全文获取类型
收费全文 | 182篇 |
免费 | 18篇 |
专业分类
化学 | 151篇 |
晶体学 | 5篇 |
力学 | 1篇 |
数学 | 5篇 |
物理学 | 38篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 14篇 |
2012年 | 15篇 |
2011年 | 14篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 22篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 13篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1995年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有200条查询结果,搜索用时 15 毫秒
61.
A characteristic new cooperative dehydration transition, in 1:1 Laponite-MMT cogel, was observed at T(c) ≈ 60 °C, a temperature at which the storage modulus (G(')) and depolarization ratio (D(p)) showed sharp increase, and the isotropic cogel turned into an anisotropic one. The dehydration dynamics could be described through power-law relations: G(') ~ (T(c)-T)(-γ) and D(p) ~ (T(c)-T)(-β) with γ ≈ β = 0.40 ± 0.05. The x-ray diffraction data revealed that the crystallite size decreased from 17 nm (at 20 °C) to 10 nm (at 80 °C) implying loss of free and inter-planar water. When this cogel was spontaneously cooled below T(c), it exhibited much larger storage modulii values which implied the existence of several metastable states in this system. This phase transition could be modeled through Landau theory, where the depolarization ratio was used as experimental order parameter (ψ). This parameter was found to scale with temperature, as ψ ~ (T(c)-T)(-α), with power-law exponent α = 0.40 ± 0.05; interestingly, we found α ≈ β ≈ γ. 相似文献
62.
Tina Chakrabarty Amaranadh Jasti N.K. Goel Vinod K. Shahi Sunil Sabharwal 《Radiation Physics and Chemistry》2011,80(7):803-809
Radiation-induced and thermal cross-linked sulfonated poly(ether sulfone) (SPS)–sulfonated poly(ether ether ketone) (SPK) composite ion-exchange membranes (SPS/SPK(γ) and SPS/SPK(T), respectively) were prepared. Their performances for water electrolysis were comparatively assessed. Thermal cross-linked membrane (SPS/SPK(T)) showed cross-linking of part functional groups (–SO3H) and thus deterioration in membrane conductivity. While, radiation-induced cross-linked membrane (SPS/SPK(γ)) avoided any cross-linking between functional groups and thus conductivity. Electrolysis performances of these membranes were evaluated in comparison with Nafion117 membrane. Relatively low current efficiency (CE) for SPS/SPK and SPS/SPK(T) membranes was due to their high mass transfer (water) via electro-osmotic drag, which was negligible for SPS/SPK(γ) membrane. SPS/SPK(γ) membrane exhibited comparable stabilities and water splitting performance with Nafion117 membrane, which revealed its suitability as substitute for electrochemical applications. 相似文献
63.
64.
Ashish Bhatnagar Sunita K. Pandey Rohit R. Shahi M. Sterlin Leo Hudson M. A. Shaz O. N. Srivastava 《Crystal Research and Technology》2013,48(8):520-531
The aim of the present investigation is to synthesize mixed sodium potassium alanate (K2NaAlH6) and to explore its hydrogen sorption characteristics. K2NaAlH6 is synthesized through ball milling of KH and NaAlH4 in the molar ratio 2:1 under hydrogen pressure of 10 bar. The temperature programmed desorption experiment shows that the synthesized K2NaAlH6 has peak desorption temperature of ∼352°C and reveals appreciable rehydrogenation kinetics under 6 bar hydrogen pressure at 300°C. The investigations are also focused on the catalytic effect of carbon nanostructures (CNS) namely, the graphene sheet (GS) and single wall carbon nanotube (SWCNT) and titanium halides (TiCl3 and TiF3) on K2NaAlH6. In the case of graphene and SWCNT catalyzed K2NaAlH6, the peak desorption temperature gets reduced to ∼347°C and ∼341°C respectively. The catalytic effects of CNS and titanium halide on K2NaAlH6 are also compared in the investigation. Between the two types of catalysts, halides are found to be better than CNS and out of the two halides, TiF3 is found to be the best catalyst for hydrogen sorption in K2NaAlH6. The peak desorption temperature decreases significantly from 352°C to ∼324°C for TiF3 catalyzed K2NaAlH6. Thus, the desorption activation energy reduces drastically from 124.43 kJ/mol (synthesized K2NaAlH6) to 88.05 kJ/mol for TiF3 catalyzed K2NaAlH6. 相似文献
65.
The symmetry reduction method based on the Fr′echet derivative of differential operators is applied to investigate symmetries of the Einstein-Maxwell field equations for magnetostatic fields, which is a coupled system of nonlinear partial differential equations of the second order. The technique yields invariant transformations that reduce the given system of partial differential equations to a system of nonlinear ordinary differential equations. Some of the reduced systems are further studied to obtain the exact solutions. 相似文献
66.
The carbosilanes RMe2Si(CH2)xSiH3, [R = 2-Th (1a, 2a), 4-Me-2-Th (3a, 4a), 2-Fu (5a, 6a), 5-Me-2-Fu (7a, 8a); x = 2 and 3], with primary SiH3 end groups undergo a facile dehydropolymerization under ambient conditions (50 °C, 48 h) in presence of Cp2TiCl2/2.2 n-BuLi catalyst to afford the corresponding poly(hydrosilane)s 1–8 bearing carbosilyl side chains appended with thienyl/furyl groups. These have been characterized by GPC, IR, multinuclear (1H, 13C{1H}, 29Si{1H}) NMR, UV and PL spectral studies. 相似文献
67.
Nisha P. Kushwah 《Journal of organometallic chemistry》2009,694(15):2375-2379
The reactions of triorgano-gallium and -indium etherate with salen ligands in benzene afforded complexes of the type [R2MOC6H4CR′NCH2-]2, (R/M/R′ = Me/Ga/H (1), Et/Ga/H (2), Me/In/H (3), Et/Ga/Me (4)) in nearly quantitative yields. These complexes have been characterized by elemental analysis, IR, UV-Vis, NMR (1H and 13C{1H}) and mass spectral data. The organogallium complexes showed photoluminescence in blue-green region. The complex, [(Me2Ga)2(O-(C6H4)CHN-CH2-)2] on recrystallization from benzene-hexane and dichloromethane gave orthorhombic and monoclinic forms, respectively. Both the forms are dimeric with gallium atoms acquiring a distorted tetrahedral configuration defined by two methyl groups, phenolate oxygen and azomethene nitrogen. The complexes [(Me2Ga)2(O-(C6H4)CHN-CH2-)2] and [(Me2In)2(O-(C6H4)CHN-CH2-)2] have been employed as alkylating agent for C-C coupling reaction of 1-bromonaphthalene in presence of PdCl2(PPh3)2. 相似文献
68.
Bijay P. Tripathi Vinod K. Shahi 《Colloids and surfaces. A, Physicochemical and engineering aspects》2009,340(1-3):10-19
We reported sulfonated poly(ether ether ketone) (SPEEK, 61% degree of sulfonation)–metal oxides (MO2:SiO2, TiO2 and ZrO2)–polyaniline composite membranes. Metal oxides were incorporated into the swelled SPEEK membrane by sol–gel method and cured by thermal treatment. SPEEK–metal oxide membranes surfaces were modified with polyaniline (PANI) by a redox polymerization process. It was observed that water retention capacity of membrane was increased and methanol permeability was reduced due to synergetic effect of metal oxides and surface modification with polyaniline. These composite membranes showed extremely low methanol permeability (1.9–1.3 × 10−7 cm2 s−1), which was lower than till reported values either for SPEEK–metal oxide or SPEEK/PANI membranes. Relatively high selectivity parameter (SP) values at 343 K of these membranes, especially S–SiO2–PANI and S–TiO2–PANI, indicated their great advantages over Nafion117 (N117) membrane for targeting on moderate temperature applications due to the synergetic effect of MO2 and PANI in SPEEK matrix. S–TiO2–PANI and N117 showed comparable cell performance in direct methanol fuel cell (DMFC). 相似文献
69.
A multiwavelength Ytterbium-doped fiber ring laser operating at 1030 nm region is demonstrated using a Sagnac loop mirror
and a Mach-Zehnder interferometer. We report the Performance comparisons of multi-wavelength oscillations in Yb3+ doped fiber lasers (YDFL) with typical commercial ytterbium doped silica fibers. By adjusting the polarization controller
(PC), a widely tunable laser range of 22 nm from 1030 nm to 1050 nm is obtained. The Mach-Zehnder interferometer (MZI) design
has exhibited simplicity in the operation for controlling the smallest wavelength spacing compared to Sagnac loop mirror method.
In our observations, the smallest achieved stable wavelength spacing in Sagnac loop mirror setup and MZI setup were 2.1 nm
and 0.7 nm, respectively. In case of nine-wavelength operation with a MZI setup, the stability, Full Width at Half Maximum
(FWHM) and side mode suppression ratio (SMSR) of laser lines are not affected by increasing pump power, While for above four
wavelength operation, the laser stability with Sagnac loop mirror becomes worse specially for higher input pump power and
the power fluctuation among the wave-lengths would be also slightly larger. 相似文献
70.
P. Nisha Santha Kumari M. Beatrice Margaret S. Kalainathan 《Crystal Research and Technology》2009,44(2):177-183
Pure and potassium doped cadmium mercury thiocyanate single crystals have been obtained from silica gel by the process of diffusion. The X‐ray diffraction studies reveal the crystal lattice of both pure and doped crystals to be tetragonal. The crystalline perfection of the grown crystals were investigated by high resolution X‐ray diffraction analysis and the quality of the crystals are found to be extremely good. Transmission and Fourier transform infrared spectra were recorded for the grown crystals. The TG/DTA analyses show that the crystals are highly thermally stable. The mechanical strength of the crystals were studied by Vickers microhardness test and a study of their second harmonic generation efficiency in comparison with urea has been made by performing Kurtz powder test. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献