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李明子 《农业图书情报学刊》2006,18(11):168-170
采用文献计量学方法对专著《鹅掌楸属树种杂交育种与利用》（2005年1月第一版）的参考文献的引文量、引文年代、引文语种、引文类型、引文学科分布和引文自引率等主要指标进行统计分析和评价,为科研提供确切的情报资料,并探讨专著的图书质量评价方法。 相似文献
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The movement towards precision agriculture has led to calls for soil maps that are more detailed and accurate than those offered in standard NCSS soil surveys. Studies have shown that soil variability can be greater than depicted in soil surveys; in fact, delineations that contain at least 50% of the soil mapped are considered satisfactory for soil survey purposes. Lacustrine plains are relatively flat and often have parent materials with uniform properties. Because soils are usually mapped using soil–landform relationships one might expect soil maps in these areas to be less accurate than average; it is difficult to delineate between map units using soil–landform relationships in such subtle landscapes. We grid-mapped a field containing lacustrine-derived soils in central Iowa and used the grid to evaluate the soil survey for accuracy. Two major and two minor soils, as determined by the area they occupy in the field, were present. For the field as a whole, the two major soils were correctly identified by the soil survey at least 63% of the time. The two minor soils were correctly identified 33% of the time or less by the soil survey. Large-scale soil mapping is expensive because of the time involved to create them in the field and in the office. Therefore, it is only economically beneficial to produce a detailed map if the map leads to significant alterations in the way a field is managed. In fields that may have uniform soil properties, it may be more cost-effective to conduct a reconnaissance survey first and then decide if more detailed mapping is required. 相似文献
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花蕾 《西北农林科技大学学报(自然科学版)》1993,21(2):99-103
枣和酸枣桃蛀果蛾生物学特性异于苹果桃蛀果蛾。在适宜温湿度下,枣和酸枣桃蛀果蛾越冬幼虫出土始期和高峰期分别比苹果桃蛀果蛾晚8d和20多d,田间成虫发生期也晚约20d。恒温条件下,前两者的前蛹期+蛹期也均比后者短。桃蛀果蛾多产卵于枣果临近的叶背基部和酸枣梗洼处。幼虫在酸枣中需生活40～50d,一年发生1代。提出了桃蛀果蛾不同的“寄主生物型”概念。 相似文献
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The frequency spectrum for the low-frequency eddy kinetic energy is estimated from a long-term current meter record obtained in a deep layer in the western North Pacific. The eddy field is characterized by three time scales: an "annual scale" with zonal dominance of eddy motions, a "temporal mesoscale" with meridional dominance, and a "monthly scale" with horizontal isotropy. About two-thirds of the eddy kinetic energy is contained in the temporal mesoscale. 相似文献
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“信、达、雅”翻译标准是清朝末年严复所提出来的,在翻译界影响深远。本文作者在概括大半个世纪以来众学者对这一标准讨论的基础上提出了自己的见解:鲁迅等人对严论的批驳是有其历史背景的,鲁迅提出的“直译”在当时的历史条件下完全是对的;“信、达、雅”的标准在讨论中不断发展和完善;实践证明,这一翻译标准是有其生命力的;对这一标准的讨论还在继续,是有益的. 相似文献
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Blood velocity measurements in intact subjects 总被引：1，自引：0，他引：1
Venous blood velocities in intact human forearms can be measured by the use of nuclear magnetic resonance techniques. In essence, two separated coils are placed over the vein, and the arm is held in a magnetic field. Radio-frequency energy in one coil "flips" over the protons in the blood stream, and the second coil detects the arrival of the "flipped" protons. Human blood in vivo and in vitro has a nominal nuclear magnetic resonance relaxation time of 0.4 second. 相似文献
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Nellis WJ Hamilton DC Holmes NC Radousky HB Ree FH Mitchell AC Nicol M 《Science (New York, N.Y.)》1988,240(4853):779-781
Data from the Voyager II spacecraft showed that Uranus has a large magnetic field with geometry similar to an offset tilted dipole. To interpret the origin of the magnetic field, measurements were made of electrical conductivity and equation-of-state data of the planetary "ices" ammonia, methane, and "synthetic Uranus" at shock pressures and temperatures up to 75 gigapascals and 5000 K. These pressures and temperatures correspond to conditions at the depths at which the surface magnetic field is generated. Above 40 gigapascals the conductivities of synthetic Uranus, water, and ammonia plateau at about 20(ohm-cm)(-1), providing an upper limit for the electrical conductivity used in kinematic or dynamo calculations. The nature of materials at the extreme conditions in the interior is discussed. 相似文献
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R M Boynton 《Science (New York, N.Y.)》1966,154(756):1581-1583
Visual adapting stimuli having different spectral distributions are used alone and then mixed together. It is found that the mixture is more effective, as an adapting field, than either component when used alone. This experiment, along with others, supports the following: although the most efficient stimulus for eliciting a visual sensation is "compact" in space, time, and wavelength, the most efficient adapting stimulus tends to be dispersed in each of these dimensions. 相似文献
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As precision agriculture strives to improve the management of agricultural industries, the importance of scientific validation must not be forgotten. Eventually, the improvement that is imparted by precision agriculture management must be considered in terms of profitability and environmental impact (both short and long term). As one form of precision agriculture, we consider site-specific crop management to be defined as: Matching resource application and agronomic practices with soil and crop requirements as they vary in space and time within a field. While the technological tools associated with precision agriculture may be most obvious, the fundamental concept will stand or fall on the basis of scientific experimentation and assessment. Crucial then to scientifically validating the concept of site-specific crop management is the proposal and testing of the null hypothesis of precision agriculture, i.e. Given the large temporal variation evident in crop yield relative to the scale of a single field, then the optimal risk aversion strategy is uniform management. The spatial and temporal variability of important crop and soil parameters is considered and their quantification for a crop field is shown to be important to subsequent experimentation and agronomic management. The philosophy of precision agriculture is explored and experimental designs for Precision agriculture are presented that can be employed in attempts to refute the proposed null hypothesis. 相似文献
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原油管道低输量运行问题 总被引：5，自引：0，他引：5
原油管道一般按油田高产期外输设计的，在油田开采的初期和末期，原油管道必然出现不满输现象，由于油田自然老化，原油外输量减少，油田自炼油增加；设计时对油田产量估计过高，导致管径设计过大等原因，使我国多数管道出现低输量情况，提出了实际输量稍高于允许最低输量叫低输量，实际输量低于允许最低输量叫超低输量等界定指标，我国盛产高粘易凝原油，低输量运行既不经济又很不安全。国外的办法一般是掺稀油输送或加药改性，延长 相似文献
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发展生物质产业 总被引：19，自引：0，他引：19
石元春 《中国农业科技导报》2006,8(1):1-5
介绍了当今全球性能源危机中生物质产业的特殊意义及发达国家在发展生物基产品（biobased products）、生物燃料（biofuels）和生物能源（bioenergy）方面的动向。对发展中国的生物质产业提出了具体建议,包括建设年产5000万t的绿色油田和开辟农业的“第三战场”。 相似文献
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不同小麦品种在缺锰土壤上的生长和产量 总被引：1，自引：0，他引：1
吕世华 《四川农业大学学报》1993,11(1):27-31
在严重缺锰土壤上设置田间试验观察了12个小麦品种对缺锰的反应。不同品种在缺锰症出现时间、症状轻重、幼苗生长、分蘖成穗、籽粒产量及时锰肥的反应各不相同。川麦22、绵阳11等不耐缺锰_而“951”在不施锰条件下也有较高的产量,表现了较强的耐性。 相似文献
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盆栽和地栽牡丹叶片叶绿素及抗氧化酶活性代谢动态 总被引：1，自引：0，他引：1
以盆栽和地栽牡丹"洛阳红"、"胡红"为试材,对其不同生长发育期叶片叶绿素含量及抗氧化酶活性动态代谢进行了比较研究。结果表明:两品种牡丹中,盆栽"洛阳红"叶绿素含量、SOD、POD、CAT活性均比地栽有不同程度的降低,而盆栽"胡红"SOD活性则高于地栽,这可能与种间特遗性有关。抗氧化酶活性的减弱,在一定程度上减弱了盆栽牡丹对高温、干旱等逆境的抵御及抗衰老能力。 相似文献
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利用常规实况场、物理量场、雷达产品资料,对2007年7月30日河南省东北部出现的雷雨大风天气进行诊断分析。结果表明,造成这次强对流天气过程的原因是副高西北侧、槽前深厚的西南气流内产生的飑线发展东北移造成的;持续5 d的深厚低压槽前较强的西南急流,一方面把大量热量、水汽和动量向北输送,使当地具有大量的不稳定能量存储,为对流的发生提供了热力和动力条件,另一方面,高低空深厚一致的西南气流决定了雷雨大风的移动方向。雷达图上,2条回波带的合并形成的"人"字型回波使对流加强,雷雨大风最大风速出现在"人"字型回波顶端及其移动路径上;根据多普勒雷达风廓线上风场的突然上传,可以提前35 min预报雷雨大风天气。 相似文献
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经４年研究证明,进入９０年代以来,山东省小麦全蚀病有两个新的为害特点,其一是全蚀病发生区有所扩大,已遍及全省１７个市地,发病县区占全省农业县区的８５％,病情仍然严重;其二是病地由以往的全蚀病单一为害,发展为近年来的以全蚀病为主、多种根腐性病害同田甚至同株侵染为害。其形成原因主要包括长期推行小麦、玉米一年两熟制,偏施氮肥,缺少有机肥和磷、钾肥,以及普遍种植感病品种等。经试验、示范,提出“三改一治”的农业生态综合治理对策,推广应用效果显著,平均防效为８５．８％。 相似文献