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排序方式: 共有71条查询结果,搜索用时 31 毫秒
11.
Dr. Yukio Hitotsuyanagi Masumi Odagiri Saori Kato Jun‐ichi Kusano Tomoyo Hasuda Haruhiko Fukaya Prof. Dr. Koichi Takeya 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2839-2846
Two bicyclic hexapeptides, allo‐RA‐V ( 4 ) and neo‐RA‐V ( 5 ), and one cyclic hexapeptide, O‐seco‐RA‐V ( 6 ), were isolated from the roots of Rubia cordifolia L. Their gross structures were elucidated on the basis of spectroscopic analysis and X‐ray crystallography of compound 5 . The absolute stereochemistry of compounds 4 and 5 were established by their total syntheses, and the absolute stereochemistry of compound 6 by chemical correlation with deoxybouvardin ( 3 ). Comparison of the 3D structures of highly active RA‐VII ( 1 ) with less‐active compounds 4 and 5 suggests that the orientation of the Tyr‐5 and/or Tyr‐6 phenyl rings plays a significant role in their biological activity. The isolation of peptides 4 – 6 , along with compound 3 , and the comparison of their structures seem to indicate that peptide 6 may be the common precursor to bicyclic peptides 3 – 5 in the plant. 相似文献
12.
Daisuke Suzuki Tomoyo Yamagata Koji Horigome Kiyoshi Shibata Akira Tsuchida Tsuneo Okubo 《Colloid and polymer science》2012,290(2):107-117
Influence of the gel size on the morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermo-sensitive
gel spheres, poly (N-isopropylacrylamide) (pNIPAm), was discussed by adding the data of two gel samples of pNIPAm(400–5) and pNIPAm(600–5) of
412 nm (at 25 °C) and 220 nm (at 45 °C) and of 517 nm (at 20 °C) and 294 nm (at 45 °C), respectively. Colloidal single crystals
formed, but not so large compared with the giant crystals of small pNIPAm gels reported previously. The suspensions even with
ion-exchange resins were turbid and hard to observe the single crystals clearly with the naked eyes as gel size increased.
The critical concentration of melting decreased sharply as the suspensions were deionized with coexistence of the mixtures
of cation- and anion-exchange resins. The critical concentration increased as the gel size increased and/or dispersion temperature
increased. Density of the gel spheres increased as their size increased. These results demonstrated that the colloidal crystallization
takes place by the extended electrical double layers formed around the gel spheres in addition of the excluded volume effect of the gels. Contribution of the electrical double layers on the crystallization increased sharply as temperature increased
and gel concentration decreased, respectively. The contribution also increased slightly as sphere size increased, when comparison
was made at the same gel concentration in wt.%. The present work clarified that the colloidal interfaces, which are inevitable
for the formation of the electrical double layers, are formed between the water phase and gel spheres, though the gel spheres
contain a lot of water molecules at the inner sphere region. 相似文献
13.
Takeshi Yamanobe Tadashi Komoto Yoshiko Sakaino 《Molecular Crystals and Liquid Crystals》2013,570(1-2):273-282
Abstract Solid state NMR measurements are carried out for polymorphs and inclusion complexes of 4,5-bis(4-methoxyphenyl)-2-(3-nitrophenyl)-1H-imidazole. Observed 13C and 15N chemical shifts are characteristic of each polymorph A, B, C and D. In addition, 15N chemical shift was a good index for understanding hydrogen bond. VT measurements revealed that B transforms to C between 93 and 113°C. From PSTMAS and 1H solid echo measurements for AcOET inclusion complex, host molecules have almost same structure as B and guest molecules have the highest mobility of all inclusion complexes. 相似文献
14.
Tsuneo Okubo Daisuke Suzuki Tomoyo Yamagata Akihiro Katsuno Masashi Mizutani Hiroshi Kimura Akira Tsuchida 《Colloid and polymer science》2011,289(7):807-816
Drying dissipative patterns were observed at 25 °C, 33 °C, and 45 °C on a cover glass, a watch glass, and a Petri glass dish
during the course of dryness of colloidal crystals of the thermo-sensitive gels of poly(N-isopropylacrylamide) (PNIPA). Two kinds of broad rings, i.e., transparent ring at the outside edge and the ring in the inner
area from the edge, were observed. Sizes of the former were the same as those of the initial liquids irrespective of gel concentration,
whereas sizes of the latter decreased as gel concentration decreased. These broad rings were composed mainly of the monomeric
and the agglomerated gel particles, respectively. Formation of the monodispersed agglomerated particles and their ordered
arrays in the inner area of the dried film were observed especially on a Petri glass dish and a watch glass. The important
role of the electrical double layers formed around the agglomerated particles is supported for the ordering of the agglomerated
particles. The essential differences in the drying patterns between PNIPA gel spheres and the typical colloidal particles
did not appear. 相似文献
15.
Uehara H Asakawa T Kakiage M Yamanobe T Komoto T 《Langmuir : the ACS journal of surfaces and colloids》2006,22(11):4985-4991
The surface-deformation characteristics of uniaxially drawn poly(ethylene terephthalate) (PET) film were successfully evaluated with multiline scratch tests using scanning probe microscopy (SPM) on a nanometer scale. The PET film was prepared by compression molding from the melt, followed by quenching in ice water. The obtained amorphous film was drawn uniaxially below its glass-transition temperature, and the resultant surface roughness could be reduced to within 5 nm. A multiline scratch with the Si(3)N(4) tip of an SPM on the oriented PET surface was made parallel and perpendicular to the drawing axis under applied loads of 5-30 nN. The perpendicular scratching generated a characteristic periodic pattern on the film surface, but the parallel scratching induced a tearing of the surface. These results suggest that surface-deformation mechanisms were dominated by molecular anisotropy. The surface-deformation properties, as evaluated from scratch-angle dependences on morphological changes on a nanometer scale, were similar to the mechanical properties of the bulk. 相似文献
16.
Comprehensive analysis system using liquid chromatography-mass spectrometry for the biosynthetic study of peptides produced by cyanobacteria 总被引:2,自引:0,他引:2
Microcystins are hepatotoxic heptapeptides and general tumor promoters produced by several species of the genera Microcystis, Anabaena, Oscillatoria and Nostoc. They are non-ribosomally synthesized via a mixed polyketide synthase/non-ribosomal peptide synthetase system called microcystin synthetase. We have carried out the detection, isolation and structural determination of non-toxic peptides produced together with microcystins by toxic cyanobacteria, which are classified into several groups on the basis of their structures and some of these non-toxic peptides are also non-ribosomally synthesized as well as microcystins. In the present study, we tried to correlate the secondary metabolic peptides produced by the hepatotoxic cyanobacteria with the corresponding peptide synthetase genes. An analytical method using LC-electroscopy ionization MS and photodiode array detection was developed for the exhaustive screening of cyanobacterial peptides in Japanese strains and it was successfully applied to the peptide fractions extracted from these strains. The established method was advantageous over conventional ones using the usual HPLC and matrix-assisted laser desorption ionization time-of-flight MS, because more structural information could be obtained and it is easier to distinguish microcystins from other peptides using this method. Small amounts of other peptides could also be detected by this method. The established method will contribute to the investigation of the relationship between genes encoding the peptide synthetase and secondary metabolic peptides. 相似文献
17.
Tamiko Takahashi Hiroaki Kameda Tomoyo Kamei Jyunichi Koyanagi Fabio Pichierri Kenji Omata Miyuki Ishizaki Hiroshi Nakamura 《Tetrahedron: Asymmetry》2013,24(17):1001-1009
Optically active 1-fluoroindan-1-carboxylic acid (FICA) was designed and prepared as its methyl ester for determining the absolute configuration of chiral molecules by both 1H and 19F NMR spectroscopies. Enantiomerically pure isomers of FICA methyl esters (FICA Me esters) were obtained by chromatographic separation using HPLC with a Daicel Chiralcel OJ-H column. The absolute configuration of the (+)-FICA Me ester was deduced to be (S) by X-ray crystallographic analysis of the (+)-FICA amide of (R)-α-phenethylamine. Both enantiomers were derived to the diastereomeric esters of chiral secondary alcohols by an ester exchange reaction. In the 1H NMR spectra, the signs of ΔδH (δR ? δS) were consistent on each side of the FICA molecular plane. Therefore, the concept of the modified Mosher’s method could be successfully applied to the FICA-based procedure. Moreover, the consistency in the signs of ΔδF (δR ? δS) values suggests that the FICA method would be reliable in assigning the absolute configurations of secondary alcohols based on 19F NMR spectroscopy. 相似文献
18.
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20.
Masami Takenaka Takeshi Yamanobe Tadashi Komoto Isao Ando Hisaya Sato Kazuo Sato 《Journal of Polymer Science.Polymer Physics》1987,25(10):2165-2178
Temperature-dependent measurements have been made on the proton NMR relaxations and proton linewidths of the cyclic paraffins (c-C24H48, c-C28H56, and c-C128H256) in the solid state. It is found that in c-C24H48 and c-C128H256 there exist two transitions, one due to the melting process and the other due to a rapid transition between trans and gauche conformers in a compact structure that consists of two parallel trans zigzag straight chains bridged at both ends in the crystalline state. In c-C28H56 there exists only the transition due to melting. Proton NMR relaxations have also been measured for c-C40H80 and c-C160H320 at room temperature, in addition to those for c-C24H48, c-C28H56, and c-C128H256. It is found that the extent of molecular motion decreases as the chain length increases. 相似文献