全文获取类型
收费全文 | 278篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
林业 | 17篇 |
农学 | 8篇 |
基础科学 | 1篇 |
40篇 | |
综合类 | 70篇 |
农作物 | 13篇 |
水产渔业 | 19篇 |
畜牧兽医 | 113篇 |
园艺 | 5篇 |
植物保护 | 13篇 |
出版年
2023年 | 4篇 |
2022年 | 2篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 4篇 |
2013年 | 17篇 |
2012年 | 23篇 |
2011年 | 24篇 |
2010年 | 10篇 |
2009年 | 7篇 |
2008年 | 19篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 16篇 |
2003年 | 14篇 |
2002年 | 15篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1997年 | 3篇 |
1995年 | 4篇 |
1993年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1948年 | 1篇 |
1947年 | 1篇 |
1919年 | 1篇 |
1886年 | 1篇 |
1884年 | 1篇 |
1883年 | 2篇 |
排序方式: 共有299条查询结果,搜索用时 281 毫秒
61.
A survey of the prevalence of anthelmintic resistant nematode populations was conducted on 32 sheep farms in the Slovak Republic. In vitro egg hatch test and larval development tests were used for the detection of resistance to benzimidazole anthelmintics and they were compared with in vivo faecal egg count reduction tests. There was agreement in the declaration of resistance between the faecal egg count reduction test and both in vitro tests. The presence of resistant populations was determined on two farms using egg hatch test. In both farms, the LD(50) values were higher than 0.1 microg TBZ/ml, indicating resistance. By using LD(99) values it might be possible to reveal relatively small proportion of resistant larvae in the population. The prevalence of benzimidazole resistance has not change on Slovak sheep farms during last decade. 相似文献
62.
Daniel R. Goethel Katelyn M. Bosley Brian J. Langseth Jonathan J. Deroba Aaron M. Berger Dana H. Hanselman Amy M. Schueller 《Fish and Fisheries》2021,22(1):141-160
Understanding spatial population structure and biocomplexity is critical for determining a species’ resilience to environmental and anthropogenic perturbations. However, integrated population models (IPMs) used to develop management advice for harvested populations have been slow to incorporate spatial dynamics. Therefore, limited research has been devoted to understanding the reliability of movement parameter estimation in spatial population models, especially for spatially dynamic marine fish populations. We implemented a spatial simulation–estimation framework that emulated a generic marine fish metapopulation to explore the impact of ontogenetic movement and climate‐induced distributional shifts between two populations. The robustness of spatially stratified IPMs was explored across a range of movement parametrizations, including ignoring connectivity or estimating movement with various levels of complexity. Ignoring connectivity was detrimental to accurate estimation of population‐specific biomass, while implementing spatial IPMs with intermediate levels of complexity (e.g. estimating movement in two‐year and two‐age blocks) performed best when no a priori information about underlying movement was available. One‐way distributional shifts mimicking climate‐induced poleward migrations presented the greatest estimation difficulties, but the incorporation of auxiliary information on connectivity (e.g. tag‐recapture data) reduced bias. The continued development of spatially stratified modelling approaches should allow harvested resources to be better utilized without increased risk. Additionally, expanded collection and incorporation of unique spatially explicit data will enhance the robustness of IPMs in the future. 相似文献
63.
Ecosystem services: Foundations,opportunities, and challenges for the forest products sector 总被引:2,自引:0,他引:2
The ecosystem service concept has been proposed as a meaningful framework for natural resource management. In theory it holds concomitant benefit and consequence for the forest product sector. However, numerous barriers impede practitioners from developing concrete and enduring responses to emerging ecosystem service markets, policies, and initiatives. Principle among these barriers is that the ecosystem service concept has a complex history, numerous definitions in use, and an astounding diversity in rationale and application. This article provides a conceptual review of ecosystem services and its economic foundations, distinguishes among several current definitions of the term and their relatedness to strategies in practical application, discusses diverse approaches to valuation, and explores potential for future relevance in forest product and other sectors. 相似文献
64.
The development and use of topical microbicides potentially offers an additional strategy to reduce the spread of the Human Immunodeficiency Virus (HIV). Carbohydrate-binding agents (CBAs) that show specificity for high mannose carbohydrates on the surface of the heavily glycosylated envelope of HIV are endowed with potent anti-HIV activity. In fact, a number of algal lectins such as cyanovirin-N, microvirin, microcystis viridis lectin, scytovirin, Oscillatoria agardhii agglutinin and griffithsin are considered as potential microbicide candidates to prevent the sexual transmission of HIV through topical applications. They not only inhibit infection of cells by cell-free virus but they can also efficiently prevent virus transmission from virus-infected cells to uninfected CD4(+) target T-lymphocytes and DC-SIGN-directed capture of HIV-1 and transmission to CD4(+) T lymphocytes. This review focuses on the structural properties and carbohydrate specificity of these algal lectins, their antiviral activity against HIV and several other enveloped viruses, their safety profile and viral resistance patterns. 相似文献
65.
The global seafood industry, influenced by consumer demand, is closely linked to the global fishing industry, which determines the variety of fish available for consumption. The recently revealed issue of seafood mislabelling threatens to weaken this link by removing consumer power to influence patterns of fisheries exploitation through informed choice. Recognizing this, there is an urgent need to go beyond the mere documentation of the phenomenon and learn more about the origins of this problem and the nature of factors influencing its occurrence to develop solutions. In an attempt to understand seafood mislabelling more thoroughly in Europe, 226 cod products were purchased from Ireland and the UK, genetically identified using a DNA barcoding technique (COI barcoding gene), and species identification results were compared against product labels. Cod mislabelling proved more severe in Ireland than in the UK (28.4% vs. 7.4%). Moreover, whereas data show that in Ireland, cheaper species are sold as cod, in the UK, threatened Atlantic cod (Gadus morhua) may be sold as ‘sustainably sourced’ Pacific cod. Considering these countries operate under the same EU policies for seafood traceability and labelling, it is likely that this situation has been influenced by heightened consumer awareness in the UK, which has created an environment where mislabelling is discouraged. In addition to identifying samples, traceability information from packaged cod was used to trace products back to supplying companies. Although inconclusive in determining blame, this exercise has demonstrated that using traceability information can add explanatory power when attempting to determine responsibility for the occurrence of mislabelling. 相似文献
66.
67.
68.
69.
Genetic and phenotypic parameter estimates for body weights and egg production in Horro chicken of Ethiopia 总被引:1,自引:0,他引:1
Nigussie Dana E. H. vander Waaij Johan A. M. van Arendonk 《Tropical animal health and production》2011,43(1):21-28
A breeding program has been established in 2008 to improve productivity of Horro chicken, an indigenous population in the
western highlands of Ethiopia. The pedigree descended from 26 sires and 260 dams. Body weights were measured every 2 weeks
from hatch to 8 weeks then every 4 weeks for the next 8 weeks. Egg production was recorded to 44 weeks of age for one generation.
Genetic parameters were estimated using animal model fitted with common environmental effects for growth traits and ignoring
common environment for egg production traits. Direct heritabilities ranged from low (0.15 ± 0.08), for body weight at 6 weeks,
to moderate (0.40 ± 0.23), for hatch weight. Heritabilities of common environmental effects on growth were high at hatch (0.39 ± 0.10)
and remained low afterwards. Age at first egg showed a very low heritability (0.06 ± 0.15). Heritabilities of egg numbers
in the first, second, third, and fourth months of laying were 0.32 (±0.13), 0.20 (±0.16), 0.56 (±0.15), and 0.25 (±0.14),
respectively. Heritabilities of cumulative of monthly records of egg numbers were from 0.24 ± 0.16 (for the first 2 months,
EP12) to 0.35 ± 0.16 (over the 6 months, EP16). Body weight at 16 weeks of age (BW16) has a strong genetic correlation with
the cumulative of monthly records: 0.92 (with EP12), 0.69 (with EP36), and 0.73 (with EP16). Besides their strong association,
BW16 and EP16 showed higher heritability, relative to their respective trait categories. These two traits seemed to have common
genes and utilizing them as selection traits would be expected to improve both egg production and growth performance of local
chicken. However, the standard errors of estimates in this study were mostly high indicating that the estimates have low precision.
Parameter estimations based on more data are needed before applying the current results in breeding programs. 相似文献
70.