全文获取类型
收费全文 | 115篇 |
免费 | 45篇 |
国内免费 | 8篇 |
专业分类
化学 | 31篇 |
晶体学 | 1篇 |
力学 | 8篇 |
综合类 | 2篇 |
数学 | 10篇 |
物理学 | 116篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 9篇 |
2013年 | 5篇 |
2012年 | 10篇 |
2011年 | 9篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1992年 | 1篇 |
1987年 | 2篇 |
排序方式: 共有168条查询结果,搜索用时 15 毫秒
1.
强偏差定理一直是国际概率论界研究的中心课题之一.通过构造适当的非负鞅,将Doob鞅收敛定理应用于几乎处处收敛的研究,给出了一类特殊非齐次树上连续状态马氏泛函的若干强偏差定理. 相似文献
2.
Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers 下载免费PDF全文
In this work, bathocuproine (BCP) and bathophenanthroline (Bphen), commonly used in small-molecule organic solar cells (OSCs), are adopted as the buffer layers to improve the performance of the polymer solar cells (PSCs) based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. By inserting BCP or Bphen between the active layer and the top cathode, all the performance parameters are dramatically improved. The power conversion efficiency is increased by about 70% and 120% with 5-nm BCP and 12-nm Bphen layers, respectively, when compared with that of the devices without any buffer layer. The performance enhancement is attributed to BCP or Bphen (i) increasing the optical field, and hence the absorption in the active layer, (ii) effectively blocking the excitons generated in MEH-PPV from quenching at organic/aluminum (Al) interface due to the large band-gap of BCP or Bphen, which results in a significant reduction in series resistance (Rs), and (iii) preventing damage to the active layer during the metal deposition. Compared with the traditional device using LiF as the buffer layer, the BCP-based devices show a comparable efficiency, while the Bphen-based devices show a much larger efficiency. This is due to the higher electron mobility in Bphen than that in BCP, which facilitates the electron transport and extraction through the buffer layer to the cathode. 相似文献
3.
The most neutron-deficient isotopes 215;216U were produced in the complete-fusion reaction 180W(40Ar, 4-5n)215,216U. Evaporation residues recoiled from the target were separated in-flight from the primary beam by the gas-filled recoil separator SHANS and subsequently identified on the basis of correlated -decay chains. Two -decaying states were identified in 216U, one for the ground state and the other for the isomeric state with 8+(h9=2f7=2) configuration. The -decay properties for 215;216U and the systematics of 8+ isomeric state in N =124,126 isotones were investigated. 相似文献
4.
采用化学氧化法制备聚苯胺与还原石墨烯复合材料。复合材料的结构、晶型和电磁参数分别通过X射线衍射仪及HP8722ES型矢量网络分析仪进行表征、测试与分析。结果表明,同聚苯胺相比,聚苯胺与还原石墨烯复合材料的介电损耗明显增加。而且在复合材料中,石墨烯的含量越大,材料的微波吸收性能越好,在频率波段(9.5~13.4GHz)反射损耗均小于-10 dB,并在频率为11.2 GHz时达到最大反射损耗-29.69 dB。聚苯胺与还原石墨烯的复合使得材料的载流子迁移率变大,吸波特性得到改善。 相似文献
5.
Enhancement of green emission by the codoping U . 3+ A+ (A - Li, Na, K) in Ca2 O3CI.Tb phosphor 下载免费PDF全文
Tb3+-doped Ca2BO3C1 compounds with different charge compensation approaches are synthesized by a hightemperature solid-state reaction method, and the luminescent properties and Commission Internationale de l'Eclairage (CIE) chromaticity coordinates are systematically characterized. Ca2BO3Cl:Tb3+ can produce green emission under 376 nm radiation excitation. With codoped A+ (A = Li, Na, K) as charge compensators, the relative emission intensities of Ca2BO3Cl:Tb3+ are enhanced by about 1.61, 1.97, and 1.81 times compared with those of the direct charge balance, which is considered to be due to the effect of the difference in ion radius on the crystal field. The CIE chromaticity coordinates of Ca2BO3CI:Tb3+, A+ (A = Li, Na, K) are (0.335, 0.584), (0.335, 0.585), and (0.335, 0.585), corresponding to the hues of green. Therefore, A+ (A = Li, Na, K) may be the optimal charge compensator for Ca2BO3Cl:Tb3+. 相似文献
6.
Improved performance of P3HT:PCBM solar cells by both anode modification and short-wavelength energy utilization using Tb(aca)3phen 下载免费PDF全文
The performance of P3HT:PCBM solar cells was improved by anode modification using spin-coated Tb(aca)3phen ultrathin films. The modification of the Tb(aca)3phen ultrathin film between the indium tin oxide(ITO) anode and the PEDOT:PSS layer resulted in a maximum power conversion efficiency(PCE) of 2.99% compared to 2.66% for the reference device, which was due to the increase in the short-circuit current density(Jsc). The PCE improvement could be attributed to the short-wavelength energy utilization and the optimized morphology of the active layers. Tb(aca)3phen with its strong down-conversion luminescence properties is suitable for the P3HT:PCBM blend active layer, and the absorption region of the ternary blend films is extended into the near ultraviolet region. Furthermore, the crystallization and the surface morphology of P3HT:PCBM films were improved with the Tb(aca)3phen ultrathin film. The ultraviolent–visible absorption spectra,atomic force microscope(AFM), and X-ray diffraction(XRD) of the films were investigated. Both anode modification and short-wavelength energy utilization using Tb(aca)3phen in P3HT:PCBM solar cells led to about a 12% PCE increase. 相似文献
7.
为了评估柱壳和锥壳结构自由振动特征数值计算的精度,分析不同边界条件、环肋、纵肋以及流体载荷对自由振动特征的影响,计算并校验了典型壳体结构在空气中、浸没以及浸没并充满水情况下的自由振动特征。结果表明,空气中干模态分析在2 kHz内、单面及双面接触水情况下的流固耦合湿模态分析在500 Hz内的计算精度能够控制在10%以内。壳体流固耦合自由振动分析时可以采用实体单元离散也可以采用壳单元离散的方法,前者精度略高,能够有效保证求解收敛的频带范围更宽,但工作量更大。径长比大于0.2时,浸没于水中的自由振动分析可以转换为内部填充水时的自由振动分析,转换时应保证两者流固耦合湿表面积相等,如半浸水和半充满水,能够有效减小计算量;环肋和流体载荷对壳体自由振动特征的影响明显,环肋使柱壳同阶自振频率增加,流体载荷使柱壳同阶自振频率减小且影响幅度更大,两者均会使得柱壳模态振型呈现错序排列;流固耦合效应对无肋柱壳和环肋柱壳自振频率的影响效果相当;柱壳内外有水相对于单面接触水而言,同阶自振频率进一步减小,模态振型基本不变;流体载荷对环肋锥壳的自振频率和模态振型的影响幅度较对环肋柱壳小。 相似文献
8.
在固态阴极射线发光中,过热电子碰撞激发有机材料而发光,因此加速层对电子的加速能力是影响器件发光亮度的关键因素之一.分别以SiO2和ZnO作为加速层.制备出两种固态阴极射线发光器件A:ITO/MEH-PPV/SiO2/Al和B:ITO/MEH-PPV/ZnO/Al.通过理论计算比较了电子从电极注入到加速层的隧穿电流密度以及SiO2层与ZnO层的电场强度,计算结果表明:在相同驱动电压下,SiO2作为电子加速层时隧穿电流的密度要大于ZnO层的隧穿电流的密度,并且SiO2层的电场强度比ZnO层的电场强度大.实验结果表明:SiO2作为加速层的器件的发光强度高于以ZnO为电子加速层器件的发光强度. 相似文献
9.
《普通高中数学课程标准》倡导"积极主动、勇于探索的学习方式".[1]于是,是否进行探究成为衡量教学是否落实新课标理念的重要标志.应当说,这是一种积极的现象.经过一段时间的教学实践,发现尽管有越来越多的教师在数学探究教学的设计和实施中表现了许多的热情和创意,但是就目前的现状而言,在数学探究教学的实践中 相似文献
10.
Ca<sub>2</sub>BO<sub>3</sub>Cl:Ce<sup>3+</sup>,Tb<sup>3+</sup>:A novel tunable emitting phosphor for white light-emitting diode 下载免费PDF全文
<正>Ca2BO3Cl:Ce3+,Ca2BO3Cl:Tb3+,and Ca2BO3Cl:Ce3+,Tb3+ phosphors are synthesized by a high temperature solid-state reaction.The emission intensity of Ce3+ or Tb3+ in Ca2BO3Cl is influenced by the Ce3+ or Tb3+ doping content,and the optimum concentrations of Ce3+ and Tb3+ are 0.03 mol and 0.05 mol,respectively.The concentration quenching effect of Ce3+ or Tb3+ in Ca2BO3Cl occurs,and the concentration quenching mechanism is d-d interaction for either Ce3+ or Tb3+.The Ca2BO3Cl:Ce3+,Tb3+ can produce colour emission from blue to green by properly tuning the relative ratio between Ce3+ and Tb3+,and the emission intensity of Tb3+ in Ca2BO3Cl can be enhanced by the energy transfer from Ce3+ to Tb3+.The results indicate that Ca2BO3Cl:Ce3+,Tb3+ may be a promising double emission phosphor for UV-based white light emitting diodes. 相似文献