全文获取类型
收费全文 | 617篇 |
免费 | 275篇 |
国内免费 | 57篇 |
专业分类
化学 | 194篇 |
晶体学 | 8篇 |
力学 | 41篇 |
综合类 | 5篇 |
数学 | 26篇 |
物理学 | 675篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 33篇 |
2021年 | 37篇 |
2020年 | 27篇 |
2019年 | 31篇 |
2018年 | 24篇 |
2017年 | 23篇 |
2016年 | 34篇 |
2015年 | 39篇 |
2014年 | 39篇 |
2013年 | 48篇 |
2012年 | 41篇 |
2011年 | 58篇 |
2010年 | 61篇 |
2009年 | 52篇 |
2008年 | 40篇 |
2007年 | 54篇 |
2006年 | 40篇 |
2005年 | 46篇 |
2004年 | 28篇 |
2003年 | 39篇 |
2002年 | 28篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有949条查询结果,搜索用时 78 毫秒
121.
122.
运用Blonder-Tinkham-Klapwijk(BTK)理论研究了硅烯/dx2-y2 +idxy 混合波超导隧道结的隧穿性质.研究发现:垂直施加的电场、超导配对势的方向角和两种混合波配对能隙的比值Δ1/Δ0 强烈地影响正常反射、Andreev反射和隧穿电导的值;当两种混合波的序参量比值较大时,隧道谱线在外加偏压E =Δ1 处出现谐振峰;系统的隧穿电导、正常反射幅和Andreev反射幅随超导方向角成周期性变化,变化周期为π/2;由于dxy-波的存在,通过改变外加电场可以对隧穿电流加以调控。 相似文献
123.
124.
本文以~(60)Co为辐照源,针对3DG111型晶体管,利用半导体参数分析仪和深能级缺陷瞬态谱仪,研究高/低剂量率和有/无氢气浸泡条件下,电性能和深能级缺陷的演化规律.试验结果表明,与高剂量率辐照相比,低剂量率辐照条件下,3DG111型晶体管的电流增益退化更加严重,这说明该器件出现了明显的低剂量率增强效应;无论是高剂量率还是低剂量率辐照条件下,3DG111晶体管的辐射损伤缺陷均是氧化物正电荷和界面态陷阱,并且低剂量率条件下,缺陷能级较深;氢气浸泡后在高剂量率辐照条件下,与未进行氢气处理的器件相比,辐射损伤程度明显加剧,且与低剂量率辐照条件下器件的损伤程度相同,缺陷数量、种类及能级也相同.因此,氢气浸泡处理可以作为低剂量率辐射损伤增强效应加速评估方法的有效手段. 相似文献
125.
The morphology evolution of carbide precipitated on grain boundary nearby different triple junctions in grain boundary engineering (GBE) treated nickel-based Inconel Alloy 690 aged at 715°C for different time was investigated by scanning electron microscopy and electron backscatter diffraction. The results show that, the diversity of triple junction types was increased by GBE significantly. The size and morphology of grain boundary carbide were not only affected by the grain boundary character, but also the nearby grain boundary character at the triple junction. The higher Σ values of the nearby grain boundaries, the larger carbide precipitated on the other grain boundary. Based on the experimental results, the effects of grain boundary characters and triple junction types on the carbide precipitation behaviours are discussed. 相似文献
126.
Xueqi Guo Yuheng Zeng Zhi Zhang Yuqing Huang Mingdun Liao Qing Yang Zhixue Wang Minyong Du Denggao Guan Baojie Yan Jichun Ye 《Current Applied Physics》2019,19(7):811-816
The junction properties of tunnel silicon oxide (SiOx) passivated contact (TOPCon) with n-type poly-Si on p-type c-Si wafer are characterized using current-voltage (J-V) and capacitance-voltage (C-V) measurements. The dark J-V curves show a standard diode characteristic with a turn-on voltage of ~0.63 V, indicating a p-n junction is formed. While the C-V curve displays an irregular shape with features of 1) a slow C increase with the decrease of the magnitude of reverse bias voltage, being used to estimate the built-in potential (Vbi), 2) a significant increase at a given positive bias voltage, corresponding to the geometric capacitance crossing the ultrathin SiOx, and 3) a sharp decrease to negative values, resulting from the charge tunneling through the SiOx layer. The C of depleting layer deviates from the normal linear curve in the 1/C2-V plot, which is caused by the diffusion of P dopants from the n-type poly-Si into the p-type c-Si wafer as confirmed by the electrochemical capacitance-voltage measurements. However, the 1/C2+γ-V plots with γ > 0 leads to linear curves with a proper γ and the Vbi can still be estimated. We find that the Vbi is the range of 0.75–0.85 V, increases with the increase of the doping ratio during the poly-Si fabrication process, and correlates with the passivation quality as measured by the reverse saturated current and implied open circuit voltage extracted from transient photoconductivity decay. 相似文献
127.
In this paper, the electrical properties and low-frequency noise for bipolar junction transistors irradiated by 170?keV proton are examined. The result indicates that for the sample under proton irradiation with fluence 1.25?×?1014?p/cm2, base current IB in low bias range (VBE < 0.7?V) increases due to superimposition of radiation-induced recombination current, while the gain decreases significantly. Meanwhile, the low-frequency noise increases in the proton-irradiated sample. By analysis of evolution of parameters extracted from low-frequency noise power spectra, it is demonstrated that radiation-induced noise is mainly originated from carrier fluctuation modulated by generation–recombination centers (G–R centers) located at the interface of Si/SiO2, which are introduced by proton-radiation-induced defects. It is also confirmed that the electrical properties and noise behavior of irradiated sample are mostly affected by the carrier recombination process caused by G–R centers at the interface of Si/SiO2 than by G–R centers in EB junctions. 相似文献
128.
Shunsaku Nii 《Physica D: Nonlinear Phenomena》2009,238(13):1050-1055
Investigated here are bifurcations of stationary solutions with triple junctions to the curvature-driven motion of curves, which arises in phase separation problems. We demonstrate that, when seen from a new perspective, typical bifurcations under perturbations of domain shape can be analyzed using only elementary geometry. 相似文献
129.
Mengtao Sun Zhipeng Li Yajun Liu Hongxing Xu 《Journal of Raman spectroscopy : JRS》2009,40(12):1942-1948
The essence of the chemical mechanism for surface‐enhanced resonance Raman scattering (SERRS) is the charge transfer (CT) between the metal and the molecule at the resonant electronic transition, which results in the mode‐selective enhancement in the SERRS spectrum. The site‐orientated CT can directly interpret the mode‐selective chemical enhancement in SERRS. However, it is a great challenge to intutively visualize the orientation and site of the CT. In this paper, for the pyrazine–Au2 complex, a three‐dimensional (3D) cubic representation is built to provide direct visual evidence for chemical mechanisms of SERRS via CT from the Au2 cluster to pyrazine at the resonant electronic transition. The relationship between the mode‐selective enhancements in SERRS and the site‐orientated CT was clearly revealed. The intracluster excitation (analog of plasmon excitation in large naonoparticles) was also visualized by the 3D cubic presentation, which provided the direct evidence of local electromagnetic field enhancement of SERRS. To study the quantum size effect and the coupling effect of the nanoparticles, the photoexcitation mechanisms of the Au20–pyrazine complex and the Au20–pyrazine–Au20 junction were also investigated. The tunneling charge transfer from one Au20 cluster to another Au20 cluster outside the pyrazine in Au20–pyrazine–Au20 junction was also revealed visually. The calculated normalized extinction spectra of Au nanoparticles using the generalized Mie theory reveal that the resonance peak is red‐shifted due to the coupling between particles. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
130.
半导体PN结具有电容的性质.在正向直流偏压下,理论计算表明,PN结扩散电容的对数与正向偏压成正比.实验发现,当正向偏压小于30mV时,这种线性关系是成立的;当正向偏压大于30mV时,会偏离这种线性关系.由于PN结还具有电阻特性,对交流信号的相位有影响.随着正向偏压增大,交流信号的相位变化出现一极值.如果将PN结等效为一个电容和一个电阻并联,就可以定性解释这种变化关系. 相似文献