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71.
J. Podìbradská R. Černý J. Drchalová P. Rovnaníková J. Šesták 《Journal of Thermal Analysis and Calorimetry》2004,77(1):85-97
Methods of thermal analysis are employed in a study of the high-temperature properties of three different types of glass fiber
reinforced cement composites together with the measurements of their thermal and hygric parameters. First, basic TG and DTG
measurements are carried out to get the first insight into the high-temperature behavior of the analyzed materials. Then,
mercury porosimetry and scanning electron microscopy of specimens subjected to the temperatures of 600 and 800°C are performed
and compared to the reference specimens not exposed to any thermal load. Finally, measurements of thermal and hygric parameters
of the studied materials are done and matched with the results of the material characterization experiments. Three main effects
are found to influence the thermal and hygric properties of the analyzed materials. The first is the decomposition of the
cement matrix, which is clearly a negative factor. The second is the positive effect of the presence of fibers that could
partially keep the cement matrix together even after significant decomposition of cement hydration products. The third important
factor affecting the thermal and hygric properties is the composition of the particular materials. The application of vermiculite
aggregates instead of sand is found to be clearly positive because of its porous character leading to the bulk density decrease
without worsening the other properties. Also, wollastonite aggregates are a better choice than sand because of its fibrous
character that could partially magnify the effect of fiber reinforcement.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
72.
Pinar Heggernes 《Discrete Mathematics》2006,306(3):297-317
Any given graph can be embedded in a chordal graph by adding edges, and the resulting chordal graph is called a triangulation of the input graph. In this paper we study minimal triangulations, which are the result of adding an inclusion minimal set of edges to produce a triangulation. This topic was first studied from the standpoint of sparse matrices and vertex elimination in graphs. Today we know that minimal triangulations are closely related to minimal separators of the input graph. Since the first papers presenting minimal triangulation algorithms appeared in 1976, several characterizations of minimal triangulations have been proved, and a variety of algorithms exist for computing minimal triangulations of both general and restricted graph classes. This survey presents and ties together these results in a unified modern notation, keeping an emphasis on the algorithms. 相似文献
73.
《印度化学会志》2022,99(11):100724
In this study, Portland Limestone Cement (PLC) was synthesized by inter-grinding method Portland clinker (PC) with two grades of limestone individually; Cement grade (LS-CG) and Marginal grade (LS-MG) at varying dosages of 0, 10, 15, 20, and 30% by weight, along with a fixed amount (5% by weight) of Gypsum-GYP. It was found that the growth of finer and wider particles was enhanced by increasing both grades of limestone (LS-CG and LS-MG). However, as Limestone per cent exceeded up to 30% in PLC, the normal consistency and specific gravity decreased in the PLC. Investigations suggested that PLC blends with up to 20% addition of LS-CG and LS-MG have qualified the specifications stipulated for blended cement in India as per the Bureau of Indian Standards. It was also observed that the compressive strength of PLC was found to be strongly associated with the 5.5 μm and 3.27 μm particles of PLC. This research suggests that LS-MG can be used to produce PLC. 相似文献
74.
75.
S.V. Goryainov 《Journal of Raman spectroscopy : JRS》2016,47(8):984-992
Thaumasite, Ca3Si(OH)6(SO4)(CO3)⋅12H2O, is an extraordinary mineral that possibly plays a special role in the carbonate–sulfate–silicate balance of the Earth's crust. Thaumasite, an undesirable component in concrete, remains a material poorly studied at high pressures in various media except for He medium (M. Ardit et al., Mineral. Mag., 2014). In the present Raman study, thaumasite samples were compressed in alcohol–water and KBr media at high pressures up to ~7 GPa: several phase transformations were identified. In samples compressed in alcohol–water, the wavenumbers of intense Raman bands of S O and С О symmetric stretching vibrations at 991 and 1074 cm−1 proved to exhibit similar dependences on pressure: during a first transition I → II at 4.4 GPa, the wavenumbers of both bands exhibited a downward jump; at a second transition II → III, which occurred at 4.9 GPa, each band split in a doublet; and then, at a third transition III → IV, which was observed at 5.4 GPa, each doublet band transformed in a singlet. In KBr medium, these and other Raman bands of thaumasite showed similar (to those in thaumasite at compression in alcohol–water) dependences on pressure, revealing several phase transitions with slightly shifted transition points, the first transition I → II, however, being not distinguished. Taking into account the similar behaviors in both media, the transitions are assumed to be polymorphic: no noticeable overhydration in thaumasite compressed in water–alcohol occurred. In phase IV, gradual widening and weakening of each band were observed; those changes can be attributed to amorphization of the material. Considerable hysteresis was observed at thaumasite decompression. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
76.
Triethanolamine (TEA), triisopropanolamine (TIPA), diethanol isopropanolamine (DEIPA) are necessary cement additives, and knowing their contents is needed for quality control and also to understand final properties of the cement. Whether it is the production of grinding aids, technical research and development or application research all involve the detection of grinding aids. This work developed a simple analytical technique for the simultaneous analysis of these alkanolamines in liquid cement grinding aids using high-performance liquid chromatography (HPLC) combined with evaporative light scattering detection (ELSD). HPLC was conducted by an XBridge C18 column (with dimensions 4.6 × 250 mm and 5 µm particles) using methanol and 0.1% trichloroacetic acid as mobile elution phases. The ELSD sprayer and drift tube temperatures were 60 ºC and 90 ºC, respectively. HPLC-ELSD developed in this work demonstrated 1) high sensitivity with limits of detection for the three analytes are 0.15, 0.54, 1.04 µg/mL; 2) good linearity with correlation coefficients equal to 0.997–0.999 over the tested concentration range; 3) excellent repeatability with intra- and interday coefficient of variation (CV) below 2.71% and 4, satisfactory accuracy with recovery in the 95.5%–100.8% range. This novel method is a powerful, time- and costeffective tool for alkanolamine analyses and quality control. 相似文献
77.
In this work two aluminic pozzolans (metakaolins) and a non-pozzolan were added to two Portland cements with very different
mineral composition, to determine the effect on the rate of heat release and the mechanisms involved. The main analytical
techniques deployed were: conduction calorimetry, pozzolanicity and XRD.
The results showed that the two metakaolins induced stimulation of the hydration reactions due to the generation of pozzolanic
activity at very early stage, because of their reactive alumina, Al2O3r− contents, mainly. Such stimulation was found to be more specific than generic for more intense C3A hydration than C3S, at least at very early on into the reaction, and more so when 7.0% SO3 was added, and for this reason, such stimulation is described as ‘indirect’ to differentiate it from the ‘direct’ variety.
As a result of both stimulations, the heat of hydration released is easy to assimilate to a Synergistic Calorific Effect. 相似文献
78.
Methods involving heat measurements have been applied in the cement industry for a long time. Differential thermal analysis (DTA) is used to explain the clinkering reactions, but it is a dynamic method which thus does not allow measurements and calculations of the thermal balance of the reactions to be made. In contrast, high temperature microcalorimetry may be used to measure the enthalpy of the clinkering reactions of industrial raw materials. Results obtained by using this technique allow us to determine the thermal profile of clinkering reactions in the kiln and to quantify the heat exchange in the solid material during its burning.Low temperature conduction microcalorimetry gives information on the hydration mechanism of the cement pastes. In this paper, we review the applications of thermal analysis in the cement industry paying special attention to new methods such as high temperature microcalorimetry.
Zusammenfassung Seit langer Zeit werden in der Zementindustrie Verfahren mit Wärmemessung angewendet. Zur Erforschung der Verschlackungsreaktionen wird DTA verwendet, was jedoch ein dynamisches Verfahren ist und keine Messungen und Berechnungen bezüglich des thermischen Gleichgewichtes erlaubt. Im Gegensatz dazu kann Hochtemperatur-Mikrokalorimetrie zur Messung der Enthalpie von Verschlackungsreaktionen industrieller Rohstoffe dienen. Mit Hilfe der durch diese Methode erlangten Resultate kann das thermische Profil von Verschlackungsreaktionen im Kiln und der Wärmeaustausch im Festmaterial beim Brennen bestimmt werden.Niedertemperatur-Konduktions-Mikrokalorimetrie liefert Informationen über den Hydratationsmechanismus von Zementleim. Unter spezieller Beachtung neuer Methoden, wie z.B. der Hochtemperatur-Mikrokalorimetrie, wird in diesem Artikel ein Überblick über die Anwendungen der Thermoanalyse in der Zementindustrie gegeben.相似文献
79.
Ewa T. Stepkowska 《Journal of Thermal Analysis and Calorimetry》2005,80(3):727-733
Summary Previous study of the hydration and ageing products of two cement pastes created the basis for the postulate of the course of solid-state reactions between the portlandite Ca(OH)2 and the CO2 from air in the hydrated and air dry cement. XRD basal spacing d(001) of portlandite exceeded the nominal value and increased with ageing, with the wetting and drying procedure and with carbonate content of the paste, indicating that a part of OH- ions was gradually substituted by CO32- ions, which are about twice bigger. IR spectroscopy showed a considerable content of portlandite, of CO32- of water and silicates. Also HCO3- H2O and CO2 in cavities between hexagonal rings and hexagonal hydrates were indicated. By MS (mass spectrometry) in vacuum the evaporation of sorbed water was detected at 100-120°C, of gel water at 350°C of portlandite water at 400°C and of high temperature water between 500 and 700°C, simultaneously with CO2 escape. Slightly higher peak temperatures were found by the TG test either in air or in argon. From these results and from geometric considerations it is postulated that the solid-state reactions take place on ageing of the cement paste and on its heating: hexagonal portlanditecalcium carbonate hydroxy hydratecalcium carbonate hydratehexagonal vaterite and/or orthorhombic aragoniterhombohedral calcite The analysis of the standard files of the calcium carbonate hydroxy hydrates supports this postulate and indicates a gradual transformation. 相似文献
80.
Barbara Pacewska I. Wilińska M. Bukowska G. Blonkowski Wiesława Nocuń-Wczelik 《Journal of Thermal Analysis and Calorimetry》2004,77(1):133-142
The so-called pozzolanic activity of waste catalysts from fluidised cracking was investigated. For this purpose a series of
cement mixtures with this waste material were prepared and subsequently the pastes and mortars were produced. Waste aluminosilicate
catalyst was used both in raw form and after grinding in a ball mill for 60 min. The hydrating mixtures were subjected to
the calorimetric measurements in a non-isothermal/non-adiabatic calorimeter. After an appointed time of curing the hydrating
materials were studied by thermal analysis methods (TG, DTG, DTA). The pozzolanic activity factors were determined, basing
on the compressive strength data. The increased activity of cement — ground pozzolana systems has been thus proved. An accelerated
Ca(OH)2 consumption as well as higher strength were found for materials containing ground waste catalyst, as compared to those, mixed
with the raw one. Thus grinding was also proved to result in mechanical activation in the case of the waste catalyst from
fluidised cracking.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献