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排序方式: 共有195条查询结果,搜索用时 15 毫秒
61.
Rossana Chiavacci 《Annali dell'Universita di Ferrara》1985,31(1):185-195
Riassunto Si introduce la nozione di “problema enumerativo complesso totalmente reale”: essa caratterizza problemi enumerativi le cui
soluzioni, in un qualche aperto dello spazio dei parametri, sono tutte reali. Si dimostra una condizione necessaria e sufficiente
affinchè un problema enumerativo complesso sia totalmente reale e vengono forniti esempi di tali problemi.
Summary In this paper we give the definition of “totally real enumerative problem”. This notion characterises those complex enumerative problems which have, on some open set of the parameter space, all real solutions. We prove a necessary and sufficient condition, for an enumerative problem, to be a totally real one and we give some examples of problems of this kind.相似文献
62.
Blanco M. López M. Fernández R. Martín L. Riccardi C. C. Mondragon I. 《Journal of Thermal Analysis and Calorimetry》2009,97(3):969-978
The kinetics of a poly(methyl methacrylate) (PMMA)-modified epoxy resin cured with different functionalities amine mixtures
was analyzed using differential scanning calorimetry (DSC) in both isothermal and dynamic conditions. A delay in the reaction
rate was observed which increased with PMMA content. An approach of kinetic features involved in curing was carried out. A
linear dependence of preexponential factors of neat systems with modifier content was considered. The approach shows the contribution
of other factors including the dilution effect of the functional groups to the observed delay. Fourier transform infrared
spectroscopy (FTIR) indicated a noticeable change in the interactions present in neat systems due to the presence of PMMA.
On the other hand, a significant influence of the ratio between each amine in the epoxy/amine mixtures on the final physical
appearance was observed. At constant curing conditions, materials from completely opaque (phase separated) to transparent
(miscible) were obtained with the increase in monoamine content. 相似文献
63.
Rubiolo P Liberto E Sgorbini B Russo R Veuthey JL Bicchi C 《Journal of separation science》2008,31(6-7):1074-1084
This study reports on the compatibility of a conventional quadrupole MS (qMS) as detector for Fast-GC in terms of separation, identification, and quantitation when applied to the analysis of peppermint essential oil (e.o.), adopted as representative of this field. The influence of Fast-GC carried out on a 10 mx0.1 mm id narrow bore column with temperature programmes from 20 to 60 degrees C/min on the results of a qMS in total ion chromatograms (TIC) at different speeds (from 999 and 11 111 amu/s) and SIM modes was evaluated on ten differently abundant components characterizing peppermint e.o. Separation measure (S), peak capacity (n), and half height peak width were taken as separation parameters; match quality, number of scans per peak (NP), spectral skewing, and TIC area repeatability were used for identification. Quantitation was in SIM mode and NP, dwell time, SIM area repeatability and calibration curves, LOD, and LOQ of the selected components were measured. The results show that the peppermint e.o. markers can successfully be analysed qualitatively and quantitatively by F-GC-qMS up to temperature programmes of 60 degrees /min provided that a suitable scan speed is applied. Fast-GC-qMS reduces analysis time by a factor greater than ten and gives results that are qualitatively reliable and quantitatively comparable to those obtained by conventional GC-qMS. 相似文献
64.
Melo RC Rosa PG Noyma NP Pereira WF Tavares LE Parreira GG Chiarini-Garcia H Roland F 《Micron (Oxford, England : 1993)》2007,38(7):714-721
The investigation of the internal organization of zooplankton communities provides important information on the plankton biology with special interest for the study of ecological processes. Zooplanktoners can play a structural function as indicators for ecosystem health or stress, but their study using histological techniques is still limited. Here we report that the internal structure of zooplanktonic organisms can be facilely observed by a histological approach that combines optimal fixation and processing with a plastic resin (glycol methacrylate) embedding, resulting in increased tissue resolution. Using copepods, organisms that can dominate zooplankton assemblages, as models, collected from a tropical ecosystem (Paraibuna river, Brazil), we showed fine histological details of their muscular, nervous and digestive systems, structure of appendages and cell features. Critical advantages of this approach are that it permits optimal preservation and adequate handling of the organisms (embedded in agar after fixation) for further histological processing and investigation. This is important because it prevents both mechanically induced artifacts and loss of these diminutive organisms during the different steps of processing. Moreover, embedding in plastic resin showed a superior imaging of copepod internal structures compared to paraffin embedding. The use of glycol methacrylate is advantageous over paraffin/paraplast embedding by avoiding heat damage, tissue retraction and allowing faster embedding procedure and better tissue resolution. The value of histological approaches in enabling high-quality imaging of the internal structure of copepods is particularly important because these organisms can be used as indicators of environmental changes. 相似文献
65.
Francesca Buiarelli Patrizia Di Filippo Carmela Riccardi Donatella Pomata Eugenio Rumolo Luigi Giannetti 《International journal of environmental analytical chemistry》2015,95(8):713-729
An effective analytical method for the screening of mycotoxins, in indoor/outdoor airborne particulate matter, was developed and method performance data are presented. Mycotoxins are natural compounds produced, in particular conditions, as secondary metabolites by filamentous fungi and moulds, and, after their production, they can be transported far from their source. To simulate real samples, an urban dust (reference material 1649a) free from mycotoxins was used as matrix and spiked by the most common mycotoxins, chosen on the basis of studies carried out previously in other real matrices: deoxynivalenol, aflatoxin B1, ochratoxin A, T-2 toxin, zearalenone and sterigmatocystin. The analytical method was optimised and structured in four successive steps: (1) accelerated solvent extraction of the (spiked) analytes from matrix, (2) solid-phase purification (SPE) of the previous extract, (3) pre-concentration of the eluates from SPE and (4) analysis of the concentrated eluates by high performance liquid chromatography tandem mass spectrometry in multiple reaction monitoring mode. After a proper sampling campaign, the method was applied to real indoor and outdoor particulate matter samples, where the clean-up step showed to be very effective and fundamental to avoid misleading analytical results. 相似文献
66.
Olea-Azar C Rigol C Mendizábal F Briones R Cerecetto H Di Maio R Risso M González M Porcal W 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(1):69-74
The electron spin resonance (ESR) spectra of free radicals obtained by electrolytic or microsomal reduction of several potential antiprotozoal 1,2,5-oxadiazoles were characterized and analyzed. Ab initio molecular orbital calculations were performed to obtain the optimized geometries and the theoretical hyperfine constant was carried out using ZINDO semiempirical methodology. Density functional theory was used to rationalize the reduction potentials of these compounds. 相似文献
67.
F. Croccolo A. Quintini R. Barni M. Ripamonti A. Malgaroli C. Riccardi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(2):477-480
An inductively coupled plasma machine has been modified to be able to apply working powers in the order of 1 kW, thus switching
to the real inductive H-mode. The plasma is generated by applying a 13.56 MHz radio-frequency to a λ/4 antenna outside the
plasma chamber in low pressure conditions. The working gas is argon at pressure in the range from 10 to 100 Pa. With this
high power source we have been able to perform plasma etching on a poly(vinyl-chloride) (PVC) film. In particular the effect
of the plasma is the selective removal of hydrogen and chlorine from the sample surface. The action of the high power plasma
on the sample has been proved to be much more effective than that of the low power one. Results similar to those obtained
with the low power machine at about 300 W for 120 min, have been obtained with the high power source at about 600 W for 30 min.
The superficial generation of a conductive layer of double C=C bonds was obtained. The samples have been investigated by means
of ATR spectroscopy, FIB/SEM microscopy and micro-electrical measurements, which revealed the change in charge conductivity. 相似文献
68.
R. Caponi E. Ciaramella E. Riccardi M. Schiano T. Tambosso G. Zaffiro 《Fiber and Integrated Optics》2013,32(4):295-309
Polarization mode dispersion of chirped Bragg gratings is analyzed in terms of key birefringence phenomena and impact on telecommunication systems performance. The influence on polarization mode dispersion (PMD) of fiber birefringence, grating chromatic dispersion, and ripples of the group delay curve is pointed out. Polarization mode dispersion influence on systems performance is investigated by numerical simulations and transmission experiments at 10 Gbit/s. The deterministic nature of Bragg gratings PMD determines a moderate, upper-limited system penalty for a transmission line employing a single compensating device. However, in the case of broadband components, a non-negligible PMD penalty may be observed due to the difficulty of controlling accurately the group delay linearity. 相似文献
69.
Tomasi C. Scavini M. Speghini A. Bettinelli M. Riccardi M. P. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):151-164
The devitrification of glassy PbGeO3 was studied and interpreted by means of isothermal and non-isothermal Johnson-Mehl-Avrami equations. In the case of the non-isothermal
approach, several approximated equations proposed by various authors were considered in order to obtain both the activation
energy E
a and the Avrami morphological coefficient n of the crystallisation process. A critical discussion of the Avrami coefficient on the basis of experimental morphological
evidence is also presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
70.
S. Zanini M. Müller C. Riccardi M. Orlandi 《Plasma Chemistry and Plasma Processing》2007,27(4):446-457
Polyethylene glycol (PEG) chains with different lengths were covalently bonded to polypropylene membranes by means of RF plasma
polymerisation of acrylic acid (pp-Aac) followed by mono-amino PEG attachment in liquid phase. Two reactor configurations
were tested for the plasma deposition of ppAAc in order to obtain high retention of carboxylic groups in the deposited thin
films. A best configuration was assessed evaluating the membrane surface modifications by means of water droplet adsorption
time and contact angles measurements, attenuated total reflection (ATR) spectroscopy and X-ray photoelectron spectroscopy
(XPS) analysis. PEG chains were covalently bonded to the best plasma modified membranes and the resulting anti-fouling properties
were evaluated. 相似文献