首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   73篇
  免费   3篇
化学   43篇
数学   1篇
物理学   32篇
  2023年   1篇
  2022年   2篇
  2021年   6篇
  2020年   5篇
  2019年   2篇
  2016年   3篇
  2015年   2篇
  2014年   3篇
  2013年   1篇
  2012年   3篇
  2011年   6篇
  2010年   1篇
  2009年   2篇
  2008年   3篇
  2007年   3篇
  2006年   7篇
  2005年   7篇
  2004年   4篇
  2003年   3篇
  2002年   1篇
  2001年   1篇
  1999年   2篇
  1996年   1篇
  1993年   1篇
  1984年   1篇
  1976年   1篇
  1973年   1篇
  1962年   1篇
  1936年   1篇
  1929年   1篇
排序方式: 共有76条查询结果,搜索用时 15 毫秒
1.
The aim of the study was to create a mathematical model useful for monitoring the release of bioactive aldehydes covalently bonded to the chitosan by reversible imine linkage, considered as a polymer–drug system. For this purpose, two hydrogels were prepared by the acid condensation reaction of chitosan with the antifungal 2-formyl-phenyl-boronic acid and their particularities; influencing the release of the antifungal aldehyde by shifting the imination equilibrium to the reagents was considered, i.e., the supramolecular nature of the hydrogels was highlighted by polarized light microscopy, while scanning electron microscopy showed their microporous morphology. Furthermore, the in vitro fungicidal activity was investigated on two fungal strains and the in vitro release curves of the antifungal aldehyde triggered by the pH stimulus were drawn. The theoretical model was developed starting from the hypothesis that the imine-chitosan system, both structurally and functionally, can be assimilated, from a mathematical point of view, with a multifractal object, and its dynamics were analyzed in the framework of the Scale Relativity Theory. Thus, through Riccati-type gauges, two synchronous dynamics, one in the scale space, associated with the fungicidal activity, and the other in the usual space, associated with the antifungal aldehyde release, become operational. Their synchronicity, reducible to the isomorphism of two SL(2R)-type groups, implies, by means of its joint invariant functions, bioactive aldehyde compound release dynamics in the form of “kink–antikink pairs” dynamics of a multifractal type. Finally, the theoretical model was validated through the experimental data.  相似文献   
2.
The classical nucleation theory (CNT) is the most common theoretical framework used to explain particle formation. However, nucleation is a complex process with reaction pathways which are often not covered by the CNT. Herein, we study the formation mechanism of copper nanospheres using in situ X‐ray absorption and scattering measurements. We reveal that their nucleation involves coordination polymer lamellae as pre‐nucleation structures occupying a local minimum in the reaction energy landscape. Having learned this, we achieved a superior monodispersity for Cu nanospheres of different sizes. This report exemplifies the importance of developing a more realistic picture of the mechanism involved in the formation of inorganic nanoparticles to develop a rational approach to their synthesis.  相似文献   
3.
In this letter observations are reported which were carried out by diffraction of a laser beam, by polar diagrams of the diffracted light and by optical microscopy, being performed on a hexagonal structure which appears in nematic liquid crystals for a twist geometry.  相似文献   
4.
We obtain the optimal time decay of the solutions of the coupled Maxwell-Klein-Gordon equations in four dimensional spacetime, provided the initial data are what we define as Coulomb. In other words, the initial data are such that the Klein-Gordon field is smooth and compactly supported and the Maxwell field is electrostatic outside this support. The problem involves charge, therefore, the initial data do not satisfy either fast decay or any smallness condition. In spite of that, we are able to obtain our result using the inversion map of the lightcone of a carefully selected origin. We thus, avoided the blow-up that takes place when using the usual conformal transformation to the Einstein spacetime.Work partially supported by FAPESP and CNPq  相似文献   
5.
6.
Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...  相似文献   
7.
In the framework of the multifractal hydrodynamic model, the correlations informational entropy–cross-entropy manages attractive and repulsive interactions through a multifractal specific potential. The classical dynamics associated with them imply Hubble-type effects, Galilei-type effects, and dependences of interaction constants with multifractal degrees at various scale resolutions, while the insertion of the relativistic amendments in the same dynamics imply multifractal transformations of a generalized Lorentz-type, multifractal metrics invariant to these transformations, and an estimation of the dimension of the multifractal Universe. In such a context, some correspondences with standard cosmologies are analyzed. Since the same types of interactions can also be obtained as harmonics mapping between the usual space and the hyperbolic plane, two measures with uniform and non-uniform temporal flows become functional, temporal measures analogous with Milne’s temporal measures in a more general manner. This work furthers the analysis published recently by our group in “Towards Interactions through Information in a Multifractal Paradigm”.  相似文献   
8.
Crystals of the first sodalite‐type zeolite containing an all‐iron framework, a ferrolite, Ba8(Fe12O24)Nay(OH)6?x H2O, were synthesized using the hydroflux method in nearly quantitative yield. Ba8(Fe12O24)Nay(OH)6?x H2O crystallizes in the cubic space group with a=10.0476(1) Å. Slightly distorted FeO4 tetrahedra are linked to form Fe4O4 and Fe6O6 rings, which in turn yield channels and internal cavities that are characteristic of the sodalite structure. Barium, sodium, and hydroxide ions and water molecules are found in the channels and provide charge balance. Magnetic measurements indicate that the ferrolite exhibits magnetic order up to at least 700 K, with the field‐cooled and zero‐field‐cooled curves diverging. Analysis of the 57Fe Mössbauer spectra revealed two spectral components that have equal spectral areas, indicating the presence of two subsets of iron centers in the structure. Dehydrated versions of the ferrolite were also prepared by heating the sample.  相似文献   
9.
飞秒激光诱导折射率变化提供了一种灵活的三维光子器件制作手段.飞秒激光光刻的II类波导具有偏振导光特性,可以作为波导偏振器,但是对于要保留的偏振分量损耗太大.本文阐述了一种利用飞秒激光在熔融石英中制作的新型低损耗波导偏振器.它由中间的一根I类波导及两侧的两根II类纳米光栅轨迹构成.基于飞秒激光诱导的纳米光栅的偏振依赖散射特性,II类纳米光栅轨迹能够对I类波导的倏逝场进行调制.偏振方向垂直于纳米光栅的模式相对于偏振方向平行于纳米光栅的模式有更大的散射损耗,因此导通的是偏振方向平行于纳米光栅的模式.研究了消光比随I类波导与II类纳米光栅轨迹之间的间距的变化关系,选择一个最佳间距来进一步研究消光比随II类纳米光栅轨迹长度的变化关系.在间距6 μm,II类纳米光栅轨迹扫描长度6 mm处实现了最大15.91 dB的消光比.通过增加II类轨迹的长度或者数量,很容易得到更高的消光比.  相似文献   
10.
Using the STM technique we have determined the sputter yield on a pristine Cu(001) surface after mild (fluence less than 0.044 ions per surface atom) bombardment of the pristine surface with 800 eV Ar+ions at normal incidence. The experiments have been performed at substrate temperatures ranging from 200 to 350 K. Making use of the positional correlation of adatoms and surface vacancies, at 200 K and 325 K, we concluded that about 1/3 of the surface adatoms originate from interstitials arriving at the surface and they give a direct indication of the buried bulk vacancies. A careful analysis of the different areas for surface vacancies and adatom then allowed a quantitative evaluation of the sputter yield at 1.2 Cu atoms per 800 eV Ar+ ion.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号