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101.
Tijana?Raki? Sava?Vemi? Biljana?Jan?i?-Stojanovi?Email author Mirjana?Medenica 《Chromatographia》2013,76(5-6):267-277
This paper proposes an innovative concept for robustness evaluation guided by two crucial aims: indubitable identification of the factors that significantly affect the LC method and avoidance of unnecessary time and money wasting. The first phase of the proposed strategy includes robustness screening during the method optimization. Initial assumptions of the method robustness can be tracked as the rate of the response change while the factors deviate within the expected range. Therefore, partial and total robustness criteria are calculated. If the results obtained are not satisfactory, re-optimization of the method should be considered. Otherwise, extensive robustness testing defined by experimental design and multi-level factors estimation should be performed to confirm the method robustness. Firstly, the important factors are investigated by the standard graphical (normal probability plots) and statistical (algorithm of Dong and error estimation based on a priori declared negligible effects) procedures. Since these approaches have several drawbacks, they can result in the appearance of false negative or false positive results. Thus, the modification of the statistical tests is advised in order to make the final conclusions. Special attention was dedicated to the advantages of the adapted algorithm of Dong (so-called 75 % approach) in the absence of the effect sparsity. The new approach is presented on the optimization and robustness testing of LC method for determination of ramipril and its five impurities. It is proved that the proposed strategy can perform an overall robustness estimation and successfully reveal all important factors. 相似文献
102.
Biljana Škrbić Károly Héberger Nataša Đurišić-Mladenović 《Analytical and bioanalytical chemistry》2013,405(25):8363-8375
Sum of ranking differences (SRD) was applied for comparing multianalyte results obtained by several analytical methods used in one or in different laboratories, i.e., for ranking the overall performances of the methods (or laboratories) in simultaneous determination of the same set of analytes. The data sets for testing of the SRD applicability contained the results reported during one of the proficiency tests (PTs) organized by EU Reference Laboratory for Polycyclic Aromatic Hydrocarbons (EU-RL-PAH). In this way, the SRD was also tested as a discriminant method alternative to existing average performance scores used to compare mutlianalyte PT results. SRD should be used along with the z scores—the most commonly used PT performance statistics. SRD was further developed to handle the same rankings (ties) among laboratories. Two benchmark concentration series were selected as reference: (a) the assigned PAH concentrations (determined precisely beforehand by the EU-RL-PAH) and (b) the averages of all individual PAH concentrations determined by each laboratory. Ranking relative to the assigned values and also to the average (or median) values pointed to the laboratories with the most extreme results, as well as revealed groups of laboratories with similar overall performances. SRD reveals differences between methods or laboratories even if classical test(s) cannot. The ranking was validated using comparison of ranks by random numbers (a randomization test) and using seven folds cross-validation, which highlighted the similarities among the (methods used in) laboratories. Principal component analysis and hierarchical cluster analysis justified the findings based on SRD ranking/grouping. If the PAH-concentrations are row-scaled, (i.e., z scores are analyzed as input for ranking) SRD can still be used for checking the normality of errors. Moreover, cross-validation of SRD on z scores groups the laboratories similarly. The SRD technique is general in nature, i.e., it can be applied to any experimental problem in which multianalyte results obtained either by several analytical procedures, analysts, instruments, or laboratories need to be compared. Figure
Sum of ranking differences (SRD) order analytical methods or laboratories according to their overall (multianalyte) performances using either the average (or median) or the assigned values as the reference for the ranking 相似文献
103.
González-García J Drouin L Banks CE Sljukić B Compton RG 《Ultrasonics sonochemistry》2007,14(2):113-116
At point of use generation of synthetically useful quantities of hydrogen peroxide in a non-optimized sono-electrochemical cell is reported. Proof-of-concept of the use of this procedure for green synthesis is given through the oxidation of benzonitrile to benzamide with yields similar to those obtained via bulk chemical synthesis. 相似文献
104.
Influence of the aryl substituent identity in 4-arylamino-3-nitrocoumarins on their thermal behavior
Biljana Dekić Suzana Samaržija-Jovanović Vojislav Jovanović Vidoslav Dekić Niko Radulović Ranko Simonović Milena Marinović-Cincović 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1619-1626
Thermal behavior of structurally similar 4-arylamino-3-nitrocoumarin derivatives substituted with different electron-donor and electron-acceptor substituents on the aryl side group was investigated. The thermal stability of these compounds was studied by non-isothermal thermo-gravimetric analysis, differential thermo-gravimetry, differential thermal analysis, and pyrolysis–gas chromatography–mass spectrometry. The thermal degradation of the three synthesized 4-arylamino-3-nitrocoumarins, possessing an iodine atom, a nitro or a methyl group, proceeds in three steps. The thermal stability of the coumarin derivative with the electron-donating methyl substituent is lower than that of the compounds with the electron-accepting nitro group or iodine atom. This least stable compound (4-[(4-methylphenyl)amino]-3-nitro-2H-chromen-2-one) was also characterized with the greatest loss in mass that accompanied the degradation, and all of the three degradation steps of this compound began at the lowest temperature in comparison to the other two. 相似文献
105.
Interaction of an Nd:YAG laser, operating at 1064 or 532 nm wavelength and pulse duration of 40 ps, with titanium implant was studied. Surface damage thresholds were estimated to 0.9 and 0.6 J/cm2 at wavelengths 1064 and 532 nm, respectively. The titanium implant surface modification was studied by the laser beam of energy density of 4.0 and 23.8 J/cm2 (at 1064 nm) and 13.6 J/cm2 (at 532 nm). The energy absorbed from the Nd:YAG laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following titanium/implant surface morphological changes were observed: (i) both laser wavelengths cause damage of the titanium in the central zone of the irradiated area, (ii) appearance of a hydrodynamic feature in the form of resolidified droplets of the material in the surrounding outer zone with the 1064 nm laser wavelength and (iii) appearance of wave-like microstructures with the 532 nm wavelength. Generally, both laser wavelengths and the corresponding laser energy densities can efficiently enhance the titanium/implant roughness. This implant roughness is expected to improve its bio-integration. The process of the laser interaction with titanium implant was accompanied by formation of plasma. 相似文献
106.
Jovana Rosi? Biljana Petrovi? Milo? I. Djuran ?ivadin D. Bugar?i? 《Monatshefte für Chemie / Chemical Monthly》2007,12(8):1-11
Substitution reactions of the complexes [Pt(dien)H2O]2+ and [PtCl(dien)]+, where dien = diethylentriamine or 1,5-diamino-3-azapentane, with some nitrogen-donor ligands such as 1,2,4-triazole, pyrazole, and pyridazine,
were studied in an aqueous 0.10 M NaClO4 at pH = 2.5 using variable-temperature spectrophotometry and 1H NMR spectroscopy. The second-order rate constants indicate that the aqua complex, [Pt(dien)H2O]2+, is more reactive than the corresponding chloro complex, [PtCl(dien)]+. The reactivity of the used ligands follows the order: 1,2,4-triazole > pyridazine > pyrazole. Activation parameters were
determined for all reactions and the negative entropies of activation (ΔS
≠) support an associative ligand substitution mechanism. 相似文献
107.
Aleksandar Kremenovi Biljana Lazic Hannes Krüger Martina Tribus Predrag Vuli 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(4):334-336
Crystals of KAlSiO4‐O1 (potassium aluminium silicate) were synthesized using a flux method and analysed utilizing single‐crystal X‐ray diffraction and electron microprobe analysis. Both methods confirm that the crystals are nonstoichiometric according to K1−xAl1−xSi1+xO4 with x = 0.04 (1). KAlSiO4‐O1 is closely related to the stuffed derivatives of tridymite, although the topology of the Si/Al‐ordered framework is different. Six‐membered rings of UUDDUD and UUUDDD (U = up and D = down; ratio 2:1) configurations are present in layers parallel to the ab plane. In contrast, the framework of tridymite exhibits UDUDUD rings. The crystals are affected by inversion, pseudo‐orthorhombic and pseudo‐hexagonal twinning. 相似文献
108.
?eljka Ljuji? Camilo Sanabria 《Topology and its Applications》2011,158(8):1012-1018
Let K⊆R2 be a compact set such that K+Z2=R2 and let K−K={a−b|a,b∈K}. We prove, via Algebraic Topology, that the integer points of the difference set of K, (K−K)∩Z2, is not contained on the coordinate axes, Z×{0}∪{0}×Z. This result implies the negative answer to the inverse problem posed by M.B. Nathanson (2010) [5]. 相似文献
109.
Petrović B Bugarčić Ž Dees A Ivanović-Burmazović I Heinemann FW Puchta R Steinmann SN Corminboeuf C van Eldik R 《Inorganic chemistry》2012,51(3):1516-1529
The kinetics and mechanism of substitution reactions of novel monofunctional [Pt(tpdm)Cl](+) and [Pd(tpdm)Cl](+) complexes (where tpdm = tripyridinedimethane) and their aqua analogues with thiourea (tu), L-methionine (L-met), glutathione (GSH), and guanosine-5'-monophosphate (5'-GMP) were studied in 0.1 M NaClO(4) at pH = 2.5 (in the presence of 10 mM NaCl for reactions of the chlorido complexes). The reactivity of the investigated nucleophiles follows the order tu > l-met > GSH > 5'-GMP. The reported rate constants showed the higher reactivity of the Pd(II) complexes as well as the higher reactivity of the aqua complex than the corresponding chlorido complex. The negative values reported for the activation entropy as well as the activation volume confirmed an associative substitution mode. In addition, the molecular and crystal structure of [Pt(tpdm)Cl]Cl was determined by X-ray crystallography. The compound crystallizes in a monoclinic space group C2/c with two independent molecules of the complex and unit cell dimensions of a = 38.303(2) ?, b = 9.2555(5) ?, c = 27.586(2) ?, β = 133.573(1)°, and V = 7058.3(8) ?(3). The cationic complex [Pt(tpdm)Cl](+) exhibits square-planar coordination around the Pt(II) center. The lability of the [Pt(tpdm)Cl](+) complex is orders of magnitude lower than that of [Pt(terpyridine)Cl](+). Quantum chemical calculations were performed on the [Pt(tpdm)Cl](+) and [Pt(terpyridine)Cl](+) complexes and their reactions with thiourea. Theoretical computations for the corresponding Ni(II) complexes clearly demonstrated that π-back-bonding properties of the terpyridine chelate can account for acceleration of the nucleophilic substitution process as compared to the tpdm chelate, where introduction of two methylene groups prevents such an effective π-back bonding. 相似文献
110.
Tijana Raki Biljana Jan
i‐Stojanovi Andjelija Malenovi Darko Ivanovi Mirjana Medenica 《Journal of Chemometrics》2012,26(10):518-525
This paper presents a newly developed demasking large dummy effects (DDE) approach for identification of significant factor interactions in Plackett–Burman experimental design. Dummy factors, as imaginary factors, are not expected to contribute to the model, so the appearance of their high effect values could indicate the significance of the interactions they are confounded with. DDE approach consists of the screening of the large estimable effects, the calculation of the interactions that contribute the most to the large dummy effects from the alias matrix, and a single pass of all subsets regressions including preselected interactions and main factors for the final model tuning. Tested on experimentally obtained data from a robustness analysis of a method for the determination of raloxifene and its four impurities, DDE approach showed to create the models that have greater statistical power than the ones described with the main factors only, which makes them more reliable and accurate for the application. Additionally, because of the interactions selection criterion and final tuning phase of the strategy, DDE approach allows the creation of models that are likely to better describe the real systems, which increases the practical value. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献