全文获取类型
收费全文 | 223篇 |
免费 | 9篇 |
专业分类
林业 | 34篇 |
农学 | 3篇 |
基础科学 | 1篇 |
26篇 | |
综合类 | 17篇 |
农作物 | 10篇 |
水产渔业 | 22篇 |
畜牧兽医 | 102篇 |
园艺 | 14篇 |
植物保护 | 3篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 11篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有232条查询结果,搜索用时 312 毫秒
41.
42.
Formation of harvest units with genetic algorithms 总被引:6,自引:0,他引:6
Operational planning is normally based on stands as the primary unit of treatment. In recent years, interest has been directed towards the use of smaller area units such that the formation of treatment units becomes part of the operational planning. Here, the method of genetic algorithms was used in order to delineate harvesting units in a forest described as a grid of 20 m × 20 m pixels. Remote sensing data and inventory plots were employed to derive pixel estimates of forest variables. Appropriate parameter settings for the algorithm were investigated for two cases that consisted of 26 × 25 pixels. Based on the experience from these tests, the algorithm was employed in forming treatment units in an area encompassing 100 × 100 grid cells, or 400 ha. Due to the size of the problem, a two-stage procedure was suggested. The solutions of the genetic algorithm were compared with a heuristic, a cell removal algorithm, that was proposed in earlier studies of treatment unit formation. The genetic algorithm performed better than the heuristic for all the cases that were tested. 相似文献
43.
Dannylo O. Sousa Hanne H. Hansen Ola Hallin Luiz G. Nussio Elisabet Nadeau 《Grass and Forage Science》2020,75(1):76-85
Red clover (Trifolium pratense) and lucerne (Medicago sativa) are among the most common legume species used for ruminant feeding systems. Besides the greater nutritive quality and first-year ley yield compared to lucerne, red clover decreases its yield over the years. However, under unfavourable soil conditions the persistency of lucerne can be compromised, not performing as expected. This study compared yield and chemical composition of eight lucerne cultivars and one tetraploid red clover cultivar, with similar growth capacity as lucerne, replicated over two years. In the second year, four lucerne cultivars and the red clover cultivar were analysed for crude protein (CP) fractions, dry matter and neutral detergent fibre (NDF) digestibility. A randomized block design was used with three field blocks per cultivar for the multiple comparisons within each year. There were differences in DM yield, concentrations of CP and NDF and CP fractions among the lucerne cultivars, but the differences were inconsistent between years and between growth cycles within year. The red clover cultivar had lower CP and NDF concentrations than a majority of the lucerne cultivars, and greater in vitro organic matter digestibility compared to all of the lucerne cultivars. Also, the red clover cultivar had greater rumen undegradable-to-degradable CP ratio but confirmed its lower yield persistency compared to the lucerne cultivars. 相似文献
44.
45.
Anna M. Johansson Maulik Upadhyay Erling Strandberg Susanne Eriksson 《Acta Agriculturae Scandinavica, Section A - Animal Sciences》2020,69(1-2):39-46
ABSTRACTThe Swedish Mountain (Fjäll) cattle and the subpopulation Fjällnära originates from northern Sweden. They are differentiated from both traditional and commercial cattle from southern Sweden. We analysed data from the GGP HD150k SNP array and investigated genetic diversity and differences between Fjäll and Fjällnära, and between different groups of Fjällnära. We found that the Fjällnära can be divided into four groups, which are differentiated from each other and from the other Fjäll cattle. We also compared allele frequencies between different groups of Fjäll and Fjällnära for some of the functional SNPs included in the SNP array. Interestingly, the B allele of Beta lactoglobulin has a very high frequency (94%) in the Fjällnära cattle, which is significantly different from the frequency in the Fjäll cattle (60%). Comparing older samples of Fjäll cattle with more recent samples, we found a significant increase in the frequency of the B allele in Fjäll cattle. 相似文献
46.
Ola Syrstad 《Livestock Production Science》1985,13(4):351-357
Data extracted from reports on cross-breeding of Bos taurus and Bos indicus cattle for milk production were used to compare the merits of various Bos taurus breeds for this purpose. The study was restricted to projects in which two or more taurus breeds had been used simultaneously, and to records on F1 crosses. The only taurus breeds represented were Friesian, Brown Swiss and Jersey.Brown Swiss crosses were the oldest and Jersey crosses the youngest at first calving; both differed significantly from Friesian crosses. In milk yield Friesian crosses were the highest and Jersey crosses the lowest, and again all differences were significant. Jersey crosses had significantly shorter calving intervals than the other crosses.The ranking of the crosses was very consistent across projects. The difference in milk yield between Friesian and Jersey crosses increased proportionately with level of production. 相似文献
47.
S Aiumlamai H Kindahl G Fredriksson L E Edqvist L Kulander O Eriksson 《Acta veterinaria Scandinavica》1992,33(2):117-127
Experimentally induced ruminal acidosis was carried out in 4 calves to investigate the possibility of resorption of endotoxins from Gram negative bacteria originating from the gastro-intestinal tract. The ruminal acidosis was induced by overfeeding of oats and the effect was evaluated by clinical and blood biochemical changes. Blood samples were collected every 2 h for 60 h before and after experimental feeding. The animals showed signs of ruminal acidosis and also the clinical and blood biochemical changes were similar to those seen after experimental endotoxaemia. However, although being less dramatic the changes in many relevant parameters such as an increase in prostaglandin F metabolite levels, body temperature, endotoxins and a decrease in iron indicate that an endotoxaemic state had occurred. The results of the present study show that ruminal acidosis/stasis is linked to resorption of endotoxins from the gastro-intestinal tract causing endotoxaemia/endotoxicosis. 相似文献
48.
Ola Syrstad 《Livestock Production Science》1985,12(4):299-307
Data extracted from reports on Bos taurus × Bos indicus crossbreeding were used to estimate the amount of heterosis in these crosses. Traits studied were age at first calving, milk yield, lactation length, and calving interval. The estimates obtained were (percent of midparent means in parentheses):
Age at first calving | ?3.2 to ?4.4 months | (?8 to ?12%) |
Milk yield | 287 to 400 kg | (18 to 25%) |
Lactation length | 7 to 15 days | (2 to 5%) |
Calving interval | ?30 to ?31 days | (?7%) |