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111.
Summary The determination of the permeability is an interesting problem of fluid dynamics of wide interdisciplinary concern. Many authors approached this subject by developing numerical models of flows through porous media at either macro-scale and micro-scale. According to the latter point of view, we present in this paper a verification of Darcy's law and a first determination of the permeability starting by the knowledge of the microstructure of a three-dimensional random medium. The flow is here reproduced by using a particular class of cellular automata with the Boltzmann approximation.
Sommario La determinazione del coefficiente di permeabilità rappresenta un interessante problema comune a molte discipline. Tale determinazione viene affrontata dai diversi autori o tramite la conoscenza di grandezze macroscopiche — come la resistività o la porositá — ovvero partendo dalla conoscenza della microstruttura del mezzo poroso e cercando di simulare il processo di moto fluido che si svolge lungo i canalicoli del mezzo stesso. Seguendo quest'ultimo punto di vista, viene qui di seguito presentata una tecnica alternativa per la verifica della legge di Darcy e, quindi, per una prima valutazione del coefficiente di permeabilità per un mezzo tridimensionale complesso. La simulazione dei moti fluidi viene effettuata tramite una particolare classe di gas reticolari che evolvono secondo le regole degli automi cellulari.相似文献
112.
Summary We describe in detail techniques and qualitative results of experiments conduced in our laboratory at Catania (Italy) on the
production of stable residing dark (polymerlike) material obtained by bombarding methane frosts with fast (100÷1500) keV proton
beams. We give, in particular, results on the cross-section of the process and show that this occurs along the intere ion
path so that thick residues are obtained. The thickness of the residues has been measured by bothin situ and remote analysis that also give information on the surface roughness and on the chemical composition. The purpose of the
experiments is to get some insight into the possibility that the interaction between energetic ions and hydrocarbon frosts
is responsible of the build-up of dark carbonaceous materials widely thought to be present in many astrophysical scenarii.
Some astrophysical applications are, in fact, discussed in a correlated paper.
Riassunto Si descrivono in dettaglio tecniche e risultati quantitativi di esperimenti condotti nel nostro laboratorio di Catania e riguardanti la produzione di materiali scuri (di tipo polimerico) resistenti a temperatura ambiente ed ottenuti dal bombardamento di metano congelato tramite fasci di protoni veloci ((100÷1500) keV). In particolare, si presentano risultati sulla sezione d'urto del processo e si mostra che questo avviene lungo l'interocammino dello ione cosicchè si ottengono residui spessi. Lo spessore di essi è stato misurato siain situ che in un'analisi remota e ciò consente di ottenere informazioni sulla topografia superficiale e sulla composizione chimica. Lo scopo degli esperimenti è di far luce sulla possibilità che l'interazione tra ioni energetici e idrocarburi congelati sia responsabile della formazione di materiale scuro carbonioso che si ritiene ampiamente presente in molti contesti astrofisici. Alcune applicazioni astrofisiche sono infatti discusse in un lavoro connesso al presente.相似文献
113.
A. Cunsolo A. Foti G. Immè G. Pappalardo G. Raciti N. Saunier 《Physics letters. [Part B]》1982,112(2):121-123
Deuteron-alpha angular correlations have been measured for the reaction and θdlab=10°. Transitions involving the 11.69 MeV (6+) and the 17.6±0.2 MeV 18O states have been analyzed. Spin and parity are confirmed for the known 11.69 MeV (6+) state and assigned to be 8+ for the 17.6 MeV level. This last is suggested to be the fifth member of the positive-parity 18O rotational band built on the 3.63 MeV (0+) level. 相似文献
114.
A procedure for the determination of trace amounts of 99Tc in filter paper and vegetation samples by neutron activation analysis has been developed. The procedure consists of the following major steps: (a) pre-irradiation separation of technetium from the sample and purification of the technetium fraction; (b) thermal neutron irradiation of the 99Tc fraction to produce 100Tc ; (c) post-irradiation separation and purification of 100Tc from other activated nuclides: (d) counting of the 16-sec 100Tc in a low-background β-counter.
The estimated detection limits for 99Tc by this procedure with irradiations at a thermal neutron flux of about 5.1013 n cm-2 sec-1 are: 5.lO-12g 99Tc in filter paper samples, and 9. 10-12 g 99Tc in vegetation samples. 相似文献
115.
Boiocchi M Bonizzoni M Fabbrizzi L Foti F Licchelli M Taglietti A Zema M 《Dalton transactions (Cambridge, England : 2003)》2004,(4):653-658
The nickel(II) complex with an open chain tetramine containing a piperazine fragment (1) displays an unusual resistance to demetallation in acidic solution and exhibits a lifetime of about five minutes in a solution 0.1 M in HClO4 and 7.0 M in NaClO4. Sluggishness with respect to the demetallation is ascribed to the occurrence of the boat-to-chair conformational conversion of the piperazine fragment, which implies the passage through the highly energetic half-boat transition state. The use of a high concentration of the inert electrolyte induces a 'salting out' effect on both thermodynamics (stability of metal complexes is enhanced) and kinetics (resistance to demetallation is increased). 相似文献
116.
117.
By reaction between the anion of mellitic acid (benzenehexacarboxylic acid) and some protonated linear polyamines (diethylenetriamine, triethylenetetramine, tetraethylene-pentamine, pentaethylenehexamine, spermidine, and spermine), fairly insoluble complexes have been obtained, with the general formula (amine)(x)(mellitate)H(6) (diethylenetriamine and spermidine, x=1; triethylenetetramine and spermine, x=0.75; tetraethylenepentamine, x=0.6 and 0.8; pentaethylenehexamine, x=0.5). K(s0) values for these complexes have been determined at I=0 mol dm(-3) and T=25 degrees C (logK(s0) ranges between -48.2 and -56.6). The solubility has been studied as a function of pH and of ionic strength. The thermal analysis, performed using air or argon flow, showed that all the solids behave in a similar way. In the range 20-120 degrees C the loss of hydration water occurs, and in the range 150-350 degrees C the first step of non oxidative decomposition takes place, with complete decomposition at 650 degrees C in air flow, whilst in argon flow the decomposition is still incomplete at 900 degrees C. Preliminary results of a parallel diffractometric study are also reported. 相似文献
118.
Effect of metal oxides on the evolution of aromatic hydrocarbons in the thermal decomposition of PVC
Alberto Ballistreri Salvatore Foti Pietro Maravigna Giorgio Montaudo Emilio Scamporrino 《Journal of polymer science. Part A, Polymer chemistry》1980,18(10):3101-3110
The thermal decomposition of poly(vinyl chloride) (PVC) mixed with several metal oxides was investigated by direct pyrolysis in a mass spectrometer (MS) and flash pyrolysis–gas chromatography. Our results show that the thermal decomposition of PVC occurs in two stages. Unsubstituted aromatic hydrocarbons (benzene, naphthalene, and anthracene) are evolved mainly in the first stage, alkyl-aromatics (e.g., toluene) in the second. Although the addition of some metal oxides results in an overall suppression of aromatic hydrocarbons, the unsubstituted aromatics are much more suppressed with respect to alkyl-aromatics. Furthermore, the formation of ZnCl2 and SnCl4 was revealed by the mass spectra of PVC–metal oxide pyrolysates. This suggests that, at least in these two cases, metal chlorides are responsible for aromatic hydrocarbon suppression. With this information a detailed reaction mechanism could be formulated for the thermal degradation of PVC. 相似文献
119.
Summary In the light of the experimental results presented in a correlated paper on the production of organic residues by bombarding
hydrocarbon frosts with fastions, we show that substantial amount of these materials can by synthesized on insterstellar grains
and objects in the solar system by cosmic-ray fluence. The IR spectra of laboratory residues are shown. The main features
we find at 2.9, 3.4, 6.2 and 6.8 μm resemble those observed on interstellar sources and on some meteoritic extracts. Some
implications these results have on grain models and evolution and on the possible similarity between interstellar grains and
objects in the solar system are also discussed.
Riassunto Alla luce di risultati sperimentali, presentati in un precedente lavoro di questa serie e concernenti la produzione di residui organici del bombardamento di idrocarburi congelati tramite ioni veloci, noi dimostriamo che apprezzabili quantit? di questi materiali possono essere sintetizzati sui grani interstellari e su oggetti nel sistema solare a causa del bombardamento di raggi cosmici. Sono mostrati gli spettri IR dei residui di laboratorio le cui bande prineipali a 2.9, 3.4, 6.2 e 6.8 μm ricordano quelle osservate su sorgenti astrofisiche e su alcuni estratti da meteoriti. Si discutono anche alcune implicazioni che questi risultati hanno sui modelli e sull'evoluzione dei grani interstellari e sulle possibili similarità tra questi grani ed oggetti nel sistema solare.
Резюме йспользуя экспериментальные резуьтаты, полученные ранее, по образованию органических остатков при бомбардировке замороженных углеводородов быстрыми ионами, мы показываем, что затемненные материалы могут быть синтезированы в заметных количествах на межзвездных зернах и обБектах в солнечной системе под действием космических лучей. Приводятся инфракрасные спектры лабораторных остатков. Главные особенности этих спектров при 2.9, 3.4, 6.2 и 6.8 мкм похожи на особенности, обнаруженные на межзвездных источниках и на некоторых метеорных экстрактах. Обсуждается применение полученных результатов к моделям зерен и эволюции. Также рассматривается возможное сходство между межзвездными зернами и обБектами в солнечной системе.相似文献
120.
A. Cunsolo F. Cappuzzello M. Cavallaro A. Foti A. Khouaja S. E.A. Orrigo J. S. Winfield L. Gasparini G. Longo T. Borello-Lewin M. R.D. Rodrigues M. D.L. Barbosa C. Nociforo H. Petrascu 《The European physical journal. Special topics》2007,150(1):343-346
The MAGNEX large-acceptance spectrometer has been
commissioned with beams from the Tandem accelerator
at INFN-LNS Catania. The optics were tested
with elastically-scattered 7Li, 16O and 48Ti
beams with various apertures mounted after the target.
The momentum dispersion was verified to be in agreement with
the optics calculations.
A demonstration of the particle identification capabilities
of the PSD start detector and the focal plane detector
was given by a measurement of the 27Al(7Li,6Li)28Al
transfer reaction at
a mean angle of 25°. The measured charge
state distribution of 48Ti ions is
in agreement with predictions for a gold stripping foil.
Preliminary
results of the software reconstruction of incident angle and
excitation energy, obtained through matrices based
on a 3D-interpolation of the measured field maps, are encouraging. 相似文献