenes) (PPVs) are synthesized by Suzuki-Miyaura-type polycondensation of 2,5-dioctyloxy-1,4-benzenediboronic acid with (Z,Z)-bis(2-bromoethenyl)benzenes, which are prepared by ruthenium-catalyzed (Z)-selective double hydrosilylation of diethynylbenzenes, followed by bromodesilylation of the resulting (Z,Z)-bis(2-silylethenyl)benzenes with N-bromosuccinimide. The all-cis PPVs thus obtained undergo one-way photoisomerization to the corresponding trans-PPVs both in solution and in the solid. This phenomenon is applied to direct microscale patterning of PPVs onto a quartz substrate. 相似文献
87.
Takemoto Y Watanabe H Uchida K Matsumura K Nakae K Tashiro E Shindo K Kitahara T Imoto M 《Chemistry & biology》2005,12(12):1337-1347
Cancer cell migration is a required step in cancer metastasis. We screened for inhibitors of cancer cell migration of microbial origin, and obtained moverastin, a member of the cylindrol family, from Aspergillus sp. F7720. However, the results of an NMR spectroscopic analysis raised the possibility that moverastin is a mixture of two diastereomers. Separation of the C-10 epimers of synthetic moverastin and a bioassay revealed that both diastereomers (moverastins A and B) had inhibitory effects on cell migration. Furthermore, we demonstrated that moverastins A and B inhibited FTase in vitro, and they also inhibited both the membrane localization of H-Ras and the activation of the PI3K/Akt pathway in EC17 cells. Thus, moverastins inhibited the migration of tumor cells by inhibiting the farnesylation of H-Ras, and subsequent H-Ras-dependent activation of the PI3K/Akt pathway. 相似文献
88.
Hideaki Kasimura Keiki Kishikawa Shigeo Kohmoto Makoto Yamamoto Kazutoshi Yamada 《Analytica chimica acta》1990
N,N′-Bis[(S)-1-phenylethyl]carbodiimide (1) was found to be an efficient chiral derivatizing agent for the diastereomeric separation of 2-N-benzyloxycarbonylamino acids (2). Diastereomeric acylureas prepared from 1 and 2 showed a large chromatographic selectivity (α). Their capacity factors and selectivity depend on the carbon chain length of the α-alkyl substituents of acylureas. 相似文献
89.
Yasuyuki Sasada Corresponding author Kazutoshi Miyazawa Dietrich Demus 《Liquid crystals》2013,40(12):1371-1375
A series of liquid crystalline 3,4-difluoropyrrole derivatives have been synthesized, and their dielectric anisotropy, birefringence, viscosity and phase sequences have been measured. This novel class of compounds showed extremely large dielectric anisotropy, exceeding that of 3,4,5-trifluorophenyl derivatives, induced by a combination of the C–F dipole moment and the electron-donating feature of the nitrogen atom in the 3,4-difluoropyrrole ring. Molecular modelling using molecular orbital calculations has been performed and the results compared with the experimentally evaluated physical properties. 相似文献
90.
Hirotada Iida Keishiro Hayashida Mitsuaki Yamada Kazumasa Takahashi Kazutoshi Yamada 《合成通讯》2013,43(3):225-230
The general synthetic method of pyrazines1 has been established. The method for synthesizing symmetrically substituted pyrazine derivatives, however, has not been well-studied.2 Especially for synthesis of the title pyrazines, it is only described in a few words by Adkins3 and co-workers that ethyl 2-aminoacetoacetate employed in process to preparing of the threonine synthesis is spontaneously autoxidized to give 2,5-dimethyl-3,6-dicarbetoxy pyrazine as a byproduct. On the basis of this finding of Adkins, we have established a convenient method for the synthesis of 2,5-di-methylpyrazine-3,6-dicarboxylic acid derivatives (D1–5) using the corresponding acetoacetic acid derivatives (A1–4) as the starting materials (Scheme). 相似文献