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181.
Photoactive polyurethane elastomers with pyridine derivatives in the polymer backbone were synthesized by chain-extending
isocyanate end-capped prepolymers with 2,3-dihydroxypyridine. The isocyanate-terminated prepolymers were obtained from poly(tetramethylene
oxide) glycol of molecular weight 1400 (Terathane 1400) and 1,6-hexamethylene diisocyanate. The properties of the linear heterocyclic
polyurethane were compared with properties of the crosslinked heterocyclic polyurethane obtained by chain extension with various
crosslinkers. Heterocyclic polyurethane elastomers were characterized using Fourier transform infrared spectroscopy (FTIR),
thermo-gravimetric analysis (TGA), dynamic mechanical analysis (DMA), contact angle measurements, and mechanical analysis.
Static mechanical measurements showed greater elongation and tensile strength for polyurethanes with a lower content of heterocyclic
groups in the hard segment. The static contact angles of the cast films of these polymers indicated that the nature of the
hard segment influences the surface polarity. The dynamic mechanical spectra revealed that linear polymers have two transition
temperatures as results from a clear phase separation caused by high-intermolecular hydrogen bonds in the regions of pyridine
units and urethane groups. Polyurethane elastomer films with pyridine moieties in the main chain form a photosensitive material.
If stored in laboratory conditions (light, ambient air atmosphere), the color of the films changes from white to black. These
photo-induced structural changes are studied by H NMR measurements. 相似文献
182.
Mojmir Uranjek Vlatko Bosiljkov Roko Žarnić Violeta Bokan-Bosiljkov 《Materials and Structures》2012,45(6):861-879
The injection of grout into multi-leaf stone masonry walls with a sufficient amount of voids can be an effective technique
for the seismic strengthening of such walls. In order to evaluate the effectiveness of different types of commercial grouts
that fulfilled the adopted criteria, the stone masonry walls of an actual building were strengthened by means of grout injection,
using cement and combined cement–lime grouts. The quality and effectiveness of grout injection technique was assessed by non-destructive
tests (sonic and radar tests), minor destructive tests (surface and in-depth probing and coring, and the double flat jack
test), and destructive test (shear-compressive test), all in situ. Preliminary laboratory tests were also performed on mortar
and stone specimens, on the injection grouts, and on cylinders representing the inner core of the strengthened walls. Finally,
the seismic resistance of the building was evaluated in non-strengthened and strengthened variants (i.e. after grout injection
of the walls with cement or lime–cement grout) by means of non-linear static analysis, using the pushover method. Obtained
results show that shear characteristics of the walls (tensile strength and stiffness) depend significantly on the type and
properties of the injected grout, i.e. on the grout’s ability to achieve a solid bond between the stones and the leaves including
the properties (strength and stiffness) of the grout itself. In the case of the type of masonry under consideration, an adequate
level of seismic resistance can be achieved also by using combined cement–lime grouts, although cement grout can provide higher
seismic resistance. 相似文献
183.
A large quantity of gold (approximately 10 tonnes yearly) is consumed, all over the world, just to decorate ceramic and glassware.
Due to their advanced chemical stability gold films are used for different high technology applications. The technologies
for obtaining the best “liquid bright gold” were intensively studied, but the quality of the decor coatings (films) were empirically
assessed. We proposed a scientific investigation of the characteristics of gold films, deposited on ceramic substrates, from
“liquid bright golds”. The composition of the film has been determined by EDS (Energy Dispersive X-ray Spectrometry). The
distribution of the elements was determined at the surface of the film and in cross-section. The surface distribution of the
elements was uniform. The diffusion process of the film into substrate and the migration of the substrate elements at the
interface region and into the film have been highlighted. 相似文献
184.
The novelty of the poly(urethane-urea) series consists in inclusion of o-dianisidine units in the main chain and cross-linking with renewable biomaterials, unused compounds so far in the synthesis of the poly(urethane-urea) (Tween 20, Span 20, Phloroglucinol). The effects of these components on the structure, surface, thermo-mechanical properties and dielectric behavior of the obtained poly(urethane-urea) were investigated by Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis, static contact angles, broadband dielectric spectroscopy, and mechanical testing. The FTIR spectra showed that the urethane hydrogen bonds decreased with the increase of o-dianisidine content. Such that, at the increase of the o-dianisidine content, decreased the thermo-mechanical properties, and increased strongly the water contact angle from 83 to 108°. By dielectric relaxation spectroscopy was studied the molecular dynamics within the polymeric matrices with identical soft segments but different structure of the hard domains. These poly(urethane-urea) materials exhibit two secondary relaxations (β and γ) and a relaxation process α, corresponding to the segmental movements in the soft phase, which occurs around the temperature of −50°C independent of the measurement frequency. o-Dianisidine prevents the formation of all the urethane hydrogen bonds and so increases the chains mobility and dipoles polarization of polymer matrix, thus increasing the dielectric constants. 相似文献
185.
Martin Schmal Mariana M.V.M. Souza Violeta Virginia Alegre Mnica Antunes Pereira da Silva Deborah Vargas Csar Carlos A.C. Perez 《Catalysis Today》2006,118(3-4):392-401
The methane combustion was studied on Pd supported catalysts searching for explanation of the effects of support, pretreatment and induction periods on the activity of the Pd/alumina, Pd/zirconia, Pd/niobia and Pd/niobia/alumina catalysts. Characterization of methane oxidation in XPS and DRIFTS chambers indicated that an induction period of at least 6 h is necessary to form Pd in a higher oxidation state Pd2+δ coexisting with PdO as the surface active phases. Similarly, DRIFTS measurements showed distinct species at the surface during the oxidation of methane after 6 h, indicating formate species on Pd/Alumina and CHx-species and O2− adsorption on the Pd/zirconia catalyst, suggesting different reaction mechanisms. The reverse pathway depends on the surface modification due to the temperature and induction time.
The activity of the Pd/niobia/alumina was better than of the Pd/niobia. The effect of the precursor was observed, indicating that palladium nitrate precursor allows to lower dispersion but better performance on methane oxidation. The stability was studied and shows that the Pd/zirconia catalyst was stable and is regenerated, while the Pd/alumina catalyst deactivates very fast and is not regenerated. The effect of pretreatment of the catalysts on the methane oxidation showed different behavior depending of the support. 相似文献
186.
This paper presents a method for combining domain knowledge and machine learning (CDKML) for classifier generation and online adaptation. The method exploits advantages in domain knowledge and machine learning as complementary information sources. Whereas machine learning may discover patterns in interest domains that are too subtle for humans to detect, domain knowledge may contain information on a domain not present in the available domain dataset. CDKML has three steps. First, prior domain knowledge is enriched with relevant patterns obtained by machine learning to create an initial classifier. Second, genetic algorithms refine the classifier. Third, the classifier is adapted online on the basis of user feedback using the Markov decision process. CDKML was applied in fall detection. Tests showed that the classifiers developed by CDKML have better performance than machine‐learning classifiers generated on a training dataset that does not adequately represent all real‐life cases of the learned concept. The accuracy of the initial classifier was 10 percentage points higher than the best machine‐learning classifier and the refinement added 3 percentage points. The online adaptation improved the accuracy of the refined classifier by an additional 15 percentage points. 相似文献
187.
Vicente Galiano Héctor Migallón Violeta Migallón José Penadés 《The Journal of supercomputing》2011,58(2):160-167
Parallel nonlinear preconditioners, for solving mildly nonlinear systems, are proposed. These algorithms are based on both
the Fletcher–Reeves version of the nonlinear conjugate gradient method and a polynomial preconditioner type based on block
two-stage methods. The behavior of these algorithms is analyzed when incomplete LU factorizations are used in order to obtain
the inner splittings of the block two-stage method. As our illustrative example we have considered a nonlinear elliptic partial
differential equation, known as the Bratu problem. The reported experiments show the performance of the algorithms designed
in this work on two multicore architectures. 相似文献
188.
Violeta Leoreanu-Fotea 《Information Sciences》2009,179(15):2710-3173
The aim of this paper is to consider and study a new kind of fuzzy n-ary hyperstructures, such as fuzzy n-ary hypergroups and fuzzy (m,n)-ary hyperrings. 相似文献
189.
Magdalena Lungu Stefania Gavriliu Elena Enescu Mariana Lucaci Violeta Tsakiris Gimi Rimbu 《Metallurgical and Materials Transactions A》2012,43(12):4464-4469
Silver-tin oxide electrical contact material with 10?wt pct stannic oxide and balance nanosized and micronsized silver was developed successfully. Stannic oxide particles chemically coated by a layer of silver nanospheres are homogeneously dispersed in a silver microcrystalline matrix made by chemical synthesis. The material processed by pressing-sintering-repressing exhibited enhanced properties: density: 97.1 to 97.9?pct relative density, Vickers hardness: 103 to 115, electrical conductivity: 65 to 69?pct IACS, volumetric shrinkage: 28.9 to 30.9?pct, and a very fine and uniform microstructure. 相似文献
190.
L. Anthony Drummond Vicente Galiano Violeta Migallón Jose Penadés 《International journal of parallel programming》2009,37(1):58-77
Many computational applications rely heavily on numerical linear algebra operations. A good number of these applications are
data and computation intensive that need to run in high performance computing environments. The ACTS Collection brings robust
and high-end software tools to the hands of application developers. However, this transfer of technology is not always successful
due in part to the intricacy of the interfaces associated with the software tools. To alleviate this, here we present PyACTS,
a set of Python based interfaces to some of the tools in the ACTS collection. We illustrate some examples of these interfaces
and their performance, and evaluate not only their performance but also how user friendly they are compared to the original
calls. We also present some examples of scientific applications that use PyACTS. 相似文献