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481.
Ciro Esposito Patrizia Colicchio Angelo Facchiano Raffaele Ragone 《Journal of colloid and interface science》1998,200(2):310
The critical micellar concentration of sodium dodecyl sulfate is strongly altered bytris(hydroxy-methyl)methylammonium ions. The effect of buffer solutions containing this weak electrolyte as the counterion source has been studied using various concentrations of the acid–base system as well as modifying the pH. Results show that counterion concentrations ranging from 0 to 340 × 10−3M induce an appreciable diminution of the critical micellar concentration from 8 to 0.7 × 10−3M. The analysis of data suggests that the critical micellar concentration of sodium dodecyl sulfate depends on the concentration of weak electrolytes in a way very similar to that of strong electrolytes. 相似文献
482.
Raffaele Montagnani Pierluigi Riani Oriano Salvetti 《Theoretical chemistry accounts》1982,60(5):399-407
A method for calculating potential energy curves of some low lying states of the diatomic radicals MeIIX (MeII = second group metal, X = halogen) is outlined. Because of the electronic structure of these compounds, applications to electronic transition lasers can be made. The first calculation regards the most simple example of this series, i.e. the BeF radical. The division of the procedure into separated steps allows a sure control of the quality of the results. 相似文献
483.
Synthesis of Methyl Virensate The synthesis of methyl virensate (=methyl 4-formyl-3,8-dihydroxy-1,6,9-trimethyl-11-oxo-11H-dibenzo-[b, e][1,4]dioxepin-7-carboxylate; 18 ) by the condensation of the substituted β-orcinol and orcinol units 9 and 10 followed by formylation and demethylation of the depsidone 13 is described. 相似文献
484.
Gilles Nicollier Michel Rebetez Raffaele Tabacchi Hans Gerlach Adolf Thalmann 《Helvetica chimica acta》1978,61(8):2899-2904
Synthesis of Evernin Two syntheses of the depside evernin 6 are described. Condensation of methyl acetoacetate and methyl crotonate followed by aromatization and reduction with Raney-Ni led to methyl orsellinate (3) . The condensation of everninic acid (4) , obtained by partial methylation of 3 and saponification of the methyl ester, with methyl 2, 4-dihydroxy-3, 6-dimethylbenzoate (methyl β-orcin carboxylate) (5) in presence of cyclohexylcarbodiimide gave evernin ( 6 ). In a second syntheis methyl dihydroorsellinate (1) was regiospecifically converted into its 4-methyl enol ether and aromatized via the benzene selenenyl derivative to yield methyl evernate (7) . Benzylation followed by saponification gave the free acid 8 . Methyl β-orcin carboxylate (5) was synthesized in an analogous way from methyl 3,6-dimethyl-2,4-dioxocyclohexanecarboxylate. Condensation of 8 with the methyl ester 5 by treatment with trifluoroacetic anhydride in toluene yielded 9 , which could be converted into evernin ( 6 ) by hydrogenolysis of the benzyl ether. 相似文献
485.
Tetrabenzyltitanium, tetraphenyltitanium, and tetramethyltitanium were studied by using NMR. spectroscopy. The spectrum of tetrabenzyltitanium depends on the procedure of its preparation. An interpretation of this finding is proposed. 相似文献
486.
Saladino R Neri V Pelliccia AR Caminiti R Sadun C 《The Journal of organic chemistry》2002,67(4):1323-1332
Novel heterogeneous compounds of methylrhenium trioxide (MTO) were prepared with poly(4-vinylpyridine) and polystyrene as polymeric supports. The wide-angle X-ray diffraction (WAXS.) analysis, performed by the application of the difference method, showed, in a representative case of the poly(4-vinylpyridine)/MTO derivatives, a slightly distorted octahedral conformation on the metal's primary coordination sphere. The Re-O and Re-C bond distances were not influenced by the polymeric nature of the ligand, while the Re-N bond distance was abnormally shorter than those previously observed for homogeneous MTO/L(n) complexes, showing a strong coordination of the rhenium atom to the support. A set of scanning electron microscopy (SEM) photographs showing the morphology of the surface of particles of poly(4-vinylpyridine)/MTO and polystyrene/MTO systems are reported. The reticulation grade of the polymer was a crucial factor for the morphology of the particles surface. Poly(4-vinylpyridine) 2% cross-linked systems were characterized by particles with very irregular shape and surface. Poly(4-vinylpyridine) 25% cross-linked systems showed particles with regular spherical shape, which morphology was similar to microcapsules obtained with polystyrene. All novel MTO compounds were efficient and selective heterogeneous catalysts for the epoxidation of olefins using environmentally friendly H2O2 as oxygen atom donor. The catalyst activity was maintained for at least five recycling experiments. 相似文献
487.
A short and efficient protocol for the asymmetric synthesis of cis‐ and trans‐3,4‐dihydro‐2,4,8‐trihydroxynaphthalen‐1(2H)‐one ( 1 and 2 , resp.) is described, with a phthalide annulation as the key step. Introduction of a OH substituent at position 2 was performed by Sharpless dihydroxylation of a silyl enol ether or by means of an N‐sulfonyloxaziridine. The absolute configuration of each isomer was determined via Mosher‐ester derivatives. By comparison with previously recorded CD spectra of our natural sample, we established that the natural trans‐ and cis‐isomers from Ceratocystis fimbriata sp. platani were the (?)‐(2S,4S)‐isomer (?)‐ 2 and the (+)‐(2S,4R)‐isomer (+)‐ 1 , respectively. 相似文献
488.
Gianantonio Battistuzzi Marco Borsari Daniela Dallari Raffaele Battistuzzi 《Transition Metal Chemistry》1995,20(2):212-219
Summary
Tris-, bis- and mono-ligand complexes of NiII with 1-phenyl-4, 6-dimethylpyrimidine-2-thione (L) having the general formulae NiL3X2·2H2O (X = ClO
inf4
p–
, BF
inf4
p–
), NiL2X2 (X = Cl–, Br–, SCN– or NO
inf3
p–
), NiL2X2·EtOAc (X = Br– or I–), NiL2X2·H2O·EtOH (X = I– or NO
inf3
p–
) and NiLCl2·3H2O, were synthesized and their structures deduced from i.r. and electronic spectra, and magnetic properties. The combined evidence is consistent with an octahedral coordination for the NiII ion in all the complexes, with the ligand acting as a bidentate N,S-chelating agent. Spectral evidence, conductivity data and electro-chemical results in DMF solution show that the complexes undergo solvolysis readily. Polarographic and c.v. data for the [NiL3](ClO4)2·2H2O complex and for the [Ni-(DMF)6](ClO4)2-L systems, at increasing ligand concentrations, have shown that in DMF solution the [Ni(DMF)6]2+ cation prevails and that the thiopyrimidine-containing species, [NiL(DMF)5]2+ (L = N-monodentate ligand)
, can be formed only in the presence of a large excess of free ligand.Author to whom all correspondence should be directed. 相似文献
489.
Teresa Pugliese Nicolas Godbert Massimo La Deda Iolinda Aiello Mauro Ghedini 《Chemical physics letters》2005,410(4-6):201-203
The electrochemistry and the optical absorption properties of a series of cyclopalladated complexes are reported. Variation of the cyclometallated ligand has been performed (azobenzene, 2-phenylpyridine and benzo[h]quinoline) as well as variation of the ancillary ligand (acetylacetone and hexafluoroacetylacetone). Results have confirmed that the LUMO energy levels of these complexes is mainly distributed on the cyclometallated ligand. High electronegativity of the fluorinated groups has a weak influence on the electrochemical and absorption properties of the complexes, except for the benzo[h]quinoline for which its planar and comparatively more aromatic character lead to a partial delocalisation of the LUMO energy level. 相似文献
490.
Castagnola M Rossetti DV Inzitari R Vitali A Lupi A Zuppi C Cabras T Fadda MB Podda I Petruzzelli R Giardina B Messana I 《Electrophoresis》2003,24(10):1612-1619
Binding of Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis in water/2,2,2-trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A(1) in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn(2+) ion, as pointed out by the strong increase of the association constant measured in water/2,2,2-trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn(2+) ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro-organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A(1) towards its biologically active structure.* 相似文献