全文获取类型
收费全文 | 281篇 |
免费 | 59篇 |
国内免费 | 38篇 |
专业分类
化学 | 77篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 7篇 |
物理学 | 148篇 |
无线电 | 143篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 7篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 15篇 |
2009年 | 23篇 |
2008年 | 25篇 |
2007年 | 11篇 |
2006年 | 17篇 |
2005年 | 8篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有378条查询结果,搜索用时 19 毫秒
81.
Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Nithin Pathoor Ansuman Halder Amitrajit Mukherjee Jaladhar Mahato Dr. Shaibal K. Sarkar Dr. Arindam Chowdhury 《Angewandte Chemie (International ed. in English)》2018,57(36):11603-11607
Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano‐emitters. Extended quantum‐confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi‐level blinking of entire individual organo–lead bromide perovskite microcrystals (volume=0.1–3 μm3) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 μm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long‐range (mesoscopic) electronic communication. 相似文献
82.
高温固相法合成了共掺Si4+的LiGa5O 8:Cr3+长余辉材料,采用X射线衍射、荧光光谱、余辉发射光 谱、余辉衰减曲线和热释光对样品分别进行了表征,并分析了Si掺杂对LiGa5O8:Cr 3+发光性能的影响。结 果表明,所合成的LiGa5O8:Cr3+,Si4+材料能产生近红外长余辉发射,主 发射峰位于717nm,归属于Cr3+的2E→4A 2 跃迁,共掺Si4+能显著提高余辉性能。掺杂浓度为0.25时,样 品的初始发光强度提高了3倍,余辉性能最佳, 余辉持续时间超过30 h。热释光曲线表明,共掺Si4+ 离子可增加有效陷阱数量,从而改善材料的余辉发光性能。 相似文献
83.
84.
Molecular beam techniques for study of collisional and spectroscopic processes have recently been enhanced by use of static electric or magnetic fields to orient or align molecules with permanent dipole moments. A more general method is now in prospect, applicable both to alignment and to spatial trapping of molecules. This exploits the anisotropic interaction of the electric field vector of intense laser radiation with the dipole moment induced in a polarizable molecule by the laser field. The interaction creates directional superpositions of field-free states that correspond to oblate spheroidal wavefunctions, with eigenenergies that decrease with increasing field strength. We suggest that this polarizability interaction produces the marked alignment found in laser-induced dissociative ionization of CO by the Saclay group. We also present calculations illustrating the feasibility of spattal trapping. In combination with supermirror focussing and buffer-gas cooling, an intense infrared laser can typically confine molecules for long-times (-hours) within a small (-picoliter) and cold (?1°K) “pocket of light.” 相似文献
85.
The rate constants of the addition of CCl3CH2ClCH3(R6) radicals to -methyl-styrene, styrene, methyl methacrylate, methyl acrylate, and acrylonitrile and of CCl3CH2(CH3)2(R7) radicals to styrene, methyl acrylate, and acrylonitrile were determined by ESR spectroscopy. It was shown that the radicals R6 and R7 possess approximately equal reactivity in addition to unsaturated compounds, despite the difference in the donor-acceptor properties of the substituents at the vinyl group. In a comparison of the reactivity of radicals R6 and R7 with the reactivity of radicals CCl3CH2H2(R1), CCl3CH2HCH3(R3), CCl3CH2HCl(R4), and ClCH2CH2Cl2(R5) [1] in addition reactions, it was shown that polar and steric effects of the substituents situated in the -position to the radical site of the above-mentioned radicals, as well as the donor-acceptor properties of the substituents at the vinyl group in the unsaturated compounds, lead to appreciable changes in reactivity.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 136–141, January, 1992. 相似文献
86.
We continue our investigation of a model of random walks on lattices with two kinds of points, black and white. The colors of the points are stochastic variables with a translation-invariant, but otherwise arbitrary, joint probability distribution. The steps of the random walk are independent of the colors. We are interested in the stochastic properties of the sequence of consecutive colors encountered by the walker. In this paper we first summarize and extend our earlier general results. Then, under the restriction that the random walk be symmetric, we derive a set of rigorous inequalities for the average length of the subwalk from the starting point to a first black point and of the subwalks between black points visited in succession. A remarkable difference in behavior is found between subwalks following an odd-numbered and subwalks following an evennumbered visit to a black point. The results can be applied to a trapping problem by identifying the black points with imperfect traps. 相似文献
87.
We consider the Laplacian
m
in 3 (or in a bounded region of 3) with Dirichlet boundary conditions on the surfaces of some identical (small) neighborhoods ofm randomly distributed points, in the limit whenm goes to infinity and their linear size decreases as 1/m. We give here a stronger form of the result showing the convergence of the above operator to – C(x), whereC(x) is the limit density of electrostatic capacity of the obstacles. In particular results on the rate of convergence and on the fluctuations of
m
around the limit operator are given. 相似文献
88.
Vygintas Jankus Chris Winscom Andrew P. Monkman 《Advanced functional materials》2011,21(13):2522-2526
Investigations are carried out into triplet transfer in bilayer films of NPB (N,N´‐diphenyl‐N,N´‐bis(1‐naphthyl)‐1,1´‐biphenyl‐4,4?‐diamine) and Ir(piq)3 (Iridium (III) Tris(1‐phenylisoquinoline) using laser light pulses to excite the upper surface of the NPB, and thereafter observing the decay dynamics in the Ir(piq)3 layer situated beneath the NPB. The NPB layer thickness is varied from 13 nm to 80 nm. The results show that up to 200 ns after excitation, the multiexponential decay of directly excited Ir(piq)3 is observed, thereafter the decay is monoexponential. It is concluded that this monoexponential decay after 200 ns is due to triplets that are transferred to the Ir(piq)3 via migration from the NPB. The thicker the NPB layer the longer it takes for the reservoir of NPB triplets to deplete via the Ir(piq)3, with the result that the apparent monoexponential lifetime of the Ir(piq)3 increases as the thickness of the NPB films increases. Based on time resolved spectra and decays, it is concluded that triplets arriving from NPB are trapped at interface sites of Ir(piq)3 and do not migrate directly to the bulk states of Ir(piq)3. A model based on exciton diffusion kinetics, including the presence of interface trap sites, is described, which accurately predicts this behavior. 相似文献
89.
Ruofei Jia Xiaofeng Wu Wei Deng Xiujuan Zhang Liming Huang Kaifeng Niu Lifeng Chi Jiansheng Jie 《Advanced functional materials》2019,29(45)
Persistent photoconductivity (PPC) in organic phototransistors provides an opportunity and broad prospects to achieve many emerging applications in optoelectronic devices. However, a fundamental understanding of PPC behavior is still a key challenge impeding its practical applications. In this study, for the first time, a mechanism for electron trapping is presented in oxygen‐induced deep levels in organic semiconductors for the clarification of PPC behavior with solid evidence. Both theoretical simulation and experimental investigation unveil that oxygen in air atmosphere plays a decisive role in determining the PPC behavior. Oxygen molecules can induce deep defect levels in the energy bandgap of organic semiconductors, which will act as deep traps for photogenerated electrons. The trapped electrons will be maintained in the traps and undergo a very slow releasing process after light illumination, thus leading to a noticeable PPC behavior for the organic phototransistors. The proposed mechanism shows good universality and can be applicable to a host of organic semiconductors for explaining the PPC behaviors. This work reveals the significant role of oxygen in PPC behavior and also provides guidelines for controlling the unique PPC behavior toward device applications. 相似文献
90.