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71.
Using pulsed-field-gradient (PFG) experiments, the sizes of the pores in ordered porous media can be estimated from the "diffraction" pattern that the signal attenuation curves exhibit. A different diffraction pattern is observed when the experiment is extended to a larger number (N) of diffusion gradient pulse pairs. Simulations to calculate signal values from arbitrary gradient waveforms are performed for diffusion in restricted geometries using a matrix operator formalism. The simulations suggest that the differences in the characteristics of the attenuation curves are expected to make it possible to measure smaller pore sizes, to improve the accuracy of pore size measurements and potentially to distinguish different pore shapes using the N-PFG technique. Moreover, when an even number of PFG pairs is used, it is possible to observe the diffraction pattern at shorter diffusion times and measure an approximation to the average pore size even when the sample contains pores with a broad distribution of sizes. 相似文献
72.
The structure of the double layer on the boundary between solid and liquid phases is described by various models, of which the Stern–Gouy–Chapman model is still commonly accepted. Generally, the solid phase is charged, which also causes the distribution of the electric charge in the adjacent diffuse layer in the liquid phase. We propose a new mathematical model of electromigration considering the high deviation from electroneutrality in the diffuse layer of the double layer when the liquid phase is composed of solution of weak multivalent electrolytes of any valence and of any complexity. The mathematical model joins together the Poisson equation, the continuity equation for electric charge, the mass continuity equations, and the modified G-function. The model is able to calculate the volume charge density, electric potential, and concentration profiles of all ionic forms of all electrolytes in the diffuse part of the double layer, which consequently enables to calculate conductivity, pH, and deviation from electroneutrality. The model can easily be implemented into the numerical simulation software such as Comsol. Its outcome is demonstrated by the numerical simulation of the double layer composed of a charged silica surface and an adjacent liquid solution composed of weak multivalent electrolytes. The validity of the model is not limited only to the diffuse part of the double layer but is valid for electromigration of electrolytes in general. 相似文献
73.
对多原子体系的量子动力学计算非常重要, 然而, 对含六原子以上的分子体系进行精确量子动力学计算仍具挑战性. 面向过程的基函数定制(PBFC)-并行迭代(PI)方法是一种高效的量子动力学方法, 已应用于对含九原子的丙二醛异构体系的氢迁移速率的精确量子计算. 本综述首先阐明了PBFC的基本思想, 之后重点回顾了PBFC-PI方法的具体内容、 该方法与其它方法的结合及其应用方面的新进展. 应用这些方法实现了对单氢迁移、 协同双氢迁移和分步双氢迁移3种类型基准体系的大规模并行计算, 有助于获得对氢迁移过程的新认识. 相似文献
74.
Both racemate and enantiomer of a novel double helix,binaphthylcyclooctaterthiophene(BN-COTh),which is a DNA-like molecule constructed by two single helices intertwined with each other via covalent bonds,have been synthesized with two building blocks,cycloocta-tetrathiophene(COTh) and cyclooctadinaphthyldithiophene(CONT) fused together via Negishi coupling reaction.Another homologue,dinaphthylcyclooctaterthiophene(DN-COTh) has been employed together as a model compound.Besides the synthetic work,BN-COTh and DN-COTh have been investigated by studying their crystal structures,spectroscopic behaviors,chiral resolution and chiral characteristics,including circular dichroism(CD) spectra and optical rotations.In addition,the novel crystal of enantiomer of(R,R,R)-BN-COTh has been explored.The enantiomer molecules packing along b-axis to form a larger and extended assembly packing due to intermolecular interactions between the enantiomer molecules and chloroform molecules in crystal. 相似文献
75.
Triple resonance solid-state NMR experiments using the spin combination 1H–13C–29Si are still rarely found in the literature. This is due to the low natural abundance of the two heteronuclei. Such experiments are, however, increasingly important to study hybrid materials such as biosilica and others. A suitable model substance, ideally labeled with both 13C and 29Si, is thus very useful to optimize the experiments before applying them to studies of more complex samples such as biosilica. Tetraphenoxysilane could be synthesized in an easy, two-step synthesis including double isotope labelling. Using tetraphenoxysilane, we established a 1H–13C–29Si double CP-based HETCOR experiment and applied it to diatom biosilica from the diatom species Thalassiosira pseudonana. Furthermore, we carried out 1H–13C{29Si} CP-REDOR experiments in order to estimate the distance between the organic matrix and the biosilica. Our experiments on diatom biosilica strongly indicate a close contact between polyamine-containing parts of the organic matrix and the silica. This corroborates the assumption that the organic matrix is essential for the control of the cell wall formation. 相似文献
76.
77.
Hiroyuki Muramatsu Kazunori Fujisawa Yong-Il Ko Kap-Seung Yang Takuya Hayashi Morinobu Endo Cheol-Min Yang Yong Chae Jung Yoong Ahm Kim 《催化学报》2014,35(6):864-868
Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 °C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 °C that gave the stoichiometry of CF0.20, CF0.30, and CF0.43, respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 °C, the strong radial breathing modes (RBMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 °C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 °C were thermally treated at 1000 °C in argon. However, in the case of the DWCNTs fluorinated at 400 °C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes. 相似文献
78.
79.
万升联 《数学物理学报(A辑)》2021,(1):237-244
该文研究一种新的解变分不等式的二次投影算法.通过构造一类新的严格分离当前迭代和变分不等式解集的超平面,进而建立了解决伪单调变分不等式投影算法的一种新的框架.通过改进已有结果的证明方法,证明了该算法生成的无穷序列是全局收敛的,并且在局部误差和Lipschitz条件下给出了收敛率分析. 相似文献
80.