首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   240篇
  免费   20篇
林业   22篇
农学   4篇
  57篇
综合类   19篇
农作物   11篇
水产渔业   11篇
畜牧兽医   123篇
园艺   2篇
植物保护   11篇
  2024年   1篇
  2023年   3篇
  2022年   2篇
  2021年   5篇
  2020年   15篇
  2019年   13篇
  2018年   7篇
  2017年   10篇
  2016年   11篇
  2015年   6篇
  2014年   11篇
  2013年   20篇
  2012年   25篇
  2011年   21篇
  2010年   12篇
  2009年   5篇
  2008年   9篇
  2007年   16篇
  2006年   7篇
  2005年   6篇
  2004年   7篇
  2003年   6篇
  2002年   8篇
  2001年   1篇
  2000年   3篇
  1998年   2篇
  1996年   2篇
  1995年   2篇
  1993年   1篇
  1989年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1981年   2篇
  1976年   3篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1967年   1篇
  1966年   1篇
  1965年   1篇
  1962年   1篇
  1959年   1篇
  1955年   2篇
  1954年   1篇
  1952年   1篇
排序方式: 共有260条查询结果,搜索用时 15 毫秒
1.
In this study, we evaluated the effects of including cassava wastewater in the diet on the feeding behavior of feedlot lambs in 35 male uncastrated Santa Inês × Dorper crossbred lambs at an approximate age of 3 months, with an average live weight of 20.0?±?3.4 kg. Diets were formulated with hay of cassava shoots (roughage) and a concentrate based on corn and soybean, with a roughage:concentrate ratio of 50:50, plus inclusion of cassava wastewater at the levels of 0, 12, 24, 36, or 48 g/kg of the total diet. Feeding behavior was evaluated between the 46th and 52nd days of the experiment. Increasing cassava wastewater levels in the diet reduced (P?<?0.05) the intakes (kg/day) of dry matter and neutral detergent fiber as well as the efficiency of rumination (g/cud and g/h) of dry matter and neutral detergent fiber. The other behavioral parameters were not affected by wastewater inclusion in the diet. Therefore, the inclusion of up to 48 g/kg of cassava wastewater on fresh matter of diets is not recommended for feedlot lambs.  相似文献   
2.
3.
4.
For investigations of CO2-stunning of feeder- and slaughter-pigs parameters of behaviour, blood-gas-analyses and electroencephalograms were chosen. The following results were obtained: 1. Blood-gas-analyses proved that the CO2-stunning does not produce unconsciousness due to a lack of oxygen. 2. The criterias of general anaesthesia: unconsciousness, muscle-relaxation and analgesia with total reversibility could be confirmed. 3. The violent convulsive symptoms were evaluated as reactions identical with the stage II of GUEDEL's scheme of anaesthesia. 4. Muscular agitation, which sometimes appeared a few seconds before the stage of excitation, was judged to belong either to the start of the excitation phase or to the end of Guedel's stage of analgesia, during which the sensitivity is decreased. Neither study of behavior nor objective measurements showed, during the first 10 to 20 seconds of exposure to the CO2, any sign of pain or suffering related to the Act for Prevention of Cruelty to Animals, and accordingly such suffering should not be ascribed to the CO2 stunning method.  相似文献   
5.
6.

Background  

Chloroplast genomes evolve slowly and many primers for PCR amplification and analysis of chloroplast sequences can be used across a wide array of genera. In some cases 'universal' primers have been designed for the purpose of working across species boundaries. However, the essential information on these primer sequences is scattered throughout the literature.  相似文献   
7.
Zusammenfassung Das Aussetzen von 24 Serien von Palmen in Kübeln in einem Krankheitsgebiet für eine beschränkte Zeit, 7 Sätze von 15–20 Palmen für einen Monat, 3 Sätze für zwei Monate und 14 Sätze für drei Monate, diente zur Ermittlung der Inkubationszeit für die Tödliche Vergilbung der Kokospalme. In den meisten Fällen, die zur Ansteckung im Krankheitsgebiet führten, lag die geschätzte Inkubationszeit zwischen 3 und 6 Monaten; nach dem aufgestellten Histogramm betrug die durchschnittliche Inkubationszeit 150–160 Tage. Die lange Expositionszeit bei der größeren Zahl der Sätze erlaubt keine genaue Festlegung der Zeitspanne. Nach Entfernen von Käfigen in einem zweiten Versuch, die als Schutz gegen Infektionen dienten, traten erstmals Symptome an Palmen nach 6 (1 Palme) und 7 (2 Palmen) Monaten auf. Unter Berücksichtigung, daß der Ausbruch einer Krankheit Schwankungen unterworfen ist und auß erdem wesentlich vom Infektionszeitpunkt abhängt, fügen sich diese Daten gut in die für die Inkubationszeit angenommene Zeitspanne ein.Bodenorganismen (Nematoden) scheiden als Überträger der Tödlichen Vergilbung aus, da die Palmen in Kübeln keinen Bodenkontakt hatten. Die Palmen in den Käfigen dagegen konnten, soweit sie in den Boden gepflanzt waren, mit ihren Wurzeln unter den Käfigrand vordringen und wären dadurch der Infektion zugänglich gewesen.Da nur in den Sätzen, die den Infektionsbedingungen eines Krankheitsgebietes zwischen den Monaten Februar und August ausgesetzt waren, einzelne Palmen in den Gruppen erkrankten, dürfte in dieser Zeitspanne der Ü berträger besonders aktiv oder in der übrigen Zeit des Jahres relativ selten sein, anders wäre die Häufung der Infektionen in diesen Monaten nicht zu erklären.
Summary A transfer experiment using 17 sets of coconut palms, planted in drums and transferred bimonthly or three-monthly from a healthy into a diseased area (2 or 3 months exposure time) and 7 sets exposed for only a month, provided us with good information about the incubation period of Lethal Yellowing in a palm. The most probable incubation period ranges between 3 and 6 months; according to the dates on the histogram the mean incubation period appeared to be 150–160 days. The long exposure time used for most of the sets does not allow a more accurate assessment of this time interval.In a second experiment, groups of coconut palms which had been protected by cages for at least a year against infections were exposed to the natural infection conditions by removal of the cages. The first case of disease was recognized 6 months after cage removal, 2 additional cases a month later. Taking into consideration that the development of symptoms varies within a time interval depending upon the date of infection, growing conditions etc, this observation agress with the inferred incubation period gained in the transfer experiment.Soil organisms (nematodes o. a.) can be excluded as transmitters of the Lethal Yellowing pathogen. The palms used in the transfer experiment which later on showed symptoms were planted in drums; the roots having no connection with the soil in the field. The soil for filling the drums was collected in a healthy area. The roots of caged palms which were planted directly into the soil could penetrate under the cage border into the unprotected part of the plot which contained a lot of naturally diseased palms scattered across the field.Only sets of palms which were partly or fully exposed to the infection conditions of a diseased area during February to August developed a number of cases of Lethal Yellowing. The occurrence of infection during this period indicates this to be a time of particular vector activity.


F.A.O.- Expert in Kingston, Jamaica; jetzt: Biologiche Bundesanstalt für Land- und Forwirschaft, Berlin-Dahlem.

F.A.O.- Associate-Expert in Kingston (Coconut Industry Board.

Biologische Bundesanstalt für Land- und Forstwirstchaft, 1 Berlin 33 Dahlem, Königin-Luise-Straße 19.  相似文献   
8.
Summary A testing procedure with a new and simple specimen shape is presented which is appropriate to characterize fracturing of inhomogeneous and complex materials like wood. With this, the fracture energy of spruce wood is determined in the TL and RL direction. The size effect, i.e. influences of specimen dimensions on KIC and Gf (specific fracture energy) are investigated. Stress and deformation distribution in the newly developed specimens are analysed with FE methods. The measured load-displacement curves are approximated by bilinear softening diagrams and FE analysis. Based on these results, it is tried to interpret typical deviations from LEFM's behaviour by mechanisms like microcracking, crack branching or crack tip bridging.The authors thank Dr. A. Teischinger for supplying the testing material and Dipl. Ing M. Elser for preparation of the diagrams. Financial support of the Fonds zur Förderung der wissenschaftlichen Forschung, Wien is gratefully acknowledged.  相似文献   
9.
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号