全文获取类型
收费全文 | 654篇 |
免费 | 30篇 |
专业分类
林业 | 45篇 |
农学 | 33篇 |
基础科学 | 1篇 |
201篇 | |
综合类 | 43篇 |
农作物 | 41篇 |
水产渔业 | 50篇 |
畜牧兽医 | 191篇 |
园艺 | 14篇 |
植物保护 | 65篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 13篇 |
2021年 | 19篇 |
2020年 | 19篇 |
2019年 | 21篇 |
2018年 | 28篇 |
2017年 | 15篇 |
2016年 | 15篇 |
2015年 | 21篇 |
2014年 | 27篇 |
2013年 | 44篇 |
2012年 | 35篇 |
2011年 | 56篇 |
2010年 | 23篇 |
2009年 | 36篇 |
2008年 | 51篇 |
2007年 | 43篇 |
2006年 | 30篇 |
2005年 | 39篇 |
2004年 | 26篇 |
2003年 | 29篇 |
2002年 | 25篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1993年 | 2篇 |
1992年 | 7篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 6篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有684条查询结果,搜索用时 15 毫秒
591.
Rapisarda P Pannuzzo P Romano G Russo G 《Journal of agricultural and food chemistry》2003,51(6):1611-1616
Fruit juice of a new pigmented citrus hybrid named Omo-31 and those of its parents clementine cv. Oroval (Citrus clementina Hort. ex Tan.) and Moro orange [Citrus sinensis (L.) Osbeck] were analyzed during fruit maturation to determine juice yield, total soluble solids (TSS), total acidity (TA), TSS/TA ratio (classical parameters of quality), and potential health beneficial components, such as vitamin C, flavanones, anthocyanins, and phenolic acids. Results showed that juice yield, TA, TSS, and TSS/TA ratio values of Omo-31 were similar to those of the Moro orange. Vitamin C content of the new hybrid was slightly higher than that of clementine and lower than that of the Moro orange, but at maturity stage no differences were observed among the three genotypes. The phenolic compounds content of the new hybrid and those of the parents and their evolution during maturation were studied. At maturity stage the amount of anthocyanins, flavanones, and hydroxycinnamic acids in Omo-31 was found to be notably higher than those of the parents. The high level of antioxidant substances makes this new fruit important for its nutritional benefits. 相似文献
592.
593.
Annual soil losses in southern Italy can exceed 100–150 t ha− 1 year− 1. Where erosion on agricultural land is particularly severe, land use change and afforestation are frequently seen as the most appropriate means of reducing erosion risk. However, the overall effectiveness of afforestation in reducing soil erosion remains uncertain, due to the poor development of the forest cover in some areas, leading to significant areas with sparse tree cover, and the erosional impact of forest harvesting, which commonly involves clearcutting. The study reported here addresses this uncertainty and focuses on two small catchments (W2 and W3) located in Calabria, southern Italy, for which measurements of suspended sediment yield are available. Both the catchments originally supported a rangeland vegetation cover and they were planted with eucalyptus trees in 1968. Currently, only catchment W3 supports a continuous forest cover. In catchment W2 the forest cover is discontinuous and there is a significant area of the catchment (ca. 20%) where the tree cover is sparse and the vegetation cover is dominated by natural grasses. Two additional erosion plots were established within catchment W2 in 1991, in order to explore the effect of the density of the tree cover on soil erosion. Information on the sediment yields from the two catchments and the plots for 10 storm events that occurred during the period December 2005–December 2006 and associated information on the 137Cs and excess 210Pb of the sediment, have been used to investigate the effectiveness of afforestation in reducing sediment mobilisation and net soil loss from the catchments involved. The results demonstrate that the areas of greatest soil loss are associated with the slopes where the tree cover is discontinuous, and that forest harvesting by clearcutting causes significant short-term increases in sediment mobilisation and sediment yield. These findings, which are consistent with previous work undertaken within the same area, emphasize the importance of vegetation cover density in influencing rates of soil loss in the study catchments. The study also provided a useful demonstration of the potential for using measurements of the 137Cs and 210Pbex content of sediment, in combination with more traditional sediment monitoring, to investigate sediment sources and to compare the sediment dynamics of catchments subjected to different land management practices. 相似文献
594.
Children's exposure to Di(2-ethylhexyl)phthalate and dibutylphthalate plasticizers from school meals
Cirillo T Fasano E Castaldi E Montuori P Amodio Cocchieri R 《Journal of agricultural and food chemistry》2011,59(19):10532-10538
Packed school meals for children 3-10 years old were studied to evaluate the levels of di(2-ethylhexyl)phthalate (DEHP) and di-n-butylphthalate (DBP) and the influence of the packaging process on meal contamination, and their contribution to daily intake was estimated. The packaging consisted of polyethylene-coated aluminum (PE/Al) dishes thermally welded by a polyethyleneterephthalate-coated aluminum (PET/Al) foil. Foodstuffs before processing were analyzed, too. Total meals before packaging and after packaging were collected. It was found that 92% of foodstuffs employed in meal preparation contained DEHP, and 76% of them DBP, at detectable levels. In cooked foods before packaging the DEHP median concentration levels varied from 111.4 to 154.8 ng/g ww and those of DBP between 32.5 and 59.5 ng/g ww. In packed meals the DEHP median values ranged from 127.0 to 253.3 ng/g ww, and DBP median values varied from 44.1 to 80.5 ng/g ww. The mean increases of median concentrations of DEHP in cooked foods before and after packaging were 113 and 125% for DBP. For nursery and primary school children DEHP intake via school meals can raise on average the respective EFSA TDI by 18 and 12% and that of DBP by 50 and 30%. 相似文献
595.
Coppa M Martin B Pradel P Leotta B Priolo A Vasta V 《Journal of agricultural and food chemistry》2011,59(9):4947-4954
The effect of animal feeding on milk volatile organic compounds (VOCs) of metabolic origin was tested on a hay-based diet (H), a highly diversified pasture under continuous grazing (CG), or a less diversified pasture under rotational grazing (RG). Individual milk of 24 Montbe?liarde cows (8 per treatment) were sampled after 2 weeks. Pasture-derived milk was richer (p < 0.05) in camphene, sabinene, β-caryophyllene, and skatole than H milk. Neither milk yield nor fat content affected the majority of VOCs measured. Skatole increased slightly with milk yield, while indole and cineole decreased slightly with milk fat content but with poor regression (R(2) < 0.54). Multivariate analysis showed that, on the basis of those VOCs of metabolic origin whose concentration differed between treatment (dimethyl-sulfone, skatole, toluene, undecanoic acid, 1-octadecene, benzeneacetaldehyde, octanoic acid, and 2-pentanone-4-hydroxy-4-methyl), it was possible to obtain good discriminations among feeding systems. This study is promising for a future use of VOCs of metabolic origin to trace animal feeding systems. 相似文献
596.
Paolo Tremolada Roberto Comolli Marco Parolini Fabio Moia Andrea Binelli 《Water, air, and soil pollution》2011,217(1-4):407-419
Soils are an important sink for persistent organic pollutants (POPs), and high mountain soils are considered a stable reservoir for many compounds due to their high organic matter content. This study focuses on the small-scale variability on the environmental distribution of dichlorodiphenyltrichloroethane (DDT) in mountain soils. Several soil samples taken from May 2007 to June 2008 in a small area at around 1,900 m?a.s.l. (Italian Central Alps) were analyzed for DDT compounds. Pedological analyses were done as well. Organic matter content, soil layer, differences in solar radiation, and sampling period were considered as possible variability factors. Organic matter content can account for a DDT concentration difference of a factor 3 among different sites, soil layer can account for a concentration difference of a factor near 2, differences in solar radiation values do not seem to affect DDT concentrations, whereas the sampling period has the greatest influence with a difference factor of three to four among different sampling dates. Summing all these variability factors together, even though operating on such a small scale, we obtain a predicted spatial variability depending on the considered variables near to one order of magnitude. In particular, it was surprising that seasonal variations could be so great. If this conclusion is to be confirmed in the future, this element must be considered very carefully by scientists and environmental agencies during monitoring campaigns. 相似文献
597.
598.
599.
600.