共查询到20条相似文献，搜索用时 31 毫秒
1.
针对目前基础有机化学教学问题,对有机合成部分提出了3点教学策略:介绍合成化学史提高学生的学习兴趣;教学中较早引入有机合成基本概念,从化学性质入手阐述逆推的方法,不断进行逆合成思维的训练,使学生建立逻辑化的有机合成思维模式;归纳总结各官能团化合物的制备与化学性质、碳骼的形成方法、官能团的引入、立体构型的要求等,使学生知识条理化。通过实践证明,上述策略是行之有效的。 相似文献
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Schreiber SL 《Science (New York, N.Y.)》2000,287(5460):1964-1969
Modern drug discovery often involves screening small molecules for their ability to bind to a preselected protein target. Target-oriented syntheses of these small molecules, individually or as collections (focused libraries), can be planned effectively with retrosynthetic analysis. Drug discovery can also involve screening small molecules for their ability to modulate a biological pathway in cells or organisms, without regard for any particular protein target. This process is likely to benefit in the future from an evolving forward analysis of synthetic pathways, used in diversity-oriented synthesis, that leads to structurally complex and diverse small molecules. One goal of diversity-oriented syntheses is to synthesize efficiently a collection of small molecules capable of perturbing any disease-related biological pathway, leading eventually to the identification of therapeutic protein targets capable of being modulated by small molecules. Several synthetic planning principles for diversity-oriented synthesis and their role in the drug discovery process are presented in this review. 相似文献
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S L Schreiber 《Science (New York, N.Y.)》1985,227(4689):857-863
A strategy for the synthesis of chiral molecules that receives growing popularity among organic chemists employs the photochemically mediated [2 + 2] cycloaddition reaction. These reactions can be performed on a multigram scale and often proceed with high yield and with stereocontrol. These features, in combination with the useful properties of the four-membered ring photoproducts in subsequent chemical transformations, make them attractive options in the early stage of a synthesis design. Various combinations of unsaturated functional groups can participate in this reaction process. Accordingly, these chemical reactions can be economical solutions to problems relating to the synthesis of a variety of target molecules. 相似文献
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Light-directed, spatially addressable parallel chemical synthesis 总被引：202，自引：0，他引：202
S P Fodor J L Read M C Pirrung L Stryer A T Lu D Solas 《Science (New York, N.Y.)》1991,251(4995):767-773
Solid-phase chemistry, photolabile protecting groups, and photolithography have been combined to achieve light-directed, spatially addressable parallel chemical synthesis to yield a highly diverse set of chemical products. Binary masking, one of many possible combinatorial synthesis strategies, yields 2n compounds in n chemical steps. An array of 1024 peptides was synthesized in ten steps, and its interaction with a monoclonal antibody was assayed by epifluorescence microscopy. High-density arrays formed by light-directed synthesis are potentially rich sources of chemical diversity for discovering new ligands that bind to biological receptors and for elucidating principles governing molecular interactions. The generality of this approach is illustrated by the light-directed synthesis of a dinucleotide. Spatially directed synthesis of complex compounds could also be used for microfabrication of devices. 相似文献
5.
Methods for the design and synthesis of ligands intended to be specific for a metal ion have been a recent chemical development. This article describes how this process can be inverted so that the specifics of the coordination environment around the metal ion can be used as a template in large-scale ligand synthesis. The synthesis of macrobicyclic ligands for ferric ion has been accomplished by using active esters of catechol ligands in which catecholate coordination to iron is a prelude to the organic chemical reactions that link the coordination subunits together into one ligand system surrounding a central metal ion coordination site. The lanthanide(III) ions, which are among the most labile metal ions known, have coordination numbers of 8 or higher, and thus their encapsulation into a macrobicyclic structure is a challenging problem. Lanthanide amine complexes have been used as metal templates in the synthesis of such macrobicyclic lanthanide complexes. There is evidence that such a complex is inert to exchange in aqueous solution. 相似文献
6.
Anions of many types, both organic and inorganic, farmiliar and exotic, can be generated in the gas phase by rational chemical synthesis in a flowing afterglow apparatus. Once formed, the rates, products, and mechanisms of their reactions with neutral species of all kinds can be studied, not only at room temperature but at higher energies in a drift field. These completely unsolvated ions undergo a large number of reactions that are analogous to those they undergo in solution, as well as some that are less familiar. New types of ions, for which there are no counterparts in solution, can be produced and their chemical reactions explored. 相似文献
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有机无机肥配施对湘北早晚稻作用特点的研究 总被引：2，自引：0，他引：2
为了研究湘北双季稻田不同有机无机肥配施对双季稻生产发育及产量的影响,在洞庭湖区湘阴县进行了大田试验。结果表明:(1)有机无机肥配施同单施化肥相比,水稻株高、分蘖、SPAD值没有显著差异,且早稻以施化肥表现较好,晚稻却以有机无机肥配施最佳,充分体现了有机肥养分释放缓慢的特点;(2)从产量来看,有机无机肥配施与单施化肥产量差异不明显,早稻以纯化肥产量最高,晚稻以20%猪粪有机堆肥产量最高,这就说明,有机无机肥配施不仅可以提高水稻产量,且可以改善土壤环境,并能有效解决农村有机废弃物排放量大、处理难等问题。 相似文献
10.
有机肥料的生产使用是一项社会产业 总被引：7，自引：0，他引：7
本文详细阐述了有机肥料的优越性及其特点,论证了有机肥料与化肥结合的必要性。当前,有些地方确有忽视有机肥料和单纯依靠化肥种田的倾向,其所带来的土壤问题和人类的健康问题,很值得重视。作者认为,只有把有机肥料的生产使用,当作一项社会产业来对待,有机肥料问题就能解决,农业生产、环境卫生和城乡面貌将会改观。 相似文献
11.
为推进农户有机肥替代化肥意愿转化为行动，促进我国化肥减施政策实施，本研究构建了农户有机肥替代化肥意愿与行为一致性的理论分析框架，基于山东省16地市404份调查问卷，运用Logit和Probit模型，从感知价值、政策规制探究了农户有机肥替代化肥意愿与行为一致性，基于政策规制和感知价值的交互效应以及有机肥替代试点参与意愿中介效应做了进一步分析。结果表明:感知经济价值、感知生态价值及激励性政策规制能够显著正向影响农户有机肥替代化肥意愿与行为一致性；政策规制在感知价值对农户有机肥替代化肥意愿与行为一致性的影响中起到一定的调节作用；有机肥替代试点参与意愿在感知经济价值对农户有机肥替代化肥意愿与行为一致性的影响中起到遮掩作用，在感知生态价值对农户有机肥替代化肥意愿与行为一致性的影响中起到部分中介作用。因此，在有机肥替代化肥的推广过程中，可以通过激励政策提高农户的感知价值水平，进而促进农户将有机肥替代化肥意愿付诸行动；在实施惩罚政策的过程中应注意力度，切忌过度的惩罚政策让农户出现逆反心理，反而出现抑制作用。 相似文献
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Grosch R Faltin F Lottmann J Kofoet A Berg G 《浙江大学学报(农业与生命科学版)》2004,30(4):393-393
The soil-borne pathogen Rhizoctonia solani Kühn (teleomorph, Thanatephorus cucumeris [A.B. Frank] Donk) is worldwide responsible for serious damage of many economically important agricultural and horticultural crops. Control of Rhizoctonia diseases is difficult because this pathogen survives for many years as sclerotia in soil or as mycelium in organic matter under numerous environmental conditions. Furthermore, the pathogen has an extremely wide host range. To date, no effective con… 相似文献
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Long-term straw addition promotes moderately labile phosphorus formation,decreasing phosphorus downward migration and loss in greenhouse vegetable soil 
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下载免费PDF全文 ZHANG Yin-Jie GAO Wei LUAN Hao-an TANG Ji-wei LI Ruo-nan LI Ming-Yue ZHANG Huai-zhi HUANG Shao-wen 《农业科学学报》2022,21(9):2734-2749
Phosphorus (P) leaching is a major problem in greenhouse vegetable production with excessive P fertilizer application. Substitution of inorganic P fertilizer with organic fertilizer is considered a potential strategy to reduce leaching, but the effect of organic material addition on soil P transformation and leaching loss remains unclear. The X-ray absorption near-edge structure (XANES) spectroscopy technique can determine P speciation at the molecular level. Here, we integrated XANES and chemical methods to explore P speciation and transformation in a 10-year field experiment with four treatments: 100% chemical fertilizer (4CN), 50% chemical N and 50% manure N (2CN+2MN), 50% chemical N and 50% straw N (2CN+2SN), and 50% chemical N and 25% manure N plus 25% straw N (2CN+2MSN). Compared with the 4CN treatment, the organic substitution treatments increased the content of labile P by 13.7–54.2% in the 0–40 cm soil layers, with newberyite and brushite being the main constituents of the labile P. Organic substitution treatments decreased the stable P content; hydroxyapatite was the main species and showed an increasing trend with increasing soil depth. Straw addition (2CN+2SN and 2CN+2MSN) resulted in a higher moderately labile P content and a lower labile P content in the subsoil (60–100 cm). Moreover, straw addition significantly reduced the concentrations and amounts of total P, dissolved inorganic P (DIP), and particulate P in leachate. DIP was the main form transferred by leaching and co-migrated with dissolved organic carbon. Partial least squares path modeling revealed that straw addition decreased P leaching by decreasing labile P and increasing moderately labile P in the subsoil. Overall, straw addition is beneficial for developing sustainable P management strategies due to increasing labile P in the upper soil layer for the utilization of plants, and decreasing P migration and leaching. 相似文献
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Russell A Milford J Bergin MS McBride S McNair L Yang Y Stockwell WR Croes B 《Science (New York, N.Y.)》1995,269(5223):491-495
Control strategies for urban ozone traditionally have been based on mass reductions in volatile organic compounds (VOCs). Studies show, however, that some organic gas species (such as alkanes and alcohols) form an order of magnitude less ozone than equal mass emissions of others (such as alkenes and aldehydes). Chemically detailed photochemical models are used to assess uncertainty and variability in reactivity quantification. VOC control strategies based on relative reactivity appear to be robust with respect to nationwide variations in environmental conditions and uncertainties in the atmospheric chemistry. Control of selective organic gas species on the basis of reactivity can offer cost savings over traditional strategies. 相似文献
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不同农作管理措施对东北地区农田土壤有机碳未来变化的模拟研究 总被引：3，自引：0，他引：3
【目的】研究与探索不同农作管理措施对东北农业土壤有机碳的影响,为东北地区高产高效低碳农业及可持续发展提供科学依据。【方法】不同农作管理措施能够影响土壤有机碳（soil organic carbon,SOC）的未来变化,该研究基于东北地区4个长期定位试验站点（黑龙江省哈尔滨站点、吉林省公主岭站点、吉林省德惠站点、辽宁省沈阳站点）的试验数据,用站点的实测作物产量和SOC双标准对DAYCENT模型进行校验。DAYCENT模型调整的相关参数包括作物参数、耕作方式参数、施肥参数、收获参数和有机肥参数等,在对所选试验站点的长期定位试验结果校验后,利用已校验的各项参数,对模型模拟情况进行验证,发现模型模拟值与实测值吻合良好,表明DAYCENT模型适用于这4个地区的作物产量和SOC模拟,可以较好地模拟SOC的动态变化。进而研究在未来气候变化情景下（representative concentration pathway 4.5,RCP 4.5）,用校验了的DAYCENT模型对这4个站点在4种不同管理情景（施用化肥、增施有机肥、秸秆还田、免耕）下的SOC变化情况进行模拟。【结果】模拟结果显示,对于哈尔滨站点,采用有机肥和氮磷钾化肥配施处理（MNPK）在短时间内使SOC升高较快,而从长远来看,配施低量有机肥与单施用化肥对SOC增加的斜率基本一致,但由于化肥和有机肥配施（MNPK）处理的初始SOC含量高,其SOC未来含量的绝对值也比较高;对于德惠站点,虽然短时间内,免耕处理SOC低于常耕处理,但长期看来,免耕更有利于增加SOC,其SOC涨幅逐渐高于常耕处理,40年间相对增加了11.88%;公主岭站点有机肥氮磷钾化肥配施和氮磷钾化肥结合秸秆还田措施较单施化肥可显著提高农田SOC;沈阳站点的未来有机碳模拟发现,在单施化肥情况下,未来的42年内SOC呈略微下降趋势,相对降低2.83%,从长远看来,单施化肥并不能使该地区SOC增加,因此,可以考虑采用有机肥和氮磷钾化肥配施等措施来提高该地区的农田SOC。【结论】DAYCENT模型可以有效地模拟作物产量和土壤有机碳的动态变化,模型适应性较强,同时DAYCENT模型可用于模拟站点未来SOC的动态变化。在东北地区农田土壤管理方面,可通过合理的有机肥化肥配施、推广免耕和秸秆还田技术来固定土壤碳,最终达到提高土壤有机碳库和促进农业可持续发展的目标。 相似文献
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Mesostructure design with gemini surfactants: supercage formation in a three-dimensional hexagonal array 总被引：1，自引：0，他引：1
At low temperatures, liquid crystal-like arrays made up of inorganic-cluster and organic molecular units readily undergo reversible lyotropic transformations. Gemini surfactants, with two quaternary ammonium head groups separated by a methylene chain of variable length and with each head group attached to a hydrophobic tail, can be used to control organic charge sitting relative to the bivariable hydrophobic tail configurations. This approach has led to the synthesis of a mesophase (SBA-2) that has three-dimensional hexagonal (P6(3)/mmc) symmetry, regular supercages that can be dimensionally tailored, and a large inner surface area. This mesostructure analog of a zeolite cage structure does not appear to have a lyotropic surfactant or lipid liquid crystal mesophase counterpart. Through the modification of gemini charge separation and each of the two organic tails, these syntheses can be used to optimize templating effects, including the synthesis of MCM-48 at room temperature. 相似文献
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WATSON JD 《Science (New York, N.Y.)》1963,140(3562):17-26
We can now have considerable confidence that the broad features of protein synthesis are understood. The involvement of RNA is very much more complicated than was imagined in 1953. There is not one functional RNA. Instead, protein synthesis demands the ordered interaction of three classes of RNA-ribosomal, soluble, and messenger. Many important questions, however, remain unanswered. For instance, there is no theoretical framework for the ribosomal subunits, nor for that matter, do we understand the functional significance of ribosomal RNA. Most satisfying is the realization that all the steps in protein replication will be shown to involve well-understood chemical forces. As yet we do not know all the details. For example, are the DNA base pairs involved in messenger RNA selection of the corresponding amino-acyl-sRNA? With luck, this will soon be known. We can thus have every expectation that future progress in understanding selective protein synthesis (and its consequences for embryology) will have a similarly well-defined and, when understood, easy-to-comprehend chemical basis (62). 相似文献
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Mann S Archibald DD Didymus JM Douglas T Heywood BR Meldrum FC Reeves NJ 《Science (New York, N.Y.)》1993,261(5126):1286-1292
Crystallization is an important process in a wide range of scientific disciplines including chemistry, physics, biology, geology, and materials science. Recent investigations of biomineralization indicate that specific molecular interactions at inorganic-organic interfaces can result in the controlled nucleation and growth of inorganic crystals. Synthetic systems have highlighted the importance of electrostatic binding or association, geometric matching (epitaxis), and stereochemical correspondence in these recognition processes. Similarly, organic molecules in solution can influence the morphology of inorganic crystals if there is molecular complementarity at the crystal-additive interface. A biomimetic approach based on these principles could lead to the development of new strategies in the controlled synthesis of inorganic nanophases, the crystal engineering of bulk solids, and the assembly of organized composite and ceramic materials. 相似文献
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长期施肥管理对红壤稻田土壤微生物量碳和微生物多样性的影响 总被引：19，自引：4，他引：19
【目的】土壤微生物在地球化学循环及维持土壤肥力和作物产量方面发挥了重要作用,为了研究长期不同施肥制度对土壤肥力状况的影响,明确施肥制度与土壤微生物的关系。【方法】采用土壤熏蒸和磷脂脂肪酸分析方法,研究了湖南宁乡不施肥处理、施用化肥、常规施肥、秸秆还田、30%有机肥+化肥和60%有机肥+化肥6个长期肥料定位试验的土壤微生物量碳及磷脂脂肪酸。【结果】与不施肥对照相比,施用化肥、秸秆还田及有机肥与化肥配合施用可以显著的提高土壤微生物量碳及总磷脂脂肪酸的量。长期施用化肥后,群落中含有iC15:0的微生物明显增多,长期施用有机肥和秸秆还田后,群落中含iC15:0微生物明显减少,而含aC15:0微生物则显著增加。通过对21种测得磷脂脂肪酸进行主成分分析,结果表明,前两个主成分可以解释总变异的87.6%。除C12:0和C15:0外,大部分的非饱和脂肪酸和环式脂肪酸的变异可以在第一主成分中反映出来。从肥料处理的主成分分析结果看,第一主成分及第二主成分可以解释肥料处理变异的89.8%,相比较而言,化肥处理和常规施肥处理相互间的差别较小,60%有机肥处理与秸秆还田处理几乎重合。【结论】不同施肥处理对土壤微生物量碳和微生物多样性有重要影响,肥料处理差异可以在微生物结构与多样性变化上得以体现。 相似文献