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   120篇
  免费   17篇
林业   3篇
农学   3篇
基础科学   2篇
  12篇
综合类   5篇
农作物   6篇
水产渔业   9篇
畜牧兽医   82篇
园艺   2篇
植物保护   13篇
  2023年   3篇
  2022年   2篇
  2021年   6篇
  2020年   9篇
  2019年   4篇
  2018年   1篇
  2017年   7篇
  2016年   8篇
  2015年   6篇
  2014年   6篇
  2013年   7篇
  2012年   4篇
  2011年   15篇
  2010年   6篇
  2009年   4篇
  2008年   9篇
  2007年   11篇
  2006年   6篇
  2005年   7篇
  2004年   9篇
  2002年   2篇
  2000年   1篇
  1996年   1篇
  1994年   1篇
  1993年   1篇
  1985年   1篇
排序方式: 共有137条查询结果,搜索用时 93 毫秒
81.
A 4-month-old Arabian filly was treated by surgical correction of an ileal impaction. The impaction was resolved through a distal jejunal enterotomy. One-year follow-up showed no post-operative complications secondary to the enterotomy. Jejunal enterotomy may be a surgical option for resolution of an ileal impaction.  相似文献   
82.
Elevated atmospheric CO2 tends to stimulate plant productivity, which could either stimulate or suppress the processing of soil carbon, thereby feeding back to atmospheric CO2 concentrations. We employed an acid-hydrolysis-incubation method and a net nitrogen-mineralization assay to assess stability of soil carbon pools and short-term nitrogen dynamics in a Florida scrub-oak ecosystem after six years of exposure to elevated CO2. We found that soil carbon concentration in the slow pool was 27% lower in elevated than ambient CO2 plots at 0-10 cm depth. The difference in carbon mass was equivalent to roughly one-third of the increase in plant biomass that occurred in the same experiment. These results concur with previous reports from this ecosystem that elevated CO2 stimulates microbial degradation of relatively stable soil organic carbon pools. Accordingly, elevated CO2 increased net N mineralization in the 10-30 cm depth, which may increase N availability, thereby allowing for continued stimulation of plant productivity by elevated CO2. Our findings suggest that soil texture and climate may explain the differential response of soil carbon among various long-term, field-based CO2 studies. Increased mineralization of stable soil organic carbon by a CO2-induced priming effect may diminish the terrestrial carbon sink globally.  相似文献   
83.
Abstract

Infectious hematopoietic necrosis virus (IHNV), viral hemorrhagic septicemia virus, and spring viremia of carp virus were concentrated and detected from freshwater and seawater samples by using hollow-fiber ultrafiltration. Within 60 min, virus in a 50-L freshwater or saltwater sample was concentrated more than 70-fold, and virus retention efficiencies were consistently greater than 88%. Retention efficiency was highly dependent upon concentrations of column blocking and sample stabilization solutions. A large column with a surface area of 1.15 m2 and a filtration capacity of 5–200 L exhibited optimal viral retention when blocked with 2% fetal bovine serum (FBS) and when the samples were supplemented with 0.1% FBS. Conversely, a small column with 100-fold less surface area and a filtering capacity of 0.5–2.0 L was optimized when blocked with 1% FBS and when the samples were supplemented with 0.1% FBS. The optimized ultrafiltration procedure was further validated with water from a tank that contained IHNV-exposed juvenile sockeye salmon Oncorhynchus nerka, resulting in an average virus retention efficiency of 91.6 ± 4.1% (mean ± SE). Virus quantification of concentrated samples demonstrated that IHNV shedding in sockeye salmon preceded mortality; shedding of the virus was observed to increase significantly as early as 7 d postchallenge and peaked at day 14, when virus levels reached 4.87 × 103 plaque-forming units/mL. We conclude that ultrafiltration is a reliable and effective method for concentrating viable aquatic rhabdoviruses from large volumes of water and has application for the analysis of environmental water samples.

Received April 22, 2011; accepted August 4, 2011  相似文献   
84.
85.
Channel changes are the consequence of changes in sediment yield from the slopes and in the connectivity between slopes and channels because of distinct land use and climate impacts. In this study, we investigated the characteristics and evolution of a short reach in the headwater of the Ijuez River, central–southern Pyrenees. Assessment of a series of sedimentary and geomorphic structures confirmed major changes to the valley bottom, mainly related to changes in the intensity of human activity. The oldest sedimentary structure is a terrace level located 3 to 4 m above the current alluvial plain. General deforestation, overgrazing and recurring fires in the montane belt (1100–1600 m a.s.l.) have led to increased soil erosion and connectivity, and to the triggering of debris flows that have been deposited on the fluvial terrace. Woody fragments from within the debris flows were dated using accelerator mass spectrometry 14C radiocarbon techniques (AMS), yielding ages between 100 and 115 cal years bp , which coincides with the period of maximum deforestation and human density in the Pyrenees. Depopulation and farmland abandonment since the beginning of the 20th century has resulted in generalized natural and artificial reforestation, a shrinkage of the eroded areas and a decline in connectivity between slopes and the channel. The most important consequence has been channel incision and narrowing, and the development of a sediment armour layer. Active sediment transport is continuing, although there has been a decrease in sediment yield from the slopes. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
86.
OBJECTIVE: To evaluate the role of adrenal and thyroid hormones in the prediction of death in a population of critically ill puppies with parvoviral diarrhea by measuring serial daily serum concentrations of cortisol and thyroxine. DESIGN: Prospective case-control study. ANIMALS: 57 critically ill puppies with parvoviral diarrhea admitted to the hospital and 17 clinically normal control puppies. PROCEDURES: Basal serum cortisol and thyroxine concentrations were measured for each dog with parvoviral diarrhea at admission (prior to treatment) and daily until death, euthanasia, or discharge. RESULTS: Median time between admission and death was 48 hours (ie, on day 3). Median serum cortisol concentration on day 1 (admission) in all dogs with parvoviral diarrhea (248 nmol/L) was significantly higher than in control dogs (77 nmol/L). No significant difference was found in the day 1 median serum cortisol concentration of 11 dogs that died (302 nmol/L) and 46 dogs that survived (238 nmol/L). A significantly higher median serum cortisol concentration was, however, found in nonsurvivor group dogs, compared with survivor group dogs, on days 2 and 3. Median serum thyroxine concentration on day 1 in dogs with parvoviral diarrhea was significantly lower than in control dogs (8.12 nmol/L vs 35 nmol/L, respectively). Median serum thyroxine concentration of nonsurvivor group dogs (4.4 nmol/L) was significantly lower than that of survivor group dogs (9.2 nmol/L) at admission and became even lower on days 2 and 3. CONCLUSIONS AND CLINICAL RELEVANCE: High serum cortisol and low serum thyroxine concentrations at 24 and 48 hours after admission were associated with death in dogs with parvoviral diarrhea.  相似文献   
87.
BACKGROUND: Genomic instability is a hallmark of cancer and may be required for the accumulation of cancer-causing mutations within cells. One form of genomic instability occurs in tandem nucleotide repeats and is known as microsatellite instability (MSI). HYPOTHESIS: We hypothesized that MSI can be observed in canine mammary gland tumors (MGT) and represents a potential carcinogenic mechanism in dogs. ANIMALS: Thirty-five dogs with MGTs and 9 dogs with other tumors were recruited from the University of Minnesota Veterinary Medical Center and referring veterinary clinics. METHODS: A panel of 21 canine microsatellite (MS) markers was amplified by polymerase chain reaction (PCR) from deoxyribonucleic acid obtained from blood and from fresh or formalin-fixed, paraffin-embedded tumor tissues. PCR products were evaluated by using capillary electrophoresis, and the chromatograms were analyzed by using genotyping software. MS genotypes obtained from fresh and formalin-fixed tumor tissues were compared, as were MS genotypes from normal tissue and tumor tissue. RESULTS: Genotypes obtained from formalin-fixed and fresh tissues were identical for all MS in 9 tumors evaluated, suggesting excellent concordance between the 2 sample types. For the 35 canine mammary tumors evaluated, 13 (37%) had stable genotypes; 22 (63%) exhibited aberrations in 1 or 2 MS; and 4 tumors (11%) demonstrated high-level instability, with aberrations in 29 to 61% of MS. CONCLUSIONS AND CLINICAL IMPORTANCE: Although some low-level MSI often is observed, high-level MSI is an infrequent finding in canine mammary tumors. Further evaluations are required to better characterize this phenomenon and to determine its relevance to canine carcinogenesis.  相似文献   
88.
Increasingly countries are seeking to reduce emission of greenhouse gases from the agricultural industries, and livestock production in particular, as part of their climate change management. While many reviews update progress in mitigation research, a quantitative assessment of the efficacy and performance-consequences of nutritional strategies to mitigate enteric methane (CH4) emissions from ruminants has been lacking. A meta-analysis was conducted based on 108 refereed papers from recent animal studies (2000–2020) to report effects on CH4 production, CH4 yield and CH4 emission intensity from 8 dietary interventions. The interventions (oils, microalgae, nitrate, ionophores, protozoal control, phytochemicals, essential oils and 3-nitrooxypropanol). Of these, macroalgae and 3-nitrooxypropanol showed greatest efficacy in reducing CH4 yield (g CH4/kg of dry matter intake) at the doses trialled. The confidence intervals derived for the mitigation efficacies could be applied to estimate the potential to reduce national livestock emissions through the implementation of these dietary interventions.  相似文献   
89.
This study assessed refined canola oil (CO) as a supplemental dietary lipid source for juvenile fall chinook salmon, Oncorhynchus tshawytscha, parr with respect to possible effects on their growth and osmoregulatory performance and body composition. Diets with equal protein ( 57%) and lipid ( 19%) content (dry weight basis) were supplemented with lipid from either anchovy oil (AO) or CO with AO so that CO comprised 0 (0CO), 11% (11CO), 22% (22CO), 33% (33CO), 43% (43CO) or 54% (54CO) of the dietary lipid content. Triplicate groups of juvenile chinook salmon were fed their prescribed diets for 104 days in freshwater (FW) and 31 days in seawater (SW) after a 4-day transition period. Dietary fatty acid compositions reflected the different proportions of AO and CO in the supplemental lipid. Diet treatment had no effect on fish growth, feed intake, feed efficiency, protein utilization, fish mortality or terminal whole body water and ash percentages. Whole body lipid percentages were higher in 11CO and 43CO fish than in 33CO fish and in 11CO fish versus 22CO fish. Whole body protein percentages were highest in 33CO, 43CO and 54CO fish and lowest in 0CO and 22CO fish. Terminal whole body fatty acid compositions were influenced strongly by the dietary fatty acid compositions. Haematocrit and muscle water percentages were not affected consistently and plasma Na+ and Cl concentrations were unaffected by diet treatment in FW or 24-h seawater challenges during FW residency. Also, diet treatment had no effect on the physiological parameters after SW residency. We conclude that dietary treatment had no effect on fish growth performance under our experimental conditions. Also, the dietary inclusion of CO neither facilitated nor impaired the transfer of chinook salmon parr to seawater. Thus, CO was found to be an excellent and cost-effective source of supplemental dietary lipid for culture of juvenile fall chinook salmon during freshwater residency.  相似文献   
90.
An analytical method based on HPLC with MS/MS detection was developed and optimized in order to determine the most useful antibiotics (sulphonamides and tetracyclines) used in aquaculture. A simple extraction procedure, without any clean‐up step, was evaluated in order to obtain maximum analyte recovery from fish samples (Sparus aurata). A mixture of methanol:water 70:30 (v/v)+1 mL EDTA 0.1 M was selected as optimum extractant solution. Because no matrix effects were observed, a standard calibration curve prepared in mobile phase was used for quantification purposes. Antibiotic‐free fish samples were spiked at different concentration levels and analysed by the optimized HPLC method. The average recoveries (n=6) obtained were satisfactory, ranging from 88% to 110% at 100 μg kg?1. The proposed methodology provided limits of detection for the tested antibiotics in the 1.2–16 μg kg?1 range, lower than 100 μg kg?1, the maximum residue level established by the European Union. Finally, commercial fish samples from different origins were analysed in order to confirm the usefulness of the developed methodology.  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