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   52篇
  免费   8篇
林业   3篇
  10篇
综合类   6篇
农作物   1篇
畜牧兽医   29篇
园艺   3篇
植物保护   8篇
  2022年   1篇
  2021年   1篇
  2017年   3篇
  2016年   1篇
  2015年   3篇
  2014年   1篇
  2013年   3篇
  2012年   1篇
  2011年   1篇
  2009年   2篇
  2008年   1篇
  2007年   3篇
  2006年   3篇
  2005年   1篇
  2004年   1篇
  2003年   4篇
  2002年   1篇
  2001年   1篇
  1999年   3篇
  1998年   1篇
  1993年   2篇
  1991年   1篇
  1989年   1篇
  1985年   2篇
  1984年   1篇
  1979年   1篇
  1977年   1篇
  1974年   1篇
  1972年   2篇
  1970年   2篇
  1969年   1篇
  1967年   2篇
  1966年   2篇
  1965年   1篇
  1964年   1篇
  1963年   1篇
  1948年   1篇
  1942年   1篇
排序方式: 共有60条查询结果,搜索用时 15 毫秒
11.
Geographic variation in some aspects of chimpanzee behavior has been interpreted as evidence for culture. Here we document similar geographic variation in orangutan behaviors. Moreover, as expected under a cultural interpretation, we find a correlation between geographic distance and cultural difference, a correlation between the abundance of opportunities for social learning and the size of the local cultural repertoire, and no effect of habitat on the content of culture. Hence, great-ape cultures exist, and may have done so for at least 14 million years.  相似文献   
12.
13.
14.
15.
16.
Abstract— Points in relation to anterior cruciate ligament rupture are considered in the light of 106 clinical cases involving ninety-eight dogs. Data is given regarding breed age and sex of animals in the series as well as observations on arthritic changes associated with this injury. A case is made for surgical repair in view of clinical and experimental findings and the author's technique for re-stabilization is described.
Resumé— n considère les circonstances d'apparition de la rupture du ligament croisé antérieur du chien à la lumière de 106 cas cliniques portant sur 98 chiens. On rapporte des données concernant la race, l'âge et le sexe des animaux de ce groupe, aussi bien que les observations concernant les modifications articulaires associées à cette affection. Une place est faite aux réparations chirurgicales a la lumière des observations cliniques et expérimentales et la technique de réduction qu'utilisent les auteurs des décrite.
Zusammenfassung— Gesichtspunkte, die in Beziehung zum Riss des vorderen Kreuzbandsstehen, werden an Hand von 106 klinischen Fällen, die 98 Hunde betreffen, besprochen. Es werden Daten des Alters und Geschlechts der Tiere sowie Beobachtungen arthritischer Veränderungen im Zusam-menhang mit dieser Verietzung mitgeteilt. Klinische und experimentelle Ergebnisse sprechen für einen chirurgischen Eingriff, und die Technik des Auton für die Restabilisierung wird beschreiben.  相似文献   
17.
 Soybean cultivars capable of nodulating with indigenous Bradyrhizobium spp. have been developed by the International Institute of Tropical Agriculture (IITA) and national programs in Africa in order to avoid artificial inoculation by resource-poor farmers in Africa. The current selection procedure for enhanced N2 fixation is based on an assessment of nodule formation which does not directly quantify the proportions of crop N derived from the atmosphere. We have monitored N accumulation patterns and N2 fixation in nine promiscuous soybean cultivars with different maturity periods, using the 15N dilution technique. Nodule development generally peaked at the early podfill stage for all cultivars except Tgx 1519-1D and Tgx 1447-2D in which it continued to increase. The proportion of crop N derived from fixation (%NDFA) ranged between 51% and 67%, 77% and 84%, and 66% and 73% at full bloom, early podfill, and physiological maturity stages, respectively. Total N accumulation increased in all soybean genotypes with increasing plant age. Significant correlations (P<0.001) were established between nodule weight and %NDFA, even though this did not explain the relationship between nodule development and N2 fixation in cultivars such as Tgx 1519-1D. Promiscuous soybean cultivars retained between 10% and 19% of total N accumulated at the final harvest, in belowground biomass. Our results indicated that these soybean cultivars can derive substantial proportions of plant N from N2 fixation in soils where compatible indigenous bradyrhizobia populations are adequate and effective. Also, we have substantiated the claims that qualitative nodulation parameters currently used to select varieties with a high N2 fixation capacity need to be validated with other measurements of N2 fixation. Received: 5 November 1998  相似文献   
18.
A survey of the knowledge, attitudes and practices (KAP) of 100 rice farmers and 50 coconut farmers was conducted in the coastal lowland agro-ecosystems of the Sierra Madre Biodiversity Corridor, Luzon, Philippines to identify current rodent management practices and to understand the extent of rat damage and the attitudes of farmers to community actions for rodent management. Pests were most commonly listed as one of the three most important rice and coconut production constraints. Other major crop production constraints were typhoons and insufficient water. Farmers consider rats to be the major pest of coconut and of rice during the wet season rice crop, with average yield losses of 3.0% and 13.2%, respectively. Rice and coconut farmers practised a wide range of rodent management techniques. These included scrub clearance, hunting and trapping. Of the 42 rice farmers and 3 coconut farmers that applied rodenticides to control rodents, all used the acute rodenticide, zinc phosphide. However, only ten rice farmers (23.8%) applied rodenticides prior to the booting stage and only seven farmers (15.6%) conducted pre-baiting before applying zinc phosphide. The majority of farmers belonged to farmer organisations and believed that rat control can only be done by farmers working together. However, during the last cropping season, less than a third of rice farmers (31.2%) applied rodent management as a group. In order to reduce the impact of rodents on the farmers of the coastal lowlands of the Sierra Madre Biodiversity Corridor, integrated management strategies need to be developed that specifically target the pest rodents in a sustainable manner, and community actions for rodent management should be promoted.  相似文献   
19.
Current reactive pest management methods have serious drawbacks such as the heavy reliance on chemicals, emerging genetic rodenticide resistance and high secondary exposure risks. Rodent control needs to be based on pest species ecology and ethology to facilitate the development of ecologically based rodent management (EBRM). An important aspect of EBRM is a strong understanding of rodent pest species ecology, behaviour and spatiotemporal factors. Gaining insight into the behaviour of pest species is a key aspect of EBRM. The landscape of fear (LOF) is a mapping of the spatial variation in the foraging cost arising from the risk of predation, and reflects the levels of fear a prey species perceives at different locations within its home range. In practice, the LOF maps habitat use as a result of perceived fear, which shows where bait or traps are most likely to be encountered and used by rodents. Several studies have linked perceived predation risk of foraging animals with quitting‐harvest rates or giving‐up densities (GUDs). GUDs have been used to reflect foraging behaviour strategies of predator avoidance, but to our knowledge very few papers have directly used GUDs in relation to pest management strategies. An opportunity for rodent control strategies lies in the integration of the LOF of rodents in EBRM methodologies. Rodent management could be more efficient and effective by concentrating on those areas where rodents perceive the least levels of predation risk. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.  相似文献   
20.
Sanchez  A. L.  Horrill  A. D.  Howard  B. J.  Singleton  D.  Mondon  K. 《Water, air, and soil pollution》1998,106(3-4):403-424
The activity concentrations of 137Cs,238 Pu, 239,240Pu and 241Am were measured in root mat and vegetation samples collected from tide washed pastures in 17 estuaries spanning the eastern seaboard of the Irish Sea, extending from the Solway in north-west England to St. David's Head in south Wales. Some of these estuaries had been investigated in previous surveys, but this study is unique in that it covered a wide geographic range using the same sampling and analytical methodology and within a comparatively short time scale. This allows for a valid comparison within the data set of the contamination levels at the different areas. Spatial distributions of the radionuclides were consistent with transport of radionuclides discharged to the Irish Sea from the Sellafield Nuclear Reprocessing Plant, with the highest activities occurring in the Esk estuary (closest to Sellafield) and lowest at the Welsh sites. Measurable activity concentrations of238 Pu and 239,240Pu were found in root mat samples from the Solway estuary to as far south as the Gwyrfai in Wales and showed an average238 Pu/239,240Pu ratio of 0.2, consistent with Sellafield-derived Pu. The ratios of137 Cs/241Am increased with distance from the source, with values of 1:1 in estuaries near Sellafield to ratios between 2 and 5 in estuaries further south and in excess of 10:1 in Wales. This is probably due to the more rapid movement of dissolved137 Cs in Irish Sea waters compared with the actinides. In contrast, 241Am and 239,240Pu behave similarly with consistent ratios of between 2:1 and 3:1, as both are associated with particulates. Dose assessment calculations suggest that external exposure would be a maximum of 530 µSv at the most contaminated spot at the Esk estuary. Relatively lower doses arise from the ingestion of animal products (along the soil-vegetation-grazing animal pathway) due to the low availability of sediment-associated radionuclides for gut transfer. The dose assessment calculations highlight the importance of using the appropriate transfer parameters that take into account this low bioavailability.  相似文献   
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