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排序方式: 共有252条查询结果,搜索用时 109 毫秒
31.
李宁 《华南农业大学学报》2005,26(Z1)
文章叙述了分子育种的前景及重要意义,并介绍了基因组学技术在动物育种实践中的应用现状. 相似文献
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Plant conservation: old problems, new perspectives 总被引:1,自引:0,他引:1
Vernon H Heywood 《Biological conservation》2003,113(3):321-335
Nature conservation has changed from an idealistic philosophy to a serious technology(J. Harper, 1992)A review is given of the major conceptual changes that have taken place during the last 50 years in our understanding of the nature of plant conservation and of the principal methodological advances in undertaking conservation assessments and actions, largely through the incorporation of tools and techniques from other disciplines. The interrelationships between conservation and sustainable use are considered as well as the impact of the development of the discipline of conservation biology, the effects of the general acceptance of the concept of biodiversity and the practical implications of the implementation of the Convention on Biological diversity. The effect on conservation policy and management of the accelerating loss or conversion of habitats throughout the world and approaches for combating this are discussed. 相似文献
34.
依据木材切削的基本知识及有限元分析方法设计刀具,首先利用ANSYS对刀具进行建模,然后对刀具进行模拟加载和结果分析,从而确定刀具前角可取57°~62°,后角可取8°~13°,最后通过超薄木片切削机实际加工加以验证.最终结果证明所采用的刀具设计方法可行,木片切削质量和效率能满足加工要求. 相似文献
35.
对芬兰Fiskars的园艺手工具设计的策略、品牌特征和使用过程、安全性考量、通用性考量、人体生理特征、感性因素等设计细节进行了详尽分析,并对经典产品的长远发展与企业文化的传承进行了论述,以期为我国园艺工具的研发中需掌握的高端设计规律和原则提供参考。 相似文献
36.
Summary The effect of 60 minutes’ intravenous infusions, before morning feeding, of ammonium acetate (18.6 micromole/min/kg of body weight) and ammonium acetate with propranolol (11 μg/min/kg of body weight) on the ruminal motility of sheep was examined. Ammonia has an adrenaline‐like action therefore propranolol, a beta‐receptor blocking agent, was administered in order to eliminate the possible effect of adrenaline on ruminal motility. The contractions of the dorsal sack of the rumen were registered by means of the balloon method, with the gauge inserted through the rumen fistula. The infusion of ammonium acetate caused an increase of the ammonia concentration in the blood to 0.6 mmolel/at the end of 60 minutes’ infusion. Already during the first 5 minutes of the intravenous infusion of ammonium acetate there was a decreased frequency of ruminal contractions, which was observed throughout the infusion. After the infusion there was a radical decrease of the concentration of ammonia in the blood, and at the same time an increase in the frequency of rumen contraction was observed. Blocking of the beta‐adrenergic receptors by propranolol did not eliminate the inhibiting action of ammonium ion on rumen motility. The infusion of the ammonium acetate caused an increase of adrenaline and glucose concentration. This response was eliminated by propranolol in the case of adrenaline but not glucose. It is assumed that the action of ammonium ion on the rumen motility is derived primarily by the central nervous system. 相似文献
37.
介绍了在研磨加工领域,主轴往复液压控制系统中的伺服阀,重点介绍该系统中特殊伺服阀的设计和计算。设计的伺服阀的阀芯驱动方式与用比例电磁铁驱动的传统伺服阀不同,该阀芯用伺服电机加滚珠丝杠的方式驱动,可以精准控制阀芯,也可以克服液动力对阀芯位移的影响。 相似文献
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Qin-Pei Lu Yong-Mei Huang Shao-Wei Liu Gang Wu Qin Yang Li-Fang Liu Hai-Tao Zhang Yi Qi Ting Wang Zhong-Ke Jiang Jun-Jie Li Hao Cai Xiu-Jun Liu Hui Luo Cheng-Hang Sun 《Marine drugs》2021,19(12)
Mangrove actinomycetia are considered one of the promising sources for discovering novel biologically active compounds. Traditional bioactivity- and/or taxonomy-based methods are inefficient and usually result in the re-discovery of known metabolites. Thus, improving selection efficiency among strain candidates is of interest especially in the early stage of the antibiotic discovery program. In this study, an integrated strategy of combining phylogenetic data and bioactivity tests with a metabolomics-based dereplication approach was applied to fast track the selection process. A total of 521 actinomycetial strains affiliated to 40 genera in 23 families were isolated from 13 different mangrove soil samples by the culture-dependent method. A total of 179 strains affiliated to 40 different genera with a unique colony morphology were selected to evaluate antibacterial activity against 12 indicator bacteria. Of the 179 tested isolates, 47 showed activities against at least one of the tested pathogens. Analysis of 23 out of 47 active isolates using UPLC-HRMS-PCA revealed six outliers. Further analysis using the OPLS-DA model identified five compounds from two outliers contributing to the bioactivity against drug-sensitive A. baumannii. Molecular networking was used to determine the relationship of significant metabolites in six outliers and to find their potentially new congeners. Finally, two Streptomyces strains (M22, H37) producing potentially new compounds were rapidly prioritized on the basis of their distinct chemistry profiles, dereplication results, and antibacterial activities, as well as taxonomical information. Two new trioxacarcins with keto-reduced trioxacarcinose B, gutingimycin B (16) and trioxacarcin G (20), together with known gutingimycin (12), were isolated from the scale-up fermentation broth of Streptomyces sp. M22. Our study demonstrated that metabolomics tools could greatly assist classic antibiotic discovery methods in strain prioritization to improve efficiency in discovering novel antibiotics from those highly productive and rich diversity ecosystems. 相似文献