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991.
RE4(Al2−xGexO7+x/2□1−x/2)O2 (RE=Gd3+ and Nd3+) oxy-cuspidine series have been prepared by ceramic method (RE=Gd3+) and freeze-dried precursor method (RE=Nd3+). The compositional ranges and the high temperature stability have been determined for both series. Gadolinium aluminium cuspidines are stable at very high temperatures but the analogous neodymium compounds are only stable below 1273 K. Joint Rietveld analyses of neutron powder diffraction (NPD) and laboratory X-ray powder diffraction (LXRPD) have been carried out for Nd4(Al2O7□1)O2 and Nd4(Al1.5Ge0.5O7.25□0.75)O2 compositions. Furthermore, Rietveld refinement of synchrotron X-ray powder diffraction (SXRPD) data were carried out for Gd4(Al1.0Ge1.0O7.5□0.5)O2 composition. The refinements have confirmed the known structural features of the cuspidine framework. These cuspidines series are oxide ion conductors with negligible electronic contribution as determined from impedance spectroscopy at variable oxygen partial pressures. The enhancement in the overall oxide conductivity along the two oxy-cuspidine series is two orders of magnitude. Typical ionic conductivity values for doped samples are around 4×10−5 S cm−1 at 973 K. 相似文献
992.
C. Salt A. J. Lennox M. Takagaki J. A. Maguire N. S. Hosmane 《Russian Chemical Bulletin》2004,53(9):1871-1888
The principles of neutron capture therapy of tumor diseases, the types of drugs, and the results of their clinical applications are discussed.Based on the report presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (Moscow, May 30–June 4, 2004).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1795–1812, September, 2004. 相似文献
993.
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
994.
Peter S Berdonosov Valeriy A Dolgikh Ronald I Smith 《Journal of solid state chemistry》2004,177(7):2632-2634
The crystal structure of Bi0.7Yb1.3WO6 (a representative of the isomorphous series Bi2−xLnxWO6; 0.3<x<1.3, for most lanthanides) has been determined. Contrary to previous suggestions, this structure type (space group A2; a=8.1070(3) Å, b=3.7048(2) Å, c=15.8379(8) Å, β=103.548(4)°) contains layers of stoichiometry WO4, containing WO6 octahedra sharing both edges and corners. These layers alternate with fluorite-like (Bi/Yb)2O2 sheets; this is a novel and unexpected arrangement and contrasts dramatically with the purely corner-sharing octahedral WO4-layer in the parent Aurivillius phase Bi2WO6. 相似文献
995.
We report the first synthesis and high-temperature in situ X-ray diffraction study of InVO3. Polycrystalline InVO3 has been prepared via reduction of InVO4 using a carbon monoxide/carbon dioxide buffer gas. InVO3 crystallizes in the bixbyite structure in space group Ia−3 (206) with a=9.80636(31) Å with In3+/V3+ disorder on the (8b) and (24d) cation sites. In situ powder X-ray diffraction experiments and thermal gravimetric analysis in a CO/CO2 buffer gas revealed the existence of the metastable phase InVO3. Bulk samples with 98.5(2)% purity were prepared using low-temperature reduction methods. The preparative methods limited the crystallinity of this new phase to approximately 225(50) Å. Magnetic susceptibility and neutron diffraction experiments suggest a spin-glass ground state for InVO3. 相似文献
996.
Yttrium-doped uranium brannerite (U1−xYxTi2O6) and thorutite (Th1−xYxTi2O6−δ) phases were synthesized in air at 1400°C. Powder X-ray diffraction revealed that these phases crystallized to form monoclinic (C2/m) structures. Crystal structures of U0.54Y0.46Ti2O6 (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 Th0.91Y0.09Ti2O6−δ (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. These two phases were isostructural, revealing planes of corner and edge-sharing TiO6 octahedra separated by irregular eight-fold coordinate U/Y or Th/Y atoms. The oxygen sites within the structure of 1 were found to be fully occupied, confirming that the doping of lower valence Y atoms occurs in conjunction with the oxidation of U(IV) to U(V). Y doping of the thorutite phase 2 does not lead to oxidation but rather the formation of oxygen vacancies within the structure. 相似文献
997.
The diffusivity of benzene in a microporous silica powder has been measured by neutron scattering and NMR techniques. The measurements have been performed on un-supported silica but the powder has the same characteristics as the active layer of a real membrane. Self-diffusion coefficients of the order of 10–10 m2s–1 are found at 300 K by both techniques so that the model of Knudsen diffusion is not valid for benzene in this microporous material. Due to the presence of small pores, the diffusion of benzene in the membrane-material approaches the diffusion regime usually observed in zeolites. Furthermore, the diffusivity of benzene follows an Arrhenius law with an activation energy of 11 kJ mol–1. 相似文献
998.
New Halogenozincates M ZnX4 (MI = Li, Na; X = Cl, Br) of Olivine Type The hitherto unknown tetrabromozincates Li2ZnBr4 and Na2ZnBr4 have been prepared. Quaternary halides Li2Zn(Cl, Br)4 and Li2Zn(Br, I)4 have been not obtained due to decomposition to mixtures of LiCl and ZnBr2, and LiBr and ZnI2. The crystal structures of the olivine-type bromides and of the high-temperature polymorph of Li2ZnCl4 have been determined by neutron powder diffraction using the Rietveld method (space group Pnma, Z = 4, a = 1 360.41(4), b = 788.47(2), c = 647.07(2) pm, RI = 9.07% (Li2ZnBr4), a = 1 446.32(5), b = 853.02(3), c = 676.61(2) pm, RI = 9.29% (Na2ZnBr4), a = 1 277.60(3), b = 741.76(2), c = 611.10(1) pm, RI = 7.63% (Li2ZnCl4)). The Raman spectra as well as the results of thermal analyses (DSC) and conductivity measurements (impedance spectroscopy) are presented and discussed. Contrary to Li2ZnCl4, Li2ZnBr4 and Na2ZnBr4 do not undergo any phase transition between 20°C and their melting points. 相似文献
999.
A preconcentration method incorporated with neutron activation analysis was developed for the accurate determination of trace metals in biological and environmental samples. Bismuth diethyldithiocarbamate, thallium diethyldithiocarbarnate, and ammonium pyrrolidinedithiocarbamate were used as the preconcentration agents for three groups of metals. Trace metals were enriched and interfering elements such as Na, Br, P. K. etc. were removed simultaneously during the preconcentration process so that the sensitivity for each metal was greatly improved. Optimal conditions for sample digestion, group preconcentration of trace metals and neutron activation analysis of biological and environmental samples were discussed. 相似文献
1000.