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131.
用固相反应法制备了La0.45Ca0.55Mn1-xVxO3(x=0.00,0.10)多晶样品.通过X射线衍射谱、质量磁化强度-温度曲线、电子自旋共振谱,研究了V5+替代Mn3+/Mn4+对La0.45Ca0.55MnO3电荷有序相和自旋玻璃态的影响.实验结果表明,当x=0.10时,不仅母体的电荷有序相基本破坏,而且母体在40K左右出现的自旋玻璃态也被融化.电荷有序相被破坏的主要原因是用V5+替代Mn3+/Mn4+后,增加了Mn3+与Mn4+的比例,使铁磁双交换作用优于反铁磁超交换作用;自旋玻璃态的融化是由于V替代Mn后破坏了反铁磁背景下有少量铁磁成分的自旋玻璃态的形成条件. 相似文献
132.
M. Khazaei A. Malekzadeh F. Amini Y. Mortazavi A. Khodadadi 《Crystal Research and Technology》2010,45(10):1064-1068
In this study the effects of citric acid concentration, used as organic emulsifier, on the perovskite phase formation of the nano strontium manganite or cobaltite samples were studied. Stoichiometric perovskites in the absence and presence of citric acid were prepared by drying a solution containing molar ratio of Sr(NO3)2/Mn(NO3)2·4H2O and Sr(NO3)2/Co(NO3)2·6H2O = 1 followed by calcination at 900 °C for 5 h. Citric acid concentration, selected to be 0.0, 0.3, 0.6, 1.0, 1.3, 2.5 and 5 times of the total number of moles of the nitrate ions. The results revealed that increase in the citric acid concentration, larger than number of moles of the nitrate ions equivalent, deteriorates the perovskite phase formation. Instead, a new phase of carbonates and metal oxides are appeared. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
133.
W. Renz 《Molecular Crystals and Liquid Crystals》2013,570(1):549-558
Competing nematic and smectic A phases of comb-like polymers are described by combining Maier-Saupe and McMillan type theories with the worm concept of semi-flexible polymers. There are as few material parameters as possible: main chain flexibility and phenomenological coupling constants. New qualitative predictions, the existence of critical points and re-entrant nematic phases, as well as quantitative predictions for comparison with experiments are provided. A new mechanism for thermotropic nematic biaxiality which is specific of side-chain polymeric liquid crystals is found. 相似文献
134.
A formalism has been developed to calculate the steady-state temperature profiles induced by a cw laser in a composite system comprising a thick medium covered with a film of another medium. The analysis is carried out assuming that thermal and optical properties of the media are temperature-independent. A concept of the effective thermal conductivity for the system is introduced in terms of the maximum temperature rise. Temperature-distributions are numerically computed in typical cases for a circular Gaussian beam to illustrate dependence on film thickness, thermal conductivities and absorption coefficients of the media and size of the laser beam. 相似文献
135.
B. Chen 《Phase Transitions》2013,86(9):839-850
ABSTRACTPb(Mg1/2W1/2)1?xMxO3 (M?=?Zr,Sn,Ti) ceramics have been prepared by the conventional ceramic process. Their crystallographic, phase transition and dielectric properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer in this paper. The solubility of the tetra-valent cation in Pb(Mg1/2W1/2)1?xMxO3 decreases in the sequence of Ti4+?>?Zr4+?>?Sn4+. The doping led to the phase transition from orthorhombic antiferroelectric to cubic paraelectric phase, the microscopic nature of which could be attributed to the contraction of Pb-O12 dodecahedron. A definition of the ordering parameter of the cubic phase was deduced to quantitatively evaluate the B-site ordering degree which decreased with the increase in doping concentration. Anti-site disordering of Mg2+ and W6+ occurred in the high-level doping compositions, which led to the relaxor behavior observed in Ti4+-doped series with x?=?0.01 composition. Both of the maximum dielectric permittivity and loss in the paraelectric phase increased with the increasing doping concentration. 相似文献
136.
采用共沉淀法制备LaNi1-xCoxO3系列催化剂(x=0,0.2,0.4,0.6,0.8,1.0),研究B位离子Co的掺杂对单钙钛矿LaNiO3催化甲烷燃烧性能的影响。通过X射线衍射(XRD)、比表面积测定(BET)、程序升温还原(H2-TPR)、扫描电镜(SEM)、热重分析(TG-DSC)等实验技术对催化剂的结构和性能进行考察,以催化甲烷燃烧为目标,考察其对催化剂性能的影响。研究结果表明:Co离子的掺杂会改变单钙钛矿的晶型结构,改善催化活性,当x=0.8时,LaNi0.2Co0.8O3的催化甲烷燃烧活性最好,其比表面积为22.4 m2.g-1,T10%(起燃温度)为475℃,T90%(完全转化温度)为610℃,反应活化能最小,为91.4KJ/mol。 相似文献
137.
Xiao Liang Mei Chen Qian Wang Shaojun Guo Huai Yang 《Angewandte Chemie (International ed. in English)》2019,58(9):2799-2803
Perovskite nanocrystals (PNCs) are emerging luminescent materials due to their fascinating physic‐optical properties. However, their sensitive surface chemistry with organic polar solvents, oxygen, and moisture greatly hinders their developments towards practical applications. Herein we promote silica‐passivated PNCs (SP‐PNCs) by in situ hydrolyzing the surface ligands of (3‐aminopropyl) triethoxysilane. The resultant SP‐PNCs possesses a high quantum yield (QY) of 80 % and are precipitable by polar solvents, such as ethanol and acetone, without destroying their surface chemistry or losing QY, which offers an eco‐friendly and efficient method for separation, purification, and phase transfer of PNCs. Moreover, we further promoted a swelling–deswelling encapsulation process to incorporate the as‐made SP‐PNCs into non‐crosslinked polystyrene microspheres (PMs), which can largely increase the stability of the SP‐PNCs against moisture for long‐term storage. 相似文献
138.
The long-term stability remains one of the main challenges for the commercialization of the rapidly developing hybrid organic-inorganic perovskite solar cells. Herein, we investigate the electronic and optical properties of the recently reported hybrid halide perovskite (CH2)2NH2PbI3 (AZPbI3), which exhibits a much better stability than the popular halide perovskites CH3NH3PbI3 and HC(NH2)2PbI3, by using density functional theory (DFT). We find that AZPbI3 possesses a band gap of 1.31 eV, ideal for single-junction solar cells, and its optical absorption is comparable with those of the popular CH3NH3PbI3 and HC(NH2)2PbI3 materials in the whole visible-light region. In addition, the conductivity of AZPbI3 can be tuned from efficient p-type to n-type, depending on the growth conditions. Besides, the charge-carrier mobilities and lifetimes are unlikely hampered by deep transition energy levels, which have higher formation energies in AZPbI3 according to our calculations. Overall, we suggest that the perovskite AZPbI3 is an excellent candidate as a stable high-performance photovoltaic absorber material. 相似文献
139.
P. Barahona O. Pea A.B. Antunes C. Campos G. Pecchi Y. Moreno C. Moure V. Gil 《Journal of magnetism and magnetic materials》2008,320(14):e61-e64
Partial substitution of manganese by cobalt in rare-earth perovskites REMnO3 leads to unusual magnetic phenomena because of the simultaneous presence of Mn3+, Mn4+, Co2+ and Co3+ species. The magnetic nature of the RE cation plays a fundamental role in the magnetic properties. We present herein two specific families: for RE=La the magnetic behavior of the |Co+Mn| network is observed, while for Gd its strong magnetic moment interacts with the transition metals, leading to a spin reversal state. Magnetic interactions are maximized at x=0.50, as if two regimes exist: for x<0.5 Co substitutes Mn in the REMnO3 manganite, and for x>0.5 Mn substitutes Co in the RECoO3 cobaltite. 相似文献
140.
F. Fajardo R. Cardona D.A. Landínez Tllez J. Arbey Rodríguez M. J. Roa-Rojas 《Journal of magnetism and magnetic materials》2008,320(14):e111-e113
We report a detailed calculation of the structural and electronic properties for the cubic complex Bi2CrCuO6 perovskite material by density functional theory. The exchange-correlation potential was included through the generalized gradient approximation. From the adjusting of Murnaghan state equation to the energy as a function of volume data, we obtain an ideal lattice parameter of 7.763 Å. The density of states study was carried out considering the two spin polarizations. Results reveal that this material behaves as a conductor to the spin-down polarization and evidence a semiconductor tendency to the spin-up configuration. This tendency to the half-metallicity character is corroborated by the integer number of magnetic moment (3.0 μB), which is attributed to the Cr-spin-up orbital contribution. 相似文献