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排序方式: 共有88条查询结果,搜索用时 31 毫秒
1.
Boulanger Yan Arseneault Dominique Boucher Yan Gauthier Sylvie Cyr Dominic Taylor Anthony R. Price David T. Dupuis Sébastien 《Landscape Ecology》2019,34(1):159-174
Landscape Ecology - Forest landscapes at the boreal–temperate ecotone have been extensively altered. Reducing the gap between current and presettlement forest conditions through... 相似文献
2.
Boucher Dominique Gauthier Sylvie Thiffault Nelson Marchand William Girardin Martin Urli Morgane 《New Forests》2020,51(4):543-571
New Forests - Climate change is projected to increase fire severity and frequency in the boreal forest, but it could also directly affect post-fire recruitment processes by impacting seed... 相似文献
3.
Sorghum ergot produces dihydroergosine (DHES) and related alkaloids, which cause hyperthermia in cattle. Proportions of infected panicles (grain heads), leaves and stems were determined in two forage sorghum crops extensively infected 2 to 4 weeks prior to sampling and the panicles were assayed for DHES. Composite samples from each crop, plus a third grain variety crop, were coarsely chopped and half of each sealed in plastic buckets for 6 weeks to simulate ensilation. The worst-infected panicles contained up to 55 mg DHES/kg, but dilution reduced average concentrations of DHES in crops to approximately 1 mg/kg, a relatively safe level for cattle. Ensilation significantly (P = 0.043) reduced mean DHES concentrations from 0.85 to 0.46 mg/kg. 相似文献
4.
Logging pattern and landscape changes over the last century at the boreal and deciduous forest transition in Eastern Canada 总被引:4,自引:0,他引:4
Forestry practices associated with the industrial era (since ~1900) have altered the natural disturbance regimes and greatly
impacted the world’s forests. We quantified twentieth century logging patterns and regional scale consequences in three sub-boreal
forest landscapes of Eastern Canada (117,000, 49,400 and 92,300 ha), comparing forestry maps depicting age and forest cover
types for early industrial (1930) and present-day (2000) conditions. Results were similar for the three landscapes, indicating
large-scale forest change during the twentieth century. In 1930, previous logging activities had been concentrated in the
lowlands and along the main hydrographical network, as compared to a more even distribution over the landscapes in 2000, reflecting
a decreasing influence of the environmental constraints on forest harvesting. In 1930, old-aged forests (>100 years) accounted
for more than 75% of the unlogged areas of the three landscapes, as compared to less than 15% for the present-day conditions.
Logging practices have thus inverted the stand age distribution of the landscapes that are currently dominated by young and
regenerating stands. The 1930 forest cover types showed a clear relationship with elevation, with conifers located in the
lowlands and mixed and deciduous stands restricted to the upper slopes. Between 1930 and 2000, 58–64% of the conifer areas
transformed to mixed and deciduous forests, such that no clear altitudinal relationships remained in 2000. We conclude that
twentieth century logging practices have strongly altered the preindustrial vegetation patterns in our study area, to the
point that ecosystem-based management strategies should be developed to restore conifer dominance, altitudinal gradients,
as well as the irregular structure inspired from old forest stands. 相似文献
5.
OBJECTIVE: To assess the validity and reliability of the most recent adaptation of Block's full-diet food-frequency questionnaire (FFQ) among a sample of Canadian women. DESIGN: Participants completed a self-administered FFQ (FFQ1), two unannounced 24-hour recalls (weekday and weekend) and a second FFQ (FFQ2) between October 2003 and February 2004. FFQs and recalls were analysed for 32 nutrients using Block Dietary Data Systems and the University of Minnesota's Nutrient Data System. Mean and median intakes were computed, along with crude and deattenuated Pearson correlation coefficients between FFQ1 and the average of two recalls (validity) and between FFQ1 and FFQ2 (reliability). SETTING: Ontario, Canada. SUBJECTS: A random population-based sample (n = 166) of women aged 25 to 74 years. RESULTS: One hundred and fifteen (69%) women completed FFQ1, 96 completed FFQ1 and both recalls, and 93 completed both FFQs, about 56 days apart. Mean intakes were similar for most nutrients. FFQ reliability was high, with Pearson correlation coefficients having a median of 0.75, ranging from 0.57 to 0.90 (macronutrients) and from 0.65 to 0.88 (micronutrients from supplements and food). FFQ validity was moderate to high, with deattenuated Pearson correlation coefficients having a median of 0.59, ranging from 0.11 to 0.73 (macronutrients) and from 0.50 to 0.76 (micronutrients from supplements and food). Our micronutrient correlations were similar to or higher than those of other studies that included supplements. Two correlations <0.40 were associated with fats. CONCLUSIONS: The validity and reliability of this full-diet version of the Block FFQ were moderate to high, supporting its use in future studies among Canadian women. 相似文献
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7.
N.R. do Nascimento G.T. Bueno E. Fritsch A.J. Herbillon Th. Allard A.J. Melfi R. Astolfo H. Boucher & Y. Li 《European Journal of Soil Science》2004,55(3):523-538
Morphological, geochemical and mineralogical studies were carried out in a representative soil catena of the low‐elevation plateaux of the upper Amazon Basin to interpret the steps and mechanisms involved in the podzolization of low‐activity clay soils. The soils are derived from Palaeozoic sandstones. They consist of Hydromorphic Podzols under tree savannah in the depressions of the plateaux and predominantly of Acrisols covered by evergreen forest elsewhere. Incipient podzolization in the uppermost Acrisols is related to the formation of organic‐rich A and Bhs horizons slightly depleted in fine‐size particles by both mechanical particle transfer and weathering. Weathering of secondary minerals by organic acids and formation of organo‐metallic complexes act simultaneously over short distances. Their vertical transfer is limited. Selective dissolution of aluminous goethite, then gibbsite and finally kaolinite favour the preferential cheluviation of first Fe and secondly Al. The relatively small amount of organo‐metallic complexes produced is related to the quartzitic parent materials, and the predominance of Al over Fe in the spodic horizons is due to the importance of gibbsite in these low‐activity clay soils. Morphologically well‐expressed podzols occur in strongly iron‐depleted topsoils of the depression. Mechanical transfer and weathering of gibbsite and kaolinite by organic acids is enhanced and leads to residual accumulation of sands. Organo‐metallic complexes are translocated in strongly permeable sandy horizons and impregnate at depth the macro‐voids of embedded soil and saprolite materials to form the spodic Bs and 2BCs horizons. Mechanical transfer of black particulate organic compounds devoid of metals has occurred later within the sandy horizons of the podzols. Their vertical transfer has formed well‐differentiated A and Bh horizons. Their lateral removal by groundwater favours the development of an albic E horizon. In an open and waterlogged environment, the general trend is therefore towards the removal of all the metals that have initially accumulated as a response to the ferralitization process and have temporarily been sequestrated in organic complexes in previous stages of soil podzolization. 相似文献
8.
Return-polyacrylamide gel electrophoresis (R-PAGE) and tomato bioassay followed by R-PAGE were compared for the detection of potato spindle tuber viroid (PSTVd) from individual true potato seed (TPS). Both methods detected PSTVd from single TPS. TPS extract formulated as sap or nucleic acids in two different buffers did not affect the percentage of viroid detection on tomato plants. There was some evidence of viroid inhibitor in TPS extracts but not in nucleic acid extracts of TPS. Because R-PAGE is more rapid than the tomato bioassay followed by R-PAGE, the former was used to determine the extent of PSTVd in TPS of China’s Keshan Potato Research Institute breeding material. Over 1700 individual TPS were tested. Twenty-four of the 46 seedlots tested (inbred and outcrossed) contained PSTVd. The viroid was detected in 70% of lots from inbred lines compared to 38% of lots from outcrosses. TPS (20 lots) stored in paper bags at room temperature as far back as 1965 were also tested, and PSTVd was detected in TPS stored for 21 years. 相似文献
9.
10.
S. Le Bouquin J.L. Jobert G. Larour L. Balaine F. Eono S. Boucher A. Huneau V. Michel 《Livestock Science》2009,125(2-3):283-290
Epizootic Rabbit Enteropathy (ERE) is a severe clinical syndrome of rabbits causing high economic losses for farmers. ERE first appeared in France in 1996. A retrospective case–control survey was carried out to identify the risk factors of acute expression of ERE, after weaning, in 96 kindling-to-finish rabbit farms in western France during 2001 and 2002. Farm status was defined according to the expression of clinical signs of ERE and mortality rates in the last five broiler rabbit batches. Comparisons of structural characteristics, rearing conditions and herd management showed that the risk factors for acute ERE expression were late weaning (rabbit age at weaning ≥ 35 days, RR = 4.44, 95% CI [1.36–21.71]), transfer of young rabbits at weaning (young rabbit transfer or combined practice RR = 2.83, 95% CI [1.16–9.33]), and high volume of the fattening room (air volume/rabbit weight in fattening room at weaning ≥ 0.14m3/kg, RR = 2.98, 95% CI [1.29–8.42]) and a high mortality rate in young rabbits before weaning (i.e. rate ≥ 10.5%; RR = 2.18, 95% CI [1.20–3.53]). 相似文献