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931.
932.
How to control the material properties by manipulating the unitcell thickness is crucial for applications of ferroelectric ultrathin films. To understand the polarization behaviour of ultrathin PbTiO3 (PTO) films grown on SrTiO3 (STO) substrate, we have systematically explored the strength and direction of polarization in each unitcell layer, using density functional theory combined with Born effective charge method. Strikingly, we find that the polar state of ultrathin PTO films is a composite result depending not only on thickness but also on boundary condition, initial polarization direction, etc. Besides, we also studied the surface effect on the polarization in the thicker PTO films for comparison with the ultrathin ones, which suggests that the surface effect is basically confined in a small range (3–5 unitcells thick at surface region) no matter what kinds of surface terminations and polarization directions. 相似文献
933.
Synthesis of α-Fe2O3 compound with regular hexahedron shape is firstly reported. X-ray diffraction and scan electron microscope are used to characterize the structure and morphology of the prepared sample, respectively. The average edge length of hexahedron is about 0.9 μm. A reaction mechanism has been proposed. The pH value is a crucial factor for the formation and shape of α-Fe2O3. Moreover, electrochemical impedance spectroscopy and charge-discharge test of α-Fe2O3 as anode material in lithium ion batteries are evaluated. The data indicate that the synthesized regular hexahedron α-Fe2O3 can show better electrochemical properties than that of the commercial. 相似文献
934.
Ordered Mesoporous Carbon and Thiolated Polyaniline Modified Electrode for Simultaneous Determination of Cadmium(II) and Lead(II) by Anodic Stripping Voltammetry
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Lin Tang Jun Chen Guangming Zeng Yuan Zhu Yi Zhang Yaoyu Zhou Xia Xie Guide Yang Sheng Zhang 《Electroanalysis》2014,26(10):2283-2291
The fabrication and evaluation of a glassy carbon electrode (GCE) modified with ordered mesoporous carbon (OMC), 2‐mercaptoethanesulfonate (MES)‐tethered polyaniline (PANI) and bismuth for simultaneous determination of trace Cd2+ and Pb2+ by differential pulse anodic stripping voltammetry (DPASV) are presented here. The morphology and electrochemical properties of the fabricated electrode were respectively characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Experimental parameters such as PANI disposition, preconcentration potential, preconcentration time and bismuth concentration were optimized. Under optimum conditions, the fabricated electrode exhibited linear calibration curves ranged from 1 to 120 nM for Cd2+ and Pb2+. The limits of detection (LOD) were 0.26 nM for Cd2+ and 0.16 nM for Pb2+ (S/N=3), respectively. Additionally, repeatability, reproducibility, interference and application were also investigated, and the proposed electrode exhibited excellent performance. The proposed method could be extended for the development of other new sensors for heavy metal determination. 相似文献
935.
Xiao-Dong Li Hong Zhang Yoshiyuki Miyamoto Yong-Jian Tang Chao-Yang Wang 《Structural chemistry》2014,25(1):177-185
A novel type of three-dimensional (3D) tetrahedral silsesquioxane-based porous frameworks (TSFs) with diamond-like structure was computationally designed using the density functional theory (DFT) and classical molecular mechanics (MM) calculations. The hydrogen adsorption and diffusion properties of these TSFs were evaluated by the methods of grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results reveal that all designed materials possess extremely high porosity (87–93 %) and large H2 accessible surface areas (5,268–6,544 m2 g?1). Impressively, the GCMC simulation results demonstrate that at 77 K and 100 bar, TSF-2 has the highest gravimetric H2 capacity of 29.80 wt%, while TSF-1 has the highest volumetric H2 uptake of 65.32 g L?1. At the same time, the gravimetric H2 uptake of TSF-2 can reach up to 4.28 wt% at the room temperature. The extraordinary performances of these TSF materials in hydrogen storage made them enter the rank of the top hydrogen storage materials so far. 相似文献
936.
937.
M. Tang 《Russian Journal of Coordination Chemistry》2014,40(8):594-597
The pentaatomic [CGa3Sn] and [CGa3Sn]? species were studied via density functional theory (DFT). Six planar geometry isomeric structures were gained, and one of them exists tetracoordinate planar carbon atom, respectively. To gain a better understanding about which electronic factors contribute to the stabilization of tetracoordinate planar carbon structures, natural bond orbital (NBO) analysis and the nucleus independent chemical shifts (NICS) were calculated. This analysis suggests that the presence of 18 valence electrons is crucial for planar geometries to be stable and preferred over tetrahedral structures. 相似文献
938.
M. Y. Tang J. Y. Liu W. Q. Chen Y. Yang S. Ren 《Russian Journal of Coordination Chemistry》2014,40(6):419-423
Two new cyano-bridged Cu(II)-Fe(II) binuclear complexes, [Cu(L1)Fe(CN)5(NO)] (I) [L1 = 1,3,6,8,11,14-hexaazatricyclo[12.2.1.18,11]octadecane and [Cu(L2)Fe(CN)5(NO)] · 2H2O (II) L2 = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.16,9]octadecane, have been assembled and structurally characterized by spectroscopy and X-ray crystallography. Complex I crystallizes in the monoclinic crystalline system of space group P21/c, while complex II crystallizes in the monoclinic crystalline system of space group P21/n. These two complexes assume a binuclear structure in which the Fe2+ ion is in an octahedron environment and the Cu2+ ion is in a square-prism geometry environment. 相似文献
939.
The evolution of amorphous calcium carbonate (ACC) into crystals in ethanol/water binary solvents under ambient temperature was investigated, and it was found to depend on the volume ratio of ethanol to water (R). Calcite remained dominant when the amount of water was high (R = 1/3). A slight change in the amount of ethanol (R = 3/1) could lead to a dramatic change in the polymorph from calcite to aragonite. However, when poly (allylamine hydrochloride) (PAH) was added at R = 3/1, almost pure vaterite could be obtained, which has a specific morphological variation (from hollow microspheres to cloud‐like). This study provides an alternative polymorphic route for the CaCO3 mineral by using the evolution of ACC in different solvent environments, which provides some useful clues for understanding the importance of kinetic control of the morphologies and polymorphs of a wide range of inorganic materials. In addition, this simple mild phase‐controlled synthetic method could be scaled up as a green chemistry route for the industrial production of different polymorphs of CaCO3. 相似文献
940.
Xiaolin Qiu Lixin Lu Zhixiong Zhang Guoyi Tang Guolin Song 《Journal of Thermal Analysis and Calorimetry》2014,118(3):1441-1449
This study focused on preparation and thermal properties of poly(stearyl methacrylate) shell (PSMA) microcapsules containing n-octadecane as a phase change material (PCM). Pentaerythritol triacrylate (PETA) and divinylbenzene (DVB) were employed as crosslinking agents. The surface morphologies, particle sizes, and distributions of the microencapsulated phase change material (microPCM) were studied by scanning electron microscopy. The thermal properties, thermal reliabilities, and thermal stabilities of the microPCMs were investigated by differential scanning calorimetry and thermal gravimetric analysis. The microPCM with DVB exhibits higher phase change enthalpies of melting (87.9 J g?1) and crystallization (94.8 J g?1) and a greater thermal stability in comparison with the microPCM with PETA. The phase change temperatures and enthalpies of the microPCMs varied little after thermal cycles. Thermal images showed that the gypsum board with PSMA/n-octadecane microPCM possessed temperature-regulated property. Therefore, microencapsulated n-octadecane with PSMA as shell has good thermal energy storage and thermal regulation potential. 相似文献