全文获取类型
收费全文 | 216篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
化学 | 116篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 40篇 |
物理学 | 52篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 4篇 |
2012年 | 16篇 |
2011年 | 17篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 16篇 |
2007年 | 20篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 7篇 |
2003年 | 5篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有218条查询结果,搜索用时 31 毫秒
191.
Alberto dos Santos Pereira Angelo C. Pinto Jari Nobrega Cardoso Francisco Radler de Aquino Neto Mnica Freiman de Souza Ramos Gisela M. Dellamora-Ortiz Elisabete Pereira dos Santos 《Journal of separation science》1998,21(7):396-400
The underivatized acetone and hexane fractions from propolis samples (predominant flora Citrus spp. and Vernonia polyanthes) were analyzed by HT-HRGC (high temperature high resolution gas chromatography) and HT-HRGC coupled to mass spectrometry (HT-HRGC-MS). Several compounds, including flavonoid aglycones, phenolic acids, and high molecular weight compounds were characterized in crude extracts by HT-HRGC-MS. HT-HRGC and HT-HRGC-MS were shown to be quick and informative tools for rapid analysis of crude extracts without need for prior derivatization and purification. 相似文献
192.
Jari Tamminen Erkki Kolehmainen Juha Linnanto Pirjo Vainiotalo Sami Vuorikoski Reijo Kauppinen 《Journal of inclusion phenomena and macrocyclic chemistry》2000,37(1-4):121-130
Lithocholic acid N-(2-aminoethyl)amide (1) and deoxycholic acid N-(2-aminoethyl)amide(2) have been prepared and characterized by1H, 13C and 15N NMR. The accurate molecular masses of 1 and 2 have been determined by ESI MS. The formation of the Cd2+-complexes (1+Cd and 2+Cd) in CD3OD solution have been detected by 1H,13C, 15N and 113Cd NMR. The 13C NMR chemical shift assignments of 1 and 2 and their Cd2+-complexes are based on DEPT-135 and z-GS 1H,13C HMQC experiments as well as comparison with the assignments of the related structures. The 15N NMR chemical shiftassignments of the ligands and theirCd2+-complexes are based on z-GS1H,15N HMBC experiments. 13C NMR chemical shift differences between 1and its 1:1 Cd2+-complex based on ab initiocalculations at Hartree-Fock SCI-PCM level using3-21G(d) basis set are in agreement with theexperimental shift changes observed onCd2+-complexation. 相似文献
193.
The spatial periodicities in Fresnel diffraction patterns produced by polarization gratings [Opt. Lett. 24 (1999) 584] and their generalizations are investigated, with particular attention to the state of polarization of the diffracted field. It is shown, e.g., that in certain planes the polarization vector can rotate periodically, while being constant in certain other parallel planes. 相似文献
194.
A mean-field theory of equilibrium polymerization on a square lattice is presented. A novel feature of the model is the treatment of the whole range of rigidity of polymers (from flexible to stiff) as well as a simultaneous account of both polymer rings and excluded volume. As a result a line of tricritical points is found. 相似文献
195.
Lajos Fodor Gbor Bernth Jari Sinkkonen Kalevi Pihlaja 《Journal of heterocyclic chemistry》2002,39(5):927-931
The ring‐closure reactions of N‐arylthiomethylaroylamide derivatives ( 1a‐g ) in the presence of phospho ‐rus oxychloride gave 2‐aryl‐4H‐1,3‐benzo‐thiazines (2a‐g). 2‐(3‐Chlorophenyl)‐6‐methyl‐4H‐1,3‐benzoth‐iazine ( 2b ) was reduced with Zn to obtain the corresponding 2,3‐dihydro derivative ( 3b ). Potassium permanganate oxidation of 2‐(4‐chlorophenyl)‐2,3‐diethoxy‐4H‐ ( 2e ) and 2‐(2‐fluorophenyl)‐6,7‐diefhoxy‐4H‐1,3‐benzo‐thiazines ( 2g ) gave the corresponding 4‐ones ( 4e,g ). The reactions of 2‐(4‐chlorophenyl)‐6‐mefhyl‐4H‐1,3‐benzofhiazine ( 2c ) with substituted acetyl chlorides led to linearly condensed ß‐lactams ( 5a,b ). The structures of the compounds studied were confirmed by 1H and 13C NMR and by their characteristic mass spectrometric fragmentations. 相似文献
196.
Korolainen MA Goldsteins G Alafuzoff I Koistinaho J Pirttilä T 《Electrophoresis》2002,23(19):3428-3433
There is a growing body of evidence that oxidative stress plays a major role in Alzheimer's disease (AD) pathogenesis. Identification of oxidatively altered proteins in AD is important for understanding the relationship between protein oxidation, protein aggregation and neurodegeneration. In this communication, we report a method that can be applied to study oxidative changes of individual proteins in brain. In order to analyze protein oxidation by detection of protein-bound carbonyls, cytosolic protein extracts were derivatized with 2,4-dinitrophenylhydrazine (DNPH) and then separated by two-dimensional (2-D) gel electrophoresis. After electrotransfer to polyvinylidene difluoride (PVDF) membranes, proteins were first stained with Sypro Ruby protein stain, and then the oxidized proteins were detected with anti-dinitrophenyl (DNP) antibody. About 150 proteins and more than 100 oxidized proteins were detected and quantified in both AD and control cases by 2-D image analysis. The amount of protein-bound carbonyls was decreased for six and increased for one protein in AD. The amount of protein was increased for three proteins in AD. Furthermore, the degree of oxidation was calculated as the ratio of protein-bound carbonyls to the total amount of an individual protein. Two proteins showed a significant decrease in the degree of oxidation in AD. Our results suggest that the balance of protein oxidation and degradation is altered in AD. 相似文献
197.
Erkki Kolehmainen Jari Tamminen Reijo Kauppinen Juha Linnanto 《Journal of inclusion phenomena and macrocyclic chemistry》1999,35(1-2):75-84
Three isomeric molecular clefts: 3,3'-bis(pyridine-n-carboxy) lithocholic acid 1,2-ethanediol diesters (n = 2–4) 1–3 have been synthesized and their structures ascertained by 1H, 13C NMR and MALDI TOF MS. Their complex formation with Ag+-cation (added as AgO3 SCF3) have been investigated by means of NMR and molecular orbital calculations. The coordination behaviour of the silver(I) cation is dependent on the isomerism of the pyridine-n-carboxy moiety. In 1 (pyridine-2-carboxylato = picolinato) both NMR and theoretical calculations strongly suggest that the coordination occurs with the lone electron pairs of the pyridine nitrogen and carbonyl oxygen in both of the arms of the molecular cleft separately. In 2 and 3 (pyridine-3-carboxylato = nicotinato and pyridine-4-carboxylato = isonicotinato) where the distance between the pyridine nitrogen and carbonyl oxygen is too large to allow the same type of coordination as in 1, 3-complexation with the pyridine ring and carbonyl oxygen of the different arms of the molecular cleft simultaneously is suggested by molecular orbital calculations and supported also by NMR. No Ag+-cation coordination was observed with the 1,2-ethanediol oxygens in 1–3. 相似文献
198.
Jari Hovinen 《Tetrahedron letters》2004,45(29):5707-5709
Treatment of 2,6-di(pyridin-2-yl)pyridin-4(1H)-one with various appropriately protected ω-substituted primary alcohols or a nucleoside (3,3′-O-diBz-dUrd) in dry THF in the presence of triphenylphosphine and diisopropylazodicarboxylate gives the corresponding 4′-substituted terpyridines in high yield. 相似文献
199.
We have developed a detailed mathematical model and numerical simulation tools based on the streamline upwind/Petrov-Galerkin (SUPG) finite element formulation for the Czochralski silicon crystal growth. In this paper we consider the mathematical modeling and numerical simulation of the time-dependent melt flow and temperature field in a rotationally symmetric crystal growth environment. Heat inside the Czochralski furnace is transferred by conduction, convection and radiation, Radiating surfaces are assumed to be opaque, diffuse and gray. Hence the radiative heat exchange can be modeled with a non-local boundary condition on the radiating part of the surface. The position of the crystal-melt interface is solved by the enthalpy method. The melt flow is assumed to be laminar and governed by the cylindrically symmetric and incompressible Navier-Stokes equations coupled with the calculation of temperature. 相似文献
200.
Mari Granström Jari Kavakka Alistair King Johanna Majoinen Valtteri Mäkelä Juho Helaja Sami Hietala Tommi Virtanen Sirkka-Liisa Maunu Dimitris S. Argyropoulos Ilkka Kilpeläinen 《Cellulose (London, England)》2008,15(3):481-488
Tosylation and acylation of cellulose were performed under mild reaction conditions using imidazolium based ionic liquids
(ILs) as solvents. The non-degradative nature, lower viscosity, as well as higher solubility of cellulose in [amim]Cl encouraged
us to carry out the reactions in this media. The reactions described here were optimised for this particular solvent in order
to obtain different cellulose derivatives with high yields, homogeneity and degree of substitution (DS). Two reagents employed
for the in situ activation of carboxylic acids were N,N′-carbonyldiimidazole (CDI) and 1-ethyl-3-(3′-dimethylaminopropyl)carbodiimide hydrochloride (EDCI). Final products were characterised
by solution and solid-state NMR techniques.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献