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41.
Kimmo Kettunen 《Computers and the Humanities》1996,30(1):77-84
This article focuses on typographical spellchecking. Typographical spellchecking verifies the use of characters such as ? ! - ; : \sp $ @ and other special purpose characters in respect to spaces or null elements. The author claims that this kind of spellchecking has not been developed to any substantial degree, although it could be of considerable practical use as writer's aid. The article discusses the basic challenges of typographical spellchecking and shows that some of the difficulties are greater than might be expected at first sight. Rules for describing the behavior of typographical characters are proposed.His research interests include computational linguistics and electronic publishing. 相似文献
42.
43.
Optimization of Electricity Retailer's Contract Portfolio Subject to Risk Preferences 总被引:1,自引:0,他引:1
44.
Kavec M Gröhn OH Kettunen MI Silvennoinen MJ Penttonen M Kauppinen RA 《Magma (New York, N.Y.)》2001,12(1):32-39
Inadequate blood supply relative to metabolic demand, a haemodynamic condition termed as misery perfusion, often occurs in
conjunction with acute ischaemic stroke. Misery perfusion results in adaptive changes in cerebral physiology including increased
cerebral blood volume (CBV) and oxygen extraction ratio (OER) to secure substrate supply for the brain. It has been suggested
that the presence of misery perfusion may be an indication of reversible ischaemia, thus detection of this condition may have
clinical impact in acute stroke imaging. The ability of single spin echo T2 to detect misery perfusion in the rat brain at 1.5 T owing to its sensitivity to blood oxygenation level dependent (BOLD)
contrast was studied both theoretically and experimentally. Based on the known physiology of misery perfusion, tissue morphometry
and blood relaxation data, T2 behaviour in misery perfusion was simulated. The interpretation of these computations was experimentally assessed by quantifying
T2 in a rat model for cerebral misery perfusion. CBF was quantified with the H2 clearance method. A drop of CBF from 58 ± 8 to 17 ± 3 ml/100 g min in the parieto-frontal cortex caused shortening of T2. from 66.9 ± 0.4 to 64.6 ± 0.5 ms. Under these conditions, no change in diffusion MRI was detected. In contrast, the cortex
with CBF of 42 ± 7 ml/100 g min showed no change in T2. Computer simulations accurately predicted these T2, responses. The present study shows that the acute drop of CBF by 70% causes a negative BOLD that is readily detectable by
T2 MRI at 1.5 T. Thus BOLD may serve as an index of misery perfusion thus revealing viable tissue with increased OER. 相似文献
45.
Vallius T Kuittinen M Turunen J Kettunen V 《Journal of the Optical Society of America. A, Optics, image science, and vision》2002,19(6):1129-1135
An extension of an approximate step-transition perturbation method is presented that permits numerically efficient diffraction analysis of pixel-structured surface profiles in the nonparaxial domain. Comparison with the rigorous diffraction theory of gratings shows that the method is reasonably accurate provided that the pixel size exceeds approximately two wavelengths even if the structure contains isolated pixels. 相似文献
46.
Design of space-variant diffractive polarization elements 总被引:1,自引:0,他引:1
Tervo J Kettunen V Honkanen M Turunen J 《Journal of the Optical Society of America. A, Optics, image science, and vision》2003,20(2):282-289
Improved diffraction efficiencies can be obtained in the paraxial domain of diffractive optics by considering light explicitly as an electromagnetic rather than a scalar field because of the extra freedoms provided by the state of polarization. For example, diffractive beam splitters with 100% efficiency are made possible by means of space-variant subwavelength-carrier surface-relief elements. Some aspects of the general design theory of polarization-modulating elements for vector fields, including design freedoms and constraints, are presented. Upper bounds of diffraction efficiency are derived and compared with those for the scalar case. Iterative design algorithms are developed. Several design examples with different constraints are presented, and the effects of replacing continuous-fringe structures by pixel structures containing locally linear gratings are evaluated. 相似文献
47.
48.
Evaluation of kinetic coefficients using integrated monod and haldane models for low-temperature acetoclastic methanogenesis 总被引:1,自引:0,他引:1
Lokshina LY Vavilin VA Kettunen RH Rintala JA Holliger C Nozhevnikova AN 《Water research》2001,35(12):2913-2922
The integrated Monod and Haldane models were used to evaluate the kinetic coefficients and their standard deviations using the methane accumulation curves of low-temperature acetoclastic methanogenesis. The linear and exponential approximations and the limitations of their applicability were deduced from the integrated models. The samples of lake sediments and biomass taken from a low-temperature upflow anaerobic sludge blanket (UASB) reactor were used as inoculum in batch assays for acetate methanation. In comparison, the Monod and Haldane models were applied to evaluate the kinetic coefficients for mesophilic acetoclastic methanogenesis accomplished by the pure culture of Methanosarcina barkeri strain MS. The Monod and Haldane models and their approximations were fitted by using non-linear regression. For the wide range of initial acetateconcentrations (4.2-84 mM: 5-100 mM) applied to the UASB biomass at 11 and 22 degrees C and for the lake sediment samples at 6 and 15 degrees C, a better fit was obtained with the Haldane models and their exponential approximations, respectively. For the lake sediments the values of inhibition coefficients decreased at decreasing temperatures. At the highest temperature of 30 degrees C no difference was found between the Haldane and Monod models and the simpler Monod model should be preferred. The values of the maximum growth rate of biomass were highest at 30 degrees C (lake sediment) and 22 degrees C (the UASB biomass) being in a range presented in the literature for mesophilic acetoclastic methanogenesis. 相似文献
49.
Biological nitrogen removal from municipal landfill leachate: low-cost nitrification in biofilters and laboratory scale in-situ denitrification 总被引:18,自引:0,他引:18
The slow leaching of nitrogen from solid waste in landfills, resulting in high concentrations of ammonia in the landfill leachate, may last for several decades. The removal of nitrogen from leachate is desirable as nitrogen can trigger eutrophication in lakes and rivers. In the present study, a low-cost nitrification-denitrification process was developed to reduce nitrogen load especially in leachates from small landfills. Nitrification was studied in laboratory and on-site pilot aerobic biofilters with waste materials as filter media (crushed brick in upflow filters and bulking agent of compost in a downflow filter) while denitrification was studied in a laboratory anoxic/anaerobic column filled with landfill waste. In the laboratory nitrification filters, start-up of nitrification took less than 3 weeks and over 90% nitrification of leachate (NH4-N between 60 and 170mg N l(-1), COD between 230 and 1,300 mg l(-1)) was obtained with loading rates between 100 and 130 mgNH4-N l(-1) d at 25 degrees C. In an on-site pilot study a level of nitrification of leachate (NH4-N between 160 and 270 mg N l(-1), COD between 1,300 and 1,600 mg l(-1)) above 90% was achieved in a crushed brick biofilter with a loading rate of 50mg NH4-N l(-1) d even at temperatures as low as 5-10 degrees C. Ammonium concentrations in all biofilter effluents were usually below the detection limit. In the denitrification column. denitrification started within 2 weeks and total oxidised nitrogen in nitrified leachate (TON between 50 and 150mg N l(-1)) usually declined below the detection limit at 25 degrees C, whereas some ammonium, probably originating from the landfill waste used in the column, was detected in the effluent. No adverse effect was observed on the methanation of waste in the denitrification column with a loading rate of 3.8 g TON-N/t-TS(waste) d. In conclusion, nitrification in a low-cost biofilter followed by denitrification in a landfill body appears applicable for the removal of nitrogen in landfill leachate in colder climates. 相似文献
50.
The effects of elevated atmospheric CO2 concentration on N2O fluxes, instant CO2 exchange and the biomass production of timothy (Phleum pratense) were studied in the laboratory. Three sets of 12 farmed sandy soil mesocosms sown with Phleum pratense were fertilised with a commercial fertiliser in order to add 5, 10 and 15 g N m−2, and equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO2 concentration was kept at atmospheric concentration (360 μmol mol−1), and in the other two at double the ambient concentration (720 μmol mol−1). Forage was harvested and the plants fertilised twice during the N2O measurements. This was followed by an extra fertilisation and harvesting. After the third harvest, the growth of P. pratense was maintained at a height of 18 cm for measurements of instant CO2 exchange, performed in two growth chambers. N2O exchange was monitored using a closed chamber technique and a gas chromatograph. Instant CO2 exchange was monitored using an infrared gas analyser. N2O was emitted from the soil in the low, moderate and high N treatments at both CO2 concentrations when the moisture content was low, the N2O probably being mainly derived from nitrification. The highest flux (3303 μg N2O m−2 h−1) occurred in the highest N treatment before thinning the stand of P. pratense under elevated CO2 concentration. P. pratense was acclimated to the elevated CO2 concentration: the NEE and P
G of the elevated growth of P. pratense decreased, in contrast to the fluxes of the normal ambient growth, when measured at the changed CO2 concentration (ambient). The rate of respiration (R
TOT) in the agroecosystem did not increase due to the elevated CO2 concentration, but instead the results indicated decreased R
TOT (on average 2049 and 1808 mg CO2 m−2 h−1 at ambient and elevated CO2 concentration, respectively) when there was an abundant N supply. This infers the possibility of enhanced C accumulation
in agriculture mineral soil via P. pratense under an increased atmospheric CO2 supply. 相似文献