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71.
A new methodology for the determination of the fluorescence quantum yield of dyes adsorbed onto microcrystalline cellulose is presented and applied to rhodamine 101, cresyl violet and auramine O. It is based on a previously reported method by Ruetten and Thomas (J. Phys. Chem., 1998, 102, 598-606), which is not applicable to the dyes used in the present study. It uses ground-state diffuse reflectance spectra obtained with and without filters, which prevents the luminescence of the dye from reaching the integrating sphere and the photodetector. New equations are presented here, correcting for the fluorescence emission of the dye, which depends on the detector sensitivity. Cut-on filters, which have a transmittance close to unity in the absorption region, and close to zero in the emission region, of the dye are used to obtain corrected reflectance spectra. The influence of the substrate was also taken into account. This methodology may be applied to other probes and surfaces or emissions of a different nature (i.e., phosphorescence or delayed fluorescence), and constitutes a very simple and general procedure to solve the important problem of luminescence quantum yield determination of probes adsorbed onto solid powdered surfaces. 相似文献
72.
J. L. C. Diniz R. D. Vieira J. T. Castro A. C. Benjamin J. L. F. Freire 《Experimental Mechanics》2006,46(6):765-775
This paper presents the analysis of stress and strain data acquired with the finite element method and with tests that used
post-yielding strain gages bonded onto the external surface of pipes that suffered thickness metal loss and that had been
loaded with internal pressure. These metal loss areas were produced by three different processes: actual internal corrosion,
careful machining of external patches by spark-erosion, and milling of internal or external patches to simulate limited or
extensive strip corrosion defects with depths up to 70% of the pipe’s thickness. Results show that: (1) the extensive longitudinal
internal or external defect areas behave as extensive strips with a high degree of freedom to deform elastically and plastically
in the circumferential and thickness directions, and (2) large restraints are offered to the longitudinal strains by the non-corroded
thick walls parallel to the strip. Using the above experimental observation, a simple mathematical model was developed to
predict the burst pressure of pipes with longitudinal extensive and reasonably constant depths of metal loss. This model employed
thin-pipe-strength-of-material equations associated to a bulging correction factor, the material’s uniaxial ultimate strength
and the von Mises criterion. The onset of plastic collapse predicted by the simple model was successfully compared with results
determined from actual hydrostatic tests that were carried out with full scale pipe specimens and from finite element results
generated by the use of a commercial program. The developed model was also helpful in showing that the yield and burst behaviors
of new or corroded pipeline specimens under laboratory test conditions can be directly compared and extended to the yield
and burst behaviors of buried pipeline in field operation. 相似文献
73.
Vivian E. Cornelio Mariele M. Pedroso André S. Afonso João B. Fernandes M.Fátima G.F. da Silva Ronaldo C. Faria Paulo C. Vieira 《Analytica chimica acta》2015
The hemoglobin (Hb) released from erythrocytes is a primary nutritive component for many blood-feeding parasites. The aspartic protease cathepsin D is a hemoglobinase that is involved in the Hb degradation process and is considered an interesting target for chemotherapy intervention. However, traditional enzymatic assays for studying Hb degradation utilize spectrophotometric techniques, which do not allow real-time monitoring and can present serious interference problems. Herein, we describe a biosensor using simple approach for the real-time monitoring of Hb hydrolysis as well as an efficient screening method for natural products as enzymatic inhibitors using a quartz crystal microbalance (QCM) technique. Hemoglobin was anchored on the quartz crystal surface using mixed self-assembled monolayers. The addition of the enzyme caused a mass change (frequency shift) due to Hb hydrolysis, which was monitored in real time. From the frequency change patterns of the Hb-functionalized QCM, we evaluated the enzymatic reaction by determining the kinetic parameters of product formation (kcat). The QCM enzymatic assay using immobilized human Hb was shown to be an excellent approach for screening possible inhibitors in complex mixtures, opening up a new avenue for the discovery of novel inhibitors. 相似文献
74.
A Novel Alkaloid from Aspidosperma pyricollum (Apocynaceae) and Complete 1H and 13C Chemical Shift Assignments 下载免费PDF全文
Hádria M. do Carmo Raimundo Braz‐Filho Ivo J. Curcino Vieira 《Helvetica chimica acta》2015,98(10):1381-1386
A novel natural product indole, alkaloid, named rel‐pyricolluminol ( 1 ), was isolated from Aspidosperma pyricollum Müll .Arg . together with six known metabolites sitsirikine ( 2 ), aparicin ( 3 ), ulein ( 4 ), stemmadenine ( 5 ), lupeol ( 6 ), and (3β)‐sitoster‐3‐yl β‐D ‐glucopyranoside ( 7 ). These compounds were characterized on the basis of their spectral data, mainly 1D‐ (1H,13C‐DEPTQ) and 2D‐NMR (1H,1H‐COSY, NOESY, HSQC, and HMBC), and mass spectra (EI‐MS and HR‐ES‐MS), involving also comparison with data from the literature. 相似文献
75.
João M. Leça Ana C. Pereira Ana C. Vieira Marco S. Reis José C. Marques 《Analytica chimica acta》2015
Vicinal diketones, namely diacetyl (DC) and pentanedione (PN), are compounds naturally found in beer that play a key role in the definition of its aroma. In lager beer, they are responsible for off-flavors (buttery flavor) and therefore their presence and quantification is of paramount importance to beer producers. Aiming at developing an accurate quantitative monitoring scheme to follow these off-flavor compounds during beer production and in the final product, the head space solid-phase microextraction (HS-SPME) analytical procedure was tuned through experiments planned in an optimal way and the final settings were fully validated. Optimal design of experiments (O-DOE) is a computational, statistically-oriented approach for designing experiences that are most informative according to a well-defined criterion. This methodology was applied for HS-SPME optimization, leading to the following optimal extraction conditions for the quantification of VDK: use a CAR/PDMS fiber, 5 ml of samples in 20 ml vial, 5 min of pre-incubation time followed by 25 min of extraction at 30 °C, with agitation. The validation of the final analytical methodology was performed using a matrix-matched calibration, in order to minimize matrix effects. The following key features were obtained: linearity (R2 > 0.999, both for diacetyl and 2,3-pentanedione), high sensitivity (LOD of 0.92 μg L−1 and 2.80 μg L−1, and LOQ of 3.30 μg L−1 and 10.01 μg L−1, for diacetyl and 2,3-pentanedione, respectively), recoveries of approximately 100% and suitable precision (repeatability and reproducibility lower than 3% and 7.5%, respectively). The applicability of the methodology was fully confirmed through an independent analysis of several beer samples, with analyte concentrations ranging from 4 to 200 g L−1. 相似文献
76.
Gabriela Furlan Giordano Luis Carlos Silveira Vieira Angelo Luiz Gobbi Renato Sousa Lima Lauro Tatsuo Kubota 《Analytica chimica acta》2015
An integrated platform was developed for point-of-use determination of ethanol in sugar cane fermentation broths. Such analysis is important because ethanol reduces its fuel production efficiency by altering the alcoholic fermentation step when in excess. The custom-designed platform integrates gas diffusion separation with voltammetric detection in a single analysis module. The detector relied on a Ni(OH)2-modified electrode. It was stabilized by uniformly depositing cobalt and cadmium hydroxides as shown by XPS measurements. Such tests were in accordance with the hypothesis related to stabilization of the Ni(OH)2 structure by insertion of Co2+ and Cd2+ ions in this structure. The separation step, in turn, was based on a hydrophobic PTFE membrane, which separates the sample from receptor solution (electrolyte) where the electrodes were placed. Parameters of limit of detection and analytical sensitivity were estimated to be 0.2% v/v and 2.90 μA % (v/v)−1, respectively. Samples of fermentation broth were analyzed by both standard addition method and direct interpolation in saline medium based-analytical curve. In this case, the saline solution exhibited ionic strength similar to those of the samples intended to surpass the tonometry colligative effect of the samples over analyte concentration data by attributing the reduction in quantity of diffused ethanol vapor majorly to the electrolyte. The approach of analytical curve provided rapid, simple and accurate analysis, thus contributing for deployment of point-of-use technologies. All of the results were accurate with respect to those obtained by FTIR method at 95% confidence level. 相似文献
77.
M. Ferreira M. M. Rodrigues N. Vieira 《Mathematical Methods in the Applied Sciences》2017,40(18):7033-7050
In this work, we obtain the fundamental solution (FS) of the multidimensional time‐fractional telegraph Dirac operator where the 2 time‐fractional derivatives of orders α∈]0,1] and β∈]1,2] are in the Caputo sense. Explicit integral and series representation of the FS are obtained for any dimension. We present and discuss some plots of the FS for some particular values of the dimension and of the fractional parameters α and β. Finally, using the FS, we study some Poisson and Cauchy problems. 相似文献
78.
The interaction of bovine serum albumin (BSA) with the ionic surfactants sodium dodecylsulfate (SDS, anionic), cetyltrimethylammonium chloride (CTAC, cationic) and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS, zwitterionic) was studied by electron paramagnetic resonance (EPR) spectroscopy of spin label covalently bound to the single free thiol group of the protein. EPR spectra simulation allows to monitor the protein dynamics at the labeling site and to estimate the changes in standard Gibbs free energy, enthalpy and entropy for transferring the nitroxide side chain from the more motionally restricted to the less restricted component. Whereas SDS and CTAC showed similar increases in the dynamics of the protein backbone for all measured concentrations, HPS presented a smaller effect at concentrations above 1.5mM. At 10mM of surfactants and 0.15 mM BSA, the standard Gibbs free energy change was consistent with protein backbone conformations more expanded and exposed to the solvent as compared to the native protein, but with a less pronounced effect for HPS. In the presence of the surfactants, the enthalpy change, related to the energy required to dissociate the nitroxide side chain from the protein, was greater, suggesting a lower water activity. The nitroxide side chain also detected a higher viscosity environment in the vicinity of the paramagnetic probe induced by the addition of the surfactants. The results suggest that the surfactant-BSA interaction, at higher surfactant concentration, is affected by the affinities of the surfactant to its own micelles and micelle-like aggregates. Complementary DLS data suggests that the temperature induced changes monitored by the nitroxide probe reflects local changes in the vicinity of the single thiol group of Cys-34 BSA residue. 相似文献
79.
Di?go P. Bezerra Ronan S. Oliveira Rodrigo S. Vieira Célio L. Cavalcante Diana C. S. Azevedo 《Adsorption》2011,17(1):235-246
Adsorption may be a potentially attractive alternative to capturing CO2 from stationary sources in the context of Carbon Capture and Sequestration (CCS) technologies. Activated carbon and zeolites
are state-of-art adsorbents which may be used for CO2 adsorption, however physisorption alone tends to be insignificant at high temperatures. In the present work, commercial adsorbents
have been impregnated with monoethanolamine (MEA) and triethanolamine (TEA) in order to investigate the effect of the modified
surface chemistry on CO2 adsorption, especially above room temperature. Adsorption isotherms for CO2, N2 and CH4 were measured in a gravimetrically system in the pressure range of UHV to 10 bar, at 298 and 348 K for activated carbon and
zeolite 13X supports. The adsorbed concentration of CO2 was significantly higher than those of CH4 and N2 for both adsorbents in the whole pressure range studied, zeolite 13X showing a remarkable affinity for CO2 at very low pressures. However, at 348 K, the adsorbed concentration of CO2 decreases significantly. The supports impregnated with concentrated amine solutions and dried in air suffered a detrimental
effect on the textural properties, although CO2 uptake became much less susceptible to temperature increase. Impregnations carried out with dilute solution followed by drying
in inert atmosphere yielded materials with very similar textural characteristics as compared to the parent support. CO2 isotherms in such materials showed a significant change with similar capacities at 348 K as compared to the original support
at 298 K in the case of activated carbons. The impregnated zeolite showed a decrease in adsorbed phase concentration in low
pressures for a given temperature, but the adsorbed amount also seemed to be less affected by temperature. These results are
promising and indicate that CO2 adsorption may be enhanced despite high process temperatures (e.g. 348 K), if convenient impregnation and drying methods
are applied. 相似文献
80.
Börner J Vieira Idos S Pawlis A Döring A Kuckling D Herres-Pawlis S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(16):4507-4512
Zinc bis(chelate) guanidine complexes promote living lactide polymerization at elevated temperatures. By means of kinetic and spectroscopic analyses the mechanism has been elucidated for these special initiators that make use of neutral N-donor ligands. The neutral guanidine function initiates the polymerization by a nucleophilic ring-opening attack on the lactide molecule. DFT calculations on the first ring-opening step show that the guanidine is able to act as a nucleophile. Three transition states were located for ligand rearrangement, nucleophilic attack, and ring-opening. The second ring-opening step was modeled as a representation for the chain growth because here, the lactate alcoholate opens the second lactide molecule via two transition states (nucleophilic attack and ring-opening). Additionally, the resulting reaction profile proceeds overall exothermically, which is the driving force for the reaction. The experimental and calculated data are in good agreement and the presented mechanism explains why the polymerization proceeds without co-initiators. 相似文献