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排序方式: 共有149条查询结果,搜索用时 15 毫秒
1.
A. Guzmn E. Luna J. Miguel-Snchez E. Calleja E. Muoz 《Infrared Physics & Technology》2003,44(5-6):377-382
In this work, we report on the design, growth and characterization of GaAsN/AlAs/AlGaAs double barrier quantum well infrared detectors to achieve intraband absorption below 4 μm. Due to the high effective mass of N-dilute alloys, it is common for these N-containing double barrier quantum well structures to have more than one bound state within the quantum well, enabling the possibility of achieving multispectral absorption from these confined levels to the quasi-bound. Based on a transfer matrix calculation we will study the influence of the potential parameters, in particular the well width and the introduction of a GaAs spacer layer in between the N-well and the AlAs barriers. We will compare the case in which there are two confined levels with the case in which only one level is bound, like in the conventional AlGaAs/AlAs/GaAs structures. On the basis of the simulation, we have grown and characterized some N-containing double barrier detectors. Moreover, an optimization of the post-growth annealing treatments of the GaAsN quantum well structures has also been performed. Finally, room temperature absorption measurements of both as-grown and annealed samples are presented and analyzed. 相似文献
2.
J. Martinez Salazar R. K. Bayer T. A. Ezquerra F. J. Baltá Calleja 《Colloid and polymer science》1989,267(5):409-413
The morphology and structure of high molecular weight linear polyethylene (M
w 450000) filled with carbon black and processed using molds that introduce an elongational flow component during injection molding has been examined using electron microscopy and x-ray diffraction techniques. The study of fracture surfaces reveals the display of shish-kebabs oriented along the injection direction with segregated longitudinal channels of carbon black particles. Molecular and lamellar changes in orientation are, furthermore, studied across the thickness of the moldings. It is shown that addition of carbon black particles to injection-molded polyethylene induces significant changes in lamellar orientation. Thus, while lamellar overgrowth proceeds perpendicular to the fiber axes within carbon free channels, lamellae grow randomly within carbon-enriched regions where flow is less pronounced. 相似文献
3.
4.
A study of the fragmentation of the \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{\left({{\rm C}_{\rm 6} {\rm H}_{\rm 6} {\rm O}} \right){\rm Fe}} \right]_{}^{_.^ + } $\end{document} ion formed from two different precursors suggests that the ions adopt different structures over that part of the energy distribution giving rise to decomposition in the ion source. 相似文献
5.
Adsorption of ethane in a slit shaped micropore system has been studied by Monte Carlo molecular simulation by considering
this hydrocarbon as a two interacting sites molecule. Ethane adsorption in pore sizes from 0.41 to 1.66 nm was simulated at
303 K. Microscopic characteristics of the adsorbed phase have been studied for pores of different size, comparing two density
profiles: the molecule centre of mass profile and the molecular interaction site profile. Averaged angle distribution of molecule
positions with respect to the slit plane across the pore width has been also obtained by simulation. These results were related
to ethane molecule packing efficiency, which is also related to the adsorption capacity in terms of the adsorbed phase density.
Packing efficiency presents an oscillation shape as the result of the adsorbate disorder inside the pore.
Pressure influence on the adsorption has been studied by following pore filling by simulation. When pore condensation takes
place and for pressures above condensation, fluid-fluid interactions are determinant in molecule disorder observed between
the two adsorbed layers. 相似文献
6.
7.
Abstract The linear and non-linear relationships of acute toxicity (as determined on five aquatic non-vertebrates and humans) to molecular structure have been investigated on 38 structurally-diverse chemicals. The compounds selected are the organic chemicals from the 50 priority chemicals prescribed by the Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) programme. The models used for the evaluations are the best combination of physico-chemical properties that could be obtained so far for each organism, using the partial least squares projection to latent structures (PLS) regression method and backpropagated neural networks (BPN). Non-linear models, whether derived from PLS regression or backpropagated neural networks, appear to be better than linear models for describing the relationship between acute toxicity and molecular structure. BPN models, in turn, outperform non-linear models obtained from PLS regression. The predictive power of BPN models for the crustacean test species are better than the model for humans (based on human lethal concentration). The physico-chemical properties found to be important to predict both human acute toxicity and the toxicity to aquatic non-vertebrates are the n?octanol water partition coefficient (Pow) and heat of formation (HF). Aside from the two former properties, the contribution of parameters that reflect size and electronic properties of the molecule to the model is also high, but the type of physico-chemical properties differs from one model to another. In all of the best BPN models, some of the principal component analysis (PCA) scores of the 13C-NMR spectrum, with electron withdrawing/accepting capacity (LUMO, HOMO and IP) are molecular size/volume (VDW or MS1) parameters are relevant. The chemical deviating from the QSAR models include non-pesticides as well as some of the pesticides tested. The latter type of chemical fits in a number of the QSAR models. Outliers for one species may be different from those of other test organisms. 相似文献
8.
Electronic and Structural Properties of Highly Aluminum Ion Doped TiO2 Nanoparticles: A Combined Experimental and Theoretical Study
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Desireé M. de los Santos Teresa Aguilar Dr. Antonio Sánchez‐Coronilla Dr. Javier Navas Dr. Norge Cruz Hernández Dr. Rodrigo Alcántara Dr. Concha Fernández‐Lorenzo Prof.Dr. Joaquín Martín‐Calleja 《Chemphyschem》2014,15(11):2267-2280
This study presents the experimental and theoretical study of highly internally Al‐doped TiO2 nanoparticles. Two synthesis methods were used and detailed characterization was performed. There were differences in the doping and the crystallinity, but the nanoparticles synthesized with the different methods share common features. Anatase to rutile transformation occurred at higher temperatures with Al doping. X‐ray photoelectron spectroscopy showed the generation of oxygen vacancies, which is an interesting feature in photocatalysis. In turn, the band‐gap energy and the valence band did not change appreciably. Periodic density functional calculations were performed to model the experimentally doped structures, the formation of the oxygen vacancies, and the band gap. Calculation of the density of states confirmed the experimental band‐gap energies. The theoretical results confirmed the presence of Ti4+ and Al3+. The charge density study and electron localization function analysis indicated that the inclusion of Al in the anatase structure resulted in a strengthening of the Ti?O bonds around the vacancy. 相似文献
9.
Gabriela Molar-Velázquez Francisco J. Renero-Carrillo Wilfrido Calleja-Arriaga 《Optik》2010,121(9):843-846
A two-dimensional optical micro-scanner, which main components are two mobile flat and a concave micro-mirrors, is designed such that, all optical components can be fabricated on the same substratum. The optical parameters, which physical dimensions are between 50 and 500 μm, are obtained within the geometrical optics. The optical performance is evaluated by means of the MTF and Rayleigh resolution criteria, given 80% of modulation for a frequency of 8 cycles/mm with a Gaussian source, the resolution limit is 30 μm. 相似文献
10.
Honrubia MA Rodrigo J Cadavid MI Calleja JM Sanz F Loza MI 《Chemical & pharmaceutical bulletin》2002,50(3):395-398
Cyproheptadine is one of the compounds exhibiting the highest activity at 5-HT2B receptors. In a previous work we analysed the relevance of the amino group in diphenylmethylenepiperidines (DPMP), which are open cyproheptadine analogues. Only compounds containing N-H or N-methyl motifs, showed significant 5-HT2B activity. Surprisingly, the corresponding quaternary ammonium salt demonstrated a total lack of activity. Therefore, the question arises whether protonation favours the interaction of these compounds with 5-HT2B receptors. Consequently, we studied the protonation influence (by varying the pH of the medium) on the antagonism of serotonin by some cyproheptadine analogues in rat stomach fundus. The main results were: 1) N-protonation increases the activity of DPMPs. 2) Alkaline pH facilitates the occurrence of a non-surmountable antagonism. 3) The contrast between the activity of protonated DPMPs and the lack of activity of the corresponding quaternary ammonium cation, suggests either that the latter is prevented from acting by steric hindrance, or that the mechanism by which protonation may increase the activity depends not only on the charge of the proton, but also on its ability to form hydrogen bonds. 相似文献