全文获取类型
收费全文 | 168篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 129篇 |
力学 | 2篇 |
数学 | 25篇 |
物理学 | 18篇 |
出版年
2022年 | 1篇 |
2020年 | 1篇 |
2019年 | 6篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2010年 | 5篇 |
2009年 | 6篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 10篇 |
2005年 | 14篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1967年 | 2篇 |
1966年 | 3篇 |
1959年 | 1篇 |
1956年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有174条查询结果,搜索用时 15 毫秒
71.
A new capillary electrophoresis method to determine simultaneously eight of the most important anti-Parkinson's disease compounds has been developed. The generic names of the drugs studied are benactyzine (BA), trihexyphenidyl (TP), fenpiverin (FP), diphemin (DF), scopolamine (BL), adiphenine (TS), diethylaminoethylester 1-phenylcyclopentane-1-carboxylate (EKK), and diethylaminoethylester tetramethoxydiphenylacetate (EKO). An untreated fused-silica capillary tube (75 microns i.d., 57 cm total length, 49.5 cm length to the detector) was used with detection at 190 nm. The optimal separation conditions were 50 mM phosphate buffer (pH 2.7) with 7 mM-beta-cyclodextrin, electrokinetic injection for 15 sec at 5 kV, temperature 25 degrees C, and 15-20 kV separation voltage. Complete separation of all compounds was achieved in less than 16 min. The procedure was applied for the determination in urine and serum. The limits of detection (LOD, S/N = 3) for serum were 209 (FP), 234 (EKO), 168 (DF), 182 (BA), 168 (TP), 220 (BL), 174 (TS), and 163 (EKK) ppb. The method can be used for the therapeutic drug monitoring of these central active cholinolytics in clinical laboratories. 相似文献
72.
By potentiometric study using a specific uranyl ion-selective electrode, the formation of 1:1 and 1:2 (metal:ligand) complexes of uranyl with various humic acids (HAs) was found. The conditional stability constants were calculated using the LETAGROP-ETITR program. Possible structures of the complexes are proposed. Stability constants were found to be rather high indicating that immobilized HA can be used, for example, to remove traces of uranyl from waste waters. 相似文献
73.
A method was developed for the selective determination of trace concentrations of uranium(VI) by flow-injection analysis (FIA) with fluorimetric detection. Uranium(VI) is selectively separated and/or pre-concentrated from a volume up to 20 ml on an activated silica gel microcolumn (2 x 40 mm) from a medium of 0.03M EDTA, 0.06M tartrate, and/or 0.05M NaF at pH = 9.3. After washing the column the uranium is eluted with a mixture of 1.33M sulphuric and phosphoric acids and determined with a relative standard deviation not exceeding 6% for concentrations in the range 10-250 mug/l. The detection limit was estimated to be 0.1-0.2 mug of uranium. The method has been verified on artificial water samples with high content of the interfering elements and applied to analysis of waste and natural waters. 相似文献
74.
In this paper, we develope the new standardization methods to eliminate the influence in capillary electrophoresis (CE). The markers were used to determine the basis position and then correct the data of sample by the migration time of standard sample, and make the migration time of samples consistent with the standard sample by the criterion of the marker. The problem of time transition was corrected in this way. Then according to the peak height or peak area of the marker in the sample (peak height was used here) compared with the standard sample, the sample data was zoomed appropriately. The absorbance error was made to be correct. The wavelet de-noise method was also used to make the data smooth and get a good baseline. 相似文献
75.
Supalkova V Beklova M Baloun J Singer C Sures B Adam V Huska D Pikula J Rauscherova L Havel L Zehnalek J Kizek R 《Bioelectrochemistry (Amsterdam, Netherlands)》2008,72(1):59-65
Within the context of application of platinum derivates based effective cytostatics, we can suppose that these risk metals can get into aquatic ecosystems where they can show biologic availability for food chain. In the present work we report on investigation of affecting of duckweed (Lemna minor) by various doses of cisplatin (0, 5, 10, 20, 40, 80 and 160 microM) for 4 days. The toxic influence of cisplatin was evaluated on the basis of growth inhibition expressed as number of leaves, growth rate, and total amount of biomass. The result value of 96hEC50, calculated from growth inhibition with comparison of growth rates, was 6.93 microM. Moreover we aimed on determination of cisplatin content using differential pulse voltammetry. The highest content of cisplatin (320 ng g(-1) of fresh weight) was determined in plants treated by 80 microM at the second day of treatment. Plants protect themselves against heavy metals by means of synthesis of cysteine-rich peptides such as glutathione and phytochelatins. Thus thiol determination in the treated plants by means of Brdicka reaction followed. The marked increase in thiol concentration detected is associated with defence reaction of the plant against stress caused by cisplatin. 相似文献
76.
Laser ablation (LA) synthesis with simultaneous time-of-flight mass spectrometric (TOF MS) analysis was used to examine the formation and composition of ternary Pp Sq Ser clusters. Clusters formed by LA of various precursors are singular, binary and ternary. Formation of negative or positive singly charged Pp, Sq and Ser clusters, where Pp + (p = 1-249), Pp* (p = 1-191), Sq* (q = 1-15), Sq + (q = 1-12), Ser* (r = 1-8) and Ser+ (r = 1-9), was identified. High numbers of binary Pp Sq, Sq Ser (35) or ternary Pp Sq Ser (138) clusters were formed by LA synthesis from the various mixtures. Most of the ternary Pp Sq Ser clusters were formed either from a mixture of P4S3 with selenium (grey) or from a mixture of SeS2 with red phosphorus. In total, 138 new ternary Pp Sq Ser clusters were identified. The conditions for the formation of such possible prospective nano-materials are given. 相似文献
77.
Humanin (HN), Met-Ala-Pro-Arg-Gly-Phe-Ser-Cys-Leu-Leu-Leu-Leu-Thr-Ser-Glu-IIe-Asp-Leu-Pro-Val-Lys-Arg-Arg-Ala, recently discovered in the human brain, is an important neuroprotective peptide. Some derivatives of HN show even higher biological activity, for example [G-14]-HN, where Ser at position 14 is replaced with Gly. As structurally related HN peptide derivatives have similar chemical properties, their separation by CE is difficult. In this work, the electrophoretic behaviour of HN derivatives including [G-14]-HN, a tryptophan HN derivative [W-14]-HN, several other HN derivatives and HN fragments was studied. While phosphate buffer was used as the general BGE, the effects of the buffer concentration and various additives were examined, including sulphate, heptane sulphonate, 2-morpholinoethanesulphonic acid N-[tris(hydroxymethyl)methyl]-2-aminoethane sulphonic acid (TES), sulphated-beta-CD and beta-CD. Separation efficiency of 200,000 theoretical plates was achieved in a BGE of 80 mM phosphate at pH 2.5 where seven out of nine major peaks were partially separated. By investigating the influence of concentration of the interrogated ions on peptides migration, the association between positively charged protonated sites of peptides and various anions was proved. Especially a strong interaction with phosphate, sulphate and sulphonate groups was established. Conditional stability constant of the [Pep(z+), (H(2)PO(4)(-))(n)](z - n) ion associate (n = 1) for [G-14]-HN equals to log K approximately 1.78. 相似文献
78.
Markta Kandrnlov Zoran Kokan Vclav Havel Marek Ne
as Vladimír indel 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(50):18350-18353
Reversible covalent bonds play a significant role in achieving the high‐yielding synthesis of mechanically interlocked molecules. Still, only a handful of such bonds have been successfully employed in synthetic procedures. Herein, we introduce a novel approach for the fast and simple preparation of interlocked molecules, combining the dynamic bond character of bis(acyloxy)iodate(I) anions with macrocyclic bambusuril anion receptors. The proof of principle was demonstrated on rotaxane synthesis, with near‐quantitative yields observed in both the classical and “in situ” approach. The rotaxane formation was confirmed in the solid‐state and solution by the X‐ray and NMR studies. Our novel approach could be utilized in the fields of dynamic combinatorial chemistry, supramolecular polymers, or molecular machines, as well inspire further research on molecules that exhibit dynamic behavior, but owing to their high reactivity, have not been considered as constituents of more elaborate supramolecular structures. 相似文献
79.
80.
Petrek J Vítecek J Vlasínová H Kizek R Kramer KJ Adam V Klejdus B Havel L 《Analytical and bioanalytical chemistry》2005,383(4):576-586
Image analysis (IA) was used to determine the areas and circumferences of clusters of early somatic embryos (ESEs) of the
Norway spruce (Picea abies /L./Karst.). Results obtained from IA were compared with the fresh weights of the ESE clusters and their esterase activities.
The areas of the ESE clusters correlated well with both the increases in fresh weight (R
2=0.99) of the ESEs and their esterase activities (R
2=0.99). In addition, we studied the viability of the ESEs, which was determined by (a) double staining with fluorescein diacetate
and propidium iodide (the resulting fluorescence was quantified by IA) and (b) determining esterase activity using a spectrofluorimetric
detector. The results obtained with IA and esterase assay were comparable (the deviation between the tangents of the bisectors
was 6.4%). IA was also used to study the effect of Pb–EDTA chelate (50, 250 and 500 μM) on the viability of the ESEs and on
the growth of clusters. The presence of Pb–EDTA markedly slowed the growth of ESEs clusters (by more than 65% with 250 μM
of Pb–EDTA after 288 h of cultivation) and decreased the viability of ESEs (by more than 30% with 500 μM of Pb–EDTA after
288 h of cultivation). The lead concentration in the ESEs was determined by differential pulse anodic stripping voltammetry
and increased with the external lead concentration and the time of treatment from 100 to 600 pg Pb/100 mg of fresh weight
of ESEs. Glutathione is a diagnostic marker of the influence of Pb–EDTA on ESEs and its content was determined by high–performance
liquid chromatography coupled with mass spectrometry. The glutathione content changed linearly with treatment time and the
applied external lead concentration. The highest glutathione content was obtained at 250 μM of Pb–EDTA after 192 h of cultivation. 相似文献