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81.
Walter N.L. dos Santos Geovani C. Brandão Lindomar A. Portugal Jorge M. David Sérgio L.C. Ferreira 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
This paper proposes the use of photo-oxidation with UV radiation/H2O2 as sample pretreatment for the determination of iron and manganese in wines by flame atomic absorption spectrometry (FAAS). The optimization involved the study of the following variables: pH and concentration of buffer solution, concentrated hydrogen peroxide volume and irradiation time. The evaluation of sample degradation was monitored by measuring the absorbance at the maximum wavelength of red wine (530 nm). Using the experimental conditions established during the optimization (irradiation time of 30 min, oxidant volume of 2.5 mL, pH 10, and a buffer concentration of 0.15 mol L− 1), this procedure allows the determination of iron and manganese with limits of detection of 30 and 22 μg L− 1, respectively, for a 5 mL volume of digested sample. The precision levels, expressed as relative standard deviation (RSD), were 2.8% and 0.65% for iron and 2.7% and 0.54% for manganese for concentrations of 0.5 and 2.0 mg L− 1, respectively. Addition/recovery tests for evaluation of the accuracy were in the ranges of 90%–111% and 95%–107% for iron and manganese, respectively. This digestion procedure has been applied for the determination of iron and manganese in six wine samples. The concentrations varied from 1.58 to 2.77 mg L− 1 for iron and from 1.30 to 1.91 mg L− 1 for manganese. The results were compared with those obtained by an acid digestion procedure and determination of the elements by FAAS. There was no significant difference between the results obtained by the two methods based on a paired t-test (at 95% confidence level). 相似文献
82.
Teobald Kupka 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2649-2658
IR studies were preformed to determine possible transition metal ion binding sites of penicillin. the observed changes in spectral position and shape of characteristic IR bands of cloxacillin in the presence of transition metal ions (both in solutions and in the solid state) indicate formation of M–L complexes with engagement of –COO− and/or –CONH– functional groups. The small shift of νC=O towards higher frequencies rules out direct M–L interaction via β-lactam carbonyl. PM3 calculations on simple model compounds (substituted formamide, cyclic ketones, lactams and substituted monocyclic β-lactams) have been performed. All structures were fully optimized and the calculated bond lengths, angles, heats of formation and C=O stretching frequencies were discussed to determine the β-lactam binding sites and to explain its susceptibility towards nucleophilic attack (hydrolysis in vitro) and biological activity. The relative changes of calculated values were critically compared with available experimental data and same correlation between structural parameters and in vivo activity was shown. 相似文献
83.
Previous studies have shown that hop biomass is capable of adsorbing significant amounts of Au(III) from aqueous solutions. Hop biomass was chemically modified to determine the contributions that the different functional groups on the biomass have on the binding and reduction of Au(III). Previously, performed batch studies showed that Au(III) binding is fast, occurring within the first 5 min of contact and in a pH dependent manner. However, esterified hop biomass behaved in a pH independent manner and the binding was found not to change with changing pH. However, the hydrolyzed biomass had a similar Au(III) binding to the native hops biomass, showing a pH dependent binding trend. X-ray absorption spectroscopy (XAS) analysis, XANES (X-ray absorption near edge structure), and EXAFS (extended X-ray absorption fine structure) were used to determine the oxidation state, coordination environment, and the average radii of the gold nanoparticles bound to the hops biomass. The XAS data confirmed the presence of Au(0) in both the native and chemically modified hop biomasses. XANES fittings show that the Au(III) was reduced to Au(0) by approximately 81%, 70%, and 83% on the native, esterified, and hydrolyzed hop biomass, respectively. In addition, the calculation of the particle radius was also in agreement with the results of previously performed transmission electron microscopy studies. The average particle could only be calculated for the native and esterified hops biomass, which showed average particle radii of 17.3 Å and 9.2 Å, respectively. 相似文献
84.
The objective of this study was to evaluate the performance of a photocatalysis/H2O2/metal membrane hybrid system in the degradation of humic acid. A metal membrane of nominal pore size 0.5 μm was used in the
experiment for separation of TiO2 particles. Hydrogen peroxide was tested as an oxidant. The efficiency of removal of CODCr and color increased rapidly for initial hydrogen peroxide concentrations up to 50 mg L−1. The efficiency of removal of CODCr and color by 50 mg L−1 initial hydrogen peroxide concentration was approximately 95 and 98%, respectively. However, addition of hydrogen peroxide
over 50 mg L−1 inhibited the efficiency of the system. Addition of hydrogen peroxide to a UV/TiO2 system enhanced efficiency of removal of CODCr and color compared with no addition of hydrogen peroxide. This may be ascribed to capture electrons ejected from TiO2 and to the production of OH radicals. Application of the metal membrane in the UV/TiO2/H2O2 system enhanced the efficiency of removal of CODCr and color because of adsorption by the metal membrane surface and the production of OH radicals. By application of a metal
membrane with a nominal pore size of 0.5 μm, TiO2 particles were effectively separated from the treated water by metal membrane rejection. The photocatalytic metal membrane
had much less resistance than the humic acid, TiO2, and humic acid/TiO2 because of the degradation of humic acid by the photocatalytic reaction. 相似文献
85.
Development of eco‐friendly, cost‐effective, and high‐performance electrocatalysts to replace precious metal platinum for oxygen reduction reaction (ORR) has received increasing attention. Herein, we adopt a facile one‐pot strategy to embed Cu nanoparticles onto N‐doped carbon‐graphene (Cu@NC‐700). The Cu@NC‐700 exhibits robust and efficient ORR catalysis with positive half‐wave potential (~0.86 V vs. RHE) and low Tafel slope (33.9 mV?dec–1) in 0.1 M KOH solution. Meanwhile, it manifests remarkable electrochemical stability, and strong tolerance to methanol crossover and carbon monoxide poisoning. The synergistic effect between Cu‐N‐C sites, Cu nanoparticles, and N‐doped carbon support speeds up ORR electrocatalysis. 相似文献
86.
《中国化学快报》2020,31(8):2077-2082
The morphological and structural design provides an efficient protocol to optimize the performance of gas sensing materials. In this work, a gas sensor with high sensitivity for triethylamine (TEA) detection is developed based on p-type NiCo2O4 hierarchical microspheres. The NiCo2O4 microspheres, synthesized by a hydrothermal route, have a three-dimensional (3D) urchin-like structure assembled by nanorod building blocks. The structure-property correlation has been investigated by powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscope, scanning electron microscope, N2 adsorption-desorption tests and comprehensive gas sensing experiments. The influence of calcination temperature on the morphological structure and sensing performances has been investigated. Results reveal that the material annealed at 300 °C has a very large specific surface area of 125.27 m2/g, thereby demonstrating the best TEA sensing properties including high response and low limit of detection (145 ppb), good selectivity and stability. The further increase of the calcination temperature leads to the collapse of the 3D hierarchical structure with significantly decreased surface area, which is found to decline the sensing performances. This work indicates the promise of ternary p-type metal oxide nanostructures for application in highly sensitive gas sensors. 相似文献
87.
P.K. Sazonov Z. D?ambaskiM.M. Shtern R. Markovi?I.P. Beletskaya 《Tetrahedron letters》2011,52(1):29-33
Bromophilic attack by the transition metal carbonyl anion, [Re(CO)5]Na (pKa = 21.1), on 2-(1-bromoalkylidene)thiazolidin-4-ones is significantly faster than abstraction of an acidic lactam hydrogen (pKa ∼17-18), when the generated carbanion is stabilized by an α-CN or α-PhCO group. The bromophilic reaction of 2-(1-bromoalkylidene)thiazolidin-4-one, having an α-CN electron-withdrawing group, resulted in formation of a new metallacyclic anionic complex. With less reactive vinyl bromides, containing an α-CONHPh or α-CO2Et group, only deprotonation is observed. The role of the metal carbonyl anion is highlighted by a comparison with the 9-methylfluorenide carbanion (pKa of 9-methylfluorene is 22.3), which reacts exclusively via a deprotonation pathway. 相似文献
88.
Health or environmental issue caused by abnormal level of metal ions like Zn2+ or Cd2+ is a worldwide concern. Developing an inexpensive and facile detection method for Zn2+ and Cd2+ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn2+ and Cd2+ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S2−). The presence of Zn2+ (or Cd2+) can “turn-on” the weak fluorescence of QDs quenched by S2− due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn2+ (or Cd2+) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd2+). The limit of detection (LOD) for Zn2+ and Cd2+ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn2+ and Cd2+ over other metal ions and was successfully used in the detection of Zn2+ or Cd2+ in real water samples. 相似文献
89.
《无机化学与普通化学杂志》2018,644(6):367-375
The hydrogenation properties of the intermetallic compounds MgPd2 and Pd2Zn, crystallizing in the Co2Si type, were studied by in situ thermal analysis (DSC) under hydrogen pressure. Pd2Zn does not show any reaction with hydrogen while MgPd2 reversibly forms the hydride MgPd2H. Neutron diffraction on the deuterides reveals the compositions MgPd2D0.861(6) (ambient) and MgPd2D0.97(1) [308(2) K, 2.56(5) MPa deuterium] with hydrogen (deuterium) occupying distorted [MgPd5] octahedral voids. Quantum mechanical calculations support the structure models and show the hydrogenation to be exergonic for MgPd2 and endergonic for Pd2Zn. MgPd2H releases hydrogen under normal conditions or vacuum. Heating under hydrogen pressure leads first reversibly to MgPd2H≈0.2 and subsequently irreversibly to MgPd3H≈1 and MgH2. MgPd2, Pd2Zn, and MgPd2H were classified in a structure map. Trends of axial ratio changes upon hydrogenation of TiNiSi type and ZrBeSi type compounds are discussed. 相似文献
90.
Pyrrolidinedithiocarbamate (PDTC) chelates of Zn(II), Cu(II), Ni(II), Co(III), Fe(III), Mn(II), Cr(III), and VO(II) were analysed by capillary GC on a DB-1701 column (30 m x 0.25 mm id) with flame ionisation detection (FID). Linear calibrations were attained within "1-30 microg/mL" for Ni(II), Fe(III), Mn(II), Cr(III), Cu(II), and VO(II), and within "2-50 microg/mL" for Co(III) and Zn(II). The limits of detection were in the "150-500 ng/mL" range, corresponding to 15-50 pg amounts reaching the FID system. The optimised method was applied to the determination of Cu(II) and Ni(II) in coins, and that of Zn(II), Cu(II), Ni(II), Fe(III), Mn(II), Cr(III), and VO(II) in pharmaceutical preparations with relative standard deviations within 1.1-5.2%. The results obtained are in good agreement with sewage water samples and the declared values for the pharmaceutical formulations, or with the results of AAS of metal contents in coins, pharmaceutical preparations, and sewage water samples. 相似文献