全文获取类型
收费全文 | 86篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
化学 | 66篇 |
力学 | 1篇 |
数学 | 3篇 |
物理学 | 23篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 10篇 |
2012年 | 3篇 |
2011年 | 11篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有93条查询结果,搜索用时 15 毫秒
21.
22.
Özlem Sarıöz Sena Öznergiz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):906-913
Abstract Functionalized mono(amino)phosphines of the type Ph2PNHR (1) and bis (amino)phosphine of the type PhP(NHR)2 (2) have been synthesized by treating Ph2PCl or PhPCl2 with 1-amino-4-methylpiperazine. Ligands react with aqueous hydrogen peroxide, elemental sulfur, or selenium to give the corresponding chalcogenides in good yields. The molybdenum complexes of the aminophosphines have been obtained. All of the new compounds were characterized by IR, 1H, and 31P-NMR spectroscopy and elemental analysis. 相似文献
23.
Lyane M. Moreira E. A. Carvalho M. J. V. Bell V. Anjos A. C. Sant’Ana Ana Paula P. Alves B. Fragneaud L. A. Sena B. S. Archanjo C. A. Achete 《Journal of Thermal Analysis and Calorimetry》2013,114(2):557-564
This work focuses on the study of thermal diffusivity and physical properties of nanofluids with very low concentrations of silver or gold nanoparticles. Thermal measurements were performed by means of thermal lens spectroscopy in the dual beam configuration. Improvements of 20 and 16 % in the thermal diffusivity were observed for silver and gold nanofluids, respectively, in comparison with pure water. The estimation of the size distribution of the metallic nanoparticles was obtained through the fitting of the extinction spectra via Mie theory and images of field emission gun scanning electron microscopy. 相似文献
24.
Eloilson Domingos Thieres M. C. Pereira Paulo R. Filgueiras Maria Izabel M. S. Bueno Eustáquio V. R. de Castro Regina C. L. Guimarães Geovane L. de Sena Werickson F.C. Rocha Wanderson Romão 《X射线光谱测定》2013,42(2):79-86
The influence of temperature (110 and 120 °C) on the ageing of piping made from polyamide 11 (PA‐11) containing 10–12% of plasticizer was studied using deionized water (pH ≈ 7.0). A clean analytical methodology has been employed for quality control of polymeric materials: energy‐dispersive X‐ray fluorescence spectrometry (ED‐XRF). It provides a fast and suitable technique to characterize chemical elements because of its multielemental capability, good sensitivity, high precision, short analytical time, and nondestructive nature. Herein, the content of additive in PA‐11 was monitored from ED‐XRF measurements where the abundance of the S line is directly related to the ageing time, agreeing with the thermogravimetric analysis. The XRF data were allied to chemometric treatment to classify PA‐11 samples according to the amount of additive and weight average molar mass change, predicting the ageing time, and viscosity values of PA‐11. Therefore, the XRF can be used as a clean analytical methodology to monitor the PA‐11 degradation, thus eliminating the use of toxic organic solvents (necessary to viscosity measurements) and reducing the working time. Also, the effect of hydrolysis on the structure over time and the material morphology were monitored through measurements of dynamic mechanical analysis and differential scanning calorimetry. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
25.
Ylmaz Seda Kuyumcu zge Kerkez Bayazit ahika Sena Ayaz Rana Muhammad Zunain Akyz Duygu Koca Atf 《Journal of Solid State Electrochemistry》2022,26(1):245-255
Journal of Solid State Electrochemistry - Modified TiO2 nanocomposites have been recognized as attractive photocatalytic materials in solar energy conversion. The aim of this study is to enhance... 相似文献
26.
Shiffler D.A. LaCour M.J. Sena M.D. Mitchell M.D. Haworth M.D. Hendricks K.J. Spencer T.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(3):517-522
Presents results of an experimental comparison of a bare carbon fiber cathode and the same cathode when coated with cesium iodide salt (CsI). An annular cathode was constructed by arranging carbon fibers in an annular tuft pattern. The cathode was then operated as a bare carbon fiber cathode and in a configuration with a CsI coating. The cathode was tested at electric field strengths ranging from 50 kV/cm to 265 kV/cm at anode-cathode (A-K) gaps of 3.175 cm. The applied voltage had a 1-μs duration and the modulator was operated at up to 1 Hz repetition rate. The system had a low base pressure (<1.0×10-7 torr). The article reports on results concerning the conditioning of the cathodes, the shot-to-shot reproducibility of the cathodes and the pressure evolution of the diode under 1 Hz operation. We also report on the impedance evolution of each of the diodes 相似文献
27.
AimThe purpose of the study is to research the effect of quercetin, which has a good antioxidant characteristic in rats exposed to sodium fluoride (NaF) toxication, on oxidant and antioxidant activity in liver tissue and erythrocyte.Material and method40 Swiss albino male rats with a weight of approximately 20–25 gr were used in the study. The rats were separated into 4 equal groups (n = 10). The first group, the control group, was given normal drinking water; the second group was given 12 mg/kg/day NaF; the third group was given 40 mg/kg/day quercetin; the fourth group was given 12 mg/kg/day NaF+40 mg/kg/day quercetin orally for 30 days. As a result of the experiment, plasma AST and ALT activities were found. Total oxidant capacity (TOC) and total antioxidant capacity (TAC) analyses were made in liver tissue and erythrocyte hemogenisate. Histopathological analyses of the liver tissue were conducted.ResultsNo changes were found in plasma ALT activities between groups. Increases were found in AST activity of all groups. While erythrocyte TAC level was found to increase in fluorine and fluorine + quercetin group when compared with the control group, erythrocyte TOC level was found to increase in all groups when compared with the control group. No significant change was found in TOC and TAC levels in the liver tissue. In liver tissue histopathology, while hydropic degeneration and cellular necrosis were found in vena centralis area in fluorine group, hydropic degeneration was found in heptocytes in centrilobular area in the quercetin group. In the fourth group, hydropic degeneration and centrilobular necrosis were more severe. It was found that in rats which are given NaF experimentally, fluorine and quercetin caused histopathological degenerations in the liver tissue during this time.ConclusionWhile no changes were found in TOC and TAC levels of liver tissue, antioxidant capacity was found to be stimulated in fluorine groups in erythrocyte. 相似文献
28.
Summary Considering the geometric theory of triply orthogonal spatial curves, the basic equations governing a steady gas flow are transformed into the intrinsic form and the results obtained are:(1) The pressure is uniform along the binormal to the stream line and the radius of curvature varies as the square of the velocity along it, for the baratropic fluids.(2) Acceleration is irrotational field when the fluid is compressible but baratropic or incompressible, in which case the relations existing between the flow quantities, curvature and torsions of the curves under consideration are obtained.(3) Considering incompressible flows, it is observed that either velocity in magnitude is uniform or the vorticity lies in the normal plane, in which case the stream lines are orthogonal to the vortex lines.Stream lines are observed to be either right circular helices or circles or straight lines.If the stream lines are not straight then the torsions of the binormal congruences and stream lines are equal.(4) The compatibility conditions of Berker1) are transformed into intrinsic form, involving the curvatures and torsions of the above curves. 相似文献
29.
Diniz M. Sena Paulo T. C. Freire Josu M. Filho Francisco E. A. Melo 《Journal of Raman spectroscopy : JRS》2010,41(3):356-359
Topiramate is a white crystalline solid with powerful anticonvulsant activity and is used to treat epilepsy. Drug manufacturing involves various physical and chemical processes, which may lead to the formation of an unexpected, or undesired, crystalline phase, in a phenomenon known as polymorphism. In this paper, the behavior of topiramate crystal is studied under pressures up to 10.8 GPa using Raman spectroscopy. Under the conditions employed, Raman spectra from topiramate under pressure showed no strong evidence of a phase change, although amorphization may be considered. This may be accounted for by its crystal structure, comprising oppositely running chains of topiramate molecules linked by asymmetric hydrogen bonds, which pose a kinetic barrier against a structural change. It is not yet safe to rule out the existence of topiramate polymorphs, which could possibly be obtained under special crystallization conditions, but not after compression, at least up to 10 GPa. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
30.
It is common in forest tree breeding that selection of populations must consider conservation of genetic diversity, while at the same time attempting to maximize response to selection. To optimize selection in these situations, the constraint on genetic diversity can be mathematically described with the numerator relationship matrix as a quadratic constraint. Pong-Wong and Woolliams formulated the optimal selection problem using semidefinite programming (SDP). Their SDP approach gave an accurate optimal value, but required rather long computation time. In this paper, we propose an second-order cone programming (SOCP) approach to reduce the heavy computation cost. First, we demonstrate that a simple SOCP formulation achieves the same numerical solution as the SDP approach. A simple SOCP formulation is, however, not much more efficient compared to the SDP approach, so we focused on the sparsity structure of the numerator relationship matrix, and we develop a more efficient SOCP formulation using Henderson’s algorithm. Numerical results show that the proposed formulation, which we call a compact SOCP, greatly reduced computation time. In a case study, an optimal selection problem that demanded 39,200 s under the SDP approach was solved in less than 2 s by the compact SOCP formulation. The proposed approach is now available as a part of the software package OPSEL. 相似文献