全文获取类型
收费全文 | 195篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
化学 | 118篇 |
晶体学 | 13篇 |
力学 | 3篇 |
数学 | 10篇 |
物理学 | 56篇 |
出版年
2020年 | 3篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2013年 | 10篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 4篇 |
2008年 | 3篇 |
2007年 | 5篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1961年 | 1篇 |
1886年 | 1篇 |
排序方式: 共有200条查询结果,搜索用时 31 毫秒
141.
Marek Tobiszewski Agata Mechliska Bogdan Zygmunt Jacek Namienik 《Trends in analytical chemistry : TRAC》2009,28(8):943-951
The principles of green chemistry are applied to not only chemical engineering and synthesis, but also increasingly analytical chemistry. We describe environment-friendly analytical techniques applied to isolate and to enrich trace organic pollutants from solid and aqueous samples. Amounts of organic solvents used in analytical laboratories are reduced by applying solventless extraction, extraction using other types of solvent, assisted solvent extraction and miniaturized analytical systems. 相似文献
142.
B. Zygmunt H. B. Hanekamp P. Bos R. W. Frei 《Fresenius' Journal of Analytical Chemistry》1982,311(3):197-200
Summary A polarographic detector with a horizontal, fast dropping mercury electrode has been applied for the determination of thiols in physiological fluids. To establish suitable detection conditions first some basic studies on the polarographic behaviour of penicillamine, glutathione and cysteine were performed. This type of detection shows a high selectivity and reasonably low detection limits for sulphhydryl compounds. Detection limits of 6×10–7 mol l–1 for penicillamine and cysteine and 8×10–7 mol l–1 for glutathione were found. A good linearity has been observed over a concentration range of three orders. The detector has successfully been applied to the determination of penicillamine in urine and serum samples.
Dedicated to Prof. Dr. H. Weisz on occasion of his 60th birthday
On leave from the Technical University of Gdansk 相似文献
Bestimmung von Sulfhydrylverbindungen in physiologischen Flüssigkeiten durch Flüssigkeits-Chromatographie mit polarographischer Detektion
Zusammenfassung Ein polarographischer Detektor mit horizontaler, schnell tropfender Quecksilberelektrode wurde zur Bestimmung von Thiolen in physiologischen Flüssigkeiten angewendet. Zur Feststellung geeigneter Bedingungen wurden zunächst grundlegende Untersuchungen zum polarographischen Verhalten von Penicillamin, Glutathion und Cystein durchgeführt. Das Verfahren bietet hohe Selektivität und niedrige Nachweisgrenzen (6 · 10–7 mol/l für Penicillamin und Cystein, 8 · 10–7 mol/l für Glutathion). Linearität besteht über drei Größenordnungen. Der Detektor wurde mit gutem Erfolg für die Penicillaminbestimmung in Harn und Serum verwendet.
Dedicated to Prof. Dr. H. Weisz on occasion of his 60th birthday
On leave from the Technical University of Gdansk 相似文献
143.
144.
Matveeva EG Gryczynski I Malicka J Gryczynski Z Goldys E Howe J Berndt KW Lakowicz JR 《Journal of fluorescence》2005,15(6):865-871
We compared plastic (polycarbonate) and high-quality glass support materials for gold-coated slides, when performing a model
immunoassay against rabbit IgG using fluorescently labeled (AlexaFluor-647) anti-rabbit IgG, and detecting surface plasmon-coupled
emission (SPCE) signals. Both, glass and plastic slides were simultaneously coated with a 48-nm layer of gold and protected
with a 10-nm layer of silica. The maximum SPCE signal of AlexaFluor-647 was only two- to three-fold smaller on plastic slides
than on glass slides. A small difference in the SPCE angles on glass (θ
F = 55°) and plastic (θ
F = 52.5°) slides was observed and can be explained with a slightly smaller refractive index of the plastic. We have not found
any difference in the angle distribution (sharpness of the fluorescence signal at optimal SPCE angle) for the plastic slide
compared to the glass slide. The kinetics of binding was monitored on the plastic slide as well as on the glass slide. Optically
dense samples, a 4% red blood cell suspension and a 15% hemoglobin solution, are causing a reduction in the immunoassay SPCE
signal by approximately 15% and three times, respectively, and the percentage of the reduction is the same for plastic and
for glass slides. We believe that plastic substrates can be readily used in any SPCE assay, with only marginally lower total
signal compared to high-quality glass slides. 相似文献
145.
Andrzej Katrusiak Zygmunt Kałuski Jerzy Skolik 《Journal of chemical crystallography》1988,18(4):353-364
The crystal structure; determined by X rays, and the13C-NMR spectra of-isosparteine perchlorate are presented. The quinolizidine moieties are present in acis ring-juncture; all piperidine rings are in a chair conformation. The two nitrogen atoms are linked by a hydrogen bond of 2.704(5) Å. The proton at N(16) is also involved in a weak hydrogen bond with the O(2) of the perchlorate anion. The two quinolizidine moieties-protonated and unprotonated-differ only slightly in conformation; the protonation caused small but significant changes in the length of the bonds about the nitrogen atoms. The title compound was obtained by chemical transformations of 17-oxosparteine and protonation with an equimolar amount of HClO4 in methanol.13C-NMR spectra in DMSO-2H6 revealed the presence of the symmetricalcis-cis bis-quinolizidine structure of the salt in solution. 相似文献
146.
A new sensitive and highly selective method is described for the spectrophotometric determination of microgram amounts of vanadium(V). First, vanadium is isolated by extraction withN-benzoyl-N-phenylhydroxylamine (BPHA) in chloroform from about 4M hydrochloric acid medium. Then, chloroform is evaporated and the residue mineralized with mixture of cone. perchloric and nitric acid. Finally, a colour reaction of vanadium(V) separated with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in an acetate buffer (pH 4.5) gives a molar absorptivity of 5.48×104l·mol–1·cm–1 at 585 nm. The proposed method was applied for the determination of traces of vanadium in aluminium samples. The results obtained show a good precision and accuracy of the method. 相似文献
147.
Solid-phase microextraction-gas chromatographic determination of volatile monoaromatic hydrocarbons in soil 总被引:1,自引:0,他引:1
Benzene, toluene, ethylbenzene, three isomers of xylene, and cumene have been isolated and enriched from soil samples by a combination of water extraction at room and elevated temperature and headspace-solid-phase microextraction before their gas chromatographic-mass spectrometric (GC-MS) determination. The conditions used for all stages of sample preparation and chromatographic analysis were optimized. Analytes sampled on a polydimethylsiloxane-coated solid-phase microextraction fiber were thermally desorbed in the split/splitless injector of a gas chromatograph (GC) coupled with a mass spectrometer (MS). The desorption temperature was optimized. The GC separation was performed in a capillary column. Detection limits were found to be of the order of ca. 1 ng g(-1). Relative recoveries of the analytes from soils were found to be highly dependent on soil organic-matter content and on compound identity; they ranged from ca 92 to 96% for sandy soil (extraction at room temperature) and from ca 27 to 55% for peaty soil (extraction at elevated temperature). A few real-world soil samples were analyzed; the individual monoaromatic hydrocarbon content ranged from below detection limits to 6.4 ng g(-1) for benzene and 8.1 for the total of p- + m-xylene. 相似文献
148.
Frackowiak D Ptak A Gryczynski Z Gryczynski I Targowski P Zelent B 《Photochemistry and photobiology》2004,79(1):11-20
Polarized steady-state fluorescence and fluorescence excitation spectra as well as time-resolved fluorescence for B-phycoerythrin (B-PE) from red algae, Porphyridium cruentum, embedded in polyvinyl stretched films were measured. The lifetimes of polarized fluorescence were analyzed using exponential components and fractal models. The interactions between various chromophores of the pigment-protein complexes investigated were discussed. The anisotropy of fluorescence excitation spectra differs from the anisotropy of absorption spectra and depends on the wavelength of observation. This shows that differently oriented chromophores take part in various paths of excitation energy transfer (ET) or change their excitation into heat with various efficiencies (or both). Also, analysis of time-resolved fluorescence measured in various spectral regions gives different polarized components of emission. Fractal analysis of lifetimes, done under supposition of the Foerster resonance ET mechanism, suggests different arrangements of energy donors and acceptors for molecules absorbing in different spectral regions. It shows that several fractions of differently oriented "forms" of chromophores exhibiting different spectral properties occur in B-PE complexes. Small changes in the orientation of the chromophores can be followed by modification of the path of excitation energy migration. Based on the results obtained a new reorientational mechanism of the State 1 --> State 2 transition was proposed: Even small conformational modifications of biliproteins, which could be caused in vivo by the change in the conditions of preillumination of bacteria, are able to modify the path of excitation ET. Such a reorientation may be responsible for the change in the partition of biliprotein excitation energy between photosystem II (PSII) and PSI (State 1 --> State 2 transition). The proposed mechanism needs further verification by the investigation of whole bacteria cells. 相似文献
149.
Various 2-substituted purine and pyrrolo[2,3-d]pyrimidine 2′-deoxyribonucleosides with methylthio ( 13a ), chloro ( 13b ), methoxy ( 9b ), and oxo ( 2, 3 ) substituents at C(2) are prepared. They are obtained either via stereoselective nucleobase-anion glycosylation or by base transformation. A three-step synthesis of the unknown 2′-deoxyisoinosine ( 2 ) from 2′-deoxyguanosine ( 15 ) is described. Compound 2 as well as its 7-deazapurine derivative 3 exhibit strong fluorescence. 相似文献
150.
Summary A method of separation and colorimetric determination of trace amounts (10–4–10–5%) of Cu, Al, Fe, Bi, Pb, Mn, Cd, Zn, Co, and M in platinum-rhodium (10%) alloys has been developed. The elements to be determined are retained on a column containing the strongly acidic cation-exchanger Amberlite IR-120, from dilute hydrochloric acid medium (pH 1–1.5), while platinum and rhodium pass through in the form of anionic chloride complexes. The individual metals are eluted and concentrated and then separated by extraction and carrier precipitation. The metals are determined by means of sensitive colorimetrie methods with dithizone (Cu, Bi, Pb, Cd, Zn), eriochromecyanine R (Al), 2-nitroso-1-naphthol (Co),-furildioxime (Ni), 1-(2-pyridylazo)-2-naphthol (Mn), and thiocyanate (Fe). The error of the determination does not exceed 15%.
Zusammenfassung Eine Trennungs- und Bestimmungsmethode für Spuren (10–4 bis 10–5%) von Cu, Al, Fe, Bi, Pb, Mn, Cd, Zn, Co und Ni in PIatm-Rhodium-(10%)-Legierungen wurde ausgearbeitet.Die angeführten Elemente werden mit Amberlit IR-120 aus der verd. salzsauren Lösung (pH 1 bis 1,5) von Platin und Rhodium getrennt, die als Anionchloridkomplexe im Eluat bleiben. Die einzelnen Metalle werden nach Elution aus ihrer Lösung durch Extraktion bzw. Mitfällung getrennt und kolorimetrisch mit Dithizon (Cu, Bi, Pb, Cd, Zn), Eriochromcyanin R (Al), 2-Nitroso-1-naphthol (Co),-Furildioxim (Ni), 1-(2-Pyridylazo)-2-naphthol (Mn) und Rhodanid (Fo) bestimmt. Der Fehler beträgt weniger als 15%,相似文献