全文获取类型
收费全文 | 445篇 |
免费 | 19篇 |
专业分类
林业 | 9篇 |
农学 | 4篇 |
32篇 | |
综合类 | 82篇 |
农作物 | 12篇 |
水产渔业 | 29篇 |
畜牧兽医 | 262篇 |
园艺 | 10篇 |
植物保护 | 24篇 |
出版年
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 7篇 |
2012年 | 22篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2008年 | 13篇 |
2007年 | 20篇 |
2006年 | 16篇 |
2005年 | 17篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 10篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 5篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1966年 | 3篇 |
排序方式: 共有464条查询结果,搜索用时 15 毫秒
31.
32.
Grundy WM Buratti BJ Cheng AF Emery JP Lunsford A McKinnon WB Moore JM Newman SF Olkin CB Reuter DC Schenk PM Spencer JR Stern SA Throop HB Weaver HA;New Horizons Team 《Science (New York, N.Y.)》2007,318(5848):234-237
The New Horizons spacecraft observed Jupiter's icy satellites Europa and Ganymede during its flyby in February and March 2007 at visible and infrared wavelengths. Infrared spectral images map H2O ice absorption and hydrated contaminants, bolstering the case for an exogenous source of Europa's "non-ice" surface material and filling large gaps in compositional maps of Ganymede's Jupiter-facing hemisphere. Visual wavelength images of Europa extend knowledge of its global pattern of arcuate troughs and show that its surface scatters light more isotropically than other icy satellites. 相似文献
33.
34.
Guam amyotrophic lateral sclerosis-parkinsonism-dementia linked to a plant excitant neurotoxin 总被引:24,自引:0,他引:24
P S Spencer P B Nunn J Hugon A C Ludolph S M Ross D N Roy R C Robertson 《Science (New York, N.Y.)》1987,237(4814):517-522
The decline in the high incidence of amyotrophic lateral sclerosis, parkinsonism, and Alzheimer-type dementia among the Chamorro population of the western Pacific islands of Guam and Rota, coupled with the absence of demonstrable viral and hereditable factors in this disease, suggests the gradual disappearance of an environmental factor selectively associated with this culture. One candidate is seed of the neurotoxic plant Cycas circinalis L., a traditional source of food and medicine which has been used less with the Americanization of the Chamorro people after World War II. Macaques were fed the Cycas amino acid beta-N-methylamino-L-alanine, a low-potency convulsant that has excitotoxic activity in mouse brain, which is attenuated by N-methyl-D-aspartate receptor antagonists. These animals developed corticomoto-neuronal dysfunction, parkinsonian features, and behavioral anomalies, with chromatolytic and degenerative changes of motor neurons in cerebral cortex and spinal cord. In concert with existing epidemiological and animal data, these findings support the hypothesis that cycad exposure plays an important role in the etiology of the Guam disease. 相似文献
35.
Spencer JR Stern SA Cheng AF Weaver HA Reuter DC Retherford K Lunsford A Moore JM Abramov O Lopes RM Perry JE Kamp L Showalter M Jessup KL Marchis F Schenk PM Dumas C 《Science (New York, N.Y.)》2007,318(5848):240-243
Jupiter's moon Io is known to host active volcanoes. In February and March 2007, the New Horizons spacecraft obtained a global snapshot of Io's volcanism. A 350-kilometer-high volcanic plume was seen to emanate from the Tvashtar volcano (62 degrees N, 122 degrees W), and its motion was observed. The plume's morphology and dynamics support nonballistic models of large Io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source. In images taken in Jupiter eclipse, nonthermal visible-wavelength emission was seen from individual volcanoes near Io's sub-Jupiter and anti-Jupiter points. Near-infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150- to 1335-kelvin range, consistent with basaltic composition. 相似文献
36.
C T Knorpp W R Merchant P W Gikas H H Spencer N W Thompson 《Science (New York, N.Y.)》1967,157(794):1312-1313
Studies in vitro indicate that hydroxyethyl starch is an effective extracellular cryoprotective agent for erythrocytes. It is as effective as polyvinylpyrrolidone in cryophylactic ability. It is degraded to glucose units in the circulation, is not retained in tissues, and is inexpensive to produce. Changes in the size and degree of hydroxyethylation of the branched-chain starch may result in a more effective cryoprotective agent. 相似文献
37.
Spencer JW 《Science (New York, N.Y.)》1914,39(1009):645-646
38.
39.
Spencer JW 《Science (New York, N.Y.)》1908,28(726):754-759
40.
Cool Water, the world's first commercial-scale, integrated coal gasification combined cycle power plant, has been operating successfully since May 1984 near Barstow, California. The 100-megawatt plant, which was completed ahead of schedule and under budget, is probably the cleanest coal-fired power generating facility now in commercial operation. An ongoing demonstration program at Cool Water shows that future baseload power plants that use this technology can be built modularly in increments of a few hundred megawatts and compete economically with much larger, conventional coal-fired power plants equipped for flue gas desulfurization. 相似文献