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排序方式: 共有1047条查询结果,搜索用时 15 毫秒
1.
《化学与健康》通识课的开设对弥补大学生相关知识的欠缺、引导他们正确认识化学对生活的影响、建立合理的膳食结构和养成健康的生活方式等具有重要意义。本文通过阐述民办高校开设《化学与健康》通识课的必要性,选定主要参考教材,筛选出合理的教学内容,探讨该课程的教学方法及考核方式等问题,旨在为该课程的教学改革提供参考,并期望获得理想的教学效果。 相似文献
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Quantifying trophic interactions and niche sizes of juvenile fishes in an invaded riverine cyprinid fish community 下载免费PDF全文
Quantifying feeding interactions between nonindigenous and indigenous fishes in invaded fish communities is important for determining how introduced species integrate into native food webs. Here, the trophic interactions of invasive 0+ European barbel Barbus barbus (L.) and the three other principal 0+ fishes in the community, Squalius cephalus (L.), Leuciscus leuciscus (L.) and Phoxinus phoxinus (L.), were investigated in the River Teme, a River Severn tributary in Western England. B. barbus has been present in the River Teme for approximately 40 years. Analyses of stomach contents from samples collected from three sites between June and September 2015 revealed that, overall, fishes displayed a generalist feeding strategy, with most prey having low frequency of selection. Relationships of diet composition versus body length and gape height were species‐specific, with increasing dietary specialisms apparent as the 0+ fishes increased in length and gape height. The trophic niche size of invasive B. barbus was always significantly smaller than S. cephalus and L. leuciscus and was significantly smaller than P. phoxinus at two sites. This was primarily due to differences in the functional morphology of the fishes; 0+ B. barbus were generally restricted to foraging on the benthos, whereas the other fishes were able to forage on prey present throughout the water column. Nevertheless, the invasive B. barbus were exploiting very similar prey items to populations in their native range, suggesting these invaders were strongly pre‐adapted to the River Teme and this arguably facilitated their establishment and invasion. 相似文献
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以张家港农田土壤作为研究对象,在实验室测定土壤重金属元素As、Cd、Cr、Cu、Zn、Ni、Pb、Hg的含量,并与土壤可见近红外高光谱数据建立土壤重金属含量的定量估测模型,以快速获取研究区农田的土壤重金属含量。为保证模型预测的精度和稳定性,首先,对原始高光谱数据进行平滑处理,并进行一阶导数、倒数一阶导数、倒数的对数一阶导数、平方根一阶导数和连续统去除等形式的光谱变换;然后,提取不同变换光谱的特征波段进行相关性分析;最后,通过逐步回归法建立重金属含量的定量估算模型。结果表明:张家港市农田土壤中Cd、Hg、Cu、Zn存在一定的污染风险。在高光谱的不同变换形式中,一阶导数和连续统去除与重金属含量的相关系数高于其他变换形式。基于8种土壤重金属含量与高光谱数据建立的定量估算模型具有良好的预测精度。Cd、Hg、Cr、As、Cu、Zn、Ni、Pb估算模型的实际值与验证值的拟合度分别为0.874、0.879、0.800、0.646、0.513、0.655、0.603和0.542,可用于预测张家港市的农田土壤重金属含量。 相似文献
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The effect of acetylation of milled rice grains of selected varieties (TDK 8, YRW 4, Reiziq, Amber 33, and SHZ 2) with varying apparent amylose contents (3.8–26.6%) on their physicochemical properties was investigated. Milled rice samples were treated with different acetic anhydride concentrations (0.004–0.04 g per 100 g of milled rice samples in 225 mL of water). Results showed that glutinous (TDK 8), very low amylose (YRW 4) and low amylose containing varieties (Reiziq) were prone to acetylation even with 0.004 g of acetic anhydride. X-ray diffraction patterns showed an increase in the crystallinity in acetylated samples and formation of V-type crystals, suggesting the possible interaction of acetic anhydride with starch. Acetylation of rice grains resulted in reduced peak and final viscosities and gel strength, particularly in glutinous (TDK 8) and very low amylose (YRW 4) rice. Differential calorimetric study showed that acetic anhydride treatment resulted in reduced thermal transition temperatures and enthalpy of all varieties. Although increase in the retrogradation thermal temperatures was observed, the enthalpy of retrogradation was reduced with increasing acetylation, suggesting that the extent of starch retrogradation was lower in all varieties with more prominent reduction in the glutinous type. Furthermore, the texture of cooked acetic anhydride treated rice grains was less hard and showed more adhesiveness. This study demonstrated that the acetylation of rice grains (instead of flour) was successfully achieved, showing the potential of applying acetylation to alter the textural, pasting, thermal and retrogradation properties of rice. 相似文献
5.
采用大田试验,分别于烟苗移栽后25、50、75 d测定土壤主要养分含量,研究施用氰氨化钙、生物炭和微生物肥+饼肥3种土壤改良剂对植烟土壤养分和酶活性的影响。结果表明:施用生物炭和微生物肥+饼肥的土壤速效钾较对照分别提高31.80%和12.52%,施用氰氨化钙的土壤速效磷和碱解氮含量分别降低7.30%和2.01%;烟苗移栽后75 d,施用改良剂土壤过氧化氢酶活性和脲酶活性较对照分别提高11.79%~15.38%、19.10%~25.14%,施用氰氨化钙的最高,生物炭的最低;施用改良剂土壤的中性磷酸酶较对照提高6.96%~14.96%,施用微生物肥+饼肥的最高,施用氰氨化钙的最低。从综合效果来看,施用生物炭改良剂效果最好。 相似文献
6.
以4个引种燕麦(Avena sativa)为典型代表,对其不同生育时期根、茎、叶中的C、N、P含量及其化学计量学特征进行测定,探讨不同生育时期燕麦C、N、P元素含量及其化学计量比的变化规律,为燕麦饲草的科学收获提供理论依据。结果表明:燕麦全株C、N、P含量分别为322.30~333.97、17.42~75.62、2.74~5.42 mg·g-1,燕麦根C、N、P含量分别为298.42~317.92、11.47~73.71、2.82~3.42 mg·g-1,燕麦茎C、N、P含量分别为311.25~338.86、10.15~75.16、2.44~5.06 mg·g-1,燕麦叶C、N、P含量分别为330.80~372.47、30.64~113.80、2.59~8.65 mg·g-1;各器官间C、N、P含量表现为叶>茎>根。此外,燕麦各器官C、N、P含量的积累过程具有一定季节特征,C含量积累过程受生育时期影响较小,表现出较强的稳定性;而N和P含量的积累过程受生育时期影响较大,其在拔节期~抽穗期均... 相似文献
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武当山地区盾叶薯蓣薯蓣皂苷元含量及生物特性的相关性研究 总被引:1,自引:0,他引:1
通过对武当山地区盾叶薯蓣(Diosorea zingiberenzis C.H.Wright)4个居群29个单株根茎的单株质量、折干率、生长速率、薯蓣皂苷元含量检测,及其各生物学特征的差异的研究,探讨了薯蓣皂苷元含量及其它生物特性的相关性。结果表明:武当山地区野生盾叶薯蓣根茎薯蓣皂苷元含量绝大多数在1.6%以上,含量超过2.0%的单株为79%,含量超过3.0%的单株为31%,最高含量达3.51%;武当山泰山庙盾叶薯蓣居群的根茎平均单株质量、平均生长速率、薯蓣皂苷元平均含量显著高于其它3个居群,折干率显著低于其它居群。盾叶薯蓣根茎的薯蓣皂苷元含量与根茎单株质量呈极显著正相关性,相关系数为0.6078,与根茎折干率呈极显著负相关,相关系数为-0.5989,与根茎生长速率不显示显著的相关性;盾叶薯蓣根茎单株质量和生长速率呈极显著正相关,相关系数为0.7199;武当山泰山庙盾叶薯蓣居群为优良的盾叶薯蓣种质,武当山区适合建立野生盾叶薯蓣的种质保护基地。 相似文献
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