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排序方式: 共有359条查询结果,搜索用时 31 毫秒
231.
The goal of this paper is to use algebraic techniques to compute sums of powers of roots of certain polynomials and derive congruences of Ankeny-Artin-Chowla types modulo p 3. 相似文献
232.
Dr. Morten Borre Hansen Dr. František Hubálek Prof.Dr. Troels Skrydstrup Dr. Thomas Hoeg‐Jensen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(5):1572-1576
Ethynylation of various tryptophan‐containing peptides and a single model protein was achieved using Waser's reagent, 1‐[(triisopropylsilyl)ethynyl]‐1,2‐benziodoxol‐3(1 H)‐one (TIPS‐EBX), under gold(I) catalysis. It was demonstrated by NMR that the ethynylation occured selectively at the C2‐position of the indole ring of tryptophan. Further, MS/MS showed that the tryptophan residues could be modified selectively with ethynyl functionalities even when the tryptophan was present as a part of the protein. Finally, the terminal alkyne was used to label a model peptide with a fluorophore by means of copper‐catalyzed click chemistry. 相似文献
233.
234.
Ability to control charge transport at nanometer scale lies in the heart of design of fast reliable electronic devices. Molecular electronics thrive to use functional molecules for such transport. If the molecule contains redox center(s), a diode-like or transistor-like behavior can be easily explored by controlling not only the voltage difference between two metallic contacts of the molecular junction but also the potential of one of the contacting electrodes with respect to some reference. Thus, one needs to understand the relationship between electrochemical electron transfer and charge transport in metal–molecule–metal junctions. This review presents latest theoretical approaches toward understanding of such relationship and discusses pivotal experimental works to validate them. Tunneling and hopping pathways may operate in parallel (two-channel model), but experimental conditions dictate the channel preference. 相似文献
235.
Daniel Haško Jaroslav Bruncko František Uherek 《Applied Physics A: Materials Science & Processing》2014,117(3):1353-1358
Amorphous oxides-based devices are exposed, during fabrication, to different processing conditions affecting their properties. Zinc oxide is a prospective candidate for transparent amorphous oxides, but its structure is changing under the influence of temperature. We investigated surface recrystallization of amorphous zinc oxide layers deposited onto fused silica, sapphire and Si substrates by pulsed laser deposition. The prepared three series of layers had highly nonequilibrium phase structures. Using atomic force microscopy and scanning electron microscopy, the effect was studied of subsequent annealing at 200, 400, 600, 800 °C for 60 min upon the surface structural properties of the layers. The following parameters were analyzed: average roughness, RMS roughness and size of formed grains on selected places with 1 × 1 μm2 area. Surface structural analysis revealed that annealing led to recrystallization of the prepared layers and roughening of the structural features on the surface. With increasing annealing temperature, the calculated parameters were increasing. The average surface roughness of zinc oxide layers annealed at 800 °C is three times higher than that of the layers annealed at lower temperatures for all substrates used. The process dynamics of thermally caused recrystallization of the layers was different for each of the substrates used. 相似文献
236.
Analyses of very complex samples involving capillary and chip electrophoresis often require dual (multiple) detection to attain sufficient selectivity of determination. The present work reviews and critically evaluates selected combinations of electrochemical detection techniques among themselves and with absorption spectrometric, fluorescence and luminescence techniques. Amperometry, contact and contactless conductometry, UV photometry and fluorescence measurements are paid special attention. Some information is also given on combinations of spectrometric techniques with mass spectrometry. The properties of the detection systems are critically discussed, examples are illustrated in figures and some details on the characteristics of dual detectors and their applications are tabulated. 相似文献
237.
Chung TW Moss CL Zimnicka M Johnson RS Moritz RL Tureček F 《Journal of the American Society for Mass Spectrometry》2011,22(1):13-30
Pyridiniummethylcarbonyl moieties that were previously designed on the basis of electronic structure analysis are now utilized
as fixed-charge tags with tunable electronic properties to be used for N-terminal peptide derivatization and sequencing by
electron-transfer dissociation. Dipeptides AK and KA were derivatized at the peptide N-terminus with 4-dimethylaminopyridinium-N-acetyl
(DMAP-ac) and pyridinium-N-acetyl (pyrid-ac) tags of increasing intrinsic recombination energies. Upon the capture of a free
electron or electron transfer from fluoranthene anions, (DMAP-ac-AK+H)2+, (DMAP-ac-KA+H)2+, (pyrid-ac-AK+H)2+ and (pyrid-ac-KA+H)2+ ions, as well as underivatized (AK+2H)2+, completely dissociated. The fixed-charge tags steered the dissociation upon electron transfer to form abundant backbone
N–Cα bond cleavages, whereas the underivatized peptide mainly underwent H-atom and side-chain losses. Precursor ion structures
for the tagged peptides were analyzed by an exhaustive conformational search combined with B3LYP/6-31+G(d,p) geometry optimization
and single-point energy calculations in order to select the global energy minima. Structures, relative energies, transition
states, ion–molecule complexes, and dissociation products were identified for several charge-reduced species from the tagged
peptides. The electronic properties of the charge tags and their interactions with the peptide moieties are discussed. Electrospray
ionization and electron-transfer dissociation of larger peptides are illustrated with a DMAP-tagged pentapeptide. 相似文献
238.
Low-density polyethylene (LDPE) samples were treated in air plasma discharge, coated by polyallyamine brush thought copolymeric grafting surface-from reaction and deposited four common antibacterial agents (benzalkonium chloride, bronopol, chlorhexidine and triclosan) to gain material with active antibacterial properties. Surface characteristics were evaluated by static contact angle measurement with surface energy evaluation ATR-FTIR, X-ray Photoelectron Spectroscopy (XPS) and SEM analysis. Inhibition zone on agar was used as in vitro test of antibacterial properties on two representative gram positive Staphylococcus aureus (S. aureus) and gram negative Escherichia coli (E. coli) strains. It was confirmed, that after grafting of polyallyamine, more antibacterial agent is immobilized on the surface. The highest increase of antibacterial activity was observed by the sample containing triclosan. Samples covered by bronopol did not show significant antibacterial activity. 相似文献
239.
Magdalena Jabłońska Lucjan Chmielarz Agnieszka Węgrzyn Katarzyna Guzik Zofia Piwowarska Stefan Witkowski Richard I. Walton Peter W. Dunne František Kovanda 《Journal of Thermal Analysis and Calorimetry》2013,114(2):731-747
Layered double hydroxides (LDHs) containing Mg2+, Cu2+ or Zn2+ cations in the MeII positions and Al3+ and Fe3+ in the MeIII positions were synthesized by co-precipitation method. Detailed studies of thermal transformation of obtained LDHs into metal oxide systems were performed using high temperature X-ray diffraction in oxidising and reducing atmosphere, thermogravimetry coupled with mass spectrometry and temperature-programmed reduction. The LDH samples calcined at 600 and 900 °C were tested in the role of catalysts for selective oxidation of ammonia into nitrogen and water vapour. It was shown that all copper congaing samples presented high catalytic activity and additionally, for the Cu–Mg–Al and Cu–Mg–Fe hydrotalcite samples calcined at 600 °C relatively high stability and selectivity to dinitrogen was obtained. An increase in calcination temperature to 900 °C resulted in a decrease of their catalytic activity, possibly due to formation of well-crystallised metal oxide phases which are less catalytically active in the process of selective oxidation of ammonia. 相似文献
240.
Olga Šolcov Pavel Topka Karel Soukup Květuše Jirátová Helena Váňová František Kaštánek 《Chemical Papers》2014,68(9):1279-1282
Combined thermal desorption and catalytic oxidation for soil decontamination was studied at the pilot plant scale. Gasoline, xylene, and 2-methylnaphthalene were used as model contaminants in the concentrations from 2 g to 10 g per kg of soil. To guarantee the flow of the exhaust gas from the thermal desorption unit into the catalytic oxidation unit, a Venturi pump was used. Based on the laboratory scale catalytic tests, the commercial catalyst EnviCat® VOC-1544 was employed in the catalytic oxidation. Residual concentrations of hydrocarbons in soil after the thermal desorption were below the detection limits of the applied analytical method (GC-MS). Although the contaminant concentrations at the inlet of the catalytic reactor significantly varied during the experiments, the efficiency of catalytic oxidation was higher than 90 % in all cases. 相似文献