全文获取类型
收费全文 | 985篇 |
免费 | 15篇 |
国内免费 | 4篇 |
专业分类
林业 | 17篇 |
农学 | 46篇 |
78篇 | |
综合类 | 306篇 |
农作物 | 27篇 |
水产渔业 | 5篇 |
畜牧兽医 | 465篇 |
园艺 | 2篇 |
植物保护 | 58篇 |
出版年
2012年 | 57篇 |
2011年 | 82篇 |
2010年 | 15篇 |
2009年 | 10篇 |
2008年 | 59篇 |
2007年 | 62篇 |
2006年 | 65篇 |
2005年 | 59篇 |
2004年 | 76篇 |
2003年 | 52篇 |
2002年 | 58篇 |
2001年 | 35篇 |
2000年 | 66篇 |
1999年 | 32篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 6篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1969年 | 6篇 |
1967年 | 4篇 |
1966年 | 3篇 |
1957年 | 7篇 |
1947年 | 3篇 |
1946年 | 3篇 |
1928年 | 5篇 |
1927年 | 4篇 |
1924年 | 3篇 |
排序方式: 共有1004条查询结果,搜索用时 15 毫秒
111.
Vermeij GJ 《Science (New York, N.Y.)》1988,240(4855):1074-1075
112.
Pollen of the primitive angiosperm family Winteraceae has been discovered in the Aptian-Albian of Israel, extending the fossil record of this phylogenetically important family of flowering plants from the uppermost Upper Cretaceous back some 40 million years to the upper Lower Cretaceous. This appears to represent the earliest known record of a magnolialean angiosperm family and is convincing evidence for the existence in the Early Cretaceous of an extant family of angiosperms. 相似文献
113.
114.
115.
Colbourne JK Pfrender ME Gilbert D Thomas WK Tucker A Oakley TH Tokishita S Aerts A Arnold GJ Basu MK Bauer DJ Cáceres CE Carmel L Casola C Choi JH Detter JC Dong Q Dusheyko S Eads BD Fröhlich T Geiler-Samerotte KA Gerlach D Hatcher P Jogdeo S Krijgsveld J Kriventseva EV Kültz D Laforsch C Lindquist E Lopez J Manak JR Muller J Pangilinan J Patwardhan RP Pitluck S Pritham EJ Rechtsteiner A Rho M Rogozin IB Sakarya O Salamov A Schaack S Shapiro H Shiga Y Skalitzky C Smith Z Souvorov A Sung W 《Science (New York, N.Y.)》2011,331(6017):555-561
We describe the draft genome of the microcrustacean Daphnia pulex, which is only 200 megabases and contains at least 30,907 genes. The high gene count is a consequence of an elevated rate of gene duplication resulting in tandem gene clusters. More than a third of Daphnia's genes have no detectable homologs in any other available proteome, and the most amplified gene families are specific to the Daphnia lineage. The coexpansion of gene families interacting within metabolic pathways suggests that the maintenance of duplicated genes is not random, and the analysis of gene expression under different environmental conditions reveals that numerous paralogs acquire divergent expression patterns soon after duplication. Daphnia-specific genes, including many additional loci within sequenced regions that are otherwise devoid of annotations, are the most responsive genes to ecological challenges. 相似文献
116.
Struvite, MgNH(4)PO(4).6H(2)O, rather than apatite or amorphous calcium phosphate is precipitated when phosphate is added to seawater containing more than 0.01M NH(4)(+) ions. Struvite may have precipitated from evaporating seawater on the primitive earth, and may have been important for prebiotic phosphorylation. 相似文献
117.
Cox GJ 《Science (New York, N.Y.)》1937,86(2241):540-542
118.
119.
Armbrust EV Berges JA Bowler C Green BR Martinez D Putnam NH Zhou S Allen AE Apt KE Bechner M Brzezinski MA Chaal BK Chiovitti A Davis AK Demarest MS Detter JC Glavina T Goodstein D Hadi MZ Hellsten U Hildebrand M Jenkins BD Jurka J Kapitonov VV Kröger N Lau WW Lane TW Larimer FW Lippmeier JC Lucas S Medina M Montsant A Obornik M Parker MS Palenik B Pazour GJ Richardson PM Rynearson TA Saito MA Schwartz DC Thamatrakoln K Valentin K Vardi A Wilkerson FP Rokhsar DS 《Science (New York, N.Y.)》2004,306(5693):79-86
Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for approximately 20% of global carbon fixation. We report the 34 million-base pair draft nuclear genome of the marine diatom Thalassiosira pseudonana and its 129 thousand-base pair plastid and 44 thousand-base pair mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, use of a range of nitrogenous compounds, and a complete urea cycle, all attributes that allow diatoms to prosper in aquatic environments. 相似文献
120.
Halder GJ Kepert CJ Moubaraki B Murray KS Cashion JD 《Science (New York, N.Y.)》2002,298(5599):1762-1765
The nanoporous metal-organic framework Fe2(azpy)4(NCS)4.(guest) (azpy is trans-4,4'-azopyridine) displays reversible uptake and release of guest molecules and contains electronic switching centers that are sensitive to the nature of the sorbed guests. The switching of this material arises from the presence of iron(II) spin crossover centers within the framework lattice, the sorbed phases undergoing "half-spin" crossovers, and the desorbed phase showing no switching property. The interpenetrated framework structure displays a considerable flexibility with guest uptake and release, causing substantial changes in the local geometry of the iron(II) centers. The generation of a host lattice that interacts with exchangeable guest species in a switchable fashion has implications for the generation of previously undeveloped advanced materials with applications in areas such as molecular sensing. 相似文献