全文获取类型
收费全文 | 808篇 |
免费 | 143篇 |
国内免费 | 67篇 |
专业分类
林业 | 1篇 |
农学 | 29篇 |
基础科学 | 2篇 |
22篇 | |
综合类 | 170篇 |
农作物 | 2篇 |
水产渔业 | 734篇 |
畜牧兽医 | 56篇 |
园艺 | 1篇 |
植物保护 | 1篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 51篇 |
2019年 | 49篇 |
2018年 | 45篇 |
2017年 | 54篇 |
2016年 | 70篇 |
2015年 | 57篇 |
2014年 | 61篇 |
2013年 | 96篇 |
2012年 | 47篇 |
2011年 | 65篇 |
2010年 | 47篇 |
2009年 | 39篇 |
2008年 | 40篇 |
2007年 | 43篇 |
2006年 | 26篇 |
2005年 | 39篇 |
2004年 | 21篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 16篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
排序方式: 共有1018条查询结果,搜索用时 625 毫秒
931.
This study examined the microscopic structure of the small intestine and digestion and absorption in the hybrid tilapia, Oreochromis niloticus×Oreochromis aureus. The small intestine was lined on the luminal face with villi, which were narrower and more dense in the proximal small intestine and became wider and sparser distally. The columnar epithelial cells lining the villi were predominantly enterocytes containing a brush border, interspersed with mucus containing goblet cells approximately every 4–6 cells. These mucus‐secreting cells contained both acid and basic mucins and increased in density in the distal and the terminal sections of the intestine. Proliferation of enterocytes was observed in the intervillus areas and lower third of the villus. Fish were fed diets of either fish meal or fish meal–wheat to which chromic oxide had been added as a non‐absorbed reference standard. Activity of the pancreatic enzymes, lipase, trypsin and amylase were determined along the small intestine relative to the non‐absorbed marker. Activity of these pancreatic enzymes was maximal in the proximal segments and decreased distally. Changes in the activity patterns of trypsin and amylase were observed with the different diets in the proximal small intestine. Net secretion of both N and fatty acids was found in the hepatic loop and absorption commenced distally decreasing in rate with distance from the pylorus. The pattern of N absorption in the proximal small intestine changed with the different diets. The structure and function of the small intestine of the tilapian omnivore thus are generally similar to mammals and digestion and absorption adapt with diet. 相似文献
932.
Tilapia (Oreochromis) nilotica were fed either a commercial diet containing 2.2% (n-3) and 0.5% (n-6) polyunsaturated fatty acids (PUFA), or a diet containing
1.0% methyl linoleate as the only PUFA. The fatty acid composition of tissue lipids generally reflected that of the diet.
Fish from both dietary groups were injected intraperitoneally with 14C-labelled linoleic acid, 18:2 (n-6), or linolenic acid, 18:3 (n-3), and the distribution of radioactivity in tissue lipids
examined. The conversion of both 18:2 (n-6) and 18:3 (n-3) to longer chain PUFA was lower in fish fed the commercial diet
than in those fed the diet containing only 18:2 (n-6). Half of the radioactivity from both substrates recovered in liver polar
lipids was present in C20 and C22 PUFA with fish maintained on the experimental diet. It is concluded that T. nilotica is capable of elongating and desaturating both 18:2 (n-6) and 18:3 (n-3), but that this conversion is suppressed by dietary
longer chain PUFA.
NERC Unit of Aquatic Biochemistry 相似文献
933.
本试验旨在研究饲料加工工艺及维生素添加量对罗非鱼生长性能、营养物质沉积和血清生化指标的影响.在基础饲料配方中添加0.50%的维生素预混料,分别制成颗粒饲料和膨化饲料;另外,再将配方中维生素预混料的添加量分别升高到0.66%、0.82%,制成膨化饲料.试验共得4组饲料,投喂平均体重为(8.0±0.1)g的罗非鱼,每组3个重复,每个重复35尾.试验期为8周.结果表明:1)在相同配方条件下,摄食膨化饲料的罗非鱼较摄食颗粒饲料的罗非鱼增重率提高8.91% (P<0.05),饲料系数降低9.42% (P<0.05);同时,其肝体指数、全鱼粗蛋白质含量、营养物质沉积率(包括蛋白质效率、蛋白质沉积率、脂肪沉积率、能量沉积率)以及血清谷草转氨酶、谷丙转氨酶活性和甘油三酯含量均较摄食颗粒饲料的罗非鱼显著或极显著升高(P<0.05或P<0.01).2)在膨化饲料组中,随着维生素预混料添加量由0.50%升高到0.66%,罗非鱼的增重率、特定生长率、蛋白质效率、蛋白质沉积率和能量沉积率显著升高(P<0.05),而饲料系数、全鱼粗灰分含量则显著降低(P<0.05);当维生素预混料添加量由0.66%继续升高到0.82%时,罗非鱼的生长性能及营养物质沉积率并没有得到进一步的改善.由此可见,在相同配方条件下,罗非鱼摄食膨化饲料较摄食颗粒饲料具有更好的生长性能和更高的营养物质沉积率;膨化饲料配方中适当的超量添加维生素,有利于提高罗非鱼的生长性能和对饲料中营养物质的利用. 相似文献
934.
应用RAPD、AFLP、SSR等3种分子标记,对吉富品系尼罗罗非鱼选育群体的多态性进行了分析.在40条RAPD引物、19对SSR引物、64对AFLP引物中,具有多态性、重复性好的引物分别为17条、19对和8对,扩增出多态性条带数分别为35、92、181条.结果表明,RAPD、AFLP、SSR多态性条带比例分别为20.35%、79.64%和58.77%,平均每个(对)多态性引物可以扩增出多态性片段数目分别为2.06、4.84和22.63.说明SSR和AFLP是研究吉富罗非鱼选育群体更为有效的分子标记. 相似文献
935.
936.
Angela Aparecida Moreira Heden Luiz Marques Moreira Alexandre Wagner Silva Hilsdorf 《Aquaculture Research》2005,36(11):1049-1055
Growth performance of two Oreochromis niloticus strains, Chitralada and Red‐Stirling, their reciprocal crossbred and the Israeli tetra‐hybrid ND‐56 were assessed in net cages under on‐farming conditions. Throughout 268 days of grow‐out, the strains were weighed monthly and mortality, feed consumption and water quality were recorded. Ten rigid net cages (1.5 × 1.5 × 1.7 m) immersed in a 10 ha reservoir were linearly arranged near the reservoir outlet following a completely randomized design with two replicates for each treatment (strain). Each cage was stocked with 459 fish (120 fish m?3) and fed twice daily to apparent satiation with a commercial tilapia diet following the recommended feeding program. The final mean weights were higher for Chitralada (557.20 g) and the reciprocal crossbreds (522.95, 496.40 g) than those of Red‐Stirling (421.90 g). All treatments outperformed the ND‐56 tetra hybrid. Daily growth showed statistical differences between Chitralada (2.04 g) and Red‐Stirling (1.52 g) but they were statistically the same when compared with the reciprocal crossbreds (1.90, 1.80 g). The relative growth ratios showed the same trend observed in the results for daily growth. The mean survival rate was 98%. The overall growth rate showed that crossbred performed as well as the parental lines. All crossbred progeny presented red colouration with variable pattern of black marks corroborating the dominant inheritance of the red trait in Red‐Stirling strain. 相似文献
937.
Mohammad T Ridha 《Aquaculture Research》2006,37(2):172-179
This study was conducted to investigate the effect of stocking density (125 or 200 fish m?3) on the growth performance of three strains of the Nile tilapia, Oreochromis niloticus: the non‐improved strain (NS), the genetically improved farmed tilapia (GIFT) and the Freshwater Aquaculture Center selected tilapia known as the FaST selected line (SL). Each strain and density combination was triplicated in 0.42 m3 fibreglass tanks within a re‐circulating water system. Water temperature was maintained at 29.0±1.0°C. Large Nile tilapia having a mean body weight of 100–110 g were stocked in each tank and hand‐fed four times daily with commercial tilapia pellets (35% protein) for 104 days. Results showed that at the two stocking densities, the GIFT and SL strains showed a significantly higher (P<0.05) mean weight (MWT), daily growth rate (DGR), specific growth rate (SGR), feed conversion ratio (FCR) and gross yield (GY) than the NS. In all three strains, growth performance was negatively affected by stocking density. The lower density (125 fish m?3) treatments had significantly higher MWT, DGR and SGR than the higher density one (200 fish m?3). However, higher FCR and GY were observed at the higher density. Survival rates were high in all treatments and were not affected by strain or density. In general, the SL strain had better growth parameters than the GIFT strain. The findings of this study demonstrated the superior growth performance of the improved strains at both densities compared with the NS. The higher density (200 fish m?3) could be more profitable for the tilapia farms in Kuwait than the lower density of (125 fish m?3) in terms of reduced land cost and facilities, demand on the limited low‐salinity underground water and manpower. 相似文献
938.
939.
This study investigated the effects of nursing duration on the subsequent performance of rohu (R) Labeo rohita and mrigal (M) Cirrhina mrigala in polyculture with monosex male Nile tilapia (T) Oreochromis niloticus at four levels of pond fertilization. Nile tilapia, rohu and mrigal were stocked at a ratio of 4:1:1 in a 90‐day trial based on 40 20‐m2 pens fixed in four 400‐m2 earthen ponds. Growth of carp fingerlings during prolonged nursing (5 or 12 months) was stunted compared with fish nursed over a conventional duration of 3 months (3) but showed superior growth subsequently. Mean daily weight gain of stunted rohu (12) ranged from 2.2 to 2.8 g per fish day?1 compared with 1.1–1.6 g per fish day?1 for younger fish (3). The comparable ranges for mrigal were 1.9–2.8 and 1.4–2.1 g per fish day?1. Growth of Nile tilapia was inversely related to duration of carp nursing at the four levels of fertilization. Nile tilapia showed more response to increasing levels of fertilizer input (Y=?1.421+1.716X, where Y is the daily weight gain of Nile tilapia and X is the fertilizer level, r2=0.98, P<0.01, n=12). At a high level of fertilization (3.0 kg N:1.5 kg P ha?1 day?1), performance of stunted fingerlings (5 and 12) of both rohu and mrigal was similar (range 2.3–2.8 g per fish day?1, P>0.05), but younger mrigal (M3) grew faster than rohu (2.1 g per fish day?1 and 1.6 g per fish day?1 respectively). Older rohu (12) appeared to perform particularly well, and Nile tilapia poorly at the lowest level of fertilization (1.5 N:0.75 kg P ha?1 day?1), suggesting the impact of age of seed on competition within polycultures. The net fish yield (NFY) of tilapia was not affected significantly (P>0.05) by differential stocking age of carps; therefore, combined NFY of the three experimental fish species was not affected by the age of carp, as tilapia was the dominant species in polyculture. The highest combined NFY of all species in the most intensively fertilized pond (3.0 N:1.5 P kg ha?1 day?1) was calculated at 4.06±0.08 g·m?2 day?1, which was significantly higher (P<0.001) than the yield (1.82±0.12 g·m?2 day?1) from the pond with the lowest fertilization. At the highest fertilizer level, tilapia, rohu and mrigal contributed 72%, 14% and 14%, respectively, to the NFY, whereas the ratio was 60%, 20% and 20% at the lowest fertilization level. The study indicated that yields from tilapia in polyculture with the two carp species in more eutrophic water can be optimized if advanced nursing of carps is practised. Moreover, higher inputs of inorganic fertilizer and advanced nursing of carp are economically attractive under Bangladeshi conditions. Advanced nursing of rohu also improves its performance in more extensive systems when tilapia densities are high. 相似文献
940.
添加不同构型肉碱对于罗非鱼生长和鱼体营养成分组成的影响 总被引:13,自引:0,他引:13
在饲料中分别添加 2 0 0mg·kg-1,40 0mg·kg-1的DL -肉碱和 2 0 0mg·kg-1的L -肉碱 ,饲养初始重为38.6 5± 0 .2 1g的罗非鱼 ,经过 34d的生长试验 ,观察不同添加量的DL -肉碱与L -肉碱对于罗非鱼生长情况、机体营养成分组成的影响。实验结果表明 ,添加两种构型肉碱对于罗非鱼并无促生长作用 ,也未明显改变全鱼和肌肉的营养成分组成 ,但是对于改变罗非鱼内脏相对重量、降低肝脂则有一定作用 ,这些作用和影响在相同添加量 (2 0 0mg·kg-1)的DL -肉碱与L -肉碱之间无显著差异 (P >0 .0 5 )。 相似文献