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101.
The dynamics of the strong-anisotropic Ising model in a transverse field is used with the purpose to explain the dielectric critical slowing down observed experimentally in the quasi-one-dimensional hydrogen-bonded ferroelectric crystal CsH2PO4. A good agreement with the experimental data of the temperature dependence of the dielectric constant and the relaxation time is obtained. 相似文献
102.
103.
The structure of water solubilized by reverse aggregates of calcium bis(2-ethylhexyl) sulfosuccinate in deuterobenzene and
toluene has been probed by Fourier transform-IR and 1H NMR spectroscopies. The νOD band of solubilized HOD (4% D2O in H2O) has been recorded as a function of the [water]/[surfactant] molar ratio, W/S. Curve fitting of this band showed the presence
of a main peak at 2550 ± 13 cm−1 and a small one at 2405 ± 15 cm−1. As a function of increasing W/S, the frequency of the main peak decreases, its full width at half-height increases, and
its area increases linearly. The 1H NMR chemical shift of solubilized H2O–D2O mixtures at W/S = 18.1 has been measured as a function of the deuterium content of the aqueous nanodroplet. These data were
used to calculate the so-called “fractionation factor” of the aggregate-solubilized water, the value of which was found to
be unity. The results of both techniques show that reverse aggregate-solubilized water, although different from bulk water,
does not seem to coexist in “layers” of different degrees of structure, as suggested, for example by the two-state water-solubilization
model.
Received: 12 July 1999/Accepted: 30 August 1999 相似文献
104.
Bruno Alves Rocha Marina Rezende Rodrigues Paula Carolina Pires Bueno Ana Rita de Mello Costa-Machado Mirela Mara de Oliveira Lima Leite Vaz Andresa Piacezzi Nascimento Hernane Silva Barud Andresa Aparecida Berretta-Silva 《Journal of Thermal Analysis and Calorimetry》2012,108(1):87-94
The propolis produced in Southeastern Brazil is known as green propolis (BGP) because of its color and the most important
plant source is Baccharis dracunculifolia. Several authors reported biological activities such as antiulcer, anti-inflammator, antimutagenic, antifungal/antibacterial,
antileishmanial/antiplasmodial for the BGP. For this reason, BGP has been extensively employed in food and beverages, thus
helping improve health and preventing diseases. Some authors related that the biological activities of BGP are mostly due
to its high levels of prenylated ρ-coumaric acids derivatives, mainly artepillin C. The inclusion complex between Brazilian
green propolis (BGP) with hydroxypropyl-β-cyclodextrin (HP-β-CD) was prepared and its characterization was investigated by
different analytical techniques (X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetry) and suggesting
that propolis was molecularly dispersed in the HP-β-CD matrix. The increasing solubility of chemical constituents was determined
using quantitation methods for total flavonoids and polyphenols. Furthermore, it was developed a method for the quantitation
and identification of the main compounds by high-performance liquid chromatography in order to evaluate the increasing water
solubility of each constituent in aqueous BGP extract (aromadendrin, isosakuranetin, and artepillin C). The antioxidant activity
was evaluated by chemical assay 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging. 相似文献
105.
Marcos A. Scapin Vera L. R. Salvador Marycel E. B. Cotrim Maria A. F. Pires Ivone M. Sato 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(3):807-811
Uranium silicide (U3Si2), 20% 235U enriched powder, is an intermetallic compound used as nuclear fuel material, which is the state-of-the-art among nuclear fuel materials used in modern research reactors. It is produced by IPEN and used as nuclear fuel of the IEA-R1 reactor (IPEN/CNEN, São Paulo, Brazil); U3Si2 has 92.3 wt% Utotal and 7.7 wt% Si. The qualification of this material requires chemical and physical tests such as Si and Utotal content, isotope ratio, impurities, density, specific surface area and particle size determination. The Si and Utotal were determined by gravimetric and volumetric procedures. Usually, these classical methods require a long time for analyses and are expensive. The objective of this study was to establish a fast and efficient analytical method to meet ISO/IEC 17025:2005 requirements in the Si and Utotal determination. The X-ray fluorescence techniques (XRF) were chosen to allow a direct and non-destructive analysis, what is the main advantage compared to other instrumental techniques, since previous chemical treatments are not necessary. In this study, the performance of the wavelength dispersive (WDXRF) and energy dispersive (EDXRF) X-ray fluorescence techniques was evaluated. Furthermore, two different sample preparation procedures, plain powdered and pressed powdered, were evaluated. Statistical tools were used to evaluate the results and a comparison between these results and the conventional methods was done. 相似文献
106.
Synthesis,characterization and assessment of the cytotoxic activity of Cu(II), Fe(III) and Mn(III) complexes of camphoric acid‐derived salen ligands 下载免费PDF全文
Dina Murtinho Zênis N. da Rocha Ana Salomé Pires Roberto P. Jiménez Ana Margarida Abrantes Mafalda Laranjo Ana Catarina Mamede João Eduardo Casalta‐Lopes Maria Filomena Botelho Alberto A. C. C. Pais Sandra C. C. Nunes Hugh D. Burrows Telma Costa M. Elisa Silva Serra 《应用有机金属化学》2015,29(7):425-432
Novel Cu(II), Fe(III) and Mn(III) salen‐type metal complexes from (1R,3S)‐N,N′‐bis[salicylidene]‐1,3‐diamino‐1,2,2‐trimethylcyclopentane were synthesized and screened for their in vitro cytotoxic activity against three human cancer cell lines: melanoma, colorectal and breast. In vitro experiments carried out with the three metal complexes show that the copper complex exhibits the highest cytotoxic activity towards all cell lines studied, presenting IC50 values of 3.32–6.71 μM. A significant improvement in the anti‐proliferative effect, by 20‐fold, is observed with this complex when compared with conventional chemotherapy. The relationship between structure, redox characteristics and biological activity in human cancer cell lines was evaluated for the most efficient Cu(II) complex and associated with theoretical calculations. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
107.
Tarik Chafik Abdelkader Darir Ouafae Achak Ana P. Carvalho João Pires 《Comptes Rendus Chimie》2012,15(6):474-481
In the present work the adsorption of toluene on microporous activated carbon was chosen as an illustrative example in order to show that different values of the heat effect might be obtained following the procedure used. Values ranging from 85 to 40 KJ/moL were obtained for the isosteric heat of adsorption at different adsorbate loadings using adsorption isotherm data measured under static conditions. However, the application of temperature programmed desorption (TPD) experiments carried out under dynamic conditions yields apparent energy of desorption values that cannot be systematically correlated with the heat of adsorption which is a thermodynamic parameter relevant to the adsorption equilibrium. This issue is of interest because the use of accurate values of the heat of adsorption is important for the correct designing and operating of adsorption facilities. 相似文献
108.
We build a gauge model based on the SU(3)c⊗SU(4)L⊗U(1)X symmetry where the scalar spectrum needed to generate gauge boson and fermion masses has a smaller scalar content than usually assumed in literature. We compute the running of its abelian gauge coupling and show that a Landau pole shows up at the TeV scale, a fact that we use to consistently implement those fermion masses that are not generated by Yukawa interactions, including neutrino masses. This is appropriately achieved by non renormalizable effective operators, suppressed by the Landau pole scale. Also, SU(3)c⊗SU(3)L⊗U(1)N models embedded in this gauge structure are bound to be strongly coupled at this same energy scale, contrary to what is generally believed, and neutrino mass generation is rather explained through the same effective operators used in the larger gauge group. Besides, their nice features, as the existence of cold dark matter candidates and the ability to reproduce the observed standard model Higgs-like phenomenology, are automatically inherited by our model. Finally, our results imply that this model is constrained to be observed or discarded soon, since it must be realized at the currently probed energy scale in LHC. 相似文献
109.
André F. Lavorante Cherrine K. Pires Ángel Morales-Rubio Miguel de la Guardia 《International journal of environmental analytical chemistry》2013,93(10):723-732
An automatic flow-analysis procedure for spectrophotometric determination of cationic surfactants in surface water using a solenoid micro-pump for propelling solutions of reagents and sample is described. The proposed method is based on a ternary formation complex between chromazurol S, the Fe(III) ion, and the cationic surfactant. The flow network comprised four solenoid micro-pumps controlled by a microcomputer, which performed the sampling step by loading a reaction coil with sample and reagent solutions and displacing the sample zone through the analytical path. The system is simple, easy to operate, and very flexible, with sufficient sensitivity to determine cationic surfactants in water without any pre-concentration or separation step. After determining the best operational conditions, favourable features such as a linear response between 0.34 and 10.2?mg?L?1 of surfactant (R?=?0.999), a relative standard deviation of 0.6% (n?=?11) for a sample containing 3.4?mg?L?1 of surfactant, a detection limit of 0.035?mg?L?1 of surfactant, and a sampling throughput of 72 determinations per hour were achieved. The system was used to determine cationic surfactant in river-water samples, and recovery values between 91 and 106% were achieved. 相似文献
110.
Marcos Costa de Souza William Pires de Macedo Thiago Silva Torres Leandro Ferreira Pedrosa Helmut G. Alt 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1885-1893
This article describes an improved method to synthesize phosphoramidic acid aminoalkyl esters from diamines by the adaptation of industrial patents. Four mono-phosphorylated products having amino sites were obtained in good a yield. Such compounds have potential coordination properties with transition metals and also potential biological activity. 相似文献