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991.
S. Grandi C. Tomasi P. Mustarelli F. Clemente C. M. Carbonaro 《Journal of Sol-Gel Science and Technology》2007,41(1):57-63
The entrapment of organic dyes in inorganic solids offers several advantage for solid-state laser applications with respect
to the use of liquid or polymer hosts. Among the various inorganic hosts, silica is preferred for its superior mechanical,
thermal and optical properties. Organic dyes, such as Rhodamine 6G (Rh6G), can be immobilised in SiO2 both physically (materials of class I), and by covalent bonds (class II materials). In the past years Rh6G-SiO2 class I hybrids were prepared. In this work we propose, for the first time, a Rh6G-SiO2 class II hybrids. We describe the preparation of a suitable sol-gel Rh6G precursor verified by FT-IR analysis and report
the characterization of the hybrid materials by means of thermal and porosimetric analysis and optical spectroscopy measurements.
The precursor is thermally stable up to ∼250°C, and its optical characteristics (UV-VIS absorbance and photoluminescence,
PL) do not change with respect to those of the pristine dye molecule. The PL spectra of the final hybrids show that they are
promising candidates for applications in solid state dye lasers. 相似文献
992.
Ma José Ruiz-Chancho Rosa Sabé José Fermin López-Sánchez Roser Rubio Patrick Thomas 《Mikrochimica acta》2005,151(3-4):241-248
Arsenic extraction in natural and spiked soil samples was studied using two main types of extractants. The extractants were
phosphoric acid used alone and with the addition of reducing agents (ascorbic acid and hydroxylammonium hydrochloride). The
stability of arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in the extracts
over time and under different storing conditions was assessed by means of LC-HG-AFS. A protocol was devised to extract arsenic
species from soils. The protocol assures the stability of the original sample species in the extract proposed by using an
extraction solution of phosphoric acid with ascorbic acid and by purging the extracts after microwave extraction.
The total As, Mn and Fe content in aqua regia and in phosphoric extracts was also measured by ICP-AES in order to perform
the mass balance. 相似文献
993.
There is considerable evidence that toxicity and physiological behavior of arsenic depends on its chemical forms. Arsenic speciation became therefore the subject of increasing interest in recent years. A sensitive method for the determination of arsenic species has been developed. The proposed procedure involves the use of high-performance liquid chromatography and inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Six arsenic compounds were separated by anion-exchange chromatography with isocratic elution using tartaric acid as mobile phase with an elution order: arsenocholine, arsenobetaine, dimethylarsinic acid, methylarsonic acid, arsenous acid and arsenic acid. The chromatographic parameters affecting the separation of the arsenic species were optimized. Analytical characterization of the method has been realized with standard solutions. The detection limits for six arsenic compounds were from 0.04 to 0.6 g/L as As element. The repeatability (expressed by R.S.D) was better than 7% for all investigated compounds. The HPLC-ICP-MS system was successfully applied to the determination of arsenic compounds in environmental and biological samples in g/L level. 相似文献
994.
A modified Su–Schrieffer–Heeger Hamiltonian‐based model is used to compute the electronic and geometric structures of fairly long polythiophene (PT) chains, neutral as well as doped. The geometry optimization is carried out by the simulated annealing method. Both Metropolis and Glauber functions are used for sampling. It is shown that a bipolaron can be structurally represented by a fragment of the PT chain containing 14 thiophene units. As a series of bipolaronic defects are introduced in a long PT chain (50–100 rings), the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap energy (Δ) becomes vanishingly small, a feature not present in the PT chains of similar sizes containing polaronic defects. The Fermi energy level (EF) also moves into the valency band and nonzero density of states at ? = EF are created. Once again, this feature is shown to be missing in PT chains containing polaronic defects. Implications of these findings are analyzed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
995.
Certified reference materials (JMS-2 and JMS-1 – Marine sediment, LKSD-1 Lake Sediment, and STSD-1 Stream Sediment) and bottom
sediment were analysed for arsenic by hydride generation atomic absorption spectrometry (HG-AAS) after digestion by different
methods (microwave digestion, digestion in aluminium block, dry digestion) and different combinations of acids (HNO3, HCl, HClO4, H2SO4). The study revealed that both wet and dry digestion can be used to digest the reference materials and bottom sediment. Exceptionally
satisfactory results were produced by the application of aqua regia, HNO3 + HCl + HClO4, and HNO3 + HCl mixtures. Addition of Mg(NO3)2 during dry digestion caused an increase in arsenic recovery in the reference materials and improved the accuracy of arsenic
determination in the bottom sediments. 相似文献
996.
Doped uranium brannerite phases (U1−xMxTi2O6; M=Ca2+, La3+ and Gd3+; x<0.5) were synthesized at 1400°C; the range of solid solution was found to vary depending on whether sintering took place in argon or air. Powder X-ray diffraction revealed that these phases crystallized to form monoclinic (C2/m) structures. In particular, the crystal structures of U0.74Ca0.26 Ti2O6 (1) (a=9.8008(2); b=3.7276(1); c=6.8745(1); β=118.38(1); V=220.97(1); Z=2; RP=7.3%; RB=4.6%) and U0.55La0.45Ti2O6 (2) (a=9.8002(7); b=3.7510(3); c=6.9990(5); β=118.37(4); V=226.40(3); Z=2; RP=4.5%; RB=2.9%) were refined from powder neutron diffraction data, revealing planes of corner and edge-sharing TiO6 octahedra separated by 8-fold coordinate U/M atoms. The oxygen sites within these structures were found to be fully occupied, confirming that the doping of lower valence M atoms occurs in conjunction with the oxidation of U(IV) to U(V). 相似文献
997.
基于密度泛函理论的燃煤飞灰未燃尽碳与烟气砷作用机理 《燃料化学学报》2003,48(11):1365-1377
基于密度泛函理论研究了燃煤飞灰中未燃尽碳(unburned carbon, UBC)组分对气态单质砷As及其氧化物AsO、AsO2和As2O3的作用机理。结果表明,单质砷优先吸附于碳桥位,吸附能在(-5.95)-(-5.88) eV。AsO分子中的砷、氧原子分别与碳原子成键时,吸附构型最稳定,吸附能最低为-7.87 eV。当AsO2在未燃尽碳表面解离形成一个AsO和表面活性氧时,体系最稳定,吸附能为-10.65 eV。当三角双锥As2O3分子以两个氧原子首先碰撞未燃尽碳表面时,将解离形成AsO和AsO2小分子,并分别与表面碳成键,此时体系吸附能相较于未解离情形而言显著降低,达到-10.64 eV。飞灰未燃尽碳与AsO或AsO2小分子的结合较紧密,局部倾向于形成特殊的五元环结构。毒性最强的三价态砷As2O3,相较于As、AsO和AsO2而言,化学性质稳定,不易发生吸附。将其催化裂解为AsO、AsO2小分子,有望成为可行的燃煤电厂烟气砷污染控制措施。 相似文献
998.
Yttria stabilized zirconia (YSZ) thin films are obtained using both spray-pyrolysis and dip-coating. The ability of YSZ films
incorporated with platinum nanospecies (Pt-YSZ) to detect oxygen is compared with that of pure YSZ thin films using a new
experimental setup. With this system, the surface electrical resistance of the films as a function the oxygen content is measured
at a fixed temperature. In addition, the effects of thermal annealing on the oxygen sensitivity of the films are observed.
Platinum doped samples, Pt-YSZ, show different kinetics of carrier diffusion as compared to pure YSZ samples. 相似文献
999.
Electroconduction of Solid Electrolyte La0.88Sr0.12Ga0.82Mg0.18O2.85: Effect of a Prolonged Exposure
S. N. Shkerin D. I. Bronin N. A. Kalashnikova S. M. Beresnev 《Russian Journal of Electrochemistry》2004,40(4):449-452
The overall resistance and resistances of the bulk and grain boundaries of solid electrolyte La0.8Sr0.12Ga0.82Mg0.18O2.85 kept for a long time in air at 773-1073 K are studied by impedance spectroscopy. The increase in the electrolyte resistance with time is shown to be connected with that in the resistance of grain boundaries. 相似文献
1000.
Kerstin Scheurell 《Journal of solid state chemistry》2007,180(2):749-758
The structural properties of vanadium doped aluminium oxyfluorides and aluminium oxides, prepared by a modified sol-gel synthesis route, were thoroughly investigated. The influence of the preparation technique and the calcination temperature on the coordination of vanadium, aluminium and fluorine was analysed by different spectroscopic methods such as Raman, MAS NMR and ESR spectroscopy. In all samples calcined at low temperatures (350 °C), vanadium coexists in two oxidation states VIV and VV, with VIV as dominating species in the vanadium doped aluminium oxyfluorides. In the fluoride containing solids aluminium as well as vanadium are coordinated by fluorine and oxygen. Thermal annealing of 800 °C leads to an extensive reorganisation of the original matrices and to the oxidation of VIV to VV in both systems. 相似文献