全文获取类型
收费全文 | 887篇 |
免费 | 192篇 |
国内免费 | 89篇 |
专业分类
化学 | 425篇 |
晶体学 | 93篇 |
力学 | 6篇 |
综合类 | 3篇 |
数学 | 4篇 |
物理学 | 637篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 22篇 |
2021年 | 23篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 49篇 |
2016年 | 75篇 |
2015年 | 36篇 |
2014年 | 66篇 |
2013年 | 73篇 |
2012年 | 100篇 |
2011年 | 62篇 |
2010年 | 34篇 |
2009年 | 58篇 |
2008年 | 57篇 |
2007年 | 52篇 |
2006年 | 69篇 |
2005年 | 61篇 |
2004年 | 45篇 |
2003年 | 31篇 |
2002年 | 40篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 17篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有1168条查询结果,搜索用时 19 毫秒
991.
This study examined the potential applications of microwave dielectric properties of La(1‐2x/3)Bax(Mg0.5Sn0.5)O3 ceramics in rectenna. The La(1‐2x/3)Bax(Mg0.5Sn0.5)O3 ceramics were prepared by the conventional solid‐state method with various sintering temperatures. An apparent density of 6.62 g/cm3, a dielectric constant of 20.3, a quality factor of 51,700 GHz, and a temperature coefficient of resonant frequency of ‐78.2 ppm/K were obtained for La2.98/3Ba0.01(Mg0.5Sn0.5)O3 ceramics that were sintered at 1550 °C for 4 h. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
993.
Andrea Scaccabarozzi Silvia Adorno Sergio Bietti Maurizio Acciarri Stefano Sanguinetti 《固体物理学:研究快报》2013,7(3):173-176
We report the fabrication procedure and the characterization of an Al0.3Ga0.7As solar cell containing high‐density GaAs strain‐free quantum dots grown by droplet epitaxy. The production of photocurrent when two sub‐bandgap energy photons are absorbed simultaneously is demonstrated. The high quality of the quantum dot/barrier pair, allowed by the high quality of nanostructured strain‐free materials, opens new opportunities for quantum dot based solar cells.
994.
The liquid–liquid structure transition (LLST) as the function of temperature and time in Sn–3.5Ag–3.5Bi melts was investigated with the help of direct current four-probe method. The LLST which occurs during first cycle heating of two cycles heating/cooling experiments can divide into two different structure changes: irreversible LLST of 650°C isothermal and step reversible LLST at 770°C–806°C on subsequent heating process. Obvious kinetic phenomena are observed during isothermal experiments. Irreversible and reversible LLST are analysed from the viewpoint of short-range order. These results will help to understand the law and mechanism of liquid field, and provide some scientific reference for the innovation of lead-free solder manufacturing. 相似文献
995.
Tushar S. Basu Baul Archana Mizar George Eng Michal Hol?apek Monique Biesemans Ray Butcher 《Journal of organometallic chemistry》2006,691(12):2605-2613
A series of cis-bis{5-[(E)-2-(aryl)-1-diazenyl]quinolinolato}dibenzyltin(IV) complexes have been synthesized by reacting sodium salts of 5-[(E)-2-(aryl)-1-diazenyl]quinolin-8-ol (LH) and dibenzyltin dichloride. These complexes have been characterized by 1H, 13C, 119Sn NMR, ESI-MS in solution and by IR and 119mSn Mössbauer, 117Sn CP-MAS NMR spectroscopy in solid state. In addition, the structures of three of the dibenzyltin(IV) complexes, viz., Bz2Sn(L2)2 (2), Bz2Sn(L3)2 (3), and Bz2Sn(L5)2 (5) (L = 5-[(E)-2-(aryl)-1-diazenyl]quinolin-8-ol: aryl = 4′-methylphenyl- (L2H), 4′-methoxylphenyl- (L3H) and 4′-bromophenyl- (L5H)) were determined by single-crystal X-ray diffraction. In general, the complexes were found to adopt a distorted cis-octahedral arrangement around the tin atom in both solution and solid state. 相似文献
996.
In this work, we present a detailed study on the optical properties of two GaAs/Al0.35Ga0.65As coupled double quantum wells (CDQWs) with inter-well barriers of different thicknesses, by using photoluminescence (PL) spectroscopy. The two CDQWs were grown in a single sample, assuring very similar experimental conditions for measurements of both. The PL spectrum of each CDQW exhibits two recombination channels which can be accurately identified as the excitonic e1-hh1 transitions originated from CDQWs of different effective dimensions. The PL spectra characteristics and the behavior of the emissions as a function of temperature and excitation power are interpreted in the scenario of the bimodal interface roughness model, taking into account the exciton migration between the two regions considered in this model and the difference in the potential fluctuation levels between those two regions. The details of the PL spectra behavior as a function of excitation power are explained in terms of the competition between the band gap renormalization (BGR) and the potential fluctuation effects. The results obtained for the two CDQWs, which have different degrees of potential fluctuation, are also compared and discussed. 相似文献
997.
998.
999.
Ti掺杂SnO2固溶体是钛基氧化物耐酸阳极的重要组成部分. 采用基于密度泛函理论的第一性原理对Sn1-xTixO2(x=0, 1/12, 1/8, 1/6, 1/4, 1/2, 3/4, 5/6)固溶体的电子结构进行计算, 分析了能带结构、 电子态密度和电荷密度以及晶格参数的变化. 结果表明, Ti掺入SnO2晶格后, 其晶格参数随组分增加近似呈直线降低, Ti-O键的共价性强于Sn-O键. 掺杂后带隙仍为直接带隙, 且随着掺杂比例的增加, 带隙逐渐减小. 当掺杂比例x=0.5时, 形成能达到最低值(-6.11 eV), 固溶体最稳定. 本文的计算结果为钛基氧化物电极材料的研究与开发提供了一定的理论依据. 相似文献
1000.
对天然芒硝和GdF3,EuF3的混合粉末,先用马弗炉在空气中1 000℃下加热30min,后用微波750℃下加热10min,制备了Na2SO4∶Eu,Gd、Na2Gd2(SO4)4∶Eu等系列荧光粉。研究了天然无水芒硝与铕浓度不变的情况下钆浓度的变化对发光性能的影响。结果表明:掺入Gd3+对样品的发光有增强作用。随着Gd3+浓度的增加Eu3+的610nm发光强度变大,因此Gd3+可能起到能量传递的桥梁作用,使能量在基质与激活剂离子之间高效传递。当Gd3+以21mol%掺入到无水芒硝(Na2SO4∶Eu)晶格中时,可以达到Eu3+的最强发光强度和最佳的色纯度,最终出现浓度猝灭现象。 相似文献