试论气候变迁对我国古代北方农业经济的影响

历史时期,我国北方地区农业经济经历了一个由盛转衰的变化过程。对于其变化的原因,许多学者都提出了各自的看法,但大多是用社会因素来解释,认为主要是北方地区频繁的战乱,特别是五胡十六国,安史之乱和夏、辽、金、元时期的社会大动乱,给北方地区带来巨大的灾难,战乱消耗了人口,摧残了北方的农业经济,造成了北方地区经济的衰落。这解种释不无道理,但把原因仅仅局限在一方面,似乎还不够全面。随着自然科学向历史学的渗透,我们越来越感到有必要在吸收前人丰富成果的基础上,从更广泛的领域,借助现代自然科学     

北方地区铁皮石斛日光温室栽培研究进展

铁皮石斛为名贵中药材,原产我国南方地区,近年来北方地区陆续开展设施温室栽培。本研究综述了北方地区日光温室栽培铁皮石斛的栽培基质、栽培方式、环境因素、病虫害防控、采收时期等,并对该地区栽培中所面临的问题进行总结,同时对栽培前景和方向进行展望。     

北方冬季羊病综合性预防措施

我国北方地区冬季有近5个月的时间。这一时期是北方养羊最困难的时期羊群常因环境质量和营养水平下降而感染疫病,出现"春乏"死亡的现象。如何搞好羊群安全越冬,减少羊群发病死亡率是北方地区养羊生产的一个重要环节。     

论中古北方社会的鱼类食用

中古时期,鱼是北方地区最常见的海产品,也是北方民众常食的肉食之一。中古时期北方良好的水环境为人们提供了丰富的鱼类资源,在长期的鱼类食用过程中,北方民众们总结出了各种各样的鱼类烹饪与加工方法,显示了我国古代饮食文化较高的发展水平。     

清末民初时期我国北方农作物种植与环境变迁研究

农作物生产是清末民初时期我国北方地区最重要的经济运作方式,农业耕种也是该时期农业生产领域中发展得最快的部门。随着我国北方农作物种植区域的持续拓展,新型农作物类别与耕种技术的引入与传播,均极大地推动了我国北方农作物种植业的发展。本文分析了清末民初时期我国北方农作物种植与环境变迁状况,并阐述了清末民初时期我国北方农作物种植与环境变迁的主要特征。     

稳定蔬菜生产 保障蔬菜产品有效供应的生产技术指导意见

近期,新型冠状病毒感染肺炎疫情对当前蔬菜生产和市场供应带来一定影响。为加强蔬菜生产管理,确保疫情期间各地蔬菜生产稳定,市场供应充足,全国农业技术推广服务中心会同农业农村部蔬菜专家指导组提出蔬菜管理技术意见。一、加强北方地区日光温室蔬菜生产管理日光温室蔬菜栽培是北方地区1月至2月份主要的生产方式。这个时期室外温度较低、光照不足,是全年日光温室管理难度最大的时期。(一)增温保温。晴朗天气采取适当增温管理,以蓄存更多的热能,同时也能促进果实成熟.     

从《齐民要术》等史籍看中国古代的肥料科学及其对后世农业发展的启示

贾思勰的《齐民要术》是中国6世纪的农业科学巨著,它也是中国古代肥料科学史籍记载的分界线。《齐民要术》记载了大量中国古代北方地区肥料科学知识,且其所述并非仅局限在北魏时期,也兼具了秦汉以来的北方地区肥料科学史籍资料。本文兼采《汜胜之书》《王祯农书》等史料中有关肥料的篇章,从而尽可能客观地展现中国古代肥料科学知识和应用的发展水平,以期为当前农业现代化和乡村振兴战略的贯彻实施提供有益借鉴。     

草莓促成栽培后期管理技术

1.定植及保温前的管理1.1定植时期及方法北方地区一般在9月上中旬定植,较寒冷的北方地区可在8月下旬定植。也可在10月上旬定植。每垄2行,栽植于垄的两边,行距20厘米,株距12～15厘米,密度1万～1.3万株/667米2。对于花序较多的品种如弗吉尼亚、新明星应适当稀植。另外,带土移栽可     

从《齐民要术》等史籍看中国古代的肥料科学及其对后世农业发展的启示

贾思勰的《齐民要术》是中国6世纪的农业科学巨著,它也是中国古代肥料科学史籍记载的分界线。《齐民要术》记载了大量中国古代北方地区肥料科学知识,且其所述并非仅局限在北魏时期,也兼具了秦汉以来的北方地区肥料科学史籍资料。本文兼采《汜胜之书》《王祯农书》等史料中有关肥料的篇章,从而尽可能客观地展现中国古代肥料科学知识和应用的发展水平,以期为当前农业现代化和乡村振兴战略的贯彻实施提供有益借鉴。     

设施农业如何应对低温雨雪天气

<正>又到了冬季大棚蔬菜管理的关键季节,今年立冬以来,北方地区的冷空气活动频繁。近段时间,北方地区出现了强降温以及强降雪,不少地方还伴有浓雾,就是这种低温寡照的天气,使得许多大棚蔬菜遭受到了冻害的影响,不少蔬菜植株的抗病性也发生了不同程度的下降,从而引发和加重了多种病虫害的发生发展。面对这些不利情况,从现在开始就要抓住有利的天气时机,及时进行救护和防治。瓜果类是北方冬春大棚种植的主要蔬菜,而冬春季是温室大棚温湿矛盾最突出的时期。因     

Alternatives, traditions, and diversity in agriculture

This review essay examines several recentbooks about agriculture, including two books on thelinks between cultural and biological diversity intraditional agriculture, two books on the US farmcrisis, and a collected volume examining globalaspects of agricultural restructuring andsustainability. Finally, a history of ``alternative'agriculture provides a framework for thinking aboutthe ways the different cases shed light on the complexrelations between tradition and innovation inagriculture. A historical perspective highlights theextent to which ``alternative' is a relative term. Themonocrop, ``factory' mode that dominate US agriculturetoday certainly differs from what has characterizedfarming for most of history and in most of the world.Small-scale, more or less organic, diversified farms,which appear so ``alternative' in the present context,have until lately counted as the norm, here andelsewhere. These books also highlight both the dangersof the currently dominant industrial agriculture andthe potential for genuine alternatives.     

Structure, dynamics, and reactivity in hemoglobin

The static structure of hemoglobin and its functional properties are very well characterized. It is still not known how energy is stored and used within the structure of the protein to promote function and functional diversity. An essential part of this question is understanding the mechanism through which the overall protein structure (quaternary structure) couples to the local environment about the oxygen binding sites. Time-resolved resonance Raman spectroscopy has been used to probe the vibrational degrees of the freedom of the binding site as a function of protein structure. Comparison of the spectra from both equilibrium and transient forms of deoxy hemoglobin from a variety of mammalian, reptilian, and fish hemoglobins reveals that for each quaternary structure there exist two tertiary states stabilized by the presence or absence of an iron-bound ligand. Pulse-probe Raman experiments show that for photodissociated, ligated hemoglobins the local tertiary structure relaxes at a solution-dependent rate extending from tens of nanoseconds to microseconds. In this local environment, the linkage between the iron and the proximal histidine proves to be the single observed structural feature that responds in a systematic and substantial manner to structural changes in the protein. The additional finding of a correlation between the frequency of the iron-proximal histidine stretching motion (nu Fe-His) and various parameters of ligand reactivity, including geminate recombination, implicates the associated localized structural element in the mechanism of protein control of ligand binding. On the basis of these and related finds, a model is presented to account for both coarse and fine control of ligand binding by the protein structure.     

Gallium, germanium, indium, and iridium in lunar samples

Neutron activation analyses of gallium, germanium, indium, and iridium in eight lunar samples and in meteorites and rocks (including four calciulnrich achondrites and five terrestrial basalts) with similar bulk compositions are reported. Lunar gallium concentrations are remarkably constant at about 5 parts per million, three times higher and four times lower than those in eucritic (calcium-rich) achondrites and terrestrial basalts, respectively. Lunar germanium concentrations range from 相似文献   

Potassium, rubidium, strontium, barium, and rare-Earth concentrations in lunar rocks and separated phases

Concentrations of potassium, rubidium, strontium, barium, and rareearth elements have been determined by mass spectrometric isotope dilution for eight Apollo 11 lunar samples and for some separated phases. Potassiumn and ritbidium are at chondritic levels, strontium at 15 times, and barium and rare earths at 30 to 100 times chondritic levels. There are trace element similarities between the lunar samples and basaltic achondrites, terrestrial dredge basalts and the bulk earth. The trace element data appear to be consistent with these lunar samples being the result of limited partial fusion of some material similar to the brecciated eucrite meteorites.     

重金属Pb、Cr、Cd对烟草生长的影响及其分布规律

[目的]研究重金属Pb、Cr、Cd对烟草的生理作用及其在烟草中的吸收累积规律.[方法]采用盆栽试验方法,测定烟草根、茎、叶等器官中Pb、Cr、Cd含量,分析不同重金属污染程度下烟草的株高及叶片干物质重的变化.[结果]重金属处理的土壤中烟草的株高都显著低于对照,呈现抑制作用,添加外源Pb和Cr处理下,烟草叶片干重随添加浓度的升高而降低,Cd处理则呈现出先升高后降低的趋势.Pb、Cr、Cd重金属在烟草器官中的含量均为根>茎>叶,根系中Pb、Cr、Cd的浓度与添加浓度具有较好的相关性,而叶片中只有Cd含量与添加浓度具有较好的相关性.[结论]烟草植株中的重金属主要来源于土壤,烟草对重金属的传输过程具有一定的滞阻作用.     

Irony,tragedy, and temporality in agricultural systems,or, how values and systems are related

In the last decade the systems approach to agricultural research has begun to subsume the older reductionist approaches. However, proponents of the systems approach often accept without critical examination a number of features that were inherited from previously accepted approaches. In particular, supporters of the systems approach frequently ignore the ironies and tragedies that are a part of all human endeavors. They may also fail to consider that all actual systems are temporally and spatially bounded. By incorporating such features into a systems perspective, it becomes possible to consider them as involving the manipulation of things, the reconstruction of institutions, and the reformulation of policies in accordance with democratic goals and objectives as part of a single web of interrelationships.