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   300篇
  免费   24篇
林业   16篇
农学   7篇
  68篇
综合类   32篇
农作物   4篇
水产渔业   33篇
畜牧兽医   140篇
园艺   9篇
植物保护   15篇
  2023年   1篇
  2022年   4篇
  2021年   11篇
  2020年   17篇
  2019年   23篇
  2018年   5篇
  2017年   8篇
  2016年   9篇
  2015年   7篇
  2014年   9篇
  2013年   15篇
  2012年   17篇
  2011年   39篇
  2010年   21篇
  2009年   17篇
  2008年   24篇
  2007年   23篇
  2006年   17篇
  2005年   15篇
  2004年   11篇
  2003年   11篇
  2002年   11篇
  2000年   2篇
  1999年   1篇
  1996年   2篇
  1995年   1篇
  1993年   1篇
  1992年   1篇
  1986年   1篇
排序方式: 共有324条查询结果,搜索用时 15 毫秒
121.
The intense tropical fruit aroma of Sauvignon blanc wines has been associated with the varietal thiols 3-mercaptohexanol (3MH), derived from odorless precursors in the grape, and 3-mercaptohexyl acetate (3MHA), arising from 3MH during fermentation. Grapes and juice were sourced from five locations in Marlborough, New Zealand, taking hand-picked grapes and samples at four stages during the mechanical harvesting process and pressing, which were then fermented in replicated 750 mL bottles. With each set of juices, the highest concentrations of Cys-3MH and Glut-3MH were found in the juices pressed to 1 bar, but these juices produced wines with lower 3MH and 3MHA concentrations. With three of the juices, there was an increase in varietal thiol content for wines made from juices that had been machine harvested compared to the hand-picked samples, which matched earlier findings of lower 3MH and 3MHA levels in wines made from hand-picked grapes. Juices that were more oxidized, and which showed a higher absorbance at 420 nm, were found to produce wines with lower 3MH and 3MHA concentrations.  相似文献   
122.
Feline spongiform encephalopathy (FSE) is thought to have resulted from consumption of food contaminated with bovine spongiform encephalopathy and the latter is believed to result from the consumption of food contaminated with scrapie. However, no direct experimental documentation exists to indicate that the scrapie agent is capable of amplifying in cats, and, therefore, crossing the species barrier. During 1979, 6 cats ranging in age from 3.5 to 18 months were intracerebrally inoculated with sheep scrapie (inoculum G-639-PP) and were observed for an extended period. Inoculated cats did not develop neurologic disease, and microscopic lesions of spongiform encephalopathy were not evident. Immunohistochemistry and Western blot techniques failed to detect the abnormal form of prion protein (PrP(res)). These results indicate that the sheep scrapie agent (G-639-PP) used in this study was not capable of amplifying in cats and therefore was unable to cross the species barrier to produce FSE.  相似文献   
123.
Case records of 21 breeding bulls suffering from advanced septic claw disorders and treated with resection of the distal interphalangeal (= DIP) joint (n = 14), resection of the proximal interphalangeal joint (n = 1) and digit amputation (n = 6) were evaluated retrospectively (1992-2005) regarding the following parameters: breed, age, body mass, pre-treatment, localisation of disease, lameness degree, diagnosis, surgical method, outcome, postoperative survival time and return to breeding use. The mean age of the bulls was 3.6+/-1.7 years and the mean body mass 840.7 + 200.8 kg; range: 500-1200 kg), Surgery was carried out to treat the following conditions: white line infection (n = 9), sole ulcers (n = 5) with osteolysis of the distal sesamoid bone, the tuberculum flexorium, infection of the deep digital flexor tendon at insertion and the DIP-joint; osteomyelitis of the distal and middle phalanx with septic arthritis of the DIP-joint following deep penetrating wounds (n = 3); open fracture of the coffin bone with severe osteolysis/osteomyelitis and septic fibrino-purulent arthritis of the DIP-joint (n = 2); purulent arthritis of the proximal interphalangeal joint after a penetrating wound (n = 1) and a severe osteolysis/osteomyelitis of the coffin bone originating from a toe ulcer (n = 1). Three bulls were culled within 2-12 weeks after surgery due to postsurgical complications. In three bulls which were treated successfully six years ago, long-term follow-up information could not be obtained. Complete recovery was considered in 15 bulls.They returned to full breeding use three to four months after surgery, with a mean postoperative survival time of 24.1 months:21.2 months after joint resection and 27.2 months after amputation. At the time of this survey three bulls were still alive with 4,7 and 84 months after surgery, respectively. Both surgical methods were successful in breeding bulls, the resection of the distal interphalangeal joint is recommended as first option.  相似文献   
124.
A 6-week-old female Simmental calf was evaluated for acute non-ambulatory tetraparesis. Physical and laboratory examinations revealed no clinically relevant abnormalities. Neurological findings were consistent with acute, progressive and painful cervical myelopathy. Radiographs displayed a fractured odontoid process (dens axis) and vertebral step misalignment at the fracture site. A traumatic origin was suspected. Advanced diagnostic imaging was considered to allow better planning of potential surgical stabilisation and to exclude any additional lesions of the cervical vertebral column. However, during trailer transportation to the advanced diagnostic imaging and surgery site, the calf deteriorated neurologically and was humanely euthanised. Magnetic resonance imaging (MRI) and computed tomography (CT) were performed immediately post-mortem for scientific reasons. The MRI examination reflected the radiographic findings and confirmed severe spinal cord compression at the fracture site. In addition, a T2W-hyperintense signal change within the paravertebral soft tissue dorsal to the fracture site was indicative of a traumatic event. CT identified the fracture site at the synchondrosis between the odontoid process and the body of the axis, and this finding was confirmed by post-mortem examination. Advanced diagnostic imaging and post-mortem examination did not identify any other cervical lesion. In summary, this calf was diagnosed with a traumatic odontoid process synchondrosis fracture, which has not been reported previously in calves but presents a challenging and well-known fracture type in young children. This case report indicates that the odontoid process synchondrosis is a potential predisposed injury site and that traumatic odontoid process synchondrosis fractures should be considered as a potential differential in calves with acute cervical pain and/or signs of a cervical myelopathy.  相似文献   
125.
126.
127.
128.
129.
In recent years, much attention has been directed to the ways in which the most important areas for inclusion in reserve networks can be identified, and the most effective ways in which existing networks can be expanded. In contrast, rather little attention has been paid to the present and likely future performance of the approaches that have actually been employed. Using Wetland Bird Survey data, the effectiveness of the current Special Protection Area (SPA) network in the UK was assessed by comparing annual counts for 17 species of migratory waterbird on SPAs with the numbers supported by hypothetical site networks selected by five alternative site-selection methods. These analyses suggest that focusing on complementarity between component sites rather than applying criteria to each site individually improved the level of representation for each species, conserved a greater percentage of the national total across the 17 species and was robust over time.  相似文献   
130.
Estimates of the number of waterbirds (principally wildfowl) wintering in Great Britain are presented, based on data from the period 1994/1995-1998/1999. These update the previous estimates for 1987/1988-1991/1992. National estimates are used to derive 1% thresholds for waterbird species which in turn form the basis for the identification of nationally important wetland sites for subsequent conservation and protection. Estimates are also used to assess changes in numbers of those species for which monitoring data are insufficient to calculate annual indices of population change. Data for calculating the estimates come from a variety of sources including the Wetland Bird Survey (WeBS, a long-term scheme which counts waterbirds by day at wetlands), goose roost censuses, site-based surveys and published reviews. Generation of the estimates is made difficult by a number of methodological and data quality issues. To account for some of the methodological problems affecting WeBS data, new methods for generating estimates have been used which account for birds missed during the counts in a more comprehensive manner. These result in large increases in the estimated numbers for many of the relevant species, although most are still considered to be underestimates. To assess the biological change in numbers since the last assessment, estimates generated from the same methods used previously are also presented. These indicate that while the majority of species have experienced increases in numbers since the late 1980s there have been some notable declines. There is however scope for improving the accuracy of estimates derived from extensive, volunteer-based monitoring schemes such as WeBS.  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