首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   201篇
  国内免费   3篇
  完全免费   24篇
  化学   228篇
  2021年   5篇
  2020年   4篇
  2019年   5篇
  2018年   7篇
  2017年   8篇
  2016年   4篇
  2015年   9篇
  2014年   22篇
  2013年   18篇
  2012年   26篇
  2011年   38篇
  2010年   17篇
  2009年   11篇
  2008年   11篇
  2007年   18篇
  2006年   7篇
  2005年   6篇
  2004年   2篇
  2002年   3篇
  2001年   1篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1993年   1篇
  1992年   1篇
排序方式: 共有228条查询结果,搜索用时 474 毫秒
1.
杀虫植物苦皮藤毒杀成分的研究   总被引:33,自引:0,他引:33       下载免费PDF全文
从苦皮藤Celastrus angulatus Max.根皮中分离出5个对粘虫Mythimna separata (walker)具有毒杀活性的新化合物。经高分辨质谱和核磁共振谱鉴定其 结构为1α,2α,6β-三乙酰氧基-4β-羟基-8α-异丁酰氧基9β-呋喃甲酰氧 基-13-异戊酰氧基-β-二氢沉香呋喃(1),1α,2α,6β-二乙酰氧基-4 β-羟基8α,13-二异丁酰氧基-9β-苯甲酰氧基-β-二氢沉香呋喃(2), 1α,2α,6β-三乙酰氧基-4β-羟基-8α-β异丁酰氧基-9β-苯甲酰氧基 -13-异戊酰氧基-β-二氢沉香呋喃(3),1α,6β,8α,13-四乙酰氧基- 2α-羟基-9α-苯甲酰氧基-β-二氢沉香呋喃(4),1α,2α-二乙酰氧基 -4β,6β-二羟基-8β-异丁酰氧基9α-苯甲酰氧基-13-异戊酰氧基-β- 二氢沉香呋喃(5)。它们对5龄粘虫的致死中量LD50分别为91.4,271.5,168.8, 388.0和135.5μg/g。  相似文献
2.
用近红外透射光谱技术测定精米蛋白质含量研究   总被引:16,自引:1,他引:15       下载免费PDF全文
应用近红外透射光谱技术.采用3种不同回归统计分析方法建立业米蛋白质含量(PC)定量回归方程。结果表明,用改进的最小二乘法(MPLS)、偏最小二乘法(PLS)和主成分回归法(PCR)进行饺正时.校正标准误差(SEC)、交叉检验标准误差(SECV)分别为0.1258、0.134O(MPLS).0.1177、0.1175(PLS).0.1207、0.1275(PCR)校正相关系数(RSQ)和交叉验证相关系数(1-VR)分别为0.9941、0.9931(MPLS).0.9950、0.9942(PLS).0.9947、0.9942(PCR)。由此可见,3种回归统计方法在建立业米蛋白质含量回归方程时差异不明显.都具有较好的预测效果。近红外透射光谱法作为一种快速而准确的定量分析手段,在稻米加工企业品质管理、大米品质分析和大米贸易检测上有广阔的应用前景。  相似文献
3.
高效液相色谱法同时分离测定仁用杏花芽中8种植物激素   总被引:11,自引:0,他引:11  
杨途熙  魏安智  郑元  杨恒  杨向娜  张睿 《分析化学》2007,35(9):1359-1361
采用Shim-Park C18 VP-ODS色谱柱(150mm×4.6mm,5μm)、岛津SPD-10A VP UV-检测器,以V(甲醇)∶V(0.075%冰乙酸水溶液)=45∶55为流动相,在流速0.7mL/min、柱温30℃、检测波长254nm的条件下,同时分离测定了仁用杏花芽中的腺素、玉米素、赤霉素、生长素、6-苄氨基嘌呤、秋水仙素、脱落酸和吲哚-3-丁酸8种植物激素。各峰的分离效果理想,加标回收率达到95.41%~103.48%;测量灵敏度达0.0001volt;精密度RSD%<0.1。  相似文献
4.
微波消解法测定饲料骨粉中磷   总被引:11,自引:0,他引:11  
利用微波加热技术,在密封增压罐内消解饲料试样,优选出酸消解体系、消解时间、酸用量等最佳条件,比色法测磷。该法快速、经济、准确。  相似文献
5.
Late embryogenesis abundant (LEA) proteins are mainly low molecular weight (10–30 kDa) proteins, which are involved in protecting higher plants from damage caused by environmental stresses, especially drought (dehydration). These findings and the fact that the breeding of drought tolerant varieties would be of great value in agriculture, form the basis of search for anti-drought inducible genes and their characterization. LEA proteins are generally classified into six groups (families) according to their amino acid sequence and corresponding mRNA homology, which are basically localized in cytoplasm and nuclear region. LEA protein synthesis, expression and biological activities are regulated by many factors (e.g. developmental stages, hormones, ion change and dehydration), signal transduction pathways and lea genes. No tissue-specific lea gene expression has been considered as one main regulatory mechanism on the basis of extensive studies with the model plant, Arabidopsis thaliana. The study of the regulatory mechanism of lea gene expression is an important feature of modern plant molecular biology.  相似文献
6.
Immunological evaluation of SW-HSA conjugate on goats   总被引:7,自引:0,他引:7  
Locoweeds cause significant livestock poisoning and economic loss all over the world. The purpose of this study was to investigate the immune effects of locoweed toxin, swainsonine (SW) and human serum albumin (HSA) conjugate (SW-HSA), on goats. Twenty-four Sannon goats were randomly separated into immune control group (eight goats), immune poisoning group I (six goats), immune poisoning group II (six goats) and poisoning control group (four goats). Immune control group, immune poisoning groups I and II were first vaccinated with SW-HSA conjugate. The poisoning control group, immune poisoning groups I and II were then fed with 10.0 g/kg BW/day dry powder of Oxytropis kansuensis Bunge everyday morning. The immune control group was supplied with an alfalfa-based diet. Blood samples of these experimental animals were collected at different time interval. Immunoassay was performed using indirect ELISA and E-rosette technique. The results show that, after second booster immunization: (1) anti-SW antibody level in some goats increased to 2(8), which proves that SW-HSA conjugate can induce experimental animals to produce high-level anti-SW antibody in their bodies; (2) the high-level antibody in their bodies could maintain 30 days, and decreased gradually after poisoning experiment (in our experiment, there was a return of the antibody level on day 21 after poisoning experiment); (3) the decreasing of the E-rosette rate of the immune poisoning group was delayed 14 days, which suggests that SW-HSA could low down the loss of the immunity of the goats; (4) swainsonine concentration in the blood was significantly lower (p<0.01) in the immune poisoning groups than that in the poisoning control group, and there was no significant difference (p>0.01) between the two immune poisoning groups within the poisoning experiment.  相似文献
7.
小白菜中残留虫酰肼的超临界流体萃取条件的研究   总被引:7,自引:0,他引:7       下载免费PDF全文
杨立荣  张兴  陈安良  李广泽 《色谱》2004,22(3):263-266
 将超临界流体萃取(supercritical fluid extraction,SFE)技术与高效液相色谱分析相结合,建立了特异性杀虫剂虫酰肼的萃取分离方法。SFE对虫酰肼的萃取条件:压力48.3 MPa(7000 psi),温度60 ℃,静态萃取时间20 min,CO2体积10 mL,改性剂甲醇添加量0.04 mL/g,丙酮为收集溶剂。在此条件下,SFE对虫酰肼的萃取率为100.75%,所得样品可直接用于高效液相色谱分析。色谱条件:紫外-二极管阵列检测器(检测波长为245 nm),C18键合色谱柱,乙腈  相似文献
8.
Salinity toxicity is a worldwide agricultural and eco-environmental problem. Many literatures show that arbuscular mycorrhizal fungi (AMF) can enhance salt tolerance of many plants and some physiological changes occurred in AM symbiosis under salt stress. However, the role of ROS-scavenging enzymes in AM tomato is still unknown in continuous salt stress. This study investigated the effect of Glomus mosseae on tomato growth, cell membrane osmosis and examined the antioxidants (superoxide-dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; peroxidase, POD) responses in roots of mycorrhizal tomato and control under different NaCl stress for 40 days in potted culture. NaCl solution (0, 0.5 and 1%) was added to organic soil in the irrigation water after 45 days inoculated by AMF (Glomus mosseae). (1) AMF inoculation improved tomato growth under salt or saltless condition and reduced cell membrane osmosis, MDA (malonaldehyde) content in salinity. So the salt tolerance of tomato was enhanced by AMF; (2) SOD, APX and POD activity in roots of AM symbiosis were significantly higher than corresponding non-AM plants in salinity or saltless condition. However, CAT activity was transiently induced by AMF and then suppressed to a level similar with non-AM seedlings; (3) higher salinity (1% level) and long stress time suppressed the effect of AMF on SOD, APX, POD and CAT activity; (4) this research suggested that the enhanced salt tolerance in AM symbiosis was mainly related with the elevated SOD, POD and APX activity by AMF which degraded more reactive oxygen species and so alleviated the cell membrane damages under salt stress. Whereas, the elevated SOD, POD and APX activity due to AMF depended on salinity environment.  相似文献
9.
10.
Yu X  van de Voort FR  Sedman J 《Talanta》2007,74(2):241-246
Spectral reconstitution (SR), a technique that has been developed to facilitate mid-FTIR transmission analysis of inherently viscous samples, was applied to simplify and automate a previously reported FTIR method for the determination of peroxide value (PV) of edible oils. The basis of the PV determination is the rapid reaction of triphenylphosphine (TPP) with the hydroperoxides present in an oil to produce triphenylphosphine oxide (TPPO), which exhibits a readily measurable absorption band at 542 cm−1. In the SR procedure, the viscosity of oil samples is reduced by mixing them with a diluent, which allows them to be readily loaded into a flow-through transmission cell. The spectra of the neat oil samples are then reconstituted from those of the diluted samples by using the absorption of a spectral marker present in the diluent to determine the dilution ratio. For the SR-based PV method, the TPP reagent was added to the diluent, which consisted of odorless mineral spirits (OMS) containing methylcyclopentadienyl manganese tricarbonyl (MMT) as the spectral marker. Sample preparation for PV analysis involved mixing ∼10 ml of oil with ∼25 ml of the TPP-containing diluent; accurate weighing or delivery of precise volumes was not required because the dilution ratio was determined spectroscopically from the intensity of the ν(CO) absorption of MMT at 1942 cm−1 in the spectrum of the diluted sample relative to that in the spectrum of the diluent. Calibration standards, prepared by gravimetric addition of TPPO to a peroxide-free oil, were handled in the same manner, and a linear calibration equation relating the concentration of TPPO (expressed as the equivalent PV) to the absorbance of TPPO at 542 cm−1 relative to a baseline at 530 cm−1 in the reconstituted spectra was obtained, with a regression S.D. of ±0.15 meq/kg oil. PV determinations on two sets of validation samples, spanning PV ranges of 0-20 and 0-2 meq/kg oil, were carried out in parallel by the AOCS titrimetric and SR-based FTIR procedures, and comparison of the results of duplicate analyses by the two methods indicated that the latter was more reproducible and slightly more sensitive. The SR-based PV method, when implemented on an autosampler-equipped FTIR system, allowed for the automated analysis of ∼90 samples per hour.  相似文献
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号