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排序方式: 共有137条查询结果,搜索用时 15 毫秒
1.
Wincenty Turek Mieczyslaw Lapkowski Agnieszka Stolarczyk 《Applied Surface Science》2005,252(3):801-806
The goal of our studies was to determine the nature of interactions between catalytic active samples, such as polypyrrole (PPy) doped with: chloride anions, heteropolyacids such as H5PMo10V2O40, or H4SiW12O40, and oxygen particles. In order to reveal the mechanism of the linkage between the catalysts and oxygen we provided the electron paramagnetic resonance (EPR) measurements of synthesized samples in O2 and N2 flow. Moreover, the X-ray photoelectron spectroscopy (XPS) measurements were performed to show the properties of doped heteropolyacids and the state of nitrogen in polypyrrole matrix. The results of EPR studies of PPy(Cl), PPy(H4SiW12O40), PPy(H5PMo10V2O40) samples, show that the polypyrrole doped with chloride anions interacts much easier with oxygen than polypyrrole doped with heteropolyacids (in the above given order, of preference with the most active polypyrrole system first). It correlates with XPS results, which show that a molybdenium-vanadium anion is more reduced than a silicon-tungsten one. The redox reactions of heteropolyacids involve the oxidation-reduction of the conjugated polymer chain, leaving no or little place for interactions with oxygen. Polypyrrole doped with H4SiW12O40 shows some oxygen sensitivity as observed in the EPR studies, as opposed to polypyrrole doped with H5PMo10V2O40, which is in line with the XPS results. 相似文献
2.
In this paper, three new direct Mutually Orthogonal Latin Squares (MOLS) constructions are presented for 7 MOLS(24), 7 MOLS(75) and 8 MOLS(36); then using recursive methods, several new constructions for 7 and 8 MOLS are obtained. These reduce the largest value for which 7 MOLS are unknown from 780 to 570, and the largest odd value for which 8 MOLS are unknown from 1935 to 419. © 2003 Wiley Periodicals, Inc. 相似文献
3.
A sensitive method of Co(II) determination by adsorptive stripping voltammetry is presented. The method exploits the enhancement of cobalt peak current observed in the system Co(II)-nioxime-cetyltrimethylammonium bromide-piperazine-N,N′-bis(2-ethanesulfonic acid). The calibration plot for an accumulation time of 60 s is linear from 5 × 10−11 to 3 × 10−9 mol L−1. The relative standard deviation is 3.8% for Co(II) determination at concentration 1 × 10−9 mol L−1. The detection limit is 1.7 × 10−11 mol L−1. The validation of the method is performed by the analyses of certified reference materials and comparing the result of Co(II) determination in river water sample by the proposed method with those obtained by ET AAS. The main advantage of this new system is the micro-trace Co(II) determination by adsorptive stripping voltammetry, as compared to those described before, a low concentration of the supporting electrolyte used, and so commercially available reagents without additional purification can be used. 相似文献
4.
Korolczuk M Moroziewicz A Grabarczyk M 《Analytical and bioanalytical chemistry》2005,382(7):1678-1682
Procedures for trace cobalt determinations by adsorptive stripping voltammetry at in situ and ex situ plated bismuth film electrodes are presented. These exploit the enhancement of the cobalt peak obtained by using the Co(II)–dimethylglyoxime–cetyltrimethylammonium bromide–piperazine-N,N-bis(2-ethanesulfonic acid) system. The calibration graph for an accumulation time of 120 s was linear from 2 × 10–10 to 2 × 10–8 mol L–1. The relative standard deviation from five determinations of cobalt at a concentration of 5 × 10–9 mol L–1 was 5.2%. The detection limit for an accumulation time of 300 s was 1.8 × 10–11 mol L–1. The proposed procedure was applied to cobalt determination in certified reference materials and in tap and river water samples. 相似文献
5.
Mieczysaw Korolczuk 《Fresenius' Journal of Analytical Chemistry》1997,357(4):389-391
A selective and sensitive method is proposed for the determination of mercury by anodic stripping voltammetry after its preconcentration
from the gas phase. Mercury from the sample solution is reduced to elemental Hg by SnCl2 and volatilized by the bubbles of a carrier gas. The gas containing mercury vapour is dried and passed through a capillary
onto a gold coated graphite electrode. An anodic stripping voltam-mogram is recorded from 0.1 mol/1 HClO4 + 3 × 10−3 mol/1 HCl solution. The calibration curve is linear from 1 × 10−9 to 4 × 10−8 mol/1 Hg(NO3)2. The absolute detection limit is 0.46 ng Hg. The relative standard deviations for 4 × 10−9 mol/1 and 2 × 10−8 mol/1 Hg(NO3)2 are 9.8% and 6.1%, respectively n = 5). 相似文献
6.
The voltammetric procedure for determination of traces of Cr(VI) [Anal. Chim. Acta (1992) 262:103] was modified by changing the temperature of the measurements. It was found that at the temperature of 40 °C the time of decrease of the Cr(III) signal was shortened from 30 to 5 min. As a result the total analysis time was drastically shortened. The modified procedure does not show any disadvantage as compared to the original method. The results of Cr(VI) determination by the modified procedure are less affected by Cr(III) as compared to the original method. The detection limit of the method was 2.5 × 10-11 mol L-1 (1.2 ng L-1). The validation of the modified procedure was performed by comparison of the results of analyses of tap and river water samples with those obtained using original procedure. 相似文献
7.
Mieczysław Korolczuk 《Analytical and bioanalytical chemistry》1997,357(4):389-391
A selective and sensitive method is proposed for the determination of mercury by anodic stripping voltammetry after its preconcentration
from the gas phase. Mercury from the sample solution is reduced to elemental Hg by SnCl2 and volatilized by the bubbles of a carrier gas. The gas containing mercury vapour is dried and passed through a capillary
onto a gold coated graphite electrode. An anodic stripping voltammogram is recorded from 0.1 mol/l HClO4+3×10-3 mol/l HCl solution. The calibration curve is linear from 1×10-9 to 4×10-8 mol/l Hg(NO3)2. The absolute detection limit is 0.46 ng Hg. The relative standard deviations for 4×10-9 mol/l and 2×10-8 mol/l Hg(NO3)2 are 9.8% and 6.1%, respectively (n=5).
Received: 18 December 1995/Revised: 16 April 1996/Accepted: 20 April 1996 相似文献
8.
9.
Korolczuk M 《Fresenius' Journal of Analytical Chemistry》2000,367(8):761-762
A modification of the voltammetric procedure for the determination of chromium in the presence of DTPA and nitrates was proposed. Morpholinoethanesulfonic (MES) acid and its sodium salt were used for stabilisation of pH instead of acetate buffer. In the presence of MES the determination of chromium can be carried out in the presence of dissolved oxygen without decrease of sensitivity of the measurements. Elimination of the purge step decreases total analysis time and saves gas. 相似文献
10.