共查询到20条相似文献，搜索用时 375 毫秒
1.
采用离子色谱电导检测法测定皮革制品中Cr（Ⅳ）,选用Metrohm86I型离子色谱仪,Metrosep A Supp5—150型阴离子分析柱,12．8mmol／LNa2C03＋4．0mmol／LNaHC03淋洗液．在10～100μg／L范围内,Cr（Ⅳ）的浓度与色谱峰面积呈线性关系,线性方程为C×100—2893．72×A＋200．136,相关系数为0．9990,最低检测浓度为4μg／L,低、中、高三个浓度的精密度分别为1．60％、1．05％、0．65％,样品加标回收率分别为91．5％、93．6％和92．3％,本方法可用于皮革中Cr（Ⅵ）的测定． 相似文献
2.
优化测定乳制品中三聚氰胺含量的高效液相色谱方法。色谱条件：ODS—SPe18柱,250mm×4．6mm（i．d．）,5μm;流动相：A为离子对缓冲液（2．02g庚烷磺酸钠和2．10g柠檬酸,加入约950mL水溶解,调节pH值至3．0后,定容至1L）,B为乙腈,配制比例为85％A＋15％B;1．0mL／min;柱温：35℃;波长：242nm;选样量：20灿。结果表明：三聚氰胺标准曲线为Y=-5．582＋42．55x,相关系数R=0．9997,在1．0-50．0μg／mL范围内线性关系良好．样品三个浓度水平的加标回收率在90．1—105．9％之间,相对标准偏差为2．04-5．26％。 相似文献
3.
建立固相萃取与UPLC—MS／MS检测食品中黄曲霉毒素M1和黄曲霉毒素B1的方法。样品经乙腈提取和SPE小柱萃取净化,提取液经氮气吹干后,用50％甲醇水溶液定容。超高效液相色谱一串联质谱（UPLC—MS／MS）测定,采用电喷雾正离子（ESI＋）模式电离,多反应监测（MRM）模式检测。流动相为0．1％甲酸水溶液和甲醇,流速0．4ml／min,使用ZORBAX Eclipse XDB—C18色谱柱（100mm×3．0mm×1．8μm）为分析柱。黄曲霉毒素AFM1在0．1～50μg／kg范围内线性关系良好、黄曲霉毒素AFB1在0．1～10ug／kg范围内线性关系良好,相关系数均大于0．999;回收率在83．75％～97．8％之间;检出限AFMl为0．05μg／kg、AFBl0．02μg／kg。该法具有分析速度快,检测准确、灵敏度和回收率高等优点,适合食品中黄曲霉毒素M1、B1含量的检测。 相似文献
4.
一、头同尾补请大家观察如下算式：21×29＝609，23×27＝621，25×25＝625．两个因数的十位数相同（称“头同”），而个位数的和为10（简“尾补”）．算法是尾×尾作为积的十位和个位，不足10的用0占位，然后把头×（头＋1）的结果写在积的左边，这种简算的理论根据是：设这两个两位数分别为10a＋b和10a＋（10－b），则（10a＋b）×［10a＋（10－b）〕＝100a2＋100a－10ab＋10ab＋b（10－b）＝100a（a＋1）＋b（10－b）．其中b（10－b）就是尾×尾，a（a＋1）就是头×（头＋1）．例如81×89＝100×8×（8＋1）＋1×9＝7200＋9＝7209．二、… 相似文献
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7．若对于任意的实数x,有x^3=a0＋a1（x-2）＋a2（x-2）^2＋a3（x-2）^3,则a2的值为（ ）.
A.3 B.6 C.9 D.12
解法1 由x^3＋a0＋a1（x-2）＋a2（x-2）^2＋a3（x-2）^3，比较两边x^3项的系数，得a3＋1，比较两边x^2项的系数，得a2＋1·3·（-2）=0，故a2=6，故选B.[第一段] 相似文献
7.
《数理天地(高中版)》2012,(8):11-12
1．设a∈R,则“a=1”是“直线l1：ax＋2y-1=0与直线l2：x＋（a＋1）y＋4=0平行”的（ ）
（A）充分不必要条件．
（B）必要不充分条件． 相似文献
8.
不同处理条件对洋葱鳞茎表皮细胞骨架形态影响的研究 总被引：1，自引：0，他引：1
细胞骨架是活细胞的重要结构,研究细胞骨架的形态对于进一步研究其功能具有重要意义。本研究以洋葱为材料,设置了4个不同的1％Triton X-100抽提非骨架蛋白时间（10min、15min、25min、40min）对洋葱细胞骨架显微观察的关键条件进行了优化,同时分析了细胞环境温度（-18℃、4℃、20℃、50℃）,紫外线照射活细胞（0min、60min）,0．1mol／L Ca^2＋处理及0．1％秋水仙素处理对洋葱细胞骨架形态观察效果的影响。结果表明：1％Triton X-100抽提非骨架蛋白25min观察效果较好;-18℃、50℃,紫外线辐射60min,0．1mol／L Ca^2＋和秋水仙素处理均会影响细胞骨架的观察。 相似文献
9.
题目：已知A（1,0）,B（0,-1）,C（-1,2）,D（2,-1）,E（4,2）五个点,抛物线y=a（x-1）＋k（a〉0）经过其中三个点．（1）求证：C,E两点不可能同时在抛物线y=a（x-1）＋k（a〉0）上;（2）点A在抛物线y=a（x-1）＋k（a〉0）上吗？为什么？（3）求a与k的值． 相似文献
10.
高国军 《数理天地(高中版)》2014,(12):9-10
题目 设不等式x^2＋ax＋1〉2x＋a,对a∈（1/4,4）恒成立,求实数x的取值范围．
解法1 由x^2＋（a-2）x＋1-a〉0对任意a∈（1/4,4）成立,
令g（a）=（x-1）a＋x^2-2x＋1,需[g（a）]min〉0. 相似文献
11.
绵羊血浆中阿维菌素的高效液相色谱法测定 总被引：1，自引：0，他引：1
测定绵羊血浆中阿维菌素的高效液相色谱法,在样本经乙酸乙酯提取分离后,直接用高效 液相色谱法进行测定(UV245nm),所测成分为阿维菌素B1a,流动相为乙腈:0.1％磷酸- 磷酸二氢钾缓冲液=65:35;检测波长:245nm;流速1.0ml.min~(-1)。 相似文献
12.
Jun-liang Wang Qing Xia An-ping Zhang Xiao-yan Hu Chun-mian Lin 《Journal of Zhejiang University. Science. B》2012,13(4):267-273
The widespread use of organophosphorus pesticides (OPs) poses a great threat to human health and has made the detection of
OP residues in food an important task, especially in view of the fact that easy and rapid detection methods are needed. Because
OPs have inhibitory effects on the activity of α-naphthyl acetate esterase (ANAE) in plants, in this work we evaluated the
possibility of detecting OPs in vegetables with ANAE extracted from commercial flour. The limits of detection (LODs) obtained
for methamidophos, dichlorvos, phoxim, dimethoate, and malathion in lettuce samples with crude ANAE were 0.17, 0.11, 0.11,
0.96, and 1.70 mg/kg, respectively. Based on the maximum residue limits (MRLs) for OPs in food stipulated by Chinese laws
which are 0.05, 0.20, 0.05, 1.00, and 8.00 mg/kg for methamidophos, dichlorvos, phoxim, dimethoate, and malathion, respectively,
the esterase inhibition method with crude ANAE had sufficient sensitivity to detect the residues of dichlorvos, dimethoate,
and malathion in lettuce, but it could not be used to guarantee the safety of the same samples if methamidophos or phoxim
residue was present. The sensitivity of the method was improved by the use of esterase purified by ammonium sulfate salting-out.
The LODs obtained for methamidophos and phoxim with purified esterase were lower than the MRLs for these OPs in food. This
is a very promising method for the detection of OP residues in vegetables using crude or purified esterase because of its
cheapness, sensitivity, and convenience. 相似文献
13.
以西双版纳可提取药用活性成分“血竭”的剑叶龙血树为材料,进行愈伤组织的诱导及增殖培养,结果显示：外植体的消毒侧芽以75％乙醇浸泡2min＋0．1％升汞浸泡8min,花蕾以75％乙醇浸泡1．5min＋0．1％升汞浸泡8min,叶片以75％乙醇浸泡3min＋0．1％升汞浸泡12min效果较好;愈伤组织诱导以花蕾为外植体效果较好,且诱导与增殖的培养基为B5＋2．0mg/L NAA＋0．5mg／L6-BA． 相似文献
14.
辛硫磷与氯氰菊酯混配增效机理初探 总被引：2，自引：0，他引：2
利用电生理和生化方法，以美洲大蠊为材料，研究辛硫磷与氯氰菊酯混用的增效机理．实验结果表明：辛硫磷与三种氯氰菊酯混配，EPSP的开始兴奋时间和阻断时间均低于各单剂单用．促进了突触间隙乙酰胆碱的积累．生化分析认为，混剂增效的原因之一是提高了对靶标酶——AchE的抑制． 相似文献
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对观赏百合品种莫娜鳞片进行组培快繁条件的优化研究．结果表明,使用75％酒精消毒10s,0．1％升汞处理10min,最后用无菌水清洗5次灭菌效果最好,污染率最低;MS＋0．5mg／L6-BA＋1mg／LNAA为最佳诱导培养基． 相似文献
17.
Minimal procedures for the demonstration of transitive inference (TI) in animals have involved the training of four simultaneous discriminations: for example, A+B?, B+C?, C+D?, and D+E?, followed by the demonstration of a preference for B over D on test trials. In Experiment 1, we found that TI in pigeons can be found with successive training involving A+B?, B+C?, A+C?, C+D?, D+E?, C+E?, and A+E?. In Experiment 2, we found that demonstration of TI did not require inclusion of experience with the nonadjacent stimulus pairs (A+C?, C+E?, A+E?). Experiment 3 provided a test of value transfer theory (VTT; Fersen, Wynne, Delius, & Staddon, 1991). When pigeons were trained with stimulus pairs that did not permit the transitive ordering of stimuli, but did permit the differential transfer of value (e.g., A+B?, C?E+, C+D?, & A+E?), preference for B over D was still found. Analyses of the relation between direct experiences with reinforced and nonreinforced responding and stimulus preferences on test trials failed to support a reinforcement-history account of TI. 相似文献
18.
采用微波消解-氢化物原子荧光法测定烟草中痕量砷:空心阴极灯电流130 mA,开启高强度模式,检测器电压为320 V,载气与保护气流速分别为200、700 mL/min,添加硫脲-抗坏血酸预还原样品中的As5+,方法检出限为0.034 ng/mL,线性相关系数为0.999。测试4种市售香烟,测试变异系数为1.34%~4.55%,加标回收率97.7%~100.2%,方法适用于烟草中砷的测定。 相似文献
19.
余国栋 《贵州教育学院学报》2002,13(2):1-3
给出周期系数Riccati型方程dx/dt＝A（t）x^2m-1 B(t)x^2k-1 C(t)（其中，A(t)，B(t），C(t）是周期为T的连续函数，m,k∈N，m＞k）存在周期解的充分条件。 相似文献
20.
《Journal of research on educational effectiveness》2013,6(4):635-661
ABSTRACTThe purpose of this study was to test the promise of the NumberShire Level 1 Gaming Intervention (NS1) to accelerate math learning for first-grade students with or at risk for math difficulties. The NS1 intervention was developed through the Institute of Education Sciences, Small Business Innovation Research Program (Gause, Fien, Baker, & Clarke, 2011) as a digitally based technology tool to allow educators to intervene early and strategically with students struggling to learn mathematics. This study used a randomized controlled trial design to test the promise of the NS1 intervention. In total, 250 first-grade students were randomly assigned within classrooms to the treatment condition or a control condition. Results indicate significant effects favoring the treatment group on proximal measures of whole-number concepts and skills. Intervention effects were not statistically significant for distal outcome measures. Treatment effects were not moderated by special education or English learner status; however, the condition by initial skill level interaction approached significance. Additionally, there was no relationship between dosage variables and students' response to the intervention. Limitations and future directions for research are discussed. 相似文献