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排序方式: 共有112条查询结果,搜索用时 10 毫秒
41.
Determination of ethoxylated bisphenol A dimethacrylate monomers in dental composites by micellar electrokinetic chromatography 总被引:1,自引:0,他引:1
Separation of monomeric constituents of ethoxylated bisphenol A (BIS-EMA) with between 2 and 15 ethoxy groups per phenol in the molecule was investigated with micellar electrokinetic chromatography at different volume percentages methanol in the background electrolyte (10 mM sodium dodecylsulfate, 100 mM borate–50 mM phosphate buffer, pH 7.0). The conditions allowed the differentiation of the lower from the higher BIS-EMA homologues and of isomers, and enabled the characterisation of commercial dental composite materials. The decay curve for the light induced radical polymerisation of BIS-EMA in composite specimens was determined. The content of leachable monomers after light curing was quantified, resulting in 6% of the initial value after the recommended curing time. The method is suited to determine monomer constituents in polymerised composite material in the ppm range. 相似文献
42.
G. Minero-Ramales D. López-Mancilla Carlos E. Castañeda G. Huerta Cuellar R. Chiu Z. J. Hugo García López R. Jaimes
Reátegui E. Villafaña Rauda C. Posadas-Castillo 《The European physical journal. Special topics》2016,225(13-14):2655-2667
This paper presents a novel electronic locking key based on discrete-time chaos synchronization. Two Chen chaos generators are synchronized using the Model-Matching Approach, from non-linear control theory, in order to perform the encryption/decryption of the signal to be transmitted. A model/transmitter system is designed, generating a key of chaotic pulses in discrete-time. A plant/receiver system uses the above mentioned key to unlock the mechanism. Two alternative schemes to transmit the private chaotic key are proposed. The first one utilizes two transmission channels. One channel is used to encrypt the chaotic key and the other is used to achieve output synchronization. The second alternative uses only one transmission channel for obtaining synchronization and encryption of the chaotic key. In both cases, the private chaotic key is encrypted again with chaos to solve secure communication-related problems. The results obtained via simulations contribute to enhance the electronic locking devices. 相似文献
43.
Luis M. Alonso Martínez Abmel Xiques Castillo Victoria N. Calzada Falcón Marylaine Pérez-Malo Cruz René Leyva Montaña Minely Zamora Barrabí Ignacio Hernández González Mariela León Pérez Alejandro Arbesú Valdivia 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(1):49-56
Concentration of activity of Cs-137 and its spatial distribution in soils and lichen Hypogymnia physodes were determined in the Gorce Mts. (several hundred km2) in S Poland. The authors distinguished two areas of the Gorce Mts. on the basis of markedly different Cs-137 depositions, whose respective average values are 4.4 and 9.9 kBq/m2 as at 1st July 2005. The average Cs-137 activity concentration in the lichen H. physodes from the Gorce is 47 Bq/kg d.m. A significant local variability of quantities measured amounts to a few dozen percent was found. 相似文献
44.
Pedro D. Vaz Dr. Mariela M. Nolasco Dr. Francisco P. S. C. Gil Dr. Paulo J. A. Ribeiro‐Claro Prof. John Tomkinson Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9010-9017
Spectroscopic evidence for C? H ??? O hydrogen bonding in chloroform ??? acetone [Cl3CH ??? O?C(CH3)2] mixtures was obtained from vibrational inelastic neutron scattering (INS) spectra. Comparison between the INS spectra of pure samples and their binary mixtures reveals the presence of new bands at about 82, 130 and 170 cm?1. Assignment of the 82 cm?1 band to the νO ??? H anti‐translational mode is considered and discussed. In addition, the βC? H mode of CHCl3 at 1242 cm?1 is split in the spectra of the mixtures, and the high‐wavenumber component is assigned to the hydrogen‐bonded complex. The plot of the integrated intensity of this component shows a maximum for x=0.5, in agreement with the 1:1 stoichiometry of the chloroform ??? acetone complex, with a calculated complexation constant of 0.15 dm3 mol?1. Results also show that the complex behaves as an independent entity, that is, despite being weak, such interactions play a key role in supramolecular chemistry. 相似文献
45.
Mariela M. Nolasco Ana M. Amado Paulo J. A. Ribeiro‐Claro 《Journal of Raman spectroscopy : JRS》2010,41(3):340-349
FT‐Raman spectroscopy turns out to be a powerful technique to evaluate the amount of polymorphic and pseudopolymorphic forms in crystalline samples—which is particularly relevant in pharmaceutical sciences. This paper presents a methodology that allows successful quantitative evaluation of the solid‐state hydration and dehydration processes, using FT‐Raman spectroscopy. All the steps required for a reliable evaluation of the hydration/dehydration process are illustrated for the caffeine system, a particularly challenging system presenting limited spectral differences between the pseudopolymorphs. The hydration process of caffeine was found to occur in a single‐step process with a half‐life time of ca 13 h, while the dehydration occurs through a two‐step mechanism. The critical relative humidity was found to be at ca 81 and 42% for anhydrous and hydrate caffeine forms, respectively. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
46.
Optimal control of linear stochastic evolution equations in Hilbert spaces and uniform observability
Viorica Mariela Ungureanu 《Czechoslovak Mathematical Journal》2009,59(2):317-342
In this paper we study the existence of the optimal (minimizing) control for a tracking problem, as well as a quadratic cost
problem subject to linear stochastic evolution equations with unbounded coefficients in the drift. The backward differential
Riccati equation (BDRE) associated with these problems (see [2], for finite dimensional stochastic equations or [21], for
infinite dimensional equations with bounded coefficients) is in general different from the conventional BDRE (see [10], [18]).
Under stabilizability and uniform observability conditions and assuming that the control weight-costs are uniformly positive,
we establish that BDRE has a unique, uniformly positive, bounded on ℝ + and stabilizing solution. Using this result we find the optimal control and the optimal cost. It is known [18] that uniform
observability does not imply detectability and consequently our results are different from those obtained under detectability
conditions (see [10]).
相似文献
47.
Mehrnoosh Arrar Fernando Martín Boubeta Maria Eugenia Szretter Mariela Sued Leonardo Boechi Daniela Rodriguez 《Journal of computational chemistry》2019,40(4):688-696
The Jarzynski equality is one of the most widely celebrated and scrutinized nonequilibrium work theorems, relating free energy to the external work performed in nonequilibrium transitions. In practice, the required ensemble average of the Boltzmann weights of infinite nonequilibrium transitions is estimated as a finite sample average, resulting in the so-called Jarzynski estimator, . Alternatively, the second-order approximation of the Jarzynski equality, though seldom invoked, is exact for Gaussian distributions and gives rise to the Fluctuation-Dissipation estimator . Here we derive the parametric maximum-likelihood estimator (MLE) of the free energy considering unidirectional work distributions belonging to Gaussian or Gamma families, and compare this estimator to . We further consider bidirectional work distributions belonging to the same families, and compare the corresponding bidirectional to the Bennett acceptance ratio () estimator. We show that, for Gaussian unidirectional work distributions, is in fact the parametric MLE of the free energy, and as such, the most efficient estimator for this statistical family. We observe that and perform better than and , for unidirectional and bidirectional distributions, respectively. These results illustrate that the characterization of the underlying work distribution permits an optimal use of the Jarzynski equality. © 2018 Wiley Periodicals, Inc. 相似文献
48.
49.
A convenient two-step procedure for the synthesis of primary (Z)-allyl amines, (Z)-homoallyl amines [(Z)-but-3-enylamines], and (Z)-pent-4-enylamines using the Wittig reaction was achieved. The use of nonstabilized ylides from triphenylphosphonium salt, potassium salt, and apolar solvent produced (Z/E)-geometric isomer ratios generally greater than 1.6. The amine moiety was masked using a phtalimide group that was removed successfully in the last step of the process in two different conditions, NH2NH2/EtOH/rt or CH3NH2/EtOH/rt. However, in some cases, reduction of the C = C double bond in the deprotection with hydrazine was concomitantly observed. 相似文献
50.
Sumati Bhatia Malte Hilsch Jose Luis Cuellar‐Camacho Kai Ludwig Chuanxiong Nie Badri Parshad Matthias Wallert Stephan Block Daniel Lauster Christoph Bttcher Andreas Herrmann Rainer Haag 《Angewandte Chemie (International ed. in English)》2020,59(30):12417-12422
Flexible multivalent 3D nanosystems that can deform and adapt onto the virus surface via specific ligand–receptor multivalent interactions can efficiently block virus adhesion onto the cell. We here report on the synthesis of a 250 nm sized flexible sialylated nanogel that adapts onto the influenza A virus (IAV) surface via multivalent binding of its sialic acid (SA) residues with hemagglutinin spike proteins on the virus surface. We could demonstrate that the high flexibility of sialylated nanogel improves IAV inhibition by 400 times as compared to a rigid sialylated nanogel in the hemagglutination inhibition assay. The flexible sialylated nanogel efficiently inhibits the influenza A/X31 (H3N2) infection with IC50 values in low picomolar concentrations and also blocks the virus entry into MDCK‐II cells. 相似文献