全文获取类型
收费全文 | 3396篇 |
免费 | 170篇 |
国内免费 | 360篇 |
专业分类
林业 | 310篇 |
农学 | 310篇 |
基础科学 | 234篇 |
661篇 | |
综合类 | 1389篇 |
农作物 | 150篇 |
水产渔业 | 95篇 |
畜牧兽医 | 519篇 |
园艺 | 76篇 |
植物保护 | 182篇 |
出版年
2024年 | 23篇 |
2023年 | 69篇 |
2022年 | 120篇 |
2021年 | 123篇 |
2020年 | 145篇 |
2019年 | 141篇 |
2018年 | 88篇 |
2017年 | 128篇 |
2016年 | 163篇 |
2015年 | 132篇 |
2014年 | 175篇 |
2013年 | 179篇 |
2012年 | 211篇 |
2011年 | 248篇 |
2010年 | 202篇 |
2009年 | 205篇 |
2008年 | 143篇 |
2007年 | 220篇 |
2006年 | 173篇 |
2005年 | 164篇 |
2004年 | 124篇 |
2003年 | 104篇 |
2002年 | 76篇 |
2001年 | 112篇 |
2000年 | 81篇 |
1999年 | 60篇 |
1998年 | 54篇 |
1997年 | 44篇 |
1996年 | 35篇 |
1995年 | 37篇 |
1994年 | 21篇 |
1993年 | 25篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有3926条查询结果,搜索用时 93 毫秒
61.
《The Journal of Applied Poultry Research》2006,15(1):82-88
The reproductive performance of 2 commercial turkey breeder lines was examined using reciprocal crosses between sires and dams of each line. One line had been selected using artificial inseminations performed at biweekly intervals, whereas the second line had been selected using inseminations performed at weekly intervals. The hypothesis was proposed that sires and dams of the 2 lines differ because of different abilities for sperm to penetrate the inner perivitelline layer (IPVL) and fertilize eggs.Fertilized eggs to hatch poults for the experiment were obtained from the primary breeders and were incubated using conditions recommended by the industry. Hens (n = 72) and toms (n = 15) from each strain were identified and reared in preparation for a reproductive cycle using commercially accepted standards. Beginning just prior to the onset of egg production and at weekly intervals thereafter, half of the hens were inseminated with semen from males of the same line, whereas the remaining half received semen from the opposite line. Eggs were collected from the pens daily and set in incubators to determine fertility and embryo survival. At biweekly intervals 3 eggs per pen were used for counting sperm penetration holes in the IPVL. Data were collected for fertility, hatchability, and time that embryos died for each of the pens. Dam and sire affected IPVL penetration independently. A dam by sire interaction influenced fertility, whereas hatchability was affected only by dam. Thus, it is concluded that selection of dam and sires for commercial breeders alters IPVL sperm penetration ability of hens as well as egg-binding ability of sires. 相似文献
62.
猪苓菌丝体多糖对小鼠免疫水平的影响 总被引:6,自引:0,他引:6
通过人工液体浅层培养方式培养猪苓菌丝体,用热水浸提法提取猪苓菌丝体多糖(PPS1),经纯化测定其糖含量,用红外光谱分析鉴定多糖,纯化鉴定的PPS1,通过小鼠进行腹腔单核巨噬细胞功能测定试验、E玫瑰花环试验、足跖肿胀厚度试验、淋巴细胞转化试验、EAC花环试验等5项免疫学试验初步探讨其免疫药理学作用,同时与猪苓菌核多糖(PPS2)进行比较。试验数据经统计学分析显示,E玫瑰花环试验中PPS1与空白对照组相比差异显著(P〈0.05);腹腔单核巨噬细胞功能测定试验、足跖肿胀厚度试验、淋巴细胞转化试验覆EAC花环试验PPS1与空白对照组相比差异极显著(P〈0.01);5项免疫学试验PPS1与PPS2相比差异均不显著。结果表明,PPS1能明显提高小鼠的免疫功能。 相似文献
63.
Effects of deficit irrigation strategies on cluster microclimate for improving fruit composition of Moscatel field-grown grapevines 总被引:1,自引:0,他引:1
Tiago Pedreira dos Santos Carlos M. Lopes M. Lucília Rodrigues Claudia R. de Souza Jorge M. Ricardo-da-Silva João P. Maroco João S. Pereira M. Manuela Chaves 《Scientia Horticulturae》2007
The grapevine plays a very important role in the economic, social and cultural sectors of many regions; however vineyards are often grown in regions under stressful conditions and thus they are vulnerable to climate change. The objective of this research was to investigate the effect of partial root-zone drying (PRD) irrigation on vine water relations, vegetative growth, plant microclimate, berry composition and yield components, compared to conventional deficit irrigation (DI, 50% ETc), full irrigation (FI, 100% of ETc) and non-irrigated vines (NI). The study was undertaken in mature ‘Moscatel’ grapevines (Vitis vinifera L.) grown in Pegões, South of Portugal. Compared to the other irrigated treatments, PRD vines showed a better microclimate at the cluster zone with higher incident photosynthetic photon flux density (PPFD). Within the more open canopies of NI and PRD treatments, berry temperatures were higher than those of denser ones (DI and FI). Compared to the conventional irrigation technique the better microclimate observed in PRD vines was a consequence of a reduction in vine growth, where lower values of leaf layer number, leaf area, canopy wideness, water shoots and shoot weight were observed. In PRD vines we observed a tendency to a development of a deeper root system, while DI and FI showed a more homogeneous root distribution throughout the different soil layers. PRD showed an improvement in berry quality with higher values of flavour precursors, and total phenols concentration without any significant yield reduction compared to DI and FI. 相似文献
64.
65.
66.
67.
The role of tree diversity and identity as determinants of soil animal community structure is little understood. In a mature deciduous forest dominated by beech we identified clusters of one, two and three tree species of beech, ash and lime allowing to investigate the role of tree species diversity and identity on the density and community structure of oribatid mites. To relate oribatid mite community structure to environmental factors we measured leaf litter input, fine root biomass, mass of organic layers, topsoil pH and C and N content. We expected oribatid mite density to increase with increasing tree diversity, but we expected the effects of tree species identity to override effects of tree diversity. Further, we hypothesized the density of oribatid mites to be reduced by the presence of beech but increased by the presence of lime and ash. As expected tree diversity little affected oribatid mite communities, whereas tree species identity strongly altered density and community structure of oribatid mites. However, in contrast to our expectations the density of oribatid mites was highest in presence of beech indicating that many oribatid mite species benefit from the presence of recalcitrant litter forming thick organic layers. Especially Oppioidea benefited from the presence of beech presumably due to an increased availability of food resources such as fungi and nematodes. Lower density of oribatid mites in monospecific clusters of lime and ash suggests that oribatid mites did not benefit from high quality litter of these species. Notably, large and strongly sclerotized oribatid mite species, such as Steganacarus magnus and Chamobates voigtsi, benefited from the presence of ash and lime. Presumably, these large species better resist harsh microclimatic conditions in shallow organic layers. 相似文献
68.
研究应用EDTA法测定强化食品中活性钙提取条件的选择问题,提出用酸液提取活性钙的方法。 相似文献
69.
选取60头杜大长仔猪进行活性酵母菌对仔猪生长性能的影响试验,结果显示,饲料中添加活性酵母可以提高猪只的日增重、料肉比,在保育期添加活性酵母菌可以显著控制仔猪腹泻的发生,提高T淋巴细胞转化率,表明添加活性酵母菌在动物饲养过程中有良好的效果。 相似文献
70.