全文获取类型
收费全文 | 132篇 |
免费 | 2篇 |
国内免费 | 4篇 |
专业分类
林业 | 33篇 |
农学 | 4篇 |
52篇 | |
综合类 | 4篇 |
农作物 | 6篇 |
水产渔业 | 5篇 |
畜牧兽医 | 30篇 |
园艺 | 4篇 |
出版年
2023年 | 1篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 4篇 |
2012年 | 3篇 |
2011年 | 12篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有138条查询结果,搜索用时 15 毫秒
11.
This article describes the Finnish meat-inspection curriculum and presents an expert-panel evaluation of meat-inspection education. The work tasks of the meat-inspection veterinarian are challenging and include classical meat inspection, meat hygiene, hygiene control, and animal disease and welfare. The meat-inspection veterinarian is not only an inspector, which by itself is very demanding, but also an expert or "consultant" on food safety. The significant role of the meat-inspection veterinarian in society puts high demands on meat-inspection education, which should provide veterinary students with sufficient tools to perform meat inspection and hygiene control in slaughterhouses, cutting premises, and further processing plants. To be of high quality, such education must be evaluated from time to time. An expert panel evaluated Finnish undergraduate meat-inspection education and found that it provides veterinary students with good knowledge of meat inspection. The structure of the curriculum, with theoretical studies followed by four weeks of practice in a slaughterhouse, was considered vital for learning and for creating interest in meat inspection. The evaluation also revealed that certain subjects should receive greater emphasis and some new subjects should be introduced. Hygiene-control tasks, in particular, have increased and should receive more emphasis in education. Personnel management and interaction skills should be introduced into the curriculum as these skills influence all the duties of the meat-inspection veterinarian. This article outlines the subjects to be included in the modern, high-quality meat-inspection curriculum recommended by the expert panel. 相似文献
12.
Short-term responses of soil decomposer and plant communities to stump harvesting in boreal forests 总被引:2,自引:0,他引:2
Recently, in addition to logging residues, stumps have become an important component in energy production since there is growing global interest in the use of renewable energy sources in order to decrease anthropogenic carbon emissions. Harvesting of stumps influences the forest floor by changing vegetation and soil organic layers and exposing mineral soil across large areas. We studied whether stump harvesting after clear felling poses further short-term changes in boreal forest soil decomposer community (microbes and mesofauna) and vegetation when compared to the traditional site preparation practice (mounding). In general, stump harvesting caused decline in enchytraeid abundance but did not induce further major changes in decomposer community otherwise nor in vegetation of each soil micro-habitat (intact soil and exposed mineral soil). However, the abundances of almost all decomposer animals were lower in the exposed mineral soil than in the intact soil. Stump removal increased the area of exposed mineral soil in the clear felled areas, leading to lower amount of high quality habitat for most decomposer organisms. Hence, it is obvious that there are (or will be) differences in the decomposer community dynamics between the treatments at the forest stand level. Both species richness and coverage of plants benefitted from large-scale exposure of mineral soil. Because the stump removal procedure disturbs soil organic layers and negatively affects the decomposer community, it has the potential to alter nutrient dynamics in forests. 相似文献
13.
14.
Both drought and fungal disease increase needle litterfall of Scots pine (Pinus sylvestris L.) trees, but most factors causing annual variation in needle litterfall are poorly understood. We hypothesized that radial growth and weather conditions favorable to growth correlate positively with needle litterfall with a lag equal to the number of needle cohorts (here being 5-6). We studied the time series of needle litterfall, stem increment, pollen cone litter and daily weather conditions in a Scots pine stand over 43 years (1961-2004). The cross-correlations of standardized time series were estimated with various lags. Model predictions of annual needle litterfall were tested against independent data. Changes in annual growth and needle litterfall correlated with lags of 0 and 4 years. The best predictors for needle litterfall were May to mid July temperature sum with a lag of 4 years, May rainfall with a lag of 2 years and September temperature with a lag of 6 years. Pollen cone litter correlated negatively with needle litterfall with a lag of 2 years. The study provided empirical evidence that needle litterfall of Scots pine in northern Finland is influenced by needle production and needle mass development that occurred 4 to 6 years earlier. 相似文献
15.
Markus Holopainen Antti Mäkinen Jussi Rasinmäki Juha Hyyppä Hannu Hyyppä Harri Kaartinen Risto Viitala Mikko Vastaranta Annika Kangas 《European Journal of Forest Research》2010,129(5):899-907
The objective was to compare tree-level airborne laser-scanning (ALS) data accuracy with standwise estimation data accuracy
as input data for forest planning, using tree- and stand-level simulators. The influence of the input data accuracy was studied
with respect to (1) timing of the next thinning or clear-cutting and (2) the relative variation in the predicted income of
the next logging expressed as the net present value (NPV). The timing and predicted NPV of thinning and clear-cutting operations
were considered separately. The research was based on Monte Carlo simulations carried out with the tree- and stand-level simulators
using a simulation and optimisation (SIMO) framework. The simulations used treewise measurements taken on 270 circular plots
measured at the Evo Field Station, Finland, as input data. Deviations in the tree data measured were generated according to
the mean standard errors found in standwise field estimation and tree-level ALS. The accuracy factors of ALS individual tree
detection were based on the EUROSDR/ISPRS Tree Extraction Project. The results show that input data accuracy significantly
affects both the timing and relative NPV of loggings. Tree-level ALS produces more accurate simulation results than standwise
estimation with the error levels assumed. Diameter-based characteristics are the most important input data in all simulations.
Accurate tree height estimates cannot be fully utilised in current simulators. 相似文献
16.
Intra-annual height growth of Scots pine (Pinus sylvestris L.) in four stands was followed for up to four growing seasons (2000-2003) in the northern boreal zone in Lapland. Elongation of the leader shoot correlated with temperature sum expressed as degree-days. Total length of the leader shoot correlated with growth rate but not with duration of the height-growth period. The longer the annual shoot at the end of the season, the greater the height increment per degree- and growing day. Height-growth cessation was defined as the date when 95% of the total shoot length was achieved. In all stands and all years, height growth ceased when, on average, 41% of the relative temperature sum of the site was achieved (range of variation 38-43%). The relative temperature sum was calculated by dividing the actual temperature sum by the long-term mean for the site. Our results suggest that annual height growth is finished when a location-specific temperature sum threshold is attained. 相似文献
17.
A fertile hexaploid oat plant was obtained after several generations of selection for seed set and plant type from a colchicine-produced
decaploid hybrid, Avena abyssinica(2n = 4x = 28, AABB) × A. sativa (2n = 6x = 42, AACCDD). The selected line proved to be stably fertile and in many characteristics equal or superior to the
hexaploid parent. The grain protein fractions showed two qualitative differences from those of the pollen parent and several
differences from the maternal parent. The fractionating extraction used was new for oats. The fatty acid composition of grains
of the hybrid derivative was similar to that of the pollen parent, but different from that of the maternal parent. The maternal
parent (A. abyssinica) had a relatively high 16:0 fatty acid content (ca. 20.5 mol%) compared with the level of the hexaploid parent and the hybrid
derivation (ca. 17.5 mol% each) in field-grown grain. However, in grain produced in the greenhouse, the hexaploids had ca.
20.5 mol% of 16:0 fatty acid and a decrease in 18:1 fatty acid, whereas seed of the A. abyssinica parent showed only a slight increase (ca.21.5 mol%) in 16:0 fatty acid. These and other responses statistically significant
may be due to adaptation to temperature conditions being wider in the hexaploids than in the East-African A. abyssinica. A new method of grain lipid extraction was introduced and showed good reproducibility. The derived hexaploid oat can be
crossed with A. sativa for breeding purposes and due to its early maturity might also have direct use in northern or high-altitude cultivation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Minna-Liisa?RantalainenEmail author Hannu?Fritze Jari?Haimi Oili?Kiikkil? Taina?Pennanen Heikki?Set?l? 《Biology and Fertility of Soils》2004,39(3):200-208
Due to their high abundance and ubiquitous existence, microbes are considered to be efficient colonisers of newly established habitats. To shed light on the dispersal mechanisms of soil microbes, a controlled microcosm experiment was established. In these microcosms, the dispersal of microbes from a source humus patch to originally sterile humus patches (embedded in a mineral soil matrix) was followed for 16 months, applying 16S and 18S ribosomal DNA-based PCR-DGGE molecular methods. Specifically, the role of enchytraeid worms and habitat (humus) corridors as possible facilitators of microbe dispersal was studied. The results showed that enchytraeid worms function efficiently as vectors for horizontal dispersal of saprophytic fungi in soil. Some of the fungi also proved to disperse through the corridors by vegetative growth, although this dispersal was inefficient as compared to dispersal with the enchytraeids. Virtually no saprophytic fungi were able to disperse through the mineral soil matrix in the absence of both enchytraeid worms and corridors. Unlike soil fungi, the dispersal of soil bacteria was not affected by any of the studied factors. The results of the present experiment provide direct evidence of the crucial role of soil fauna in aiding the horizontal dispersal of soil fungi. The role of enchytraeids as a functionally important species in boreal forest soils is further emphasized, since bringing microbes into contact with new resources is likely to enhance the rate of decomposition in soils. 相似文献
19.
Hannu T. Koponen Claudia Escudé Duran Jyrki Hytönen 《Soil biology & biochemistry》2006,38(7):1779-1787
Both NO and N2O are produced in soil microbial processes and have importance in atmospheric physics and chemistry. In recent years several studies have shown that N2O emissions from organic soils can be high at low temperatures. However, the effects of low temperature on NO emissions from soil are unknown. We studied in laboratory conditions, using undisturbed soil cores, the emissions of NO and N2O from organic soils at various temperatures, with an emphasis on processes and emissions during soil freezing and thawing periods. We found no soil freezing- or thawing-related emission maxima for NO, while the N2O emissions were higher both during soil freezing and thawing periods. The results suggest that different factors are involved in the regulation of NO and N2O emissions at low temperatures. 相似文献
20.
Juliane?HahnEmail authorView authors OrcID profile Heli?Juottonen Hannu?Fritze Eeva-Stiina?Tuittila 《Biology and Fertility of Soils》2018,54(4):533-547
Peatland restoration via rewetting aims to recover biological communities and biogeochemical processes typical to pristine peatlands. While rewetting promotes recovery of C accumulation favorable for climate mitigation, it also promotes methane (CH4) emissions. The potential for exceptionally high emissions after rewetting has been measured for Central European peatland sites previously grazed by cattle. We addressed the hypothesis that these exceptionally high CH4 emissions result from the previous land use. We analyzed the effects of cattle dung application to peat soils in a short- (2 weeks), a medium- (1 year) and a long-term (grazing) approach. We measured the CH4 production potentials, determined the numbers of methanogens by mcrA qPCR, and analyzed the methanogen community by mcrA T-RFLP-cloning-sequencing. Dung application significantly increased the CH4 production potential in the short- and the medium-term approach and non-significantly at the cattle-grazed site. The number of methanogens correlated with the CH4 production in the short- and the long-term approach. At all three time horizons, we found a shift in methanogen community due to dung application and a transfer of rumen methanogen sequences (Methanobrevibacter spp.) to the peatland soil that seemed related to increased CH4 production potential. Our findings indicate that cattle grazing of drained peatlands changes their methanogenic microbial community, may introduce rumen-associated methanogens and leads to increased CH4 production. Consequently, rewetting of previously cattle-grazed peatlands has the potential to lead to increased CH4 emissions. Careful consideration of land use history is crucial for successful climate mitigation with peatland rewetting. 相似文献