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41.
The softening of the IR active 300 cm−1 phonon mode in Tl-2223 superconductor, aroundT
c has been explained by considering a sixth order polarization potential at the off-center oxygen ion site in the Tl-O plane,
and by using a nonlinear lattice dynamical theory. The present theory explains, more or less satisfactorily, the unusual temperature
dependence of oxygen ion vibration and frequency shifts at higher temperature. The existence of strong nonlinear electron-phonon
interaction atT
c has been emphasized. 相似文献
42.
43.
Molecular recognition in structured matrixes: control of guest localization in block copolymer films
Shenhar R Xu H Frankamp BL Mates TE Sanyal A Uzun O Rotello VM 《Journal of the American Chemical Society》2005,127(46):16318-16324
We demonstrate the use of molecular recognition to control the spatial distribution of guest molecules within block copolymer films. Block copolymers bearing recognition units were combined with complementary and noncomplementary molecules, and the extent of segregation of these molecules into the different domain types within microphase-separated thin films was quantitatively analyzed using dynamic secondary ion mass spectrometry (SIMS). Complementarity between the guest molecules and the polymer functionalities proved to be a key factor and an efficient tool for directing the segregation preference of the molecules to the different domain types. The effect of segregation preference on the glass transition temperature was studied using differential scanning calorimetry (DSC), and the results corroborate the SIMS findings. In a complementary study, guests with tunable sizes (via dendron substituents) were used to control block copolymer morphology. Morphological characterization using transmission electron microscopy (TEM) and X-ray diffraction reveal that selectivity differences can be directly translated into the ability to obtain different morphologies from recognition unit-functionalized block copolymer scaffolds. 相似文献
44.
K. Shahi Nitish K. Sanyal S. Chandra 《Journal of Physics and Chemistry of Solids》1975,36(12):1349-1352
Thermoelectric power using reversible silver electrodes and electrical conductivity on the compressed pellets of (Me4N)2Ag13I15, and (Et4N)2Ag13I15 have been measured between room temperature and below 160°C. The results of θ can be expressed by the equations:?θ = 0.115 (103/T)+0.2905VK?1 and ?θ = 0.150 (103/T) + 0.305mV K?1; and those of conductivity by the equations; σ = 28.7 exp (?0.17eV/kT) ohm?1cm?1 and ohm?1cm?1; respectively for Me- and Et-electrolytes. The results are discussed and compared with those of previous authors. 相似文献
45.
46.
S. Dechoudhury Vaishali Naik Manas Mondal Hemendra Kumar Pandey Avik Chatterjee Dirtha Sanyal Debasis Bhowmick Alok Chakrabarti 《Pramana》2010,75(3):485-499
The design of a medium energy beam transport (MEBT) line comprising of a re-buncher and four quadrupoles, two upstream and
the other two downstream of the re-buncher, has been presented. The design was done to ensure almost 100% transport of heavy-ion
beams of about 99 keV/u energy from RFQ having a q/A not less than 1/14 through the re-buncher and then through IH Linac of about 0.6 m length in which beam would be accelerated
to about 185 keV/u. The re-buncher has been designed to operate at 37.8 MHz, the resonating frequency of both the RFQ and
the IH Linac. The entire beam line has been installed and recently O5+ beam from RFQ has been transported through the re-buncher and subsequently accelerated in the IH Linac successfully. 相似文献
47.
The structural and elastic properties of praseodymium monochalcogenides (PrX: X = S, Se, Te) and monopnictides (PrY: Y = P, As, Sb, Bi) with NaCl-type structure have been investigated by using an interionic potential theory with necessary modification to include the effect of Coulomb screening due to the delocalized f-electrons of rare earth ion. The calculations are done at ambient as well as at high pressure. The structure of the high pressure phase of PrX compounds is CsCl-type while all the PrY compounds have been found to undergo from their initial NaCl-type structure to high pressure body centered tetragonal (BCT) structure, which can be seen as the distorted CsCl-type with c/a ratio ≈ 0.82–0.87. The calculated transition pressures are in good agreement with the experimental results. The elastic properties like second-order elastic constants for PrX, Y compounds are calculated for the first time. The nature of the bonding is also predicted by calculating the distance between the ions with the increasing pressure. 相似文献
48.
The structural phase transition and electronic properties at ambient (B 1-phase) and high pressure (B 2-phase) of heavy rare earth monoantimonides (RESb; RE?=?Ho, Er, and Tm) have been studied theoretically using the self-consistent tight binding linear muffin tin orbital method. These compounds show metallic behavior under ambient condition and undergo a structural phase transition to the B 2 phase at high pressure. We predict a structural phase transition from the B 1 to B 2 phase in the pressure range 30.0–35.0?GPa. Apart from this, the ground state properties, such as lattice parameter and bulk modulus are calculated and compared with the available theoretical and experimental results. 相似文献
49.
Yuhe Cao Kuang Zhang Oishi Sanyal William J. Koros 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(35):12277-12281
Dip coating and pyrolysis processes are used to create multi‐layer asymmetric carbon molecular sieve (CMS) hollow fiber membranes with excellent gas separation properties. Coating of an economical engineered support with a high‐performance polyimide to create precursor fibers with a dense skin layer reduces material cost by 25‐fold compared to monolithic precursors or ceramic supports. CMS permeation results with CO2/CH4 (50:50) mixed gas feed show attractive CO2/CH4 selectivity of 58.8 and CO2 permeance of 310 GPU at 35 °C. 相似文献
50.
Soft Phonon Modes Leading to Ultralow Thermal Conductivity and High Thermoelectric Performance in AgCuTe
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Subhajit Roychowdhury Manoj K. Jana Jaysree Pan Satya N. Guin Prof. Dirtha Sanyal Prof. Umesh V. Waghmare Prof. Kanishka Biswas 《Angewandte Chemie (International ed. in English)》2018,57(15):4043-4047
Crystalline solids with intrinsically low lattice thermal conductivity (κL) are crucial to realizing high‐performance thermoelectric (TE) materials. Herein, we show an ultralow κL of 0.35 Wm?1 K?1 in AgCuTe, which has a remarkable TE figure‐of‐merit, zT of 1.6 at 670 K when alloyed with 10 mol % Se. First‐principles DFT calculation reveals several soft phonon modes in its room‐temperature hexagonal phase, which are also evident from low‐temperature heat‐capacity measurement. These phonon modes, dominated by Ag vibrations, soften further with temperature giving a dynamic cation disorder and driving the superionic transition. Intrinsic factors cause an ultralow κL in the room‐temperature hexagonal phase, while the dynamic disorder of Ag/Cu cations leads to reduced phonon frequencies and mean free paths in the high‐temperature rocksalt phase. Despite the cation disorder at elevated temperatures, the crystalline conduits of the rigid anion sublattice give a high power factor. 相似文献