全文获取类型
收费全文 | 214篇 |
免费 | 73篇 |
国内免费 | 90篇 |
专业分类
化学 | 110篇 |
晶体学 | 4篇 |
力学 | 36篇 |
综合类 | 6篇 |
数学 | 31篇 |
物理学 | 190篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 14篇 |
2012年 | 15篇 |
2011年 | 12篇 |
2010年 | 18篇 |
2009年 | 7篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 21篇 |
2005年 | 20篇 |
2004年 | 11篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 13篇 |
2000年 | 5篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1985年 | 3篇 |
1981年 | 2篇 |
1963年 | 1篇 |
1960年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有377条查询结果,搜索用时 437 毫秒
231.
Praseodymium-ion-doped gain materials have the superiority of lasing at various visible wavelengths directly.Simple and compact visible lasers are booming with the development of blue laser diodes in recent years. In this Letter, we demonstrate the watt-level red laser with a single blue laser diode and Pr:YLiF_4 crystal. On this basis,the passively Q-switched pulse lasers are obtained with monolayer graphene and Co:ZnO thin film as the Q-switchers in the visible range. 相似文献
232.
233.
234.
Influence of small-molecule material on performance of polymer solar cells based on MEH-PPV:PCBM blend 下载免费PDF全文
In this work,the influence of a small-molecule material,tris(8-hydroxyquinoline) aluminum (Alq 3),on bulk het-erojunction (BHJ) polymer solar cells (PSCs) is investigated in devices based on the blend of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and [6,6]-phenyl-C 61-butyric acid methyl ester (PCBM).By dop-ing Alq 3 into MEH-PPV:PCBM solution,the number of MEH-PPV excitons can be effectively increased due to the energy transfer from Alq 3 to MEH-PPV,which probably induces the increase of photocurrent generated by excitons dissociation.However,the low carrier mobility of Alq 3 is detrimental to the efficient charge transport,thereby blocking the charge collection by the respective electrodes.The balance between photon absorption and charge transport in the active layer plays a key role in the performance of PSCs.For the case of 5 wt.% Alq 3 doping,the device performance is deteriorated rather than improved as compared with that of the undoped device.On the other hand,we adopt Alq 3 as a buffer layer instead of commonly used LiF.All the photovoltaic parameters are improved,yielding an 80% increase in power conversion efficiency (PCE) at the optimum thickness (1 nm) as compared with that of the device without any buffer layer.Even for the 5 wt.% Alq 3 doped device,the PCE has a slight enhancement compared with that of the standard device after modification with 1 nm (or 2 nm) thermally evaporated Alq 3.The performance deterioration of Alq 3-doped devices can be explained by the low solubility of Alq 3,which probably deteriorates the bicontinuous D-A network morphology;while the performance improvement of the devices with Alq 3 as a buffer layer is attributed to the increased light harvesting,as well as blocking the hole leakage from MEH-PPV to the aluminum (Al) electrode due to the lower highest occupied molecular orbital (HOMO) level of Alq 3 compared with that of MEH-PPV. 相似文献
235.
为了避免DEA自动分配的权重为零的情况发生,对DEA评价的输入输出指标权重应该加以条件限制.通过利用熵值法分析指标内在的差异性,得到输入输出指标权重的比例关系,将其作为限制条件加入超效率DEA评价模型中,构建基于熵值权重限制的超效率DEA评价模型.此模型既可以客观的揭示指标间的内在关系,又可以使得评价对象实现全排序,评价结果更加符合实际.最后将此模型应用于河北省工程中心的实证分析,结果显示新的模型较传统的DEA模型和超效率DEA模型具有明显的优势. 相似文献
236.
采用基于密度泛函理论的第一性原理计算了锐钛矿相和金红石相TiO2:Nb的晶体结构、电子结构和光学性质. 结果表明, 在相等的摩尔掺杂浓度下(6.25%), 锐钛矿相TiO2:Nb的导带底电子有效质量小于金红石相TiO2:Nb, 且前者室温载流子浓度是后者的两倍左右, 即具有更大的施主杂质电离率, 从而解释了锐钛矿相TiO2:Nb比金红石相TiO2:Nb具有更优异电学性能的实验现象. 光学计算也表明锐钛矿相在可见光区有更大的透过率, 从而在理论上解释了锐钛矿相TiO2:Nb比金红石相TiO2:Nb更适于做透明导电材料的原因. 计算结果与实验数据能较好符合.
关键词:
2:Nb')" href="#">TiO2:Nb
第一性原理
电子结构
光学性能 相似文献
237.
238.
First principles study of the magnetism driven by cation defects in CeO2: the important role of O2p states 下载免费PDF全文
The magnetism driven by cation defects in undoped CeO2 bulk and thin films is studied by the density functional theory corrected for on-site Coulomb interactions (DFT+U) with U = 5 eV for the Ce4f states and U = 7 eV for the O2p states. It is found that the Ce vacancies can induce a magnetic moment of the -4 gB/supercell, which arises mainly from the 2p hole state of the nearest neighbouring O atom (-1μB on per oxygen) to the Ce vacancy. The effect of the methodology is investigated, indicating that U = 7 eV for the O2p state is necessary to obtain the localized O2p hole state in defective ceria with cation vacancies. 相似文献
239.
First principles study of the magnetism driven by cation defects in CeO<sub>2</sub>:the important role of O2p states 下载免费PDF全文
The magnetism driven by cation defects in undoped CeO 2 bulk and thin films is studied by the density functional theory corrected for on-site Coulomb interactions (DFT+U) with U = 5 eV for the Ce4f states and U = 7 eV for the O2p states. It is found that the Ce vacancies can induce a magnetic moment of the ~ 4 μ B /supercell, which arises mainly from the 2p hole state of the nearest neighbouring O atom (~ 1 μ B on per oxygen) to the Ce vacancy. The effect of the methodology is investigated, indicating that U = 7 eV for the O2p state is necessary to obtain the localized O2p hole state in defective ceria with cation vacancies. 相似文献
240.
采用基于广义梯度近似的投影缀加平面波(Projector augmented wave)赝势和具有三维周期性边界条件的超晶胞模型,用第一原理计算方法,计算并分析了Rh在CeO_2(111)表面吸附所形成的Rh/CeO_2(111)界面体系的吸附能,价键结构和局域电子结构.考虑了Rh在不同吸附位置的吸附情况.结果表明:1)Rh在CeO_2(111)面有较大的吸附能,表明Rh与CeO_2(111)面有较强的相互作用,而且Rh在位于表面O的三度位,且位于次层氧的顶位的吸附最强;2)Rh的4d态同衬底O的2p态有明显的杂化作用,这是Rh同CeO_2较强作用的主要原因;3)Rh被CeO_2(主要是Rh的次近邻的Ce)氧化为Rh~(3+),并伴随着Ce~(4+)→Ce~(3+)反应的发生. 相似文献