全文获取类型
收费全文 | 727篇 |
免费 | 55篇 |
国内免费 | 113篇 |
专业分类
化学 | 562篇 |
晶体学 | 9篇 |
力学 | 1篇 |
综合类 | 1篇 |
物理学 | 322篇 |
出版年
2024年 | 11篇 |
2023年 | 93篇 |
2022年 | 27篇 |
2021年 | 32篇 |
2020年 | 30篇 |
2019年 | 23篇 |
2018年 | 29篇 |
2017年 | 20篇 |
2016年 | 25篇 |
2015年 | 24篇 |
2014年 | 23篇 |
2013年 | 37篇 |
2012年 | 29篇 |
2011年 | 70篇 |
2010年 | 31篇 |
2009年 | 56篇 |
2008年 | 61篇 |
2007年 | 43篇 |
2006年 | 36篇 |
2005年 | 40篇 |
2004年 | 49篇 |
2003年 | 21篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有895条查询结果,搜索用时 15 毫秒
131.
Zhao Juan 《Journal of magnetism and magnetic materials》2009,321(1):43-46
In this paper, nanosized particles of (La0.47Gd0.2)Sr0.33MnO3 perovskite-type oxides were successfully synthesized at a relatively low calcinated temperature at 800 °C for 10 h using amorphous molecular alloy as precursor. X-ray diffraction (XRD) and electron diffraction (ED) revealed that the resulting product is of pure single-phase rhombohedral structure. The Curie temperature TC and magnetic entropy change (MCE) in (La0.47Gd0.2)Sr0.33MnO3 polycrystalline nanoparticles are determined and compared to those of similar systems prepared by the conventional solid-state reaction method. The Curie temperature TC is shifted to 298 k, and a relatively large MCE with a broad peak around Curie temperature is observed in (La0.47Gd0.2)Sr0.33MnO3 polycrystalline particles. These results suggested that this material is a suitable candidate as working substance in magnetic refrigeration near room temperature. 相似文献
132.
S.P. Crane C. Bihler S.T.B. Goennenwein R. Ramesh 《Journal of magnetism and magnetic materials》2009,321(4):L5
Multifunctional thin film nanostructures containing soft magnetic materials such as nickel ferrite are interesting for potential applications in microwave signal processing because of the possibility to shrink the size of device architecture and limit device power consumption. An essential prerequisite to future applications of such a system is a firm understanding of its magnetic properties. We show that nanostructures composed of ferrimagnetic NiFe2O4 pillars in a multiferroic BiFeO3 matrix can be tuned magnetically by altering the aspect ratio of the pillars by depositing films of varying thickness. Magnetic anisotropy is studied using ferromagnetic resonance, which shows that the uniaxial magnetic anisotropy in the growth direction changes sign upon increasing the film thickness. The magnitude of this anisotropy contribution can be explained via a combination of shape and magnetostatic effects, using the object-oriented micromagnetic framework (OOMMF). The key factors determining the magnetic properties of the films are shown to be the aspect ratio of individual pillars and magnetostatic interactions between neighboring pillars. 相似文献
133.
R. Dhahri M. Hajlaoui M.A. Valente 《Journal of magnetism and magnetic materials》2009,321(11):1735-1738
Electrical conductance and X-ray diffraction (XRD) measurements of lanthanum-deficiency La1−x□xMnO3 (x=0.05, 0.10 and 0.20) polycrystalline samples were performed to examine the effect of the internal pressure at B-site on the conduction mechanism. The structural study reveals that all samples crystallize in the rhombohedral system. The electronic conduction appears to be thermally activated at high temperature, which indicates the presence of semiconductor behaviour. The increase of the x content converts 3x Mn3+ to 3x Mn4+ ions with smaller ionic radius, which reduces the internal pressure and leads to the increase of the one-electron bandwidth W. This increase causes the appearance of metallic behaviour at low temperature for x=0.10 and 0.20 content. 相似文献
134.
We observed persistent photoconductivity (PPC) in La-based perovskite manganese oxides, La0.9Sr0.1MnO3 (LSMO) and La0.9Ca0.1MnO3 (LCMO), under X-ray irradiation. The PPC in LSMO was attributed to the collapse of the charge- and orbital-ordered (CO and OO, respectively) states, similar to that reported in previous papers. This PPC effect was different from that observed in a similar compound with a slightly different composition. This difference was explained in terms of doped carriers. This observation of PPC in LCMO is the first result of the PPC in a compound in which the ground state is not the CO phase; it was attributed to the collapse of the OO ground state. We proposed that OO ground state is a prerequisite for the occurrence of PPC in these compounds. 相似文献
135.
Brendan J. Kennedy Paul J. Saines Qingdi Zhou 《Journal of solid state chemistry》2009,182(10):2858-2866
The crystal structures of the perovskite manganites SrxCa1−x−yNdyMnO3 with y=0.1 or 0.2 have been investigated using synchrotron X-ray powder diffraction. At room temperature the structures change from depending on the cation distribution, the different structures exhibiting different tilts of the MnO6 octahedra. High temperature diffraction measurements demonstrate the presence of, an apparently continuous, isosymmetric I4/mcm to I4/mcm phase transition associated with the removal of long range orbital ordering. Heating the manganites to still higher temperatures results in a continuous transition to the cubic structure. A feature of such transitions is the continuous evolution of the octahedral tilt angle through the I4/mcm to I4/mcm phase transition. The orthorhombic structures do not exhibit orbital ordering and although a first order transition to the tetragonal structure is observed in Sr0.4Ca0.5Nd0.1MnO3, this high temperature tetragonal structure does not exhibit orbital ordering. 相似文献
136.
Brendan J. Kennedy Jimmy Ting Zhaoming Zhang Michihiro Miyake 《Journal of solid state chemistry》2009,182(4):954-90
Fifteen perovskite-type compounds Sr0.9−xCaxCe0.1MnO3, x=0-0.9 in steps as fine as 0.05, have been synthesised by solid state methods, and the room temperature structures characterised using X-ray synchrotron powder diffraction. At low Ca contents (x?0.45) the structures are tetragonal in space group I4/mcm and at high Ca contents (x?0.55) the compounds are orthorhombic in space group Pbnm. At room temperature these two phases co-exist in the compound with x=0.5. XANES measurements show the Ce to be present as Ce4+ in all the oxides. High temperature structures are reported for selected members. 相似文献
137.
Lijie He Hongming Yuan Keke Huang Chen Yan Guanghua Li Qiaoru He Yang Yu Shouhua Feng 《Journal of solid state chemistry》2009,182(8):2208-2212
The single crystals of perovskite fluorides (NH4)2NaVF6 and Na3VF6 were synthesized under mild hydrothermal conditions. The structures of the compounds were determined by means of single-crystal and powder X-ray diffraction analyses, respectively. (NH4)2NaVF6 has a cubic elpasolite-type structure and crystallizes in the space group with lattice constant a=8.495(0) Å. Rietveld refinement indicates that Na3VF6 has a monoclinic structure and is in space group P21/n. The compounds were characterized by scanning electron microscopy, thermogravimetric and differential thermal analysis, and variable temperature magnetic susceptibility. With the temperature decreasing, the magnetic studies of the compounds showed the magnetic ordering was related to the crystallographic features and isolated magnetic units. 相似文献
138.
Anirban Ghosh Jyoti Ranjan Sahu S. Venkataprasad Bhat C.N.R. Rao 《Solid State Sciences》2009,11(9):1639-1642
Magnetic and dielectric measurements confirm the multiferroic nature of LuMnO3. Raman spectra of LuMnO3 have been recorded in the 77–800 K range covering both the antiferromagnetic transition at 90 K and the ferroelectric–paraelectric transition at 750 K. The changes in the phonon modes frequencies and band-widths indicate the presence of phonon–spin coupling in the antiferromagnetically ordered phase. The ferroelectric–paraelectric transition is accompanied by the broadening and disappearance of many of the phonon modes. Some of the phonon modes also show anomalies at the ferroelectric transition. 相似文献
139.
通过在氧化还原稳定的钙钛矿材料钛铌酸盐的B位晶格中掺杂具有氧化还原活性的锰元素提高固体氧化物电解池复合电极电催化性能.研究发现,锰元素成功取代钛铌酸盐B位的Ti/Nb.掺杂后的样品的离子电导率在800℃下的氧化气氛和还原气氛下的离子电导率分别提高了约1和0.5个数量级.基于掺杂后的钛铌酸盐基复合阴极,氧离子传导型固体氧化物电解池电解水蒸汽的电流效率在有和无还原气体保护下分别提高了25%和30%. 相似文献
140.
Perovskite-type Ba0.5Sr0.5Al0.1Fe0.9O3-δ as Intermediate-Temperature Solid Oxide Fuel Cell Cathode 下载免费PDF全文
A cobalt-free perovskite-type Ba0.5Sr0.5Al0.1Fe0.9O3-δ (BSAF) is developed and electro-chemically studied as solid oxide fuel cell (SOFC) cathode. The structures, electrical con-ductivity, and electrode polarizations in symmetrical cell based on mixed ion conducting electrolyte were investigated, respectively. The temperature dependence of conductivity of BSAF in air shows a typical semiconductor behavior with positive temperature coefficient up to 450 oC where the conductivity reaches 14.0 S/cm while above this temperature the negative temperature coefficient dominates the total conductivity. Electrochemical charac-terizations show desirable polarization resistance of BSAF cathode in a symmetric cell based on mixed ion conducting electrolyte at 650-700 oC. A single SOFC with BSAF cathode shows OCV of 1.0 V and maximum output of 420 mW/cm2 at 700 oC with humidified hydrogen fuel and static air oxidant. 相似文献