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   58篇
  免费   7篇
林业   2篇
农学   3篇
  4篇
综合类   10篇
农作物   3篇
水产渔业   3篇
畜牧兽医   37篇
植物保护   3篇
  2023年   1篇
  2021年   1篇
  2020年   1篇
  2019年   1篇
  2016年   7篇
  2015年   3篇
  2013年   6篇
  2012年   1篇
  2011年   2篇
  2010年   1篇
  2007年   1篇
  2006年   2篇
  2005年   2篇
  2003年   3篇
  2002年   1篇
  2001年   5篇
  1999年   4篇
  1998年   3篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1993年   4篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
  1979年   1篇
  1976年   1篇
  1960年   1篇
排序方式: 共有65条查询结果,搜索用时 15 毫秒
51.
The paper deals with growth of Japanese anchovy (Engraulis japonicus) and variations in length by area and maturity of anchovy and some selected fish species obtained during surveys with R/V “Bei Dou” in the Yellow Sea and East China Sea,in 1984-1999.Demersal trawl catch rates for some selected fish species from the same surveys are also included.No density-dependent growth in length or weight of anchovy was found.Reduced length at maturity of small yellow croaker was apparent from 1986 to 1994.  相似文献   
52.
Abstract

CASE HISTORIES: Four adult kunekune pigs developed facial swelling at the base of the right ear that ruptured and discharged food material. A further six pigs that had similar clinical signs were reported by members of the New Zealand Kunekune Association who responded to an email survey, one of which was confirmed by post-mortem examination.

CLINICAL FINDINGS: Inside the mouth of each pig there was an opening at the junction of the body and ramus of the mandible just lateral to the most caudal visible molar that was impacted with masticated feed. The food packed into the mandible resulted in infection and progressive erosion of the medullary cavity of the bone until it reached the ramus where it eroded through the lateral cortex. The feed material then tracked through the soft tissues to form a subcutaneous abscess, which eventually ruptured resulting in a draining lesion. In Case 2, which had had the lesion for 2 years, the cavity in the mandible was lined with mucosa that had healed to the skin to produce a fistula. In all four pigs there was also a lesion in the left side of the mandible that was not as developed as that on the right side.

DIAGNOSIS: The facial swellings were produced by feed material that had impacted into the mandible through an opening immediately caudal to the cheek teeth and then emerged through one or more lesions in the lateral aspect of the ramus of the mandible.

CLINICAL RELEVANCE: Although it has not been previously reported, anecdotal reports and our survey suggest that this condition may occur relatively frequently in kunekune pigs. It should be considered as a differential diagnosis for facial swellings and discharging lesions in these animals.  相似文献   
53.
IntroductionProductivity of an ecosystem may be measured in terms of structure,abundance and growth of keyspecies.Stock structure,measured as age or size composition in a given stock may indicate whether the stockis in a state of growing,stable or declining.Individual growth may be measured in terms of annual growth ofindividual age groups and maturity of key species will similarly reflect the potential of the species to copewith the influence of a changing environment of predators and human i…  相似文献   
54.
55.
56.
Ice-edge eddies in the fram strait marginal ice zone   总被引:1,自引:0,他引:1  
Five prominent ice-edge eddies in Fram Strait on the scale of 30 to 40 kilometers were observed over deep water within 77 degrees N to 79 degrees N and 5 degrees W to 3 degrees E. The use of remote sensing, a satellite-tracked buoy, and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days. Ice ablation measurements made within one of these ice-ocean eddies indicated that melting, which proceeded at rates of 20 to 40 centimeters per day, is an important process in determining the ice-edge position. These studies give new insight on the formation, propagation, and dissipation of ice-edge eddies.  相似文献   
57.
Bull  K.R.  Achermann  B.  Bashkin  V.  Chrast  R.  Fenech  G.  Forsius  M.  Gregor  H.-D.  Guardans  R.  Haubmann  T.  Hayes  F.  Hettelingh  J.-P.  Johannessen  T.  Krzyzanowski  M.  Kucera  V.  Kvaeven  B.  Lorenz  M.  Lundin  L.  Mills  G.  Posch  M.  Skjelkvåle  B. L.  Ulstein  M. J. 《Water, air, and soil pollution》2001,130(1-4):119-130
For 20 years the Convention on Long-range Transboundary Air Pollution has worked to control air pollutant emissions in Europe and North America. Its Working Group on Effects (WGE) has been responsible for much of the underpinning science. The WGE's six International Cooperative Programmes (ICPs) on Waters, Natural Vegetation and Crops, Forests, Materials and Cultural Heritage, Integrated Monitoring, and Modelling and Mapping, together with a Joint Task Force on Human Health with WHO, quantify air pollution effects on the environment through monitoring, modelling and scientific review. Early work found evidence to support the need for decreases in emissions of sulphur and nitrogen pollutants. More recently, monitoring results and models have provided the scientific basis, e.g. critical loads and levels, for effects-based Protocols and for evaluating their effectiveness. ICP studies on trends show recovery from acidification effects in keeping with the fall in sulphur emissions. Steady-state models provide an indication of long-term improvements. Recent increased emphasis on developing dynamic models will enable better links between recovery rates and abatement strategies. The scientific network of the ICPs and the monitoring and modelling results have been key to the development of the Convention and are an essential component for its success in the future.  相似文献   
58.
59.
Recent research using microwave satellite remote sensing data has established that there has been a reduction of about 3 percent per decade in the areal extent of the Arctic sea ice cover since 1978, although it is unknown whether the nature of the perennial ice pack has changed. These data were used to quantify changes in the ice cover's composition, revealing a substantial reduction of about 14 percent in the area of multiyear ice in winter during the period from 1978 to 1998. There also appears to be a strong correlation between the area of multiyear ice and the spatially averaged thickness of the perennial ice pack, which suggests that the satellite-derived areal decreases represent substantial rather than only peripheral changes. If this apparent transformation continues, it may lead to a markedly different ice regime in the Arctic, altering heat and mass exchanges as well as ocean stratification.  相似文献   
60.
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