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排序方式: 共有66条查询结果,搜索用时 15 毫秒
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2.
Continuous flow injection and UV spectrophotometric detection have been proposed for simultaneous determination of the two binary mixtures, butylated hydroxytoluene (BHT)/n-propyl gallate (n-PG) and butylated hydroxytoluene (BHT)/butylated hydroxyanisole (BHA), in food and cosmetics samples. The method is based on the different residence times of each antioxidant when the flow cell is packed to a height of 25 mm with silica C18 using methanol-water 50:50% (v/v) as a carrier with a flow rate of 1.25 and 1.10 ml min−1, respectively. The determination of each antioxidant is based on the measurement of its absorbance at its maximum wavelengths using a DAD detector at 30 and 180 s for the mixture n-PG-BHT and 90 and 220 s for BHA-BHT. Calibration graphs were linear over the range 10.0-300.0 μg ml−1 for each antioxidant in both mixtures. The relative standard deviations were 2.5% for BHT and 2.0% for the co-existing antioxidant. Resolution of the n-PG-BHT mixture in ratios between 1:8 and 8:1 and the BHA-BHT mixture in ratios between 1:10 and 10:1 is possible. The method was applied to the determination of both antioxidants in fat foods and cosmetics samples with recoveries ranging between 101 and 105%. 相似文献
3.
Concentration sensitivity is a key performance indicator for analytical techniques including for capillary electrophoresis-mass spectrometry (CE–MS) with electrospray ionization (ESI). In this study, a flow-through microvial interface was used to couple CE with MS and improve the ESI stability and detection sensitivity. By infusing a peptide mixture through the interface into an MS detector at a typical flow rate for CE-MS analysis, the spatial region near the interface was mapped for MS signal intensity. When the sprayer tip was within a 6 × 6.5 × 5 mm region in front of the MS inlet, the ESI was stable with no significant loss of signal intensity for ions with m/z 239. Finite element simulations showed that the average electric field strength at the emitter tip did not change significantly with minor changes in emitter tip location. Experiments were conducted with four different mass spectrometer platforms coupled to CE via the flow-through microvial interface. Key performance indicators, that is, limit of detection (LOD) and linearity of calibration curves were measured for nine amino acids and five peptides. Inter- and intraday reproducibility were also tested. The results were shown to be suitable for quantification when internal standards were used. 相似文献
4.
以石墨管为基体,十六烷基三甲基溴化铵为电活性物质,制备了带有内参比电极(Ag/AgC l)的管状流通式阴离子表面活性剂选择性电极,对其性能进行了测试。实验结果表明,其线性响应范围为1.6×10-7~5.1×10-3mol/L,斜率为52.0 mV/dec,检出限为2.0×10-8mol/L。利用该电极进行测试时,常用的无机阴离子C l-、SO42-、NO3-、PO43-等不会对其产生干扰;该电极适宜的pH值范围为2.50~10.50。对水样测定,回收率为95%~104%。电极可连续使用50 d左右。 相似文献
5.
A.J. Groszek 《Applied Surface Science》2007,253(13):5882-5887
Exposure of pure iron nano-flakes to hydrogen generates a high heat evolution associated with hydrogen uptakes shown by flow-through microcalorimetry. A large part of the hydrogen was found to be irreversibly absorbed by the iron flakes at 220 °C and atmospheric pressure, but an increased desorption of hydrogen was achieved by noble gases, such as helium and argon. Thus the iron surfaces displayed strong affinity for hydrogen, but also, surprisingly, for the noble gases, which were found to be able to displace hydrogen from the iron surfaces.The uptake of hydrogen by the iron flakes was observed to reach 9 wt.% after exposure for 5 h, which may be of interest in hydrogen storage applications. Desorption with the help of argon may provide an acceptable method of hydrogen recovery. 相似文献
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In the present study, the flow-through silica, featured with hierarchical pores, i.e., tunable mesopores and penetrable macropores, was attempted as the chromatographic stationary phase matrix to immobilize gold nanoparticles (AuNPs). It was first modified by mercapto groups (named as SiO2-SH), and then by AuNPs (named as SiO2-S-Au). Thanks to the characteristic macropores, the column backpressure of SiO2-S-Au was comparable to SiO2-SH, which effectively overcame the difficulty of high column backpressure upon the nanoparticles were introduced to the chromatographic matrix. Both the reversed-phase and hydrophilic interaction liquid chromatographic performance were observed on these two columns but with different selectivities. Hydrophobic, hydrophilic, hydrogen bond and electrostatic interactions between the SiO2-S-Au stationary phase and analytes could contribute to the retention. The SiO2-S-Au column showed excellent aqueous compatibility by “Stop-flow” test with the relative standard deviations (RSD) of analyte’s k (capacity factor) values from 0.59% to 2.88%. The reproducibility of SiO2-S-Au was acceptable with RSDs of analyte’s k values in the range of 3.13%-5.03%. In addition, compared with the SiO2-SH column, the SiO2-S-Au column had better separation performance and selectivity. The results demonstrated that the flow-through silica was a promising matrix for nanoparticles with low backpressure and different selectivities. 相似文献
8.
Lutz I Kloas W Springer TA Holden LR Wolf JC Krueger HO Hosmer AJ 《Analytical and bioanalytical chemistry》2008,390(8):2031-2048
Xenopus laevis has been introduced as a model to study effects of endocrine-active compounds (EAC) on development and sexual differentiation.
However, variable and inconsistent data have raised questions about the reliability of the test methods applied. The current
study was conducted in two laboratories to develop, refine, and standardize procedures and protocols. Larvae were exposed
in flow-through systems to 17β-estradiol (E2), at concentrations from 0.2 to 6.0 μg E2 L−1 in Experiment 1A, and 0.015 to 2.0 μg E2 L−1 in Experiment 1B. In both studies survival (92%, 99%) and percentage of animals that completed metamorphosis (97%, 99%) indicated
reproducible biological performance. Furthermore, minor variations in husbandry led to significant differences in snout-to-vent
length, weight, and gonad size. In Experiment 1A, almost complete feminization occurred in all E2 treatment groups whereas
a concentration response was observed in Experiment 1B resulting in an EC50 of 0.12 μg E2 L−1. The final verified protocol is suitable for determining effects of EAC on development and sexual differentiation in X. laevis. 相似文献
9.
Myung Jun Kim Mutya A. Cruz Feichen Yang Benjamin J. Wiley 《Current Opinion in Electrochemistry》2019
Scalable, solution-phase syntheses of metal nanowires are enabling their increased use in electrochemical processes. This review highlights recent results demonstrating how metal nanowires can exhibit better durability and higher activity than traditional metal nanoparticle electrocatalysts on carbon supports. Metal nanowires can also form interconnected two-dimensional and three-dimensional (3D) networks that eliminate the need for a carbon support, thus eliminating the detrimental effects of carbon corrosion. Porous 3D networks of nanowires can be used as flow-through electrodes with the highest specific surface areas and mass transport coefficients obtained to date, enabling dramatic increases in the productivity of electrochemical reactions. Nanowire networks are also serving as 3D current collectors that improve the capacity of batteries. The tunable surface structure and dimensions of metal nanowires offer researchers a new opportunity to create electrodes that are tailored from the atomic scale to the microscale to improve electrochemical performance. 相似文献
10.
E. Beinrohr 《Accreditation and quality assurance》2001,6(7):321-324
The possibility of calibration-less determination of trace concentrations of some electrochemically active elements such as
Ag, As, Cd, Hg, Pb, etc. by flow-through coulometry is described. The analyte species are collected quantitative-ly from the
flowing sample solution on a porous working electrode made of vi- treous carbon particles set at either a constant potential
or constant current. The deposit is stripped by a constant current in the next step and the correspond- ing electrical charge
is measured and evaluated. The analyte concentration is calculated by making use of the com- bined Faraday’s laws of electrolysis.
The method exerts detection limits about 1 μg/l or lower and a linear concentration range over 3 orders of magnitude. 相似文献