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   150篇
  免费   4篇
林业   16篇
农学   10篇
基础科学   2篇
  12篇
综合类   11篇
农作物   7篇
水产渔业   22篇
畜牧兽医   60篇
园艺   3篇
植物保护   11篇
  2022年   9篇
  2021年   11篇
  2020年   6篇
  2019年   1篇
  2018年   7篇
  2017年   3篇
  2016年   5篇
  2015年   4篇
  2014年   2篇
  2013年   13篇
  2012年   10篇
  2011年   12篇
  2010年   5篇
  2009年   8篇
  2008年   9篇
  2007年   7篇
  2006年   6篇
  2005年   6篇
  2004年   4篇
  2003年   3篇
  2002年   4篇
  2001年   3篇
  2000年   2篇
  1999年   1篇
  1996年   2篇
  1992年   1篇
  1990年   2篇
  1989年   1篇
  1985年   2篇
  1984年   2篇
  1982年   1篇
  1979年   1篇
  1970年   1篇
排序方式: 共有154条查询结果,搜索用时 0 毫秒
81.
Hinoki (Chamaecyparis obtusa) wood has been used as a structural material in Japan because of its superior mechanical properties, its excellent durability and the beautiful color of its heartwood. Variations of termite resistance and compositions of extractives among hinoki trees have been reported. However, genetic variation of termite resistance and the effect of heartwood color on termite resistance remain unknown. In this study, we report the characteristics of termite resistance and color indexes (L*, a* and b*) of heartwood of hinoki half-sib families in a progeny test stand. The survival days of termites and the mass loss of samples of hinoki heartwood differed significantly among hinoki families. Families with red-color heartwood had larger termite resistance than families with yellow-color heartwood. The termite resistances of individual samples from two families with yellow-color heartwood were as small as that of Pinus densiflora. Larger a* and smaller b* induced larger termite resistance of heartwood. The effect of DBH (diameter at breast height) of hinoki trees on termite resistance of hinoki families was small.  相似文献   
82.
83.
Nineteen fig varieties and lines from Europe and Asia have been fingerprinted by ISSR, RAPD, and SSR markers, respectively, using 13, 19, and 13 primer combinations. All primers produced 258 loci, with the highest number of loci (119) generated by RAPD (R p: 48.42). Clustering analysis was applied to the three marker datasets to elucidate the genetic structure and relationships among these varieties. Mean genetic similarities were 0.787, 0.717, and 0.749, respectively, as determined using ISSR, RAPD, and SSR. Each marker system produced incompletely separated clusters, although a weak binding group based on race type appeared in the combined dataset. Comparisons of coefficients revealed no correlation between different similarity matrices; congruence was observed between similarity matrices and co-phenetic matrices in all markers. Analysis of molecular variance (AMOVA) showed that most of the total polymorphism was attributable to within-group variance (ISSRs + RAPDs, 97.41%; SSRs, 90.18%). These results suggest that the genetic diversity of this fig population is low and that multiple marker utilization is critical to estimate the relatedness of figs at the variety level. Additionally, it was presumed that ‘Houraihi’, the oldest variety in Japan, was disseminated independently of other foreign varieties in the 17th century or before then.  相似文献   
84.
Microbubbled air may be efficiently supplied to the culture solution, since microbubbles are more efficiently dissolved in water than millibubbles. To establish an enhanced air supply method in the hydroponic culture of vegetables, microbubbles were applied using the deep flow technique to a hydroponic culture system of spinach. Spinach was cultivated in culture solution treated microbubbles for 21 days, then harvested and measured growth and concentrations of inorganic components and chlorophyll in the leaf blade. The results showed that microbubbles applied to the culture solution promoted the growth of spinach more than that by millibubbles. Using microbubbles, cultivars maintained a high concentration of dissolved oxygen at the middle growth stage, during which the dissolved oxygen concentration in the culture solution was reduced by the active root respiration. This result suggests that microbubbles are more effective than millibubbles in the hydroponic culture of vegetables.  相似文献   
85.
DAS-ELISA was used to study the presence of viruses in four aphid species ( Aphis gossypii , Aphis craccivora , Myzus persicae and Macrosiphum euphorbiae ) and in their host plants potato, capsicum and tomato. Samples were collected in different regions in Tunisia: north, Cap Bon, Sahel, centre and south. A. gossypii and M. persicae carried all the viruses detected: Cucumber mosaic cucumovirus , Tomato aspermy cucumovirus , Tobacco etch potyvirus , Potato Y potyvirus , Alfalfa mosaic alfamovirus and Potato leafroll polerovirus . These two aphids were also those that occurred most frequently on the crops concerned.  相似文献   
86.
The objective of this study was to evaluate the effects of grazing on the accretion of energy and chemical components in steers, using the comparative slaughter technique and taking into consideration the growth rate. Twelve Holstein steers aged 6 months and weighing 160 kg were divided into three treatment groups – an initial, grazing and control group. The initial group was slaughtered at the beginning of the experiment. The grazing group was grazed on timothy pastures for 18 weeks. The control group was kept in a stable and offered concentrate and timothy hay in a proportion of 2:1 throughout the 18 weeks. The amount of ration offered to the control group was adjusted in order to obtain a growth rate similar to that of the grazing group. The grazing and control groups were slaughtered at the end of the experiment. The grazing and the control groups had similar growth rates of approximately 0.8 kg/day throughout the experimental period and similar final live weights of approximately 260 kg. The grazing group had lower fat and energy deposition rates than the control group (P < 0.05). Deposition rates of protein, fat, ash, moisture and energy were 130, 32, 30, 374 g/day and 4.4 MJ/day, respectively, in the grazing group and 117, 85, 32, 381 g/day and 6.2 MJ/day, respectively, in the control group. The net energy for growth was lower in the grazing group (7.7 MJ/kg) than in the control group (9.9 MJ/kg, P < 0.05). The grazing group had higher plasma concentrations in growth hormone and lower plasma concentrations in insulin and insulin‐like growth factor 1 than those in the control group (P < 0.05).  相似文献   
87.
In many irrigation schemes, Water Users Associations (WUAs) acquired the responsibility for water management after withdrawal of the state. Based on the success of some indigenous irrigation schemes, it was assumed that farmers could easily become managers. As decision-making was the exclusive terrain of the governmental agencies that ran the schemes, farmers never gained the necessary experience with water management. Therefore, training of farmers and WUAs on the principles and processes of water management is essential. This paper demonstrates a practical example of training material on water management that incorporates research results on the process of Irrigation Management Transfer and resulting farmers’ water management for the case of the Office du Niger irrigation scheme. The results of the paper explain how input from research was used in the four steps of the construction of training material. These steps are (1) setting the training agenda, (2) selecting and adapting information to be featured, (3) targeting the audience and (4) designing the actual training material. A first validation of the approach and examples of the actual training material were obtained in a workshop uniting all stakeholders.  相似文献   
88.
A 13-year-old spayed female Cavalier King Charles Spaniel presented with chronic swelling and pruritus on the palmar aspect of the left forepaw and on the tail. Cutaneous epitheliotropic lymphoma (CEL) was diagnosed by histopathology and immunocytochemistry. Prednisolone was initially used alone as an alternative treatment for CEL. Despite long-term corticosteroid therapy, the patient’s physiological (pruritus) and dermatological signs (alopecia, erythema, erosion, and ulceration with crust) progressed and showed no evidence of improvement. To address the worsening condition of pruritus, lokivetmab was started in combination with prednisolone. Once on lokivetmab, the pruritus steadily improved and was effective in resolving and maintaining remission. Further investigation on the critical role of IL-31 in the pruritus pathway of dogs with CEL is required.  相似文献   
89.
In the Sahel region of West Africa, the traditional organization of the population and the grazing land avoided overexploitation of pastures. Since independence in the 1960s, grazing lands have been opened to all without specific guidance, and the vulnerability of the pastures to degradation has increased. Rotational grazing is postulated as a possible solution to provide higher pasture productivity, higher animal loads per unit land, and perhaps improved soil carbon storage. The objective of this study was to conduct a simulation-based assessment of the impact of rotational grazing management on pasture biomass production, grazing efficiency, animal grazing requirement satisfaction, and soil carbon storage in the Madiama Commune, Mali. The results showed that grazing intensity is the primary factor influencing the productivity of annual pastures and their capacity to provide for animal grazing requirements. Rotating the animals in paddocks is a positive practice for pasture protection that showed advantage as the grazing pressure increased. Increasing the size of the reserve biomass not available for grazing, which triggers the decision of taking the animals off the field, provided better pasture protection but reduced animal grazing requirements satisfaction. In terms of soil carbon storage, all management scenarios led to reduction of soil carbon at the end of the 50-year simulation periods, ranging between 4% and 5% of the initial storage. The differences in reduction as a function of grazing intensity were of no practical significance in these soils with very low organic matter content, mostly resistant to decomposition.  相似文献   
90.
We examined the age and growth of the marbled sole Pseudopleuronectes yokohamae collected from Tokyo Bay, Japan, during two study periods between 2002 and 2008, when the stock size was consistently low. The von Bertalanffy growth equations were found to differ significantly between sexes, and females attained a larger standard length than males of the same age. These results were then compared with those reported for 1974–1983 and 1986–1988, two study periods when the stock size was high. The growth of both sexes of marbled sole in Tokyo Bay during the 2000s was found to be significantly higher than that in the 1970s and 1980s. To explore possible factors causing these changes in the growth, we examined bottom water temperature and population density. We found that the population density decreased and the bottom water temperature increased between the late 1970s and the late 2000s. However, despite evidence of changes in population densities and water temperatures, further study is needed to determine the main factors causing the observed changes in growth.  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