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排序方式: 共有862条查询结果,搜索用时 296 毫秒
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2.
Lenz M Drillich M Heuwieser W 《Berliner und Münchener tier?rztliche Wochenschrift》2007,120(5-6):237-244
The aim of this study was to determine signs of subclinical endometritis found by ultrasound that are associated with reduced fertility in dairy cows.The maximum diameter of the uterine lumen was determined by ultrasound in 324 cows without clinical signs of endometritis after evaluation of the genital tract 21 to 27 days postpartum. Cows were classified into healthy or with subclinical endometritis by three threshold values for the maximum uterine lumen diameter of 0.2 cm, 0.5 cm or 0.8 cm. Examinations by rectal palpation and ultrasound as well as classifications were repeated 14 days later. In addition, ovaries were scanned by ultrasound to determine the stage of the estrous cycle. In a subgroup of 103 cows the echotexture of the uterus and its contents was evaluated. In these cows the diagnosis of subclinical endometritis was performed by a scoring system. The diameter of the uterine lumen was significantly affected by stage of the estrous cycle at the time of examination. However, no effects were found for the stage of the cycle at the time of examination on subsequent reproductive performance. A uterine lumen with a maximum diameter of more than 0.2 cm showed a significant negative association with conception rate and proportion of cows pregnant. Classification based on higher threshold values did not reveal an association with reproductive performance. Echogenic content in the uterus also decreased reproductive performance. A classification based on the echotexture of the uterus and its contents revealed significant differences between healthy cows and cows with subclinical endometritis regarding the proportion of cows inseminated and pregnant.The results of this study showed that the diagnostic of bovine endometritis should be broadend by ultrasonography. The definition of subclinical endometritis diagnosed by means of ultrasonography has to be evaluated in further studies. 相似文献
3.
RATIONALE FOR THIS STUDY: The purpose of this study was to compare the success during the first academic year of students who underwent an admissions procedure (class 2005) and students of the three previous classes (2002-2004), who did not undergo an admissions procedure but took their exams under the same curricular framework. METHODOLOGY: Exam results of 802 students of the 2002-2004 classes were compared with those of 181 students from the 2005 class. RESULTS: Students of the 2005 class were more likely to pass all three exams given in the first academic year than students of the 2002-2004 classes (p < 0.001; OR = 3.2), and the quality of two of the three exams (indicated by individual scores) was also significantly better in 2005 than in the preceding classes (p < 0.001). In unselected classes, 25% to 31% of students showed no successful attempts to pass any of the three exams currently administered. CONCLUSION: The implementation of an admissions procedure measuring, among other indicators, academic ability has significantly improved first-year exam performance. Incoming students presenting with higher scores on academic standards are more likely to complete their courses successfully. 相似文献
4.
A GC-MS method capable of completely separating the four pairs of diastereoisomers of cyfluthrin is presented and the method used to show that isomerisation of the cyfluthrin enantiomers occurs in methanol. This methanol-induced isomerisation could also be demonstrated by bioassays using water fleas. The biological activities of the various cyfluthrin isomers contained in the commercial products cyfluthrin and beta-cyfluthrin were assayed using several strains of lepidopteran larvae including Plutella xylostella, Heliothis virescens and Spodoptera frugiperda. With the susceptible strains, the efficiencies of the isomers mixtures of cyfluthrin and beta-cyfluthrin were shown to obey the rules of additivity. However, in tests with a resistant strain of P. xylostella originating from Thailand, the ‘inactive’ isomer III acted synergistically with the active isomer IV. Resistance factors in strains of H. virescens and P. xylostella were found to be higher with cis than with trans isomers. This probably contributes to the superior action of cyfluthrin and beta-cyfluthrin against various pests of agricultural importance since the commercial products contain a high content of trans isomers (‘high trans pyrethroids’). 相似文献
5.
R. Westerhof P. Buurman C. van Griethuysen M. Ayarza L. Vilela W. Zech 《Geoderma》1999,90(3-4):277-290
In the Cerrado savanna region in Brazil, the effects of different land use on Oxisol aggregation were studied using laser diffraction grain size analyses. The topsoil of plowed systems had significantly lower amount of macroaggregates (2000–194 μm) and a significantly higher amount of soil in the microaggregate size and primary particle fraction (<76 μm) compared to pastures and the native Cerrado. In plowed systems low in soil organic carbon (SOC), lime had a negative effect on aggregate stability. Lime addition had no effect on topsoil aggregation in land use systems that were not plowed regularly and generally had a higher SOC content. For all the studied topsoils, pHKCl was positively correlated with the amount of clay dispersed after 3 h of shaking in water. SOC did not influence clay dispersion in the range of soils studied. In continuous cropping systems in the Cerrado region, with a combination of mechanical stress and low SOC, liming will cause an increase in small aggregates and primary particles and hence contribute to a destabilization of the soil structure. 相似文献
6.
Stereoselectivity of the generation of 3-mercaptohexanal and 3-mercaptohexanol by lipase-catalyzed hydrolysis of 3-acetylthioesters 总被引:1,自引:0,他引:1
Wakabayashi H Wakabayashi M Eisenreich W Engel KH 《Journal of agricultural and food chemistry》2003,51(15):4349-4355
The enantioselectivity of the generation of 3-mercaptohexanal and 3-mercaptohexanol, two potent sulfur-containing aroma compounds, by lipase-catalyzed hydrolysis of the corresponding 3-acetylthioesters was investigated. The stereochemical course of the kinetic resolutions was followed by capillary gas chromatography using modified cyclodextrins as chiral stationary phases. The enzyme preparations tested varied significantly in terms of activity and enantioselectivity (E). The highest E value (E = 36) was observed for the hydrolysis of 3-acetylthiohexanal catalyzed by lipase B from Candida antarctica resulting in (S)-configured thiol products. Immobilization of the enzyme (E = 85) and the use of tert-butyl alcohol as cosolvent (E = 49) improved the enantioselectivity. Modification of the acyl moiety of the substrate (3-benzoylthiohexanal) had no significant impact. The sulfur-containing compounds investigated possess attractive odor properties, and only one of the enantiomers exhibits the pleasant citrus type note. 相似文献
7.
Soils of two climosequences in Russia were investigated by 31P-NMR spectroscopy. They comprised Dystric Podzoluvisols, Haplic Greyzems, Calcic Chernozems, and Gypsic Kastanozems, which are located along temperature and precipitation gradients of the Russian Plain. Another sequence of soils included forest Humic Cambisols and Umbric Leptosols of subalpine and alpine meadows, which are formed in different climatic conditions along a climosequence of the Mt. Malaya Khatipara (northern Caucasus). The results showed that accumulation of DNA was high in the cold, wet, and acid soils (Dystric Podzoluvisol, alpine Umbric Leptosol), while phospholipids and teichoic acids mainly accumulated in the more microbially active soils. We performed a laboratory incubation experiment to test the relationship between microbial biomass P and P species identified in soil extracts. The proportions of P compounds resonating at 0.5-3.0 ppm in the NaHCO3 and H2SO4 extracts from the incubated Humic Cambisol increased. The amounts of phosphate diesters resonating at 0 ppm in the same extracts and in the subsequent NaOH extracts decreased after incubation. Based on the results of 31P-NMR spectroscopy of native soils and of the laboratory incubation experiment we concluded that signals at 0 ppm in spectra of soil alkaline extracts belong to DNA P which is mainly stabilised in soil organic matter outside microbial cells (at least in soils with relatively low microbial activity). Phospholipids-teichoic acids P extracted with 0.5 M NaHCO3 seems to be derived from soil microbial biomass, and its proportion can reflect the microbial activity in the soil. 相似文献
8.
Enchytraeids are saprophagous soil organisms, appearing in high abundances and contributing to ecological processes within the soil. For decades they have been used as model species for biological research. In the framework of research on genetically modified plants, however, they have not been considered to date. Following the ISO/DIS guideline, survival and reproduction of Enchytraeus albidus, fed with diets containing Bt-maize (N4640Bt Cry1Ab, DKC5143Bt Cry3Bb1) leaf material were analysed. For comparison, diets with the corresponding untransformed near-isolines (N4640, DKC5143) were examined. Additionally a high quality control diet (oat flakes) was included. Survival and reproduction showed no significant differences between the Cry3Bb1 treatment and the treatment with the untransformed counterpart. For the Cry1Ab treatment survival was significantly higher than for the treatment with the corresponding near-isoline. In contrast, reproduction was significantly lower for the Cry1Ab treatment compared to that for the isoline. For the Cry3Bb1 treatment, no effect was shown on survival or reproduction. For the Cry1Ab variety and its untransformed counterpart, a contrasting result was detected, which is unlikely to be caused by the Bt-protein but rather by differences in other plant components. Overall survival and reproduction were highest for the control. 相似文献
9.
Sabine Augustin Jan Evers Hans-Peter Dietrich Johannes Eichhorn Thomas Haussmann Regina Icke Ansgar Isenberg Wolfgang Lux Monica Musio Hans Pretzsch Winfried Riek Thomas Rötzer Bernd Schultze Andreas Schulze Jörg Schröder Walter Seidling Nicole Wellbrock Klaus von Wilpert Barbara Wolff 《European Journal of Forest Research》2005,124(4):251-260
In the 1970s unexpected forest damages, called “new type of forest damage” or “forest decline”, were observed in Germany and
other European countries. The Federal Republic of Germany and the German Federal States implemented a forest monitoring system
in the early 1980s, in order to monitor and assess the forest condition. Due to the growing public awareness of possible adverse
effects of air pollution on forests, in 1985 the ICP Forests was launched under the convention on long-range transboundary
air pollution (CLRTAP) of the United Nations Economic Commission for Europe (UN-ECE). The German experience in forest monitoring
was a base for the implementation of the European monitoring system. In 2001 the interdisciplinary case study “concept and
feasibility study for the integrated evaluation of environmental monitoring data in forests”, funded by the German Federal
Ministry of Education and Research, concentrated on in-depths evaluations of the German data of forest monitoring. The objectives
of the study were: (a) a reliable assessment of the vitality and functioning of forest ecosystems, (b) the identification
and quantification of factors influencing forest vitality, and (c) the clarification of cause-effect-relationships leading
to leaf/needle loss. For these purposes additional data from external sources were acquired: climate and deposition, for selected
level I plots tree growth data, as well as data on groundwater quality. The results show that in particular time series analysis
(crown condition, tree growth, and tree ring analysis), in combination with climate and deposition are valuable and informative,
as well as integrated evaluation of soil, tree nutrition and crown condition data. Methods to combine information from the
extensive and the intensive monitoring, and to transfer process information to the large scale should be elaborated in future.
相似文献
Sabine AugustinEmail: |
10.
An image-based stated choice approach was used to investigate the conditions determining why visitors to an urban forest in Vienna feel crowded or not. Respondents (N=213) evaluated several sets of images depicting trail use scenarios with different levels of social crowding conditions and several types of social interferences. Forest users were segmented into three groups based on their global evaluations of use levels during weekends and work days, resulting in a crowding-averse, a crowding-tolerant, and a crowding-indifferent segment. Crowding-averse respondents reacted much more negatively to scenarios with high-use levels, heterogeneous trail use conditions, and violations of personal minimum spatial requirements caused by the presence of others. This user group felt overcrowded because social conditions experienced in the area interfered with their main visiting goals, especially to walk with their dog unleashed and to recreate. By contrast, crowding-tolerant respondents disliked very low-use and high-use situations, and preferred a certain amount of social stimulation in the form of some encounters, and more heterogeneous trail use conditions. 相似文献