全文获取类型
收费全文 | 255篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 2篇 |
丛书文集 | 2篇 |
教育与普及 | 1篇 |
理论与方法论 | 1篇 |
现状及发展 | 64篇 |
研究方法 | 59篇 |
综合类 | 118篇 |
自然研究 | 10篇 |
出版年
2019年 | 1篇 |
2018年 | 12篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 5篇 |
2012年 | 18篇 |
2011年 | 46篇 |
2010年 | 13篇 |
2009年 | 4篇 |
2008年 | 15篇 |
2007年 | 21篇 |
2006年 | 19篇 |
2005年 | 17篇 |
2004年 | 15篇 |
2003年 | 17篇 |
2002年 | 17篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有257条查询结果,搜索用时 140 毫秒
251.
Giovannoni SJ Bibbs L Cho JC Stapels MD Desiderio R Vergin KL Rappé MS Laney S Wilhelm LJ Tripp HJ Mathur EJ Barofsky DF 《Nature》2005,438(7064):82-85
Proteorhodopsins are light-dependent proton pumps that are predicted to have an important role in the ecology of the oceans by supplying energy for microbial metabolism. Proteorhodopsin genes were first discovered through the cloning and sequencing of large genomic DNA fragments from seawater. They were later shown to be widely distributed, phylogenetically diverse, and active in the oceans. Proteorhodopsin genes have not been found in cultured bacteria, and on the basis of environmental sequence data, it has not yet been possible to reconstruct the genomes of uncultured bacterial strains that have proteorhodopsin genes. Although the metabolic effect of proteorhodopsins is uncertain, they are thought to function in cells for which the primary mode of metabolism is the heterotrophic assimilation of dissolved organic carbon. Here we report that SAR11 strain HTCC1062 ('Pelagibacter ubique'), the first cultivated member of the extraordinarily abundant SAR11 clade, expresses a proteorhodopsin gene when cultured in autoclaved seawater and in its natural environment, the ocean. The Pelagibacter proteorhodopsin functions as a light-dependent proton pump. The gene is expressed by cells grown in either diurnal light or in darkness, and there is no difference between the growth rates or cell yields of cultures grown in light or darkness. 相似文献
252.
Yamada K Andrews C Chan WM McKeown CA Magli A de Berardinis T Loewenstein A Lazar M O'Keefe M Letson R London A Ruttum M Matsumoto N Saito N Morris L Del Monte M Johnson RH Uyama E Houtman WA de Vries B Carlow TJ Hart BL Krawiecki N Shoffner J Vogel MC Katowitz J Goldstein SM Levin AV Sener EC Ozturk BT Akarsu AN Brodsky MC Hanisch F Cruse RP Zubcov AA Robb RM Roggenkäemper P Gottlob I Kowal L Battu R Traboulsi EI Franceschini P Newlin A Demer JL Engle EC 《Nature genetics》2003,35(4):318-321
Congenital fibrosis of the extraocular muscles type 1 (CFEOM1; OMIM #135700) is an autosomal dominant strabismus disorder associated with defects of the oculomotor nerve. We show that individuals with CFEOM1 harbor heterozygous missense mutations in a kinesin motor protein encoded by KIF21A. We identified six different mutations in 44 of 45 probands. The primary mutational hotspots are in the stalk domain, highlighting an important new role for KIF21A and its stalk in the formation of the oculomotor axis. 相似文献
253.
254.
Extracellular Ca(2+) (Ca(2+)(o)) is required for various physiological and developmental processes in animals and plants. In response to varied Ca(2+)(o) levels, plants maintain relatively constant internal Ca(2+) content, suggesting a precise regulatory mechanism for Ca(2+) homeostasis. However, little is known about how plants monitor Ca(2+)(o) status and whether Ca(2+)(o)-sensing receptors exist. The effects of Ca(2+)(o) on guard cells in promoting stomatal closure by inducing increases in the concentration of cytosolic Ca(2+) ([Ca(2+)](i)) provide a clue to Ca(2+)(o) sensing. Here we have used a functional screening assay in mammalian cells to isolate an Arabidopsis complementary DNA clone encoding a Ca(2+)-sensing receptor, CAS. CAS is localized to the plasma membrane, exhibits low-affinity/high-capacity Ca(2+) binding, and mediates Ca(2+)(o)-induced [Ca(2+)](i) increases. CAS is expressed predominantly in the shoot, including guard cells. Repression of CAS disrupts Ca(2+)(o) signalling in guard cells, and impairs bolting (swift upward growth at the transition to seed production) in response to Ca(2+) deficiency, so we conclude that CAS may be a primary transducer of Ca(2+)(o) in plants. 相似文献
255.
256.
Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry 总被引:6,自引:0,他引:6
Monteith DT Stoddard JL Evans CD de Wit HA Forsius M Høgåsen T Wilander A Skjelkvåle BL Jeffries DS Vuorenmaa J Keller B Kopácek J Vesely J 《Nature》2007,450(7169):537-540
Several hypotheses have been proposed to explain recent, widespread increases in concentrations of dissolved organic carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors. 相似文献
257.
Replicating genotype-phenotype associations 总被引:1,自引:0,他引:1
NCI-NHGRI Working Group on Replication in Association Studies Chanock SJ Manolio T Boehnke M Boerwinkle E Hunter DJ Thomas G Hirschhorn JN Abecasis G Altshuler D Bailey-Wilson JE Brooks LD Cardon LR Daly M Donnelly P Fraumeni JF Freimer NB Gerhard DS Gunter C Guttmacher AE Guyer MS Harris EL Hoh J Hoover R Kong CA Merikangas KR Morton CC Palmer LJ Phimister EG Rice JP Roberts J Rotimi C Tucker MA Vogan KJ Wacholder S Wijsman EM Winn DM Collins FS 《Nature》2007,447(7145):655-660