全文获取类型
收费全文 | 221篇 |
免费 | 18篇 |
国内免费 | 27篇 |
专业分类
化学 | 148篇 |
晶体学 | 4篇 |
力学 | 14篇 |
综合类 | 3篇 |
数学 | 49篇 |
物理学 | 48篇 |
出版年
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 8篇 |
2015年 | 18篇 |
2014年 | 16篇 |
2013年 | 18篇 |
2012年 | 23篇 |
2011年 | 18篇 |
2010年 | 10篇 |
2009年 | 22篇 |
2008年 | 18篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有266条查询结果,搜索用时 113 毫秒
11.
SHI Wensheng CHEN Zhenghao LIU Ningning L Huibin ZHOU Yueliang CUI Dafu YANG Guozhen 《中国科学A辑(英文版)》2000,43(5)
Pulsed laser ablation epitaxial Strancky-Krastanow growth of self-organized complex oxide Ce:BaTiO3 quantum dots on MgO(100) substrates is demonstrated.Atomic force microscopy and X-ray diffraction are used to observe the structure and the growth process of the self-organized complex oxide quantum dots.The average dimension,height,and the density of self-organized complex oxide Ce:BaTiO3 quantum dots are given.The nonlinear refractive indexes of the wetting layer and the self-organized ordered quantum dots are determined by the single beam Z-scan method.The mechanisms of the nonlinear effect enhancement for these low-dimensional structure are discussed. 相似文献
12.
13.
Focused proton beam writing has been utilized to fabricate optical channel waveguides in Nd:GGG crystals. The 1?MeV proton beam irradiation creates a local modified region with positive refractive index changes at the end of the proton trajectory, in which the channel waveguide could confine the light field in a symmetric way. Room-temperature laser emission has been achieved at 1063.7?nm, with absorbed pump power of 61?mW (at 808?nm). The obtained slope efficiency of the Nd:GGG waveguide laser system is as high as 66%, which is, to our best knowledge, the highest value for integrated lasers from ion beam processed channel waveguide systems. 相似文献
14.
超声喷雾共沉淀法制备纳米氧化锡粉体及其气敏性研究 总被引:1,自引:0,他引:1
采用超声波喷雾技术,以SnCl4·5H2O和CO(NH2)2为前驱体原料制备了氧化锡以及Ce稀土离子掺杂纳米粉体.详细地研究了超声喷雾条件、反应时间以及化学组分对纳米SnO2粉体的形貌和尺寸的影响规律,以及前驱体沉淀物脱水化学处理的条件.用XRD,TEM研究了所获纳米粒子的晶相和形貌.结果表明,制备的SnO2纳米粒子呈球状,尺寸在10~20 nm,纳米颗粒均匀,分散性好.以该粉体为基础制备了相应的气敏元件,测定了气体灵敏度与温度和稀土元素掺杂的关系.研究测试表明,纳米SnO2半导体气敏元件对NO2气体有着良好的响应-恢复特性,并且具有较高的灵敏度和较低的工作温度.稀土元素铈的掺杂能明显提高纳米SnO2粉体的气敏性能. 相似文献
15.
Ningning Zhao Kang Wang Wenjun Li Yongzhong Bian Changyan Sun Zhidong Chang Hongxia Fan 《Solid State Sciences》2011,13(11):1948-1953
A series of transition metal coordination polymers [Co(H3L)2(4,4′- bpy)(H2O)2]n?n(4,4′-bpy) (1), [Ni(H2L)(4,4′-bpy)(H2O)2]n (2), [Co2(L)(phen)2(H2O)4]n?(H2O)2n (3), and [Ni2(L)(phen)2(H2O)4]n?(H2O)2n (4) have been assembled from a semirigid multicarboxylate ligand 3,3′-(1,4-phenylenebis(oxy))diphthalic acid (H4L) with the help of 4,4′-bipyridine (4,4′-bpy) ligand or 1,10-phenanthroline (phen) ligand. X-ray single crystal diffraction analysis reveals that complex 1 crystallizes in the space group of P − 1 and displays a one-dimensional (1D) chain structure constructed from 4,4′-bpy ligand and H3L ligand, which was further interlinked to form a three-dimensional network via hydrogen bonds. In complex 2, Ni(II) atoms are coordinated by L ligand in monodentate fashion to form alternate left- and right-helices, which are further bridged together by the coordination interactions between Ni(II) atoms and 4,4′-bpy, leading to a 2-fold (4, 4)-connected interpenetrating network. Isostructural complexes 3 and 4 belong to the space group P − 1 and display a 1D chain structure constructed from phen and L ligands, which was further interlinked to form a 2D plane via π–π interactions. In addition, their thermal and luminescent properties were also investigated. 相似文献
16.
Li1.1Mn2???2x Co x Ni x O4 (x?=?0, 0.075) spinel powders were successfully synthesized using a liquid stirred tank reactor method. The electrochemical performances of the undoped and doped spinels at 4.3 and 5 V were investigated by X-ray diffraction, field-emission scanning electron microscopy, and electrochemical impedance spectroscopy. The capacity of Li1.1Mn2???2x Co x Ni x O4 could be divided into two parts, with 4.3 V as the dividing line in the 3–5 V charge–discharge range. Low capacity and good cyclic performance were obtained when cycled in the 3–4.3 V range for the multi-doped Li1.1Mn2???2x Co x Ni x O4 spinel. In comparison with multi-doped spinel at 4.3 V, the results of the cyclic performance worsened at 5 V because the structure underwent further shrinkage, the charge transfer resistance rose and the electrolyte decomposed. 相似文献
17.
Wenbin Chen Puying Chen Max Gunzburger Ningning Yan 《Mathematical Methods in the Applied Sciences》2010,33(13):1605-1617
We consider a superconvergence analysis for quadratic finite element approximations of the Stokes–Darcy system. The superclose property of an extra half order is proven for uniform triangular meshes. Based on the result of the superclose property, global superconvergence is derived by applying a postprocessing technique. In addition, some numerical examples are presented to demonstrate our theoretical results. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
18.
利用半导体激光泵浦输出1064 nm波长的全固态连续Nd:YVO4激光器作为泵浦源,采用周期调谐和温度调谐组合调谐技术,对基于掺氧化镁周期性极化铌酸锂晶体(MgO:LiNbO3, PPMgLN)准相位匹配(QPM)的全固态连续波(CW)光学参量振荡器(OPO)宽波段无分立连续调谐输出特性进行研究。实验采用连续工作模式和外腔结构,基于多周期PPMgLN晶体的30.2,30.4和30.6 m周期,在改变晶体的极化周期的基础上,同时在30~100 ℃范围内调节晶体工作温度。实验结果表明:CW PPMgLN OPO的泵浦阈值仅为0.22 W;不同极化周期需要的温度调谐范围不同;信号光在1 559.8~1 597.2 nm近红外波段和闲频光在3 187.3~3 347.3 nm中红外波段连续调谐输出。实现了外腔式全固态CW OPO在信号光和闲频光波段的无分立连续调谐输出。 相似文献
19.
In this paper we consider the finite element approximation of the Stokes eigenvalue problems based on projection method, and derive some superconvergence results and the related recovery type a posteriori error estimators. The projection method is a postprocessing procedure that constructs a new approximation by using the least squares strategy. The results are based on some regularity assumptions for the Stokes equations, and are applicable to the finite element approximations of the Stokes eigenvalue problems with general quasi-regular partitions. Numerical results are presented to verify the superconvergence results and the efficiency of the recovery type a posteriori error estimators. 相似文献
20.
Ordered Sr2CrReO6 has been synthesized recently. It is measured to be ferrimagnetic semiconductor, in contrary to the previous reports of metallic properties. To solve the discrepancy, we have investigated the compound by using the density functional theory. The semiconducting behavior is reproduced by including the electron correlation and spin–orbit coupling simultaneously. The calculated band gap is 0.22 eV, close to the experimental value of 0.21 eV. A large orbital moment of 0.69µB is found for Re, which is caused by the Coulomb‐enhanced spin–orbit coupling. By applying pressure, a semiconductor to half‐metal transition is observed through 5% volume compression.