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61.
Formation and stabilization of persistent free radicals   总被引:2,自引:0,他引:2  
We demonstrate that stable and relatively unreactive “environmentally persistent free radicals (PFRs)” can be readily formed in the post-flame and cool-zone regions of combustion systems and other thermal processes. These resonance-stabilized radicals, including semiquinones, phenoxyls, and cyclopentadienyls, can be formed by the thermal decomposition of molecular precursors including catechols, hydroquinones and phenols. Association with the surfaces of fine particles imparts additional stabilization to these radicals such that they can persist almost indefinitely in the environment. A mechanism of chemisorption and electron transfer from the molecular adsorbate to a redox-active transition metal or other receptor is shown through experiment, and supported by molecular orbital calculations, to result in PFR formation. Both oxygen-centered and carbon-centered PFRs are possible that can significantly affect their environmental and biological reactivity.  相似文献   
62.
The accurate analysis of hard CuP and CuPAg‐type solders using X‐ray fluorescence spectrometry is a difficult task. Surface milling, the most common sample preparation method for calibration materials, results in poor accuracy for the phosphorus analysis, as evidenced by the unacceptable values of the root mean square error. Meanwhile, the analysis of real samples provides incorrect results, and microstructural effects are the main source of error. Thus, this effect was negated by considering the information depth of the phosphorus Kα line and the microstructure size of the alloys. Phosphorus was measured using a thin layer of the sample (a thickness of several micrometers). As a result, the analyzed layer was a poor representative of the sample. Two different approaches for solving the microstructural effect issue were proposed. In the first method, the alloy was remelted under controlled conditions to obtain fine‐grain samples, which successfully limited the microstructural effects. The second solution used specially prepared thin layer samples, and the sample dissolution eliminated the microstructural effect. Using the developed sample treatment methods resulted in an improvement in the accuracy of the phosphorus calibration curves. This allowed for the correct determination of phosphorus and other alloying elements in the Cu‐based alloys with low uncertainties.  相似文献   
63.
An attempt has been made to detect the effect of a small dose of ionizing radiation on the course of α,β-globulin thermal denaturation in aqueous solutions. Doses of 0.1 and 1.8 Gy have been delivered using γ-rays emitted by 60Co isotope while doses of 10 and 100 Gy have been supplied by X-rays produced by linear accelerator. The highest dose has visibly changed DSC curve of protein solution while the changes due to lower doses are hardly detectable. Although very weak, the irradiation effect found has been dose dependent. The results suggest that the influence of ionizing radiation on globulins solution is bigger when the dose rate is lower at given dose. The opposite direction of differences between irradiated and control samples for fresh and stored protein solutions suggests various characters of changes in initial and later period of sample aging. This may be an important reason for difficulties in an investigation of the effect of ionizing radiation on protein solution, especially for low doses delivered very slowly.  相似文献   
64.
The osmotic and activity coefficients of aqueous sodium and potassium methyl sulfates have been determined at 25°C by the isopiestic method, in the molality range from ca.0.2 to 25 and 19 mol-kg–1, respectively. The results have been discussed in terms of the ion–ion and ion–water interactions on the basis of the Pitzer and Mayorga model and a method developed in our laboratory.  相似文献   
65.
HONO/1,1-dichloroethylene/Ar matrices were subjected to UV radiation (lambda > 340 nm) from a medium pressure mercury lamp. The products of the photolysis were studied experimentally by means of FTIR spectroscopy and theoretically using the ab initio MP2 method. Two conformers of 2-nitroso-2,2-dichloroethanol molecule have been identified as the final products of the double addition reaction of the OH, NO radicals to 1,1-dichloroethylene. The additional reactive species observed in the matrix is tentatively identified as an 1,1-dichloro-2-hydroxyethyl radical, an intermediate formed by single addition of OH to 1,1-dichloroethylene. The three photoproducts have been identified and observed for the first time. The identities of the products have been justified by comparison with the experiments with deuterated DONO and by performing concentration and annealing studies as well as by reference to the spectral data of related molecules. The results of the quantum mechanical calculations confirmed both the assignment of the new molecules and mechanism of the reaction observed in our experiment.  相似文献   
66.
Performance of MnOx/Al2O3 catalytic systems was studied after they were roasted at different temperatures in the range of 650 – 1100°C. The maximum activity of the catalysts was reached when the catalyst roasting temperature was 1000°C. To explain the results, the X-ray diffraction analyses of THE catalysts were performed.  相似文献   
67.
Summary The effect of pH on the thermal denaturation of BSA containing fatty acids was studied by use of differential scanning calorimetry (DSC). Thermal scanning of BSA aqueous solutions gave various types of DSC curves depending on the protein concentration and on the pH. The broad bimodal endothermic transition was suggested to be connected with loose protein structure in contradistinction to single peak for compact molecule structure. The propensity toward precipitation at pH conditions ranging from 3.8 to 5 was observed. A scan-rate independent and partly reversible behavior of the thermal heating of BSA was found. Deconvolution of DSC traces in non-two-state model with assumption of two- or three-component transition allowed to study the effect of pH on different parts of BSA molecule.  相似文献   
68.
Parent genistein and its new amine complexes with morpholine and piperazine were studied comparatively in the solid and liquid states by X-ray crystallography and 13C and 15N NMR spectroscopy. Biochanine A and its complexes were used as reference. Secondary deuterium isotope effects on 13C chemical shifts in solution were studied in parent isoflavones and their morpholine and piperazine complexes to aid in evaluation of the electronic distribution in both systems. In addition, to quantify the extent of proton transfer as well as to establish strong hydrogen bonding of the 7-OH group in a morpholine complex, proton transfer from the 7-OH group to the piperazine nitrogen atom was also confirmed by 13C NMR in the solid state and by X-ray studies. The effect of 7-OH deprotonation yields a high frequency shift of 7-8 ppm on the C-7 carbon atom of the piperazine complex whereas it is as large as 12 ppm in the morpholine complex in the solid. The former trend is confirmed from solution state concentration studies which also show that the isoflavones have a strong tendency to form complexes with bases. Depending on the pKa difference between the isoflavones and the base this leads either to proton transfer and ion-pair formation or, in the case of a larger pKa difference, to a hydrogen bonded ion pair. The concentration studies show formation of a 1:1 genistein-piperazine complex in DMSO. Addition of water leads to formation of solvent separated ions. The C-5 OH group is involved in strong intramolecular hydrogen bonding leading to a pseudo aromatic ring extending the aromatic part of the drug pharmacophore. The analysis also suggests the way that both the C-7 and C-4' hydroxyl group of genistein may participate in stabilising the ternary inhibitor complexes of tyrosine-specific kinases or DNA topoisomerase II.  相似文献   
69.
Dimerization of the keto tautomer of acetohydroxamic acid has been studied using FTIR matrix isolation spectroscopy and DFT(B3LYP)/6-31+G(d,p) calculations. Analysis of CH3CONHOH/Ar matrix spectra indicates formation of two dimers in which two intramolecular CO...HON bonds within two interacting acetohydroxamic acid molecules are retained. A chain dimer I is stabilized by the intermolecular CO...HN hydrogen bond, whereas the cyclic dimer II is stabilized by two intermolecular NH...O(H)N bonds. Twelve vibrations were identified for dimer I and six vibrations for dimer II; the observed frequency shifts show a good agreement with the calculated ones for the structures I and II. Both dimers have comparable binding energies (DeltaE(ZPE)(CP)I, II=-7.02, -6.34 kcal mol-1) being less stable than calculated structures III and IV (DeltaE(ZPE)(CP)III, IV=-9.50, -8.87 kcal mol-1) in which one or two intramolecular hydrogen bonds are disrupted. In the most stable 10-membered cyclic dimer III, two intermolecular CO...HON hydrogen bonds are formed at expense of intramolecular hydrogen bonds of the same type. The formation of the less stable (AHA)2 dimers in the studied matrixes indicates that the formation of (AHA)2 is kinetically and not thermodynamically controlled.  相似文献   
70.
Anthranilates of Tb-Lu prepared in the reaction of the rare earth hydroxides withortho-aminobenzoic acid (anthranilic acid) have the general formulaLn(C6H4NH2COO)3·2H2O whereLn=Tb, Dy, Ho, Er, Tm, Yb, Lu. The water molecules in the hydrated compounds are in the outer coordination sphere. On heating in air at 493K dehydration occurs and the anhydrous anthranilatesLn(C6H4NH2COO)3 are formed. On the basis of the IR spectra it was found that the metal in dihydrated anthranilates was simultaneously coordinated through amino and carboxyl groups whereas in anhydrous anthranilates only through the bidentate carboxyl group. From X-ray analysis it was stated that the anthranilatesLn(C6H4NH2COO)3·2H2O are isostructural, whereas the anhydrous compoundsLn(C6H4NH2COO)3 are isostructural in the two groups Tb-Er and Tm-Lu.
Die Komplexe der schweren Selteneerdmetalle mit Orthoaminobenzoesäure
Zusammenfassung Zur Darstellung der Verbindungen des TypsLn(C6H4NH2COO)3·2H2O (mitLn=Tb bis Lu) wurde die berechnete Menge vonLn(OH)3 und C6H4NH2COOH-Lösung gemischt und bei 363K schnell zur Kristallisation gebracht. Die Produkte werden schnell abfiltriert, mit Wasser gewaschen und bis zur Gewichtskonstanz getrocknet. Die VerbindungenLn(C6H4NH2COO)3·2H2O sind isostrukturell mit der Dichte ungefähr 1.6g·cm–1 und geringer Löslichkeit in Wasser bei Raumtemperatur. Beim Erhitzen folgt zunächst Entwässerung bei 493 K, später Zersetzung zu Tb4O7 undLn 2O3. Die wasserfreien VerbindungenLn(C6H4NH2COO)3 sind isostrukturell in 2 Strukturtypen: Tb-Er and Tm-Lu. Die Infrarotspektren von wasserfreien Verbindungen und Doppelhydraten wurden registriert. Es wurde festgestellt, daß die Koordinierung der Seltenerdmetalle mit Liganden in den Dihydraten sowohl durch die Amino- als auch durch Carboxylgruppen erfolgt. In den wasserfreien Komplexen tritt die Koordinierung nur durch Carboxylgruppen auf.
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