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排序方式: 共有535条查询结果,搜索用时 15 毫秒
51.
This paper investigates the effect of particle size distribution on the properties of blended cements incorporating ground granulated blast-furnace slag (GGBFS) and natural pozzolan (NP). Pure Portland cement (PPC), NP and GGBFS were used to obtain blended cements that contain 10, 20, 30% additives. The cements were produced by intergrinding and separate grinding and then blending. Each group had two different Blaine fineness of 280 m2/g and 480 m2/g. According to the particle size distribution (PSD) curves, 46% of the coarser specimens and 69% of the finer specimens passed through the 20 μm sieve. It was observed that the separately ground specimens were relatively finer than the interground ones and had higher compressive strength and sulfate resistance. The separately ground coarser specimens had the lowest heat of hydration. The separately ground finer specimens, which had the highest compressive strength and sulfate resistance, had the highest percent passing for each sieve size. For these specimens 34, 69, 81 and 99% passed through 5, 20, 30 and 55 μm sieves, respectively. For the interground specimens, which had the same fineness, the respective values for the same sieves were 32, 68, 75 and 94%. 相似文献
52.
Laminated composites with ceramic front layers and metallic or composite backing layers have gained attractiveness as lightweight
armours, as they exhibit the same ballistic performance with lower areal densities as compared to steels. Drop-weight testing
(DWT) has potential for evaluating the low velocity impact behaviour of materials. This testing gives significant ideas and
information about failure mechanisms and behaviour of materials under low velocity impact. In this study, DWT of alumina/aluminum
laminated composites was done in order to investigate the effects of lamination type, density with respect to area and mechanical
property of backing material on the low velocity ballistic performance of these composites. The experimental results showed
that the laminated composite with ceramic front layer and aged-aluminum alloy as backing layer was the most effective among
different investigated specimens against low velocity impact loads. 相似文献
53.
Ilkay Orhan Murat Kartal Qamar Naz Asma Ejaz Gülderen Yilmaz Yüksel Kan Belma Konuklugil Bilge Şener M. Iqbal Choudhary 《Food chemistry》2007,103(4):1247-1254
Since Salvia species (Lamiaceae) have been recorded to be used against memory loss in European folk medicine, we herein examined in vitro anticholinesterase and antioxidant activities of 56 extracts prepared with petroleum ether, chloroform, ethyl acetate and methanol obtained from 14 Salvia species (Salvia albimaculata Hedge and Hub, Salvia aucheri Bentham var. canescens Boiss and Heldr, Salvia candidissima Vahl. ssp. occidentalis, Salvia ceratophylla L., Salvia cryptantha Montbret and Bentham, Salvia cyanescens Boiss and Bal., Salvia frigida Boiss, Salvia forskahlei L., Salvia halophilaHedge, Salvia migrostegia Boiss and Bal., Salvia multicaulis Vahl., Salvia sclarea L., Salvia syriaca L., Salvia verticillata L. ssp. amasiaca) growing in Turkey. The antioxidant activities were assessed by both chemical and enzymatic methods against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging and xanthine/xanthine oxidase (XO) system generated superoxide anion radical inhibition. Anticholinesterase effect of the extracts was tested against both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at concentrations of 0.2 and 1 mg/ml using a microplate-reader assay based on the Ellman method. Most of the extracts did not show any activity against AChE at 0.2 mg/ml, while the chloroform extracts had noticeable inhibition against BChE between 47.7% and 74.7%. The most active extracts at 1 mg/ml for AChE inhibition were observed to be petroleum ether extract of Salvia albimaculata (89.4%) and chloroform extract of Salvia cyanescens (80.2%), whereas ethyl acetate extracts of Salvia frigida and Salvia migrostegia, chloroform extracts of Salvia candidissima ssp. occidentalis and Salvia ceratophylla, as well as petroleum ether extract of Salvia cyanescens were found to inhibit potently BChE (92.2%, 89.6%, 91.1%, 91.3%, and 91.8%, respectively). Particularly, the ethyl acetate and methanol extracts were observed to be highly active against both DPPH and XO. Our data indicates that nonpolar extracts of Salvia species for anticholinesterase activity and the polar extracts for antioxidant activity are worth further phytochemical evaluation for identifying their active components. 相似文献
54.
In many wood products manufacturing processes, it is important to ensure that the physical properties of the raw material lie within acceptable ranges and are measured reliably. It is also important for practical use that the measurement process is robust, low-maintenance, fast and preferably non-contacting. This paper describes the development and demonstration of a microwave system for simultaneously identifying wood grain angle, moisture and density. The method involves propagating a microwave beam through the wood and measuring the resulting depolarization, attenuation and phase shift. The wood physical properties can then be identified from these measurements. In a series of measurements, the prototype microwave system successfully identified wood grain angles for hemlock and Douglas fir respectively with standard errors of 0.9° and 2.5° (measured range = -90° to +90°), moisture content 1.2% and 1.9% (measured range = 7–28%), moisture density 3.7 kg/m3 and 7.9 kg/m3 (measured range = 40–150 kg/m3, and dry density 16 kg/m3 and 30 kg/m3 (measured range = 325–625 kg/m3). 相似文献
55.
Mehmet Kaya Abdulcelil Buğutekin Nuri Orhan 《International Journal of Thermophysics》2011,32(3):665-673
In this study, a new solution treatment “solution treatment under loading” was applied to a porous Ni–50 at.%Ti shape memory
alloy (SMA), which was fabricated by self-propagating high-temperature synthesis (SHS), to explore the microstructural improvement
regarding single-phase NiTi. The effects of solution treatment under loading and without loading on the phase constituent
and thermal conductivity were investigated and discussed. The phase constituent and thermal conductivity of the specimens
considerably changed with solution treatment under loading, but they were not affected significantly with solution treatment
without loading. Intermetallic phases such as B19′(NiTi), Ti2Ni, and Ni4Ti3 disappeared, the density of the B2(NiTi) phase increased with solution treatment under loading, and thus the thermal conductivity
was increased. It was also seen that the thermal conductivity of porous NiTi was less than that of solid NiTi. 相似文献
56.
The purposes of this study were to determine energy consumption of input and output used in sugar beet production, and to make a cost analysis in Tokat, Turkey. Data were collected from 146 sugar beet farms in Tokat, Turkey by using a face-to-face questionnaire performed in January and February 2005. Farms were selected based on random sampling method. The results revealed that total energy consumption in sugar beet production was 39 685.51 MJ ha−1, and accounted for 49.33% of fertilizer energy, and 24.16% of diesel energy. The output/input energy ratio was 25.75 and energy productivity was 1.53 kg MJ ha−1. Results further indicated that 82.43% of total energy input was in non-renewable energy form, and only 12.82% was in renewable form. Economic analyses showed that profit–cost ratio of farms was 1.17. The highest energy cost items were labor, land renting, depreciation and fertilizers. Although intensive energy consumption in sugar beet production increased the yield, it also resulted in problems such as global warming, land degradation, nutrient loading and pesticide pollution. Therefore, there is a need to pursue a new policy to force producers to undertake energy-efficient practices to establish sustainable production systems without disrupting the natural resources. In addition, extension activities are needed to improve the efficiency of energy consumption and to sustain the natural resources. 相似文献
57.
OBJECTIVE: This study was conducted to determine the reliability of detecting features and making diagnoses of lower respiratory infections from chest radiograms in young infants. METHODS: Forty chest radiograms of infants younger than 6 months of age admitted with lower respiratory tract infection to a tertiary care pediatric hospital were independently reviewed on two separate occasions by three pediatric radiologists blinded to the patients' clinical diagnoses. For each radiograph the radiologists noted whether a feature was present, absent or equivocal on a standardized form. The features examined were hyperinflation, peribronchial thickening, perihilar linear opacities, atelectasis and consolidation. On the same form each radiologist indicated whether the radiograph was normal or showed airways and/or airspace disease. Within and between observer agreement were calculated by the average weighted kappa statistic. RESULTS: Within observer agreement for the radiologic features of hyperinflation, peribronchial wall thickening, perihilar linear opacities, atelectasis and consolidation were 0.85, 0.76, 0.87, 0.86 and 0.91, respectively. The between observer kappa results for these features were 0.83, 0.55, 0.82, 0.78 and 0.79, respectively. The within and between observer kappa statistics for interpretation of the radiographic features were best for airspace disease (within, 0.92; between, 0.91), and lower for normal (within, 0.80; between, 0.66) radiogram and for airways disease (within, 0.68; between, 0.48). The presence of consolidation was highly correlated with a diagnosis of airspace disease by all three radiologists. CONCLUSIONS: Clinicians basing the diagnosis of lower respiratory infections in young infants on radiographic diagnosis should be aware that there is variation in intraobserver and interobserver agreement among radiologists on the radiographic features used for diagnosis. There is also variation in how specific radiologic features are used in interpreting the radiogram. However, the cardial finding of consolidation for the diagnosis of pneumonia appears to be highly reliable. 相似文献
58.
The differential attenuation coefficients for total scattering have been measured using the Si(Li) detector at photon excitation energy of 59.5 keV for Fe2O3, Y2O3, Nb2O5, SeO2, Sb2O5 and BaO compounds at seven angles ranging from 60° to 120° at intervals of 10°. The obtained results have been compared with relativistic and non-relativistic theoretical values. 相似文献
59.
Mehmet F. Orhan Ibrahim Dincer Marc A. Rosen 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2009,155(1-2):132-137
The role of the Cu–Cl cycle for thermochemical water decomposition, potentially driven by heat from a nuclear power generation station, in producing hydrogen in a sustainable way is investigated by examining efficiencies. The energy efficiency of the cycle is found to be 45% and the exergy efficiency 10%. The energy and exergy efficiencies of the cycle are observed to vary with temperatures of the reactions and reference-environment, and cycle heat losses. A parametric study is carried out considering several heat losses, reaction and reference-environment temperatures, and component-efficiency scenarios. 相似文献
60.
The classical spherical diffusion equation is expressed in terms of a residual concentration. Thus, it becomes possible to eliminate the second derivative of the concentration with respect to the radial coordinate from the diffusion equation. This, in turn, leads to the advantage that diffusion on the surface of a spherical cavity can be studied by considering the cavity surface only. The case of a point source on the cavity surface is presented as an example for the application of the proposed Residual Concentration Method. 相似文献