全文获取类型
收费全文 | 858篇 |
免费 | 237篇 |
国内免费 | 102篇 |
专业分类
化学 | 467篇 |
晶体学 | 104篇 |
力学 | 54篇 |
综合类 | 13篇 |
数学 | 31篇 |
物理学 | 528篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 32篇 |
2021年 | 45篇 |
2020年 | 34篇 |
2019年 | 26篇 |
2018年 | 30篇 |
2017年 | 55篇 |
2016年 | 67篇 |
2015年 | 26篇 |
2014年 | 38篇 |
2013年 | 86篇 |
2012年 | 62篇 |
2011年 | 55篇 |
2010年 | 42篇 |
2009年 | 61篇 |
2008年 | 55篇 |
2007年 | 57篇 |
2006年 | 59篇 |
2005年 | 33篇 |
2004年 | 43篇 |
2003年 | 34篇 |
2002年 | 34篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 21篇 |
1998年 | 19篇 |
1997年 | 22篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1197条查询结果,搜索用时 31 毫秒
91.
(Na0.5K0.5)0.975Li0.025Nb0.82−xSbxTa0.18O3 lead-free piezoceramics were prepared by the conventional solid-state sintering method. All samples possess a pure perovskite phase, and no secondary phase could be certified. The crystal structure changes from tetragonal to pseudo-cubic with increasing amount of Sb. The ferroelectric Curie temperature (Tc) shifts to lower temperature while the tetragonal to orthorhombic phase transition temperature (To-t) shows no obvious change with increasing Sb5+. Enhanced piezoelectric and electromechanical properties are obtained with x=0.06: d33=352 pC/N, kp=47% and kt=38%, showing that they could be promising candidates as lead-free piezoelectric materials. 相似文献
92.
93.
Ezhil Jothinathan Kim VanmeenselJef Vleugels Tamara KharlamovaVladislav Sadykov Svetlana PavlovaGeorgia Sourkouni Christian SzepanskiChristos Argirusis Omer Van der Biest 《Solid State Ionics》2011,192(1):419-423
Apatite type rare earth silicates are being extensively studied as electrolyte material for intermediate temperature solid oxide fuel cells (SOFC). In this paper we presents results on synthesis of Al and/or Fe-doped ATLS, the design of compatible anode materials, thermal expansion properties and co-sintering of half-cells from expansion matched materials using the advanced pulsed electric current sintering (PECS) technique. The issues related to the co-sintering of half cells have been addressed successfully by the combined use of nano powders and PECS. 相似文献
94.
Ce0.8Gd0.05Y0.15O1.9 (GYDC) electrolyte was prepared by a carbonate co-precipitation method. Lithium nitrate at 1, 1.5, 2 and 3 mol% was added to GYDC as sintering additive. 96% relative density was achieved for GYDC at sintering temperature of 800 °C with addition of 1.5 mol% LiNO3. The conductivities of GYDC with sintering aids LiNO3 were measured by a.c. impedance spectroscopy and showed comparable values to that of pure GYDC sample sintered at 1400 °C. A single cell with 1.5 mol% LiNO3 infiltrated GYDC electrolyte was fabricated by sintering at 800 °C for only 2 h. Lithiated NiO was synthesized by the glycine-nitrate combustion method and employed as cathode material. The cell was tested at temperatures from 500 to 575 °C and a maximum power density of 73 mW cm− 2 was obtained at 575 °C. These preliminary results indicate that LiNO3 is a very effective sintering additive for intermediate temperature solid oxide fuel cell fabrication. 相似文献
95.
G. Murtaza Rai M.A. IqbalI.G. Will Z.C. Huang 《Journal of magnetism and magnetic materials》2011,323(24):3239-3245
The samarium doping zinc oxide (Zn1-xSmxO) with (x=0.0, 0.04, 0.05 and 0.17) polycrystalline thin films have been deposited on n-Si(1 0 0) substrate using thermal evaporation technique. Ceramic targets for deposition were prepared by the standard solid-state reaction method and sintered in nitrogen atmospheres. X-ray diffraction and scanning electron microscopy analyses show that the bulk and films features reveal wurtzite crystal structure with a preferential (1 0 1) crystallographic orientation and grows as hexagonal shape grains. According to the results of the Hall effect measurements, all the films show p-type conductivity, possibly a result of nitrogen incorporation into the Sm-doped ZnO samples. Magnetic measurements show that ferromagnetic behavior depends on the Sm3+ concentration. For a film with lower Sm2O3 contents (x=0.04), a phenomenon of paramagnetism has been observed. While, with further increase of Sm3+ contents (x=0.05) the ferromagnetic behavior has been observed at room temperature. However, at higher doping content of Sm3+, the ferromagnetic behavior was suppressed. The decrease of ferromagnetism with increasing doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Zn1-xSmxO films. 相似文献
96.
Se Hoon KimJin Woo Kim Tae Sun JoYoung Do Kim 《Journal of magnetism and magnetic materials》2011,323(22):2851-2854
The fabrication of Nd11Dy4Fe76.5TM2.5B6 (TM=Co, Cu, Al, and Nb: at%) sintered magnets via a two-step sintering process was demonstrated. A densification of greater than 99% was achieved using the two-step sintering of the Nd-Fe-B powder. This process produced a sample with an average grain size of 6.2 μm in the Nd2Fe14B phase, resulting in an enhancement of the coercivity compared to that of the isothermally sintered sample. The suppression of grain growth was considered to be affected by the relatively low temperature during the two-step sintering and by the presence of a B-rich phase at the triple junction. Consequently, the two-step sintering process led to suppression of grain growth and a uniform grain size distribution, which resulted in improved magnetic properties, in particular in the intrinsic coercivity. 相似文献
97.
Karger-Kocsis J. Shang P. P. Moskala E. J. 《Journal of Thermal Analysis and Calorimetry》1999,55(1):21-28
The tensile loading-induced necking in notched specimens of an amorphous copolyester (aCOP) was studied by modulated differential
scanning calorimetry (MDSC). It was shown that necking occurred by cold drawing since the enthalpy of cold crystallization
and that of the subsequent melting agreed fairly with each other. Increasing deformation in the necking zone and increasing
deformation rate of the specimens shifted the onset of cold crystallization toward lower temperatures and yielded a slightly
higher glass transition temperature (Tg). This was attributed to the molecular orientation caused by mechanical loading. The finding that the melting contained a
non-reversing part was considered as appearance of possible microcrystallinity. The Tg range was strongly influenced by the deformation rate and reflects the thermomechanical history of the samples accordingly.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
98.
We analyzed the thermal crystallization, glass‐transition behavior, and mechanical properties of melt‐extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass‐transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass‐transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 °C but decreased above that temperature. In addition, the glass‐transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within 1 h on annealing at 50 °C. Consequently, the change in the glass‐transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold‐crystallization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920–1927, 2001 相似文献
99.
本文建立了一种乳化的非牛顿相变功能流体的循环储冷模型,对影响其储冷性能的各项参数进行了模拟计算和分析。得出了描述不同储冷条件下与初始温度相关联的显热段和与乳液浓度相关联的潜热段储冷性能特征的无量纲关联式,以及储冷速率的相对比较。计算结果与有限条件下的测试结果基本吻合。该研究结果对采用潜热型功能相变流体储冷装置的设计具有参考价值。 相似文献
100.
提出了采用四台阶相位光栅与微透镜阵列组合产生一种新颖的表面空心微光阱阵列的方案,研究了表面空心微光阱阵列的光强分布,计算了相应的光学囚禁势,并讨论了该微光阱阵列在原子分子光学中的潜在应用.研究表明当用1W的YAG激光照射时,在1cm2面积上可产生近104个空心光阱,每个光阱具有较小的囚禁体积和较大的有效光强及其强度梯度,对85Rb原子的光学囚禁势可达190μK.如此深的光阱足以囚禁冷原子或冷分子,并可用于实现全光型原子或分子玻色-爱因斯坦凝聚,甚至制备新颖的光学晶格等.
关键词:
空心光阱
冷原子或冷分子
光学晶格 相似文献