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101.
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103.
The problem of matrix interference encountered in the determination of lead in natural and drinking waters by graphite furnace atomic absorption spectrometry is examined by looking at the individual effects of various constituent salts (NaCl, KCl, MgCl2 and CaCl2, Na2SO4, KH2PO4 and Mg(NO3)2), of which MgCl2 and Na2SO4 interfered most severely. The use of the L'vov platform decreased the sulphate interference, but was not successful in removing the other interferences. The mixture of 0.05% (w/v) lanthanum (as LaCl3) and 1% (v/v) nitric acid previously proposed for wall atomisation was found to be effective in controlling the interferences. Nitric acid alone removed almost completely the effects of MgCl2 and CaCl2, but had little effect on the interference of sulphate, which required the addition of lanthanum for suppression. The removal of interferences in real water samples by the lanthanum/nitric acid mixture is demonstrated by comparison of results obtained by this approach with those obtained by atomic fluorescence spectrometry and by flame atomic absorption spectrometry after preconcentration by evaporation. 相似文献
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105.
(C6F5)3Sb has been found to react with interhalogens and halo-pseudohalogens, IX(X = Cl, Br, N3 and NCO), pseudohalogen (SCN), and elemental sulphur to give oxidative addition products (I–VI). (C6F5)3SbS(VI) may also be prepared by the reaction of (C6F5)3SbCl2 with H2S. Metathetical reactions of (C6F5)3SbCl2 with appropriate metallic salts yield covalent pentacoordinate disubstituted products (V, VII–XII) of the general formula, (C6F5)3SbY2 (Y = NCS, NCO, ?ONCMe2, ?ONCMePh O and p-NO2C6H4OCO). Treatment of (C6F5)3SbCl2 with aqueous NaN3 gives the binuclear oxo-bridge compound, [(C6F5)3SbOSb(C6F5)3](N3)2·(III) and (IV) are also accessible by displacement reaction of (I) or (II) with the corresponding metallic salt. Molecular weight, conductance measurements, and IR spectra on the new organoantimony(V) derivatives have been obtained.Reductive cleavage reactions of (C6F5)3SbS with hexaaryldileads, Ar6Pb2(Ar = Phenyl, p-tolyl) produce (C6F5)3Sb and the corresponding bis(triaryllead) sulphide but treatment of (C6F5)3SbX2(X = NCO, Cl) with Ar6Pb2 gave Ar4Pb and Ar2PbX2 together with (C6F5)3Sb.(C6F5)3SbCl2 and bis(triorganotin)sulphides undergo exchange of anionic groups. 相似文献
106.
The reaction of methyl 5(4)-cyanomethylimidazole-4(5)-carboxylate with hydroxylamine provided methyl 5(4)-carboxamidoximylmethylimidazole-4(5)-carboxylate which cyclized on reduction Lo yield 3-deazaguanine. 相似文献
107.
Rakesh?Kumar?Mahajan Jyoti?Chawla Mandeep?Singh?BakshiEmail author Gurinder?Kaur Vinod?Kumar?Aswal Prem?Sagar?Goyal 《Colloid and polymer science》2004,283(2):164-168
Small-angle neutron scattering (SANS) and turbidity measurements have been carried out on the nonionic surfactants Tween 20 and Tween 80, in the presence of diethyleneglycol (DEG), triethyleneglycol (TEG), ethylene glycol monoethyl ether (EGMEE), and ethyleneglycol mono butyl ether (EGMBE). SANS measurements show that the shapes of the Tween 20 and Tween 80 micelles are oblate ellipsoidal, which do not change predominantly in the presence of DEG and TEG. However, the presence of EGMBE and EGMEE reduces the aggregation number of Tween. This has been attributed to the solubilization of EGMBE and EGMEE in the Tween micelles, providing them with additional hydrophobicity. 相似文献
108.
The structures of thermodynamically stable aromatic boronic acid : cyclic carbohydrate chelates in aqueous alkaline media have been studied using 1H NMR spectroscopy and molecular modelling. It is found that interacting saccharides must necessarily possess a synperiplanar diol functionality for complexation to occur. While this is possible for furanose structures which tend to have a puckered planar geometry, for pyranose forms it is postulated that bis-complexation occurs with twist conformers of the pyranose ring, providing the ring has the requisite 1,2 : 3,4 polyol stereochemistry; specifically axial,equatorial : equatorial,axial or equatorial,axial : axial,equatorial orientations. In this respect it is possible to be predictive with regard to individual carbohydrate boronic acid interactions and to give reasonably comprehensive structural assignments to complexed components. In this paper twenty four polyhydroxy compounds have been screened using 1H NMR to monitor complexation along with computational techniques on a model system to substantiate proposed structures. It has been found that all of these materials interact with aromatic mono boronic acids as expected and structures for the resulting chelates are proposed. 相似文献
109.
Summary The kinetics of oxidation of malonic acid by both [MnO4]– and MnO2 have been studied in an HClO4 medium. The oxidation product of the organic acid was found to be glyoxylic acid. A reaction mechanism assuming complexation between MnO2 and malonic acid is suggested. The rate is independent of [H+]. 相似文献
110.
4'-(2,6,6-Trimethyl-2-cyclohexen-1-yl)-3'-buten-2'-ketoxime-N-O-alkyl ethers have been synthesized starting from alpha-ionone, separated into their E and Z isomers and characterized on the basis of (1)H-NMR and mass spectra. 相似文献