全文获取类型
收费全文 | 168篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
林业 | 4篇 |
农学 | 5篇 |
63篇 | |
综合类 | 18篇 |
农作物 | 16篇 |
水产渔业 | 10篇 |
畜牧兽医 | 47篇 |
园艺 | 1篇 |
植物保护 | 13篇 |
出版年
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 10篇 |
2012年 | 14篇 |
2011年 | 19篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 10篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 2篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1945年 | 1篇 |
排序方式: 共有177条查询结果,搜索用时 0 毫秒
101.
Rueckes T Kim K Joselevich E Tseng GY Cheung CL Lieber CM 《Science (New York, N.Y.)》2000,289(5476):94-97
A concept for molecular electronics exploiting carbon nanotubes as both molecular device elements and molecular wires for reading and writing information was developed. Each device element is based on a suspended, crossed nanotube geometry that leads to bistable, electrostatically switchable ON/OFF states. The device elements are naturally addressable in large arrays by the carbon nanotube molecular wires making up the devices. These reversible, bistable device elements could be used to construct nonvolatile random access memory and logic function tables at an integration level approaching 10(12) elements per square centimeter and an element operation frequency in excess of 100 gigahertz. The viability of this concept is demonstrated by detailed calculations and by the experimental realization of a reversible, bistable nanotube-based bit. 相似文献
102.
103.
104.
Nuclear pre-messenger RNA (pre-mRNA) splicing is an essential processing step for the production of mature mRNAs from most eukaryotic genes. Splicing is catalyzed by a large ribonucleoprotein complex, the spliceosome, which is composed of five small nuclear RNAs and more than 100 protein factors. Despite the complexity of the spliceosome, the chemistry of the splicing reaction is simple, consisting of two consecutive transesterification reactions. The presence of introns in spliceosomal RNAs of certain fungi has suggested that splicing may be reversible; however, this has never been demonstrated experimentally. By using affinity-purified spliceosomes, we have shown that both catalytic steps of splicing can be efficiently reversed under appropriate conditions. These results provide considerable insight into the catalytic flexibility of the spliceosome. 相似文献
105.
Out of Tibet: Pliocene woolly rhino suggests high-plateau origin of Ice Age megaherbivores 总被引:1,自引:0,他引:1
Deng T Wang X Fortelius M Li Q Wang Y Tseng ZJ Takeuchi GT Saylor JE Säilä LK Xie G 《Science (New York, N.Y.)》2011,333(6047):1285-1288
Ice Age megafauna have long been known to be associated with global cooling during the Pleistocene, and their adaptations to cold environments, such as large body size, long hair, and snow-sweeping structures, are best exemplified by the woolly mammoths and woolly rhinos. These traits were assumed to have evolved as a response to the ice sheet expansion. We report a new Pliocene mammal assemblage from a high-altitude basin in the western Himalayas, including a primitive woolly rhino. These new Tibetan fossils suggest that some megaherbivores first evolved in Tibet before the beginning of the Ice Age. The cold winters in high Tibet served as a habituation ground for the megaherbivores, which became preadapted for the Ice Age, successfully expanding to the Eurasian mammoth steppe. 相似文献
106.
Comparative herbarium studies, floral anatomy, and distributional data show that Tetraplasandra gymnocarpa, an araliad with hypogynous flowers, evolved in Hawaii from ancestors with epigynous flowers. Suggested causes for this reversal of a well-known evolutionary trend are (i) isolation of the ancestors from flowereating predators and (ii) selection for increased outcrossing. 相似文献
107.
108.
Toong Long Jeng Chang Sheng Wang Tung Hai Tseng Min Tze Wu Jih Min Sung 《Journal of Cereal Science》2009
Spontaneous and induced waxy phenotype, associated with endosperm containing little or no amylose, has been recognized in rice (Oryza sativa L.). Mutation of a dominant gene Wx into a recessive gene wx, which causes the inactivation or absence of granule bound starch synthase, is believed to be responsible for the change in endosperm starch leading to the waxy grain. In the present study, the nucleotide polymorphism in the Wx gene of rice genotype Tainung 67 (wild type) and its 35 NaN3-induced wx mutants were examined. Iodine staining confirmed that all the mutants had waxy grain trait. The G-to-T single base substitution analysis indicated that the wild type genotype Tainung 67 and its waxy mutants carried Wxb allele. Moreover, 23-bp duplication in exon 2 was detected in all the waxy mutants. Microsatellite polymorphism (CT)n was also detectable on the Wx gene of the tested genotypes and mutants, with at least 5 classes of (CT)n microsatellites identified at the Wx locus. Electrophoretic analyses also confirmed the observed nucleotide polymorphsim. Thus, nucleotide polymorphsim exist among NaN3-induced waxy mutants in rice. However, only the 23-bp duplication in exon 2 may be used as a molecular marker to characterize waxy grain trait in rice genotypes. 相似文献
109.
Teolis BD Jones GH Miles PF Tokar RL Magee BA Waite JH Roussos E Young DT Crary FJ Coates AJ Johnson RE Tseng WL Baragiola RA 《Science (New York, N.Y.)》2010,330(6012):1813-1815
The flyby measurements of the Cassini spacecraft at Saturn's moon Rhea reveal a tenuous oxygen (O(2))-carbon dioxide (CO(2)) atmosphere. The atmosphere appears to be sustained by chemical decomposition of the surface water ice under irradiation from Saturn's magnetospheric plasma. This in situ detection of an oxidizing atmosphere is consistent with remote observations of other icy bodies, such as Jupiter's moons Europa and Ganymede, and suggestive of a reservoir of radiolytic O(2) locked within Rhea's ice. The presence of CO(2) suggests radiolysis reactions between surface oxidants and organics or sputtering and/or outgassing of CO(2) endogenic to Rhea's ice. Observations of outflowing positive and negative ions give evidence for pickup ionization as a major atmospheric loss mechanism. 相似文献
110.
Seven new sesquiterpenoids, lochmolins A-G (1-7), were isolated from a Taiwanese soft coral Sinularia lochmodes. The structures of these metabolites were elucidated by extensive spectroscopic study. Compounds 1-4 were found to inhibit the accumulation of the LPS-induced pro-inflammatory COX-2 protein in RAW264.7 macrophage cells. 相似文献