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51.
采用嵌入原子势,使用分子动力学方法对金属Al不同低指数晶面的表面熔化现象分别进行了模拟.分析了熔化过程中样品结构组态的变化.模拟结果表明对于不同的自由表面,表面熔化呈现出明显的各向异性行为.Al(110)面在低于熔点的温度之下发生预熔化;(111)与(001)面都出现过热现象.与(111)面不同,(001)面发生过热现象时表面原子层为类液层,而(111)面仍然保持很好的晶格结构,即预熔化的Al(001)面在高于熔点的温度下,仍可以在很长的时间内处于相对稳定的亚稳态.由模拟得到Al的热力学熔点为950 K左右,与实验值基本符合.
关键词:
分子动力学
表面熔化
过热 相似文献
52.
A fundamental mode Nd:YAG laser is experimentally demonstrated with a stagger pumped laser module and a special resonator. The rod is pumped symmetrically by staggered bar modules. A dynamic fundamental mode is achieved with the special resonator under different pump levels. A maximal continuous wave output of 61 W (M^2 = 1.4) is achieved with a single rod. An average output of 47 W, pulse width of 54 ns, pulse energy of 4.7 mJ and peak power of 87kW are obtained under the Q-switched operation of 10 kHz. 相似文献
53.
建立了反相高效液相色谱(RP-HPLC)定量检测离子液体溴化1-乙基-3-甲基咪唑-水体系中青蒿素含量的方法.检测条件为:室温(25±1)℃,C18反向柱(250 mm×4.6 mm, 5 μm),以V(甲醇): V(0.01 mol/L HAc-NaAc溶液,pH=5.9)=60: 40混合溶液为流动相,流速0.5 mL/min,检测波长为260 nm.青蒿素浓度在5~30 mg/L之间线性回归方程为y=2.20326×107x-30928.7,相关系数r=0.9990.本方法回收率为100 2%;相对标准偏差(RSD)为0.42%. 相似文献
54.
Orientation dependence of structural transition in fcc Al driven under uniaxial compression by atomistic simulations 下载免费PDF全文
By molecular dynamics simulations employing an embedded atom method potential,we have investigated structural transformations in single crystal Al caused by uniaxial strain loading along the [001],[011] and [111] directions. We find that the structural transition is strongly dependent on the crystal orientations. The entire structure phase transition only occurs when loading along the [001] direction,and the increased amplitude of temperature for [001] loading is evidently lower than that for other orientations. The morphology evolutions of the structural transition for [011] and [111] loadings are analysed in detail. The results indicate that only 20% of atoms transit to the hcp phase for [011] and [111] loadings,and the appearance of the hcp phase is due to the partial dislocation moving forward on {111} fcc family. For [011] loading,the hcp phase grows to form laminar morphology in four planes,which belong to the {111} fcc family; while for [111] loading,the hcp phase grows into a laminar structure in three planes,which belong to the {111} fcc family except for the (111) plane. In addition,the phase transition is evaluated by using the radial distribution functions. 相似文献
55.
Silicon germanium(SiGe) heterojunction bipolar transistor(HBT) on thin silicon-on-insulator(SOI) has recently been demonstrated and integrated into the latest SOI BiCMOS technology.The Early effect of the SOI SiGe HBT is analysed considering vertical and horizontal collector depletion,which is different from that of a bulk counterpart.A new compact formula of the Early voltage is presented and validated by an ISE TCAD simulation.The Early voltage shows a kink with the increase of the reverse base-collector bias.Large differences are observed between SOI devices and their bulk counterparts.The presented Early effect model can be employed for a fast evaluation of the Early voltage and is useful to the design,the simulation and the fabrication of high performance SOI SiGe devices and circuits. 相似文献
56.
Effect of Mg-Preflow for p-AlGaN Electron Blocking Layer on the Electroluminescence of Green LEDs with V-Shaped Pits 下载免费PDF全文
In GaN-based green light-emitting diodes(LEDs) with and without Mg-preflow before the growth of p-Al GaN electron blocking layer(EBL) are investigated experimentally.A higher Mg doping concentration is achieved in the EBL after Mg-preflow treatment,effectively alleviating the commonly observed efficiency collapse and electrons overflowing at cryogenic temperatures.However,unexpected decline in quantum efficiency is observed after Mg-preflow treatment at room temperature.Our conclusions are drawn such that the efficiency decline is probably the result of different emission positions.Higher Mg doping concentration in the EBL after Mg-preflow treatment will make it easier for a hole to be injected into multiple quantum wells with emission closer to pGaN side through the(8-plane rather than the V-shape pits,which is not favorable to luminous efficiency due to the preferred occurrence of accumulated strain relaxation and structural defects in upper QWs closer to p-GaN.Within this framework,apparently disparate experimental observations regarding electroluminescence properties,in this work,are well reconciled. 相似文献
57.
58.
采用MOCVD技术在图形化硅衬底上生长了InGaN/GaN多量子阱黄光LED外延材料,研究了不同的量子阱生长气压对黄光LED光电性能的影响。使用高分辨率X射线衍射仪(HRXRD)和荧光显微镜(FL)对晶体质量进行了表征,使用电致发光系统积分球测试对光电性能进行了表征。结果表明:随着气压升高,In的并入量略有降低且均匀性更好,量子阱中的点缺陷数目降低,但是阱垒间界面质量有所下降。在实验选取的4个气压4,6.65,10,13.3 kPa下,外量子效率最大值随着量子阱生长气压的上升而显著升高,分别为16.60%、23.07%、26.40%、27.66%,但是13.3 kPa下生长的样品在大电流下EQE随电流droop效应有所加剧,在20 A·cm-2的工作电流下,样品A、B、C、D的EQE分别为16.60%、19.77%、20.03%、19.45%,10 kPa下生长的量子阱的整体光电性能最好。 相似文献
59.
60.
利用金属有机化合物气相外延沉积技术在2inch(5.08cm)Si(111)图形衬底上生长了GaN外延薄膜,在Al组分渐变AlGaN缓冲层与GaN成核层之间引入了AlN插入层,研究了AlN插入层对GaN薄膜生长的影响。结果表明,随着AlN插入层厚度的增加,GaN外延膜(002)面与(102)面X射线衍射摇摆曲线半峰全宽明显变小,晶体质量变好,同时外延膜在放置过程中所产生的裂纹密度逐渐减小直至不产生裂纹。原因在于AlN插入层的厚度对GaN成核层的生长模式有明显影响,较厚的AlN插入层使GaN成核层倾向于岛状生长,造成后续生长的nGaN外延膜具有更多的侧向外延成分,从而降低了GaN外延膜中的位错密度,减少了GaN外延膜中的残余张应力。同时还提出了一种利用荧光显微镜观察黄带发光形貌来表征GaN成核层形貌和生长模式的新方法。 相似文献