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1.
Polycrystalline SrCo1·2Fe10·8O19 (SCFO) and SrMn1·2Fe10·8O19 (SMFO) samples were prepared by the normal ceramic technique. Powder X-ray diffraction patterns indicated the crystallization in the M-type hexaferrite structure of the samples. X-ray absorption analyses proved Co2+ and Mn3+,4+ ions existing in SCFO and SMFO, respectively. Though Fe3+ is dominant in both the compounds, small amounts of Fe2+ and Fe4+ are present in SCFO and SMFO, respectively. Mössbauer spectra analyses also confirmed the dominance of Fe3+ in both the samples. Additionally, Fe3+ ions in the 12 k, 4f1, 4f2, and 2a sites could be attributed to the high-spin state (S = 5/2). A large QS value for the sextet assigned to the 2b site indicated that in this case Fe3+ could be in the low-spin state (S = 1/2) or there was the addition of Fe2+ (or Fe4+) when Fe in SrFe12O19 was partially replaced by Co2+ (or Mn3+,4+). The mixture of transition-metal ions with different oxidation states influenced the magnetic properties and microwave shielding ability. At frequencies f = 10–18 GHz, we have found SCFO showing the lowest reflection loss with RL = −11.1 dB at 13.2 GHz and the thickness t = 2.2 mm. With an absorption bandwidth of 0.7 GHz, and about 92% microwave energy being absorbed, SCFO is considered as a potential candidate for microwave shielding applications.  相似文献   
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缩酮席夫碱是良好的阴离子识别剂,利用量子化学密度泛函理论研究了3种缩酮席夫碱阴离子受体与阴离子客体相结合的空间结构、电荷分布、结合能等方面的变化,计算结果表明,阴离子受体分子的阴离子结合位点位于亚氨基-NH-部,受体分子和阴离子间通过氢键相互作用,阴离子有一部分负电荷转移到受体分子中,且转移的电荷量为R3-3 R3-2 R3-1,在考察的阴离子中,F~-与受体分子的结合能最大,而在3种受体分子中,R3-3对阴离子结合能最大.计算模拟结果,与实验情况相吻合.  相似文献   
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《Physics letters. A》2019,383(24):2897-2902
In the regime of above-threshold ionization of gas atom in the field of laser radiation, plasma with photoelectron distribution consisting of peaks at discrete energy values is formed. It is shown that the number of longitudinal waves in such plasma coincides with the number of peaks in the distribution function. When peaks practically don't overlap, the dispersion law of each wave in the region of short waves is determined by electrons from the corresponding peak. In this case the phase and group velocities of the waves are close to the electron velocity, which corresponds to the peak maximum. It is possible to talk about such waves as an electronic sound, since the perturbations of the electron density mainly arise due to pressure perturbations. When the peaks are narrow, but having a finite width, the Cherenkov damping of waves is exponentially small. Numerical calculations the dispersion laws for of the two and four waves in photoionized xenon plasma, in which the electron distribution function consists of two or four narrow peaks are given.  相似文献   
5.
本文构建了三种不同堆叠形式下的二维InSe/SnSe2范德华异质结模型,利用基于密度泛函理论的第一性原理方法综合考察了二维InSe/SnSe2三种不同堆叠情况下的几何构型及稳定性,在此基础上选取具有最稳定性能的构型.该异质结呈现出Ⅱ型能带对齐特征,带隙值为1.118 eV,可以实现电子-空穴的有效分离.另外,相比与单层二维InSe/SnSe2范德华异质结的光吸收能力达到明显提升,在紫外光范围内吸收系数达到10~6 cm-1.研究结果将为相关物理实验及机理研究提供理论基础,对二维InSe/SnSe2范德华异质结在光电器件中的应用具有重要的物理意义.  相似文献   
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基于密度泛函理论第一性原理的方法,计算了GaN、C单掺、Mg单掺和C-Mg共掺体系的电子结构和光学性质,计算结果表明:掺杂后,GaN体系的晶格发生畸变,有利于光生空穴-电子对的分离,C-Mg共掺体系结构最稳定,掺杂体系的禁带宽度均减小,其中C-Mg共掺体系的禁带宽度最小,在禁带中引入了杂质能级,说明掺杂可有效降低电子跃迁所需的能量.在光学性质方面,掺杂后,GaN在低能区介电峰和吸收峰均发生红移,且静介电常数增大;其中C-Mg共掺体系的对可见光的吸收最强,极化能力最强,因此C-Mg共掺将有望提高GaN在光催化性能和极化能力.  相似文献   
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We carried out first-principles electronic structure calculation to study the structural stability and magnetic properties of Mn-doped WS2 ultra-thin films within the density functional theory. Adopting various configurations of Mn doping into WS2 bilayer, we find that the magnetic phase can be manipulated among the ferromagnetic, antiferromagnetic, or ferrimagnetic phases by altering doping level and growth environment. Magnetic phase and strength are determined by magnetic coupling of Mn dopants 3d electrons which can be attributed crucially to the exchange interaction mediated by neighboring S atoms 3p electrons. Accompanying to the magnetic phase transition, the electronic structure reveals that transport properties switch from semiconducting with various bandgap to half-metallic states. This result implicates possible way to develop magnetic semiconductors based on Mn doped 2D WS2 ultra-thin films for spintronics applications.  相似文献   
8.
《Physics letters. A》2019,383(25):3138-3142
Based on the first-principle method, the effects of carbon dopants on AlP are studied. Our investigations indicate carbons substituting aluminum (CAl) or phosphorus (CP) cannot induce the AlP to be magnetic system. The AlP with CAl defects shows n-type metallic characteristic. As the carbons forming the interstitial doped configurations (Cint), a few percent of Cint could induce the AlP to be a half-metallic ferromagnet, and the half-metallic gaps could reach 0.45∼0.48 eV. Mean field theory predicts the Curie temperature for Cint doped configurations would be above room temperature. Formation energies indicate that Cint, CAl and CP defects could be realized experimentally. Positive pair binding energies indicate that carbon would form homogenous distribution in AlP host. This research suggests carbon is a promising dopant, and could be utilized to functionalize the AlP's properties for versatile applications.  相似文献   
9.
《中国化学快报》2020,31(4):1000-1003
Ti_3C_2 belongs to MXenes family,which is a new two-dimensional material and has been applied in many fields.With simple method of hydrothermal and high temperature calcination,nano structured Ni/Ti_3C_2T_x hybrid was synthesized.The stable layer structure of Ti_3C_2 MXene providing high surface area as well as excellent electronic conductivity are beneficial for deposition and decomposition of discharge product Li_2O_2.Furthermore,possessing special catalytic activity,Ni nanoparticles with size of about 20 nm could accelerate Li_2O_2 breaking down.Taking advantage of two kinds of materials,Ni/Ti_3C_2T_x hybrid as cathode of Li-O_2 battery can achieve a maximal specific capacity of 20,264 mAh/g in 100 mA/g and 10,699 mAh/g in 500 mA/g at the first cycle.This work confirms that the prepared Ni/Ti_3C_2T_x hybrid exhibiting better cycling stability points out a new guideline to improve the electrochemical performance of lithium-oxygen batteries.  相似文献   
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采用基于密度泛函理论的第一性原理计算方法,对未掺杂及La掺杂4H-SiC的电子结构和光学性质进行理论计算。计算结果表明,未掺杂4C-SiC其禁带宽度为2.257 eV。La掺杂后带隙宽度下降为1.1143eV,导带最低点为G点,价带最高点为F点,是P型间接半导体。掺杂La原子在价带的低能区间贡献比较大,而对价带的高能区和导带的贡献比较小。未掺杂4H-SiC在光子能量为6.25 eV时,出现一个介电峰,这是由于价带电子向导带电子跃迁产生。而La掺杂后,出现3个介电峰,分别对应的光子能量为0.47eV、2.67eV、6.21eV,前两个介电峰是由于价带电子向杂质能级跃迁产生,第三个介电峰是由于价带电子向导带电子跃迁产生。La掺杂后4H-SiC变成负介电半导体材料。未掺杂4h-SiC的静态介电常数为2.01,La掺杂的静态常数为12.01。  相似文献   
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