全文获取类型
收费全文 | 21201篇 |
免费 | 4093篇 |
国内免费 | 6045篇 |
专业分类
化学 | 17137篇 |
晶体学 | 735篇 |
力学 | 1272篇 |
综合类 | 703篇 |
数学 | 2605篇 |
物理学 | 8887篇 |
出版年
2024年 | 50篇 |
2023年 | 287篇 |
2022年 | 744篇 |
2021年 | 705篇 |
2020年 | 785篇 |
2019年 | 796篇 |
2018年 | 729篇 |
2017年 | 922篇 |
2016年 | 886篇 |
2015年 | 1121篇 |
2014年 | 1344篇 |
2013年 | 1714篇 |
2012年 | 1805篇 |
2011年 | 2026篇 |
2010年 | 1751篇 |
2009年 | 1772篇 |
2008年 | 1986篇 |
2007年 | 1765篇 |
2006年 | 1588篇 |
2005年 | 1385篇 |
2004年 | 1060篇 |
2003年 | 833篇 |
2002年 | 918篇 |
2001年 | 846篇 |
2000年 | 849篇 |
1999年 | 496篇 |
1998年 | 280篇 |
1997年 | 194篇 |
1996年 | 217篇 |
1995年 | 186篇 |
1994年 | 188篇 |
1993年 | 162篇 |
1992年 | 155篇 |
1991年 | 101篇 |
1990年 | 117篇 |
1989年 | 96篇 |
1988年 | 92篇 |
1987年 | 80篇 |
1986年 | 45篇 |
1985年 | 40篇 |
1984年 | 37篇 |
1983年 | 43篇 |
1982年 | 20篇 |
1981年 | 21篇 |
1980年 | 19篇 |
1979年 | 22篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1974年 | 7篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
181.
Reduction of Dislocations in GaN Epilayer Grown on Si (111) Substrates using a GaN Intermedial Layer
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
GaN intermedial layers grown under different pressures are inserted between GaN epilayers and AIN/Si(111) substrates. In situ optical reflectivity measurements show that a transition from the three-dimensional (3D) mode to the 2I) one occurs during the GaN epilayer growth when a higher growth pressure is used during the preceding GaN intermedial layer growth, and an improvement of the crystalline quality of GaN epilayer will be made. Combining the in situ reflectivity and transmission electron microscopy (TEM) measurements, it is suggested that the lateral growth at the transition of growth mode is favourable for bending of dislocation lines, thus reducing the density of threading dislocations in the epilayer. 相似文献
182.
183.
Zhe Wang Hongzhe Ni Chengji Zhao Xianfeng Li Tiezhu Fu Hui Na 《Journal of Polymer Science.Polymer Physics》2006,44(14):1967-1978
The sulfonated poly(ether ether ketone sulfone) (SPEEKS)/heteropolyacid (HPA) composite membranes with different HPA content in SPEEKS copolymers matrix with different degree of sulfonation (DS) were investigated for high temperature proton exchange membrane fuel cells. Composite membranes were characterized by Fourier transfer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR band shifts suggested that the sulfonic acid groups on the copolymer backbone strongly interact with HPA particles. SEM pictures showed that the HPA particles were uniformly distributed throughout the SPEEKS membranes matrix and particle sizes decreased with the increment of copolymers' DS. The holes were not found in SPEEKS‐4/HPA30 (consisting of 70% SPEEKS copolymers with DS = 0.8 and 30% HPA) composite membrane after composite membranes were treated with boiling water for 24 h. Thermal stabilities of the composite membranes were better than those of pure sulfonated copolymers membranes. Although the composite membranes possessed lower water uptake, it exhibited higher proton conductivity for SPEEKS‐4/HPA30 especially at high temperature (above 100 °C). Its proton conductivity linearly increased from 0.068 S/cm at 25 °C to 0.095 S/cm at 120 °C, which was higher than 0.06 S/cm of Nafion 117. In contrast, proton conductivity of pure SPEEKS‐4 membrane only increased from 0.062 S/cm at 25 °C to 0.078 S/cm at 80 °C. At 120 °C, proton conductivity decreased to poor 0.073 S/cm. The result indicated that composite membranes exhibited high proton conductivity at high temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1967–1978, 2006 相似文献
184.
185.
建立了Littlewood—Paley g-函数在Heisenberg群上某些Herz型空间上的有界性. 相似文献
186.
JIANG Zhong-zhang 《数学季刊》2006,21(3):381-384
In 1984, Isaacs proposed the theories of Bπ-character and Iπ-character in n-separated group. This paper gives some new extension conditions of Iπcharacters. 相似文献
187.
用飞秒激光(200 fs,1 kHz,800 nm)脉冲在掺杂稀土离子Ce3 的聚甲基丙烯酸甲酯(PMMA)膜中进行了光存储实验研究,包括对样品的吸收光谱、激光照射前后的电子旋转共振(Electron spin resonance,ESR)光谱的测量和讨论。结果表明掺杂稀土离子Ce3 的聚甲基丙烯酸甲酯膜具有较低的写入阈值,有利于高速、并行的三维光存储。实验结果采用传统光学显微镜并行读出。给出了四层存储结果(点间距和层间距分别是4μm和16μm),并讨论了脉冲能量的大小对空腔尺寸的影响,进行高密度存储时,在保证读出信号灰度值足够大的情况下,应选择尽量小的激光脉冲写入能量。实验结果表明这种材料可以应用于三维光信息存储。 相似文献
188.
Model and empirical study on some collaboration networks 总被引:8,自引:0,他引:8
Pei-Pei Zhang Kan Chen Yue He Tao Zhou Bei-Bei Su Yingdi Jin Hui Chang Yue-Ping Zhou Li-Cheng Sun Bing-Hong Wang Da-Ren He 《Physica A》2006,360(2):599-616
In this paper we present an empirical study of a few practical systems described by cooperation networks, and propose a model to understand the results obtained. We study four non-social systems, which are the Bus Route Networks of Beijing and Yangzhou, the Travel Route Network of China, Huai-Yang recipes of Chinese cooked food, and a social system, which is the Collaboration Network of Hollywood Actors. In order to explain the results related to the degree distribution, act-degree distribution and act-size distribution (especially about the degree distribution, which may be better fitted using a stretched exponential distribution (SED)), we suggest a simple model to show a possible evolutionary mechanism for the emergence of such networks. The analytic and numerical results obtained from the model are in good agreement with the empirical results. 相似文献
189.
Li CHEN Hui Zhao LIU 《数学学报(英文版)》2006,22(2):455-468
The existence and uniqueness of the generalized solution for a kind of nonparametric curvature flow problem are obtained. This kind of curvature flow problem describes the evolution of graphs with speed depending on the reciprocal of the Gauss curvature. 相似文献
190.
ZHANG Jing wen * ZHAO Jian zhang ZHANG Xiao long JIANG Yu lin MA Xiu li SUN Yun xiu JIANG Wen pu LI Yao xian XU Zhi luo 《高等学校化学研究》1998,(2)
ChemoselectiveCatalyticHydrogenationofα,β┐UnsaturatedKetonesandα,β┐UnsaturatedCarboxylicEstersZHANGJing-wen*,ZHAOJian-zhang,Z... 相似文献