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   144篇
  免费   2篇
化学   79篇
晶体学   6篇
力学   5篇
数学   20篇
物理学   36篇
  2022年   8篇
  2021年   2篇
  2020年   3篇
  2017年   3篇
  2016年   2篇
  2015年   2篇
  2013年   17篇
  2012年   7篇
  2011年   8篇
  2010年   1篇
  2009年   7篇
  2008年   6篇
  2007年   6篇
  2006年   6篇
  2005年   5篇
  2004年   7篇
  2003年   4篇
  2002年   3篇
  2001年   1篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1997年   2篇
  1996年   2篇
  1995年   3篇
  1994年   2篇
  1993年   1篇
  1992年   1篇
  1990年   2篇
  1988年   3篇
  1987年   1篇
  1986年   3篇
  1985年   1篇
  1984年   1篇
  1983年   2篇
  1982年   5篇
  1981年   4篇
  1980年   1篇
  1979年   2篇
  1978年   2篇
  1977年   1篇
  1976年   2篇
  1975年   1篇
  1973年   2篇
  1971年   1篇
排序方式: 共有146条查询结果,搜索用时 31 毫秒
121.
NiH3IO6 · 6 H2O — Crystal Structures and Vibrational Spectra The crystal structure of NiH3IO6 · 6 H2O has been determined by X-ray single-crystal diffraction (Pc, Z = 2, a = 516.74(9), b = 981.5(2), c = 1052.5(2) pm, β = 116.496(8)°) on the basis of 4169 unique reflections (R = 1.96%). The structure is built up of distorted Ni(H2O)62+ and H3IO62? octahedra linked by hydrogen bonding. IR and Raman spectra of both the title compound and isostructural MgH3IO6 · 6 H2O as well as of deuterated specimens are given. There are up to 14 different OH(OD) modes in the spectra of isotopically dilute samples due to the 15 different hydrogen positions of the structure. The internal modes of the meridional H3IO62? ions (pseudo C2v symmetry) are discussed with respect to that double T-shaped entity, which gives rise to only two instead of 3I? O, I? O(H), and OH stretches in the IR and Raman spectra, i.e. the same as for facial (C3v) structured ions.  相似文献   
122.
Zusammenfassung In der vorliegenden Arbeit wird der Isotopeneffekt als Einflu\faktor nicht nur beim thermischen Dehydratationsproze\, sondern auch beim thermischen Zersetzungsvorgang der aus gewöhnlichen und deuterierten Hydraten erhaltenen wasserfreien Verbindungen bewiesen. Diese Untersuchungen werden mit der Hilfe der DTA- und DSC-Methode durchgeführt. Die Unterschiede in der thermischen StabilitÄt der Hydrate werden durchT Deh,T Ph, H Deh und kinetische Parameter (E * undA) charakterisiert. Es werden durch EM-Aufnahmen die verschiedene KristallinitÄt und Partikelgrö\e der Oxide als Endprodukte der thermischen Zersetzung von gewöhnlichen und deuterierten Nitrat-Hydraten festgestellt.
In the present work the isotope effect has been studied by DTA and DSC technique not only in the thermal dehydration process but also in the thermal decomposition of water-free compounds formed from normal and deuterated hydrates. The differences in the thermal stability of the hydrates were characterized byT Deh,T Ph, H Deh and kinetic parameters (E * andA). The degree of crystallinity and particle size of the oxides formed as products of thermal decomposition of normal and deuterated hydrates of nitrates have been determined by electron microscopy.
  相似文献   
123.
124.
Rate constants for substitution of the 2-methylsulfanyl group in 1- and 3-methyl-2-methylsulfanyl-pyrimidin-4-ones and their 5-fluoro analogs were measured in the reaction with butylamine, alkaline hydrolysis, and methanolysis. The rate of substitution in 1-methyl isomers having a zwitterionic structure is greater by a factor of ~2 than the rate of substitution in 3-methyl isomers with conjugated double bonds in the ring. The presence of a fluorine atom in position 5 accelerates nucleophilic substitution in 1-methyl isomers, while 5-fluoro-3-methyl-2-methylsulfanylpyrimidin-4-ones react at a lower rate than their 5-unsubstituted analogs. According to the NMR data, the reactions involve formation of a tetrahedral intermediate. Anchimeric effect of the methyl group on N1 hampersattack by basic reagent on the C6atom.  相似文献   
125.
A new experimental method for measuring the optical anisotropy induced at photochemical reactions is proposed. The method is based on polarization holography and is a zero-background high sensitive technique. It is used to measure the molecular dichroism of fluorescein and the birefrigence induced at the additional photopolymerization of PMMA.  相似文献   
126.
The form of the utility function over multi-dimensional consequences depends on the point estimates of the scaling constants. Fuzzy rational decision makers elicit those in the form of uncertainty intervals. The paper proposes an analytical justification and a numerical realization of the uniform method that finds point estimates of interval scaling constants. The main assumption of the technique is that constants are uniformly distributed in their uncertainty intervals. The density of the constants’ sum is constructed using preliminarily chosen knots. A new numerical procedure to calculate the I type error p value of a two-tail test for singularity of the constants’ sum is proposed. All numerical procedures are embodied into program functions. The application of the method is demonstrated in examples. The connection between precision and time for analysis is investigated. Comparison of the analytical uniform method and an earlier proposed simulation realization is also conducted.  相似文献   
127.
The performance of a linear t-error correcting code over a q-ary symmetric memoryless channel with symbol error probability ε is characterized by the probability that a transmission error will remain undetected. This probability is a function of ε involving the code weight distribution and the weight distribution of the cosets of minimum weight at most t. When the undetectable error probability is an increasing function of ε, the code is called t-proper.

The paper presents sufficient conditions for t-properness and a list of codes known to be proper, many of which have been studied by these sufficient conditions. Special attention is paid to error detecting codes of interest in modern communication.  相似文献   

128.
Summary. The dehydration kinetics of crystallohydrates of beryllium, magnesium and calcium selenites were studied under non-isothermal conditions. The values of the activation energy of dehydration, the pre-exponential factor in Arrhenius equation and the change of entropy for the formation of the activated complex were calculated using the calculation procedure of Coats and Redfern. Thermal stability and activation energy of dehydration of the crystallohydrates were found to increase by the same order. The relationships observed were interpreted using Klopman’s generalized perturbation theory of chemical reactivity. The same theory was applied to explain the differences in the IR spectra of the selenite crystallohydrates studied.  相似文献   
129.
The polarization sensitivity of holographic recording in Bi12SiO20 is experimentally studied. The shape of the obtained curves depends on the magnitude of the applied electric field, crystal thickness, spatial frequency of the recorded gratings, and the order of diffraction.  相似文献   
130.
The ambiguity of the solution of the inverse vibrational problem is related to the results of the intensity calculations for two isotopic molecular species. A relationship between the derivatives ?μi/?Qj for both molecules is derived. The theory is applied to the case of the isotopic pair HCN-DCN. Comparison of the solutions obtained separately from the vibrational data and the intensity data allowed us to distinguish the physical solution.  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