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71.
The complexes of yttrium and heavy lanthanides with 2,4-dimethoxybenzoic acid of the formula: Ln(C9H9O4)3×nH2O, where Ln=Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(III), n=2 for Tb(III), Dy(III), Ho(III), Er(III), Tm(III)
and Y(III), and n=0 for Yb(III) and Lu(III), have been synthesized and characterized by elemental analysis, IR spectroscopy, themogravimetric
studies, as well as X–ray and magnetic susceptibility measurements. The complexes have a colour typical of Ln
3+ salts (Tb, Dy, Tm, Yb, Lu, Y – white, Ho – cream, Er – pink). The carboxylate group in these complexes is a bidentate, chelating
ligand. The compounds form crystals of various symmetry. 2,4-Dimethoxybenzoates of Yb(III) and Lu(III) are isostructural.
2,4-Dimethoxybenzoates of yttrium and heavy lanthanides decompose in various ways on heating in air to 1173 K. The hydrated
complexes first lose water to form anhydrous salts and then decompose to the oxides of respective metals. The ytterbium and
lutetium 2,4-dimethoxybenzoates decompose in one step to form Yb2O3 and Lu2O3.
The solubilities of the 2,4-dimethoxybenzoates of yttrium and heavy lanthanides in water and ethanol at 293 K are of the order
of: 10–3 and 10–3 –10–2 mol dm–3, respectively. The magnetic moments for the complexes were determined over the range of 77–298 K. They obey the Curie–Weiss
law. The results show that there is no influence of the ligand field on the 4f electrons of lanthanide ions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
72.
A new method for the intramolecular glycosylation of alcohols is described. Utilizing carbohydrate-derived silanes, the catalytic dehydrogenative silylation of alcohols is followed by intramolecular glycosylation. Appropriate combinations of silane position and protecting groups allow highly selective access to β-manno, α-gluco, or β-gluco stereochemical relationships as well as 2-azido-2-deoxy-β-gluco- and 2-deoxy-β-glucosides. Intramolecular aglycone delivery from the C-2 or C-6 position provides 1,2-cis or 1,2-trans glycosides, respectively. Multifunctional acceptor substrates such as hydroxyketones and diols are tolerated and are glycosylated in a site-selective manner. 相似文献
73.
74.
Lattice QCD is widely considered the correct theory of the strong force and is able to make quantitative statements in the low energy regime where perturbation theory is not applicable. The partition function of lattice QCD can be mapped onto a statistical mechanics system which then allows for the use of calculational methods such as Monte Carlo simulations. In recent years, the enormous success of GPU programming has also arrived at the lattice community. In this article, we give a short overview of Lattice QCD and motivate this need for large computing power. In our simulations we concentrate on a specific fermionic discretization, so-called Neuberger-Dirac fermions, which respect an exact chiral symmetry. We will discuss the algorithms we use in our GPU implementation which turns out to be an order of magnitude faster then the conventional CPU-equivalent. As an application we present results on the eigenvalue spectra in QCD and compare them to analytical calculations from Random Matrix Theory. 相似文献
75.
Claus O. Schmidt Harro J. Bouwmeester Jan-Willem de Kraker Wilfried A. Knig 《Angewandte Chemie (International ed. in English)》1998,37(10):1400-1402
Two different enantioselective sesquiterpene synthases catalyze the biosynthesis of the enantiomers (+)- and (−)-germacrene D ( 1 a and 1 b , respectively) in the plant Solidago canadensis, from which they were isolated and characterized for the first time. 相似文献
76.
77.
The complexes of yttrium and heavy lanthanides with 3,4-dimethoxybenzoic acid of the formula: Ln(C9 H9 O4 )3 ×n H2 O, where Ln =Y(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III), and n =4 for Tb(III), Dy(III), n =3 for Ho(III), and n =0 for Er(III), Tm(III), Yb(III), Lu(III) and Y(III) have been prepared and characterized by elemental analysis, IR spectroscopy,
thermogravimetric and magnetic studies and X-ray diffraction measurements. The complexes have colours typical of Ln3+ ions (Ho - cream, Tb, Dy, Yb, Lu, Y - white, Er - salmon). The carboxylate group in these complexes is a symmetrical, bidentate,
chelating ligand. They are crystalline compounds characterized by various symmetry. On heating in air to 1273 K the hydrated
3,4-dimethoxybenzoates decompose in two steps while those of anhydrous only in one stage. The tetrahydrates of Tb and Dy and
trihydrate of Ho 3,4-dimethoxybenzoates are firstly dehydrated to form anhydrous salts that next are decomposed to the oxides
of the respective metals. The complexes of Er, Tm, Yb, Lu and Y are directly decomposed to the oxides of the appropriate elements.
The solubility in water at 293 K for yttrium and heavy lanthanides is in the order of 10-4 -10-3 mol dm-3 . The magnetic moments of the complexes were determined over the range 77–298 K. They obey the Curie-Weiss law. The values
of μeff calculated for all compounds are close to those obtained for Ln3+ by Hund and van Vleck. The results show that there is no influence of the ligand field on 4f electrons of lanthanide ions
in these polycrystalline compounds and 4f electrons do not take part in the formation of M-O bonding.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
78.
Thermal and spectral properties of 2,3-, 2,4- and 3,4- dimethoxybenzoates of light lanthanides 总被引:2,自引:0,他引:2
The physico-chemical properties and thermal stability in air of light lanthanide 2,3-, 2,4- and 3,4-dimethoxybenzoates were
compared and the influence of -OCH3 substituent on their thermal stability was investigated. The complexes of these series are crystalline, hydrated or anhydrous
salts with colours typical of Ln3+ ions. The carboxylate group is a bidentate, chelating (2,4- and 3,4-dimethoxybenzoates) or tridentate chelating and bridging
ligand (2,3- dimethoxybenzoates). The thermal stability of 2,4- , 3,4- and 2,3- dimethoxybenzoates of light lanthanides was
studied in the temperature range 273-1173 K. The positions of methoxy groups in benzene ring influence the thermal properties
of the complexes and their decomposition mechanism.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
79.
80.
Harro Walk 《Mathematische Annalen》1970,186(1):36-44
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