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131.
An efficient synthesis of 3-amino-1H,3H-quinazolinedione by the action of hydrazine on the readily accessible 3-phenyl-2,4(1H,3H)-quinazolinedione and 2-anilino-4H-3,1-benzoxazin-4-one are described. 相似文献
132.
Nashwa M. El-Metwally Issam M. Gabr Ahmed A. El-Asmy Azza A. Abou-Hussen 《Transition Metal Chemistry》2006,31(1):71-78
Mono- and binuclear complexes of malonyl bis(thiosemicarbazide), H4 MBT, with VO2+, Co2+, Ni2+, Cu2+, Cd2+ and Pt4+ have been isolated. The elemental analyses, magnetic moments, spectra [u.v.–vis., i.r., e.s.r. (for Cu2+; VO2+) and mass], thermal and voltammetric measurements [for Co2+ and Ni2+] have been used to characterize the isolated complexes. The ligand behaves as binegative quadridentate with Cu2+, Co2+ and VO2+ ions, binegative pentadentate with Pt4+ and hexadentate, either as trinegative in [Cd2(HMBT)(OC2H5)(C2H5OH)]H2O or mononegative in [Ni2(H3MBT)(OAc)3(C2H5OH)]. The lack of thiol and/or enol hydrogen during the complex formation was confirmed pH-metrically. The pK’s (10.70, 8.50 and 8.15) of H4MBT reveal the removal of CSNH protons in one step and CONH in two steps. Also, the stability constants reveal a higher value
for the Cu2+ complex and a lower one for VO2+. The TG analyses suggest high stability for most complexes followed by thermal decomposition in different steps. The kinetic
and thermodynamic parameters for some decomposition steps in VO2+and Pt4+ thermograms have been calculated 相似文献
133.
The thermal transformation of goethite to hematite and the temperature dependence of the degree of crystallinity have been
investigated using transmission and diffraction electron microscopy and infrared spectroscopy.
The electron microscopy results reveal that the treatment of natural goethite by NaOH or citrate dithionite-bicarbonate (CDB)
has no effect on its structure but leads to increase in the crystallinity of the ore. On the other hand, heat treatment of
the untreated or treated sample is found to convert goethite ore to hematite with increase in its crystallinity. An infrared
spectroscopic technique is applied for quantitative calculation of the crystallinity changes. 相似文献
134.
A selective, precise, and accurate method was developed for the determination of cimetidine (C), famotidine (F), and ranitidine hydrochloride (R x HCl) in the presence of their sulfoxide derivatives. The method involves quantitative densitometric evaluation of mixtures of the drugs and their derivatives after separation by high-performance thin-layer chromatography on silica gel plates (10 x 20 cm) with ethyl acetate-isopropanol-20% ammonia (9 + 5 + 4, v/v) as the mobile phase for both C and F and ethyl acetate-methanol-20% ammonia (10 + 2 + 2, v/v) as the mobile phase for R x HCl; Rf values for C, F, and R x HCl and their corresponding derivatives were 0.85 and 0.59, 0.73 and 0.41, and 0.56 and 0.33, respectively. Developing time was approximately 20 min. For densitometric evaluation, peak areas were recorded at 218, 265, and 313 nm for C, F, and R x HCl, respectively. The relationship between concentration and the corresponding peak area was plotted for the ranges of 5-50 microg/spot for C and 2-20 microg/spot for F and R x HCl. Mean recoveries were 100.39 +/- 1.33, 99.77 +/- 1.30, and 100.09 +/- 0.69% for C, F, and R x HCl, respectively. The proposed method was used successfully for stability testing of the pure drugs in the presence of up to 90% of their degradates, in bulk powder and dosage forms. The results obtained were analyzed statistically and compared with those obtained by the official methods. 相似文献
135.
The electrochemical corrosion behavior of the non‐precious Ni‐Cr Wirolloy, being used in dentistry, was investigated before and after applying of two types of eco‐friendly coatings, polyvinyl silsesquioxane (PVS) and nano‐hydroxyapatite (nHAP) separately in artificial saliva solution at 37 °C for 14 d of immersion. The study aimed to investigate the effectiveness of the introduced coating films in enhancing the corrosion resistance of the alloy, and in decreasing the leaching of the toxic Ni ions from the alloy into the environment. The electrochemical corrosion investigation methods used are; open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The evaluated results revealed that the electrochemically coated alloy with PVS. prepared at cathodic potential showed higher corrosion resistance and more stable film compared to that prepared by conventional dip‐coating method. At the same time, the nHAP electrochemically coated film provided the best anti‐corrosion properties over all examined time intervals. The obtained results were confirmed via surface analysis, which assured the formation of the prepared coatings on the alloy surface. Chemical analysis of the corrosion product/solutions showed that the effect of electrochemically deposited nHAP and PVS. polymer films in suppression of Ni ions leaching is similar and slightly higher than that of the chemically coated PVS. one; however, all of them are efficient in decreasing the leaching of the risky Ni ions into the solution. 相似文献
136.
Robert Y Xie Victor P.Y Gadzekpo Azza M Kadry Yehia A Ibrahim Jaromir Růžička Gary D Christian 《Analytica chimica acta》1986
A flow-injection system based on microconduits is used to investigate electrode characteristics such as selectivity, detection limit, and response and equilibrium times of the new ionophore, N,N,N′,N′-tetraisobutyl-5,5-dimethyl-3,7-dioxanonane diamide, in lithium ion-selective electrodes. These characteristics were compared with those of the ionophore N,N′-diheptyl-N,N′,5,5-tetramethyl-3,7-dioxanone diamide. The new ionophore has superior detection limits and shorter response and equilibrium time, but the other exhibits better selectivity for lithium with respect to sodium. Values of KPotLiNa for the new ionophore vary from 0.0450 to 0.566, depending on the methods of measurement and solution conditions. This phenomenon is discussed. Stop-flow experiments effectively demonstrated the response and equilibrium time differences between these two ionophore membranes. 相似文献
137.
Non‐isothermal studies by means of thermogravimetric (TG) measurements were carried out using a derivatograph to obtain the number of water molecules per repeat unit of yeast ribonucleic acid (RNA) before and after exposure to γ‐doses of 3 to 600 Gray. IR spectroscopy was utilized to determine which molecular subgroups of RNA adsorb water molecules and to investigate the conformational changes produced in RNA after γ‐irradiation. γ‐Irradiation was found to lead to ring opening or bond cleavage per unit nucleotide, which results in the formation of crosslinked regions (increase in molecular size). Such cleavage becomes more pronounced at doses >300 Gy leading to an increase in the number of water molecules per repeat unit and a decrease in molecular weight (degradation effect). A γ‐dose of 300 Gy may be considered as a critical damaging dose for yeast RNA molecules. 相似文献
138.