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101.
Flameproof enclosures having internal electrical components are generally used in classified hazardous areas such as underground coalmines, refineries and places where explosive gas atmosphere may be formed. Flameproof enclosure can withstand the pressure developed during an internal explosion of an explosive mixture due to electrical arc, spark or hot surface of internal electrical components. The internal electrical component of a flameproof enclosure can form ignition source and also work as an obstacle in the explosion wave propagation. The ignition source position and obstacle in a flameproof enclosure have significant effect on explosion pressure development and rate of explosion pressure rise. To study this effect three cylindrical flameproof enclosures with different diameters and heights are chosen to perform the experiment. The explosive mixture used for the experiment is stoichiometric composition of methane in air at normal atmospheric pressure and temperature.It is observed that the development of maximum explosion pressure (Pmax) and maximum rate of explosion pressure rise (dp/dt)ex in a cylindrical flameproof enclosure are influenced by the position of ignition source, presence of internal metal or non-metal obstacles (component). The severity index, KG is also calculated for the cylindrical enclosures and found that it is influenced by position of ignition source as well as blockage ratios (BR) of the obstacles in the enclosures. 相似文献
102.
Gray jays (Perisoreus canadensis) cache thousands of food items during each summer for use during the subsequent winter. Previous work on the economics of gray jay scatter-hoarding behavior was based on the assumption that the jays maximize the rate at which they store food energy; alternative currencies were not considered. Here we develop and test models based on two currencies, net rate (net recoverable energy stored per unit time) and efficiency (recoverable energy stored per unit energy expended). Our experiment involved providing gray jays with two options. After collecting a single food item upon arrival at a feeding apparatus, a jay could wait for two additional food items to become (simultaneously) available and then transport all three items for storage in scattered arboreal sites. Alternatively, the jay could immediately transport the single item to a storage site and return to the source repeatedly for additional single-item loads. By incrementally increasing the amount of time jays were required to wait for multipleitem loads, we were able to determine how long jays would wait before switching from multiple- to single-item caching trips. In contrast with the finding in a variety of species that efficiency-maximization models provide a better account of foraging behavior, the net rate-maximization model was a better predictor of the jays' switching point than was the efficiency-maximization model (Figs. 2 and 3). We discuss these conflicting results in the context of recent theory that describes the conditions favoring rate- versus efficiency-maximizing behavior (Ydenberg et al. 1994).
Offprint requests to: T.A. Waite 相似文献
103.
城市景观水体中腐殖酸的臭氧氧化去除 总被引:1,自引:0,他引:1
以南京师范大学德风园池底泥中提取的腐殖酸(HA)为研究对象,采用臭氧氧化技术对其进行去除,对初始pH值、混合气体流量、腐殖酸(HA)初始浓度以及水中常见离子等因素对去除效果的影响进行了研究。实验结果表明:腐殖酸(HA)的去除率随初始pH值的升高而提高,随混合气体流量减少而提高;当腐殖酸(HA)初始浓度为5 mg/L时,反应过程中溶液的UV254升高,紫外扫描结果发现,溶液在200~220 nm内出现杂乱的吸收峰,表明有新物质生成;水中常见的无机阴离子(CO32-、HCO3-)和二价金属离子(Ca2+、Cu2+)的存在会降低臭氧对腐殖酸(HA)的去除率。 相似文献
104.
105.
106.
生物除铁、锰的需氧量试验研究 总被引:2,自引:0,他引:2
研究锰砂滤层去除铁、锰过程中溶解氧因素对去除效果的影响,为生物法除铁、锰的实际运行提供了参考依据。在其他运行条件相同的情况下,只改变其中DO一项,进行去除率试验对比。DO在一定范围内的变化对生物除铁除锰效率的提高无显著影响。从经济性和微生物角度考虑原水DO维持在3mg/L左右既可满足运行要求。 相似文献
107.
Calvo-Iglesias MS Fra-Paleo U Crecente-Maseda R Díaz-Varela RA 《Environmental management》2006,38(6):921-933
The aim of this work is the analysis of the dynamics in cultural landscapes, focused on the spatial distribution of changes
in land cover and landscape patterns, and their possible linkages. These dynamics have been analyzed for the years 1957 and
2000 in a sector of the north of Galicia (NW Spain) characterized with diverse landscapes. Afforestation processes linked
to agriculture abandonment and forestry specialization were the main processes observed in the study area, with the exception
of the southern mountainous sector that was dominated by ploughing of scrubland for conversion into grassland, reflecting
a specialization in livestock production. The structural changes that have taken place in most of the study area were related
to the heterogeneity aspects, although the mountainous sectors were characterized by changes in heterogeneity and fragmentation.
According to the tests performed, the comparison of the spatial distribution of both dynamics showed a certain statistical
significance, reflecting the interrelationship between patterns and processes. This approach could be useful for the identification
of areas with similar characteristics in terms of spatial dynamics so as to define more effective and targeted landscape planning
and management strategies. 相似文献
108.
To forestall, control, and mitigate the detrimental effects of aluminium dust, a 20-L near-spherical dust explosion experimental system and an HY16429 type dust-cloud ignition temperature test device were employed to explore the explosion characteristics of micron-sized aluminium powder under different ignition energies, dust particle sizes, and dust cloud concentration (Cdust) values; the minimum ignition temperature (MIT) values of aluminium powder under different dust particle sizes and Cdust were also examined. Flame images at different times were photographed by a high-speed camera. Results revealed that under similar dust-cloud concentrations and with dust particle size increasing from 42.89 to 141.70 μm, the MIT of aluminium powder increased. Under various Cdust values, the MIT of aluminium dust clouds attained peak value when concentrations enhanced. Furthermore, the increase of ignition energy contributed to the increase of the explosion pressure (Pex) and the rate of explosion pressure rise [(dP/dt)ex]. When dust particle size was augmented gradually, the Pex and (dP/dt)ex attenuated. Decreasing particle size lowered both the most violent explosion concentration and explosive limits. 相似文献
109.
Biodegradation rates of 2-methylisoborneol (MIB) and geosmin through sand filters and in bioreactors 总被引:8,自引:0,他引:8
Taste and odour (T&O) causing compounds, in particular, 2-methylisoborneol (MIB) and geosmin, are a problem for water authorities as they are recalcitrant to conventional water treatment. In this study, biological sand filtration was shown to be an effective process for the complete removal of MIB and geosmin, with removal shown to be predominantly through biodegradation. In addition, MIB and geosmin were also effectively degraded in batch bioreactor experiments using biofilm sourced from one of the sand filters as the microbial inoculum. The biodegradation of MIB and geosmin was determined to be a pseudo-first-order reaction with rate constants ranging between 0.10 and 0.58 d−1 in the bioreactor experiments. Rate constants were shown to be dependent upon the initial concentration of the microbial inoculum but not the initial concentration of MIB and geosmin when target concentrations of 200 and 50 ng l−1 were used. Furthermore, rate constants were shown to increase upon re-exposure of the biofilm to both T&O compounds. Enrichment cultures with subsequent community profile analysis using 16S rRNA-directed PCR-DGGE identified four bacteria most likely involved in the biodegradation of geosmin within the sand filters and bioreactors. These included a Pseudomonas sp., Alphaproteobacterium, Sphingomonas sp. and an Acidobacteriaceae member. 相似文献