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排序方式: 共有297条查询结果,搜索用时 62 毫秒
21.
Philip N. Onyewu Chi-Tang Ho Henryk Daun 《Journal of the American Oil Chemists' Society》1986,63(11):1437-1441
A model system developed in our laboratory for the study of thermal degradation products (TDP) of carotenoids was employed.β-Carotene (10 g) in glycerol was heated at 210 C for 4 hr, 1 hr, 15 min and 5 min. The time and temperature chosen were similar
to edible oil deodorization and deep fat frying. In this study, the TDP ofβ-carotene were quantified as influenced by time and temperature of heating. Results indicate that at 210 C, degradation is
almost complete after 4 hr and most of the nonvolatile products are viscous, yellow-brownish material. Shorter times (1 hr,
15 min and 5 min) cause less degradation. TDP include nonpolar as well as oxidized derivatives ofβ-carotene. The results of this study provide information on the type, amount and mechanism of formation of compounds resulting
from heating carotenoids.
Presented at the AOCS meeting in Dallas, Texas, in 1984. 相似文献
22.
A simplified formulation of the geometric stiffness matrix for plate elements is presented. In this formulation the transverse displacement is defined along the element boundary but not for the element interior as with the usual formulation. As such the formulation is particularly suitable for use with hybrid stress or discrete Kirchhoff methods which are also based on boundary approximation of the transverse displacement.
The simplicity, computational economy and accuracy obtained with the formulation compare favorably with the usual order formulation. 相似文献
23.
Vibrational spectroscopy and periodic DFT studies of LaMg2PdH7: A material with two types of hydride
Stewart F. Parker Jon W. Taylor Henryk Herman Jean-Philippe Rapin Nicolas Penin Klaus Yvon 《Journal of Alloys and Compounds》2009,470(1-2):80-84
The need for a safe, reliable and cheap method for hydrogen transportation has prompted an intense effort in the synthesis of novel hydrides. To direct the search for better materials, it is essential to understand the bonding present in these systems. A newly synthesized material is LaMg2PdH7 which is best formulated as {La3+}{Mg2+}2{[PdH4]4−}{H−}3. Thus hydrogen is formally present both as a free hydride ion and also as a covalently bound ligand. The combination of inelastic neutron scattering (INS), infrared and Raman spectroscopies and periodic density functional theory (DFT) has been used to characterise the material. We find that the material is less ionic than Ba2[PdH4], which also contains [PdH4]4−. The charges carried by both the coordinating and free hydrides are similar which hints at a degree of covalency in the interactions between the interstitial hydrides and the lanthanum and magnesium ions. 相似文献
24.
Anthocyanins,total polyphenols and antioxidant activity in amaranth and quinoa seeds and sprouts during their growth 总被引:8,自引:0,他引:8
Paweł Paśko Henryk Bartoń Paweł Zagrodzki Shela Gorinstein Maria Fołta Zofia Zachwieja 《Food chemistry》2009
Total antioxidant capacity, total phenolic contents (TP) and anthocyanins contents (ANT) were determined in Amaranthus cruentus and Chenopodium quinoa seeds and sprouts. Antioxidant activity of the investigated seeds decreased in the following order: quinoa, amaranth v. Rawa, amaranth v. Aztek for FRAP and quinoa, amaranth v. Aztek, amaranth v. Rawa for both ABTS and DPPH. Sprouts activity depended on the length of their growth, and the peak values were reached on the fourth day in the case of amaranth and on the sixth day in the case of quinoa. The data obtained by the three methods showed significant correlation between TP content in seeds and sprouts. In sprouts grown in the daylight and in the darkness we observed some significant changes of TP, ANT and antioxidant activity. Amaranth and quinoa seeds and sprouts can be used in food, because it is a good source of ANT and TP with high antioxidant activity. 相似文献
25.
The quality of results obtained from surface geochemical exploration depends not only on the character of deep petroleum accumulations but also on the influence of many sub-surface factors. One of important factors is the presence of soil moisture in the sampling interval. This research presents the influence of soil moisture on concentrations of gaseous hydrocarbons in sampled soil gases. The comparative analysis was made on for two populations of gaseous hydrocarbon (methane, ethane, propane, i-butane, n-butane, propylene, 1-butene) concentrations measured in soil gas samples collected from the water-saturated (“wet” sampling interval) and water-free (“dry” sampling interval) environments. The comparison was based upon chromatographic analyses of 2974 samples of soil gas, in which 684 samples originated from “wet” sampling intervals and 2290 samples were taken from “dry” interval. Samples were collected in the areas of known gas deposits located in the Fore-sudetic Monocline (SW Poland). Samples collected from the “wet” intervals reveal higher concentrations of almost all analyzed hydrocarbons in comparison with samples from “dry” intervals. Highest differences were observed for methane concentrations and lowest — for total alkanes C2–C4. The increase of concentrations in “wet” sampling intervals can be explained by sub-surface accumulation of hydrocarbons caused by decreasing permeability of water-saturated soils, by the different solubilities of alkanes and alkenes in water as well as by recent generation of methane and alkenes. Considering the results obtained from the area of the Tarchaly gas deposit, it was found that surface pattern of methane anomalies does not reflect the presence of deep gas accumulations, as well as the total alkanes C2–C4 distribution. Hence, the procedure was proposed of elimination of soil moisture influence on the pattern of surface methane anomalies. The procedure includes normalization of measured methane concentrations to the reference levels of geochemical background, which characterize “wet” and “dry” sampling intervals. As a result, the distribution of anomalous methane concentrations was obtained, which, along with the distribution of total alkanes C2–C4, confirms the presence of assessed accumulation of gaseous hydrocarbons. Therefore, the proposed method is correct and supports the application of methane indicator as a petroleum exploration tool. 相似文献
26.
Anna Michalska Alicja Ceglińska Henryk Zieliński 《European Food Research and Technology》2007,225(3-4):545-551
Rye flours with extraction rate of 100% (wholemeal flour), 95% (brown flour), 90% (brown flour) and 70% (light flour) were
prepared in order to study the relation between flour extraction rates and content of bioactive compounds. The following compounds
were analysed: total phenolic compounds (TPC), total flavonoids (TF), inositol hexaphosphate (IP6), reduced (GSH) and oxidized
(GSSG) glutathione, tocopherols (T) and tocotrienols (T3). The reduced/oxidized glutathione status (GSH/GSSG) of the flours
was examined as a potential index of flour resistance against oxidative stress. The following observations were made in relation
to the flour extraction rates and bioactive compounds contents: (a) milling process caused decrease in content in TPC, TF,
IP6, GSH and GSSG, T and T3, (b) the most resistant against oxidation processes were suggested a brown flours, then light
and finally wholemeal flour, (c) the ratio of tocotrienols to tocopherols (T3/T) was the highest in rye flours with extraction
rate of 100–90% whereas light flour was the poorest source of tocopherols and tocotrienols. The provided data support current
trend to increase number of rye products from wholemeal or brown flours. 相似文献
27.
Victor Chabanenko Roman Puźniak Adam Nabiałek Sergei Vasiliev Vladimir Rusakov Loh Huanqian Ritta Szymczak Henryk Szymczak Jan Jun Janusz Karpiński Vitaly Finkel 《Journal of Low Temperature Physics》2003,130(3-4):175-191
We present a study of magneto-thermal instabilities in polycrystalline MgB2 superconductor, by magnetic hysteresis loop measurements and by investigations of magnetic flux dynamics with a miniature Hall probe. Temperature and magnetic field ranges where the flux jumps may be observed have been determined. On the basis of measurements of the magnetic flux dynamics, an average magnetic diffusivity describing the process of the flux jump is estimated. This parameter is compared with the thermal and magnetic diffusivities calculated on the basis of available data for thermal conductivity, heat capacity and resistivity. It is shown that the estimated value of the field of the first flux jump is influenced significantly by the field dependence of specific heat. In order to explain the observed phenomenon, the temperature reached by the sample during the flux jump at different magnetic fields is calculated. 相似文献
28.
Brice T. Hughes Jordan M. Berg Darryl L. James Akif Ibraguimov Shaorong Liu Henryk Temkin 《Microfluidics and nanofluidics》2008,5(6):761-774
This paper presents a numerical steady-state model of ion transport in micro- and nanofluidic devices with widely varying
geometric scale, such as transitions between micro- and nanochannels. Finite element or finite volume simulation of such problems
is challenging, due to the number of elements needed to produce a satisfactory mesh. Here, only the lengthwise channel dimension
is meshed; standard analytical approximations are used to incorporate cross-channel properties. Singularly perturbed cases
are built up by continuation. The method is shown to reproduce our previously reported measurements of electric double-layer
effects on conductivity, ion concentration, and ion enhancement and depletion. Comparison with 2-D simulations reported in
the literature shows that effects on accuracy due to the 1-D approximation are small. The model incorporates analytical models
of surface charge density taken from the literature. This enables predictive simulation with reasonable accuracy using published
parameter values, or these values may be tuned based on experiment to give improved results. Use of the model for iterative
design and parameter estimation is demonstrated. 相似文献
29.
Henryk Tomaszewski Jan Strzeszewski Lech Adamowicz Valter Sergo 《Journal of the American Ceramic Society》2002,85(11):2855-2857
A method is proposed for the indirect determination of the stress dependence (expressed as piezospectroscopic (PS) coefficients) of spectroscopic bands of ceramic materials/phases. This method is based on the intimate mixture (intimate at the microstructural, grain-size level) of two phases/materials when the stress in one is independently known; it is used to determine the PS coefficients of the most intense Raman bands in ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP). Different amounts of Ce-TZP were mixed with alumina and the composite pellets sintered; subsequently, the stress in alumina was determined through the PS coefficient of its R2 luminescence band and the stress in Ce-TZP derived from the static equilibrium condition. The frequency shifts of each Raman band of Ce-TZP have been plotted against the stress and the slopes provide the PS coefficients. The method has the advantage of not requiring any type of loading device (i.e., diamond anvil-cell, bending jig). Finally, the limits are also discussed, the most important one being the requirement of immiscibility of the two materials/phases. 相似文献
30.
A new method of preparation of carboxyl cation exchangers directly from methacrylic acid and divinylbenzene is described. A suspension technique with a concentrated aqueous calcium chloride solution as the water phase was used. n-Octane and toluene were inert diluents of the monomers. The copolymers obtained have high ion-exchange capacity (9.6–10.6 mequ./g) and porous structure. 相似文献