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81.
82.
A whole range of Robson-type tetraiminodiphenol macrocyclic ligands have been prepared as their perchlorate salts [H4L](ClO4)2 in high yield (ca. 90%) by a single-step [2 + 2] condensation reaction between 4-methyl(or tert-butyl)-2,6-diformyl(or diacyl)phenols and alpha,omega-diaminoalkanes (C2-C12) in the presence of acetic acid and NaClO4. The reduction of these 18- to 38-membered macrocyclic salts with NaBH4 have afforded corresponding tetraaminodiphenol macrocycles H2L'. The X-ray crystal structures of two of the tetraiminodiphenol macrocycles with the C2 and C4 lateral chains have been determined, and the optimized configurations for all of the macrocycles have been obtained by molecular mechanics calculations. The macrocycles have been characterized by elemental analysis and by IR, absorption, emission, and NMR spectroscopic study. The protonated tetraiminodiphenol macrocycles exhibit strong fluoroscence in methanol, acetonitrile, and nitromethane and undergo quenching when treated with triethylamine. The neutral macrocycles H2L, isolated by treating [H4L](ClO4)2 with excess of triethylamine, lack luminescence, as do the reduced tetraaminodiphenol macrocycles H2L'. The hydrolytic cleavage of [H4L](ClO4)2 has been studied. 相似文献
83.
We use an ab initio pseudopotential method within the local-density approximation to determine the structural and electronic properties of the BeSe(1 1 0) surface. The relaxed geometry of this surface shows tilted cation-anion chains, with the anions being raised. The general pattern of the electronic structure of this surface is similar to that on other II-VI(1 1 0) surfaces. The phonon spectrum and corresponding surface density of states are also calculated using a linear response approach based on the density functional perturbation theory. In our calculations, we have found two localized phonon modes in the acoustic-optical gap region. The atomic displacement patterns of these surface phonon modes are presented and discussed. 相似文献
84.
We present a numerical investigation of the tunneling dynamics of a particle moving in a bistable potential with fluctuating
barrier which is coupled to a non-integrable classical system and study the interplay between classical chaos and barrier
fluctuation in the tunneling dynamics. We found that the coupling of the quantum system with the classical subsystem decreases
the tunneling rate irrespective of whether the classical subsystem is regular or chaotic and also irrespective of the fact
that whether the barrier fluctuates or not. Presence of classical chaos always enhances the tunneling rate constant. The effect
of barrier fluctuation on the tunneling rate in a mixed quantum-classical system is to suppress the tunneling rate. In contrast
to the case of regular subsystem, the suppression arising due to barrier fluctuation is more visible when the subsystem is
chaotic.
相似文献
85.
Pozo OJ Barreda M Sancho JV Hernández F Ll Lliberia J Cortés MA Bagó B 《Analytical and bioanalytical chemistry》2007,389(6):1765-1771
Ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC–MS–MS) has been used for screening and quantification
of 32 pesticides and metabolites in two fruit matrices. The compounds investigated belonged to different chemical families
of insecticides, acaricides, fungicides, and herbicides; several metabolites were also included. Quantification was conducted
using matrix-matched standards calibration; response was a linear function of concentration in the range tested (10–500 ng
mL−1). The method was validated with blank samples of lemon and raisin spiked at 0.01 and 0.1 mg kg−1, and recoveries were satisfactory, between 70 and 110%, for most of the pesticides tested and relative standard deviations
were below 15% (n = 5 at each spiking level). Excellent sensitivity resulted in limits of detection for all compounds well below 0.01 mg kg−1, with the limit of quantification being validated at 0.01 mg kg−1. The UPLC system generates narrow peaks (approx. 5 s), thus increasing peak height and improving sensitivity. This improved
separation efficiency facilitates adequate resolution not only of the analytes but also of matrix interferences compared with
conventional HPLC. The method developed could also resolve some geometric isomers. The main advantage of this approach is
the high sample throughput achieved because of the short analysis time, which enables satisfactory separation of all the compounds
in less than 5 min per sample. 相似文献
86.
D. Rana K. Bag S. N. Bhattacharyya B. M. Mandal 《Journal of Polymer Science.Polymer Physics》2000,38(3):369-375
A miscible homopolymer–copolymer pair viz., poly(ethyl methacrylate) (PEMA)–poly(styrene‐co‐butyl acrylate) (SBA) is reported. The miscibility has been studied using differential scanning calorimetry. While 1 : 1 (w/w) blends with SBA containing 23 and 34 wt % styrene (ST) become miscible only above 225 and 185 °C respectively indicating existence of UCST, those with SBA containing 63 wt % ST is miscible at the lowest mixing temperature (i.e., Tg's) but become immiscible when heated at ca 250 °C indicating the existence of LCST. Miscibility for blends with SBA of still higher ST content could not be determined by this method because of the closeness of the Tg's of the components. The miscibility window at 230 °C refers to the two copolymer compositions of which one with the lower ST content is near the UCST, while the other with the higher ST content is near the LCST. Using these compositions and the mean field theory binary interaction parameters between the monomer residues have been calculated. The values are χST‐BA = 0.087 and χEMA‐BA = 0.013 at 230 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 369–375, 2000 相似文献
87.
88.
Dejan Stekovic Dr. Pradip Bag Pritam Shankhari Prof. Boniface P. T. Fokwa Prof. Mikhail E. Itkis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(16):4166-4174
The ability to tune the physical properties of bistable organic functional materials by means of chemistry can facilitate their development for molecular electronic switching components. The butylamine-containing biphenalenyl boron neutral radical, [Bu]2B, crystalline compound has recently attracted significant attention by displaying a hysteretic phase transition accompanied by simultaneous bistability in magnetic, electrical, and optical properties close to room temperature. In this report, substitutional doping was applied to [Bu]2B by crystallizing solid solutions of bistable [Bu]2B and its non-radical-containing counterpart [Bu]2Be. With increasing doping degree, the hysteretic phase transition is gradually suppressed in terms of reducing the height, but conserves the width of the hysteresis loop as observed through magnetic susceptibility and electrical conductivity measurements. At the critical doping level of about 6 %, the abrupt transformation of the crystal structure to that of the pure [Bu]2Be crystal packing was observed, accompanied by a complete collapse of the hysteresis loop. Further study of the structure–properties relationships of bistable neutral radical conductors based on the [Bu]2B host can be conducted utilizing a variety of biphenalenyl-based molecular conductors. 相似文献
89.
Sáez-Muñoz Marina Bagán Héctor Tarancón Alex García José F. Ortiz Josefina Carlos Sofía Martorell Sebastián 《Journal of Radioanalytical and Nuclear Chemistry》2019,322(3):1397-1408
Journal of Radioanalytical and Nuclear Chemistry - This study describes a rapid and novelty method for radiostrontium determination in aerosol filters and vegetation based on the use of plastic... 相似文献
90.