共查询到20条相似文献,搜索用时 31 毫秒
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通过PCR产物克隆测序和直接产物测序的方法对禾本科小麦族仲彬草属10个物种的rDNA内转录间隔区(ITS)及5.8SrDNA进行了序列测定和系统发育分析。结果表明:该属植物ITS区直接产物测序与克隆测序存在较大差异,克隆测序序列反映的系统发育关系与形态学、地理分布、细胞学、分子标记分析结果基本一致。因此,采用克隆测序的方法对仲彬草属植物系统发育分析比直接测序方法更为可靠。 相似文献
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介绍了我国的粮食直补政策模式,采用可计算一般均衡(CGE)理论,提出了我国粮食直补政策模型的构建方案。在遵循市场的完全竞争性,资本、劳动力不存在国家间的移动,汇率不变、产品的不完全替代性,行为主体为具有代表性的家庭、生产者、地方政府、中央政府所组成等假设的基础上,构建出我国粮食直补政策的CGE模型。该CGE模型需要的相关参数包括:中间合成产品、投资合成品和消费合成品在进口和国产之间的Arm ingtion替代弹性,生产要素之间的替代弹性,总销售在国内吸收和出口之间的转换弹性,居民支出弹性和价格弹性,出口需求弹性,以及资本存量中各部门的相对份额等。并指出CGE模型在分析粮食直补政策方面的优势及局限性。 相似文献
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以1984~2006年的时间序列数据为基础,采用农产品出口(EX)、农产品进口(IM)、总贸易额(TEI)和外商直接投资(FDI)为变量,利用Eviews5.0软件,运用协整分析和VAR模型对农业FDI与农产品国际贸易额变量之间的动态关系进行实证分析,结果显示:农业FDI与我国农产品进出口增长存在长期的协整关系,但在短期内可能发生FDI对进口的替代而偏离长期均衡关系的现象。因此笔者针对农业FDI对农产品出口额具有促进作用,提出了完善市场体系和加强对外资企业的进口管理两项政策建议,以缓解我国农产品进口压力。 相似文献
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依据2005~2009年相关数据,选择5个影响因素(直接和间接)指标作为参考数列,以显性比较优势指数和贸易专业化指数作为评价指标数列,运用灰色关联分析方法对山东省农产品外贸竞争力的影响因素进行分析与评价。结果表明,直接因素与农产品外贸竞争力因素灰关联度较强,间接因素则相对较弱。在此基础上提出了增强山东农产品外贸竞争力的建议。 相似文献
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对北京市农产品直接销售模式发展现状和特点及利弊进行了分析,并从搭建信息平台、发展物流、健全销售网点三个方面,对提升北京市农产品直接销售水平提出了对策建议。 相似文献
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采用多元线性逐步回归分析法建立烤烟中性致香成分与评吸结果的回归方程,并对回归方程进行显著性测验及偏相关分析和通径分析,研究烤烟中性致香成分与评吸结果的关系。结果表明,建立的香气量、香气质和评吸总分的3个回归方程经显著性测验均达到极显著水平。烟叶中的6类25种中性致香成分对香气量、香气质和评吸总分的直接影响各不相同。香气量受类胡萝卜素降解产物6-甲基-5-庚烯-2-酮的直接正面影响最大,而受苯丙氨酸代谢产物苯乙醇的直接负面影响最大;香气质受棕化反应产物2-乙酰基呋喃的直接正面影响最大,新植二烯的直接负面影响最大;评吸总分受棕化反应产物2-乙酰基呋喃的直接正面影响最大,类胡萝卜素降解产物6-甲基-5庚烯-2-酮的直接负面影响最大。仅有类胡萝卜素降解产物香叶基丙酮和二氢猕猴桃内酯对香气质、香气量和评吸总分均有直接正面影响,而类胡萝卜素降解产物2,4-庚二烯醛和6-甲基-2-庚酮对香气质、香气量和评吸总分均有直接负面影响。说明可以通过调节烟叶调制条件提高对评吸结果有益的香气成分,尽量降低对评吸结果不利的香气成分。 相似文献
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Pitts JN Lokensgard DM Ripley PS VAN Cauwenberghe KA VAN Vaeck L Shaffer SD Thill AJ Belser WL 《Science (New York, N.Y.)》1980,210(4476):1347-1349
Benzo[a]pyrene deposited on a glass fiber filter reacts rapidly in the dark or light with ambient levels of ozone to yield a mixture of products that display strong direct mutagenicity in the Ames assay. The major stable contributor to this activity has been identified as benzo[a]pyrene-4,5-oxide, a DNA-binding metabolite in biological systems, known to be a strong direct mutagen with Salmonella typhimurium strain TA98. 相似文献
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Restoring Value to the World's Degraded Lands 总被引:4,自引:0,他引:4
Daily GC 《Science (New York, N.Y.)》1995,269(5222):350-354
Roughly 43 percent of Earth's terrestrial vegetated surface has diminished capacity to supply benefits to humanity because of recent, direct impacts of land use. This represents an approximately 10 percent reduction in potential direct instrumental value (PDIV), defined as the potential to yield direct benefits such as agricultural, forestry, industrial, and medicinal products. If present trends continue, the global loss of PDIV could reach approximately 20 percent by 2020. From a biophysical perspective, recovery of approximately 5 percent of PDIV is feasible over the next 25 years. Capitalizing on natural recovery mechanisms is urgently needed to prevent further irreversible degradation and to retain the multiple values of productive land. 相似文献
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【目的】探索桑蚕一代杂交种成品卵质量检验新方法,提高成品卵质量检验的准确性、高效性及可操作性。【方法】分别采用直接计数蚁蚕法、称量计算蚁蚕法、直接计数良卵法,进行蚕种孵化率和良卵数调查,并比较3种方法的调查效率。【结果】采用称量法计算蚁蚕头数与直接计数蚁蚕头数的结果无显著性差异,采用直接计数良卵数与实际良卵孵化值误差达到极显著水平;在效率方面,直接计数良卵法耗时是直接计数蚁蚕法的56.75%,而称量计算蚁蚕法耗时仅是直接计数蚁蚕法的21.83%,节省约4/5的调查时间,工作效率极大提高。【结论】将称量计算蚁蚕法应用于良卵数和孵化率调查是可行的,且具有操作性好、省时、省工、效率高,准确性高等优点。 相似文献
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Cochlear distortion: effect of direct-current polarization 总被引:1,自引:0,他引:1
Intermodulation components (combination tones) appearing in microphonic potentials were measured from guinea pig cochleas with and without polarizing direct currents passing through the cochlear partition. At moderate intensities of stimulus the polarization had a qualitatively different effect on the distortion components than on their eliciting primaries or on pure tones simulating the distortion products. At high intensities, the primaries and the combination tones were similarly influenced by the polarizing current. It is concluded that cochlear distortion is a two-stage process, mechano-electrical at low levels and mechano-hydraulic at high levels. 相似文献
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Cartier SF Chen ZY Walder GJ Sleppy CR Castleman AW 《Science (New York, N.Y.)》1993,260(5105):195-196
Macroscopic quantities of the metallo-carbohedrenes TI(8)C(12) and V(8)C(12) have been synthesized with an arc discharge technique. Mass spectroscopy of raw soot samples generated in both an alternating and direct current arc between two metal-graphite powder composite electrodes establishes that the titanium and vanadium analogs of the metallo-carbohedrenes have been produced. An estimated yield of approximately 1 percent is obtained, and significantly, the products are stable in air. 相似文献
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Kim M Hohman JN Cao Y Houk KN Ma H Jen AK Weiss PS 《Science (New York, N.Y.)》2011,331(6022):1312-1315
The products of photoreactions of conjugated organic molecules may be allowed by selection rules but not observed in solution reactions because of unfavorable reaction geometries. We have used defect sites in self-assembled alkanethiolate monolayers on gold surfaces to direct geometrically unfavorable photochemical reactions between individual organic molecules. High conductivity and stochastic switching of anthracene-terminated phenylethynylthiolates within alkanethiolate monolayers, as well as in situ photochemical transformations, have been observed and distinguished with the scanning tunneling microscope (STM). Ultraviolet light absorbed during imaging increases the apparent heights of excited molecules in STM images, a direct manifestation of probing electronically excited states. 相似文献
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近几年,中国大宗农产品普遍出现进口快速增加与国内库存高企并存的现象。直接原因是国内外价格倒挂,深层次的原因是中国现行的农产品价格调控政策急需完善。通过对中国大宗农产品贸易情况、国内最低收购价和临时收储价格变化情况的分析,阐述了政策性收储价格逐年提高导致国内价格高于国外价格是近几年进口大幅增加的主要原因,进而提出完善最低收购价和临时收储政策的思考。 相似文献
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