全文获取类型
收费全文 | 3331篇 |
免费 | 241篇 |
国内免费 | 1篇 |
专业分类
3573篇 |
出版年
2023年 | 26篇 |
2022年 | 57篇 |
2021年 | 127篇 |
2020年 | 61篇 |
2019年 | 94篇 |
2018年 | 79篇 |
2017年 | 69篇 |
2016年 | 129篇 |
2015年 | 200篇 |
2014年 | 202篇 |
2013年 | 227篇 |
2012年 | 297篇 |
2011年 | 240篇 |
2010年 | 150篇 |
2009年 | 124篇 |
2008年 | 158篇 |
2007年 | 146篇 |
2006年 | 147篇 |
2005年 | 136篇 |
2004年 | 124篇 |
2003年 | 125篇 |
2002年 | 109篇 |
2001年 | 13篇 |
2000年 | 23篇 |
1999年 | 20篇 |
1998年 | 24篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 24篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 8篇 |
1985年 | 23篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1976年 | 7篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1968年 | 7篇 |
1967年 | 9篇 |
1963年 | 9篇 |
排序方式: 共有3573条查询结果,搜索用时 0 毫秒
91.
92.
Xavier López‐Medellín Exequiel Ezcurra Charlotte González‐Abraham Jon Hak Louis S. Santiago James O. Sickman 《植被学杂志》2011,22(1):143-151
Question: Although mangrove forests are generally regarded as highly threatened, some studies have shown that mangrove canopies in the Pacific coast of Mexico have been increasing in recent decades. We investigated the possible causes driving this reported mangrove expansion. Location: The mangrove lagoons of Magdalena Bay in Baja California, Mexico. Methods: We used 50‐year‐old aerial photographs and 24‐year‐old satellite images to compare long‐term vegetation change, surveyed a coastal vegetation transect to analyse flooding levels, compiled six decades of tidal and oceanographic information, as well as hurricane data to analyse changes in storm frequency or sea‐level conditions, and used isotopic analysis to date the age of trees along the gradient. Results: A significant increase in mangrove cover has occurred in backwaters of the lagoons during the last 40 years, and especially during the El Niño anomalies of the 1980s and 1990s, while at the same time the mangrove fringe has been receding. Conclusions: The observed change can be attributed to the combined action of the warm surface waters of El Niño events and sea‐level rise. Jointly, these two effects are sufficient to flood large areas of previously non‐flooded salt flats, dispersing mangrove seedlings inland. The inland expansion of mangroves, however, does not ease conservation concerns, as it is the seaward fringes, and not the inland margins, that provide the most valuable environmental services for fisheries and coastal protection. 相似文献
93.
Developmental programming: State‐of‐the‐science and future directions–Summary from a Pennington Biomedical symposium 下载免费PDF全文
94.
Sheng-Da Zhang Claire-Lise Santini Wei-Jia Zhang Valérie Barbe Sophie Mangenot Charlotte Guyomar Marc Garel Hai-Tao Chen Xue-Gong Li Qun-Jian Yin Yuan Zhao Jean Armengaud Jean-Charles Gaillard Séverine Martini Nathalie Pradel Claude Vidaud François Alberto Claudine Médigue Christian Tamburini Long-Fei Wu 《Extremophiles : life under extreme conditions》2016,20(3):301-310
Bacteria of the genus Photobacterium thrive worldwide in oceans and show substantial eco-physiological diversity including free-living, symbiotic and piezophilic life styles. Genomic characteristics underlying this variability across species are poorly understood. Here we carried out genomic and physiological analysis of Photobacterium phosphoreum strain ANT-2200, the first deep-sea luminous bacterium of which the genome has been sequenced. Using optical mapping we updated the genomic data and reassembled it into two chromosomes and a large plasmid. Genomic analysis revealed a versatile energy metabolic potential and physiological analysis confirmed its growth capacity by deriving energy from fermentation of glucose or maltose, by respiration with formate as electron donor and trimethlyamine N-oxide (TMAO), nitrate or fumarate as electron acceptors, or by chemo-organo-heterotrophic growth in rich media. Despite that it was isolated at a site with saturated dissolved oxygen, the ANT-2200 strain possesses four gene clusters coding for typical anaerobic enzymes, the TMAO reductases. Elevated hydrostatic pressure enhances the TMAO reductase activity, mainly due to the increase of isoenzyme TorA1. The high copy number of the TMAO reductase isoenzymes and pressure-enhanced activity might imply a strategy developed by bacteria to adapt to deep-sea habitats where the instant TMAO availability may increase with depth. 相似文献
95.
96.
Simon J. Watson Pinky Langat Scott M. Reid Tommy Tsan-Yuk Lam Matthew Cotten Michael Kelly Kristien Van Reeth Yu Qiu Ga?lle Simon Emilie Bonin Emanuela Foni Chiara Chiapponi Lars Larsen Charlotte Hjulsager Iwona Markowska-Daniel Kinga Urbaniak Ralf Dürrwald Michael Schlegel Anita Huovilainen Irit Davidson ádám Dán Willie Loeffen Stephanie Edwards Michel Bublot Thais Vila Jaime Maldonado Laura Valls ESNIP Consortium Ian H. Brown Oliver G. Pybus Paul Kellam 《Journal of virology》2015,89(19):9920-9931
97.
98.
Histone H4K20 tri‐methylation at late‐firing origins ensures timely heterochromatin replication 下载免费PDF全文
Charlotte Grimaud Paulina Prorok Christelle Cayrou Gunnar Schotta Alhassan F Abdelsamie Jérôme Déjardin Marcel Méchali Giuseppe Baldacci Claude Sardet Jean‐Charles Cadoret Aloys Schepers Eric Julien 《The EMBO journal》2017,36(18):2726-2741
Among other targets, the protein lysine methyltransferase PR‐Set7 induces histone H4 lysine 20 monomethylation (H4K20me1), which is the substrate for further methylation by the Suv4‐20h methyltransferase. Although these enzymes have been implicated in control of replication origins, the specific contribution of H4K20 methylation to DNA replication remains unclear. Here, we show that H4K20 mutation in mammalian cells, unlike in Drosophila, partially impairs S‐phase progression and protects from DNA re‐replication induced by stabilization of PR‐Set7. Using Epstein–Barr virus‐derived episomes, we further demonstrate that conversion of H4K20me1 to higher H4K20me2/3 states by Suv4‐20h is not sufficient to define an efficient origin per se, but rather serves as an enhancer for MCM2‐7 helicase loading and replication activation at defined origins. Consistent with this, we find that Suv4‐20h‐mediated H4K20 tri‐methylation (H4K20me3) is required to sustain the licensing and activity of a subset of ORCA/LRWD1‐associated origins, which ensure proper replication timing of late‐replicating heterochromatin domains. Altogether, these results reveal Suv4‐20h‐mediated H4K20 tri‐methylation as a critical determinant in the selection of active replication initiation sites in heterochromatin regions of mammalian genomes. 相似文献
99.