Long-term agroecosystem experiments: assessing agricultural sustainability and global change   总被引：3，自引：0，他引：3  

PE Rasmussen  KWT Goulding  JR Brown  PR Grace  HH Janzen  M Korschens 《Science (New York, N.Y.)》1998,282(5390):893-896

Long-term agroecosystem experiments can be defined as large-scale field experiments more than 20 years old that study crop production, nutrient cycling, and environmental impacts of agriculture. They provide a resource for evaluating biological, biogeochemical, and environmental dimensions of agricultural sustainability; for predicting future global changes; and for validating model competence and performance. A systematic assessment is needed to determine the merits of all known experiments and to identify any that may exist in tropical and subtropical environments. The establishment of an international network to coordinate data collection and link sites would facilitate more precise prediction of agroecosystem sustainability and future global change.  相似文献   

Magnetic microstructure of magnetotactic bacteria by electron holography     

RE Dunin-Borkowski  MR McCartney  RB Frankel  DA Bazylinski  M Posfai  PR Buseck 《Science (New York, N.Y.)》1998,282(5395):1868-1870

Off-axis electron holography in the transmission electron microscope was used to correlate the physical and magnetic microstructure of magnetite nanocrystals in magnetotactic bacteria. The magnetite crystals were all single magnetic domains, and the magnetization directions of small superparamagnetic crystals were constrained by magnetic interactions with larger crystals in the chains. Shape anisotropy was found to dominate magnetocrystalline anisotropy in elongated crystals. A coercive field between 300 and 450 oersted was determined for one chain.  相似文献   

Copper-Catalyzed Oxidation of Alcohols to Aldehydes and Ketones: An Efficient, Aerobic Alternative   总被引：1，自引：0，他引：1  

IE Marko  PR Giles  M Tsukazaki  SM Brown  CJ Urch 《Science (New York, N.Y.)》1996,274(5295):2044-2046

An efficient, copper-based catalyst has been discovered that oxidizes a wide range of alcohols into aldehydes and ketones under mild conditions. This catalytic system utilizes oxygen or air as the ultimate, stoichiometric oxidant, producing water as the only by-product.  相似文献   

Coastal taipan (Oxyuranus scutellatus) envenomation of a dog          下载免费PDF全文

PR Judge 《Australian veterinary journal》2015,93(11):412-416

  相似文献   

Differential Rotation and Dynamics of the Solar Interior     

MJ Thompson  J Toomre  ER Anderson  HM Antia  G Berthomieu  D Burtonclay  SM Chitre  J Christensen-Dalsgaard  T Corbard  M DeRosa  CR Genovese  DO Gough  DA Haber  JW Harvey  F Hill  R Howe  SG Korzennik  AG Kosovichev  JW Leibacher  FP Pijpers  J Provost  EJ Rhodes  J Schou  T Sekii  PB Stark  PR Wilson 《Science (New York, N.Y.)》1996,272(5266):1300-1305

Splitting of the sun's global oscillation frequencies by large-scale flows can be used to investigate how rotation varies with radius and latitude within the solar interior. The nearly uninterrupted observations by the Global Oscillation Network Group (GONG) yield oscillation power spectra with high duty cycles and high signal-to-noise ratios. Frequency splittings derived from GONG observations confirm that the variation of rotation rate with latitude seen at the surface carries through much of the convection zone, at the base of which is an adjustment layer leading to latitudinally independent rotation at greater depths. A distinctive shear layer just below the surface is discernible at low to mid-latitudes.  相似文献   

Seasonality of sarcoptic mange in pigs in South Australia     

PR DAVIES  MJ MOORE  AM POINTON 《Australian veterinary journal》1991,68(12):390-392

Retrospective analysis of records, from July 1987 to June 1991, of 1140 inspections of slaughtered pigs from 154 swine herds in the Pig Health Monitoring Scheme of South Australia was conducted to evaluate patterns of variation in the prevalence and severity of skin lesions typical of sarcoptic mange. An increase in the severity of sarcoptic mange in winter and spring was observed. There was a substantial reduction in the severity of mange over the period of monitoring. These observations support the role of monitoring at slaughter in the management of endemic disease. They provide some basis for refining control programs for mange to improve cost-effectiveness.  相似文献   

Letter to the editor     

Wakeley PC 《Science (New York, N.Y.)》1974,183(4120):32-33

  相似文献   

长胚芽鞘小麦品种耐深播出苗好   总被引：1，自引：0，他引：1  

文学飞  潘前颖  潘田园  史引红  潘田雨  潘幸来 《小麦研究》2011,(2)

综述澳美欧亚非30多国百多家有关研究表明,胚芽鞘长、细、硬、快的小麦品种耐深播、立苗好。从细胞能性角度阐述胚轴划分并澄清小麦胚芽鞘的错位描述及地中茎的混淆定义。图示双胚苗的第二胚芽鞘自然开裂。图释深播地中拔节现象值得春化学者关注。概述胚芽鞘遗传长度、生理长度及环境长度。提到小麦脂肪优质育种问题。对国内麦学界提出3个具有理论或实践意义的建议。  相似文献   

Embryonic Development and Gene Expression in Oocytes Cultured In Vitro in Supplemented Pre‐Maturation and Maturation Media     

PR Adona  THC de Bem  LG Mesquita  RC Rochetti  CLV Leal 《Reproduction in domestic animals》2011,46(1):e31-e38

  相似文献   

An ELISA for the detection of anergic tuberculous cattle   总被引：6，自引：0，他引：6  

P. PLACKETT  J. RIPPER  LA. CORNER  K. SMALL†  K. de. WITTE†  L. MELVILLE†  S. HIDES‡  PR. WOOD 《Australian veterinary journal》1989,66(1):15-19

An enzyme-linked immunosorbent assay (ELISA) for bovine antibody to antigens in unheated Mycobacterium bovis culture filtrate was standardised against a reference serum from an experimentally infected cow. Two Northern Territory herds with a total of 561 cattle were tested. All cattle reacting in the caudal fold tuberculin test, those giving strong reactions in the ELISA and those with visible lesions of tuberculosis were subjected to a detailed bacteriological examination. Of the 19 cattle which yielded isolates of M. bovis, only 4 were positive to the tuberculin test. Serum samples from 5 cattle gave ELISA values greater than 7.0 units. None of these 5 reacted in the tuberculin-test and 2 had no visible lesions. Of the 10 remaining cattle from which M. bovis was isolated, 3 had ELISA values between 6.5 and 7.0 units and were also without visible lesions. The ELISA values for the remaining 7 infected cattle ranged down to 4.6 units. Forty cattle yielded no M. bovis on culture of their tissues. They included 7 which were reactors in the tuberculin test and 23 with ELISA values of 7.0 units or more. The evident low specificity and sensitivity of the ELISA make it of little value as an alternative to the tuberculin test, but it can detect some anergic cattle at the cost of increasing the number of false positive reactors. This may be acceptable in some circumstances and would justify the use of the ELISA as a complement to the tuberculin test or to an in vitro assay of T-cell immunity. In the 2 Northern Territory herds described, the removal of 5 of the anergic cattle would have required a cull of 28 animals of 5% of the total. A cut off value of 6.5 units would have eliminated 3 more, but at the cost of culling 80 animals or nearly 15% of the cattle. Even so, 7 cattle from which M. bovis was isolated would have remained undetected by either test.  相似文献