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91.
Shanru He Yuanyuan Chen Lulu Wang Xue Bai Tingting Bu Jie Zhang Ming Lu Nam-Chul Ha Chunshan Quan Ki Hyun Nam Yongbin Xu 《Molecules (Basel, Switzerland)》2022,27(15)
Pyridoxal 5′-phosphate (PLP) is the active form of vitamin B6, but it is highly reactive and poisonous in its free form. YggS is a PLP-binding protein found in bacteria and humans that mediates PLP homeostasis by delivering PLP to target enzymes or by performing a protective function. Several biochemical and structural studies of YggS have been reported, but the mechanism by which YggS recognizes PLP has not been fully elucidated. Here, we report a functional and structural analysis of YggS from Fusobacterium nucleatum (FnYggS). The PLP molecule could bind to native FnYggS, but no PLP binding was observed for selenomethionine (SeMet)-derivatized FnYggS. The crystal structure of FnYggS showed a type III TIM barrel fold, exhibiting structural homology with several other PLP-dependent enzymes. Although FnYggS exhibited low (<35%) amino acid sequence similarity with previously studied YggS proteins, its overall structure and PLP-binding site were highly conserved. In the PLP-binding site of FnYggS, the sulfate ion was coordinated by the conserved residues Ser201, Gly218, and Thr219, which were positioned to provide the binding moiety for the phosphate group of PLP. The mutagenesis study showed that the conserved Ser201 residue in FnYggS was the key residue for PLP binding. These results will expand the knowledge of the molecular properties and function of the YggS family. 相似文献
92.
The Pauli master equation describes the statistical equilibration of a closed quantum system. Simplifying and generalizing an approach developed in two previous papers, we present a derivation of that equation using concepts developed in quantum chaos and random-matrix theory. We assume that the system consists of subsystems with strong internal mixing. We can then model the system as an ensemble of random matrices. Equilibration results from averaging over the ensemble. The direction of the arrow of time is determined by an (ever-so-small) coupling to the outside world. The master equation holds for sufficiently large times if the average level densities in all subsystems are sufficiently smooth. These conditions are quantified in the text, and leading-order correction terms are given. 相似文献
93.
Yingzi Peng Dexuan Huo Liang Zheng Zhenghong Qian 《Particle & Particle Systems Characterization》2012,29(1):3-7
ZnO microstructures have been grown from zinc chloride (ZnCl2) and ammonia solution at 100 °C for 1 – 24 hours. X‐ray diffraction, scanning electron microscope and field‐emission scanning microscope were utilized to investigate the structural properties and morphology of the ZnO crystals. Structural investigations show that phase‐pure hexagonal structure ZnO has been successfully synthesized, and the hexagonal structure ZnO can be achieved in solutions with an appropriate range of concentrations. Under our experimental conditions, several different morphologies of ZnO structures were obtained, including flower‐like and bar flower‐like. The relationship between the morphology and experimental conditions are discussed. 相似文献
94.
基于一维光子晶体超晶格的多通道平顶透射特性 总被引:1,自引:0,他引:1
基于一维光子晶体超晶格理论及耦合腔理论,提出了一种具有多个平顶透射峰的超晶格结构.把传统单一材料的耦合腔换成有限周期的光子晶体结构,形成一种超晶格结构.通过使插入的光子晶体的光场有效耦合,能够产生多个平顶透射峰.运用传输矩阵法,研究了该结构的光谱特性以及结构和材料参量对透射峰的位置和半峰全宽的影响.计算结果表明,该结构具有较宽的带隙,并且多个平顶透射峰对称分布,透射率高,误差容忍度好.详细讨论了透射峰确切位置的计算方法,并给出了严格的解析表达式. 相似文献
95.
利用折射率椭球基本理论对线性电光效应进行了分析,对单轴晶体铌酸锂电光相位调制器的温度特性进行了研究。通过计算机进行数值模拟计算,分析了加电场时光通过LiNbO3电光调制器后出射光的相位变化与温度间的关系,得出在横向和纵向调制中温度对相位改变的影响。研究发现,无论在横向还是在纵向调制下,入射光偏振方向不同但其各自受温度影响的相位变化趋势大体一致,即随着晶体中温度的增加而增大。计算结果表明,LiNbO3电光调制的最佳使用方案为:电场沿x主轴方向施加,入射光偏振方向为感应主轴x’方向,且LiNbO3电光调制器粟用横向相位调制方式。 相似文献
96.
固-液结构圆柱声子晶体中弹性波的模式和带隙 总被引:2,自引:1,他引:2
利用一维固-液结构圆柱声子晶体中弹性波横向受限的条件,推导弹性波在一维固-液结构圆柱声子晶体中各个模式满足的关系式,研究各个模式弹性波的特征.并用色散函数计算各模式弹性波的带隙随模式量子数和圆柱半径的变化规律.得出一维固-液结构圆柱声子晶体的带隙由模式量子数和圆柱半径确定. 相似文献
97.
98.
3-Carboxy-2-pyrazinehydroxamic acid was prepared by a one pot reaction starting from pyrazine-2,3-dicarboxylic anhydride with a high yield, and characterized by IR, Mass spectrum, 1H NMR and 13C NMR spectra and single-crystal X-ray diffraction. It crystallizes in triclinic, space group Pī with a=4.8659(10), b=7.4233(15), c=11.602(2), α=96.904(2), β=92.422(3), γ=107.454(2)°, V=395.51(14)3 , Z=2, Dc=1.689g/cm3 , F(000)=208, μ(MoKα)=0.149 mm-1 , the final R=0.0473 and wR=0.1306 for 2853 observed reflections (I>2σ (I)). A three-dimensional framework was assembled through intermolecular hydrogen bonding between water and 3-carboxy-2-pyrazine-carbohydroxamic acid molecules. 相似文献
99.
100.
The microstructure, electrical conductivity and rheological properties of a nematic liquid crystal (5CB) doped at concentrations up to 4.5 wt% of montmorillonite (MMT) or organomontmorillonite (OMMT) clay nanoplatelets, were investigated at temperatures between 293 and 310 K. Microscopy and electrical conductivity assessment revealed noticeable differences in aggregation in MMT and OMMT suspensions, MMT nanoplatelets showing a strong tendency to aggregation. The incubation of 5CB in the presence of MMT initially produced loose aggregation, followed by the formation of compact aggregates. The latter had practically no influence on the surrounding inter-aggregate regions. In the case of OMMT, a greater degree of integration of the nanoplatelets was observed within the liquid crystal structure of 5CB, resulting in a noticeable effect on electrical conductivity and activation energy of the composite material. Thixotropy was observed in suspensions of 5CB composites formed with either MMT or OMMT. A composite of 5CB with OMMT also exhibited anomalous viscous thinning at shear rates below 100 s?1. A structural model is suggested to explain this behaviour. 相似文献