全文获取类型
收费全文 | 537篇 |
免费 | 70篇 |
专业分类
林业 | 16篇 |
农学 | 2篇 |
41篇 | |
综合类 | 85篇 |
农作物 | 15篇 |
水产渔业 | 27篇 |
畜牧兽医 | 392篇 |
园艺 | 15篇 |
植物保护 | 14篇 |
出版年
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 17篇 |
2016年 | 10篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 39篇 |
2012年 | 24篇 |
2011年 | 20篇 |
2010年 | 15篇 |
2009年 | 13篇 |
2008年 | 23篇 |
2007年 | 25篇 |
2006年 | 23篇 |
2005年 | 20篇 |
2004年 | 24篇 |
2003年 | 28篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 15篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1992年 | 4篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1974年 | 7篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1970年 | 4篇 |
1969年 | 6篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1966年 | 6篇 |
1962年 | 3篇 |
1960年 | 4篇 |
1928年 | 3篇 |
排序方式: 共有607条查询结果,搜索用时 31 毫秒
51.
52.
Prinn R Cunnold D Rasmussen R Simmonds P Alyea F Crawford A Fraser P Rosen R 《Science (New York, N.Y.)》1987,238(4829):945-950
Frequent atmospheric measurements of the anthropogenic compound methylchloroform that were made between 1978 and 1985 indicate that this species is continuing to increase significantly around the world. Reaction with the major atmospheric oxidant, the hydroxyl radical (OH), is the principal sink for this species. The observed mean trends for methylchloroform are 4.8, 5.4, 6.4, and 6.9 percent per year at Aldrigole (Ireland) and Cape Meares (Oregon), Ragged Point (Barbados), Point Matatula (American Samoa), and Cape Grim (Tasmania), respectively, from July 1978 to June 1985. These measured trends, combined with knowledge of industrial emissions, were used in an optimal estimation inversion scheme to deduce a globally averaged methylchloroform atmospheric lifetime of 6.3 (+ 1.2, -0.9) years (1sigma uncertainty) and a globally averaged tropospheric hydroxyl radical concentration of (7.7 +/- 1.4) x 10(5) radicals per cubic centimeter (1sigma uncertainty). These 7 years of gas chromatographic measurements, which comprise about 60,000 individual calibrated real-time air analyses, provide the most accurate estimates yet of the trends and lifetime of methylchloroform and of the global average for tropospheric hydroxyl radical levels. Accurate determination of hydroxyl radical levels is crucial to understanding global atmospheric chemical cycles and trends in the levels of trace gases such as methane. 相似文献
53.
Eigner J Watson JD Haselkorn R Signer E Fraser D Echols H 《Science (New York, N.Y.)》1968,162(3853):511
54.
55.
Ainley DG Ballard G Emslie SD Fraser WR Wilson PR Woehler EJ 《Science (New York, N.Y.)》2003,300(5618):429-30; author reply 429-30
56.
57.
Much has been gained from genomic and evolutionary studies of species. Combining the perspectives of these different approaches suggests that an integrated phylogenomic approach will be beneficial. 相似文献
58.
DH Lowndes DB Geohegan AA Puretzky DP Norton CM Rouleau 《Science (New York, N.Y.)》1996,273(5277):898-903
Pulsed laser deposition (PLD) is a conceptually and experimentally simple yet highly versatile tool for thin-film and multilayer research. Its advantages for the film growth of oxides and other chemically complex materials include stoichiometric transfer, growth from an energetic beam, reactive deposition, and inherent simplicity for the growth of multilayered structures. With the use of PLD, artificially layered materials and metastable phases have been created and their properties varied by control of the layer thicknesses. In situ monitoring techniques have provided information about the role of energetic species in the formation of ultrahard phases and in the doping of semiconductors. Cluster-assembled nanocrystalline and composite films offer opportunities to control and produce new combinations of properties with PLD. 相似文献
59.
The Air noncoding RNA epigenetically silences transcription by targeting G9a to chromatin 总被引:1,自引:0,他引:1
Nagano T Mitchell JA Sanz LA Pauler FM Ferguson-Smith AC Feil R Fraser P 《Science (New York, N.Y.)》2008,322(5908):1717-1720
60.
Seshadri R Adrian L Fouts DE Eisen JA Phillippy AM Methe BA Ward NL Nelson WC Deboy RT Khouri HM Kolonay JF Dodson RJ Daugherty SC Brinkac LM Sullivan SA Madupu R Nelson KE Kang KH Impraim M Tran K Robinson JM Forberger HA Fraser CM Zinder SH Heidelberg JF 《Science (New York, N.Y.)》2005,307(5706):105-108