全文获取类型
收费全文 | 378篇 |
免费 | 32篇 |
国内免费 | 1篇 |
专业分类
林业 | 14篇 |
农学 | 4篇 |
基础科学 | 4篇 |
53篇 | |
综合类 | 66篇 |
农作物 | 9篇 |
水产渔业 | 20篇 |
畜牧兽医 | 225篇 |
园艺 | 1篇 |
植物保护 | 15篇 |
出版年
2023年 | 3篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 16篇 |
2012年 | 26篇 |
2011年 | 19篇 |
2010年 | 6篇 |
2009年 | 9篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 12篇 |
2005年 | 13篇 |
2004年 | 8篇 |
2003年 | 18篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 17篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1995年 | 4篇 |
1993年 | 3篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1979年 | 3篇 |
1977年 | 8篇 |
1974年 | 5篇 |
1972年 | 6篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1966年 | 3篇 |
1957年 | 2篇 |
1941年 | 2篇 |
1938年 | 2篇 |
排序方式: 共有411条查询结果,搜索用时 15 毫秒
131.
Here we review information on maternal behaviour in dogs, defined as a combination of all the acts of the mother towards her offspring, which begins before parturition and continues until weaning. In dogs, maternal care is measured using the most commonly observed behaviours, such as the time spent in contact, licking/grooming and nursing of the puppies. Since newborn puppies have a very limited capacity for movement, maternal interaction is essential to their survival, nourishment and protection. It is also an important element of the bonding process between puppies and the bitch and is thought to play a role in the social development of the puppies. Nevertheless, some questions still need to be clarified, such as the best way to quantify factors that may interfere with maternal behaviour. In recent studies, maternal care, or maternal style, was measured using a scoring system and found to be influenced by factors such as litter size, breed and parity, or even human interaction. However, the impact of the emotional state of the bitch and the quality of maternal behaviour on puppy survival and development remain unclear. The long-lasting effects of mother–puppy interactions on puppy behaviour during their adult life are still poorly understood, despite their importance for breeders who wish to prevent future problem behaviours. 相似文献
132.
Thermal shock can disrupt meiosis II in fish oocytes, producing embryos with an extra set of maternal chromosomes from the second polar body; such shocks have been used to induce diploid gynogenesis or triploidy with varied success in different salmonid species. We investigated the effect of thermal shocks on the success of inducing diploid gynogenesis in chinook salmon (Oncorhynchus tshawytscha) oocytes. Different times of initiation (8, 16, and 24 min post-activation) resulted in similar survival. A treatment duration of 20 min resulted in significantly higher gynogen survival to hatch compared to 5 or 15 min, and a 10-min duration resulted in the lowest mean survival. The effect of temperature on induced retention of the second polar body is unclear due to varied results dependent on the maternal egg source; however, the mean survival to hatch for 25°C treatment groups was significantly higher than the mean of 29°C groups. 相似文献
133.
Th. Beck 《植物养料与土壤学杂志》1971,130(1):68-81
The determination of Catalase Activity in Soils by Dr. Beck 1. The elaboration of a method for the determination of the activity of catalase in soils is described. The method envolves the gasvolumetric determination of oxygen released by decomposition of a H2O2-solution by soils, suspended in buffers in the presence and absence of the catalase inhibitor NaN3. 2. The influences of the following factors on catalase activity were studied: Methods for the determination of developed oxygen, enzyme- and substrate concentration, inhibition of catalase by NaN3, pH- and temperature-optima of catalase and the presence of plant residues in soils. 3. It was found, that there was only a little decrease in catalase activity when fresh or dried samples of soils were stored over a periode of 4 months under laboratory conditions. The catalase activity of different soils showed very good correspondence to the dehydrogenase activity of the soils and less correspondence to the amount of soil respiration and the amylase activity. No relation could be found to the number of microorganisms in soil. 相似文献
134.
135.
Beck A Baird JD Slavić D 《The Canadian veterinary journal. La revue veterinaire canadienne》2011,52(5):513-514
This is the first report of the isolation of Actinomyces denticolens, an opportunistic pathogen, from a draining submandibular lymph node abscess in a horse in Ontario. Due to the similarity of the clinical signs with strangles, this pathogen should be included in the differential diagnosis of submandibular lymphadenopathy in the horse. 相似文献
136.
A total of 131 faecal samples from 57 mammalian species housed at the zoo of Zagreb, Croatia, were tested for the presence of Giardia spp. cysts using epifluorescence microscopy. The overall prevalence (29%) was high, yet all animals were asymptomatic at the time of sampling. Positive samples were characterized by PCR and sequence analysis of both conserved and variable loci, for the identification of Giardia species and G. duodenalis assemblages and genotypes. Assemblages A and C were identified in Artiodactyla, assemblage B in Primates, Rodentia and Hyracoidea, and assemblages A, B, C and D, as well as Giardia microti, in Carnivora. Genotyping at the ITS1-5.8S-ITS2 region, at the triose phosphate isomerase, glutamate dehydrogenase and beta-giardin genes revealed extensive polymorphisms, particularly among assemblage B isolates. A phylogenetic analysis of concatenated sequences showed that isolates from captive mammals housed at the zoo are genetically different from isolates of human and domestic animal origin. This is the first survey in a zoological garden to include a molecular characterization of the parasite, and provides novel sequence data of G. duodenalis from many previously uncharacterized hosts. 相似文献
137.
Saving the sagebrush sea: An ecosystem conservation plan for big sagebrush plant communities 总被引:6,自引:0,他引:6
Kirk W. Davies Chad S. Boyd Jeffrey L. Beck Jon D. Bates Tony J. Svejcar Michael A. Gregg 《Biological conservation》2011,144(11):2573-2584
Vegetation change and anthropogenic development are altering ecosystems and decreasing biodiversity. Successful management of ecosystems threatened by multiple stressors requires development of ecosystem conservation plans rather than single species plans. We selected the big sagebrush (Artemisia tridentata Nutt.) ecosystem to demonstrate this approach. The area occupied by the sagebrush ecosystem is declining and becoming increasingly fragmented at an alarming rate because of conifer encroachment, exotic annual grass invasion, and anthropogenic development. This is causing range-wide declines and localized extirpations of sagebrush associated fauna and flora. To develop an ecosystem conservation plan, a synthesis of existing knowledge is needed to prioritize and direct management and research. Based on the synthesis, we concluded that efforts to restore higher elevation conifer-encroached, sagebrush communities were frequently successful, while restoration of exotic annual grass-invaded, lower elevation, sagebrush communities often failed. Overcoming exotic annual grass invasion is challenging and needs additional research to improve the probability of restoration and identify areas where success would be more probable. Management of fire regimes will be paramount to conserving sagebrush communities, as infrequent fires facilitate conifer encroachment and too frequent fires promote exotic annual grasses. Anthropogenic development needs to be mitigated and reduced to protect sagebrush communities and this probably includes more conservation easements and other incentives to landowners to not develop their properties. Threats to the sustainability of sagebrush ecosystem are daunting, but a coordinated ecosystem conservation plan that focuses on applying successful practices and research to overcome limitations to conservation is most likely to yield success. 相似文献
138.
Responses of herbage P,Ca, K and Mg content and Ca/P and K/(Ca + Mg) ratios to long‐term continuous and discontinued cattle grazing on a rough fescue grassland 下载免费PDF全文
X. Gao X. Hao D. H. Marchbank R. Beck W. D. Willms M. Zhao 《Grass and Forage Science》2017,72(3):581-589
Herbage minerals affect performance of grazing cattle. We investigated the response of herbage P, K, Ca and Mg contents and Ca/P and K/(Ca + Mg) ratios to long‐term stocking rate, continuous vs. discontinued grazing practice, and sampling year. Cattle had been stocked at 2·4 and 4·8 animal unit months ha?1 since 1949. Exclosures were installed in April 1998. Herbage samples were collected near peak herbage mass in 2001, 2003, 2008 and 2012 and analysed for mineral content. Mineral contents were similar between the two stocking rates, but were lower (P < 0·05) under discontinued than continuous stocking, with the exception of similar P contents. The content of P and K in herbage was higher and the content of Ca and Mg was lower (P < 0·05) in years with greater precipitation and lower temperatures. Herbage mineral content, with the exception of P, exceeded minimum recommended levels for cattle. Given the low P content in herbage (0·74–1·19 g kg?1) and high Ca/P ratios during the dry and hot year (of 2001), a dietary P supplement should be considered for cattle grazing rough fescue grassland in drought years. The low K/(Ca + Mg) ratios (<2·2) suggest there is little risk of grass tetany in cattle grazing on this grassland. 相似文献
139.
140.