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991.
The coordination numbers of rigid spheres were simulated on a computer to obtain an improved empirical equation when surrounding spheres are of uniform size. In the case of two different species of surrounding spheres, the coordination numbers vary as a function of local composition and radius ratios. By fitting simulation results, correlations were proposed, which are expected to be of practical use in thermodynamic of real solutions. 相似文献
992.
Summary We calculate several features in the dynamical behaviour of the reactions O(3P)+XY→OX+Y (XY=Br2, BrCl) using the quasi-classical trajectory method. The results are compared to analogous results for the reactions O(3P)+Cl2, I2. The similarities observed in this homologous series of reactions indicate that the dynamics are influenced to a significant
degree by the long-range repulsive forces between the reactants. 相似文献
993.
994.
Camellia Panatarani 《Journal of Physics and Chemistry of Solids》2004,65(11):1843-1847
A europium doped ZnO (ZnO:Eu) particle was directly synthesized by the spray pyrolysis method. The crystal structure of samples was designated by the europium ion and the synthesis temperature. We identified the coexistence of Eu2+ and Eu3+ ions in the as prepared ZnO, which was strongly influenced by the doping concentration and the synthesis temperature. With addition of a 0.5 mol% concentration of europium ions, only the Eu2+ ion existed in particles, while both Eu2+ and Eu3+ ions existed in sample using 1 mol% or higher concentration of europium ions. Changing the wavelength of the excitation source, we also found that both the blue and red luminescence can be obtained. 相似文献
995.
P.M. Sousa M.E. Melo Jorge M.D. Carvalho R.P. Borges M. Godinho 《Journal of Physics and Chemistry of Solids》2004,65(11):1823-1829
Ca4Mn3−xCrxO10 compounds were synthesized in order to investigate the role of an isoelectronic substitution in the layered manganite. Induced structural changes are mainly described as a distortion of the two types of octahedra in the n=3 RP structure. The results indicate that Cr3+ is not the only significant valence state for chromium ions. Electrical and magnetic characterization allow to conclude that chromium does not favour the double exchange mechanism in these compounds. 相似文献
996.
Vera-Maria Graubner Thomas Lippert Alexander Wokaun Laurent Servant 《Applied Surface Science》2006,252(13):4781-4785
Poly(dimethylsiloxane) (PDMS) has been irradiated with a frequency quadrupled Nd:YAG laser and a KrF*-excimer laser at a repetition rate of 1 Hz. The analysis of ablation depth versus pulse number data reveals a pronounced incubation behavior. The thresholds of ablation (266 nm: 210 mJ cm−2, 248 nm: 940 mJ cm−2) and the corresponding effective absorption coefficients αeff (266 nm: 48900 cm−1, 248 nm: 32700 cm−1, αlin = 2 cm−1) were determined. The significant differences in the ablation thresholds for both irradiation wavelengths are probably due to the different pulse lengths of both lasers. Since the shorter pulse length yields a lower ablation threshold, the observed incubation can be due to a thermally induced and/or a multi-photon absorption processes of the material or impurities in the polymer.Incubation of polymers is normally related to changes of the chemical structure of the polymer. In the case of PDMS, incubation is associated with local chemical transformations up to several hundred micrometers below the polymer surface. It is possible to study these local chemical transformations by confocal Raman microscopy, because PDMS is transparent in the visible. The domains of transformation consist of carbon and silicon, as indicated by the appearance of the carbon D- and G-bands between 1310 and 1610 cm−1, a band appearing between 502 and 520 cm−1 can be assigned to mono- and/or polycrystalline silicon.The ablation products, which are detected in the surroundings of the ablation crater consist of carbon and amorphous SiOx (x ≈ 1.5) as detected by infrared spectroscopy. 相似文献
997.
Lihong Zhang 《Journal of Physics and Chemistry of Solids》2006,67(8):1678-1686
Analogous layered double hydroxides (LDHs) with the Cu2+/Ni2+/Cr3+ molar ratio of 1/2/1 on the brucite-like layers and interlayer anions (viz sulfate, nitrate and carbonate, respectively) were synthesized by a coprecipitation method. For the first time, the effects of interlayer anions on the structural properties of as-synthesized LDHs and resulting calcined products at 773 K were investigated by means of powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The results indicate that the nature of interlayer anions involved within the hydrotalcite (HT)-like structure has a larger influence on the thermal stability of LDHs precursors. Calcination of well-crystallized LDHs leads to the formation of mixed metal oxides including CuO, NiO and Cu2+-, Ni2+- and Cr3+-containing spinel phases, the composition distributions of which obtained from LDHs precursors depend on the nature of interlayer anions, thus resulting in the difference of the reducibility of reducible metal species in the calcined LDHs. Moreover, the surface basicity of the calcined material, which is related to the different behaviour of LDHs precursors during the thermal decomposition depending on the interlayer anions, increases progressively following the order of calcined LDHs from sulfate to nitrate and carbonate. 相似文献
998.
Although chlorinated paraffins (CP) are produced in large amounts (300 000 tonnes per year), little is known about their occurrence in the environment due to the lack of specific and sensitive analytical methods. The present paper describes the GC/MS analysis of different CP's using capillary gas chromatography with on-column injection and negative ion chemical ionization (NCI) mass spectrometry. Chromatographic resolution of groups of isomers and homologues was obtained. The chromatograms and mass spectra are discussed. The suitability of this method for trace analysis of a CP sample using multiple ion detection (MID) is described. 相似文献
999.
Optical properties of SnO2 thin films in the 4–60 eV energy range are determined by reflection electron energy loss spectroscopy. Bulk and surface electron loss functions, real and imaginary parts of the dielectric function, refraction index, extinction and absorption coefficients are obtained from the analysis of the electron energy loss spectra. Electronic transitions are identified through the interpretation of the optical data. The samples (250–500 nm thick) were produced by ion beam-induced chemical vapor deposition. It is found that the compacity of the SnO2 thin films affects their optical properties and therefore the relative intensity of the observed electronic transitions. The advantages of this method to determine optical properties of thin films are discussed. Inelastic mean free paths (6.2, 17 and 41 Å for electrons traveling in SnO2 with kinetic energies of 300, 800 and 2000 eV, respectively) are obtained from the corresponding inelastic electron scattering cross-sections. 相似文献
1000.
In the present study the synthesis of metastable alloys of the noble metal Au and the semimetal Sb is realized by using high pressure techniques. The influence of Au on bulk Sb is shown experimentally by stepwise substitution. In addition to the effect of the most electronegative noble metal on Pauling's scale in the binary Au‐Sb phases, some ternary compounds with In, Sn, As, and Te in addition to Au and Sb are discussed. The experiments are planned to obtain a better knowledge on the reasons for building up a simple cubic Sb partial lattice, and their crystallographic results are used to construct model structures for new electronic structure calculations from first principles on the metastable π‐phases. Using the LCAO‐CO ansatz and density‐functional methods, we study total energies, band structures, densities of states and charge transfer properties according to Bader's method by integrating zero flux surfaces. Finally, from electronic band structure analysis, the quantities “chemical potential” μ, and “chemical hardness”, η, are derived according to the original ideas of Pearson and Parr and are applied to solid state problems using special points of the Brillouin zones within a band structure approximation for the first time. The results are shown to support the experimental findings about the substitution path within the system Au‐Sb. 相似文献