全文获取类型
收费全文 | 2301篇 |
免费 | 253篇 |
国内免费 | 32篇 |
专业分类
林业 | 209篇 |
农学 | 118篇 |
基础科学 | 74篇 |
153篇 | |
综合类 | 1025篇 |
农作物 | 68篇 |
水产渔业 | 378篇 |
畜牧兽医 | 392篇 |
园艺 | 33篇 |
植物保护 | 136篇 |
出版年
2024年 | 10篇 |
2023年 | 48篇 |
2022年 | 52篇 |
2021年 | 109篇 |
2020年 | 77篇 |
2019年 | 118篇 |
2018年 | 98篇 |
2017年 | 97篇 |
2016年 | 92篇 |
2015年 | 91篇 |
2014年 | 108篇 |
2013年 | 196篇 |
2012年 | 159篇 |
2011年 | 165篇 |
2010年 | 121篇 |
2009年 | 116篇 |
2008年 | 115篇 |
2007年 | 118篇 |
2006年 | 132篇 |
2005年 | 106篇 |
2004年 | 55篇 |
2003年 | 66篇 |
2002年 | 52篇 |
2001年 | 51篇 |
2000年 | 38篇 |
1999年 | 25篇 |
1998年 | 14篇 |
1997年 | 30篇 |
1996年 | 17篇 |
1995年 | 24篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 16篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
排序方式: 共有2586条查询结果,搜索用时 13 毫秒
101.
102.
Two experiments were carried out to study the grunting of sows during nursing and the sucking be-haviour of piglets. In experimental I,six Yorkshire sows and their litters were observed and managed in farrowing crates.In experimental Ⅱ,six Harbin White sows and their litters were selected and housed in farrowing pens.The behaviours and activities of the sows during nursing and the actities of piglest during sucking were recorded with a portable video camera (PanasonicNV-VX22EN)The results showed that the characteristic patterns of grunting by the sows consist of an initial period of rhythmic grunting at a fairly constant rate and followesd by a period of more rapid grunting,and then a decline in grunting rate toward the completion of nursing.The pattern of vocalization showed by the mothers bears a reliable synchronization to the sucking behaviour of the piglets.The rate of grunting varied little during jostling for teat and nosing the udder.The beginning of slow sucking usually occurred during of just after the increase in grunt rate.The rapid sucking began 15-25seconds after the period of most rapid grunting,fol-lowingthe decrease of grunt rate.afterwards the nursing ended.There were individualities found in sows‘grunting patterns.It is found that vocalizations attracted the piglets to the sows and synchronized sucking activities of piglets,but the results indicated that the premassaging time and numbers of piglets enagaing massaging influ-enced the grunting pattern and the onset of the milk ejection.As more piglets were involved the massaging,the higher the grunting rate peak,the faster the milk ejection. 相似文献
103.
《Journal Of Agricultural & Food Information》2013,14(4):15-46
ABSTRACT The Grange was founded during a time when farmers were the majority of the population and secrecy was a means of survival. More than one hundred thirty-five years later, those characteristics are still strongly associated with it. Yet there is a growing consciousness among many members that the Grange has to become better at promoting itself among nontraditional constituencies-or it will die. This article explores the Grange experiences of five members. All have been profoundly affected by their membership. All are struggling with the need to reconcile loyalty to tradition with the need to change and adapt. In sharing their thoughts and feelings, the study has the opportunity to consider what the Grange's past was, what its present is, and what its future may become. 相似文献
104.
有效的社会管理是经济持续健康发展的前提,是社会稳定的基石.当前,我国正处在经济社会转型的重要时期,伴随着经济的快速增长,各类社会矛盾和社会问题呈现出多样、多发的态势,这给社会的管理带来了新的挑战.我们必须加强和创新社会管理,在战略全局上重视,同时注重改善民生、加强对权力的监督、建立健全的制度等不断提升和创新社会管理的整体实力. 相似文献
105.
潘明娟 《干旱区资源与环境》2013,(9):54-59
根据地方灾害史料记载,统计出唐代关中旱灾的发生规律。结果表明:唐代290年的时间内,共发生旱灾112年次,可以按照旱灾发生的频率将唐代划分为五个阶段。关中旱灾的连续性特征非常明显,连续三年以上的干旱链现象突出。旱灾在月份和季节中的分布极不均匀,季节性连续干旱偏多。唐代关中旱灾灾情较为严重。频繁的旱灾给唐代关中地区的社会生活和自然环境带来了极大的影响。 相似文献
106.
M. C. Makrakis L. E. Miranda S. Makrakis D. R. Fernandez J. O. Garcia J. H. P. Dias 《Ecology of Freshwater Fish》2007,16(3):410-416
Abstract – We studied the migratory behaviour of armado, Pterodoras granulosus , in the Paraná River Basin of Brazil, Paraguay and Argentina, during 1997–2005. This species invaded the Upper Paraná River after upstream dispersal was facilitated when Itaipu Reservoir inundated a natural barrier. Fish were tagged ( N = 8051) in the mainstems of the Yacyreta and Itaipu reservoirs, bays of major tributaries, the Paraná River floodplain above Itaipu Reservoir, and below dams. In all, 420 fish were recaptured of which 61% moved away from the release area. Fish moved a maximum of 215 km (mean 42), and at a maximum rate of 9.4 km·day−1 (mean 0.6). Of the 256 armados that moved away from the release site, 145 moved upstream towards unimpounded stretches of the Paraná River and 111 moved downstream into the reservoir and bays of its tributaries (maximum 150 km). Based on the observed migratory movements, we suspect that most of the reproductive output originates in tributaries to the reservoirs. The ability of this species to expand its range presents a conundrum by pitting fishery management interests against conservation needs. Maintenance of the important armado fisheries depends on the ability of the species to migrate freely to use spawning and nursery areas in reservoir tributaries and floodplains. However, its ability to migrate long distances can allow this non-native species the opportunity to invade most of the Upper Paraná River. 相似文献
107.
从江泽民同志“四个同样重要”理论出发,结合云南农业大学大学精神建设、社会科学学科建设、学报社科版建设以及校园文化建设等方面的基本情况,论证了进一步解放思想对于繁荣高校哲学社会科学的重要意义。 相似文献
108.
Abstract – Topeka shiners ( Notropis topeka ), an endangered minnow species, typically spawn on or around breeding Lepomis sunfish (Centrarchidae) nests. Why spawning Topeka shiners are attracted to these nests is unclear, but having the nesting sunfish provide shiner eggs with improved aeration, a lessening of siltation, and protection from egg predators are possibilities. We tested the substrate utilisation of Topeka shiners in outdoor tanks in the absence of sunfish to determine the shiner's fundamental choice. Shiners were provided with substrate patches of cleaned sand, small gravel, large gravel, and small cobble, and the bare floor of the tank. The substrate above which a male shiner established his territory was used as evidence of choice. A statistically significant choice for sand substrates was demonstrated. This fundamental choice might influence which sunfish nests Topeka shiners use, given that nest substrate characteristics differ both between sunfish species and within species by spawning site location. 相似文献
109.
K.H. Walker L.R. Fell L.A. Reddacliff R.J. Kilgour J.R. House S.C. Wilson P.J. Nicholls 《Livestock Science》2007,106(2-3):210-217
Two experiments were conducted to determine the effect of weaning in small yards, with or without a feed bunk training procedure, on the subsequent behaviour and performance of Bos taurus steers in a feedlot. A reduction in the incidence of bovine respiratory disease (BRD) was the primary objective. In each experiment, about 200 male beef calves (Angus × Hereford and Hereford) were separated from their mothers at 7–9 months of age and allocated to one of three matched weaning treatment groups. The treatments were (1) yard weaning with hay or silage, (2) yard weaning with hay or silage plus a novel handling procedure to train the animals to be able to find a grain ration in a trough, and (3) paddock weaning without supplement or handling according to common industry practice in southeastern Australia. Paddock weaning is the practice of abrupt separation of cows and calves followed by return to separate pasture paddocks, whereas yard weaning involves abrupt separation but the calves remain in the yards for several days. Experimental vaccines against the major BRD pathogens were given to half of each group 1–2 months prior to entry into a commercial feedlot. The yard weaned and yard trained cattle had a significantly greater weight gain in the first month and over the 90-day feeding period than the paddock weaned control groups. There was no difference between the groups in pre-feedlot weight gain. The yard trained groups showed greater feeding activity during the first few days in the feedlot, but were not significantly different in weight gain from yard weaned. The vaccination treatment also significantly improved the weight gain in the first month and over 80 days. The combination of yard weaning and vaccination produced the highest weight gains overall. There was consistently less morbidity in the yard weaned groups compared to paddock weaned controls. The morbidity in yard trained groups was intermediate between these two. Weaning in small yards and the appropriate use of effective BRD vaccines 1–2 months before feedlot entry are recommended for B. taurus feeder steers in southeastern Australia to minimise sickness and improve productivity in the feedlot. Associated benefits are reduced risks of antibiotic residues and of animal welfare problems. 相似文献
110.