检索结果-南通市图书馆

我国农产品流通效率时空演变、地区差异与收敛性

在线全文

学校读者我要写书评

暂无评论

经济问题 2025年第1期 100-112页

作者：高国生叶林祥支海兵南京财经大学粮食和物资学院江苏南京210003 南京审计大学金审学院管理学院江苏南京210023 南京财经大学经济学院江苏南京210003

农产品流通效率事关我国粮食安全和全国统一大市场的建成。运用熵值法测度了2011—2022年我国31个省级行政区的农产品流通效率,并使用Moran’s I、Kernel核密度估计、Markov链、Dagum基尼系数和β收敛模型分别分析了我国农产品流通效率... 详细信息

农产品流通效率事关我国粮食安全和全国统一大市场的建成。运用熵值法测度了2011—2022年我国31个省级行政区的农产品流通效率,并使用Moran’s I、Kernel核密度估计、Markov链、Dagum基尼系数和β收敛模型分别分析了我国农产品流通效率的时空演变、地区差异与收敛性情况。结果显示:研究期内我国农产品流通效率存在显著正向空间相关性,“高—高”集聚和“低—低”集聚特征明显;核密度曲线宽度变大呈现右拖尾和高度差明显的双峰形态,表明农产品流通效率逐渐提升,地区内部存在极化趋势;相邻省区市空间滞后水平对本省区市农产品流通效率维持原有状态或向更高水平发展均有较大影响;地区间差异是造成农产品流通效率总体差异显著的主要原因;农产品流通效率存在显著绝对β收敛和条件β收敛。据此,对如何提高农产品流通效率和缩小地区间差距提出了相关政策建议。

关键词：农产品流通效率时空演变空间分布地区差异

Exact Solutions of the （3＋1）—Dimensional KP and KdV—Type Equations

在线全文

学校读者我要写书评

暂无评论

Communications in Theoretical Physics 2003年第3期39卷 267-275页

作者： LIDe－sheng LUZhuo－sheng 等 DepartmentofAppliedMathematics DalianUniversityofTechnologyDalian116024China

Abundant new soliton-like and period form solutions for certain (3+1)-dimensional physically important nonlinear evolution equations are obtained by using a further extended tanh method and symbolic computation system... 详细信息

关键词：非线性偏微分方程 KdV型方程严格解

Theoretical Study on the Reaction Mechanism of F_2+2HBr = 2HF+Br_2

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Structural Chemistry 2005年第11期24卷 1328-1333页

作者： SUN De-sheng WANG Zun-Yao YANG Chun-sheng School of Chemistry and Chemical Engineering Nanjing University of Technology Jiangsu Nanjing 210009 China Department of Chemical Engineering Yancheng Institute of Technology Jiangsu Yancheng 224003 China

The gas phase reaction mechanism of F2 ＋ 2HBr = 2HF ＋ Br2 has been investigated by （U）MP2 at 6-311G＊＊ level, and a series of four-center and three-center transition states have been obtained. The reaction mechanism was achieved by comparing the activation energy of seven reaction paths, i.e. the dissociation energy of F2 is less than the activation energy of the bimolecular elementary reaction F2 ＋ HBr → HF ＋ BrF. Thus it is theoretically proved that the title reaction occurs more easily in the free radical reaction with three medium steps.

关键词： (U)MP2,transition state reaction mechanism free radical reaction.

A Note about Minimal Hypercones

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2021年第11期37卷 1794-1802页

作者： Yong sheng ZHANG School of Mathematical Sciences&IAS Tongji UniversityShanghai 200092P.R.China

This short note is concerned with a measure version criterion for hypersurfaces to be *** natural flows and associated reflections for many minimal hypercones,including minimal isoparametric hypercones and area-minimi... 详细信息

关键词： Minimal hypercone measure invariant flow foliation

Multivariate Analysis, Description, and Ecological Interpretation of Weed Vegetation in the Summer Crop Fields of Anhui Province, China

在线全文

学校读者我要写书评

暂无评论

Journal of Integrative Plant Biology 2005年第10期47卷 1193-1210页

作者： sheng QIANG Weed Research Laboratory Nanjing Agricultural University Nanjing 210095 China

Two surveys were conducted to investigate weed vegetation in a 153-hm^2 sampling area of summer crop fields from Anhui Province, China, through visual scoring of the level of weed infestation compared with summer crops on a seven-class scale. In total, 155 sampling sites were selected in the field based on crops, tillage, rotation systems, geographical regions, and soil types across the province. Data on weed communities and environmental factors were collected and analyzed through principal component analysis （PCA） and canonical correspondence analysis （CCA）, and the output was interpreted ecologically. Results showed that the main factors influencing the structure and distribution of weed communities in summer crop fields were the soil submersion period, latitude, and soil type and pH. The CCA indicated a significant relationship between weed dominance and soil submersion duration, latitude, and soil pH. From the result of the PCA and CCA ordination, the 155 sampling sites could be divided into three groups based on geographic and floristic composition, as well as weed abundance. The southern dry land group, which was characterized by a double-cropping system in the hilly regions of southern and central Anhui Province with a continuous summer crop and an autumn dry land crop, was dominated by Galium aparine Linn. var. tenerum （Gren. et Godr） Robb., Avenafatua L., and Veronica persica Poir. The northern dry land group, which had the same cropping system as the southern dry land group, was dominated by G. aparine var. tenerum, Galium tricorne Stokes, Descurainia sophia （L.） Schur., and Lithospermum arvense L. in the North Anhui Province, China. These two dry land groups could be combined into one large dry land group, in which the Galium weed vegetation type dominated. The third group was the paddy soil group, which was characterized by a continu- ous summer crop and double- or triple-cropping systems of rice, and prevailed in the south and central areas of Anhui Pr

关键词： canonical correspondence analysis (CCA) ecological interpretation principal component analysis (PCA) saturated soil humidity summer crop fields weed communities weed vegetation.

Carbon nanotube supported bifunctional electrocatalysts containing iron-nitrogen-carbon active sites for zinc-air batteries

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Nano Research 2021年第12期14卷 4541-4547页

作者： Jian sheng sheng Zhu Guodong Jia Xu Liu Yan Li Beijing National Laboratory for Molecular Sciences Key Laboratory for the Physics and Chemistry of NanodevicesState Key Laboratory of Rare Earth Materials Chemistry and ApplicationsCollege of Chemistry and Molecular EngineeringPeking UniversityBeijing100871China Peking University Shenzhen Institute Shenzhen518057China PKU-HKUST ShenZhen-HongKong Institution Shenzhen518057China

Bifunctional electrocatalysts with high activity toward both oxygen reduction and evolution reaction are highly desirable for rechargeable Zn-air batteries. Herein, a kind of carbon nanotube (CNT) supported single-site Fe-N-C catalyst was fabricated via pyrolyzing in-situ grown Fe-containing zeolitic imidazolate frameworks on CNTs. CNTs not only serve as the physical supports of the Fe-N-C active sites but also provide a conductive network to facilitate the fast electron and ion transfer. The as-synthesized catalysts exhibit a half-wave potential of 0.865 V for oxygen reduction reaction and a low overpotential of 0.442 V at 10 mA·cm^(−2) for oxygen evolution, which is 310 mV smaller than that of Fe-N-C without CNTs. The rechargeable Zn-air batteries fabricated with such hybrid catalysts display a high peak power density of 182 mW·cm^(−2) and an excellent cycling stability of over 1,000 h at 10 mA·cm^(−2), which outperforms commercial Pt-C and most of the reported catalysts. This facile strategy of combining single-site Metal-N-C with CNTs network is effective for preparing highly active bifunctional electrocatalysts.

关键词： single atoms Fe-N-C sites carbon nanotube bifunctional electrocatalyst zinc-air batteries

Creating Multiple Stereocenters via Rational Design Chiral Ligands and Reactions

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Creating Multiple Stereocenters via Rational Design Chiral L...

3-Blocks with Abelian Defect Groups Isomorphic to Z3m × Z3n

中国化学会第六届全国分子手性学术研讨会

作者： hanmin Huang State key laboratory for Oxo Synthesis and Selective Oxidation Lanzhou Institute of Chemical PhysicsChinese Academy of Sciences

Organic motifs with multiple stereocenters exist in numerous natural and unnatural products that exhibit important biological *** selective synthesis of these chiral compounds from simple starting materials is a *** designing efficient chiral catalysts as well as developing new strategies for controlling the stereoselectivity are critical in this research *** the past several years,Huang and co-workers mainly focused on exploration of efficient enantioselectivity-controlling strategies and designing new catalysts for construction of efficient reactions toward creating multiple *** new chiral diamine ligands and efficient strategies have been developed by rational design,which led to establishing a series of new asymmetric reactions1"*** this presentation,he will demonstrate some progress on this subject.

关键词： asymmetric catalysis tandem reaction chiral ligands multiple stereocenters

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2013年第12期29卷 2245-2250页

作者： sheng YANG Department of Mathematics Wenzhou University

Let G be a finite group and let p be a fixed prime number. Let B be a p-block of G with defect group D. In this paper, we give results on 3-blocks with abelian defect groups isomorphic to Z3m ×Z3n. We are particularly interested in the number of irreducible ordinary characters and the number of irreducible Brauer characters in the block. We calculate two important block invariants k（B） and l（B） in this case.

关键词： Blocks defect groups inertial quotient inertial index

On the control of fusion in the local category for the p-block with a minimal nonabelian defect group

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2011年第2期54卷 325-340页

作者： YANG sheng GAO sheng School of Mathematical Sciences Peking University Beijing 100871 China

If B is a p-block of a finite group G with a minimal nonabelian defect group D (p is an odd prime number) and (D, b D ) is a Sylow B-subpair of G, then N G (D, b D ) controls B-fusion of G in most cases. This result is of great importance, because we can use it to obtain a complete set of representatives of G-conjugate classes of B-subsections and to calculate the number of ordinary irreducible characters in B. This result is key to the calculation of the structure invariants of the block with a minimal nonablian defect group. On the other hand, we improve Brauer's famous formula k(B) =Σ (ω,b ω ) l(b ω ),where (ω, b ω ) ∈ [(G : sp(B))]. Let p be any prime number, B be a p-block of a finite group G and (D, b D ) be a Sylow B-subpair of G. H is a subgroup of N G (D, b D ) satisfying N G (R, b R ) = N H (R, b R )C G (R), (R, b R ) ∈ A 0 (D, b D ), N G ( w , b w' ) = N H ( w , b w' )C G (w' ), (w' , b w' ) ∈ (D, b D ). If w 1 , . . . , w l is a complete set of representatives of H-conjugate classes of D, then (w 1 , b w 1 ), . . . , (w l , b w l ) is a complete set of representatives of G-conjugate classes of B-subsections in G. In particular, we have k(B) =Σ l j=1 l(b w j ).

关键词： defect group subpair control of fusion Brauer's net