穴盘规格和苗龄对塑料大棚菜豆性状及产量的影响

本试验以菜豆品种先行者为试材,采用32孔、50孔两种规格穴盘,设置10、15、20、25 d等4个苗龄段,通过研究不同穴盘规格和苗龄对菜豆性状及产量的影响,筛选出适合菜豆育苗的穴盘规格和适宜的苗龄。结果表明：穴盘育苗的营养面积增大,菜豆产量随之增加,25 d苗龄条件下,32孔穴盘的前期产量和总产量均显著高于50孔穴盘;随着苗龄的增长,菜豆的前期产量和总产量呈增加趋势,其中25 d苗龄的产量显著高于其他苗龄。综合上述各项指标,菜豆育苗阶段,10 d苗龄可选用32孔、50孔穴盘,15 d以上秧苗选用32孔穴盘为宜。     

不同基因型小麦苗期耐低氮性评价及筛选

氮素作为重要的营养元素,限制着小麦的生长发育和经济产量,筛选和培育耐低氮小麦品种是提高氮素利用率、降低生产成本的有效途径。以118份不同基因型小麦为材料,在低氮(0.1 mmol·L^-1)和正常氮(5 mmol·L^-1)条件下苗期水培,测定根干重、茎叶干重、根冠比、植株干重、最大根长、初生根数和二级初生根数等相关指标,采用模糊隶属函数法、主成分分析以及聚类分析法综合评价小麦品种的耐低氮性。结果表明,在低氮胁迫下小麦幼苗的根干重、根冠比和初生根数目显著提高,茎叶干重、植株干重和最大根长不同程度的降低,7个苗期性状指标在两个氮水平下均存在显著性差异。主成分分析提取3个主成分,贡献率分别为 43.575%、22.904%和17.873%,累积贡献率达 84.351%。以耐低氮性综合评价D值进行聚类分析,将118份小麦品种划分为强耐低氮型、耐低氮型、中间型、较敏感型和敏感型5类。筛选出3份耐低氮型小麦（齐大195、金丰7183和天民198）和2份强耐低氮型小麦（山农0917和鲁麦8号）。不同小麦品种的耐低氮机制不同,研究结果为小麦耐低氮品种的选育提供理论依据和材料基础。     

一串红N、P、K、Ca、Mg、Fe缺素症状研究

以‘展望红’为材料,研究N、P、K、Ca、Mg、Fe缺乏对其生长发育的影响,并总结缺素症状,研究结果表明:N缺乏时植株矮小,叶发黄;P缺乏时叶色暗绿,且影响开花;K缺乏时基部叶枯黄,并易落叶;缺Fe症状较为明显,但能正常开花;Ca、Mg未表现出缺素症状,且各项指标要优于全素处理;N、P显著影响一串红的生长发育,K对开花品质的影响较大。     

Segregation of form, color, movement, and depth: anatomy, physiology, and perception

Anatomical and physiological observations in monkeys indicate that the primate visual system consists of several separate and independent subdivisions that analyze different aspects of the same retinal image: cells in cortical visual areas 1 and 2 and higher visual areas are segregated into three interdigitating subdivisions that differ in their selectivity for color, stereopsis, movement, and orientation. The pathways selective for form and color seem to be derived mainly from the parvocellular geniculate subdivisions, the depth- and movement-selective components from the magnocellular. At lower levels, in the retina and in the geniculate, cells in these two subdivisions differ in their color selectivity, contrast sensitivity, temporal properties, and spatial resolution. These major differences in the properties of cells at lower levels in each of the subdivisions led to the prediction that different visual functions, such as color, depth, movement, and form perception, should exhibit corresponding differences. Human perceptual experiments are remarkably consistent with these predictions. Moreover, perceptual experiments can be designed to ask which subdivisions of the system are responsible for particular visual abilities, such as figure/ground discrimination or perception of depth from perspective or relative movement--functions that might be difficult to deduce from single-cell response properties.     

ICP-OES法同时测定果蔬中铅、砷、镉、铬、铜、锡含量

果蔬样品经混酸消化后,控制一定的酸度,定容后应用等离子体发射光谱法(ICP-OES)对果蔬中铅、砷、镉、铬、铜、锡六种有害重金属进行测定,研究了分析测定条件,方法简单快速。测定结果表明,五种元素的加标平均回收率在91.0%~107%之间。其RSD均小于3.5%。按该方法进行处理及测定铅、砷、镉、铬、铜、锡,在选择的测定条件下最低检出限分别为0.0006 mg/kg、0.0003 mg/kg、0.00003 mg/kg、0.00005 mg/kg、0.00003 mg/kg、0.0006 mg/kg。     

Space, stars, c60, and soot

Although carbon has been subjected to far more study than all other elements put together, the buckminsterfullerene hollow-cage structure, recently proposed to account for the exceptional stability of the C(60) cluster, has shed a totally new and revealing light on several important aspects of carbon's chemical and physical properties that were quite unsuspected and others that were not previously well understood. Most significant is the discovery that C(60) appears to form spontaneously, and this has particularly important implications for particle formation in combustion and in space as well as for the chemistry of polyaromatic compounds. The intriguing revelation that 12 pentagonal "defects" convert a planar hexagonal array of any size into a quasi-icosahedral cage explains why some intrinsically planar materials form quasi-crystalline particles, as appears to occur in the case of soot. Although the novel structural proposal has still to be unequivocally confirmed, this article pays particular attention to the way in which it provides convincing explanations of puzzling observations in several fields, so lending credence to the structure proposed for C(60).     

Strategic command, control, communications, and intelligence

Command, control, communications, and intelligence (C(3)l) for nuclear forces are essential elements in the deterrence of nuclear war. The present C(3)l) system has vulnerabilities associated with its reliability, survivability, and endurance under attack, thereby weakening deterrence by increasing the ambiguity in our capabilities. Development of a reliable and enduring C(3)l) system would reduce this ambiguity. Its reliable, positive control of nuclear forces would give the national leadership more time to assess situations, ensure discriminate retaliation, and improve our ability to manage crises in general. These capabilities could help to stop a war rapidly should one start. A reliable and enduring C(3)1) system will be needed for a long time to come, even if a freeze on strategic nuclear forces is accomplished or other arms control successes achieved. Indeed, C(3)l) may be the best source today of confidence-building measures to reduce tensions and the threat of nuclear catastrophe.     

Fiber, food, fuel, and fungal symbionts

Virtually all plants of economic importance form mycorrhizae. These absorbing organs of higher plants result from a symbiotic union of beneficial soil fungi and feeder roots. In forestry, the manipulation of fungal symbionts ecologically adapted to the planting site can increase survival and growth of forest trees, particularly on adverse sites. Vesicular-arbuscular mycorrhizae, which occur not only on many trees but also on most cultivated crops, are undoubtedly more important to world food crops. Imperatives for mycorrhizal research in forestry and agriculture are (i) the development of mass inoculum of mycorrhizal fungi, (ii) the interdisciplinary coordination with soil management, plant breeding, cultivation practices, and pest control to ensure maximum survival and development of fungal symbionts in the soil, and (iii) the institution of nursery and field tests to determine the circumstances in which mycorrhizae benefit plant growth in forestry and agri-ecosystems.     

Nonconversion of o,p'-DDT to p,p'-DDT in rats, sheep, chickens, and quail

The finding of appreciable quantities of p,p'-DDT after feeding o,p'-DDT to rats led to the proposal of a theory, that an isomeric metabolic conversion occurs. The presence of p,p'-DDT as an impurity in supposedly pure samples of o,p'-DDT is the correct explanation for the appearance of p,p'-DDT. Purified o,p'-DDT and (14)C-labeled o,p'-DDT yielded no data to support the idea that o,p'-DDT is converted to the p,p'-DDT isomer.     

Mineralogy, petrology, and surface features of lunar samples 10062,35, 10067,9, 10069,30, and 10085,16

The primary rocks are a sequence of titanium-rich basic volcanics, composed of clinopyroxene, plagioclase, and ilmenite with minor olivine, troilite, and native iron. The soil and microbreccias are respectively loose and compacted mixtures of fragments and aggregates of similar rocks, minerals, and glassy fragments and spheres. Impact events are reflected by the presence of shock metamorphosed rock fragments, breccias, and glasses and their resulting compaction to form complex breccias, glass-spattered surfaces, and numerous glass-lined craters. Chemistry of the glasses formed by the impact events is highly variable, and the high iron and nickel content of a few moundlike features suggests that at least some of the projectiles are iron and nickel-rich meteorites.     

Strong, transparent, multifunctional, carbon nanotube sheets

Individual carbon nanotubes are like minute bits of string, and many trillions of these invisible strings must be assembled to make useful macroscopic articles. We demonstrated such assembly at rates above 7 meters per minute by cooperatively rotating carbon nanotubes in vertically oriented nanotube arrays (forests) and made 5-centimeter-wide, meter-long transparent sheets. These self-supporting nanotube sheets are initially formed as a highly anisotropic electronically conducting aerogel that can be densified into strong sheets that are as thin as 50 nanometers. The measured gravimetric strength of orthogonally oriented sheet arrays exceeds that of sheets of high-strength steel. These nanotube sheets have been used in laboratory demonstrations for the microwave bonding of plastics and for making transparent, highly elastomeric electrodes; planar sources of polarized broad-band radiation; conducting appliqués; and flexible organic light-emitting diodes.