芸薹属查尔酮异构酶基因家族RNA干扰载体的构建

作为类黄酮途径的第二步关键酶,查尔酮异构酶(chalcone isomerase,CHI)催化四羟基查尔酮成为柚皮素,用于合成各种类黄酮物质,影响多种性状。芸薹属含有多种重要的油料、蔬菜和观赏植物。本研究从甘蓝型油菜克隆了芸薹属CHI基因家族的干扰片段BCHII(761bp),采用NcoⅠ+AatⅡ和BamHⅠ+XbaⅠ双酶切方案分别将其反义片段和正义片段亚克隆到植物RNA干扰(RNAi)平台载体pFGC5941M的启动子与间隔区、间隔区与终止子之间,形成了11674bp的RNAi载体pFGC5941M-BCHII(简称pBCHII),多种PCR检测表明2个片段的插入方向正确,重组载体完整,将其转化根癌农杆菌菌株LBA4404以后获得了工程菌株LBA4404-pBCHII-①。本研究结果将促进研究CHI与芸薹属异花授粉、植株色彩、黄籽和抗逆性等性状的关系和开展相关分子育种。     

木材裂纹尖端应力场的有限元分析和开裂方向预测

以鱼鳞云杉木材三点弯曲试件为例,应用ABAQUS有限元软件分析裂纹体与木材顺纹向倾角分别为90°,60°,30°,0°时的应力场,并采用"切向比正应力准则"对裂纹的启始开裂方向进行预测.结果表明:1)以裂尖为中心作径向平面,4种裂纹体试件的最大Mises应力所在的径向线均沿着木材的顺纹理方向;2)在除去裂尖奇异点以外的一个较大区域中,垂直裂纹表面的拉应力σY和平行裂纹表面的拉应力σX的比值σY/σX几乎是一个常数,在1～5之间;3)无论初始裂纹与木材顺纹向的夹角如何,其裂尖处的切向比正应力(R)均在顺纹方向上最大,理论预测和试验结果均表明裂纹将折向顺纹方向启裂.最后讨论木细胞间的低界面强度对木材的增韧作用.     

论毛泽东农业建设思想及对新农村建设的启示

对毛泽东农业建设思想进行了分析，并提出了其对新农村建设的影响。     

昆虫蛋白营养特性及其在水产饲料中的应用

昆虫繁殖快、数量多、生长周期短、易于低成本养殖、具有较高的营养价值和独特的生理作用等优点,是一种可持续利用的生物蛋白资源。其富含蛋白质、油脂,较多的矿物质、维生素以及无氮浸出物,还含有未知的促生长因子,已引起了人们的广泛关注。文章综述了昆虫营养特性及其生物活性,其在水产饲料上的研究新进展及应用展望,并初步阐述了昆虫蛋白在实际生产、加工、蛋白原料应用和推广等方面所面临的问题,以期为缓解水产业所面临的鱼粉等蛋白资源短缺的局面提供参考。     

也谈提高犬的注意力应注意的问题

犬有灵敏的嗅觉和听觉,快速的驰骋力,极强的凶猛性和对人的忠诚依恋性,具备良好的警用品质,经过人为地严格挑选和强化训练就能作为侦察破案的工具投入使用.     

Quantitative dietary methionine requirement of juvenile golden pompano Trachinotus ovatus at a constant dietary cystine level

A feeding trial was conducted to determine the dietary methionine requirement of juvenile golden pompano (initial body weight 12.40 ± 0.02 g). Six diets were formulated with six graded levels of methionine (8.6, 9.2, 10.4, 11.5, 13.2 and 14.5 g kg⁻¹). Each diet was randomly assigned to triplicate groups of 20 juvenile fish in seawater floating net cages (1.0 m × 1.0 m × 1.5 m). Fish were fed twice daily (08:30 and 16:30) to apparent satiation for 56 days. Weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), feed efficiency (FE), nitrogen retention efficiency (NRE), proximate body composition, morphometry and haematology were significantly (P < 0.05) affected by the dietary methionine levels. WG, SGR and FE increased with increasing levels of methionine up to 13.2 g kg⁻¹ diet (P < 0.05) and remained nearly the same thereafter. NRE also increased with increasing levels of methionine up to 13.2 g kg⁻¹ diet (P < 0.05) and remained nearly the same thereafter. Linear regression analysis on WG and NRE indicated that the recommended optimum dietary methionine levels for optimal growth of juvenile pompano were 10.6 and 12.7 g kg⁻¹ diet, respectively, corresponding to 24.6 and 29.5 g kg⁻¹ dietary protein, respectively, so the level of dietary methionine should be between 10.6 and 12.7 g kg⁻¹ diet, corresponding to 24.6–29.5 g kg⁻¹ dietary protein. Additionally, the estimated requirements for the other essential amino acids were calculated from A/E ratios of whole‐body amino acid profile based on the methionine requirement determined from the present experiment.     

Dynamic Viscoelastic Properties of Tilapia (Oreochromis niloticus) Skin Gelatin

ABSTRACT

The viscoelastic properties of gelatin extracted from tilapia skin (protein yield: 21.2%) were evaluated using dynamic rheology tests. The flow curves of tilapia gelatin sols (1.0–6.6% w/w, 40°C; 0.5%, 2–40°C) complied with the Herschel-Bulkley model (R² = 0.92–0.99), indicating the presence of yield stress, while the gelling and melting temperature of gelatin dispersions (1.0–6.6%) fit well with the Eldridge-Ferry model (R² = 0.97). Tilapia skin gelatin displayed good thermo-stability and strong gel-forming properties, showing great potential as an alternative for mammal-based gelatin applied in various food products.     

Parseval定理在广义积分中的应用

本文从Fourier级数的展开式及Fourier变换两个角度出发，利用Parseval定理分别求解了在工程物理学及信号分析学中常用到的两类积分。这两类积分的求解，不仅给广义积分的求解提供了新的思路，而且丰富了Parseval定理的应用。     

冀西北旱地马铃薯肥料效应数学模型的研究

本试验采用正交旋转回归设计的方法，选取氮（ｘ１）、磷（ｘ２）、有机肥（ｘ３）三个因素为决策变量，以马铃薯鲜薯产量为目标函数，通过田间试验获得的数据，建立了冀西北旱地马铃薯产量与参试因子间的数学模型。对模型进行解析的结果表明：施用有机肥对旱地马铃薯增产很重要，但施氮磷化肥也能增产；而且有机肥施用可以促进氮肥的增产效果，降低磷肥的增产效果。最后，通过计算机模拟寻优获得了１５００ｋｇ／６６７ｍ２以上施肥方案。