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91.
Asymmetric induction is observed in the additioin of chlorine to alkenes as well as in the synthesis of 0-acetyl cyanohydrins under phase-transfer conditions using (?)-benzylcinchonidinium chloride and (?)-N-dodecyl-N-methylephedrinium bromide as chiral catalysts. 相似文献
92.
Silistino-Souza R Peruquetti RL Taboga SR Vilela de Azeredo-Oliveira MT 《Micron (Oxford, England : 1993)》2012,43(9):954-960
In this study, we analyzed fibrillarin nucleolar protein expression in CBs of spermatogenic cells from testicular follicles of Triatoma sordida and Triatoma infestans. In the structural and ultrastructural analysis, it was used impregnation by silver ions, immunocytochemistry, immunofluorescence and transmission electron microscopy using antibodies against fibrillarin. Regarding the results, the fibrillarin nucleolar protein marked the nucleus and some cytoplasmic spots of germ cells during spermatogenesis in triatomines. These data suggest that fibrillarin could be a constituent of the CB that was most likely derived from nucleolar fragmentation. This is the first time that fibrillarin protein expression has been shown in the CB during spermatogenesis progression in triatomines. The knowledge regarding CB constituents may help to expand the understanding of the physiological role of this structure and the role that it plays in the reproductive biology of triatomines, which are vectors of Chagas Disease. 相似文献
93.
Sebastián Bouzat Damián H. Zanette 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):557-565
We study an SIS epidemiological model for a sexually
transmitted infection in a monogamous population where the formation
and breaking of couples is governed by individual preferences. The
mechanism of couple recombination is based on the so-called bar
dynamics for the marriage problem. We compare the results with those
of random recombination – where no individual preferences exist –
for which we calculate analytically the infection incidence and the
endemic threshold. We find that individual preferences give rise to
a large dispersion in the average duration of different couples,
causing substantial changes in the incidence of the infection and in
the endemic threshold. Our analysis yields also new results on the
bar dynamics, that may be of interest beyond the field of
epidemiological models. 相似文献
94.
A. Carvalho P.J. Sebastião A. Ferraz A.C. Ribeiro H.T. Nguyen 《The European physical journal. E, Soft matter》2000,2(4):351-358
In this work we present a proton NMR comparative study of the molecular order in the smectic C2 (), smectic C^* () and anticlinic smectic C phases ( and ) of two liquid crystalline compounds. The second moments of the experimental proton NMR spectra are well explained taking
into account two different molecular orientations models. From the analysis of our experimental results it was possible to
estimate the tilt angles for all the smectic C phases studied in this work.
Received 15 September 1999 and Received in final form 18 January 2000 相似文献
95.
Barroso M Chattopadhyay N Klymchenko AS Demchenko AP Arnaut LG Formosinho SJ 《The journal of physical chemistry. A》2006,110(50):13419-13424
Steady-state fluorescence of 4'-dimethylamino-3-hydroxyflavone (DMA3HF) was observed in supercritical carbon dioxide (scCO(2)). Excited-state intramolecular proton transfer (ESIPT) occurs resulting in two well-separated emission bands corresponding to the normal and tautomer forms. As the scCO(2) density exceeds 0.7 g/mL, the relative intensity of the two bands tends to a constant value, comparable to that observed for organic solvents with ET(30) = 33.0 +/- 0.5 kcal/mol, such as toluene and di-n-butyl ether. At lower densities, the substantial decrease of the total fluorescence intensity (a 600-fold decrease as the pressure decreases from 100 to 80 bar) is accompanied by an even more accentuated decrease of the tautomer fluorescence. This can be explained by a shift in the equilibrium between normal and tautomer forms, concomitant with a more efficient quenching of the less solvated fluorophore, that may change the thermodynamic control of the relative population of the two emissive species to a kinetic control. 相似文献
96.
Sérgio M. Soares Sebastião S. Lemos Maria José A. Sales Davi F. Back Ernesto S. Lang 《Polyhedron》2009,28(17):3811-3815
The reaction of cadmium(II) acetate dehydrate with the complexing agents tropolone (tropH), 2-hydroxynaphthoquinone (nqH), 1,2-dihydroxyanthraquinone (alizH2), and 1,8-dihydroxyanthraquinone (chryzH2), afforded the complexes [Cd(trop)2] 1, [Cd2(nq)4(H2O)4]·3H2O 2·3H2O, [Cd(alizH)2(H2O)3] 3, and [Cd(chryzH)2(H2O)2] 4, respectively. The X-ray molecular structure of the dinuclear complex 2·3H2O reveals that each cadmium(II) atom is seven-coordinated. The nature of water molecules (lattice or coordinated) was discerned by thermogravimetric studies. The 113Cd NMR spectra were discussed in light of the chemical exchange. 相似文献
97.
Nathalie González‐Vidal Antxon Martínez De Ilarduya Sebastián Muñoz‐Guerra 《Journal of polymer science. Part A, Polymer chemistry》2009,47(22):5954-5966
Cyclic oligomer fractions of ethylene terephthalate c(ET)n and 1,4‐cyclohexylenedimethylene terephthalate c(CT)n were obtained by cyclodepolymerization of their respective polyesters, the former containing around 80 mol % of trimer and the latter with around 70 mol % of trimer to pentamer. Mixtures of these fractions at selected compositions were subjected to ring opening copolymerization to give a series of poly(ethylene‐co‐cyclohexylenedimethylene terephthalate) copolyesters with ET/CT comonomer ratios ranging from 90/10 to 10/90. The copolyesters were characterized by GPC and NMR, and their thermal properties were evaluated by DSC and TGA. They had essentially the same composition as the feed from which they were produced and had an average‐weight molecular weights between 30,000 and 40,000 g/mol with polydispersities between 2 and 2.7. The distribution of the monomeric units in these copolyesters was essentially at random although it evolved to be a blocky microstructure as the contents in the two comonomers became more dissimilar. Their thermal behavior was the expected one for these types of copolyesters with crystallinity and heating stability decreasing with the content in CT units. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5954–5966, 2009 相似文献
98.
Romina Marín Antxon Martínez de Ilarduya Sebastián Muñoz‐Guerra 《Journal of polymer science. Part A, Polymer chemistry》2009,47(9):2391-2407
Naturally occurring tartaric acid was used as raw material for the synthesis of novel linear polyurethanes (PURs) bearing two carboxylate side‐groups in the repeating unit. Aliphatic and aromatic PURs were obtained by reaction in solution of alkyl and benzyl tartrates with hexamethylene diisocyanate and 4,4′‐methylene‐bis(phenyl isocyanate), respectively. All the novel PURs were thermally stable and optically active. The aliphatic carboxylate‐containing PURs had Mw in the 40–70 kDa range, with PD between 2.1 and 2.5; all were semicrystalline polymers with melting temperatures between 100 and 150 °C and Tg in the 50–80 °C range. The aromatic PURs were amorphous materials with molecular weights between 18 kDa and 25 kDa and Tg above 130 °C. Hydrogenolysis of the PUR made from hexamethylene diisocyanate and benzyl tartrate yielded PURs containing up to 40% of free carboxylic side‐groups. The tartrate‐derived PURs displayed enhanced sensitivity to hydrolysis compared with their unsubstituted 2,6‐PUR homologs. The PURs bearing free carboxylic groups were unique in being degraded by water upon incubation under physiological conditions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2391–2407, 2009 相似文献
99.
Consider a firm providing home-delivery of small parcels within a short period of time. The paper proposes a method to estimate
the productivity of each driver on any fictitious route using linear regressions. The method separates the trip time in terms
of the time spent: with customers, driving, and all other activities. Our tests show that productivity, measured in terms
of number of customers visited per hour, vary across drivers. Even more, the same driver’s productivity vary for peak and
off-peak demand periods considerably. This methodology should enhance the reliability of the driver scheduling programs, since
it reduces the error and bias of the productivity offered by the assigned set of drivers. It shall also improve the reliability
of the delivery time promised to the customer. 相似文献
100.