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61.
62.
S. Vratislav J. Zajíček Z. Jirák A.F. Andresen 《Journal of magnetism and magnetic materials》1977,5(1):41-50
Neutron diffraction study on samples MnxCr3?xO4 with x=1.0, 1.2, 1.4 and 1.6 has been performed at temperatures below ~40 K where magnetic ordering is present. At 5 K the structure of the MnCr2O4 compound was found to be a general LKDM magnetic spiral with the propagation vector deviating by 13.3″ from the [110] axis. This results differs from previous findings. At about 16 K the structure becomes collinear. In samples higher content of manganese the magnetic structure is collinear over the whole temperature region (5–40) K, i.e. in the sense of long range ordering. However, a short range ordering of the transverse components of the spins is present both in these samples and in MnCr2O4 above 16 K. 相似文献
63.
M. Dlouhá J. Hejtmánek Z. Jirák K. Kní?ek P. Tome? S. Vratislav 《Journal of magnetism and magnetic materials》2010,322(9-12):1189-1191
The electric transport and magnetic susceptibility of double perovskites La2?xSrxCoRuO6 have been studied over a temperature range up to 800–1000 K. The crystal and magnetic structure has been determined by neutron diffraction on two samples of the series, x=0.6 and 1.4, which represent the electron- and hole-doped systems with respect to “ideal” single-valent insulator x=1. The study shows that spins in both the Co and Ru f. c. c. like sublattices exhibit a long-range ordering of the antiferromagnetic type II (TN=60 K for x=0.6 and TN=60–80 K for x=1.4). 相似文献
64.
Sýkora J Blechta V Sychrovský V Hetflejs J Sabata S Soukupová L Schraml J 《Magnetic resonance in chemistry : MRC》2006,44(7):669-674
29Si-13C couplings were measured in para substituted silylated phenols, X--C6H4--O--SiR1R2R3 (X = NO2, CF3, Cl, F, H, CH3, CH3O). The SiR1R2R3 silyl groups included trimethylsilyl (Si(CH3)3, TMS), tert-butyldimethylsilyl (Si(CH3)2C(CH3)3, TBDMS), dimethylsilyl (SiH(CH3)2, DMS), and tert- butyldiphenylsilyl (Si(C6H5)2C(CH3)3, TBDPS). Previously developed (Si,C,Si)gHMQC methods and narrow 29Si lines allowed the determination of coupling constants over up to five bonds. Besides the number of intervening bonds between the silicon and carbon atoms, all the measurable couplings depend also on the nature of the substituents on the silicon. The two- and three-bond couplings are not affected by ring substitution in the para position. These properties render the 29Si-13C couplings suitable for line assignment in the spectra of silylated polyphenols. The experimental results are in reasonable agreement with theoretical calculations. The calculations show, in agreement with the data reported in the literature for couplings between other nuclei, that the two-bond and three-bond couplings, which are of similar magnitudes, are of opposite signs. If the signs of these geminal and vicinal couplings could be determined experimentally, they would greatly facilitate the line assignment. The four- and five-bond couplings are affected by the substituent X in a nontrivial manner. 相似文献
65.
Eva Scholtzová Vratislav Langer Ľubomír Smrčok Miroslav Koóš Vlasta Sasinková Ján Hirsch 《Journal of chemical crystallography》2011,41(2):167-174
Abstract
The crystal structure of benzyl 2,3-anhydro-β-d-ribopyranoside is orthorhombic, P212121, Z = 4. The pyranose ring adopts the E O conformation distorted considerably to the 5 H O direction. The molecules of the title compound are linked into infinite chains running along the a-axis by bifurcated O–H···O hydrogen bonds. Interaction energies of these hydrogen bonds are significantly different, ~−5.4 for the bond with the smaller and ~−1.1 kcal/mol for the bond with the larger O···O separation. The hydrogen-bond pattern is completed by the two weaker C–H···O intermolecular hydrogen bonds, aiming at the epoxy oxygen atom. IR vibrational spectrum was interpreted by means of comparison with the full list of vibrational modes predicted using DFT method in the solid state. While till 1495 cm−1 the individual bands can be reconciled with single calculated modes, the region below this limit is populated by heavily overlapped HCH, HCO, HOC, COC and HCC bending modes merged with few ν(CC) and ν(CO) modes. The respective “red” shifts of the positions of the ν(OH) bands correlate well with the size of the O···O separation. 相似文献66.
Abu-Youssef MA Soliman SM Langer V Gohar YM Hasanen AA Makhyoun MA Zaky AH Öhrström LR 《Inorganic chemistry》2010,49(21):9788-9797
[Ag(2-amino-3-methylpyridine)(2)]NO(3) (1) and [Ag(pyridine-2-carboxaldoxime)NO(3)] (2) were prepared from corresponding ligands and AgNO(3) in water/ethanol solutions, and the products were characterized by IR, elemental analysis, NMR, and TGA. The X-ray crystal structures of the two compounds show that the geometry around the silver(I) ion is bent for complex 1 with nitrate as an anion and trigonal planar for complex 2 with nitrate coordinated. ESI-MS results of solutions of 2 indicate the independent existence in solution of the [Ag(pyridine-2-carboxaldoxime)](+) ion. The geometries of the complexes are well described by DFT calculations using the ZORA relativistic approach. The compounds were tested against 14 different clinically isolated and four ATCC standard bacteria and yeasts and also compared with 17 commonly used antibiotics. Both 1 and 2 exhibited considerable activity against S. lutea , M. lutea , and S. aureus and against the yeast Candida albicans , while 2-amino-3-methylpyridine is slightly active and pyridine-2-carboxaldoxime shows no antimicrobial activity. In addition, the interaction of these metal complexes with DNA was investigated. Both 1 and 2 bind to DNA and reduce its electrophoretic mobility with different patterns of migration, while the ligands themselves induce no change. 相似文献
67.
Pavel Mach Vratislav Langer Eva Scholtzov Tom Sol
an
ubomír Smr
ok 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):o544-o546
Molecules of the title compound, C11H10N2O, are effectively planar. In the crystal structure, they are stabilized primarily by electrostatic interactions, as the dipole moment of the molecule is 4.56 D. In addition, the molecules are linked by weak C—H⋯N and C—H⋯O hydrogen bonds. An analysis of bonding conditions in the molecule was carried out using natural bond orbital (NBO) formalism. 相似文献
68.
Syntheses, crystal structures and thermal behavior of two new hydrated cerium(III) sulfates are reported, Ce2(SO4)3·4H2O ( I ) and β‐Ce2(SO4)3·8H2O ( II ), both forming three‐dimensional networks. Compound I crystallizes in the space group P21/n. There are two non‐equivalent cerium atoms in the structure of I , one nine‐ and one ten‐fold coordinated to oxygen atoms. The cerium polyhedra are edge sharing, forming helically propagating chains, held together by sulfate groups. The structure is compact, all the sulfate groups are edge‐sharing with cerium polyhedra and one third of the oxygen atoms, belonging to sulfate groups, are in the S–Oμ3–Ce2 bonding mode. Compound II constitutes a new structure type among the octahydrated rare‐earth sulfates which belongs to the space group Pn. Each cerium atom is in contact with nine oxygen atoms, these belong to four water molecules, three corner sharing and one edge sharing sulfate groups. The crystal structure is built up by layers of [Ce(H2O)4(SO4)]nn+ held together by doubly edge sharing sulfate groups. The dehydration of II is a three step process, forming Ce2(SO4)3·5H2O, Ce2(SO4)3·4H2O and Ce2(SO4)3, respectively. During the oxidative decomposition of the anhydrous form, Ce2(SO4)3, into the final product CeO2, small amount of CeO(SO4) as an intermediate species was detected. 相似文献
69.
New Zn(II), Fe(II) and Mn(II) complexes with a combination of nitrogen-donor ligands and trithiocyanuric acid (ttcH3) were prepared and characterized by elemental analysis, IR and UV–Vis spectroscopies. The antitumor activity of the prepared complexes, together with already known Ni(II) species, were assayed in vitro against G-361 (human malignant melanoma), HOS (human osteogenic sarcoma), K-562 (human chronic myelogenous leukaemia) and MCF-7 (human breast adenocarcinoma) tumor cell lines. The IC50 values of the Fe(II) and Mn(II) compounds turned out to be lower than those of cisplatin and oxaliplatin. The antimicrobial activities were evaluated by MIC against bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecalis). The molecular structure of [Zn(taa)(ttcH)] · H2O (taa = tris(2-aminoethyl)amine) was determined by X-ray diffraction. The central atom is pentacoordinated by four N atoms of taa and one N atom of the ttcH dianion. 相似文献
70.
Schraml J Tkadlecová M Pataridis S Soukupová L Blechta V Roithová J Exner O 《Magnetic resonance in chemistry : MRC》2005,43(7):535-542
NMR spectra (1H, 13C, 15N) of para- and meta-substituted benzohydroxamic acids were studied in dry dimethyl sulfoxide solutions. The 13C chemical shifts were very close to those found by cross-polarization magic angle spinning in solids, the hydroxamic (not hydroximic) structure of which is unambiguous. The hydroxamic structure of these acids in DMSO solutions was proved independently by their 15N chemical shifts. The 15N and 1H chemical shifts of the NH-OH fragment showed excellent mutual dependences and dependences on the nature of the ring substituent. According to these dependences and ab initio energy calculations, all the acids assume the same Z conformation. Proton exchange between hydroxamic OH and NH groups in DMSO proceeded by both intra- and intermolecular exchange and the rates did not exhibit any simple relationship to the substituent constants. 相似文献