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591.
D. Diana Paola Vargas G. Liliana Giraldo P. Juan Carlos Moreno 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1067-1072
In this study, energetic interactions between activated carbon monoliths and various liquids were evaluated by determining immersion enthalpies in C6H6, H2O and aqueous solutions of NaOH and HCl. Immersion enthalpies depend on both the surface chemistry and the interactions between specific groups, and were compared with results from volumetric titrations. Immersion enthalpies of activated carbon monoliths were between ?95.85 and ?176.5 J g?1 for C6H6 and between ?11.19 and ?68.31 J g?1 for H2O; whereas immersion enthalpies in NaOH and HCl solutions were between ?20.36 and ?82.25 J g?1 and ?18.81 and ?96.16 J g?1, respectively. In support of these results, a high level of acidic groups was found on the surface of the activated carbon monoliths by Boehm volumetric titrations, with values between 719 and 1,290 g mol?1, in agreement with the higher immersion enthalpies observed in NaOH. Correlations were established between immersion enthalpies in the liquids and the surface chemistry properties of the activated carbon monoliths determined by volumetric titrations, demonstrating that immersion enthalpy is a useful parameter for characterisation of these materials in specific liquids. 相似文献
592.
Everton Luiz de PaulaValdir Mano Fabiano Vargas Pereira 《Polymer Degradation and Stability》2011,96(9):1631-1638
This paper reports the preparation of bionanocomposites based on poly(d,l-lactide) and cellulose nanowhiskers (PDLLA/CNWs) and studies the influence of the CNWs on the hydrolytic degradation behavior of the polylactide. The hydrolytic degradation process was studied in a phosphate buffer medium through the sample weight loss and also by FTIR, DSC and TGA measurements. The presence of CNWs induced a strong delay in the hydrolytic degradation of the PDLLA, even when the concentration of the nanofillers was only 1%. This effect was related to the physical barrier created by the highly crystalline CNWs that inhibited water absorption and hence retarded the hydrolytic degradation of the bionanocomposites. In addition, the incorporation of cellulose nanocrystals in the PDLLA also made the biopolymer more thermally stable, increasing the initial temperature of mass loss even after the degradation in phosphate medium. The results presented here show the possibility of controlling the biodegradability and prolonging the service life of a polylactide through the incorporation of a small quantity of nanofillers obtained from renewable materials. 相似文献
593.
Diana Paola Vargas Liliana Giraldo Joaquín Silvestre-Albero Juan Carlos Moreno-Piraján 《Adsorption》2011,17(3):497-504
A series of activated carbon monoliths have been prepared by chemical activation of two lignocellulosic precursors, coconut
shell (CACM) and African palm stones (PACM). The incorporation of a conforming step between the impregnation with H3PO4 and the activation step allows the successful development of disc-shape monoliths without the use of a binder. Textural characterization
results using N2 adsorption at 77 K show that the effect of the activating agent highly depends on the nature of the carbon precursor used.
While chemical activation with phosphoric acid has mainly no effect when using coconut shell, a large development of both
micro- and mesoporosity is observed for African palm stones. Large concentrations of the activating agent produce the partial
shrinkage of the narrow microporous structure independently of the precursor used. Concerning the adsorption of CO2 at atmospheric pressure and 273 K, both series of activated carbon monoliths exhibit an improved adsorption behaviour with
the activation degree up to an optimum value around ∼164 mg CO2/g, for sample CACM-32, and ∼162 mg CO2/g, for sample PACM-28, the amount adsorbed decreasing thereafter. Apparently, the total amount of CO2 adsorbed under these experimental conditions is defined by the volume of narrow micropores (V
n
). 相似文献
594.
Erika Cristina Vargas de Oliveira Naira Rezende Maciel Lia Queiroz do Amaral 《Journal of Dispersion Science and Technology》2013,34(12):1656-1662
Oil-in-water emulsions were developed employing the HLB system and emulsion phase inversion (EPI) method. X-ray diffraction revealed that the anisotropic structures around the inner phase globules were lamellar gel network phases. The calculated distances between the lamellae made after preparation and 3 month latter showed that there was no swelling of the lamellar gel network indicating good stability and few changes during storage. The developed emulsions were stable and have potential to be employed for cosmetic and pharmaceutical purposes. The gel phase network and vegetal components seemed to be contributing factors. 相似文献
595.
Clovis Peppe Fabiano Molinos de Andrade Jaqueline Pinto Vargas Melina de Azevedo Mello Railander Alves Barcellos Robert A. Burrow Rubia Mara Siqueira da Silva 《Journal of organometallic chemistry》2009,694(14):2228-2233
Halogenomethyl-dihalogen-indium(III) compounds X2InCH2X (X = Br, I) obtained from indium monohalides and methylene dihalides were reacted with the soft donor ligands dialkylsulfides, R2S (R = CH3, CH2Ph) to afford the corresponding dialkylsulfonium methylide complexes of InX3, X3InCH2SR2 (X = Br, R = CH3, 1; X = I, R = CH3, 2; X= I, R = CH2Ph, 3). Compound 1 was reacted with the hard donor ligands dimethylsulfoxide or triphenylphosphine oxide to give the corresponding 1:1 adduct, Br3(L)InCH2S(CH3)2 (L = (CH3)2SO, 4; L = (C6H5)3PO, 5). Compounds 1-5 were fully characterized in solution by NMR spectroscopy and in the solid state by X-ray methods. 相似文献
596.
Amanda P. Neves Kelly C.B. Maia Maria D. Vargas Lorenzo C. Visentin Annelise Casellato Miguel A. Novak Antônio S. Mangrich 《Polyhedron》2010
A novel versatile tridentate 3-(aminomethyl)naphthoquinone proligand, 3-[N-(2-pyridylmethyl)aminobenzyl]-2-hydroxy-1,4-naphthoquinone (HL), was obtained from the Mannich reaction of 2-hydroxy-1,4-naphthoquinone (Lawsone) with 2-aminomethylpyridine (amp) and benzaldehyde. The reactions of HL with CuCl2·2H2O yielded two novel dinuclear copper(II) complexes, [Cu(L)(H2O)(μ-Cl)Cu(L)Cl] (1b), [CuCl(L)(μ-Cl)Cu(amp)Cl] (2) and a polymeric compound, [Cu(L)Cl)]n (1a), whose relative yields were sensitive to temperature, reagents concentration and presence of base. The crystalline structures of 1b and 2 were determined by X-ray diffraction studies. The two copper atoms in complex 1b are connected by a single chloro bridge with a Cu?Cu separation of 4.1342(8) Å and Cu(1)–Cl(1)–Cu(2) angle of 109.31(4)°. In complex 2 the two copper atoms are held together by a chloro and a naphthalen-2-olate bridges [Cu(1)–Cl(2)–Cu(2) and Cu(1)–O(1)–Cu(2) angles being 83.31(3) and 109.70(9)°, respectively, and the Cu?Cu separation, 3.3476(9) Å]. As expected, variable-temperature magnetic susceptibility measurements of complex 1b showed weak antiferromagnetic intramolecular coupling between the copper(II) centers, with J = −5.7 cm−1, and evidenced for complex 2 strong antiferromagnetic coupling, with J ∼ −120 cm−1. Furthermore, the magnetic behaviour of compound 1a suggested an infinite 1D coordination polymeric structure in which the copper(II) centers are connected by Cl–Cu–Cl bridges. Solution data (UV–Vis spectroscopy and cyclic voltammetry) indicated structural changes of 2 and 1a in CH3CN, and evidenced conversion of polymer 1a into dimer 1b. 相似文献
597.