全文获取类型
收费全文 | 382篇 |
免费 | 6篇 |
专业分类
化学 | 219篇 |
力学 | 30篇 |
数学 | 80篇 |
物理学 | 59篇 |
出版年
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 9篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 8篇 |
2013年 | 17篇 |
2012年 | 27篇 |
2011年 | 21篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 15篇 |
2007年 | 25篇 |
2006年 | 13篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 5篇 |
1999年 | 3篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1992年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有388条查询结果,搜索用时 15 毫秒
1.
The influence of different referencing methods on the accuracy of δ13C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry 下载免费PDF全文
2.
Donato Pocar Pasqualina Trimarco Gabriella Bombieri 《Journal of heterocyclic chemistry》1998,35(3):687-692
Pyrolysis of 4-aryl-5-amino-v-triazolines affords, generally, amidines and/or benzanilides. Pyrolysis of 4-aryl-5-morpholino-v-triazolines 6 , together with the expected amidines 7 and/or aryanilides 8 , produced the morpholinopyrroles 9 . The reaction mechanism of this unusual transformation is discussed. Influence of solvent dipole moment in pyrrole formation is suggested. Pyrrole 9a [i.e. 2-(3-morpholin-4-yl-2,4-pyrrol-1-yl)-benzonitrile] has been fully characterized and its molecular structure has been determined by X-ray diffraction analysis. 相似文献
3.
M. A. Macrì C. Del Gratta L. Di Donato S. Di Luzio G. L. Romani S. Della Penna A. Pasquarelli 《Il Nuovo Cimento D》1994,16(5):425-432
Summary A preliminary study is here reported on a new potential marker for biomagnetic measurements. The marker consists of superparamagnetic
polymer microspheres which were detected in the presence of external steady magnetic fields by means of an r.f.-SQUID magnetometer.
The particles were prepared in samples differing in the concentration value and immersed in a homogeneous magnetic field of
variable intensity. A simple model was taken into account for the distribution of the microspheres in the samples, so that
the theoretical values were compared to the marker field values measured by the biomagnetic sensor. The overall sensitivity
of the experimental apparatus and the minimum concentration value of the marker were then estimated. 相似文献
4.
We consider the Abelian gauge theory related to the interaction between the solitary waves of the nonlinear Klein-Gordon equation
and the electromagnetic field. We analyze the existence of electromagnetostatic solutions and, in particular, of vortices.
Dedicated to the memory of Professor Aldo Cossu 相似文献
5.
The periodic unfolding method was introduced in 2002 by D. Cioranescu et al. for the study of classical periodic homogenization. In this Note, we extend this method to perforated domains introducing also a boundary unfolding operator. As an application, we study the homogenization of some elliptic problems with Robin condition on the boundary of the holes. To cite this article: D. Cioranescu et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
6.
Alessandro D' Aprano Dorina Ines Donato Antonio Carrubba Doctor in Chemistry thesis of A. Carrubba 《Journal of solution chemistry》1983,12(3):209-220
Conductance measurements are reported for LiPi, NaPi, KPi, RbPi, CsPi, Bu4NPi, Bu4NBr, Bu4NClO4, Bu4NNO3, and Bu4NBBu4 at 25°C in -butyrolactone-sulfolane mixtures. In these mixtures of solvents that are practically homomorphous, isodielectic and with comparable dipole moments, the ion pair association and ionic mobilities of large ions conform to the expectations of the primitive model. Electrolytes containing lithium or sodium ions show anomalies indicating that other factors besides shape, dipole moment, and polarizability of the solvent molecules are involved in the association and transport processes of these ions. 相似文献
7.
A. D'Aprano I. D. Donato F. Pinio V. Turco Liveri 《Journal of solution chemistry》1989,18(10):949-955
A calorimetric method to evaluate, at the same time, the distribution constant and the standard enthalpy of transfer of a solute partitioned between organic phase and reversed micelles is proposed. The method was applied to the partition of methanol, 1-propanol and 1-pentanol between n-heptane and AOT reversed micelles containing water at 25°C. The results show that the distribution constant decreases as the alcohol alkyl chain length increases and that the solubilization site can change as the water content of reversed AOT micelles increases. In particular, at sufficiently high water content, methanol seems to be preferably solubilized in the aqueous pseudophase whereas 1-pentanol prefers always the palisade layer as site of solubilization.In part from Doctor in Biology thesis of F. Pinio, University of Palermo, Italy. 相似文献
8.
Trichochromes, the peculiar pigments of red human hair, featuring the Delta(2,2)(')-bi(2H-1,4-benzothiazine) skeleton, are known to arise from cysteinyldopas, mainly the 5-S-isomer (5). However, the mode of formation and the direct precursors have remained largely undefined. To fill this gap, we investigated the oxidation of 5 in air or with chemical and enzymatic agents under biomimetic conditions. In the presence of zinc ions, which occur in epidermal tissues at significant concentrations, the reaction course is diverted toward the formation of a labile 3-carboxy-2H-1,4-benzothiazine intermediate (11), which was identified by direct NMR analysis. Structural formulation was supported by characterization of the analogous compound 13 isolated from oxidation of the model 5-methyl-3-S-cysteinylcatechol (12) after methylation. In the further stages of the oxidation, diastereomeric 2,2'-bi(2H-1,4-benzothiazine) 15 and 14 were obtained from 5 and 12, respectively, the reaction proceeding at a higher rate and to a greater extent in the presence of acids. The dimers were shown to readily convert to each other in the presence of acids. In the case of the methylated dimers 14, a 2,2'-bi(4H-1,4-benzothiazine) intermediate (16) was isolated and characterized. In acidic media, trichochrome C (1a), the most abundant in red human hair, was smoothly formed from aerial oxidation of 15, and under similar conditions, trichochrome-related products (17 and 18) were obtained from 14 prior to or after methylation. The presence of 1a and precursors 5 and 15 was investigated by HPLC analysis of red hair samples following mild proteolytic digestion. On the basis of these data, a likely biosynthetic route to trichochrome pigments of red human hair is depicted. 相似文献
9.
Paolesse R Monti D La Monica L Venanzi M Froiio A Nardis S Di Natale C Martinelli E D'Amico A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(11):2476-2483
Porphyrin diad 1 was synthesized by reaction of the acyl chloride of porphyrin 2 and trans-1,2-dithiane-4,5-diol. The Co complex of this diad was studied as a potential enantioselective receptor for chiral recognition in solution and in the solid state. In solution both enantiomers of limonene induce significant changes in the visible and circular dichroism (CD) spectra of [Co2(1)], while a different behavior is observed in the case of the enantiomeric pair of trans-1,2-diaminocyclohexane. A different efficiency of [Co2(1)] chiral recognition is obtained for these compounds, with a remarkable degree of enantiodiscrimination observed in the case of limonene. Self-assembled monolayers of [Co2(1)] were deposited onto the gold electrodes of quartz crystal microbalances to be used as sensing materials of nanogravimetric sensors operating in the gas phase. The enantiodiscrimination properties of these sensors towards the enantiomeric pairs of chiral analytes have been studied. While in the case of analytes bearing donor ligand atoms we did not observe a remarkable enantioselectivity, a significant degree of chiral discrimination was observed in the case of limonene; this result is particularly encouraging for the potential development of enantioselective chemical sensors for use in an array configuration. 相似文献
10.
Alessandro D'Aprano Ines Dorina Donato Vincenzo Turco Liveri 《Journal of solution chemistry》1989,18(8):785-793
Static dielectric constants, refractive indices and viscosities of 1-pentanol +2-methyl-2-butanol mixtures were measured at 5, 25 and 45°C. The results show that the mixing of the two isomers modifies the polarizability and the resistence of viscous flow of the system depending on the composition and temperature. Short range intermolecular interactions producing hetero-alcohol open dimers are considered. 相似文献