全文获取类型
收费全文 | 456篇 |
免费 | 21篇 |
专业分类
林业 | 6篇 |
农学 | 2篇 |
35篇 | |
综合类 | 40篇 |
农作物 | 50篇 |
水产渔业 | 29篇 |
畜牧兽医 | 296篇 |
园艺 | 4篇 |
植物保护 | 15篇 |
出版年
2023年 | 3篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 9篇 |
2014年 | 6篇 |
2013年 | 19篇 |
2012年 | 22篇 |
2011年 | 27篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 18篇 |
2007年 | 15篇 |
2006年 | 23篇 |
2005年 | 21篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 20篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1983年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1966年 | 2篇 |
1947年 | 4篇 |
1946年 | 8篇 |
1945年 | 7篇 |
1944年 | 6篇 |
1943年 | 6篇 |
1941年 | 3篇 |
排序方式: 共有477条查询结果,搜索用时 0 毫秒
31.
32.
Lindsay Naylor 《Agriculture and Human Values》2014,31(2):273-284
At the same time as fair trade certified products are capturing an increasing market share, a growing number of scholars and practitioners are raising serious questions about who benefits from certification. Through a critique of north–south narratives, this paper draws on contemporary themes in fair trade scholarship to draw out different ways of thinking about fair trade outside of the dichotomous north–south framing. I argue that, through the creation of fair trade subjects of the “global north” and “global south,” certification has normalized and naturalized dichotomous power relations. The primary concern of this paper is to demonstrate the problems with situating certification and scholarship in the north–south binary and to push examination toward a more nuanced analysis of how certification and development are shaped in-place. This intervention is important for assisting with stepping away from long-standing debates regarding the effectiveness of certification, and additionally in contributing to critical thinking on economic development more broadly. 相似文献
33.
34.
A. G. Burnie J. W. Simpson D. Lindsay R. S. Miles 《Veterinary research communications》1983,6(1):133-138
Faecal samples were collected from impounded stray dogs, classified as under or over six months of age, on their arrival in kennels and again 5–7 days later. The faeces were examined for the presence of campylobacters, salmonella andGiardia lamblia. No significant difference was found in the rate of isolation of these organisms between the two age groups. There was, however, a significant increase in the rate of isolation at days 5–7 compared with day 1. It is suggested that while dogs may acquire campylobacter infection in kennels, excretion of the organism may be intermittent and may be precipitated by stress. A low incidence of salmonellae andGiardia lamblia excretion was detected. 相似文献
35.
Catherine M Shilton Margret S Thompson René Meisner Brad Lock William A Lindsay 《Journal of zoo and wildlife medicine》2002,33(4):371-377
An 18- to 25-yr-old intact female Bengal tiger (Panthera tigris) was diagnosed antemortem and postmortem with nasopharyngeal myxosarcoma metastatic to the lung, chronic lymphoplasmacytic otitis media, and lymphoplasmacytic and eosinophilic stomatitis. Myxosarcomas are rare in domestic animals and seldom metastasize; this tumor has not been previously reported in an exotic felid. Computed tomography of the skull was used during the diagnoses. 相似文献
36.
37.
Nickel activities were measured in 11 alkaline and slightly acidic soils using the chelate method. The measured activities ranged from 10?6.82 to 10?8.78 M and were inversely related to the pH of the soils. The measured Ni2+ activities in the 11 soils could be predicted using the following expression: (Ni2+) = 106.95 (H+)2. The solubility of Ni was plotted on a log (Ni2+) vs. pH solubility diagram for various Ni solid phase compounds. It is most likely that NiFe2O4 (trevorite) is the solid phase controlling Ni solubility in these soils. Identification of the presence of this mineral needs further investigation. 相似文献
38.
Images of the DNA double helix in water 总被引:8,自引:0,他引:8
S M Lindsay T Thundat L Nagahara U Knipping R L Rill 《Science (New York, N.Y.)》1989,244(4908):1063-1064
The scanning tunneling microscope can image uncoated DNA submerged in water. The grooves of the double helix were clearly resolved in images of the 146-base pair fragment extracted from calf thymus nucleosome. In contrast to images obtained with dry DNA, the helix pitch varied only a small amount (36 +/- 5 angstroms). The path of the helix shows considerable variation. It is quite straight when the molecules are densely packed, but it curves and bends in isolated molecules. 相似文献
39.
A persistent oxygen anomaly reveals the fate of spilled methane in the deep Gulf of Mexico 总被引:3,自引:0,他引:3
Kessler JD Valentine DL Redmond MC Du M Chan EW Mendes SD Quiroz EW Villanueva CJ Shusta SS Werra LM Yvon-Lewis SA Weber TC 《Science (New York, N.Y.)》2011,331(6015):312-315
Methane was the most abundant hydrocarbon released during the 2010 Deepwater Horizon oil spill in the Gulf of Mexico. Beyond relevancy to this anthropogenic event, this methane release simulates a rapid and relatively short-term natural release from hydrates into deep water. Based on methane and oxygen distributions measured at 207 stations throughout the affected region, we find that within ~120 days from the onset of release ~3.0 × 10(10) to 3.9 × 10(10) moles of oxygen were respired, primarily by methanotrophs, and left behind a residual microbial community containing methanotrophic bacteria. We suggest that a vigorous deepwater bacterial bloom respired nearly all the released methane within this time, and that by analogy, large-scale releases of methane from hydrate in the deep ocean are likely to be met by a similarly rapid methanotrophic response. 相似文献
40.
Ramachandran GK Hopson TJ Rawlett AM Nagahara LA Primak A Lindsay SM 《Science (New York, N.Y.)》2003,300(5624):1413-1416
Stochastic on-off conductivity switching observed in phenylene-ethynylene oligomers has been explained in terms of changes in ring conformations, or electron localization, or both. We report the observation of stochastic on-off switching in the simplest of wired molecules: octanedithiol, decanedithiol, and dodecanedithiol bonded on an Au(111) surface. Stochastic switching was observed even when a top gold contact was pressed on by a conducting atomic force microscope tip at constant force. The rate of switching increased substantially at 60 degrees C, a temperature at which these films are commonly annealed. Because such switching in alkanethiols is unlikely to be caused by internal molecular electronic changes and cannot be fully accounted for by breaking of the top contact, we argue that the cause is the well-known mobility of molecules tethered to gold via a thiol linkage. 相似文献