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排序方式: 共有249条查询结果,搜索用时 15 毫秒
41.
Hua Tian Ludmila Ermolenko Marion Gabant Carine Vergne Cline Moriou Pascal Retailleau Ali Al‐Mourabit 《Advanced Synthesis \u0026amp; Catalysis》2011,353(9):1525-1533
A new procedure for the aerobic oxidation of α‐amino acids acylated by pyrrole‐carboxylic acid with triplet dioxygen is introduced. The reaction is general for a variety of pyrrole‐amino acid derivatives and represents a very practical and controllable method for the selective preparation of α‐hydroperoxy‐ or α‐hydroxy‐α‐amino acid diketopiperazines with molecular dioxygen. Furthermore, the non‐catalyzed direct oxidation of amino acid derivatives at the α‐position with molecular dioxygen represents a fundamental question. 相似文献
42.
43.
Andrea Trnková Kateřina Šancová Martina Zapletalová Jitka Kašparovská Kateřina Dadáková Ludmila Křížová Jan Lochman Sylvie Hadrová Ivana Ihnatová Tomáš Kašparovský 《Journal of dairy science》2018,101(6):5134-5144
The aim of this study was to determine the degradation of dietary isoflavones in rumen fluid under 2 feeding regimens. The experiments were performed in vitro using a rumen fluid buffer system. The rumen fluid was taken from cows fed either a hay diet or a concentrate-rich diet (the diet consisted of 34.6% maize silage, 17.6% haylage, 12.8% alfalfa hay, and 35.0% supplemental mixture on a dry matter basis). As a source of isoflavones, 40% soybean extract (Biomedica, Prague, Czech Republic) at levels of 5, 25, 50, and 75 mg per 40 mL of rumen fluid was used. Samples of soybean extract were incubated in triplicate at 39°C for 0, 3.0, 6.0, 12.0, and 24.0 h in incubation solution. The metabolism of daidzein and genistein was faster under concentrate-rich diet conditions. In general, production of equol started after 3 to 6 h of incubation and reached the highest rate after approximately 12 h of incubation regardless of the type of diet or concentration of extract. In most of the experiments, production of equol continued after 24 h of incubation. Generally, equol production was greater under the hay diet conditions. Furthermore, experiments with higher amounts of added soybean extract revealed possible inhibitory effects of high levels of isoflavones on the rumen microflora. 相似文献
44.
The high-temperature corrosion behaviour of the Cr containing ferritic alloys Crofer 22 APU and Crofer 22 H were investigated for their potential application as interconnects in planar-type solid oxide electrolysis cells (SOECs) operating at 800 °C for syngas production in steam/CO2 co-electrolysis mode. To simulate the operating conditions for this application, oxidation tests in relevant atmospheres with and without electric current were conducted. The corrosion behaviour was influenced by the electric current resulting in accelerated oxidation on the negative side and suppressed oxidation on the positive side. The scale structure was influenced by a combination of atmosphere and electric current effects. The modified oxidation of the interconnect steels due to the electric current effect could have detrimental impact for the O2 side and beneficial effect for the CO2/H2O side in an SOEC stack operating in co-electrolysis mode. 相似文献
45.
Yulia?A.?Piskun Irina?V.?Vasilenko Ludmila?V.?Gaponik Sergei?V.?KostjukEmail author 《Polymer Bulletin》2012,68(6):1501-1513
The activated anionic ring-opening polymerization of ε-caprolactam initiated by 0.35 mol% of combined initiator, i.e., equimolar
mixture of magnesium di(ε-caprolactamate) (CL2Mg) with magnesium halides (MgCl2, MgBr2, and MgI2) as well as of ε-caprolactam magnesium bromide (CLMgBr) in the presence of 0.35 mol% of N-acetyl-ε-caprolactam as an activator has been investigated in the temperature range 140–200 °C. It was found that the reaction
rate increased while the apparent activation energy decreased in the following series: CL2Mg/MgCl2 < CL2Mg/MgBr2 ~ CLMgBr < CL2Mg/MgI2. In addition, the poly(ε-caprolactam)s prepared with CL2Mg/MgX2 (MgX2 = MgCl2, MgBr2, and MgI2) are characterized by slightly higher thermal stability than polymers obtained with CLMgBr as initiator. These observations
were explained in terms of the coordination of Lewis acids (MgX2, where X = Cl, Br, and I) with imide carbonyl of N-acyllactam end groups leading to the increase of their reactivity and stability. 相似文献
46.
Du N Park HB Robertson GP Dal-Cin MM Visser T Scoles L Guiver MD 《Nature materials》2011,10(5):372-375
Microporous organic polymers (MOPs) are of potential significance for gas storage, gas separation and low-dielectric applications. Among many approaches for obtaining such materials, solution-processable MOPs derived from rigid and contorted macromolecular structures are promising because of their excellent mass transport and mass exchange capability. Here we show a class of amorphous MOP, prepared by [2+3] cycloaddition modification of a polymer containing an aromatic nitrile group with an azide compound, showing super-permeable characteristics and outstanding CO(2) separation performance, even under polymer plasticization conditions such as CO(2)/light gas mixtures. This unprecedented result arises from the introduction of tetrazole groups into highly microporous polymeric frameworks, leading to more favourable CO(2) sorption with superior affinity in gas mixtures, and selective CO(2) transport by presorbed CO(2) molecules that limit access by other light gas molecules. This strategy provides a direction in the design of MOP membrane materials for economic CO(2) capture processes. 相似文献
47.
Vladimir Kocourek Ludmila Havlíková Irena Zemanová 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1987,185(1):14-16
Summary The kinetics of the photodegradation of synthetic pyrethroids (permethrin, cypermethrin and deltamethrin) on the surface of treated grain were investigated. Pyrethroids are quickly degraded if spread in a thin layer on a glass plate and photodecomposition proceeds more slowly on UV-irradiated grain. Moreover, in the latter case the degradation of pyrethroids was incomplete. The residual levels of all compounds after 15 min UV-irradiation depended on the storage time which elapsed between treatment of the grain and irradiation. The results indicate that the synthetic pyrethroids are able to penetrate inside the grain and that the UV-irradiation technique could be a tool to study this penetration.
Die Photostabilität der synthetischen Pyrethroide auf Getreide
Zusammenfassung Die Kinetik der Zersetzung durch Licht synthetischer Pyrethroide (Permethrin, Cypermethrin und Deltamethrin) auf der Oberfläche von Getreidekörnern wurde untersucht. Pyrethroide, die in einer dünnen Schicht auf eine Glasplatte gesprüht sind, zerfallen schnell, ihre Zersetzung auf der Oberfläche des Getreidekornes erfolgt nach UV-Behandlung langsamer. Die Zersetzung der Pyrethroide war unter diesen Bedingungen unvollständig und der Gehalt an Rückstand hängt bei allen Pyrethroiden (nach 15 min UV-Belichtung) von der Zeit zwischen Körnerbehandlung und Belichtung ab. Diese Ergebnisse weisen darauf hin, daß die synthetischen Pyrethroide ins Korninnere dringen können und daß die Technik der UV-Behandlung für die Untersuchung dieser Effekte verwendet werden kann.相似文献
48.
Epoxy/poly(ɛ‐caprolactone) nanocomposites: Effect of transformations of structure on crystallization
Jaroslav Kratochvíl Jakub Rotrekl Ludmila Kaprálková Jiřina Hromádková Ivan Kelnar 《应用聚合物科学杂志》2013,130(5):3197-3204
The influence of morphology of the epoxy/poly(?‐caprolactone) (PCL) system and corresponding nanocomposites with organophilized layered silicate on PCL crystallization was studied by differential scanning calorimetry, scanning, and transmission electron microscopy. The results obtained indicate a significant affecting of nonisothermal PCL crystallization by phase morphology brought about by the reaction‐induced phase separation (RIPS) influenced either by various nanoclay contents or the epoxy/PCL ratio. Dispersed morphology of PCL matrix with epoxy globules induces crystallization at higher temperatures. The inverse dispersed morphology of epoxy matrix with PCL inclusions causes crystallization at lower temperature. The co‐continuous morphology induces crystallization in both steps. Rate of the second crystallization step is substantially higher than that in the first step. No nucleation effect has been found in the nanocomposites with the added nanofiller. Multicomponent samples show retarded crystallization, i.e., lower crystallinities and lower overall crystallization rate compared with neat PCL. The results obtained suggest that it is primarily morphological/interfacial effects that play a decisive role in the crystallization behavior of PCL in the epoxy/PCL/clay system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3197–3204, 2013 相似文献
49.
Water remediation by micelle-clay system: case study for tetracycline and sulfonamide antibiotics 总被引:3,自引:0,他引:3
Removal of tetracycline and sulfonamide antibiotics from water by micelles pre-adsorbed on montmorillonite was studied. Micelles of benzyldimethylhexadecylammonium (BDMHDA) were used. Batch experiments demonstrated that the micelle-clay complexes (1% w/w) removed 96-99.9% of antibiotics from their water solutions containing from 5 to 50 mg/L of pharmaceuticals. Column filters (25 cm) made of a mixture of quartz sand and BDMHDA micelle-clay complex at 100:1 w/w ratio removed 94-99.9% of above pharmaceuticals from initial solutions containing 10mg/L and 89% of sulfamethizole from an initial solution containing 10 microg/L of this antibiotic. These filters were also very efficient in the removal of antibiotics in the presence of dissolved soil organic matter removing 89-99% of tetracycline and sulfamethizol from initial solutions containing 10 mg/L of antibiotic in the presence of 8 mg/L of humic acid, or 9 mg/L of fulvic acid. These data indicate that micelle-clay complexes are very efficient for water purification from tetracycline and sulfonamide antibiotics. 相似文献
50.
Jordanova NV Jordanova DV Veneva L Yorova K Petrovsky E 《Environmental science & technology》2003,37(19):4417-4424
Fast and cost-effective detection of industrial pollution can significantly promote its ecological, economic, and social assessment. A magnetometric method, used for qualitative determination of anthropogenic contamination, meets these requirements but needs further development in more quantitative terms. It could be used successfully in numerous cases when the heavy metals coexist with strongly magnetic iron oxide particles in the source dust. We present an integrated magnetic and geochemical study that examines the utility of magnetometric techniques for rapid, qualitative detection of metallic pollutants in soils and vegetation. The new aspect of our approach, in comparison with previously published articles on this subject, is the combined investigation (magnetic and geochemical) of both soils and vegetation, thus using an additional medium for employing the magnetometry as a pollution proxy at a site. The study area is a small (approximately 3 km2) region in the suburbs of Sofia (Bulgaria), with the main pollution source being a metallurgical factory. Soil samples have been taken from the topmost 20 cm from private gardens, located at different distances from the factory. Vegetation samples were taken from ryegrass (both leaves and roots) and leaves from two kinds of deciduous trees (maple and acacia). The results show that both vegetation and soils are characterized by enhanced magnetic properties, compared to background material, which is due to the presence of magnetite particles of anthropogenic origin accompanying heavy metal emissions. SEM images and microprobe analyses reveal the presence of a significant amount of particles, containing heavy metals (including iron) in vegetation samples taken close to the main pollution source. Correlation analyses show a statistically significant link (correlation coefficients ranging from 0.6 to 0.7) between magnetic susceptibility and the main heavy metals (Cu, Zn, Pb) in soil samples, indicating that the magnetic susceptibility can provide a proxy method for identifying the relative contribution of industrial pollution in soils and vegetation, that is reliable, inexpensive, and less time-consuming than standard chemical analyses. 相似文献