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591.
The influences of electrical and optical excitations on the conductivity characteristic are investigated in bulk and edge devices of ITO/TiO_2/ITO structure. Driven by the electrical and optical stimuli independently, the conductivity relaxation behaviors of the pristine resistive state(PRS) are observed and ascribed to the electron trapping and the oxygen transport processes. For a resistive switching(RS) device, the conductance change under optical illumination is about two orders of magnitude smaller than the conductance change corresponding to the variation of background current due to the emergence of a great number of oxygen vacancies in the RS device. With the illumination being off, the conductance slowly decays,which suggests that the oxygen diffusion process dominates the conductance relaxation. The difference in conductance relaxation between the bulk and edge devices indicates that the oxygen exchange plays a critical role in the relaxation process of conductivity. The synergistic effects of both electrical and optical excitations on the RS devices could be used for novel applications in integrated optoelectronic memory devices. 相似文献
592.
Oxygen vacancy (Ov) has significant influence on physical and chemical properties of TiO2 systems,especially on surface catalytic processes.In this work,we investigate the effects of O v on the adsorption of formaldehyde (HCHO) on TiO2(110) surfaces through firstprinciples calculations.With the existence of Ov,we find the spatial distribution of surface excess charge can change the relative stability of various adsorption configurations.In this case,the bidentate adsorption at five-coordinated Ti (Ti5c) can be less stable than the monodentate adsorption.And HCHO adsorbed in Ov becomes the most stable structure.These results are in good agreement with experimental observations,which reconcile the long-standing deviation between the theoretical prediction and experimental results.This work brings insights into how the excess charge affects the molecule adsorption on metal oxide surface. 相似文献
593.
具有一定能量的光照导致低温绝缘二氧化钒(VO_2)发生绝缘体金属转变.本文通过密度泛函理论的Heyd-Scuseria-Ernzerhof杂化泛函方法对含氧空穴的低温绝缘VO_2非磁M1相进行第一性原理研究.研究发现,含氧空穴的M1的晶格参数几乎不变,但氧空穴附近的长的V—V键长却变短了.进一步研究发现,尽管纯的非磁M1的带隙是0.68 eV,但含O1和O2位的氧空穴非磁M1带隙分别为0.23 eV和0.20 eV,同时含有O1和O2位氧空穴非磁M1带隙为0.15 eV,这很好地解释了实验结果. 相似文献
594.
595.
使用DFT和DFT+U方法研究了Ca,Ba,Sm与Zr在CeO2体系中的掺杂能及其掺杂对缺陷形成能和氧离子迁移能的影响规律. 计算结果表明,对未含有氧离子空位的掺杂体系,掺杂能随着掺杂离子半径的增大而增大;对含有氧离子空位的掺杂体系,掺杂能受到掺杂离子半径和价态的影响;对各种掺杂体系电子结构的研究发现,在还原CeO2,Zr和Sm掺杂的CeO2体系中,由于氧空位捕获电子使Fermi能级升高;在碱土金属掺杂的CeO2体系中,由于Ca2+和Ba2+取代高价态Ce4+而产生的负电荷恰恰与氧离子空位产生的正电荷中和,因此Fermi能级几乎没有移动;还原CeO2和Zr掺杂的CeO2体系均含有Ce3+,其新态位于Ce4f和O2p之间,这将导致CeO2体系具有离子和电子导电特性;Ca,Ba和Sm的掺杂均抑制了CeO2体系中Ce4+的变价. 使用NEB方法对氧离子迁移能进行了研究,且结果表明,氧离子到空位的迁移路径几乎沿一条直线进行;当掺杂Ca,Ba,Sm与Zr时,氧离子迁移能均小于纯CeO2体系的;在这些掺杂体系中,Ba掺杂的体系氧离子迁移能最小,掺杂能较大,这可能导致在实验中常通过加入第三类掺杂物来引入Ba. 相似文献
596.
Chen-biao Xu Wen-shao Yang Qing Guo Dong-xu Dai Mao-du Chen Xue-ming Yang 《化学物理学报(中文版)》2013,26(6):646-650
We have investigated creation of variable concentrations of defects on TiO2(110)-(1×1) sur-face by 266 nm laser using temperature programmed desorption technique. Oxygen-vacancy defects can be easily induced by ultraviolet light, the defects concentration has a linear dependence on power density higher than 50 mW/cm2 for 90 s irradiation. No observa-tion of O2 molecule and Ti atom desorption suggests that UV induced defects creation on TiO2(110)-(1×1) is an effective and gentle method. With pre-dosage of thin films of water,the rate of defects creation on TiO2(110)-(1×1) is slower at least by two orders of magnitude than bare TiO2(110)-(1×1) surface. Further investigations show that water can be moreeasily desorbed by UV light, and thus desorption of bridging oxygen is depressed. 相似文献
597.
The electronic structures of Ni, Pd, Pt, Cu, and Zn atoms adsorbed on the perfect MgO(1 0 0) surface and on a surface oxygen vacancy have been studied at the DFT/B3LYP level of theory using both the bare cluster and embedded cluster models. Ni, Pd, Pt, and Cu atoms can form stable adsorption complexes on the regular O site of the perfect MgO(1 0 0) surface with the binding energies of 19.0, 25.2, 46.7, and 17.3 kcal/mol, respectively, despite very little electron transfer between the surface and the metal atoms. On the other hand, adsorptions of Ni, Pd, Pt, and Cu atoms show strong interaction with an oxygen vacancy on the MgO(1 0 0) surface by transferring a significant number of electron charges from the vacancy to the adsorbed metal atoms and thus forming ionic bonds with the vacancy site. These interactions on the vacancy site for Ni, Pd, Pt, and Cu atoms increase the binding energies by 25.8, 59.7, 85.2, and 19.1 kcal/mol, respectively, compared to those on the perfect surface. Zn atom interacts very weakly with the perfect surface as well as the surface oxygen vacancy. We observed that the interaction increases from Ni to Pt in the same group and decreases from Ni to Zn in the same transition metal period in both perfect and vacancy systems. These relationships correlate well with the degrees of electron transfer from the surface to the adsorbed metal atom. The changes in the ionization potentials of the surface also correlate with the adsorption energies or degrees of electron transfers. Madelung potential is found to have significant effects on the electronic properties of metal atom adsorptions on the MgO(1 0 0) surface as well as on an oxygen vacancy, though it is more so for the latter. Furthermore, the Madelung potential facilitates electron transfer from the surface to the adsorbed metal atoms but not in the other direction. 相似文献
598.
高温蠕变空位凝聚区的凝聚扩散 总被引:1,自引:0,他引:1
讨论局域凝聚扩散现象,导出局域凝聚扩散方程并给出了解的存在唯一性定理,对凝聚-扩散方程的稳定性的分析获得结论,定态解的稳定性由凝聚函数控制,并导出一元系统和二元系统的失稳临界条件表达式。 相似文献
599.
In this paper we investigate self-diffusion of Ti and Al along interfaces present in the lamellar L10 TiAl by atomistic computer modeling. The interactions between the atoms are described by central-force many-body potentials. The approach adopted is similar to that used in earlier atomistic modeling of bulk diffusion in TiAl [1, 2]. Both the formation and migration of vacancies is examined. The interfaces studied are the three types of –interfaces: ordinary twin, pseudotwin and 120° rotational fault. For the latter two interfaces the diffusion was investigated not only for the stoichiometric case but also when the interfaces possess a surplus of titanium in the form of a layer with the composition and structure of Ti3Al, as was found in an earlier Monte Carlo study of titanium segregation to these interfaces. The calculations suggest that the diffusivity along –interfaces is higher than in the bulk. However, the difference between bulk and interfacial diffusivity is not as drastic as it may be encountered in grain boundaries. At the same time the above mentioned surplus of Ti appears to affect the interfacial diffusion only marginally. 相似文献
600.
G Ananthakrishna 《Pramana》1982,19(6):633-643
It is known that the density of vacancy loops in quenched aluminium and stacking fault tetrahedra in quenched gold show a
saturation for low ageing temperatures. The physical mechanism leading to this effect is not well understood. In this paper
we consider a simple model which allows us to obtain the temperature dependence of total density. The analysis shows that
the plateau region arises due to the fact that the number of absorption sites of a cluster is larger than the number of emission
sites. The temperature dependence of the average number of vacancies in a cluster and the single vacancy concentration in
equilibrium with the clusters are discussed. 相似文献