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1.
中国南方水田土壤的承载能力和粘附性能预测 总被引：8，自引：0，他引：8
为了探讨中国南方水田土壤的力学性质及其影响因素, 测定了典型水田土壤的有关参数。据测定结果, 分析了水田土壤的承载能力与软泥层深度之间的关系和对钢与对橡胶的粘附力之间的关系。结果表明,承载能力与软泥层深度在一定程度上呈线性关系; 水田土壤对钢的粘附力(x)和对橡胶的粘附力(y) 之间的关系可用方程y = x 拟合, 即两者间没有显著差异。 相似文献
2.
A. Yu. Izmailov I. V. Liskin Ya. P. Lobachevsky S. A. Sidorov V. K. Khoroshenkov A. V. Mironova E. S. Luzhnova 《Russian Agricultural Sciences》2017,43(1):71-74
This article considers the conditions for creating the soil-cutting blade wear model proceeding from abrasive wear mechanics. The basic determiners of the nature and rate of blade wear are identified. The influence of external factors is considered that are related to power consumption for overcoming the soil resistance to destruction. The soil resistance forces include the ones that deform the soil at compaction, and the inertia forces that originate at the uplift and displacement of the soil layer. The necessary and sufficient conditions for creating a model similar to natural in the domain of desired properties are considered. The similarity criteria of the model-nature system are determined that characterize the processes observed during the blade wear in actual soil conditions. The numerical values of the similarity criteria determined for the model are identical to the natural loamy soil. 相似文献
3.
河南省部分地区鸡志贺氏菌病病原分离鉴定及药敏试验 总被引：3，自引：2，他引：1
为了对河南省部分地区鸡志贺氏菌病的病原进行分离鉴定和药物敏感性调查,对河南省6个地区的鸡腹泻病病料进行了细菌学检查,经细菌分离培养、形态染色镜检、生化试验和动物试验,共分离鉴定出12株鸡源志贺氏菌。血清学试验结果显示,分离菌株存在种和型的差异,其中8株为福氏志贺氏菌,3株为鲍氏多价志贺氏菌,1株为痢疾Ⅱ型志贺氏菌。动物试验结果表明,分离的12株鸡志贺氏菌均具有致病性,且毒力不同,其中,从三门峡分离的菌株有很强的毒力,发病率和死亡率均为100%。药敏试验结果显示,大多数鸡志贺氏菌对氨苄/舒巴坦和阿米卡星较为敏感,对其他药物具有严重的耐药性,且不同地区分离的鸡志贺氏菌对药物的敏感性不同。 相似文献
4.
Apollo Preliminary Examination Team 《Science (New York, N.Y.)》1973,179(4068):23-34
The preliminary characterization of the rocks and soils returned from the Apollo 16 site has substantiated the inference that the lunar terra are commonly underlain by plagioclase-rich or anorthositic rocks. No evidence has been found for volcanic rocks underlying the regolith in the Apollo 16 region. In their place, we have found anorthositic rocks that are thoroughly modified by crushing and partial melting. The textural and chemical variations in these rocks provide some evidence for the existence of anorthositic complexes that have differentiated on a scale of tens to hundreds of meters. The occurrence of deep-seated or plutonic rocks in place of volcanic or pyroclastic materials at this site suggests that the inference from physiographic evidence that the latter materials are widespread in terra regions may be incorrect. Several additional, more specific conclusions derived from this preliminary examination are: 1) The combination of data from the Descartes region with data from the orbital x-ray fluorescence experiment indicates that some backside, highland regions are underlain by materials that consist of more than 80 percent plagioclase. 2) The soil or upper regolith between North Ray and South Ray has not been completely homogenized since the time of formation of these craters. 3) The chemistry of the soil indicates that rocks rich in potassium, uranium, and thorium, similar to those that prevail at the Fra Mauro site, are relatively abundant (10 to 20 percent) in the Descartes region. 4) The K/U ratio of the lunar crust is similar to that of the KREEP basalts. 5) The carbon content of the premare lunar crust is even lower than that of the mare volcanic rocks. 相似文献
5.
【研究目的】为了研究猪圆环病毒的分子生物学特征及其发病机理和致病机制,【研究方法】将疑似猪圆环病毒2型的猪脾脏、淋巴结用胰蛋白酶消化处理后接种PK-15细胞,盲传6代后,病毒已经适应PK-15细胞,【研究结果】然后设计一对特异性引物利用PCR技术扩增出ORF2片段中540bp的基因。第6代细胞病毒液经间接免疫荧光检测表明,在荧光显微镜下可见PCV特征的荧光斑,表明毒株具有感染性。【结论】将病毒纯化后进行电镜观察,病毒粒子直径约17nm,圆形,无囊膜,研究结果表明分离的病毒为猪圆环病毒。 相似文献
6.
The discovery and characterization of structurally ordered and disordered phases that are intermediate between amphiboles and micas have shown that the biopyriboles are a much more complex family of minerals than has previously been recognized. In addition to single-chain, double-chain, and sheet structures, there are also minerals with triple chains and with alternating double and triple chains. Many crystals exhibit disorder in the sequence of double and triple chains, and isolated chains that are wider than triple are common. This structural disorder helps to explain why asbestiform amphiboles are fibrous. The new phases have now been found in several localities, and it is possible that similar phenomena in other minerals could also have been overlooked. In particular, there is no reason to suppose that analogous substances and structures with both single and double chains do not occur between the pyroxenes and the amphiboles. Since the pyroxenes are used extensively by geologists to assess rock histories and formation temperatures and pressures, it is essential that the extent of this type of disorder be evaluated. It is possible that what appears to be only an interesting mineralogical problem may prove to be a petrological nightmare. 相似文献
7.
通过PCR、细菌培养鉴定和血涂片镜检对20例以高热为特征的疑似蓝耳病病例进行病原检测诊断,并根据病因提出综合防治措施。发现蓝耳病(PRRS)阳性率100%,圆环病毒病(PCV-2)阳性率40%,伪狂犬(PRV)阳性率40%,非典型性猪瘟(CSFV)阳性率10%,猪流感(SI)及猪传染性胸膜肺炎(APP)均为阴性,附红细胞体阳性率90%,并有少量细菌感染。结果表明我市猪高热病为高致病性蓝耳病,发病猪并分别不同程度地混合或继发感染了其他病原体,病原一般3～5种,病原多样化导致病情复杂化,增加了诊断和治疗难度,所以本病宜采取综合防治。 相似文献
8.
参考GenBank上公布的禽呼肠孤病毒(ARV)和番鸭呼肠孤病毒(MDRV)σ非结构基因(σNS)序列设计合成一对引物,对番鸭源呼肠孤病毒YJL株σNS全基因进行RT-PCR扩增,克隆到pMD18-T载体中,并对克隆产物进行PCR鉴定和测序;YJL株σNS的编码基因位于S4节段,基因全长1192 bp,其5′端和3′端序列分别为5′-GCTTTT和3′-TATTCATC,具有典型的禽正呼肠孤病毒基因末端碱基序列;σNS基因只有一个有效阅读框(24-1127 bp),编码由367个氨基酸组成的σNS蛋白;σNS蛋白的分子质量约为40.57 ku,等电点(PI)为7.875.YJL株与法国MDRV-89026株σNS基因核苷酸的同源性为77.8%,推导氨基酸的同源性为90.2%;与ARV-S1133株σNS基因的同源性为99.4%,推导氨基酸的同源性为99.5%;系统进化树分析表明,YJL株σNS基因和蛋白与S1133株的亲缘关系更近,处在ARV分支上.可见,番鸭源呼肠孤病毒YJL株属于ARV,同时也表明我国发病番鸭群中存在不同基因群的呼肠孤病毒感染. 相似文献
9.
The role of the T cell receptor in positive and negative selection of developing T cells 总被引：73，自引：0，他引：73
Although many combinations of alpha beta T cell receptors are available to the T cells in any given organism, far fewer are actually used by mature T cells. The combinations used are limited by two selective processes, positive selection of T cells bearing receptors that will be useful to the host, and clonal elimination or inactivation of T cells bearing receptors that will be damaging to the host. The ways in which these two apparently contradictory processes occur, and the hypotheses that have been suggested to reconcile them, are discussed. 相似文献
10.
观赏桃园害虫及天敌群落结构研究 总被引：1，自引：0，他引：1
对观赏桃园昆虫群落的时间结构研究表明:桃园昆虫有64种,隶属于11目48科。物种数随季节变化而变化,主要优势种为桃小绿叶蝉(Empoasca flavescensFabr.)和山楂叶螨(Tetranychus viennesisZacher)。在不同时间其优势度、多样性、均匀性等也不断变化。根据群落的相异系数对桃园6~9月的昆虫群落进行分析表明,8月中旬与8月下旬的昆虫群落最为相似,其次是7月上旬与7月中旬。 相似文献
11.
The current (synthetic) theory of evolution has been criticized on the grounds that it implies that macroevolutionary processes (speciation and morphological diversification) are gradual. The extent to which macroevolution is gradual or punctuational remains to be ascertained. Macroevolutionary processes are underlain by microevolutionary phenomena and are compatible with the synthetic theory of evolution. But microevolutionary principles are compatible with both gradualism and punctualism; therefore, logically they entail neither. Thus, macroevolution and microevolution are decoupled in the important sense that macroevolutionary patterns cannot be deduced from microevolutionary principles. 相似文献
12.
采用光镜、扫描电镜、透射电镜和同步辐射等方法对长蛸平衡囊的形态和神经支配进行了研究。平衡囊位于长蛸头后部两侧的软骨腔中,表面是近似椭圆形的膜质结构。平衡囊表面缠绕的大量纤维丝,与软骨壁粘联后使囊悬浮于腔内的淋巴液中。平衡囊中的感觉毛细胞分为感觉斑(macula)和感觉脊(crista)两个区域,其中感觉斑毛细胞区被包裹着胶质粘液层的耳石覆盖,毛细胞动纤毛顶端嵌入耳石底层钙质微晶体间隙中;感觉脊区毛细胞呈带状螺旋型排列,共分九节,其毛细胞均由胶质顶(cupula)覆盖。毛细胞仅含等长、9+2微管型动纤毛,无静纤毛,其周围细胞含微绒毛。平衡囊内的一软骨凸起结构,相对感觉脊(anticrista),其表面无感觉毛细胞。同步辐射结果表明:支配感觉斑区的神经仅一条,而感觉脊区却由两条神经束从脑部经囊表后分支进入各自支配的毛细胞节区。 相似文献
13.
专家系统领域中，知识规则是由前提和结论组成的。专家系统在进行推理时，首先要获取前提，有些前提可以直接通过人机交互得到(称直接前提)，而有些前提需根据模型间接得到(称间接前提)。运用面向对象方法学的原则，将直接前提用属性表示，间接前提用方法表示，也将为得出结论所运用的模型用方法表示，再将相关的属性和方法封装在一起，构成一个类，则整个知识规则可抽象成由具有面向对象特点的类组成的知识表示形式，它将描述问题空间的属性和方法有机地结合在一起；同时，在构造推理机时，仍然按面向对象的原则匹配对象，构成了问题空间和求解空间的一致性。这样的软件具有稳定性好、易维护、易扩充的特点。 相似文献
14.
Chondrulelike objects in short-period comet 81P/Wild 2 总被引：1，自引：0，他引：1
Nakamura T Noguchi T Tsuchiyama A Ushikubo T Kita NT Valley JW Zolensky ME Kakazu Y Sakamoto K Mashio E Uesugi K Nakano T 《Science (New York, N.Y.)》2008,321(5896):1664-1667
The Stardust spacecraft returned cometary samples that contain crystalline material, but the origin of the material is not yet well understood. We found four crystalline particles from comet 81P/Wild 2 that were apparently formed by flash-melting at a high temperature and are texturally, mineralogically, and compositionally similar to chondrules. Chondrules are submillimeter particles that dominate chondrites and are believed to have formed in the inner solar nebula. The comet particles show oxygen isotope compositions similar to chondrules in carbonaceous chondrites that compose the middle-to-outer asteroid belt. The presence of the chondrulelike objects in the comet suggests that chondrules have been transported out to the cold outer solar nebula and spread widely over the early solar system. 相似文献
15.
西安地区及周边观赏草应用调查 总被引：2，自引：0，他引：2
对西安市周边11个样点应用的观赏草种类及应用方式进行了调查分析。结果表明,西安市应用的观赏草共计39种(品种),分别属于禾本科、莎草科、天南星科、灯心草科、香蒲科、木贼科,应用最多的属是禾本科的芒属(Miscanthus Anderss.)和狼尾草属(Pennisetum Rich.),应用频度最多的种是细叶芒(Miscanthus sinensis Anderss.cv.Gracillimus),种类最丰富的样点是西安市雁塔南路和西安世界园艺博览园。观赏草的应用方式主要有孤植、丛植、片植、地被,搭配方式有水体搭配、岩石搭配、乔灌木搭配、宿根搭配等,应用类型最多的是片植。综合分析表明,很多观赏草已在西安市得到应用,但不均衡,今后需要丰富观赏草种类,适当开发乡土资源。 相似文献
16.
本文主要研究东北产硬阔叶小径材的干燥工艺问题。通过对柞木、水曲柳和桦木板材的常规干燥试验,提出了可行的干燥基准,确定了合理的干燥工艺。试验的板材厚度均取25mm。试验结果表明,在保证干燥质量的前提下,与普通锯材比较,干燥时间大大缩短。测定了三个树种的干缩系数,并和普通锯材作了比较。分析了边材、心材和髓心材的干缩特点,阐明了小径材弦径向干缩差异大是其难干的一个主要原因。另外,髓心对干燥缺陷的产生影响较大。讨论了热湿处理与干燥速度、弦径向干缩比和干燥应力之间的关系。 相似文献
17.
蒙古栎种源选择试验研究 总被引：1，自引：0，他引：1
蒙古栎多点种源试验研究表明：蒙古栎生长性状地理变异以经、纬向渐变为主;采用多性状综合评定法选择出松花湖生态区优良种源为宽甸和磐石种源,白石山及毗邻地区优良种源为磐石和美溪种源;采用环境指数法对种源稳定性进行评价,确定磐石、美溪、岫岩、宽甸、红石、白石山种源为高产型种源.蒙古栎种源遗传参数估算结果显示：松花湖生态区优良种源树高、胸径、地径遗传力分别为0.835 8,0.890 9和0.727 5,遗传增益分别为44.22%,65.89%和35%;白石山及毗邻地区优良种源树高、胸径、地径遗传力分别为0.848 0,0.720 7和0.726 8,遗传增益分别为34.67%,48.28%和23.83%. 相似文献
18.
Activated proto-onc genes: sufficient or necessary for cancer? 总被引：20，自引：0，他引：20
P H Duesberg 《Science (New York, N.Y.)》1985,228(4700):669-677
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20.
对观赏桃园昆虫群落的时间结构研究表明：桃园昆虫有64种,隶属于11目48科。物种数随季节变化而变化,主要优势种为桃小绿叶蝉(Empoasca flavescens Fabr. )和山楂叶螨（Tetranychus viennesis Zacher）。在不同时间其优势度、多样性、均匀性等也不断变化。根据群落的相异系数对桃园6～9月的昆虫群落进行分析表明,8月中旬与8月下旬的昆虫群落最为相似,其次是7月上旬与7月中旬。 相似文献