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排序方式: 共有163条查询结果,搜索用时 31 毫秒
41.
Ahmed Mohammed M. Houssein Essam H. Hassanien Aboul Ella Taha Ayman Hassanien Ehab 《Telecommunication Systems》2019,72(2):243-259
Telecommunication Systems - The sink nodes in large-scale wireless sensor networks (LSWSNs) are responsible for receiving and processing the collected data from sensor nodes. Identifying the... 相似文献
42.
Rustem R. Amirov Asiya R. Mustafina Zuleikha T. Nugaeva Svetlana V. Fedorenko Ella Kh. Kazakova Alexandr I. Konovalov Wolf D. Habicher 《Journal of inclusion phenomena and macrocyclic chemistry》2004,49(3-4):203-209
The stoichiometry and binding constant of the paramagnetic lanthanide ion(Gd3+) with sulfonatomethylated calix[4]resorcinarene (H8Xna4) were evaluated from the NMR relaxation data. Both 1H NMR spectroscopy and NMR relaxation data indicate that interaction of tetramethylammonium (TEMA) and N-methylpyridinium (MePy) cations with H8Xna4 in the presence of Ln3+ (Lu3+ or Gd3+) results in theformation of ternary complexes [Ln(G)H8X] with lanthanide ions,coordinated via sulfonate groups and organic cation included intothe cavity of H8Xna4. The inclusion of long-chainedN-decyl-(DePy) and N-cetylpyridinium (CPy) ions into H8Xna4 cavity leads to self-assembling which can be revealed by NMR relaxation method with Gd3+ probe ions. The excess of alkylpyridinium or TEMA cations leads to disassembling of (Gd)n(H8X)m(RPy)maggregates. 相似文献
43.
Noha A. K. Aboul‐Gheit 《中国化学会会志》2007,54(5):1211-1222
Cyclohexene (CHE) hydroconversion was performed in a flow reactor at atmospheric pressure and temperatures of 50–400 °C using: Pd/H‐ZSM‐5, Pd/H‐ZSM‐5(HCl), and Pd/H‐ZSM‐5(HF) catalysts. These catalysts were characterized for acid site strength distribution via NH3 TPD, Pd dispersion via H2 chemisorption, TPR via reduction of the metal oxide in the catalysts and XRD for tracing crystallinity The hydroconversion steps proceeded as follows: CHE → Cyclohexane (CHA); CHE → Methylcyclopentenes (MCPEs) → Methylcyclopentane (MCPA); CHE → Cyclohexadienes (CHDEs) → Benzene → Alkylbenzenes; CHE and others → Hydrocrackedproducts. The overall hydroconversion of CHE was achieved in the catalyst order: Pd/H‐ZSM‐5 > Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). CHE hydrogenation step was the major reaction at low temperatures which significantly inhibited via HCl treatment, but slightly enhanced via HF treatment. At medium temperatures, on all catalysts, isomerisation to MCPEs and MCPA increase to a maximum then a decline with a further increase of temperature. The overall isomerisation of CHE was highest on the untreated catalyst. During the higher temperature range, dehydrogenation, alkylation and hydrocracking were increased with temperature. Dehydrogenation of CHE always yielded larger amounts of 1,3‐CHDE than 1,4‐CHDE. These cyclohexadienes were produced in the catalyst order: Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5. In general, benzene alkylation to toluene exceeded that of xylenes, indicating that the second methylation is more difficult than the first. However, the catalytic activities for benzene and toluene production were in the order: Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5(HF), whereas for xylenes production, Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). Intrapore diffusion plays an important role during the dehydrogenation reactions as well as during the interconversion of individual aromatic hydrocarbons. 相似文献
44.
Khaldun M. Al Azzam Bahruddin Saad Hassan Y. Aboul‐Enein 《Biomedical chromatography : BMC》2010,24(9):948-953
Capillary zone electrophoresis coupled with a capacitively coupled contactless conductivity detector (CE‐C4D) has been employed for the determination of atenolol and amiloride in pharmaceutical formulations. Acetic acid (150 mm ) was used as background electrolyte. The influence of several factors (detector excitation voltage and frequency, buffer concentration, applied voltage, capillary temperature and injection time) was studied. Non‐UV‐absorbing L‐valine was used as internal standard; the analytes were all separated in less than 7 min. The separation was carried out in normal polarity mode at 28°C, 25 kV and using hydrodynamic injection (25 s). The separation was effected in an uncoated fused‐silica capillary (75 μm, i.d. × 52 cm). The CE‐C4D method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 5–250 μg/mL for the studied analytes. The relative standard deviations of intra‐ and inter‐day migration times and corrected peak areas were less than 6.0%. The method showed good precision and accuracy and was successfully applied to the simultaneous determination of atenolol and amiloride in different pharmaceutical tablet formulations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
45.
Albina Y. Ziganshina Sergey V. Kharlamov Dmitry E. Korshin Rezeda K. Mukhitova Ella Kh. Kazakova Shamil K. Latypov Vitaly V. Yanilkin Alexandr I. Konovalov 《Tetrahedron letters》2008,49(36):5312-5315
A new molecular capsule based on viologen-resorcinarene and sulfonatomethylene-resorcinarene is synthesized and its redox-controlled stability is investigated. 相似文献
46.
Vitamin K is an essential micronutrient required for blood coagulation, regulation of vascular calcification and bone mineralization. Plasma and serum measurements of vitamin K1(phylloquinone, K1) made using high-performance liquid chromatography with fluorescence detection, or tandem mass spectrometry are used clinically and in population studies to assess vitamin K status. Standard reference materials provide a validation tool for laboratories, helping assure clinical diagnosis and the comparability of data from different populations. We manufactured two K1 standard reference materials, in 2009 (KEQAS SRM-001) and in 2019 (KEQAS SRM-002). The target concentrations of K1 were assigned to each SRM using the All Laboratory Trimmed Mean of results reported by selected laboratories enrolled in the Vitamin K External Quality Assurance Scheme (KEQAS). The assigned concentrations of K1 for KEQAS SRM-001 and SRM-002 were 0.25 and 0.36 μg/L respectively. In 2019 KEQAS SRM-001 was re-analysed simultaneously with KEQAS SRM-002 to provide traceability between the two standards, therefore aiding comparability of analysis performed using these materials. Both standards were stored as aliquots at −80°C in the dark; annual re-analysis of the materials indicated that K1 is stable for at least 12 years in these conditions. 相似文献
47.
Samir M. Osman Ahmed M. Abdel‐Megied Mohammed H. Zain Eldain Simimole Haleema Chithra Gopinath Sarojini Amma Sumalekshmy Hassan Y. Aboul‐Enein 《Biomedical chromatography : BMC》2019,33(11)
The commercial value of cashew nut shell liquid (CNSL) has become a cornerstone of the agrowaste industry. It is the by‐product of the cashew industry and has an 1/8 inch thickness of soft honeycomb structure. CNSL contains phenolic lipids with aliphatic chains such as anacardic acid, cardanol, cardol and methyl cardol, and their derivatives. The developed GC–MS method is rapid, accurate and selective using a selected derivatizing reagent, namely N‐methyl‐N‐(trimethylsilyl)‐trifluoroacetamide that was previously diluted 1:1% with anhydrous pyridine. The proposed GC–MS method was applied for the analysis of different CNSL samples. The results showed that all classes of CNSL compounds were detected. The four alkyl phenols were detected with their different alkyl sidechains without any interference. This method is also specified for the detection of fatty acids of saturated and unsaturated chains. Silylation did not cause any alteration in the chemical structure of CNSL compounds regardless of esterification action. Silylation is considered a safe derivatizing agent compatible with GC chromatography and specific for all volatile and nonvolatile polar and nonpolar CNSL compounds that could be detected in CNSL samples. 相似文献
48.
Khaldun M. Al Azzam Bahruddin Saad Hassan Y. Aboul‐Enein 《Biomedical chromatography : BMC》2010,24(9):977-981
Capillary zone electrophoresis methods for the simultaneous determination of the β‐blocker drugs, atenolol, chlorthalidone and amiloride, in pharmaceutical formulations have been developed. The influences of several factors (buffer pH, concentration, applied voltage, capillary temperature and injection time) were studied. Using phenobarbital as internal standard, the analytes were all separated in less than 4 min. The separation was carried out in normal polarity mode at 25°C, 25 kV and using hydrodynamic injection (10 s). The separation was effected in an uncoated fused‐silica capillary (75 μm i.d. × 52 cm) and a background electrolyte of 25 mm H3PO4 adjusted with 1 m NaOH solution (pH 9.0) and detection at 198 nm. The method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 1–250 μg/mL for atenolol and chlorthalidone and from 2.5–250 μg/mL for amiloride. The relative standard deviations of intra‐ and inter‐day migration times and corrected peak areas were less than 6.0%. The method showed good precision and accuracy and was successfully applied to the simultaneous determination of atenolol, chlorthalidone and amiloride in various pharmaceutical tablets formulations. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
49.
The selection of the optimal ensembles of classifiers in multiple-classifier selection technique is un-decidable in many cases and it is potentially subjected to a trial-and-error search. This paper introduces a quantitative meta-learning approach based on neural network and rough set theory in the selection of the best predictive model. This approach depends directly on the characteristic, meta-features of the input data sets. The employed meta-features are the degree of discreteness and the distribution of the features in the input data set, the fuzziness of these features related to the target class labels and finally the correlation and covariance between the different features. The experimental work that consider these criteria are applied on twenty nine data sets using different classification techniques including support vector machine, decision tables and Bayesian believe model. The measures of these criteria and the best result classification technique are used to build a meta data set. The role of the neural network is to perform a black-box prediction of the optimal, best fitting, classification technique. The role of the rough set theory is the generation of the decision rules that controls this prediction approach. Finally, formal concept analysis is applied for the visualization of the generated rules. 相似文献
50.
The significance of this research is the application of thin-layer chromatography (TLC) to fractionate well-characterized aquatic humic materials coupled with the novel evaluation of the trihalomethane formation potential (THMFP) of the fractionated materials. Disinfection by-products such as trihalomethanes (THMs) form when natural water is treated by chlorination. Nordic Aquatic and Suwannee River fulvic and humic acids, obtained from the International Humic Substances Society, were prepared at pH 6 and 9 and fractionated on silica gel plates using a mobile phase consisting of methanol and ethyl acetate (2:1, v:v). Based on retention factor (R(f)) values, three common fractions were identified in all substances examined. Additionally, other fractions were noted that were characteristic of specific humic substances. Each of the three primary fractions derived from Nordic Aquatic fulvic acid at pH 6 demonstrated the potential to contribute to formation of THMs. This research provides data to support the hypothesis that differences in the chemical structure and composition of natural organic matter (NOM) significantly affect the potential to react with chlorine to form THMs. 相似文献