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31.
周波 《应用数学学报(英文版)》2001,(3)
A digraph G is called primitive if there ekists a positive integer k such that there isa walk of length k from u to v for each ordered pair of not necessarily distinct vertices uand v. The smallest such k is called the exponent of G, denoted by γ(G). Exponents forprimitive digraphs have been studied extensively due to their intrinsic importance in graphtheory, combinatorics, matrix theory, and their applications in communication problems. Asa generalization of exponents, Brualdi and Liu[1] … 相似文献
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We have investigated the persistent current in a mesoscopic ring with a side-coupled quantum dot. The problems are probed by using the one-impurity Anderson Hamiltonian and are treated with the slave boson mean field theory. It is shown that the persistent current in this system has the spin fluctuations, and the charge transfers between the two subsystems are suppressed in the limit of Δ/T_K^0《1. The minimum value of the persistent current for ξ_K/L=5 of the odd parity system provides an opportunity to detect the Kondo screening cloud. 相似文献
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多核超顺磁性Ni0.5Zn0.5Fe2O4/SiO2催化载体的制备与表征 总被引:3,自引:2,他引:1
采用化学共沉淀法与溶胶-凝胶法相结合, 在制备过程中改变磁性纳米粒子和TEOS的引入方式, 成功地制备了多核超顺磁性Ni0.5Zn0.5Fe2O4/SiO2催化剂载体. 采用透射电子显微镜(TEM)、氮气吸附、X射线衍射(XRD)及物理性质综合测试系统(PPMS)对样品进行了表征, 利用永磁铁对载体的分离效果进行了验证. 研究结果表明, 改进制备方法后, 制备的载体比表面积明显增大, 这有利于催化剂在载体上的分散与固载; 样品的饱和磁化强度明显增加, 表明样品具有很好的磁响应能力, 有利于催化剂的分离, 同时, 载体的超顺磁特性也有利于液相催化体系中催化剂的分散. 相似文献
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Peptide frictions in water nanofilms of various thicknesses on a mica surface are studied via molecular dynamics simulations. We find that the forced lateral motion of the peptide exhibits stick-slip behaviour at low water coverage; in contrast, the smooth gliding motion is observed at higher water coverage. The adsorbed peptide can form direct peptide-surface hydrogen bonds as well as indirect peptide-water-surface hydrogen bonds with the substrate. We propose that the stick-slip phenomenon is attributed to the overall effects of direct and indirect hydrogen bonds formed between the surface and the peptide. 相似文献
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Using a first-principles approach based on density functional theory,this paper studies the electronic and dynamical properties of β-V2O5.A smaller band gap and much wider split-off bands have been observed in comparison with αV2O5.The Ramanand infrared-active modes at the Γ point of the Brillouin zone are evaluated with LO/TO splitting,where the symbol denotes the longitudinal and transverse optical model.The nonresonant Raman spectrum of a βV2O5 powder sample is also computed,providing benchmark theoretical results for the assignment of the experimental spectrum.The computed spectrum agrees with the available experimental data very well.This calculation helps to gain a better understanding of the transition from αto β-V2O5. 相似文献
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