全文获取类型
收费全文 | 137篇 |
免费 | 8篇 |
专业分类
化学 | 80篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 16篇 |
物理学 | 36篇 |
出版年
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 1篇 |
2013年 | 11篇 |
2012年 | 6篇 |
2011年 | 11篇 |
2010年 | 5篇 |
2009年 | 6篇 |
2008年 | 4篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1987年 | 1篇 |
排序方式: 共有145条查询结果,搜索用时 46 毫秒
61.
In this Letter, Exp-function method is employed to obtain traveling wave solutions of the Fisher equation. It is shown that, on this example, the Exp-function method is easy to implement and concise method for nonlinear evolution equations in mathematical physics. 相似文献
62.
Polyisobutylene‐based polyurethanes. IX. synthesis,characterization, and properties of polyisobutylene‐based poly(urethane‐ureas) 下载免费PDF全文
Kalman Toth Nihan Nugay Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》2016,54(15):2361-2369
Polyisobutylene (PIB)‐based polyurethanes (PUs) exhibit unparalleled hydrolytic‐oxidative‐biologic stability and are melt processible, however, their mechanical (strength) properties are modest mainly due to insufficient H bonds. We posited and demonstrate that the ultimate properties of PIB‐PUs are enhanced, while their melt processibility is maintained, by the judicious introduction of urea linkages, i.e., strong bifurcated H bonds, in the chain. The incorporation of bifurcated H bonds in PIB‐PUs was achieved by using the conventional butane diol chain extender (CE) in combination with controlled amounts of amino alcohol as co‐chain extender (co‐CE). Polyurethanes containing both urethane and urea linkages are polyurethane‐ureas (PUU). Specifically, PIB‐PUUs prepared with PIB‐diol/MDI together with 80/20 mole % butane diol/amino butanol exhibited ~30 MPa tensile strength, ~550% elongation, ~80 Shore A hardness, and ~137 °C flow temperature. Other amino alcohols, i.e., amino ethanol, ‐propanol, and ‐hexanol, were less effective co‐CEs. 1H‐NMR and FT‐IR spectroscopies indicate the presence of bifurcated H bonds in PIB‐PUUs prepared with CE/co‐CE combinations. Characterization by differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis, and creep experiments also suggest bifurcated H bonds in PIB‐PUU. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2361–2369 相似文献
63.
Turgut Önder 《manuscripta mathematica》1995,86(1):393-407
LetG be a finite group and letM be a unitary representation space ofG. We consider the existence problem of equivariant frame fields on the unit sphereS(M) whose orthogonal complements in the tangent bundleT(S(M)) admitG-equivariant complex structures. Under mild fixed point conditions we give a complete solution for this problem whenG is either ℤ/2ℤ or a finite group of odd order.
This article was processed by the author using theLaTEX style filecljourl from Springer-Verlag. 相似文献
64.
65.
W incorporated tin oxide (TO) thin films were grown via spray pyrolysis with various tungsten contents. The films were observed to be polycrystalline tetragonal crystal nature with (301) and (211) preferential planes. From EDX analysis, it was seen the tungsten concentrations in the TO films were slightly higher than ones in the starting solutions. Polyhedron-like and small rod like grains were observed in the SEM images. 3 at % W doped tin oxide film has minimum sheet resistance (44.67 Ohm) and resistivity (3.685 × 10?3 Ohm cm) values and maximum figure of merit (75.74 × 10?5 Ohm?1) value. The optical band gap (Eg) of pure film raised from 3.84 to 3.91 eV with 3 at % W contribution level. 相似文献
66.
Kalman Toth Nur Cicek Kekec Nihan Nugay Joseph. P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》2016,54(8):1119-1131
We describe the synthesis, characterization, and select properties of a novel polyurethane (PU) prepared using a new polyisobutylene diol, HO‐CH2CH2‐S‐PIB‐S‐CH2CH2‐OH, soft segment and conventional hard segments. The diol is synthesized by terminal functionalization of ally‐telechelic PIB followed by low‐cost thiol‐ene click chemistry. Properties of ‐S‐ containing PU (PIBS‐PU) containing 72.5% PIB were investigated and compared to similar PUs made with HO‐PIB‐OH (PIBO‐PU). Hydrolytic resistance was studied by contact with phosphate‐buffered saline, oxidative resistance by immersing in concentrated HNO3, and metal ion oxidation resistance by exposure to CoCl2/H2O2. Hydrolytic and oxidative resistances of PIBS‐PU and PIBO‐PU are similar and superior to a commercial PDMS‐based PU, Elast‐Eon? E2A. According to 1H NMR spectroscopy the ‐S‐ in PIBS‐PUs remained unchanged upon treatment with HNO3, however, oxidized mainly to ‐SO2‐ by CoCl2/H2O2. Static mechanical properties of PIBS‐PU and PIBO‐PU are similar, except creep resistance of PIBS‐PU is surprisingly superior. The thermal stability of PIBS‐PUs is ~15 °C higher than that of PIBO‐PU. FTIR spectroscopy indicates H bonded S atoms (N‐H…S) between soft and hard segments, which noticeably affect properties. DSC and XRD studies suggest random low‐periodicity crystals dispersed within a soft matrix. Energy dispersive X‐ray spectroscopy–scanning electron microscopy indicates homogeneous distribution of S atoms on PIBS‐PU surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1119–1131 相似文献
67.
Polyisobutylene‐based polyurethanes: VII. structure/property investigations for medical applications
Kalman Toth Nihan Nugay Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》2016,54(4):532-543
The outstanding hydrolytic and oxidative stabilities of polyisobutylene‐based polyurethanes (PIB‐based PUs) were reported earlier. Herein, we summarize recent investigations aimed at further enhancing hydrolytic‐oxidative stabilities (in terms of resistance to aqueous buffer, nitric acid and CoCl2/H2O2) together with excellent mechanical properties. The purity and dryness of ingredients together with precise NCO/OH stoichiometry (~1.05) are essential to obtain PIB‐based PUs with improved properties. Static and dynamic mechanical properties were optimized by analyzing stress–strain traces, thermal (TGA, DSC) responses, self‐organization (XRD) profiles, and rheological (DMA, creep) information. According to microstructure and surface analyses (AFM, contact angle) annealing increases the segregation of individual segments and increases surface hydrophobicity, which in turn enhances the shielding of hydrolytically oxidatively vulnerable carbamate bonds by inert PIB barriers, and thus significantly improves hydrolytic‐oxidative stability. Annealing does not much affect bulk properties, such as static and dynamic mechanical and thermal properties; however, it increases damping over a wide temperature range. Annealed PIB‐based PU containing 72.5% PIB exhibits outstanding hydrolytic‐oxidative stability together with ~26 MPa tensile strength, ~500% elongation, and ~77 Microshore hardness. PIB‐based PUs are significantly more resistant to hydrolytic and oxidative degradation than ElastEon? E2A, a commercially available PDMS‐based PU, widely used for medical applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 532–543 相似文献
68.
Hatice Turgut Dr. Guillaume Delaittre 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(4):1511-1521
The chemoselectivity of two thiol‐based modular ligations operating under mild conditions is assessed. For this purpose, a macromolecular scaffold possessing allyl and pentafluorophenyl groups in two distinct parts is employed, which enables facile characterization by NMR spectroscopy (1H and 19F) and size‐exclusion chromatography. By using appropriate triggers (introduction of a base or light irradiation), it is possible to direct thiols to an arbitrarily chosen part of the scaffold, without any change to the other part and with no involvement of protecting group chemistry. Dual functionalization experiments are achieved by applying these triggers consecutively with no consideration of the reaction sequence order, evidencing full bidirectionality. A set of one‐pot, purification‐free procedures that enable near‐quantitative to full dual functionalization in (very) short reaction times (17–180 min) is also presented. 相似文献
69.
Yılmaz Turgut Murat Azizoglu Aslı Erdogan Nevin Arslan Halil Hosgoren 《Tetrahedron: Asymmetry》2013,24(13-14):853-859
In order to find the most effective catalyst for the enantioselective reduction of a prochiral ketone, a series of novel β-hydroxyamide derivatives of salicylic acid and chiral amino alcohols were synthesized. Different substituted prochiral ketones have been reduced in high yield (up to 99%) and the corresponding secondary alcohols are formed with good enantiomeric excess (up to 86%). The mechanism of this type of catalyst can be explained by considering the reaction mechanism for the CBS catalyst. 相似文献
70.
一个解剖基人体下肢的生物动力模型--第三部分:肌肉效应 总被引:1,自引:0,他引:1
本将人体下肢的肌肉根据其解剖特征,分为5个肌群,并在由本第一部分所建立的基本的解剖基模型的基础上,计入其对人体下肢动力运动的效应。本所建立的5个肌群,则主要代表着膝关节处的运动和稳定肌。最后,作为应用,研究了一个献中的特例。 相似文献