全文获取类型
收费全文 | 98篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
化学 | 63篇 |
晶体学 | 1篇 |
数学 | 23篇 |
物理学 | 16篇 |
出版年
2019年 | 1篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1960年 | 2篇 |
1909年 | 1篇 |
1881年 | 1篇 |
排序方式: 共有103条查询结果,搜索用时 31 毫秒
71.
A. Perjéssy 《Tetrahedron》1973,29(20):3189-3194
The Seth-Paul-Van Duyse equation (SPVDE) correlating the CO stretching frequencies of a great number of R1COR2 molecules with X (R) substituent constants has been reinvestigated. A simple empirical relation defining new X+(R) constants on the basis of electrophilic σ constants has been derived: X+ (R) = 0·238 σ+ + 1·077. The three earlier reported relationships between the X(R) constants and Hammett σ values have been replaced by this single relationships and a set of new X+(R) constants has been calculated. The new X+(R) constants applied to 287 R1COR2 compounds containing the para- or meta-substituted benzene rings fit very well the SPVDE. It has been possible to extend the SPVDE to various aromatic systems. 相似文献
72.
Summary The wavenumbers of the carbonyl stretching vibrations of 2-pyrrolidinone (P), 1-methyl-2-pyrrolidinone (MP), 1-isopropyl-2-pyrrolidinone (IPP), 1-(2-hydroxyethyl)-2-pyrrolidinone (HEP), 2-oxobenzothiazole (OBT), and 3-octyl-2-oxobenzothiazole (OOBT) were measured inn-hexane/CDCl3, acetonitrile/D2O, methanol/D2O, and 2-butoxyethanol/D2O mixtures and compared with similar data for 1-cyclohexyl-2-pyrrolidinone (CHP) and dimethylacetamide (DMA). The dependencies of the wavenumbers on the mole fraction of the less polar cosolvent in binary mixtures allow a distinction and assignment of all species resulting from weak solute-solvent and solute-solute interactions. The slopes of the dependencies of the wavenumbers on the mole fraction for similar intermolecular species inn-hexane/CDCl3 mixtures correlate well with the relative hydrogen bond basicities (i.e. hydrogen bonding abilities with phenol) and reveal that the solvent sensitivities significantly depend on the steric requirements in the vicinity of the C=O group. On the other hand, the slopes of similar dependencies in acetonitrile/D2O mixtures are proportional to the electron donating effects of alkyl groups attached to the nitrogen atom of the pyrrolidinone ring. In the case of mixtures formed by two strongly hydrogen bonding cosolvents (alcohols/D2O), a competitive equilibrium occurs between the hydrogen bonding tendency of both cosolvents and 1-substituted 2-pyrrolidinones. In solutions of 1-substituted 2-pyrrolidinones in water-rich 2-butoxyethanol/D2O mixtures, microheterogeneous domains occur before classic mixtures of two polar liquids are formed.
Infrarotuntersuchungen über Wechselwirkungen von 1-substituierten 2-Pyrrolidinonen und verwandten Verbindungen mit Lösungsmitteln
Zusammenfassung Die Wellenzahlen der Carbonylstreckschwingungen von 2-Pyrrolidinon (P), 1-Methyl-2-pyrrolidinon (MP), 1-Isopropyl-2-pyrrolidinon (IPP), 1-(2-Hydroxyethyl)-2-pyrrolidinon (HEP), 2-Oxobenzothiazol (OBT) und 3-Octyl-2-oxobenzothiazol (OOBT) wurden inn-Hexan/CDCl3, Acetonitril/D2O, methanol/D2O und 2-Butoxyethanol/D2O gemessen und mit den entsprechenden Daten für 1-Cyclohexyl-2-pyrrolidinon (CHP) und Dimethylacetamid (DMA) verglichen. Die Abhängigkeit der Wellenzahlen vom Molenbruch des weniger polaren Lösungsmittels in binären Mischungen erlaubt eine Unterscheidung und Zuordnung aller durch schwache Wechselwirkungen zwischen gelöster Substanz und Lösungsmittel bzw. durch Wechselwirkungen der gelösten Moleküle untereinander entstehenden Spezies. Für ähnliche Moleküle inn-Hexan/CDCl3 — Mischungen korrelieren die Steigungen der Abhängigkeiten der Wellenzahlen vom Molenbruch gut mit den relativen Basizitäten der Wasserstoffbrückenbindungen (d.h. mit der Fähigkeit zur Ausbildung von Wasserstoffbrückenbindungen mit Phenol) und beweisen, daß die Lösungsmittelabhängigkeiten wesentlich von sterischen Faktoren in der Umgebung der Carbonylgruppe abhängen. Andererseits sind die Steigungen entsprechender Korrelationen in Acetonitril/D2O — Mischungen zur Elektronendonatorfähigkeit von an das Stickstoffatom des Pyrrolidinonrings gebundenen Alkylgruppen proportional. Im Fall von Mischungen aus zwei stark wasserstoffbrückenbildenden Lösungsmitteln (Alkohole/D2O) stellt sich ein kompetitives. Gleichgewicht zwischen der Tendenz zur Wasserstoffbrückenbindungsbildung beider Lösungsmittel und den 1-substituierten 2-Pyrrolidinonen ein. In Lösungen von 1-substituierten 2-Pyrrolidinonen in 2-Butoxyethanol/D2O — Mischungen mit hohem Wasseranteil treten vor der Ausbildung klassischer Mischungen zweier polarer Flüssigkeiten mikroheterogene Domänen auf.相似文献
73.
Alexander Perjéssy János Lázár Gábor Bernáth 《Monatshefte für Chemie / Chemical Monthly》1986,117(1):97-104
The C=O stretching frequencies of 32 5,6-polymethylenepyrimidin-4(3H)-one (1a–1w) andcis-5,6-polymethylene-5,6-dihydropyrimidin-4(3H)-one (2a–2h) derivatives were measured in tetrachlormethane and in chloroform and correlated with the substituent constantsX
+ (R) in the sense of the modified and extendedSeth-Paul-Van Duyse equation. It was found that the C=O stretching frequency and the transmission of substituent effects through the heterocyclic ring are significantly influenced by the size of the fused hydrocarbon ring. Evidence was obtained that in molecules linked by intermolecular hydrogen bonds the substituent effects are transmitted to the C=O group predominantly via the C=N–C=C part of the pyrimidinone ring. In the free molecules the transmission of substituent effects takes place mainly through the NH group.
Gesättigte Heterocyclen, 68. Mitt.: Anwendung der Seth-Paul-Van Duyse-Gleichung, IX. Die C=O-Streck-Frequenzen und Substituenteneffekte bei 5,6-Polymethylenpyrimidin-4(3H)-on Derivaten
Zusammenfassung Es wurden die C=O-Streck-Frequenzen von 32 5,6-Polymethylenpyrimidin-4(3H)-onen (1a–1w) undcis-5,6-polymethylen-5,6-dihydropyrimidin-4(3H)-onen (2a–2h) in CCl4 und CHCl3 gemessen und mit den SubstituentenkonstantenX + (R) im Sinn der modifizierten und erweitertenSeth-Paul-Van Duyse-Gleichung korreliert. Es wurde festgestellt, daß die C=O-Streck-Frequenzen und die Übertragung von Substituenteneffekten durch den heterocyclischen Ring von der Größe des kondensierten Kohlenwasserstoffringes signifikant beeinflußt werden. Es konnte belegt werden, daß in Molekülen, die mit Wasserstoffbrücken verbunden sind, die Substituenteneffekte vorwiegend über den C=N–C=C-Teil des Pyrimidinonringes zur C=O-Gruppe übertragen werden. In den freien Molekülen erfolgt die Übertragung der Substituenteneffekte hauptsächlich über die NH-Gruppe.相似文献
74.
Soják L Perjéssy A Kubinec R Cambáliková J Giumanini AG Verardo G Magnan MM 《Journal of chromatography. A》2000,878(2):235-247
Gas chromatographic retention data, Fourier transform infrared and mass spectrometric (electron impact, electron attachment and methane chemical ionization) profiles are reported for the products of mono- and dinitration of N,N-dimethyldiphenylacetamide. Differentiations of analytical importance among isomers could be gathered by the study which led to their complete identification. 相似文献
75.
A space X is said to be κ-resolvable (resp., almost κ-resolvable) if it contains κ dense sets that are pairwise disjoint (resp., almost disjoint over the ideal of nowhere dense subsets). X is maximally resolvable if and only if it is Δ(X)-resolvable, where Δ(X) = min{|G| : G ≠ open}.
We show that every crowded monotonically normal (in short: MN) space is ω-resolvable and almost μ-resolvable, where μ = min{2
ω
, ω
2}. On the other hand, if κ is a measurable cardinal then there is a MN space X with Δ(X) = κ such that no subspace of X is ω
1-resolvable.
Any MN space of cardinality < ℵ
ω
is maximally resolvable. But from a supercompact cardinal we obtain the consistency of the existence of a MN space X with |X| = Δ(X) = ℵ
ω
such that no subspace of X is ω
2-resolvable.
The preparation of this paper was supported by OTKA grant no. 61600 相似文献
76.
Lajos Tamássy 《Differential Geometry and its Applications》2008,26(5):483-494
In a connected Finsler space Fn=(M,F) every ordered pair of points p,q∈M determines a distance ?F(p,q) as the infimum of the arc length of curves joining p to q. (M,?F) is a metric space if Fn is absolutely homogeneous, and it is quasi-metric space (i.e. the symmetry: ?F(p,q)=?F(q,p) fails) if Fn is positively homogeneous only. It is known the Busemann-Mayer relation , for any differentiable curve p(t) in an Fn. This establishes a 1:1 relation between Finsler spaces Fn=(M,F) and (quasi-) metric spaces (M,?F).We show that a distance function ?(p,q) (with the differentiability property of ?F) needs not to be a ?F. This means that the family {(M,?)} is wider than {(M,?F)}. We give a necessary and sufficient condition in two versions for a ? to be a ?F, i.e. for a (quasi-) metric space (M,?) to be equivalent (with respect to the distance) to a Finsler space (M,F). 相似文献
77.
Ambroz Almssy Zuzana Benkov Branislav Horvth Andrej Boh
《Journal of organometallic chemistry》2008,693(20):3223-3232
The compositions of regioisomeric mixtures of tricarbonyliron complexes of 2-methyltropone (1a,b), 3-methyltropone (2a,b) and 2,6-dimethyltropone (3a,b) are studied and compared with the results of ab initio computations. The structures, frontier orbitals, and population analysis are evaluated by means of density functional theory. The thermodynamic and kinetic parameters of regioisomerizations are determined using dynamic 1H NMR technique. The influence of methyl-substituent(s) on the equilibrium ratio of regioisomers resulting from the haptotropic rearrangement is discussed. Significant differences in the reactivity of C-protonized methyl- and dimethyl-substituted tricarbonyl(tropone)iron complexes 4–6 in nucleophilic additions and corresponding O-trimethylsilylated complexes 7–9 in [3+2] cycloadditions are explained in terms of electronic and steric effects of the methyl group(s). Various hydroazulenone cycloadducts of tricarbonyl(η4-2,6-dimethyltropone)iron 3a,b have been prepared by stereoselective [3+2] cycloaddition with Fp-reagents 12–14 and characterized. Formerly proposed mechanism of [3+2] cycloaddition was approved. 相似文献
78.
M Ostermann M Berglund P D Taylor M Máriássy 《Fresenius' Journal of Analytical Chemistry》2001,371(6):721-725
The Slovak Institute of Metrology and the Institute for Reference Materials and Measurements have collaborated in the certification of the two chlorine reference materials IRMM-641 and IRMM-642. Until now no isotopically enriched chlorine isotopic reference material certified for isotopic composition and content has been available commercially. The isotopic reference materials IRMM-641 and IRMM-642 described herein are certified for isotopic composition and for chlorine content. The chlorine content of the reference material IRMM-641 was certified by use of high-precision argentometric coulometric titration at the Slovak Institute of Metrology. The base material used for IRMM-641 is NIST Standard Reference Material 975. The chlorine content of the reference material IRMM-642 was measured by isotope dilution, using negative thermal ionization mass spectrometry at the Institute for Reference Materials and Measurements. Both standard reference materials were prepared by dissolving NaCl in water. The reference material IRMM-641 contains 0.025022 +/- 0.00011 mol kg(-1) chlorine of natural isotopic composition with an n(37Cl)/n(35Cl) ratio of 0.31977 +/- 0.00082. The reference material IRMM-642 contains 0.004458 +/- 0.000028 mol kg(-1) chlorine with an n(37Cl)/n(35Cl) ratio of 0.01914 +/- 0.00088. 相似文献
79.
A. Vértes K. Süvegh M. Bokor A. Domján T. Marek M. Klapper C. U. Chisholm M. El-Sharif K. Tompa Zs. Nemes-Vetéssy K. Burger 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(1):29-36
Our work proves that positron annihilation spectroscopy is an excellent tool to follow the structural changes in chemical
species. We present four examples to support the above statement. The sizes of defects in electrodeposited chromium layers
were studied and estimated on the basis of positron lifetime spectra decomposed into two components. Vacancies, di-vacancies
and vacancy-clusters could be identified in the electrodeposites. The changes of the size distribution of the free volume
units in poly(methylmetacrylate) on the dependence of molecular weight and dispersity were described by the correlation between
the lifetime ofortho-Ps and the free volume units in polymers. It was found that the free volume is affected by both the molecular weight and
dispersity. The effect of dispersity was explained by the sample preparation technique, namely by the application of high
pressure. The ortho-para conversion ofortho-Ps was used to follow the partial spin-crossover in [Fe(1-ethyl-1H-tetrazole)6](BF4)2. The spin-crossover temperature was identified to be 105 K. A conformal structural transformation was found in [Zn(1-propyl-1H-tetrazole)6](BF4)2 between 170 and 90 K by positronium lifetime measurement and the role of (BF4)2− anion, in this transformation, was proved by19F NMR spectroscopy. 相似文献
80.