全文获取类型
收费全文 | 17019篇 |
免费 | 2810篇 |
国内免费 | 2998篇 |
专业分类
化学 | 13527篇 |
晶体学 | 351篇 |
力学 | 841篇 |
综合类 | 268篇 |
数学 | 1847篇 |
物理学 | 5993篇 |
出版年
2024年 | 57篇 |
2023年 | 318篇 |
2022年 | 586篇 |
2021年 | 631篇 |
2020年 | 712篇 |
2019年 | 712篇 |
2018年 | 639篇 |
2017年 | 647篇 |
2016年 | 783篇 |
2015年 | 907篇 |
2014年 | 999篇 |
2013年 | 1355篇 |
2012年 | 1446篇 |
2011年 | 1535篇 |
2010年 | 1238篇 |
2009年 | 1158篇 |
2008年 | 1273篇 |
2007年 | 1145篇 |
2006年 | 976篇 |
2005年 | 880篇 |
2004年 | 710篇 |
2003年 | 567篇 |
2002年 | 614篇 |
2001年 | 550篇 |
2000年 | 440篇 |
1999年 | 326篇 |
1998年 | 239篇 |
1997年 | 190篇 |
1996年 | 205篇 |
1995年 | 150篇 |
1994年 | 159篇 |
1993年 | 99篇 |
1992年 | 89篇 |
1991年 | 78篇 |
1990年 | 70篇 |
1989年 | 48篇 |
1988年 | 42篇 |
1987年 | 50篇 |
1986年 | 31篇 |
1985年 | 40篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1969年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
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
53.
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
54.
Theformationofanewtypeofself_assembledmultilayerfilms,moleculardeposition(MD)films[1,2],isafastdevelopingareaofthinfilmresearch.Thisnewmethodoffilmpreparationisbasedonionicattractionbetweenoppositechargedchromophores.IncomparisonwiththeclassicLangmuir_Blo… 相似文献
55.
56.
57.
58.
59.
Shaw NM Blanis D Bodek A Budd H Coombes R Eno S Fry CA Harada H Ho YH Kim YK Kumita T Mori T Olsen SL Sill A Thorndike EH Ueno K Zheng HW Imlay R Kirk P Lim J McNeil RR Metcalf W Myung SS Cheng CP Gu P Li J Li YK Mao ZP Xu YT Zhu YC Abashian A Gotow K Hu K Low EH Mattson ME Naito F Piilonen L Sterner KL Lusin S Rosenfeld C Wang AT Wilson S Frautschi M Kagan H Kass R Trahern CG Breedon RE Kim GN Ko W Lander RL Maeshima K Malchow RL Smith JR Sparks K Williams MC Abe K Fujii Y Higashi Y Kim SK 《Physical review letters》1989,63(13):1342-1345
60.
以典型的轻希土镧和重希土镝及碱土金属锶作为A位离子,以过渡金属锰、铁、钴、镍作为B位离子,合成了K2NiF4型结构的A2-xSrxBO4希土复合氧化物,采用粉末X射线衍射技术考察了反应条件等因素对生成K2NiF4型四方(T)结构上析影响,实现结果表明,四方结构的形成不仅与几何因素有关,而且与各组分的物理化学性质有关。各个不同的组成,生成四方相的温度范围也有所不同。适当地提高反应温度以及延长灼烧时间 相似文献