全文获取类型
收费全文 | 251篇 |
免费 | 29篇 |
国内免费 | 25篇 |
专业分类
化学 | 82篇 |
晶体学 | 1篇 |
力学 | 92篇 |
综合类 | 2篇 |
数学 | 48篇 |
物理学 | 80篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 10篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 20篇 |
2012年 | 6篇 |
2011年 | 8篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 10篇 |
2005年 | 16篇 |
2004年 | 10篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1989年 | 1篇 |
1986年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有305条查询结果,搜索用时 31 毫秒
221.
Sn(Ⅱ)/Sn(Ⅳ)对PtSn/C乙醇电化学氧化活性的影响 总被引:3,自引:0,他引:3
在乙二醇共还原H2PtCl6和SnCl2的过程中加入Ni(NO3)2作为助剂制备了PtSn/C-Ni催化剂. 程序升温还原实验检测到该催化剂中存在Sn(Ⅱ)/Sn(Ⅳ)氧化还原电对. 线性扫描、单电池性能测试和CO溶出实验表明,提高催化剂中Sn(Ⅱ)/Sn(Ⅳ)的比值能显著提高催化剂的乙醇电化学氧化活性和抗CO中毒能力. 催化剂电催化活性提高的原因可能是Sn(Ⅱ)/Sn(Ⅳ)电对加快了(OH)ads 物种在催化剂中的传递速率,促进了乙醇电化学氧化过程中产生的类CO中间物种在Pt表面的氧化. 相似文献
222.
Glutathione (GSH), in addition to serving as a redox buffer in cellular environment, has been suggested as a modulator in metal regulation and homeostasis by metallothioneins (MTs). The interactions of MTs with both GSH and its oxidized form GSSG have been shown to govern the direction of metal transfer. Common methods for the determination of zinc release from MTs modulated by GSH/GSSG either involve radioactive species or enzymes or are labor‐intensive. In this study, upon separation of Zn2+ from the reaction mixture of MTs and GSH with a centrifugal filter membrane, differential pulse voltammetry (DPV) was used for the Zn2+ quantification. The same approach is extended to the studies of metal transfer between Zn7MT with a GSH/GSSG mixture and that between Zn7MT with GSSG. The concomitant conversion between the free thiol and disulfide bonds was confirmed with UV‐vis spectrophotometry. The results demonstrate that GSSG, GSH, and the GSH/GSSG mixture all modulate zinc release from Zn7MT. The percentage of zinc release increases in the order of GSH, GSSG, and the GSH/GSSG mixture. The new approach is demonstrated to be well suited for investigation of redox regulation of MT and its reaction with zinc‐containing enzymes. 相似文献
223.
《Journal of computational chemistry》2017,38(20):1780-1788
The (nitro)(N‐methyldithiocarbamato)(trimethylphospane)nickel(II), [Ni(NO2)(S2CNHMe)(PMe3)] complex catalyses efficiently the O‐atom transfer reactions to CO and acetylene. Energetically feasible sequence of elementary steps involved in the catalytic cycle of the air oxidation of CO and acetylene are proposed promoted by the Ni(NO2)(S2CNHMe)(PMe3)] ↔ Ni(NO2)(S2CNHMe)(PMe3) redox couple using DFT methods both in vacuum and dichloromethane solutions. The catalytic air oxidation of HC≡CH involves formation of a five‐member metallacycle intermediate, via a [3 + 2] cyclo‐addition reaction of HC≡CH to the Ni‐N = O moiety of the Ni(NO2)(S2CNHMe)(PMe3)] complex, followed by a β H‐atom migration toward the Cα carbon atom of the coordinated acetylene and release of the oxidation product (ketene). The geometric and energetic reaction profile for the reversible [Ni( ‐NO2)(S2CNHMe)(PMe3)] [Ni( ‐ONO)(S2CNHMe)(PMe3)] linkage isomerization has also been modeled by DFT calculations. © 2017 Wiley Periodicals, Inc. 相似文献
224.
225.
用SU(2 )陪集表象来表示氰化氘分子 (DCN)两个耦合的伸缩振动模式 ,在混沌运动研究中 ,这是一个最简单的SU (2 )对称被破坏的模型。研究表明 ,当振动能量小于 1 2 5 0 2cm- 1 时 ,体系呈现规则运动 ;能量处于 1 2 5 0 2cm- 1 和 1 82 4 6cm- 1 之间 ,规则和混沌运动并存 ;能量高于 1 82 4 6cm- 1 时 ,体系呈现完全的混沌运动。同时 ,在庞加莱截面上观察到了周期 3轨道 ,由Sarkovskii定理 ,这意味着混沌的出现。另外还表明 ,D -C伸缩键的量子数激发决定体系的混沌运动 相似文献
226.
光折变晶体均匀多重全息图存储研究 总被引:8,自引:3,他引:5
本文推导了光折变晶体角度编码多重全息存储中写入均匀光栅时的曝光时间递推公式.分析了散射效应对光栅写入时间常数的影响和写入光耦合对光栅振幅的影响,给出了两种因素影响下曝光时间计算的修正递推公式.数值计算结果表明,按照这种修正公式计算所得多重存储中各幅全息光栅振幅不仅均匀性好,而且振幅相对较大,这种曝光方法有利于提高晶体的存储容量.实验中以递推公式所得时间进行曝光记录,在厚度为0.6mm的Fe:LiNbO3晶体中采用角度编码很容易存储了30幅全息图. 相似文献
227.
This study is concerned with the reflection and transmission of plane waves at an imperfectly bonded interface between two orthotropic micropolar elastic half-spaces with different elastic and micropolar properties. There exist three types of coupled waves in xy-plane. The reflection and transmission coefficients of quasi-longitudinal (QLD) wave, quasi-coupled transverse microrotational (QCTM) wave and quasi-coupled transverse displacement (QCTD) wave have been derived for different incidence waves and deduced for normal force stiffness, transverse force stiffness, transverse couple stiffness and perfect bonding. The numerical values of modules of the reflection and transmission coefficients are presented graphically with the angle of incidence for orthotropic micropolar medium (MOS) and isotropic micrpolar medium (MIS). Some particular cases of interest have been deduced from the present investigation. 相似文献
228.
This paper analyses the modal interactions in the nonlinear, size-dependent dynamics of geometrically imperfect microplates. Based on the modified couple stress theory,the equations of motion for the in-plane and out-of-plane motions are obtained employing the von Kármán plate theory as well as Kirchhoff's hypotheses by means of the Lagrange equations. The equations of motions are solved using the pseudo-arclength continuation technique and direct timeintegration method. The system parameters are tuned to the values associated with modal interactions, and then nonlinear resonant responses and energy transfer are analysed.Nonlinear motion characteristics are shown in the form of frequency-response and force-response curves, time histories, phase-plane portraits, and fast Fourier transforms. 相似文献
229.
230.