全文获取类型
收费全文 | 242篇 |
免费 | 14篇 |
专业分类
化学 | 221篇 |
晶体学 | 3篇 |
数学 | 16篇 |
物理学 | 16篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 8篇 |
2016年 | 18篇 |
2015年 | 10篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 13篇 |
2011年 | 17篇 |
2010年 | 11篇 |
2009年 | 11篇 |
2008年 | 11篇 |
2007年 | 10篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1948年 | 2篇 |
1944年 | 2篇 |
排序方式: 共有256条查询结果,搜索用时 15 毫秒
61.
Ilona Šperlingová Ludmila Dabrowská Vladimír Stránský Šárka Dušková Jan Kučera Monika Tvrdíková Milon Tichy 《Analytical and bioanalytical chemistry》2010,397(2):433-438
Ethylene glycol monobutyl ether (EGBE), an industrial solvent, is absorbed by the body not only by inhalation but also by
dermal absorption (liquid or vapour). EGBE is metabolized to butoxyacetic acid (BAA). Pooled freeze-dried urine candidate
reference material (RM) was prepared from urine obtained from persons occupationally exposed to EGBE. This material has the
advantage of containing butoxyacetic acid in both the free and conjugated (glutamine and glycine) forms, as found in native
urine. In all GC method modifications used, acid hydrolysis was used to release BAA from its conjugated form. The amount of
butoxyacetic acid in homogeneity and stability testing was measured by GC after derivatisation with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide. Detection was by MS in EI mode, in the authors’ laboratory. For interlaboratory comparison of the
reference material GC methods with MS, FID, and ECD were used. Different extraction solvents (dichloromethane–isopropanol
2:1, ethyl acetate, or dichloromethane) and derivatisation reagents (trimethylsilyldiazomethane, N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide) were used. Using ANOVA (at the statistical level α = 0.05) no changes were found in the concentration of butoxyacetic acid during fifteen month isochronous stability testing,
or in homogeneity testing. The uncertainty contributions were u
h = 8.8 mg L−1 and u
s = 6.5 mg L−1. The concentration of butoxyacetic acid in freeze-dried urine RM was evaluated from the results of eight laboratory data
sets within an interlaboratory comparison by use of the interactive statistical software IPECA. The contribution to total
uncertainty derived from interlaboratory comparison was u
i = 12.7 mg L−1. The reference value (c = 273 ± 33 mg L−1) is an unweighted arithmetic average of accepted results. The value is traceable to the pure butoxyacetic acid (98% w/w; Acros Organic #257760010) used as calibrant. The uncertainty given is combined expanded uncertainty derived from the results
from interlaboratory comparison, and from homogeneity and stability tests (k = 2). The reference material will be used to verify method performance in the biological monitoring of occupational exposure
to EGBE. 相似文献
62.
Julia Bkowicz Ilona Turowska‐Tyrk 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(8):o377-o380
The crystal structures of 2‐oxo‐2‐phenyl‐N‐[(R)‐1‐phenylethyl]acetamide, C16H15NO2, (I), and N,N‐dimethyl‐2‐(1‐naphthyl)‐2‐oxoacetamide, C14H13NO2, (II), were determined in an attempt to understand the reason for the lack of Yang photocyclization in their respective crystals. In the case of (I), the long distance between the O atom of the carbonyl group and the γ‐H atom, and between the C atom of the carbonyl group and the γ‐C atom, preclude Yang photocyclization. For (II), the deviation of the γ‐H atom from the plane of the carbonyl group and interactions between the naphthalene rings are regarded as possible reasons for the chemical inertia. The two independent molecules of (I) differ in their conformation. N—H...O hydrogen bonds link molecules of (I) into chains extended along the b axis. 相似文献
63.
64.
István Simonyi und Ilona Kékesy 《Fresenius' Journal of Analytical Chemistry》1966,215(3):187-190
Zusammenfassung Eine Methode zur Bestimmung aliphatischer und aromatischer Säurechloride wird beschrieben. Hierbei werden die Säurechloride mit acetonhaltiger Natriumjodidlösung quantitativ zu Natriumchlorid und Säurejodid umgesetzt. Das in Aceton unlösliche Natriumchlorid wird abfiltriert, in Wasser gelöst und nach Volhard bestimmt. Die üblichen Zersetzungsprodukte stören die Bestimmung nicht. Die Fehler liegen meist unter 1%.
Summary A method is recommended for the determination of aliphatic and aromatic acid chlorides. It consists in converting the acid chlorides to the iodides by sodium iodide in acetonic solution, filtering off the sodium chloride formed quantitatively by this reaction and insoluble in acetone, dissolving it in water and titrating by Volhard's method. The determination is not influenced by the usual decomposition products of acid chlorides. Errors are mostly smaller than 1%.相似文献
65.
Ruohola AM Koissi N Andersson S Lepistö I Neuvonen K Mikkola S Lönnberg H 《Organic & biomolecular chemistry》2004,2(13):1943-1950
Reactions of 9-ethylguanine, 2'-deoxyguanosine and guanosine with bromomalondialdehyde in aqueous buffers over a wide pH-range were studied. The main products were isolated and characterized by (1)H and (13)C NMR and mass spectroscopy. The final products formed under acidic and basic conditions were different, but they shared the common feature of being derived from glyoxal. Among the 1 : 1 adducts, 1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (6) predominated at pH < 6 and N(2)-carboxymethylguanine adduct (10a,b) at pH > 7. In addition to these, an N(2)-(4,5-dihydroxy-1,3-dioxolan-2-yl)methylene adduct (11a,b) and an N(2)-carboxymethyl-1,N(2)-(trans-1,2-dihydroxyethano)guanine adduct (12) were obtained at pH 10. The results of kinetic experiments suggest that bromomalondialdehyde is significantly decomposed to formic acid and glycolaldehyde under the conditions required to obtain guanine adducts. Glycolaldehyde is oxidized to glyoxal, which then modifies the guanine base more readily than bromomalondialdehyde. Besides the glyoxal-derived adducts, 1,N(2)-ethenoguanine (5a-c) and N(2),3-ethenoguanine adducts (4a-c) were formed as minor products, and a transient accumulation of two unstable intermediates, tentatively identified as 1,N(2)-(1,2,2,3-tetrahydroxypropano)(8) and 1,N(2)-(2-formyl-1,2,3-trihydroxypropano)(9) adducts, was observed. 相似文献
66.
A capillary electrophoretic (CE) method has been developed for the determination of ivermectin (CAS 70288-86-7), a new generation drug with antiparasitic activity, in pig and horse plasma. The method was statistically validated for its linearity, accuracy, precision and selectivity. The linear range was from 1 to 30 ng mL(-1) with correlation coefficients greater than 0.999. The limit of detection was 0.3 ng mL(-1), while the quantitative limit was 1 ng mL(-1), using a 0.5 mL sample size. The validated procedure was used to determination of pharmacokinetic parameters of ivermectin after ingestion of 0.1 mg for pigs and 0.2 mg dose per kg body weight for horses, respectively. Studies were performed on a group of eight pigs and six horses. There were no significant differences between pigs and horses in any of the estimated pharmacokinetic parameters. 相似文献
67.
1,5-Dihydropentalene (4) is formed as the main product on treatment of trans-1,2-bis(2,2-dibromocyclo-propyl)ethene 3 with methyllithium at −40°. In addition the reaction affords 1- and 2-propadienylcyclopentadienes (5a) and (5b), and trans-1,2,4,6,7-octapentaene (6), new C8H8 isomers. Diels-Alder adducts of 4, 5a and 5b were obt in the reaction with perfluorobut-2-yne. The formation of 1,5-dihydropentalene 4 is explained by a double ring expansion sequence involving consecutive carbene-carbene rearrangements with 1,3-carbon and subsequent 1,2-hydrogen shifts, supported by the reaction of double labelled (13C-depleted) 3. From readily available 3 at low temperatures formation and fusion of two 5-membered rings are achieved in one step. 相似文献
68.
Summary The chromatographic characteristics of the thiazolidine carboxylic acids formed by the reaction of D- and L-penicillamine
with various substituted benzaldehydes and heterocyclic aldehydes have been studied on Chiralplate layers. It has been found
that the nature and position of substituents strongly affect the RF values and resolution factors (RS) of the isomers. An unambiguous relationship has been established between the RS values of the L- and D-enantiomers and the dipole moment of the aldehydes. The transformation to thiazolidine carboxylic
acids with benzaldehyde and substituted benzaldehydes, however, is not complete, thus the reaction with formaldehyde is still
more suitable for quantitative determination of penicillamine isomers. 相似文献
69.
Björn Alriksson Ilona Sárvári Horváth Anders Sjöde Nils-Olof Nilvebrant Leif J. Jönsson 《Applied biochemistry and biotechnology》2005,124(1-3):911-922
When dilute-acid hydrolysates from spruce are fermented to produce ethanol, detoxification is required to make the hydrolysates
fermentable at reasonable rates. Treatment with alkali, usually by overliming, is one of the most efficient approaches. Several
nutrients, such as ammonium and phosphate, are added to the hydrolysates prior to fermentation. We investigated the use of
NH4OH for simultaneous detoxification and addition of nitrogen source. Treatment with NH4OH compared favorably with Ca(OH)2, Mg(OH)2, Ba(OH)2, and NaOH to improve fermentability using Saccharomyces cerevisiae. Analysis of monosaccharides, furan aldehydes, phenols, and aliphatic acids was performed after the different treatments.
The NH4OH treatments, performed at pH 10.0, resulted in a substantial decrease in the concentrations of furfural and hydroxymethylfurfural.
Under the conditions studied, NH4OH treatments gave better results than Ca(OH)2 treatments. The addition of an extra nitrogen source in the form of NH4Cl at pH 5.5 did not result in any improvement in fermentability that was comparable to NH4OH treatments at alkaline conditions. The addition of CaCl2 or NH4Cl at pH 5.5 after treatment with NH4OH or Ca(OH)2 resulted in poorer fermentability, and the negative effects were attributed to salt stress. The results strongly suggest
that the highly positive effects of NH4OH treatments are owing to chemical conversions rather than stimulation of the yeast cells by ammonium ions during the fermentation. 相似文献
70.
Wolfgang A. Herrmann Ilona Schweizer Michael Creswick Ivan Bernal 《Journal of organometallic chemistry》1979,165(1):C17-C20
the μ-heteromethylenecobalt complexes, which have been synthesized by photolysis of (η5-C5H5)Co(CO)2 in the presence of the corresponding diazoacetates at < ?90°C in tetrahydrofuran, undergo a novel type of intramolecular irreversible rearrangement yielding two isomers. The structure of one of the isomers has been established by X-ray analysis. A comparison of the structural parameters of all known μ-methylene-transition metal complexes shows that the internal angles α of the cyclopropane-like systems are far less sensitive to the compositions and structures of the molecules than the external angles β. The internal angles cannot be readily correlated with other features of the molecule. 相似文献