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821.
The spectroscopic properties of alpha-chymotrypsin (alpha-Chym), L-tryptophan (Trp) and N-acetyl-L-tryptophan (NAT) solubilized in hydrated reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate in iso-octane were followed by fluorescence as a function of the amount of intramicellar water and initial pH. The lack of pH dependence observed for Trp in these systems, as opposed to what occurs in bulk water, and the similarities found for the protein in both media foresee different locations of these probes. In reverse micelles, fluorescence quenching studies using acrylamide emphasize the existence of structural alterations within the protein when its global charge changes from positive (pH = 7) to negative (pH = 10). The ensemble of the data points to an interfacial location of the zwitterionic Trp, an intermediate region of less tightly bound water for the location of the anionic Trp and NAT and an almost bulk water environment for alpha-Chym. 相似文献
822.
A method is presented for the detection and determination of hydrogen sulfide. It is based on the selective and reversible adsorption of hydrogen sulfide on the surface of a piezoelectric crystal coated with a cadmium iodide/urea/-glycerol solution. The proposed detector has a response time of 30 s with linear response over the concentration range 2–25 μl l?1 (ppm). 相似文献
823.
Classification of edible vegetables affected by different traffic intensities using potential curves
Heavy metals in soils have largely been used to evaluate the impact of motorised traffic in the vicinity of motorways. Also in this field of work it is of paramount importance to analyse the vegetables grown in these areas since their consumption is one of the main sources of metal intake by people; not in vain human food is directly or indirectly derived from plants. Accordingly, a set of edible vegetable samples were first analysed and, then, classified employing different multivariate chemometric techniques; among them, SIMCA and a simplified mode of potential curves. The analytical variables were selected after a comprehensive study of roadside soil pollution where Pb, Cd and Cu were found to be the main metallic pollution tracers. Different groups of vegetables were obtained which were explained as a function of both the agricultural conditions (private versus commercial) and the different traffic intensities supported by the cultivated areas. 相似文献
824.
A. Carlosena D. Prada J. M. Andrade P. López S. Muniategui 《Fresenius' Journal of Analytical Chemistry》1996,355(3-4):289-291
The need to determine micronutrients and toxic elements in soils has grown in recent years and cadmium is of special interest. A method has been developed for the determination of cadmium in soils based on a prior acid digestion of the samples with nitric acid in closed Teflon vessels, into a microwave over. The cadmium determination was carried out by graphite furnace atomic absorption spectrometry (GFAAS) with Lvov platform. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. The best matrix modifier was found to be ammonium dihydrogen phosphate. The interferences are greatly reduced under these operating conditions and calibration can be performed with simple aqueous solutions of the metal standard. The method is rapid and provides accurate and precise results that agree with certified values for two reference materials: BCR 141 (calcareous loam soil) and BCR 277 (estuarine sediment). 相似文献
825.
Measurements and analysis of excess molar volumes for the ternary mixture MTBE + 1-pentanol + decane
P. V. Verdes M. M. Mato J. Salgado J. L. Legido M. I. Paz Andrade 《Journal of Thermal Analysis and Calorimetry》2005,80(2):323-327
Summary Densities at 298.15 K and atmospheric pressure have been measured, using a DMA 4500 Anton Paar densimeter, for the ternary mixture methyl tert-butyl ether (MTBE)+1-pentanol+decane and for the involved binary mixtures MTBE+1-pentanol and 1-pentanol+decane. The excess molar volumes for the binary mixture MTBE+decane was reported in an earlier work [1]. In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. Suitable fitting equations have been used in order to correlate adequately the excess molar volumes. The empirical expressions of Kohler [18], Jacob and Fitzner [19], Colinet [20], Knobeloch and Schwartz [21], Tsao and Smith [22], Toop [23], Scatchard et al. [24], Hillert [25], Mathieson and Thynne [26] were applied to estimate ternary properties from binary results. 相似文献
826.
A flow-injection system is described for the semi-automatic determination of arsenic (10–1000 μg l?1) by hydride generation and inductively-coupled plasma atomic emission spectrometry. The elements which were found to interfere were Co, Ni, Ag, Au, Bi, Te and Sn. Standard reference materials were analyzed with good accuracy. Approximately 200 injection h?1 are possible. The detection limit is 1.4 ng arsenic. 相似文献
827.
Walter L. dos Santos Carla M. M. dos Santos Jorge L. O. Costa Heloysa M. C. Andrade Srgio L. C. Ferreira 《Microchemical Journal》2004,77(2):123-129
The present paper proposes an on-line pre-concentration procedure for lead determination in drinking water and saline waste from oil refinery by flame atomic absorption spectrometry (FAAS). It is based on the sorption of lead (II) ions in a minicolumn of polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol (PAR) reagent. The optimization step was performed using Doehlert matrix involving the variables: sampling flow rate (SR), buffer concentration (BC), pH and eluent concentration (EC). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line system, precision, robustness, effect of other ions in the pre-concentration system and accuracy. Using the established experimental conditions, the procedure allows lead determination with detection limit (3δ/S) of 0.4 μg l−1, quantification limit (10δ/S) of 1.4 μg l−1, and a precision, calculated as relative standard deviation (RSD) of 5.7 (n=8) and 2.1% (n=8) for lead concentration of 5 and 50 μg l−1, respectively. The pre-concentration factor (PF) considering the ratio among the slopes of the analytical curves with and without pre-concentration is 51. The achieved recovery for lead determination in presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The accuracy was confirmed by analysis of the standard reference material NIST 1640 Trace elements in natural water. The sorption process was characterized by the Langmuir isotherm. The method was applied for lead determination in drinking water collected in Salvador City, Brazil and in saline effluent samples from oil refinery. The lead content for 16 samples of drinking water analyzed varied from 0.77 to 6.98 μg l−1. 相似文献
828.
L. M. Ferreira J. M. S. Rocha M. E. Andrade M. H. Gil 《Radiation Physics and Chemistry》1998,52(1-6):207-212
In the last few years new copolymeric supports for the immobilization of biological compounds have been developed. The graft copolymer polyethylene-g.co-hydroxyethyl methacrylate, partially hydrolyzed, has shown to be a very promising support for this purpose.
The more recent work in the preparation and characterization of this copolymer, as well as the immobilization of a lipase, is reported in this paper. Branches of poly(hydroxyethyl methacrylate) were grafted onto low density polyethylene by using gamma radiation. The influence of the presence and absence of air, as well as the monomer concentration on the yield of grafting were evaluated.
The obtained copolymers were characterized by DSC and FTIR. The influence of the support properties on the synthesis biocatalytic activity was detected. 相似文献
829.
A rapid method of determining zinc and iron in food by flame atomic-absorption spectrophotometry with slurry nebulization into an air-acetylene flame has been developed. A V-groove, clog-free Babington-type nebulizer, coupled to a single-line flow-injection analysis (FIA) system, was employed to introduce the slurry into the spray chamber. Under the FIA conditions described, an injection frequency of 120/hr is possible, with negligible carry-over and memory effects. The calibration graphs were obtained by using various concentrations (up to 0.1 g/ml) of white bean homogenate as standards, rather than solutions. The method has been applied to various kinds of foods, including grains, vegetables, fruits and sausage. Homogenization of semi-prepared samples to form slurries took only 4 min. Relative deviations between results by the slurry and solution methods for both elements averaged 2-3%. Detection limits by the slurry method were 0.3 mug/ml Zn and 0.6 mug/ml Fe. 相似文献
830.
H. A. de Salles Andrade L. Hainberger S. J. und K. L. Behmel 《Fresenius' Journal of Analytical Chemistry》1971,253(5):351-353
Zusammenfassung Es wird eine neue spektrophotometrische Bestimmung von Niob beschrieben. Nach Entwicklung des Farbkomplexes in konz. Schwefelsäure unter Verwendung von 0,1 g/ml Salicylsäure wurde die Absorption bei 430 nm gemessen. Auf diese Weise konnten bis zur unteren Grenze 9 g Nb/ml bestimmt werden.Ti, W, Re und V stören und müssen entfernt werden. Ta stört nicht, außer wenn es in zu großen Mengen vorhanden ist. Abtrennungsmethoden für die störenden Substanzen und die Arbeitsweise werden angegeben, die Vorteile werden diskutiert.
Spectrophotometric determination of niobium with salicylic acid
A new method is described consisting of the development of a color produced by a conc. sulphuric acid solution of niobium with salycilic acid. The final concentration of the salicylic acid is 0.100 g/ml of solution and the measurements are made at 430 nm. The minimum limit of determination is 9 g Nb/ml.Ti, W, Re and V interfere and must be previously extracted. Ta does not interfere up to certain limits. Separation processes for interferents, sample handling, as well as the advantages of the method, are discussed.相似文献