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41.
[STRUCTURE: SEE TEXT] A novel broad-spectrum aminoglycoside antibiotic, pyrankacin, has been prepared. In addition to the synthetic innovation in dideoxygenation and regioselective Staudinger reduction, we have obtained prominent antibacterial activity against several clinically important pathogens in the course of this work. 相似文献
42.
Lorenzo Torrisi Marcin Rosinski Dominika Terwinska Przemyslaw Tchorz Mariapompea Cutroneo Alfio Torrisi 《等离子体物理论文集》2020,60(4):e201900187
Non-equilibrium plasma was obtained by irradiating Al foils in vacuum with a femtosecond (fs) laser at intensities of the order of 1018 W/cm2. Protons and other light ions were accelerated in the forward direction by using the target-normal-sheath acceleration regime. Time-of-flight technique was employed to measure the ions' kinetic energy using SiC detectors placed at known distances and angles. The ion acceleration was monitored under different conditions of laser focal position, laser pulse energy, and laser contrast. The target was irradiated using different thicknesses and anti-reflecting graphene films. By optimizing the laser parameters, irradiation conditions, and target properties, it was possible to accelerate up to 2.3 MeV per charge state, as will be presented and discussed. 相似文献
43.
[reaction: see text] Enzymatic production of glycoconjugates is hampered by expensive phosphagens such as acetyl phosphate (AcP) and phosphoenolpyruvate (PEP). Here, we introduce creatine phosphate--creatine kinase system as a novel and practical energy source in carbohydrate synthesis. This system was successfully demonstrated in the production of bioactive oligosaccharides with different sugar nucleotide regeneration systems. 相似文献
44.
Summary. The sessile drop method has been used to measure density and surface tension for pure Ag, Bi, Sn, and their mixtures. For
pure metals and Bi–Sn alloys negative temperature coefficients of surface tension have been obtained. In case of Ag–Bi and
Ag–Sn alloys the temperature coefficients of surface tension take negative or positive values depending on composition. Experimental
values of the surface tension for Ag–Bi, Ag–Sn, and Bi–Sn are compared with those computed from Butler’s model. A relatively good agreement is observed. 相似文献
45.
Melania Bednarek Przemyslaw Kubisa 《Journal of polymer science. Part A, Polymer chemistry》1999,37(17):3455-3463
Cationic copolymerization of tetrahydrofuran (THF) with ethylene oxide (EO) in the presence of diols leads to dihydroxy terminated telechelic copolymers. In the present article the influence of copolymerization conditions on the copolymer structure was studied in view of conclusions derived from studies of copolymerization kinetics and mechanism. It was shown that according to established copolymerization mechanism, the number average molecular weights increase linearly with conversion up to Mn ≅ 2500, hydroxyl end groups are bound exclusively to EO units and copolymers are composed of [EO]–[THF]y segments. Microstructure of copolymers may be to some extent regulated by changing reaction conditions. Some physical properties of copolymers also were studied. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3455–3463, 1999 相似文献
46.
Polyethers of low and medium molecular weight containing at both ends stable ionic groups (phosphonium ions) were obtained by living cationic polymerization of tetrahydrofuran initiated by difunctional initiator, trifluoromethanesulfonic anhydride, followed by termination with triphenylphosphine. It was shown, that products contain significant quantities of low molecular weight diphosphonium salt; a plausible explanation is presented. Alternative approach to the synthesis of diionically terminated polyethers was based on the conversion of hydroxyl end-groups of polyether diols, which can be obtained by cationic Activated Monomer (AM) polymerization of e.g. oxiranes, into phosphonium ion end-groups. Using this approach, poly(ethylene oxide)'s with Mn ranging from 300 to 3400, terminated at both ends with stable ionic groups, were prepared and characterized. Measurements of NMR relaxation times and viscosity measurements provide the evidence for the aggregation of ionic end-groups. The potential applications of inter- and intramolecular aggregation are discussed. It is shown, that intramolecular aggregation of ionic terminal groups in low molecular weight poly(ethylene oxide) leads to cyclic structures resembling crown ethers and showing comparable efficiency for complexing cations. 相似文献
47.
48.
Przemyslaw Zagrodzki 《International Journal of Solids and Structures》2009,46(11-12):2463-2476
Sliding systems with frictional heating exhibit thermoelastic instability (TEI) when the sliding speed exceeds the critical value. TEI can lead to hot spots on contact surfaces and is generally of great practical importance in friction brakes and clutches. The phenomenon is well defined in terms of the theory of stability with a classic perturbation approach being commonly used. While the perturbation analysis determines the stability limit, recent interest extends further towards exploration of the unstable behavior. This is motivated by practical reasons, namely by the fact that many common friction brakes and clutches operate instantaneously at speeds exceeding the critical speed for TEI, i.e. in the unstable regime. In order to determine a transient solution, possible mechanisms of excitation of unstable modes of different nature need to be accurately defined and quantified. These mechanisms are normally not considered in stability analysis of the steady-state where an initial perturbation of the thermoelastic field is assumed. In many realistic situations, however, there is no indication of the existence of meaningful initial temperature variation. Lack of full understanding of these mechanisms has perhaps limited broader industrial applications of recent theoretical advances in TEI. In this paper a method of solving the transient thermoelastic process in frictional systems using finite element spatial discretization and modal superposition is presented. Then mechanisms that excite the unstable thermoelastic modes other than the initial perturbation of temperature are studied. The role of the background process (corresponding to nominal applied loads) in the excitation is shown in a clear form and illustrated by practical examples for automotive friction clutches. It is demonstrated, in particular, that while for some geometries and configurations of the sliding system the imperfections determine the excitation of unstable modes, with other configurations strong excitation occurs even in the absence of imperfections. 相似文献
49.
50.
Barbara Lejczak Pawel Kafarski Helena Sztajer Przemyslaw Mastalerz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4)
Abstract A series of 32 dipeptides containing N-terminal alanine or leu-cine and a variety of racemic 1-aminoalkanephosphonic acids vere prepared by standard procedures and tested for growth inhibition of six bacterial species (Escherichia coli, Klebsiella aerogenes, Serratia mercescens, Staphylococcus aureus, Streptococcus faeca-lis and Bacillus subtilis). The aminophosphonate residues were racemic and included Va1P, LeuP, ProP, PheP, α-methyl-AlaP, Glu-α-P, O-methyl-DOPAP, cyclohexane-1-amino-1-phosphonic acid, t-LeuP, O-acetyl-SerP, and GlyP derivatives RCH(NH2)PO3H2 where R=cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and adaman-tyl. N-Ala and N-Leu peptides of racemic AlaP were used as positive control. MIC and IC50 values indicate that the peptides containing 4-amino-4-phosphonobutyric acid (Glu-α-P) and α-methyl-AlaP are potent antibiotics, comparable in activity with LeuAlaP and AlaAlaP (Alafosfalin). Weak activity was observed for peptides of ProP, LeuP, ValP, PheP, cyclohexane-1-amino-1-phosphonic acid and 1-aminocyclopentylmethanephosphonic acid. While the activity of the α-methyl-AlaP peptides may be explained by inhibition of alanine racemase, the mechanism of action of the Glu-α-P peptides remains unknown. 相似文献