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691.
Bicchi C Cordero C Liberto E Sgorbini B Rubiolo P 《Journal of chromatography. A》2007,1152(1-2):138-149
This article evaluates the HS-SPME recovery repeatability, intermediate precision and their performance over time when applied to HS-SPME sampling for quality control of medicinal and aromatic plants. Experiments were carried out on two sets of fibres coated with two different coatings and belonging to different lots (i.e 100 microm polydimethylsyloxane (PDMS) and Carboxen/divinylbenzene/PDMS 50/30 microm, l: 1 cm (CAR/DVB/PDMS)) and on chamomile (Matricaria chamomilla L.), sage (Salvia lavandulifolia Vahl.) and a standard solution containing 3-hexanol, isoamyl acetate, 1,8-cineole and menthol in diisobutyl phthalate. The performance of each set of fibres was evaluated by determining a group of complementary statistical parameters including: (i) repeatability of the absolute areas of each marker from each matrix with each fibre; (ii) intra-fibre repeatability of the total absolute areas of the markers of each matrix obtained with each fibre of each set; (iii) inter-fibre intermediate precision of the total absolute areas of the markers of each matrix obtained with all fibres of each set; and (iv) analysis of variance by one-way ANOVA with Fisher and Tukey tests. The influence of the number of analyses on fibre effectiveness (fibre life-time) was studied by linear regression analysis (LRA). The results proved that HS-SPME can successfully be used for routine control analysis of aromatic ad medicinal plants since both types of fibres showed good repeatability and intermediate precision of analytes recovery and consistency over time. Unlike data previously reported by other authors, CAR/DVB/PDMS coated fibres gave better results than those coated with PDMS. The fibre-life seemed mainly to be influenced by the number and conditions of samplings and nature of the matrix investigated. 相似文献
692.
Patrizia Beraldi Antonio Violi Nadia Scordino Nicola Sorrentino 《Applied Mathematical Modelling》2011,35(8):3980-3990
This paper addresses the problem faced by a large electricity consumer in determining the optimal procurement plan over a short-term time horizon. The inherent complexity of the problem, due to its dynamic and stochastic nature, is dealt by means of the stochastic programming modeling framework. In particular, a two-stage problem is formulated with the aim of establishing the optimal amount of electricity to be purchased through bilateral contracts and in the Day-Ahead Electricity Market. Recourse actions are used to hedge against uncertainty related to future electricity prices and consumer’s needs. The optimal plan is defined so to minimize the overall cost and to control risk, which is measured in the form of violation of budget constraints. The stochastic model is dynamically solved in a rolling horizon fashion by iteratively considering more and more recent information and a planning horizon of decreasing length. Extensive numerical experiments have been carried out to assess the performance of the proposed dynamic decision approach. The results collected considering a real test case are very encouraging and provide evidence of the superiority of the approach also in comparison with other alternative procurement strategies. 相似文献
693.
Ciminiello P Dell'Aversano C Dello Iacovo E Fattorusso E Forino M Tartaglione L Rossi R Soprano V Capozzo D Serpe L 《Analytical and bioanalytical chemistry》2011,401(3):1043-1050
Blooms of Ostreopsis spp. have been recently reported along the Mediterranean coasts of Spain, France, Italy, and Greece posing serious risks
to human health. Occurrence of Ostreopsis spp. may result in palytoxin contamination of seafood and, in order to prevent sanitary risks, the need exists to develop
efficient extraction procedures to be coupled to rapid and sensitive monitoring methods of palytoxin-like compounds in seafood.
In the present study, the best conditions for both extraction of palytoxin from seafood and palytoxin quantification by using
liquid chromatography tandem mass spectrometry (LC-MS/MS) were investigated. Three seafood matrices (mussels, sea-urchins,
and anchovies) were selected and five different extraction systems were tested, namely: the official protocol for extraction
of lipophilic toxins and various aqueous methanol or acetonitrile solutions (MeOH/H2O 1:1, MeOH/H2O 8:2, MeCN/H2O 8:2 and MeOH 100%). Extraction with MeOH/H2O 8:2 provided the best results in terms of accuracy and matrix interference on LC-MS/MS detection of palytoxin. Accuracy
and intra-day reproducibility (n = 3) were evaluated for all the selected matrices but only for mussels at three spiking concentration levels, including the
provisional limit proposed by the Community Reference Laboratory for marine biotoxins (250 μg kg−1). Limits of quantitation of palytoxin in mussels, sea-urchins and anchovies tissues were calculated using matrix-matched
standards; taking into account extraction efficiency of MeOH/H2O 8:2, they resulted to be 228, 343, and 500 μg kg−1, respectively. 相似文献
694.
De Paoli P Isse AA Bortolamei N Gennaro A 《Chemical communications (Cambridge, England)》2011,47(12):3580-3582
The kinetics of activation of RX by a Cu(I) complex has been investigated in MeCN both in the absence and presence of halide ions. The system Cu(I)/L/X(-) (L = Me(6)TREN) is mainly composed of Cu(I)L(+), XCu(I)L and Cu(I)X(2)(-), but only Cu(I)L(+) is found to be an active catalyst reacting with RX. 相似文献
695.
696.
Patrizia Stefanelli Tiziana Generali Silvana Girolimetti Danilo Attard Barbini 《Accreditation and quality assurance》2013,18(4):313-322
The implementation of the internal quality assurance program allows for demonstration of the performance characteristics of a method, as well as the avoidance of erroneous results. There is increasing concern in testing laboratories to ensure that the analytical process remains stable, giving reliable results under statistical control. Robustness is tested by introducing variations in experimental conditions and examining the effects on the results. The European document SANCO/12495/2011, “Method validation and quality control procedures for pesticide residue analysis in food and feed”, defines robustness as a parameter that can be derived from ongoing method verification. Internal quality control tools, such as the recovery control chart, were employed in this study to enhance the stability of the recovery rates and to investigate the experimental conditions that have a major influence on the quantification of recovery rates. The method investigated in this study permitted us to investigate eighteen pesticides in olive oil by using a gas chromatography–mass spectrometry technique. This method has been accredited to ISO/IEC 17025:2005 standards and was applied for 1 year in routine conditions for pesticide residues at the Italian National Reference Laboratory. The recovery control chart has showed that all recovery rates for 1 year were close to the maximum limit (120 %) of recovery performance criteria. Consequently, a “positive” bias has affected all data over longer periods of time. A robustness test was planned in order to investigate the grounds that most influenced the variability of the results. The robustness test involved the following three parameters: solvent used to dissolve the final extract, internal standards, and type of olive oil. 相似文献
697.
Dr. Simona Rizzo Prof. Tiziana Benincori Dr. Valentina Bonometti Dr. Roberto Cirilli Prof. Patrizia R. Mussini Prof. Marco Pierini Dr. Tullio Pilati Prof. Francesco Sannicolò 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):182-194
A series of tris‐aryl phosphanes, structurally designed to exist as residual enantiomers or diastereoisomers, bearing substituents differing in size and electronic properties on the aryl rings, were synthesized and characterized. Their electronic properties were evaluated on the basis of their electrochemical oxidation potential determined by voltammetry. The configurational stability of residual phosphanes, evaluated by dynamic HPLC on a chiral stationary phase or/and by dynamic 1H and 31P NMR spectroscopy, was found to be rather modest (barriers of about 18–20 kcal mol?1), much lower than that shown by the corresponding phosphane oxides (barriers of about 25–29 kcal mol?1). For the first time, the residual antipodes of a tris‐aryl phosphane were isolated in enantiopure state and the absolute configuration assigned to them by single‐crystal anomalous X‐ray diffraction analysis. In this case, the racemization barrier could be calculated also by CD signal decay kinetics. A detailed computational investigation was carried out to clarify the helix reversal mechanism. Calculations indicated that the low configurational stability of tris‐aryl phosphanes can be attributed to an unexpectedly easy phosphorus pyramidal inversion which, depending upon the substituents present on the blades, can occur even on the most stable of the four conformers constituting a single residual stereoisomer. 相似文献
698.
Alberto Cassol Plinio Di Bernardo Pier Luigi Zanonato Sergio Tamburini Patrizia Tomasin Pietro Alessandro Vigato 《Supramolecular chemistry》2013,25(3):469-488
Abstract The asymmetric compartmental macrocycles containing one N2O2 or N3O2 Schiff base and one O2O3 or O2O4 crown-ether like chamber, have been obtained by condensation reaction of the formyl precursors 3,3′-(3-oxapentane-1, 5-diyldioxy) bis (2-hydroxybenzaldehyde) or 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)-bis(2-hydroxybenzaldehyde) with ethyl ethylenediamine (H2LA, H2LC), 1,5-diamino-3-azamethylpentane(H2LB, H2LD), also in the presence of metal ions as templating agents. These ditopic ligands, with dissimilar coordination sites, have been designed and used for the selective complexation of “d” and/or “s” metal ions, respectively into the Schiff base and the crown ether chamber. The selectivity of these processes strongly depends on the size and on the donor atom sets of the sites. The possibility to obtain mononuclear M(L)·nH2O (M = Ni2+, Cu2+, Co2+), Mn(L)(CH3COO)·nH2O or Na(L) and hetero-dinuclear MNa(L)(CH3COO) (M = Ni2+, Cu2+, Co2+) and MnNa(L)(CH3COO)2·nH2O complexes has been successfully tested. The ligands and complexes have been characterized by ir, nmr, mass spectrometry and magnetic susceptibility measurements. Two of the ligands used for the preparation of the solid samples, i.e., to H2LA and H2LB, have been employed to study complexation reactions of Co(II) and Na(I) in solution. In order to obtain information on the ligand preorganization effect toward the complex stabilities, a simpler open chain parent compound of H2LB (H2LE) has been also prepared and studied. FT-IR spectra show that H2LA is unable to complex Na+ in DMSO while the complexation reactions of Na+ by H2LB and of Co2+ by H2LA take place with slow kinetics. Therefore, thermodynamic data have been obtained only for the systems Co2+/H2LB and Co2+/H2LE. The thermodynamic parameters obtained for the complexation reactions show that the pre-organization of the donor atoms in H2LB does not add a significant contribution to the stabilities of the complexes. Both H2LB and H2LE form in DMSO 1:1, 1:2 and 1:3 = M:L complexes with very similar stabilities and almost equal enthalpies of formation. Physico-chemical studies suggest besides that the slow reaction of Na+ with H2LB is probably due to the formation of a 1:1 complex where the metal cation, initially occupying the O3 cage of the ligand, slowly binds also the oxygens of the phenolic moieties. Spectral and calorimetric data on solutions containing H2LB and different Co2+: Na+ ratios evidence that in DMSO no stable heterodinuclear complexes form when the neutral ligand is considered. 相似文献
699.
Caracciolo G Pozzi D Capriotti AL Cavaliere C Foglia P Amenitsch H Laganà A 《Langmuir : the ACS journal of surfaces and colloids》2011,27(24):15048-15053
The concept that the effective unit of interest in the cell-nanomaterial interaction is the particle and its corona of associated proteins is emerging. Here we investigate the compositional evolution of the protein corona of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) cationic liposomes (CLs) and DOTAP/DNA lipoplexes over a wide range of plasma concentrations (2.5-80%). The composition of the hard corona of lipoplexes is quite stable, but that of CLs does evolve considerably. We show that the protein corona of CLs is made of both low-affinity and competitive-binding proteins whose relative abundance changes with the plasma concentration. This result may have deep biological implications for the application of lipid-based gene vectors both in vitro and in vivo. 相似文献
700.
Daniela Cupelli Fiore P. Nicoletta Giovanni De Filpo Patrizia Formoso Giuseppe Chidichimo 《Journal of Polymer Science.Polymer Physics》2011,49(4):257-262
The development of electrically activated chromogenic materials is important for their potential applications in smart windows. Several previous works have reported on reverse mode operation polymer dispersed liquid crystals (PDLCs) based on negative dielectric anisotropy liquid crystals. They have a transparent OFF state, which turns opaque after the application of a suitable external electric field. Nevertheless, these devices have some limitations such as the use of large amount of expensive liquid crystals with peculiar physical‐chemical properties. In addition, a good matching between the refractive index of liquid crystal and the polymer matrix one is required. The main result of this work is the achievement of reverse mode operation devices prepared with a positive dielectric anisotropy liquid crystal and characterized by a high OFF state transmittance obtained by the onset of high intensity built‐in DC electric fields in a direct mode operation PDLC, which allows the OFF state homeotropic alignment of liquid crystal directors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献