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排序方式: 共有124条查询结果,搜索用时 31 毫秒
31.
Carlos M. C. Infante Vitória R. B. Soares Mauro Korn Fábio R. P. Rocha 《Mikrochimica acta》2008,161(1-2):279-283
A flow system designed with solenoid micro-pumps is introduced for spectrophotometric determination of total tannins based
on the Folin– Denis reaction. The procedure minimizes the main drawbacks related to the AOAC batch procedure, i.e. interferences
from reducing species in the samples, high reagent consumption and waste generation, and low sampling rate. Linear response
was observed for tannic acid concentrations in the range 2–100 mg L−1, with a detection limit (99.7% confidence level) of 0.3 mg L−1. The sampling rate and coefficient of variation (n = 10) were estimated as 75 measurements per hour and 1.1%, respectively. Results of determination of total tannin in tea,
beer and wine samples were in agreement with those achieved by the batch reference procedure at the 95% confidence level.
In comparison to the batch procedure, the reagent consumption and effluent generation were 83 and 60-fold lower, respectively.
Correspondence: Fábio R. P. Rocha, Instituto de Química, Universidade de S?o Paulo, PO Box 26077, S?o Paulo, 05513-970 SP,
Brazil 相似文献
32.
33.
Some Factors Affecting the Molecular Weight Distribution (MWD) in Low Density Polyethylene Multizone Autoclave Polymerization Reactors
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35.
Luciana B. O. dos Santos Carlos M. C. Infante Jorge C. Masini 《Journal of separation science》2009,32(4):494-500
This paper describes the development of a sequential injection chromatography (SIC) procedure for separation and quantification of the herbicides simazine, atrazine, and propazine exploring the low backpressure of a 2.5 cm long monolithic C18 column. The separation of the three compounds was achieved in less than 90 s with resolution >1.5 using a mobile phase composed by ACN/1.25 mmol/L acetate buffer (pH 4.5) at the volumetric ratio of 35:65 and flow rate of 40 μL/s. Detection was made at 223 nm using a flow cell with 40 mm of optical path length. The LOD was 10 μg/L for the three triazines and the quantification limits were of 30 μg/L for simazine and propazine and 40 μg/L for atrazine. The sampling frequency is 27 samples per hour, consuming 1.1 mL of ACN per analysis. The proposed methodology was applied to spiked water samples and no statistically significant differences were observed in comparison to a conventional HPLC–UV method. The major metabolites of atrazine and other herbicides did not interfere in the analysis, being eluted from the column either together with the unretained peak, or at retention times well‐resolved from the studied compounds. 相似文献
36.
Rosa M Rosa Infante M Miguel Mda G Lindman B 《Langmuir : the ACS journal of surfaces and colloids》2006,22(13):5588-5596
Mixed catanionic surfactant systems based on amino acids were investigated with respect to the formation of liquid crystal dispersions and the stability of the dispersions. The surfactants used were arginine-N-lauroyl amide dihydrochloride (ALA) and N(alpha)-lauroyl-arginine-methyl ester hydrochloride (LAM), which are arginine-based cationic surfactants; sodium hydrogenated tallow glutamate (HS), a glutamic-based anionic surfactant; and the anionic surfactants sodium octyl sulfate (SOS) and sodium cetyl sulfate (SCS). It is demonstrated that in certain ranges of composition there is a spontaneous formation of vesicular, cubic, and hexagonal structures. The solutions were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and turbidity measurements. Vesicles formed spontaneously and were found for all systems studied; their size distribution is presented for the systems ALA/SCS/W and ALA/SOS/W; they are all markedly polydisperse. The aging process for the system ALA/SOS/W was monitored both by turbidity and by cryo-TEM imaging; the size distribution profile for the system becomes narrower and the number average radius decreases with time. The presence of dispersed particles with internal cubic structure (cubosomes) and internal hexagonal structure (hexosomes) was documented for the systems containing ALA and HS. The particles formed spontaneously and remained stably dispersed in solution; no stabilizer was required. (Cubosome and hexosome are USPTO registered trademarks of Camurus AB, Sweden.) The spontaneous formation of particles and their stability, together with favorable biological responses, suggests a number of applications. 相似文献
37.
A multiplex-polymerase chain reaction (PCR) system was developed for the authentication of the mackerel Scomber colias in commercial canned products. This novel method consists of an S. colias-specific fragment [159 base pairs (bp)] located in the nontranscribed spacer (NTS) sequence, and a Scomber genus-specific PCR product in the 5S rRNA gene (196-201 bp) as a positive amplification control. The system was assayed using 18 different canned products labeled as S. colias. A positive identification was made in all but one sample, revealing this methodology as a potential molecular tool for direct application in the authentication of S. colias canned products. 相似文献
38.
Velasco E Infante M Durán M Esteban-Cardeñosa E Lastra E García-Girón C Miner C 《Electrophoresis》2005,26(13):2539-2552
Mutational analysis of large multiexon genes without prevalent mutations is a laborious undertaking that requires the use of a high-throughput scanning technique. The Human Genome Project has enabled the development of powerful techniques for mutation detection in large multiexon genes. We have transferred heteroduplex analysis (HA) by conformation-sensitive gel electrophoresis of the two major breast cancer (BC) predisposing genes, BRCA1 and BRCA2, to a multicapillary DNA sequencer in order to increase the throughput of this technique. This new method that we have called heteroduplex analysis by capillary array electrophoresis (HA-CAE) is based on the use of multiplex-polymerase chain reaction (PCR), different fluorescent labels and HA in a 16-capillary DNA sequencer. To date, a total of 114 different DNA sequence variants (19 insertions/deletions and 95 single-nucleotide substitutions - SNS) of BRCA1 and BRCA2 from 431 unrelated BC families have been successfully detected by HA-CAE. In addition, we have optimized the multiplex-PCR conditions for the colorectal cancer genes MLH1 and MSH2 in order to analyze them by HA-CAE. Both genes have been amplified in 13 multiplex groups, which contain the 35 exons, and their corresponding flanking intronic sequences. MLH1 and MSH2 have been analyzed in nine hereditary nonpolyposis colorectal cancer patients, and we have found six different DNA changes: one complex deletion/insertion mutation in MLH1 exon 19 and another five SNS. Only the complex mutation and one SNS may be classified as cancer-prone mutations. Our experience has revealed that HA-CAE is a simple, fast, reproducible and sensitive method to scan the sequences of complex genes. 相似文献
39.
In this paper we investigate the existence of multiple nontrivial solutions of a nonlinear heat flow problem with nonlocal boundary conditions. Our approach relies on the properties of a vector field on the phase plane and utilizes Sperner’s Lemma, combined with the continuum property of the solutions funnel. 相似文献
40.
Morán MC Pinazo A Clapés P Infante MR Pons R 《The journal of physical chemistry. B》2005,109(48):22899-22908
Monoacylglycerol amino acid conjugates constitute a novel class of specific biocompatible surfactants that can be considered analogues to partial glycerides and lysophospholipids. They consist of one aliphatic chain and one polar head, i.e., the amino acid, linked through a glycerol moiety. In a previous work, we synthesized monolauroylated amino acid glyceride conjugates, 1-O-lauroyl-rac-glycero-3-O-(N(alpha)-acetyl-L-amino acid), changing the amino acid headgroup systematically: arginine (compound 2), aspartic acid (compound 3), glutamic acid (compound 4), asparagine (compound 5), glutamine (compound 6), and tyrosine (compound 7), to elucidate the structure-properties relationship governing the occurrence of their polymorphism. The thermotropism of the new compounds was measured with polarizing light microscopy, differential scanning calorimetry, and X-ray diffraction and compared with the classical monoglyceride rac-1-lauroylglycerol (compound 1). The experiments were performed for a sequence of heating, cooling, and reheating scans. The results showed that compounds 1-6 exhibit a thermotropic smectic phase. As a consequence, the substitution of the polar head did not engender any curvature into the system, which might lead to the formation of cubic or columnar phases. Interestingly, liquid crystalline phases were not found in the case of compound 7. Small-angle X-ray diffraction data in the gel phase revealed that the substitution of the polar head by the different amino acid structures did not modify significantly the lamellar repeat distance relative to that of the reference one. The observed area per molecule, however, was larger for the new compounds. Consequently, interdigitation was promoted in compounds 2-7. The diffraction patterns were analyzed in terms of electron density profiles, using a modified Caillé theory plus a Gaussian electron density representation (MCG method) on X-ray diffraction data. 相似文献