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   54篇
  免费   3篇
林业   14篇
基础科学   1篇
  16篇
综合类   2篇
农作物   1篇
畜牧兽医   15篇
园艺   5篇
植物保护   3篇
  2023年   1篇
  2019年   2篇
  2018年   1篇
  2017年   3篇
  2016年   1篇
  2015年   1篇
  2014年   3篇
  2012年   3篇
  2011年   6篇
  2010年   1篇
  2008年   3篇
  2007年   3篇
  2006年   3篇
  2005年   3篇
  2003年   1篇
  2002年   6篇
  2001年   2篇
  1999年   1篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1993年   1篇
  1991年   2篇
  1990年   1篇
  1984年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
排序方式: 共有57条查询结果,搜索用时 15 毫秒
41.
The participation of agricultural producers in financing losses caused by livestock epidemics has been debated in many countries. One of the issues raised is how reluctant producers are to participate voluntarily in the financing of disease losses before an outbreak occurs. This study contributes to the literature by examining whether disease losses should be financed through pre- or post-outbreak premiums or their combination. A Monte Carlo simulation was employed to illustrate the costs of financing two diseases of different profiles. The profiles differed in the probability in which the damage occurs and in the average damage per event. Three hypothetical financing schemes were compared based on their ability to reduce utility losses in the case of risk-neutral and risk-averse producer groups. The schemes were examined in a dynamic setting where premiums depended on the compensation history of the sector. If producers choose the preferred financing scheme based on utility losses, results suggest that the timing of the premiums, the transaction costs of the scheme, the degree of risk aversion of the producer, and the level and the volatility of premiums affect the choice of the financing scheme.  相似文献   
42.
Rapid structural change and concentration of pig production in regions with most intensive production has raised concerns about whether the risk of large-scale disease losses has increased in Finland. This paper examines the pig industry's losses due to classical swine fever (CSF) epidemics. The work is based on economic and epidemiological models providing insights to the consequences of epidemics to infected and uninfected farms, government and meat processing. The economic analysis was carried out by use of a sector model, which simulated the recovery of pig production, starting from the recognition of the disease in the country and ending at a steady-state market equilibrium about 12 years later. The model explicitly took into account profit-maximising behaviour of producers and the effects of decrease in export demand.

Epidemiological evidence suggests that under the current spatially diversified structure of Finnish pig farming and related industries, the probability of a severe disease epidemic counting dozens of infected farms is small. Even for epidemics considered large in Finland (5–33 infected farms) combined with a major reduction in export demand, the median loss was simulated to be only €19.2 million. The majority of these losses were due to loss of exports corresponding almost 20% of pig meat production in Finland. While the current structure of pig farming in Finland incurs higher production costs than the most intensive structures in Europe, it also seems to decrease the probability of ‘catastrophic’ economic losses. The results suggest that the response of export markets and the number of uninfected farms affected by preventive measures are critical to the magnitude of losses, as they can amplify losses even if only few farms become infected.  相似文献   

43.
The opinions of animal owners and practising veterinarians concerning a new restraint-reversal medication (medetomidine-atipamezole) for dogs were obtained by two questionnaires in connection with a clinical study. Four alternative answers to each statement question scored as "completely agree", "somewhat agree", "somewhat disagree" and "completely disagree". The questionnaires were completed by 21 veterinarians and 245 dog owners. The overall response to the treatment was clearly positive. Both groups had a favourable attitude towards drug use with mean combined scores (from 1 to 4; 4 = most favourable) of 48.1 (max 56) for the dog owners and 39.2 (max 52) for the veterinarians. Only a little information was gained about the background of negative sentiments. Some pet owners (19%) opposed to medication on a priori grounds, some (26%) reacted strongly to the dizziness of their animals and some owners (21%) complained because of general anxiety before, during and after their pets were treated.  相似文献   
44.
45.
46.
The analysis of random amplified microsatellite (RAMS) markers among aecia of the causal agent of the resin top disease (Peridermium pini) on Scots pine (Pinus sylvestris) suggested that the genetic variation between the populations of this rust fungus is low in Finland. The method used allowed the identification of heterozygotic aecia in two loci, where the degree of heterozygosity was, however, low. The RAMS patterns of the Finnish aeciospores, other aeciospores from Thetford, UK and Cronartium flaccidum from Italy were highly similar suggesting that the autoecious and heteroecious forms of these rust fungi would be genetically closely related.  相似文献   
47.
Thermotolerant coliform bacteria and fecal streptococci were monitored in polluted rivers using random sampling and a distribution-free method of estimating percentiles. The objective was to investigate the wide temporal and spatial variation observed earlier in some of these rivers and to monitor for compliance with the standard of acceptable swimming water (1000 thermotolerant coliform bacteria per 100mL). In the summer of 1986 eleven river reaches were visited in random order 3 to 10 times, randomly sampling 2 to 13 sites per reach and visit. Thermotolerant coliform bacteria and fecal streptococci were determined by the membrane filtration technique from 341 and 232 samples, respectively. The results were evaluated on the basis of statistical parameters, percentiles and analysis of variance. Bacterial concentrations varied widely in every reach due to fluctuations of loading and/or hydrological phenomena. During dry periods the bacterial concentrations in rivers were lower than during wet periods. The standard of acceptable swimming water was temporarily exceeded during wet periods but never during dry periods. The use of random sampling and calculation of percentiles was found to provide a good overall picture of the variability of water quality in the rivers. It is recommended to evaluate the bacterial concentrations separately during wet and dry periods.  相似文献   
48.
The behaviour of Hg in mineral pine forest (Pinussylvestris soil profiles (0–16 cm) was studied usinga lysimeter experimental design combined with thelabeling technique with 203HgCl2. Thelabeled surface soils were exposed to four differenttreatments: (i) normal precipitation (600 mma-1), (ii) four-fold precipitation, (iii) soilP-K fertilizing with normal precipitation, and (iv) the increased acidity in the rainwater with normalamount of precipitation. After the treatment period of97 days the 203Hg and methyl 203Hg weremeasured. The distribution of Hg in different soilmatrices was determined by extracting the soil withdistilled water, 1 M NH4-acetate, 1 M HCl, and 0.1 M NaOH.The results showed that the organic surface layer,especially the living moss (Pleuroziumschreberi), was the dominant scavenger of the added203Hg. Methyl 203Hg formation was mostintensive in this layer, too. Increased precipitationmobilized a part of the 203Hg from the moss layerto the deeper layers and leachate water. In thefertilized soil with increased pH, the accumulation ofboth total 203Hg and methyl 203Hg wasrecorded in the organic surface soil. A small increasein rainwater acidity had no clear effect on thebehavior of 203Hg in soil. 203Hg was mainlyassociated in the organic fraction (NaOH-extractable)whether in the living moss or humus layer. Thefertilized soil yielded the highest concentration ofwater extractable 203Hg. In view of the climatechange with increasing precipitation, the use offertilizers, in the watersheds should be minimal andwell-controlled. This is, because soil fertilizingseems to increase the availability of Hg formethylation, and because the mobilization of bothtotal Hg and methyl Hg from watershed soils to lakes,and probably to ground water, increases whenprecipitation increases.  相似文献   
49.
Proanthocyanidin oligomers with different degrees of polymerization were isolated from Saskatoon berries (Amelanchier alnifolia) by means of gel adsorption and normal-phase liquid chromatography. The proanthocyanidins were identified using electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and thiolytic degradation coupled with reversed-phase liquid chromatography. The results established that Saskatoon berries contain proanthocyanidins from dimers through heptamers and higher polymers. Saskatoon proanthocyanidins are essentially of procyanidin type, consisting mainly of epicatechin units linked by B-type bonds. The simple procyanidin profile of Saskatoon berries allowed the procyanidins to be separated precisely according to their degrees of polymerization. In the future they can be used as standard compounds for qualitative and quantitative analysis of procyanidins as well as for elucidation of the biological activities of proanthocyanidins.  相似文献   
50.
This paper develops a Bayesian approach for spatial inference on animal density from line transect survey data. We model the spatial distribution of animals within a geographical area of interest by an inhomogeneous Poisson process whose intensity function incorporates both covariate effects and spatial smoothing of residual variation. Independently thinning the animal locations according to their estimated detection probabilities results into another spatial Poisson process for the sightings (the observations). Prior distributions are elicited for all unknown model parameters. Due to the sparsity of data in the application we consider, eliciting sensible prior distributions is important in order to get meaningful estimation results. A reversible jump Markov Chain Monte Carlo (MCMC) algorithm for simulation of the posterior distribution is developed. We present results for simulated data and a real data set of minke whale pods from Antarctic waters. The main advantages of our method compared to design-based analyses are that it can use data arising from sources other than specifically designed surveys and its ability to link covariate effects to variation of animal density. The Bayesian paradigm provides a coherent framework for quantifying uncertainty in estimation results.  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