全文获取类型
收费全文 | 263篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
林业 | 67篇 |
农学 | 9篇 |
基础科学 | 2篇 |
68篇 | |
综合类 | 28篇 |
农作物 | 4篇 |
水产渔业 | 3篇 |
畜牧兽医 | 70篇 |
园艺 | 6篇 |
植物保护 | 19篇 |
出版年
2021年 | 3篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 5篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1987年 | 3篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 4篇 |
1970年 | 3篇 |
1967年 | 2篇 |
1955年 | 3篇 |
1954年 | 2篇 |
1953年 | 5篇 |
1948年 | 2篇 |
1937年 | 5篇 |
1936年 | 6篇 |
1935年 | 4篇 |
1934年 | 6篇 |
1933年 | 8篇 |
1932年 | 2篇 |
1931年 | 2篇 |
1929年 | 2篇 |
1908年 | 2篇 |
排序方式: 共有276条查询结果,搜索用时 171 毫秒
271.
272.
Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability 总被引:6,自引:0,他引:6
Preserving multicentennial climate variability in long tree-ring records is critically important for reconstructing the full range of temperature variability over the past 1000 years. This allows the putative "Medieval Warm Period" (MWP) to be described and to be compared with 20th-century warming in modeling and attribution studies. We demonstrate that carefully selected tree-ring chronologies from 14 sites in the Northern Hemisphere (NH) extratropics can preserve such coherent large-scale, multicentennial temperature trends if proper methods of analysis are used. In addition, we show that the average of these chronologies supports the large-scale occurrence of the MWP over the NH extratropics. 相似文献
273.
T. Druet S. Fritz E. Sellem B. Basso O. Gérard L. Salas-Cortes P. Humblot X. Druart & A. Eggen 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2009,126(4):269-277
A QTL detection experiment was performed in French dairy cattle to search for QTL related to male fertility. Ten families, involving a total of 515 bulls, were phenotyped for ejaculated volume and sperm concentration, number of spermatozoa, motility, velocity, percentage of motile spermatozoa after thawing and abnormal spermatozoa. A set of 148 microsatellite markers were used to realize a genome scan. First, genetic parameters were estimated for all traits. Semen production traits were found to have moderate heritabilities (from 0.15 to 0.30) while some of the semen quality traits such as motility had high heritabilities (close to 0.60). Genetic correlations among traits showed negative relationships between volume and concentration and between volume and most quality traits such as motility or abnormal sperm while correlations between concentration and these traits were rather favourable. Percentages of abnormal sperm were negatively related to quality traits, especially with motility and velocity of spermatozoa. Three QTL related to abnormal sperm frequencies were significant at p < 0.01. In total, 11 QTL (p < 0.05) were detected. However, the number of QTL detected was within the range of expected false positives. Because of the lack of power to find QTL in this design further analyses are required to confirm these QTL. 相似文献
274.
Identification of trees with key microhabitats as well as knowledge of their ecological formation is important for the conservation of epiphytic bryophytes and lichens on beech. Based on the hypothesis that certain types of stem damage are crucial for the occurrence of epiphytes of conservation concern, we surveyed 145 beech trees (57-280 years) for different types of stem damage and analysed their relationship to other tree characteristics, epiphyte species and wood-inhabiting fungi in a forest landscape on acid soils.Three main types of stem damage were identified; canker, rot hole and surface rot. The incidence of rot holes was highest on trees with a low growth rate during the last 50 years, but was unrelated to tree size or age per se. Bark pH was significantly higher below than above rot holes, whereas no such relationship was found for cankers. Wood mould from rot holes had a very high pH, explaining the higher bark pH below this type of damage. The number of epiphyte species of conservation concern was strongly positively related to rot holes and high bark pH. Cankers had a weaker, yet significant positive effect. The fungus Psathyrella cernua was associated with the rot holes and is suggested to be a key species involved in creating this microhabitat.We conclude that slow-growing trees with rot holes are important for the conservation of epiphytes and should be selected as retention trees in managed forests. The study also highlights a potential for habitat restoration by inducing artificial damage and inoculation of decay fungi in beech trees. 相似文献
275.
Two related segregating populations of Theobroma cacao L. were analysed for their resistance to Phytophthora palmivora. The first F1 population was obtained by crossing two susceptible cacao clones of Catongo (a highly homozygous genotype) and Pound 12(a
highly heterozygous genotype) and the second population was obtained by backcrossing a single F1 tree with Catongo. The genetic maps obtained for each population were compared. The F1 map includes 162 loci and the backcross has 140 loci. The two maps, F1 and BC1, exhibit high co-linear loci organization covering respectively, 772 and 944 cM.Phytophthora resistance was assessed by measuring the size increase of a lesion at five (DL5)and ten days (DL10) after pod inoculation.
Six different QTL were detected in the F1 and BC1 populations. One QTL was found in both populations, and appeared to be a major component of disease resistance, and explaining
nearly 48% of the phenotypic variance in the F1 population. The absence of some yield QTL detection in the BC1 in comparison with the F1 population is due to the lack of transmission of the favouring alleles for these QTL from the single F1 tree used for the backcross. The phenotypic variance explained by the action of the quantitative trait alleles indicated
that genetic factors of both major and minor effects were involved in the control of the character studied. QTL conferring
increased resistance to Phytophthorawere identified in both susceptible parents, suggesting the presence of transgressive traits and the possibility of selection
in cacao. Pleiotropic and epistatic effects for the QTL were also detected. Finally, the use of marker assisted selection
(MAS) in cacao breeding programs is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
276.
When mycelium of Botrytis cinerea was treated with low concentrations of the anilinopyrimidine fungicide pyrimethanil the total amount of free amino acids increased. Qualitative variations were also induced: alanine, glutamine, lysine, glycine, histidine, asparagine, arginine, threonine and moreover, α-aminobutyrate and β-alanine were accumulated; cyst(e)ine, valine, leucine and citrulline were reduced. When mycelium of B. cinerea was incubated with Na2[35S]O4, pyrimethanil at 1·5 μM induced a decrease of [35S]methionine and simultaneously an increase of [35S]cystathionine. These data indicate that the anilinopyrimidine fungicide pyrimethanil inhibits the biosynthesis of methionine and suggest that the primary target could be the cystathionine β-lyase. © 1997 SCI. 相似文献