全文获取类型
收费全文 | 369篇 |
免费 | 25篇 |
国内免费 | 54篇 |
专业分类
化学 | 264篇 |
晶体学 | 1篇 |
力学 | 21篇 |
综合类 | 5篇 |
数学 | 95篇 |
物理学 | 62篇 |
出版年
2023年 | 39篇 |
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 17篇 |
2019年 | 16篇 |
2018年 | 19篇 |
2017年 | 12篇 |
2016年 | 17篇 |
2015年 | 6篇 |
2014年 | 19篇 |
2013年 | 29篇 |
2012年 | 18篇 |
2011年 | 21篇 |
2010年 | 19篇 |
2009年 | 29篇 |
2008年 | 20篇 |
2007年 | 30篇 |
2006年 | 14篇 |
2005年 | 21篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1987年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
排序方式: 共有448条查询结果,搜索用时 15 毫秒
171.
172.
本文讨论了正延迟更新序列半群D^+的I0类构成。证明了更新序列半群D^+的I0类由一切形如V(∞,1,p)(0<p<1)和D^+中满足limn→∞vn=1的单调上升序列(vn)所成。 相似文献
173.
E. Fontananova G. Di Profio E. Curcio L. Giorno E. Drioli 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):537-543
In this paper a new method for the functionalization of porous membranes with β-CD is reported. Porous polypropylene (PP)
hollow fibres have been impregnated with a mixture composed by a partially cross-linked polydimethylsiloxane (PDMS) and β-cyclodextrin
(β-CD). The prepolymerization of the PDMS components was necessary to avoid their inclusion in the β-CD cavity. The firm heterogenization
of the β-CD was obtained by in situ cross-linking of the PDMS/β-CD network in the porous membranes.
The presence of the PDMS/β-CD network in the membranes was confirmed by FT-IR-ATR (on the outer and inner surfaces) and EDX
analyses (on the cross-section).The effect of the impregnation times on membrane morphology, loading and porosity has been
investigated.
The binding capacity of the heterogenized β-CDs has been tested using the phenolphthalein as guest molecule. 相似文献
174.
Cross-linking of functionalised polysiloxanes is an important tool to adjust their viscoelastic properties and can be achieved by the reaction with alumatrane. The cross-linking reaction has been found to proceed only with hydrolyzed alumatrane species. Siloxane model compounds with different functional groups such as alkoxy, siloxy, and hydroxy groups were considered in order to optimise the rheological properties of the polymer. The activation energy barriers of the related reactions were analysed using the density functional theory under the assumption of the presence of Al-OH groups formed by the hydrolysis of alumatrane. The cross-linking involving hydroxy groups of siloxane and hydrolyzed alumatrane has been found to have the lowest activation energy (−14 kJ/mol). As the reaction of the Si-O-Si-polymer backbone with the hydroxy groups of the hydrolyzed alumatrane turned out to have the very low activation energy of +2 kJ/mol, this type of reaction is predicted to play a key role for the cross-linking of polysiloxanes with hydrolyzed alumatrane. The involved water molecules are formed back in the course of subsequent polycondensation reactions, therefore H2O can be considered as a cross-linking catalyst in these systems. 相似文献
175.
Control of hollow size of micron-sized monodispersed polymer particles having a hollow structure 总被引:2,自引:0,他引:2
Micron-sized monodispersed cross-linked polymer particles having one hollow in the inside were produced by seeded polymerization for the dispersion of (toluene/divinylbenzene)-swollen PS particles prepared utilizing the dynamic swelling method which the authors proposed. In order to control the hollow size, the weight ratio of toluene/PS was changed in the range of 520. The hollow size increased with an increase in the weight ratio. Even if benzene and xylene were used in place of toluene, similar hollow particles were produced, though the hollow size was affected by their solubility in water.Part CLIII of the series Studies on Suspension and Emulsion 相似文献
176.
Formation mechanism of micron-sized monodispersed polymer particles having a hollow structure 总被引:1,自引:0,他引:1
Recently, the authors reported that micron-sized monodispersed cross-linked polymer particles having a single hollow in the
inside were produced by seeded polymerization for the dispersion of (toluene/divinylbenzene)-swollen polystyrene (PS) particles
prepared utilizing the dynamic swelling method which the authors had proposed. In this article, the particles at various conversions
of the seeded polymerization were observed with an optical microscope in detail. From the obtained results, the formation
mechanism of the hollow structure is suggested as follows. As seeded polymerization proceeds, poly-divinylbenzene (PDVB) molecules
precipitated in the swollen particle are trapped near the interface and gradually pile at the inner surface, which results
in a cross-linked PDVB shell. PS which dissolves in the swollen particles is repelled gradually to the inside. After the completion
of the polymerization, toluene in the hollow evaporates by drying, and PS clings to the inner wall of the shell uniformly.
Received: 14 February 1997 Accepted: 16 April 1997 相似文献
177.
Xiang-Ji Liao Dongdong Pu Li Yuan Jingjing Tong Shuai Xing Dr. Zhen-Long Tu Prof. Jing-Lin Zuo Prof. Wen-Hua Zheng Prof. You-Xuan Zheng 《Angewandte Chemie (International ed. in English)》2023,62(6):e202217045
Chiral boron/nitrogen doped multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters are promising for highly efficient and color-pure circularly polarized organic light-emitting diodes (CP-OLEDs). Herein, we report two pairs of MR-TADF materials (Czp-tBuCzB, Czp-POAB) based on planar chiral paracyclophane with photoluminescence quantum yields of up to 98 %. The enantiomers showed symmetric circularly polarized photoluminescence spectra with dissymmetry factors |gPL| of up to 1.6×10−3 in doped films. Meanwhile, the sky-blue CP-OLEDs with (R/S)-Czp-tBuCzB showed an external quantum efficiency of 32.1 % with the narrowest full-width at half-maximum of 24 nm among the reported CP-OLEDs, while the devices with (R/S)-Czp-POAB displayed the first nearly pure green CP electroluminescence with |gEL| factors at the 10−3 level. These results demonstrate the incorporation of planar chirality into MR-TADF emitter is a reliable strategy for constructing of efficient CP-OLEDs. 相似文献
178.
Sen Wu Le Zhang Jingxiang Wang Abhishek Kumar Gupta Ifor D. W. Samuel Eli Zysman-Colman 《Angewandte Chemie (International ed. in English)》2023,62(28):e202305182
Multiresonant thermally activated delayed fluorescence (MR-TADF) compounds are attractive as emitters for organic light-emitting diodes (OLEDs) as they can simultaneously harvest both singlet and triplet excitons to produce light in the device and show very narrow emission spectra, which translates to excellent color purity. Here, we report the first example of an MR-TADF emitter (DOBDiKTa) that fuses together fragments from the two major classes of MR-TADF compounds, those containing boron (DOBNA) and those containing carbonyl groups (DiKTa) as acceptor fragments in the MR-TADF skeleton. The resulting molecular design, this compound shows desirable narrowband pure blue emission and efficient TADF character. The co-host OLED with DOBDiKTa as the emitter showed a maximum external quantum efficiency (EQEmax) of 17.4 %, an efficiency roll-off of 32 % at 100 cd m−2, and Commission Internationale de l’Éclairage (CIE) coordinates of (0.14, 0.12). Compared to DOBNA and DiKTa, DOBDiKTa shows higher device efficiency with reduced efficiency roll-off while maintaining a high color purity, which demonstrates the promise of the proposed molecular design. 相似文献
179.
Vanessa Rück Mikkel B. Liisberg Christian Brinch Mollerup Yanmei He Junsheng Chen Cecilia Cerretani Tom Vosch 《Angewandte Chemie (International ed. in English)》2023,62(39):e202309760
DNA-stabilized silver nanoclusters (DNA-AgNCs) are easily tunable emitters with intriguing photophysical properties. Here, a DNA-AgNC with dual emission in the red and near-infrared (NIR) regions is presented. Mass spectrometry data showed that two DNA strands stabilize 18 silver atoms with a nanocluster charge of 12+. Besides determining the composition and charge of DNA2[Ag18]12+, steady-state and time-resolved methods were applied to characterize the picosecond red fluorescence and the relatively intense microsecond-lived NIR luminescence. During this process, the luminescence-to-fluorescence ratio was found to be excitation-intensity-dependent. This peculiar feature is very rare for molecular emitters and allows the use of DNA2[Ag18]12+ as a nanoscale excitation intensity probe. For this purpose, calibration curves were constructed using three different approaches based either on steady-state or time-resolved emission measurements. The results showed that processes like thermally activated delayed fluorescence (TADF) or photon upconversion through triplet-triplet annihilation (TTA) could be excluded for DNA2[Ag18]12+. We, therefore, speculate that the ratiometric excitation intensity response could be the result of optically activated delayed fluorescence. 相似文献
180.
Chen Cao Ji-Hua Tan Dr. Ze-Lin Zhu Jiu-Dong Lin Hong-Ji Tan Huan Chen Dr. Yi Yuan Dr. Man-Kit Tse Dr. Wen-Cheng Chen Prof. Chun-Sing Lee 《Angewandte Chemie (International ed. in English)》2023,62(10):e202215226
Rationally tuning the emission position and narrowing the full width at half-maximum (FWHM) of an emitter is of great importance for many applications. By synergistically improving rigidity, strengthening the resonant strength, inhibiting molecular bending and rocking, and destabilizing the HOMO energy level, a deep-blue emitter (CZ2CO) with a peak wavelength of 440 nm and an ultranarrow spectral FWHM of 16 nm (0.10 eV) was developed via intramolecular cyclization in a carbonyl/N resonant core (QAO). The dominant υ0-0 transition character of CZ2CO gives a Commission Internationale de I’Éclairage coordinates (CIE) of (0.144, 0.042), nicely complying with the BT.2020 standard. Moreover, a hyper-fluorescent device based on CZ2CO shows a high maximum external quantum efficiency (EQEmax) of 25.6 % and maintains an EQE of 22.4 % at a practical brightness of 1000 cd m−2. 相似文献