充分利用福建滨海沙滩植被资源发展种植业

福建滨海沙滩位于北纬23°37′—27°10′范围,面积约5.33×10~4ha,已植防护林近2.0×10~4ha,尚约有3.34×10~4ha 未开发利用,其中分布于闽江口以南岸段和岛屿约2.86×10~4ha,     

黄淮海平原高产田作物群体结构特征

本文利用实测资料分析了高产田作物群体结构特征。精播高产栽培麦田春季最大蘖数12×10~6/ha,群体最大叶面积指数5.5—6.0,成穗4.5—5.25×10~6/ha。传统高产栽培麦田春季最大蘖数15—18×10~6/ha,群体最大叶面积指数6.0—6.5,成穗6.0—7.5×10~6/ha。小麦营养生长与生殖生长期叶日积比,精播高产栽培麦田是1∶0.89,传统高产栽培麦田为1∶0.73。夏玉米种植密度主要受叶倾角的影响。紧凑型玉米品种的叶倾角大于65°,种植密度7.5—8.25×10~4/ha;平展型玉米品种的叶倾角小于50°,种植密度5.25—6.0×10~4/ha。     

总结旱地农业经验加强农业生态建设

河北省武安市位于太行山东麓,山多地少,丘陵起伏,沟壑纵横。总面积1806km~2,耕地6.2×10~4ha,其中60%以上分布在丘陵山地。境内地势倾斜,高差较大,西部最高海拔1898m,东部最低海拔仅92m。荒山植被稀疏,水土流失严重。平均年降水量529mm,季节分     

安徽涡阳县桐农间作类型及其效益分析

一、概况涡阳县位于黄淮平原南部,安徽省的西北部。全县土地面积2.09×10~5ha,其中耕地面积1.44×10~5ha。人口105万。本县属暖温带半湿润季风气候区,年平均气温14.6℃,降水量824mm,蒸发量1974.5mm。太阳辐射总量5.22×10~5J·m~(-2)。气候温和,水热同季,     

对水旱轮作农业生态效应的探讨

多年来,人们对水旱轮作的增产效果和经济效益有很多研究,但对它的生态效益研究不多。其实,水旱轮作之所以增产,产生巨大的经济效益,其根源还是水旱轮作所带来的良好的生态效益所致。本文从生态效应的角度,初步探讨了水旱轮作的增产原因。一、综合治理“水袋子”,大力开展水旱轮作1.开展水旱轮作,促进粮棉高产稳产全县现有耕地7.087×10~4ha,其中稻田4.197×10~4ha;棉田1.607×10~4ha。利用本县丰富的水资源(年客水量1.36×10~9m~3),根据农田生产线基本平行于水位线的特点,1970年开始实行水旱轮作,随着水利条件的逐     

人体细胞漫谈

人体细胞的数目人和所有行有性生殖的生物一样,都是由一个细胞——受精卵发育而来的.据推算,刚出生的婴儿全身约有二十万亿(2×10~(18))个细胞.经过二十多年的分裂生长,成人体内细胞约为三百万亿(3×10~(14))个. 据估算,人体神经系统内含有10~(11)个神经细胞(又叫神经元),仅大脑皮层就约含140亿个神经细胞.如果以成人体内血量平均为4.5升计算,成年男性体内红细胞约为2.25×10~(10)个(500万个/mm~3×4.5×10~3);女性体内红细胞约1.89×10~(10)个(420万个/mm~3×4.5×10~3;白细胞2.25×10~7～4.5×10~7个;血小板约为4.5×10~8～1.35×10~9个.     

双向转换的系统结构调控方法与半干旱地区的农作物布局

一、临猗县农业生产条件特点及存在问题临猗县位于山西西南部,是晋南盆地中的一个大县。全县面积1356km~2,耕地1.0×10~5ha,水浇地5.27×10~4ha,占耕地的52.7%,人均占有耕地0.227ha。地势平坦,土地肥沃,农业生产条件较好。年降水量为500mm 左右,最高年份曾达到849.8mm,其中5—10月份的降雨量为450mm 左右,同期≥10℃的活动积温在     

二○○○年生物固氮研究的展望

地球上每年由于生物固定的氮约为175×10~6吨,其中在农田中固定的氮约为90×10~6吨。种植豆科植物和豆科牧草每年约固定80×10~6吨氮,其中种植豆科植物固定的氮约37×10~6吨。这个数字接近于每年世界工业合成的氮肥量约40×10~6吨氮。虽然现代合成氨工业高度发展,但是近年     

灌丛在“三北”防护林体系中的效益评价

一、前言绵亘于我国北疆的“三北”地区,包括西北、华北北部、东北西部12个省(市、自治区),总面积约为3.85×10~6km~2。这一辽阔地域的绝大部分处在干旱和半干旱的气候条件控制之下,风沙干旱、水土流失等自然灾害严重地威胁着区内2.2×10~7ha农田和4.0×10~7ha草牧场。为了改变“三北”地区的自然面貌,1978年国家批准了“三北防护林建设”,从此,三北防护林作为一项伟大的工程为国内外所瞩目。建设一个什么样的防护林体系,怎样建立这个体系是工程所要解决的重要问题。在近八九年的探索与实践中,这样的认识逐渐为人们所接受。即,“三北防护林体系建设”是广义     

生态环境与汾河水库输沙量的灰色关联分析和预测

汾河水库1960年开始拦洪,设计总库容量为7.2×10~7m~3。它担负着太原市的防洪、工业用水和1.0×10~5ha 的农田灌溉。水库上游包括宁武、静乐、岚县、娄烦四县,总流域面积为5268km~2。年平均降水量450—500mm,其中汛期降水占全年降水量的70—80%。建库前,多年平均输沙量达2.105×10~7m~3,年侵蚀模数     

Stages of life: A new metaphysics of conceptionism

When a human being comes into existence is crucial in bioethics. Conceptionism is the view that a human being comes into existence at conception. The twinning argument is an influential objection to this view. All versions of the twinning argument rely on a metaphysics of material objects, namely, endurantism. Given this, a strategy for defending conceptionism against the twinning argument is to deny endurantism and adopt an alternative metaphysics of material objects. A version of this strategy which has been debated in this journal is to adopt perdurantism, or the ‘multiple occupancy view’, on which monozygotic twins share the zygote region as a temporal part. We present a novel version of this strategy: conceptionists can evade the twinning argument by adopting an exdurantist metaphysics of material objects. We suggest reasons for thinking that this is a plausible and, indeed, preferable way for conceptionists to avoid the twinning argument.     

传粉昆虫行为的研究方法探讨

昆虫访花行为能对植物与传粉者相互作用的很多方面产生直接的影响, 因此相关研究对于理解植物的多样性和植物生殖生态过程非常重要。本文介绍了主要的传粉昆虫种类及其特征, 并探讨了昆虫访花行为及其影响因素的研究方法。同时还探讨了进行夜间传粉昆虫和群落水平上昆虫行为研究的方法, 以期能为植物-传粉者相互作用这一多学科交叉领域的学者, 尤其是植物学家和昆虫学家提供有益的参考资料。     

A hybrid approach to identify the risk priority of sources of greenhouse gases

Abstract

Examination of greenhouse gas emissions is crucial for understanding the global warming. For this reason, identification of the sources of greenhouse gas emissions is crucial. This paper presents a hybrid multi criteria decision making method, which combines analytic hierarchy process and technique for order preference by similarity to ideal solution and compares this method with actual data for identifying the risk priority of sources of greenhouse gas emissions. For this purpose, the historical data of 25-years, for six-greenhouse gas sources and three-greenhouse gases (CO₂, CH_4, N₂O) are considered. Consequently, it was found that while incineration of wastes caused the minimum GHG emissions, energy sector caused the maximum GHG emissions. The results of this paper show that use of this hybrid method is easy and intelligible, and has a good potential for sorting the risk priority of sources of greenhouse gas emissions.     

Prospects for the involvement of cancer stem cells in the pathogenesis of osteosarcoma

Osteosarcoma (OS) is one of the most common bone tumors in children and adolescents that cause a high rate of mortality in this age group and tends to be metastatic, in spite of chemotherapy and surgery. The main reason for this can be returned to a small group of malignant cells called cancer stem cells (CSCs). OS-CSCs play a key role in the resistance to treatment and relapse and metastasis through self-renewal and differentiation abilities. In this review, we intend to go through the different aspects of this malignant disease, including the cancer stem cell-phenotype, methods for isolating CSCs, signaling pathways, and molecular markers in this disease, and drugs showing resistance in treatment efforts of OS.     

Robustness of the approximate likelihood of the protracted speciation model

The protracted speciation model presents a realistic and parsimonious explanation for the observed slowdown in lineage accumulation through time, by accounting for the fact that speciation takes time. A method to compute the likelihood for this model given a phylogeny is available and allows estimation of its parameters (rate of initiation of speciation, rate of completion of speciation and extinction rate) and statistical comparison of this model to other proposed models of diversification. However, this likelihood computation method makes an approximation of the protracted speciation model to be mathematically tractable: it sometimes counts fewer species than one would do from a biological perspective. This approximation may have large consequences for likelihood‐based inferences: it may render any conclusions based on this method completely irrelevant. Here, we study to what extent this approximation affects parameter estimations. We simulated phylogenies from which we reconstructed the tree of extant species according to the original, biologically meaningful protracted speciation model and according to the approximation. We then compared the resulting parameter estimates. We found that the differences were larger for high values of extinction rates and small values of speciation‐completion rates. Indeed, a long speciation‐completion time and a high extinction rate promote the appearance of cases to which the approximation applies. However, surprisingly, the deviation introduced is largely negligible over the parameter space explored, suggesting that this approximate likelihood can be applied reliably in practice to estimate biologically relevant parameters under the original protracted speciation model.     

荨麻科楼梯草属七种植物果实的补充描述

楼梯草属植物的果实形态特征是属下系的划分和种类鉴定的重要依据之一,对于研究该属演化关系具有重要意义。通过标本查阅及野外调查,为该属七种植物的果实进行了补充描述,对该属的进一步分类修订提供有价值的信息。     

龟嗜皮菌的快速鉴定及其在鳄蜥 皮肤病原检测中的应用

龟嗜皮菌(Austwickia chelonae)感染爬行类、鸟类、哺乳类等,造成野生动物和家养动物患皮肤病甚至死亡,近年来这种病原体在Ⅰ级保护动物鳄蜥(Shinisaurus crocodilurus)的救护种群中暴发。传统的病原检测方法费时耗力。本文基于龟嗜皮菌全基因组序列开发了特异性高、方便快捷的龟嗜皮菌检测方法,并应用于鳄蜥的皮肤病风险预测。本研究开发的3对检测龟嗜皮菌的特异引物中,AC3引物的使用效果最好。     

Bias of heritability estimates from twin data in presence of errors of zygosity determination

Simple heritability estimators of continuous as well as discrete traits from twin data are known to overestimate the degree of genetic determination of the measured traits for several reasons. Errors of zygosity determination will, however, underestimate the true heritability. The bias due to wrong assignment of dizygous twin pairs into monozygous type is evaluated here, and the results indicate that this negative bias has a compensatory effect on the estimate of the degree of genetic determination when other factors of similarity between twin pairs are taken into account. It is shown that when an estimate of zygosity error is available, the bias due to this factor can be evaluated quantitatively, and hence the adjustment for zygosity error can be incorporated in the estimation of the degree of genetic determination of a trait. Although this theory is explicitly developed here for twin studies, the general principle also applies for other types of errors of determining the degree of biological relationships for estimation of heritability, in which case this type of error may be more important than the simple zygosity error.