全文获取类型
收费全文 | 192篇 |
免费 | 5篇 |
专业分类
林业 | 23篇 |
农学 | 3篇 |
基础科学 | 2篇 |
41篇 | |
综合类 | 13篇 |
农作物 | 8篇 |
水产渔业 | 11篇 |
畜牧兽医 | 85篇 |
园艺 | 6篇 |
植物保护 | 5篇 |
出版年
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 15篇 |
2012年 | 9篇 |
2011年 | 12篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 11篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有197条查询结果,搜索用时 15 毫秒
191.
Variation in quercetin content was investigated in field-cured onions (Allium cepa L.) that had been supplied with different nitrogen fertilizer levels and lifted at different developmental stages. Quercetin content varied significantly between years and was well correlated to global radiation in August. Field curing generally resulted in significant increases in quercetin content compared to levels at lifting. Nitrogen fertilizer level did not affect quercetin content, suggesting that nitrogen leakage from soil may be minimized without effects on flavonol content. Lifting time had minor effects on quercetin content in field-cured onions. Cultivar differences in quercetin content were significant but not consistent in all years. Quercetin content increased significantly less in dark environments compared to field curing, but some quercetin synthesis occurred regardless of light. Field curing with or without foliage still attached did not affect quercetin content, suggesting that no transportation from the foliage to the scales occurred. 相似文献
192.
The factors affecting mechano-sorptive creep of wood and paper have been investigated for a long time. It has also been argued that single wood fibres do not exhibit mechano-sorptive creep and that the reasons for the accelerated creep under moisture cycling conditions instead are related to the bonds between the fibres. In order to examine the relevance of this argument, measurements on single pulp fibres of different composition were performed in tension, and the mechano-sorptive creep was compared to that of papers made from the same source of pulp fibres. All fibres tested were found to exhibit an increased creep rate during moisture cycling as compared to constant humidity conditions. Thus, pulp fibres show mechano-sorptive creep and in this sense behave similar to solid wood or paper products made thereof. A linear relation between the creep strain rate during cyclic humidity and the creep strain rate at a constant humidity was also noted for both fibres and paper. This relation was not affected by changes in hemicelluloses content or composition, neither for fibres nor for papers made of these fibres. However, in all cases, papers showed a much higher mechano-sorptive creep than the corresponding fibres they were made of. 相似文献
193.
Magnus Magnusson Jörgen Olsson Henrik Hedenås 《Scandinavian Journal of Forest Research》2014,29(5):455-465
Many wood-inhabiting fungi are today threatened as modern forestry practices drastically reduce the amount of dead wood available in various forest ecosystems. We investigated whether the occurrence of red-listed wood-inhabiting fungi differed between natural and managed forest landscapes adjacent to the timberline in the middle part of Sweden. We assessed whether environmental variables such as the degree of human impact, length of forest roads, dead wood volume and quality affected species richness and abundance. The effects of forestry on wood-inhabiting fungi have been assessed in several studies in lowland Swedish forests. Few studies have, however, been conducted in forest landscapes adjacent to the timberline in Sweden. This is potentially important since forests close to the Swedish mountains have been pointed out as one of few intact forest landscapes in Fennoscandia and they are subjected to increasing logging pressure. Similar to other studies, species numbers and abundances were positively correlated with larger volumes of logs in various decay stages. However, never shown previously, the length of forest roads was negatively correlated with species abundance and occurrence of red-listed species. We suggest that a low amount of forest roads can be used as a conservation indicator to localize still-intact forest landscapes. 相似文献
194.
Classical fear conditioning investigates how animals learn to associate environmental stimuli with an aversive event. We examined how the mechanisms of fear conditioning apply when humans learn to associate social ingroup and outgroup members with a fearful event, with the goal of advancing our understanding of basic learning theory and social group interaction. Primates more readily associate stimuli from certain fear-relevant natural categories, such as snakes, with a negative outcome relative to stimuli from fear-irrelevant categories, such as birds. We assessed whether this bias in fear conditioning extends to social groups defined by race. Our results indicate that individuals from a racial group other than one's own are more readily associated with an aversive stimulus than individuals of one's own race, among both white and black Americans. This prepared fear response might be reduced by close, positive interracial contact. 相似文献
195.
Throughout the northern hemisphere old forests with high abundance of dead wood are rare features in most landscapes today, and the loss of dead wood constitutes a serious threat to the existence of many species. This study, using field surveys and dendrochronology, examines the relationship between wood-inhabiting fungi and past forest utilisation along a gradient of early logging activity. Data were collected in three late-successional Scots pine forests in northern Sweden. Nonmetric Multidimensional Scaling (NMS) was then used to assess differences in species composition among the forests. Our results show that minor forest logging (22-26 cut stumps ha−1) carried out a century ago may have continuing effects on forest characteristics, including dead wood dynamics and the wood-inhabiting fungal community - especially the abundance of red-listed species. The most important effects are lower numbers of logs in early and intermediate stages of decomposition. Additionally, numbers of species (including red-listed species) can be high in forests that have been subject to low levels of logging. Overall, the high species numbers recorded in this study (n = 60-87) show that old, low-productivity pine forests harbour a considerable fraction of the total diversity of Basidiomycetes in northern Fennoscandian boreal forests. We conclude that the formation of a framework linking forest history and environmental data is vital for understanding the ecology and formulating goals for future management of these forests. 相似文献
196.
The health of 3081 heifer calves born in 122 dairy herds in the south-west of Sweden from 1 January to 31 December, 1998, was monitored from birth until 90 days of age. The calves were kept either in individual pens (n=2167), in group pens, with 3–8 calves to a pen and manual feeding of milk (n=440), in group pens with 6–30 calves per pen and an automatic milk-feeding system (n=431), or with their dams (n=43). Disease incidence was recorded by farmers and project veterinarians, who clinically examined the calves and auscultated their lungs every 2–3 months. A disease was graded as ‘severe’ if the general loss of condition or of appetite in the calf continued for >2 days or if the animal suffered severe weight loss due to the disease. The effects of season, breed, housing, and type of colostrum feeding, and time, place and supervision of calving on the incidences of diarrhea, severe diarrhea, respiratory disease, other infectious disease and moderately to severely increased respiratory sounds, were analyzed by logistic-regression models (with herd as a random effect). The total morbidity rate was 0.081 cases per calf-month at risk. Incidence rates of arthritis, diarrhea, omphalophlebitis, respiratory disease and ringworm were 0.002, 0.035, 0.005, 0.025 and 0.009 cases per calf-months at risk, respectively. The odds ratios for diarrhea and severe diarrhea were increased in Swedish Red and Whites (OR: 1.6, 2.3) and in calves that received colostrum from first-lactation cows (OR: 1.3–1.8), and for severe diarrhea in calves born in summer or that received colostrum through suckling (OR: 1.7, 1.8). The odds ratios for respiratory disease and increased respiratory sounds were increased in calves housed in large-group pens with an automatic milk-feeding system (OR: 2.2, 2.8). Supervision of calving was associated with a decreased odds ratio for respiratory disease (OR: 0.7) and birth in individual maternity pen or tie stalls with a decreased odds ratio for increased respiratory sounds (OR: 0.5–0.6). Cross-breeds with beef breeds were associated with increased odds ratios for increased respiratory sounds (OR: 2.1–4.3) and colostrum from second-lactation cows and birth during night for other infectious disease (OR: 1.6, 1.5). 相似文献
197.
Agneta Egenvall Peter Franzn Anders Gunnarsson Eva Olsson Engvall Ivar Vgsholm Ulla-Britt Wikstrm Karin Artursson 《Preventive veterinary medicine》2001,49(3-4)
A cross-sectional study of the seroprevalence to Borrelia burgdorferi sensu lato and granulocytic Ehrlichia spp. in Swedish horses was conducted to evaluate associations with demographic, clinical and tick-exposure factors. From September 1997–1998, blood samples from 2018 horses were collected from the animals presented to veterinary clinics affiliated with the Swedish Horserace Totalizator Board (regardless of the primary cause for consultation). Standardized questionnaires with information both from owners and attending veterinarians accompanied each blood sample. The apparent seroprevalences to B. burgdorferi s. l. and granulocytic Ehrlichia spp. were 16.8 and 16.7%, respectively. The northern region had the lowest seroprevalences. Four logistic models were developed (controlling for demographic variables). In the disease model of seropositivity to B. burgdorferi s. l., age, breed, geographic region, the serologic titer to granulocytic Ehrlichia spp., season and the diagnosis coffin-joint arthritis were significant. In the tick-exposure model of B. burgdorferi s. l., pasture access the previous year and gender were significant. Age, racing activity, geographic region, season and the serologic titer to B. burgdorferi s. l. were associated with positivity to granulocytic Ehrlichia spp. In the tick-exposure model of granulocytic Ehrlichia spp., pasture access was a risk factor. An interaction between racing activity and geographic region showed that the risk of positive serologic reactions to Ehrlichia spp. was increased in the horse population in the south and middle of Sweden, but only among horses not used for racing. Except for the positive association between coffin-joint arthritis and serologic reactions to B. burgdorferi s. l., there were no significant associations in the multivariable models between non-specific or specific clinical sign or disease with seropositivity to either of these agents. 相似文献