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71.
Aerodyne Aerosol Mass Spectrometers (AMS) are routinely operated with a constant vaporizer temperature (Tvap) of 600°C in order to facilitate quantitative detection of non-refractory submicron (NR-PM1) species. By analogy with other thermal desorption instruments, systematically varying Tvap may provide additional information regarding NR-PM1 chemical composition and relative volatility, and was explored during two ambient studies. The performance of the AMS generally and the functional integrity of the vaporizer were not negatively impacted during vaporizer temperature cycling (VTC) periods. NR-PM1 species signals change substantially as Tvap decreases with that change being consistent with previous relative volatility measurements: large decreases in lower volatility components (e.g., sulfate, organic aerosol [OA]) with little, if any, decrease in higher volatility components (e.g., nitrate, ammonium) as Tvap decreases. At Tvap < 600°C, slower evaporation was observed as a shift in particle time-of-flight distributions and an increase in “particle beam blocked” (background) concentrations. Some chemically reduced (i.e., CxHy+) OA ions at higher m/z are enhanced at lower Tvap, indicating that this method may improve the analysis of some chemically reduced OA systems. The OA spectra changes dramatically with Tvap; however, the observed trends cannot easily be interpreted to derive volatility information. Reducing Tvap increases the relative O:C and CO2+, contrary to what is expected from measured volatility. This is interpreted as continuing decomposition of low volatility species that decreases more slowly (as Tvap decreases) than does the evaporation of reduced species. The reactive vaporizer surface and the inability to reach Tvap much below 200°C of the standard AMS limit the ability of this method to study the volatility of oxidized OA species.

Copyright 2015 American Association for Aerosol Research  相似文献   
72.
The effect of depth of intake and controlled discharge of heated waters (Δ T—10°C) on a natural phytoplankton community in a cold water lake was studied using polyethylene enclosures. Changes in plankton species composition and cell concentrations were used as indicators of temperature effects. Of three intake-discharge arrangements studied (surface intake-surface discharge; deep intake-deep discharge; deep intake-surface discharge) only the first design produced statistically significant increases in plankton numbers. A deep intake-surface discharge resulted in the least biological and physical changes in the lake water. Phytoplankton species succession in the heated water was similar to patterns observed in the open lake.  相似文献   
73.
Gelatinase A, a member of the matrix metalloproteinase (MMP) family, is secreted possessing an 80 amino acid N-terminal propeptide that must be removed in order to generate the active enzyme. Purified progelatinase A was activated to 38% of maximum by a 6 h incubation at 37 degrees C with equimolar concentrations of trypsin-activated interstitial collagenase (another MMP). The increase in activity was accompanied by cleavage of the M(r) 72,000 progelatinase A to the M(r) 66,000 active enzyme that has Y81 as its N-terminus. At low concentrations, progelatinase A was processed via an inactive intermediate, suggesting that its activation is a biphasic process. This was confirmed by the action of collagenase on proE375-->A (a mutant of progelatinase A that cannot become active) because, in this instance, only an M(r) 68,000 species with L38 as the N-terminus was produced. The remaining propeptide amino acids to Y81 could be readily removed by added active gelatinase A, indicating that collagenase works by generating an intermediate that is susceptible to autolytic activation. Although relatively slow, the rate of activation could be increased approximately 10-fold by the addition of 100 micrograms/mL heparin. This binds to the C-terminal domain of collagenase and progelatinase A and presumably acts as a template that positions the reactants close to one another. Collagenase activated by trypsin retains 8 or 14 amino acids of its propeptide.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
74.
BACKGROUND: Water under high pressure can produce vaginal injury. Previous reports suggest that postmenarcheal maturation and the presence of a vaginal foreign body contributed to water slide injuries in women. METHODS: A case of a vaginal injury from a water slide in a premenarcheal patient is presented. A literature review of water-related vaginal injuries in adults and children compares the mechanism of injury with that previously reported. RESULTS: The patient underwent operative repair of her injury. CONCLUSIONS: Vaginal injury in premenarcheal patients may result from a water slide. The emergency physician must be aware of this potential injury mechanism and the need for complete examination under anesthesia when vaginal bleeding is present.  相似文献   
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Two pressure-controlled inlets (PCI) have been designed and integrated into the Aerodyne Aerosol Mass Spectrometer (AMS) inlet system containing an aerodynamic aerosol lens system for use in airborne measurements. Laboratory experiments show that size calibration and mass flow rate into the AMS are not affected by changes in upstream pressure (P 0 ) of the PCI as long as the pressure within the PCI chamber (P PCI ) is controlled to values lower than P 0 . Numerous experiments were conducted at different P PCI , P 0 , and AMS lens pressures (P Lens ) to determine particle transmission efficiency into the AMS. Based on the results, optimum operating conditions were selected which allow for constant pressure sampling with close to 100% transmission efficiency of particles in the size range of ~ 100–700 nm vacuum aerodynamic diameter (d va ) at altitudes up to ~ 6.5 km. Data from an airborne field study are presented for illustration.  相似文献   
78.
Climate change in the Arctic is expected to have a major impact on stream ecosystems, affecting hydrological and thermal regimes. Although temperature is important to a range of in‐stream processes, previous Arctic stream temperature research is limited—focused on glacierised headwaters in summer—with limited attention to snowmelt streams and winter. This is the first high‐resolution study on stream temperature in north‐east Greenland (Zackenberg). Data were collected from five streams from September 2013 to September 2015 (24 months). During the winter, streams were largely frozen solid and water temperature variability low. Spring ice‐off date occurred simultaneously across all streams, but 11 days earlier in 2014 compared with 2015 due to thicker snow insulation. During summer, water temperature was highly variable and exhibited a strong relationship with meteorological variables, particularly incoming shortwave radiation and air temperature. Mean summer water temperature in these snowmelt streams was high compared with streams studied previously in Svalbard, yet was lower in Swedish Lapland, as was expected given latitude. With global warning, Arctic stream thermal variability may be less in summer and increased during the winter due to higher summer air temperature and elevated winter precipitation, and the spring and autumn ice‐on and ice‐off dates may extend the flowing water season—in turn affecting stream productivity and diversity.  相似文献   
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A recently developed method to rapidly quantify the elemental composition of bulk organic aerosols (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is improved and applied to ambient measurements. Atomic oxygen-to-carbon (O/C) ratios characterize the oxidation state of OA, and O/C from ambient urban OA ranges from 0.2 to 0.8 with a diurnal cycle that decreases with primary emissions and increases because of photochemical processing and secondary OA (SOA) production. Regional O/C approaches approximately 0.9. The hydrogen-to-carbon (H/C, 1.4--1.9) urban diurnal profile increases with primary OA (POA) as does the nitrogen-to-carbon (N/C, approximately 0.02). Ambient organic-mass-to-organic-carbon ratios (OM/OC) are directly quantified and correlate well with O/C (R2 = 0.997) for ambient OA because of low N/C. Ambient O/C and OM/OC have values consistent with those recently reported from other techniques. Positive matrix factorization applied to ambient OA identifies factors with distinct O/C and OM/OC trends. The highest O/C and OM/OC (1.0 and 2.5, respectively) are observed for aged ambient oxygenated OA, significantly exceeding values for traditional chamber SOA,while laboratory-produced primary biomass burning OA (BBOA) is similar to ambient BBOA, O/C of 0.3--0.4. Hydrocarbon-like OA (HOA), a surrogate for urban combustion POA, has the lowest O/C (0.06--0.10), similar to vehicle exhaust. An approximation for predicting O/C from unit mass resolution data is also presented.  相似文献   
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