全文获取类型
收费全文 | 391篇 |
免费 | 17篇 |
专业分类
林业 | 38篇 |
农学 | 4篇 |
基础科学 | 2篇 |
84篇 | |
综合类 | 35篇 |
农作物 | 15篇 |
水产渔业 | 27篇 |
畜牧兽医 | 170篇 |
园艺 | 17篇 |
植物保护 | 16篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 6篇 |
2014年 | 21篇 |
2013年 | 38篇 |
2012年 | 33篇 |
2011年 | 29篇 |
2010年 | 16篇 |
2009年 | 9篇 |
2008年 | 23篇 |
2007年 | 22篇 |
2006年 | 23篇 |
2005年 | 21篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 21篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1967年 | 3篇 |
1930年 | 2篇 |
1928年 | 1篇 |
排序方式: 共有408条查询结果,搜索用时 15 毫秒
21.
Lene Lottrup Ulrika K. Stigsdotter Henrik Meilby Sus Sola Corazon 《Urban Forestry & Urban Greening》2012,11(2):159-168
Today, office work in western societies is more sedentary and more mentally demanding than ever before. This way of working plays a role in the increase in lifestyle diseases related to sedentary routines and stress. Green outdoor environments have been found to motivate physical activity and reduce stress levels. In this study, we therefore considered these environments to have a positive affect on work force health and wellbeing. However, research on the workplace outdoor environment is still limited. To investigate how and why the workplace outdoor environment is used by office workers and the impact of these environments on office workers’ health and wellbeing, five research questions were formulated. The questions addressed the use of the outdoor environments; the outdoor activities; encouragement and impediments for going outdoors; characteristics of the outdoor environment, and the impact of workplace outdoor environments on employees’ health, job satisfaction and work performance. In order to answer these research questions, we conducted a web-based questionnaire, completed by (N) 402 office workers from six Danish companies. The results show that 37.8% of the respondents spent time outdoors during their working day, and that the proportion of men spending time outdoors was higher than the proportion of women. Eight outdoor activities were identified, and significant relationships between the outdoor activities and perceived sensory dimensions (PSD) of the outdoor environment were found, indicating that the presence of the dimension ‘serene’ increased the odds for respondents going outdoors and that five of the eight activities would be performed. Only few significant relationships between outdoor environment use and employee health, job satisfaction and work performance were identified. 相似文献
22.
Ashoka Dangolla Preben Willeberg Henrik Bj rn Allan Roepstorff 《Preventive veterinary medicine》1996,27(3-4):197-209
Associations of the occurrence of Ascaris suum and Oesophagostomum spp. in sows with herd management factors were examined using logistic-binomial regression. The information used was from 11 to 78 sows sampled from each of 83 breeding herds (2961 sows in total) and examined for eggs per gram of faeces (EPG). A sow excreting at least 20 EPG was defined as ‘infected’. Management factors of the study herds were recorded using a questionnaire. A total of 263 sows from 50 herds (8.9% of sows) and 375 sows from 20 herds (12.7% of sows) were infected with A. suum and Oesophagostomum spp., respectively. For A. suum, sows from herds with more than 85 sows had significantly higher odds of being infected compared with those from 30 to 85 sows (P < 0.05). When bedding was provided for sows, the odds of A. suum infection was 5.4 compared with sows from herds in which bedding was not provided (P < 0.05). For Oesophagostomum spp., sows from herds with different specific pathogen free status had about one tenth the odds of being infected compared with those from conventional herds (P < 0.05). Sows that had been treated with anthelmintics had very low odds of being infected with Oesophagostomum spp. compared with those that were not treated (P < 0.05). The effects of these management factors in both final models did not differ when the definition of an ‘infected’ sow was changed. The present results suggest the importance of disposal of bedding material from pens in reducing the prevalence of A. suum in larger sow herds. Anthelmintic treatment is important in reducing the prevalence of Oesophagostomum spp. infection of sows. 相似文献
23.
24.
Young JF Rosenvold K Stagsted J Nielsen JH Andersen HJ 《Journal of agricultural and food chemistry》2005,53(3):745-749
The present study investigates the combined effects of feed-induced increase in polyunsaturated fatty acids (PUFA) content and/or alpha-tocopherol content in pig muscles and preslaughter stress on cell integrity. Cell integrity was determined by plasma lactate dehydrogenase (LDH) activity, and antioxidative status of muscle was measured by activities of the antioxidative enzymes catalase, superoxide dismutase, and glutathione peroxidase. Preslaughter stress increased LDH activity, reflecting loss in cell membrane integrity independent of increased content of PUFA and/or alpha-tocopherol. However, feed-induced increase of PUFA decreased the LDH activity in plasma immediately after slaughter. Catalase activity in the muscle tissue increased as a consequence of the high-PUFA diet, which may indicate an increased demand caused by introduction of oxidative labile PUFA. 相似文献
25.
A general model for assessment of the carbon sequestration potential of afforestation projects 总被引:1,自引:0,他引:1
Among the objectives of afforestation projects, carbon sequestration is attracting increasing political attention. Therefore, there is a need for understanding the carbon sequestration ??mechanism?? and for ex-ante assessment of the sequestration potential of afforestation projects. Such assessment must be based on parameter estimates that are inherently uncertain, making the basis for applying an advanced sequestration model weak. This paper presents a transparent, simple and general model for quantification of the carbon sequestration in afforestation projects. The model can easily be modified so as to fit specific conditions, and it is held sufficiently reliable when taking into account the ex-ante character of the decision problem. The use of the model is exemplified by application to a yield table for Sitka spruce. Limitations of the model framework and its application in combination with scenarios of climate change are discussed. 相似文献
26.
When semi-natural pastures are abandoned, specialized grassland species are lost as a consequence of succession. As a counter-measure, previously abandoned grasslands may be restored by clearing shrubs and trees and re-introducing grazing livestock. In order to examine the effects of this type of habitat restoration, we compared species richness of plants and of specialized plants thought to be dependent on continuous management and species richness and abundance of butterflies and red-listed butterflies in 12 sets of matched continuously managed, abandoned and restored grassland in southern Sweden. We found no differences in species richness or abundance between the three grassland types. There were, however, some negative effects of abandonment. The number of management-dependent plants decreased with increasing cover of trees and shrubs, and in restored sites species richness of all groups decreased with increasing cover of trees and shrubs before restoration. Also the present management significantly affected both butterflies and plants. Species richness of both groups increased with increasing vegetation height and differed between sites depending on the species of grazers, with negative effects of sheep compared to cattle or horses. Our study indicates that for grassland management to be efficient, the restoration actions should mainly be directed towards sites where the post-abandonment succession has not proceeded too far. 相似文献
27.
Young JF Rosenvold K Stagsted J Steffensen CL Nielsen JH Andersen HJ 《Journal of agricultural and food chemistry》2003,51(23):6877-6881
Polyunsaturated fatty acids (PUFAs) and exercise-induced stress are known to increase the oxidative susceptibility of lipids in muscle tissue. In contrast, antioxidative enzymes, e.g., catalase, superoxide dismutase, and glutathione peroxidase, are known to help sustain the delicate oxidative balance in biological tissue upon the application of stressors. The present study investigates the combined effect of different diet-induced muscle PUFA contents and preslaughter stress on the activity of antioxidative muscle enzymes and the oxidative stability of cooked meat. An increased content of unsaturated fatty acids in the tissue led to a decreased activity of lactate dehydrogenase in the plasma, indicating increased cell integrity. Catalase activity in the muscle tissue increased with increasing PUFA levels. However, this upregulation in antioxidative status of the muscle could not counteract the subsequent development of accelerated lipid oxidation in cooked meat as measured in terms of thiobarbituric acid reactive substances. Moreover, preslaughter stress induced increasing oxidative changes with elevated PUFA levels in the muscle tissue. 相似文献
28.
When we look at our hands, we immediately know that they are part of our own body. This feeling of ownership of our limbs is a fundamental aspect of self-consciousness. We have studied the neuronal counterparts of this experience. A perceptual illusion was used to manipulate feelings of ownership of a rubber hand presented in front of healthy subjects while brain activity was measured by functional magnetic resonance imaging. The neural activity in the premotor cortex reflected the feeling of ownership of the hand. This suggests that multisensory integration in the premotor cortex provides a mechanism for bodily self-attribution. 相似文献
29.
Mammalian sex chromosomes have undergone profound changes since evolving from ancestral autosomes. By examining retroposed genes in the human and mouse genomes, we demonstrate that, during evolution, the mammalian X chromosome has generated and recruited a disproportionately high number of functional retroposed genes, whereas the autosomes experienced lower gene turnover. Most autosomal copies originating from X-linked genes exhibited testis-biased expression. Such export is incompatible with mutational bias and is likely driven by natural selection to attain male germline function. However, the excess recruitment is consistent with a combination of both natural selection and mutational bias. 相似文献
30.