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   126篇
  免费   4篇
林业   2篇
农学   6篇
  5篇
综合类   25篇
农作物   1篇
水产渔业   6篇
畜牧兽医   76篇
植物保护   9篇
  2020年   3篇
  2018年   5篇
  2017年   1篇
  2016年   1篇
  2015年   1篇
  2014年   1篇
  2013年   21篇
  2012年   1篇
  2011年   2篇
  2010年   2篇
  2009年   3篇
  2006年   2篇
  2005年   2篇
  2004年   1篇
  2001年   1篇
  1999年   1篇
  1998年   7篇
  1997年   2篇
  1996年   5篇
  1995年   2篇
  1993年   4篇
  1992年   3篇
  1991年   6篇
  1990年   3篇
  1989年   3篇
  1988年   2篇
  1987年   2篇
  1986年   4篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1981年   2篇
  1980年   2篇
  1979年   1篇
  1976年   1篇
  1975年   1篇
  1974年   3篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1963年   1篇
  1961年   3篇
  1959年   1篇
  1957年   1篇
  1954年   2篇
  1953年   6篇
  1951年   1篇
  1950年   2篇
  1949年   1篇
  1946年   1篇
排序方式: 共有130条查询结果,搜索用时 15 毫秒
91.
Reasons for performing study: It is important to ascertain the prevalence of superficial digital flexor tendon (SDFT) injuries and to improve methods of predicting injury in National Hunt (NH) racehorses. Objectives: To establish: 1) the prevalence of SDFT tendinopathy in NH horses; 2) whether routine ultrasonography can be used to predict SDFT injuries; 3) whether previous tendinopathy predisposes to reinjury; 4) a normal range for the SDFT cross‐sectional area (CSA); and 5) the effects of gender, age, background (ex‐flat or exstore), limb, training and rest periods on SDFT CSA. Methods: Routine ultrasound assessment of the palmar metacarpal soft tissues of 263 NH racehorses was performed on up to 6 occasions over 2 NH racing seasons. Results: The prevalence of SDFT pathology detected using ultrasonography was 24% (n = 148), with a nonsignificant variation between yards of 10–40%. No changes in SDFT CSA or ultrasonographic appearance were detected prior to injury. Older horses had a significantly higher prevalence of SDFT pathology compared to younger horses, and horses with tendinopathy were more likely to suffer an acute injury compared to horses with no evidence of pathology. A reference range for normal CSA measurements was established as 77–139 mm2 at level 4, from 142 horses with no ultrasonographic evidence of SDFT pathology. The CSA of normal horses did not vary significantly with age, limb or over 2 racing seasons, but did with sex and background. Conclusions: The study confirms that SDFT tendinopathy is common in NH horses, with substantial variation between training yards. Ultrasonography at 3 month intervals did not seem to predict acute SDFT injuries. Potential relevance: Variation in the prevalence of tendinopathy between yards suggests that training methods may influence injury rate. It was not possible to predict injury using routine ultrasonography and therefore other methods must be identified. A normal reference range for SDFT CSA is provided.  相似文献   
92.
干旱已成为制约我国农业发展的关键环境因素之一。植物因固着生长,当外界水分因子变化时不能主动逃避胁迫,只能依赖自身机制来抵御外界胁迫,因此,植物的耐干性研究显得十分迫切。本文对前人有关植物耐干研究的工作进行了综述,重点阐明了耐干植物的分类、耐干植物在失水再复水期间形态结构、生理及分子水平上的响应机制,以期为挖掘耐干植物耐干基因、创制耐干种质资源和培育耐干新品种提供新思路。  相似文献   
93.
94.
95.
96.
97.
Abstract. Morbidity of intensively cultured red abalone, Haliotis rufescens , as well as experimentally stressed (elevated temperature and hyper-oxygenation) abalone, was studied using clinical, histological, immunofluorescent and bacteriological techniques. Histological study showed a typical pattern of bacterial infection from all groups studied, characterized by epithelial exfoliation or rupture and systemic growth of the bacteria along vascular sinuses and along neural sheaths. Peripheral neurons degenerated rapidly and a responsive host cellular infiltrate did not appear to effectively retard the advancement of the infection. Nine bacterial isolates from the culture system water or sick animals were characterized biochemically. All were Gram-negative, facultatively anaerobic, non-aerogenic, oxidase-positive rods with single polar flagella and thus appeared related to the Vibrio group. Further characterization showed that most isolates did not correspond to specifically characterized vibrios, Antiserum prepared to the isolates contained antibody both to common group antigens (from all nine strains) and to strain-specific antigens. Selection of antiserum and subsequent absorption permitted the use of the antiserum for specific recognition of each isolate. Immunofluorescent studies clearly demonstrated that antiserum to an isolate corresponding to Vibrio alginolyticus was the predominant antiserum producing positive staining of infecting bacteria in the typical lesions in abalone tissues. The pattern of positive staining corresponded to histopathological observations of the disease. The disease can be managed in husbandry systems by both limiting the number of potentially pathogenic bacteria and by limiting the exposure of the animals to physico-chemical stresses.  相似文献   
98.
An ELISA for the detection of anergic tuberculous cattle   总被引:6,自引:0,他引:6  
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   
99.
Aerial application of pesticides is generally the method used by the United States Department of Agriculture (USDA) in the control of pests of rangeland, cultivated crops, and forested areas. With increased restrictions placed on pesticides, then- continued use requires improved application technology to meet acceptable levels of risk at reasonable cost The Animal and Plant Health Inspection Service of USDA is developing an aerial spray drift model for use by their field personnel to minimize drift from aerial application of pesticides to environmentally sensitive areas. Input information utilizing a low cost, field-deployable microcomputer includes aircraft type, application technique and hardware, pesticide formulation, meteorological conditions, and type (roughness) and extent of the site. Expected output computations will be: 1) distribution pattern of downwind deposition, including evaporation corrections and matching to empirical field measurement; 2) optimal aircraft swath spacing; and 3) buffer distance between the target area and the environmentally sensitive areas.  相似文献   
100.
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