全文获取类型
收费全文 | 920篇 |
免费 | 35篇 |
专业分类
林业 | 468篇 |
农学 | 8篇 |
106篇 | |
综合类 | 56篇 |
农作物 | 16篇 |
水产渔业 | 30篇 |
畜牧兽医 | 196篇 |
园艺 | 24篇 |
植物保护 | 51篇 |
出版年
2022年 | 10篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 11篇 |
2017年 | 23篇 |
2016年 | 24篇 |
2015年 | 16篇 |
2014年 | 23篇 |
2013年 | 23篇 |
2012年 | 39篇 |
2011年 | 46篇 |
2010年 | 20篇 |
2009年 | 23篇 |
2008年 | 34篇 |
2007年 | 36篇 |
2006年 | 42篇 |
2005年 | 26篇 |
2004年 | 30篇 |
2003年 | 23篇 |
2002年 | 19篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1995年 | 4篇 |
1987年 | 5篇 |
1948年 | 30篇 |
1944年 | 5篇 |
1943年 | 13篇 |
1942年 | 49篇 |
1941年 | 32篇 |
1940年 | 36篇 |
1939年 | 45篇 |
1938年 | 27篇 |
1937年 | 21篇 |
1936年 | 14篇 |
1935年 | 35篇 |
1934年 | 7篇 |
1931年 | 14篇 |
1930年 | 7篇 |
1927年 | 5篇 |
1926年 | 6篇 |
1925年 | 4篇 |
1919年 | 3篇 |
1913年 | 3篇 |
1912年 | 4篇 |
1911年 | 3篇 |
1910年 | 3篇 |
1902年 | 3篇 |
1901年 | 5篇 |
排序方式: 共有955条查询结果,搜索用时 16 毫秒
1.
Marine fisheries target and catch fish both for direct human consumption (DHC) as well as for fishmeal and fish oil, and other products. We derived the fractions used for each for 1950–2010 by fishing country, and thus provide a factual foundation for discussions of the optimal use of fisheries resources. From 1950 to 2010, 27% (~20 million tonnes annually) of globally reconstructed marine fisheries landings were destined for uses other than DHC. Importantly, 90% of fish destined for uses other than DHC are food‐grade or prime food‐grade fish, while fish without a ready market for DHC make up a much smaller proportion. These findings have implications for how we are using fish to feed ourselves or, more appropriately, how we are not using fish to feed ourselves. 相似文献
2.
Baudron Frédéric Schultner Jannik Duriaux Jean-Yves Gergel Sarah E. Sunderland Terry 《Landscape Ecology》2019,34(2):341-356
Landscape Ecology - It remains unclear how agricultural landscapes can best serve multiple purposes such as simultaneously maintaining agricultural productivity and conserving biodiversity. Our... 相似文献
3.
Estelle C.C. ?gren Jan Johansson Jenny Fr?ssling Helene Wahlstr?m Ulf Emanuelson Susanna Sternberg-Lewerin 《Acta veterinaria Scandinavica》2015,57(1)
Background
The Swedish control program for salmonella includes restrictions and on-farm control measures when salmonella is detected in a herd. Required control measures are subsidised by the government. This provides an opportunity to study costs for on-farm salmonella control. The aim of this study was to describe the costs for on-farm salmonella control in Swedish cattle herds and to investigate the effects of herd factors on these costs in dairy herds.Results
During the 15 years studied there had been a total of 124 restriction periods in 118 cattle herds; 89 dairy herds, 28 specialised fattening herds and three suckler herds. The average costs per herd for on-farm salmonella control was 4.60 million SEK with a median of 1.06 million SEK corresponding to approximately 490 000 and 110 000 EUR. The range was 0.01 to 41 million SEK corresponding to 1080 EUR to 4.44 million EUR per farm. The costs cover measures required in herd-specific control plans, generally measures improving herd hygiene. A mixed linear model was used to investigate associations between herd factors and costs for on-farm salmonella control in dairy herds. Herd size and length of the restriction period were both significantly associated with costs for on-farm control of salmonella with larger herds and longer periods of restrictions leading to higher costs. Serotype detected and administrative changes in the Swedish Board of Agriculture aiming at reducing costs were not associated with costs for on-farm salmonella control.Conclusions
On-farm control of salmonella in Swedish cattle herds incurred high costs but the costs also varied largely between herds. Larger herds and longer restriction periods increased the costs for on-farm control of salmonella in Swedish dairy herds. This causes concern for future costs for the Swedish salmonella control program as herd sizes are increasing. 相似文献4.
Serge MORAND Frédéric BORDES Hsuan‐Wien CHEN Julien CLAUDE Jean‐François COSSON Maxime GALAN Gábor Á CZIRJÁK Alex D GREENWOOD Alice LATINNE Johan MICHAUX Alexis RIBAS 《Integrative zoology》2015,10(5):409-423
We summarize the current knowledge on parasitism‐related invasion processes of the globally invasive Rattus lineages, originating from Asia, and how these invasions have impacted the local epidemiology of rodent‐borne diseases. Parasites play an important role in the invasion processes and successes of their hosts through multiple biological mechanisms such as “parasite release,” “immunocompetence advantage,” “biotic resistance” and “novel weapon.” Parasites may also greatly increase the impact of invasions by spillover of parasites and other pathogens, introduced with invasive hosts, into new hosts, potentially leading to novel emerging diseases. Another potential impact is the ability of the invader to amplify local parasites by spillback. In both cases, local fauna and humans may be exposed to new health risks, which may decrease biodiversity and potentially cause increases in human morbidity and mortality. Here we review the current knowledge on these processes and propose some research priorities. 相似文献
5.
Rodents are recognized reservoir hosts for many human zoonotic pathogens. The current trends resulting from anthropocene defaunation suggest that in the future they, along with other small mammals, are likely to become the dominant mammals in almost all human‐modified environments. Recent intricate studies on bat‐borne emerging diseases have highlighted that many gaps exist in our understanding of the zoonotic transmission of rodent‐borne pathogens. This has emphasized the need for scientists interested in rodent‐borne diseases to integrate rodent ecology into their analysis of rodent‐borne pathogen transmission in order to identify in more detail the mechanisms of spillover and chains of transmission. Further studies are required to better understand the true impact of rodent abundance and the importance of pathogen sharing and circulation in multi‐host– multi‐pathogen communities. We also need to explore in more depth the roles of generalist and abundant species as the potential links between pathogen‐sharing, co‐infections and disease transmission. 相似文献
6.
Bruno Vila Michel Vennetier Christian Ripert Olivier Chandioux Eryuan Liang Frédéric Guibal Franck Torre 《Annals of Forest Science》2008,65(7):709-709
7.
8.
9.
Mathieu Jonard Frédéric André François Jonard Nicolas Mouton Pierre Procès Quentin Ponette 《Annals of Forest Science》2007,64(2):141-150
Total Soil Respiration (TSR) was measured in pure and mixed stands of oak and beech and was partitioned into two contributions using the forest floor removal technique: Mineral Soil Respiration (MSR) and Forest Floor Respiration (FFR). In addition, laboratory incubations of the forest floor and the Ah horizon were performed to evaluate the heterotrophic respiration and the DOC production of these horizons. The relationships between soil temperature and the various soil respiration contributions in the three stands were compared using Q 10 functions. In situ, significant differences (α = 0,05) between stands were observed for the R 10 parameter (respiration rate at 10 °C) of the TSR, MSR and FFR contributions, while only the temperature sensitivity (Q 10) of TSR was significantly affected by stand composition. The effect of soil water content was only significant on MSR and followed different patterns according to stand composition. Under controlled conditions, the R 10 of the forest floor and of the Ah horizon varied with stand composition and the Q 10 of the forest floor decreased in the order: oak (2.27) > mixture (2.01) > beech (1.71). 相似文献
10.
Stéphanie Mariette Emilie Balsemin Solenn Stoeckel Muriel Tavaud Hervé Le Bouler Frédérique Santi Michel Verger 《Annals of Forest Science》2007,64(5):533-539
Parents and progenies genetic diversity, and male and female contributions to the seed crop were assessed in three experimental Prunus avium seed orchards. Collected data were used to compare different effective population sizes, based on phenological, seed crop and paternity analysis. Our results did not show any difference of genetic diversity between parents and progenies. A limited pollen pollution was detected. We showed that distance and coflowering among clones had a significant effect on effective pollination, and a significant effect of the production of flowers was revealed in one of the seed orchards. Our study also revealed a quite low number of effective size of fathers per mother, but high effective sizes of mothers, fathers and parents at the level of the seed orchard. Finally, the calculation of effective size of mothers, fathers and parents was not highly modified when having the complete information based on the paternity analysis. 相似文献