全文获取类型
收费全文 | 243篇 |
免费 | 3篇 |
专业分类
化学 | 211篇 |
晶体学 | 5篇 |
力学 | 1篇 |
数学 | 15篇 |
物理学 | 14篇 |
出版年
2022年 | 12篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 12篇 |
2009年 | 6篇 |
2008年 | 17篇 |
2007年 | 13篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1968年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 0 毫秒
1.
Margaret C. Etter Zofia Urbańczyk-Lipkowska Touradj M. Ameli Thomas W. Panunto 《Journal of chemical crystallography》1988,18(5):491-507
The crystal structures, solid-state infrared patterns, and thermal properties of two polymorphs of 4-nitrosalicylanilide are presented. In both polymorphs, intramolecular hydrogen bonds are found between the phenol oxygen and the amide proton, and intermolecular hydrogen bonds are found between the amide carbonyl oxygen and the phenol proton. These hydrogen bond patterns are compared to those found in other known salicylamide derivatives and an analysis is given of the factors contributing to preferences for intra- or intermolecular hydrogen bonds in these structures. Crystal data: polymorph, orthorhombic,Pbca,a=11.003(4),b=27.959(7),c=7.622(5) Å,Z=4,V=2345(3) Å3, andR=0.038 (1351 reflections); polymorph, monoclinic,P21/a,a=28.36(1),b=11.64(1),c=7.293(8) Å,=90.68(6)°,Z=8,V=2408 Å3, andR=0.043 (2425 reflections). 相似文献
2.
Zofia Kowalewska E. Bulska A. Hulanicki 《Fresenius' Journal of Analytical Chemistry》1998,362(1):125-129
Different methods for the determination of several metals in soils by flame atomic absorption spectrometry (FAAS) were investigated.
Different procedures for total dissolution of soil: I – HF+HClO4, H3BO3, HCl digestion (conventional heating), II – HF+HClO4, H3BO3 digestion followed by fusion with LiBO2 (conventional heating) and III – HF+HCl+HNO3, H3BO3 digestion (microwave heating), as well as a leaching procedure with HNO3+HClO4, HCl were tested and compared. For quality assessment, the certified reference material S-1 soil was used. For most of the
investigated metals, the best accuracy and precision were achieved when the procedure I or III were used. The developed procedure
was applied to the analysis of soil samples from crude oil refinery and dump of petroleum origin wastes regions.
Received: 22 Dezember 1997 / Revised: 9 February 1998 / Accepted: 12 February 1998 相似文献
3.
Koichi Tanaka Hideyuki Takano Zofia Urbanczyk-lipkowska 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(3-4):281-285
The host compounds 1,1’-binaphthyl-2,2′-dihydroxy-5,5′-dicarboxylic acid (1) and 1,1′-binaphthyl-2,2′-dihydroxy-6,6′-dicarboxylic acid (2) have been synthesized, and their inclusion properties have been studied. Inclusion complexes formed by 1 and 2 with volatile guests such as acetone and methanol release the guests only at much higher temperatures than their boiling
points. The crystal structures of the inclusion complexes have been determined from single crystal X-ray diffraction data
and show different host lattices. 相似文献
4.
Development of a capillary electrophoretic method for the analysis of amino acids containing tablets 总被引:6,自引:0,他引:6
Ketosteril is an enteral medicinal product indicated for prevention and therapy in chronic renal insufficiency in connection with a low protein diet. Tablets of Ketosteril contain five essential amino acids like: Lys, His, Thr, Trp, Tyr and another five amino acids in the form of their hydroxy and keto analogues as calcium salts, that are: alpha-ketoleucine, alpha-ketoisoleucine, alpha-ketovaline, alpha-ketophenylalanine and alpha-hydroxymethionine. The composition of Ketosteril tablets is routinely tested with three LC methods. Capillary electrophoretic method seems to be a good alternative for amino acids and their analogues determination in multicomponent pharmaceuticals because of short analysis time and the possibility to assay all components during a single run without any pretreatment. Electrophoresis was performed in 50 microm I.D. fused-silica capillaries with 65 cm distance to the detector. Capillaries were installed in Waters Quanta 4000 electrophoretic equipment with a positive power supply and on-line UV detection at 214 nm. Separations were done in a buffer containing 40 mM Tris and 160 mM boric acid titrated with NaOH to pH 10. The method developed allows the separation of all investigated analytes with an efficiency of n = 230,000 and 20 min analysis time. The method was applied for determination of all components of Ketosteril in commercial tablets. 相似文献
5.
Dombrowski GW Dinnocenzo JP Zielinski PA Farid S Wosinska ZM Gould IR 《The Journal of organic chemistry》2005,70(10):3791-3800
[reaction: see text] Deprotonation of the radical cations of aromatic amines, such as anilines, generally occurs much more slowly than other fragmentation reactions. Here we report a stereoelectronic effect involving twisting of the anilino group out of the plane of the benzene ring that results in a significantly increased rate of reactivity toward deprotonation. Quantitative studies of the rate constants for deprotonation as a function of aniline radical cation pKa (Br?nsted plots) demonstrate that the effect is not simply due to a change in the reaction thermodynamics. By combining this stereoelectronic effect with covalent attachment of carboxylate as a base, aniline radical cations that undergo unimolecular deprotonation with rate constants as high as 10(8) s(-1), even in unfavorable protic media, are described. 相似文献
6.
Excipient compatibility of a new chemical entity was assessed using an isothermal microcalorimeter. Mixtures of an active
pharmaceutical ingredient with a primary amine group and excipients were prepared in a 1:1 ratio and compatibility monitored
by exposing to 50, 60 and 70°C in presence of 200 mL of water. The new chemical entity, a primary amine, reacted with reducing
sugars such as lactose and resulted in a brown discoloration. This reaction is the Maillard type condensation reaction between
amines and reducing sugars. The rate of reaction was dependent on the temperature with rapid degradation at higher temperatures.
No other incompatibility was apparent between the primary amine and other excipients
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Oleg M. Demchuk Aleksandra Martyna Mateusz Kwanik Katarzyna Szwaczko Dorota Strzelecka Barbara Mirosaw Kazimierz Micha Pietrusiewicz Zofia Urbanczyk-Lipkowska 《Molecules (Basel, Switzerland)》2022,27(17)
The series of C2-symmetric biaryl core-based non-racemic bisphosphines possessing substituents of different electronic properties: both EDG and EWG were obtained in a short sequence of good yielding transformations, started from commercial 1,3-dimethyl-2-nitrobenzene. Several different approaches leading to the desirable ligands were practically evaluated. Notably, the synthesis of the entire series of ligands could be performed with the utilization of a single early-stage precursor DIDAB (6,6′-diiodo-2,2′,4,4′-tetramethylbiphenyl-3,3′-diamine), which could be easily obtained in enantiomerically pure form. The obtained compounds at concentrations of 50 and 200 µM showed various biological activity against normal human dermal fibroblast, ranging from inactivity through time-dependent action and ending up with high toxicity. 相似文献
8.
In this paper, the photochemistry of glyoxal–hydroxylamine (Gly–HA) complexes is studied using FTIR matrix isolation spectroscopy and ab initio calculations. The irradiation of the Gly–HA complexes with the filtered output of a mercury lamp (λ > 370 nm) leads to their photoconversion to hydroxyketene–hydroxylamine complexes and the formation of hydroxy(hydroxyamino)acetaldehyde with a hemiaminal structure. The first product is the result of a double hydrogen exchange reaction between the aldehyde group of Gly and the amino or hydroxyl group of HA. The second product is formed as a result of the addition of the nitrogen atom of HA to the carbon atom of one aldehyde group of Gly, followed by the migration of the hydrogen atom from the amino group of hydroxylamine to the oxygen atom of the carbonyl group of glyoxal. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structures and vibrational spectra of the identified species. 相似文献
9.
Micha Kosno Tomasz Laskowski Joanna E. Frackowiak Agnieszka Potga Agnieszka Kurdyn Witold Andraoj Julia Borzyszkowska-Bukowska Katarzyna Szwarc-Karabyka Zofia Mazerska 《Molecules (Basel, Switzerland)》2022,27(13)
Unsymmetrical bisacridines (UAs) represent a novel class of anticancer agents previously synthesized by our group. Our recent studies have demonstrated their high antitumor potential against multiple cancer cell lines and human tumor xenografts in nude mice. At the cellular level, these compounds affected 3D cancer spheroid growth and their cellular uptake was selectively modulated by quantum dots. UAs were shown to undergo metabolic transformations in vitro and in tumor cells. However, the physicochemical properties of UAs, which could possibly affect their interactions with molecular targets, remain unknown. Therefore, we selected four highly active UAs for the assessment of physicochemical parameters under various pH conditions. We determined the compounds’ pKa dissociation constants as well as their potential to self-associate. Both parameters were determined by detailed and complex chemometric analysis of UV-Vis spectra supported by nuclear magnetic resonance (NMR) spectroscopy. The obtained results indicate that general molecular properties of UAs in aqueous media, including their protonation state, self-association ratio, and solubility, are strongly pH-dependent, particularly in the physiological pH range of 6 to 8. In conclusion, we describe the detailed physicochemical characteristics of UAs, which might contribute to their selectivity towards tumour cells as opposed to their effect on normal cells. 相似文献
10.
Rafa? Janus Piotr Natkański Anna Wach Marek Drozdek Zofia Piwowarska Pegie Cool Piotr Ku?trowski 《Journal of Thermal Analysis and Calorimetry》2012,110(1):119-125
Thermogravimetry, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used for the studying of thermally induced structural changes of polyacrylonitrile (PAN) deposited on the surface of SBA-15 type mesoporous silica. Polymer was introduced onto the support by the precipitation polymerization of acrylonitrile in aqueous suspension of SBA-15. Low temperature transformation (to 723?K) of the deposited PAN was analyzed. It was found that at about 523?K, exothermic cyclization of polymer chains to the so-called ladder form of PAN occurred. However, the total cyclization of PAN required higher carbonization temperatures, at which gradual dehydrogenation followed by graphitization was initiated. XPS revealed that the cyclic form of PAN and a relatively large amount of carbonyl species, formed during the carbonization of the PAN/SBA-15 composite at 623?K, were responsible for the high sorption capacity in the methyl?Cethyl ketone (MEK) vapor elimination. The efficiency in the MEK adsorption was also influenced by the content of PAN-derived carbon deposited on the SBA-15 surface. 相似文献