全文获取类型
收费全文 | 5700篇 |
免费 | 476篇 |
出版年
2023年 | 50篇 |
2022年 | 23篇 |
2021年 | 228篇 |
2020年 | 97篇 |
2019年 | 144篇 |
2018年 | 165篇 |
2017年 | 152篇 |
2016年 | 238篇 |
2015年 | 409篇 |
2014年 | 441篇 |
2013年 | 456篇 |
2012年 | 599篇 |
2011年 | 567篇 |
2010年 | 328篇 |
2009年 | 242篇 |
2008年 | 348篇 |
2007年 | 335篇 |
2006年 | 278篇 |
2005年 | 229篇 |
2004年 | 178篇 |
2003年 | 188篇 |
2002年 | 171篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 28篇 |
1998年 | 23篇 |
1997年 | 25篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1984年 | 4篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1969年 | 4篇 |
1967年 | 5篇 |
1966年 | 3篇 |
排序方式: 共有6176条查询结果,搜索用时 15 毫秒
91.
Sebastian M. Marcuccio Bryan C. Elmes George Holan E. John Middleton 《Nucleosides, nucleotides & nucleic acids》2013,32(10):1695-1701
Abstract An economical two pot synthesis of 2′,3′-dideoxycytidine (2) from N4-acetyl-cytidine (4) has been developed. The key feature of this sequence is the in situ reductive elimination of a mixture of 1-(3-bromo-3-deoxy-2,5-di-O-acetyl-β-D-xylofuranosyl)-N4-acetylcytosine (5) and 1-(2-bromo-3-deoxy-3,5-di-O-acetyl-β-D-arabinofuranosyl)-N4-acetylcytosine (6) and subsequent hydrogenation of the resultant olefin over palladised charcoal. 相似文献
92.
Sebastian Fernandez-Pol Zdenek Slouka Souvik Bhattacharjee Yana Fedotova Stefan Freed Xiuli An Anthony A. Holder Estela Campanella Philip S. Low Narla Mohandas Kasturi Haldar 《Eukaryotic cell》2013,12(9):1179-1191
Eukaryotic parasites of the genus Plasmodium cause malaria by invading and developing within host erythrocytes. Here, we demonstrate that PfShelph2, a gene product of Plasmodium falciparum that belongs to the Shewanella-like phosphatase (Shelph) subfamily, selectively hydrolyzes phosphotyrosine, as shown for other previously studied Shelph family members. In the extracellular merozoite stage, PfShelph2 localizes to vesicles that appear to be distinct from those of rhoptry, dense granule, or microneme organelles. During invasion, PfShelph2 is released from these vesicles and exported to the host erythrocyte. In vitro, PfShelph2 shows tyrosine phosphatase activity against the host erythrocyte protein Band 3, which is the most abundant tyrosine-phosphorylated species of the erythrocyte. During P. falciparum invasion, Band 3 undergoes dynamic and rapid clearance from the invasion junction within 1 to 2 s of parasite attachment to the erythrocyte. Release of Pfshelph2 occurs after clearance of Band 3 from the parasite-host cell interface and when the parasite is nearly or completely enclosed in the nascent vacuole. We propose a model in which the phosphatase modifies Band 3 in time to restore its interaction with the cytoskeleton and thus reestablishes the erythrocyte cytoskeletal network at the end of the invasion process. 相似文献
93.
Claudio Ghiglione Maria Chiara Alvaro Huw J. Griffiths Katrin Linse Stefano Schiaparelli 《ZooKeys》2013,(341):37-48
Information regarding the molluscs in this dataset is based on the Rauschert dredge samples collected during the Latitudinal Gradient Program (LGP) on board the R/V “Italica” in the Ross Sea (Antarctica) in the austral summer 2004. A total of 18 epibenthic dredge deployments/samplings have been performed at four different locations at depths ranging from 84 to 515m by using a Rauschert dredge with a mesh size of 500μm. In total 8,359 specimens have been collected belonging to a total of 161 species. Considering this dataset in terms of occurrences, it corresponds to 505 discrete distributional records (incidence data). Of these, in order of abundance, 5,965 specimens were Gastropoda (accounting for 113 species), 1,323 were Bivalvia (accounting for 36 species), 949 were Aplacophora (accounting for 7 species), 74 specimens were Scaphopoda (3 species), 38 were Monoplacophora (1 species) and, finally, 10 specimens were Polyplacophora (1 species). This data set represents the first large-scale survey of benthic micro-molluscs for the area and provides important information about the distribution of several species, which have been seldom or never recorded before in the Ross Sea. All vouchers are permanently stored at the Italian National Antarctic Museum (MNA), Section of Genoa, enabling future comparison and crosschecking. This material is also currently under study, from a molecular point of view, by the barcoding project “BAMBi” (PNRA 2010/A1.10). 相似文献
94.
95.
Helen S. Findlay Yuri Artioli Juan Moreno Navas Sebastian J. Hennige Laura C. Wicks Veerle A. I. Huvenne E. Malcolm S. Woodward J. Murray Roberts 《Global Change Biology》2013,19(9):2708-2719
Cold‐water coral (CWC) reefs are recognized as ecologically and biologically significant areas that generate habitats and diversity. The interaction between hydrodynamics and CWCs has been well studied at the Mingulay Reef Complex, a relatively shallow area of reefs found on the continental shelf off Scotland, UK. Within ‘Mingulay Area 01’ a rapid tidal downwelling of surface waters, brought about as an internal wave, is known to supply warmer, phytoplankton‐rich waters to corals growing on the northern flank of an east‐west trending seabed ridge. This study shows that this tidal downwelling also causes short‐term perturbations in the inorganic carbon (CT) and nutrient dynamics through the water column and immediately above the reef. Over a 14 h period, corresponding to one semi‐diurnal tidal cycle, seawater pH overlying the reef varied by ca. 0.1 pH unit, while pCO2 shifted by >60 μatm, a shift equivalent to a ca. 25 year jump into the future, with respect to atmospheric pCO2. During the summer stratified period, these downwelling events result in the reef being washed over with surface water that has higher pH, is warmer, nutrient depleted, but rich in phytoplankton‐derived particles compared to the deeper waters in which the corals sit. Empirical observations, together with outputs from the European Regional Shelf Sea Ecosystem Model, demonstrate that the variability that the CWC reefs experience changes through the seasons and into the future. Hence, as ocean acidification and warming increase into the future, the downwelling event specific to this site could provide short‐term amelioration of corrosive conditions at certain times of the year; however, it could additionally result in enhanced detrimental impacts of warming on CWCs. Natural variability in the CT and nutrient conditions, as well as local hydrodynamic regimes, must be accounted for in any future predictions concerning the responses of marine ecosystems to climate change. 相似文献
96.
Rajesh Kalladan Sebastian Worch Hardy Rolletschek Vokkaliga T. Harshavardhan Lissy Kuntze Christiane Seiler Nese Sreenivasulu Marion S. Röder 《Molecular breeding : new strategies in plant improvement》2013,32(1):71-90
Drought is a major limiting factor for barley production, especially in the primary areas of its cultivation. Wild barley represents a major source of favourable alleles for increasing the genetic variation for multiple traits including resistance to both biotic and abiotic stresses. We used advanced backcross quantitative trait locus (AB-QTL) analysis of a BC3-doubled haploid population developed between the cultivated parent Brenda (Hordeum vulgare ssp. vulgare) and the wild accession HS584 (H. vulgare ssp. spontaneum) to study the contribution of wild barley in improving various agronomic and seed quality traits under post-anthesis drought. The experiment was carried out at two different locations (IPK, Gatersleben and Nordsaat, Böhnshausen) and terminal drought was imposed by withholding water or spraying with potassium iodide at 10 days after flowering under greenhouse or field conditions, respectively. QTL analysis indicated that wild barley contributed favourably to most of the traits studied under both control and drought conditions. A total of seven hot-spot QTL regions with co-localizing QTL for various traits harboured more than 80 % of the stable QTL detected in the present study. For yield and thousand-grain weight and their respective drought tolerance indices, most of the QTL were derived from Brenda. On the other hand, for traits like seed length and seed nitrogen content, all the QTL were contributed by HS584, the parent having higher trait value. A significantly reduced carbon/nitrogen (C/N) ratio in the selected contrasting inferior lines compared to superior ones suggests that C/N ratio could be a potential parameter for screening not just seed quality parameters but also grain weight performance under terminal drought. 相似文献
97.
98.
99.
100.
Carsten Frühbeis Dominik Fr?hlich Wen Ping Kuo Jesa Amphornrat Sebastian Thilemann Aiman S. Saab Frank Kirchhoff Wiebke M?bius Sandra Goebbels Klaus-Armin Nave Anja Schneider Mikael Simons Matthias Klugmann Jacqueline Trotter Eva-Maria Kr?mer-Albers 《PLoS biology》2013,11(7)
Reciprocal interactions between neurons and oligodendrocytes are not only crucial for myelination, but also for long-term survival of axons. Degeneration of axons occurs in several human myelin diseases, however the molecular mechanisms of axon-glia communication maintaining axon integrity are poorly understood. Here, we describe the signal-mediated transfer of exosomes from oligodendrocytes to neurons. These endosome-derived vesicles are secreted by oligodendrocytes and carry specific protein and RNA cargo. We show that activity-dependent release of the neurotransmitter glutamate triggers oligodendroglial exosome secretion mediated by Ca2+ entry through oligodendroglial NMDA and AMPA receptors. In turn, neurons internalize the released exosomes by endocytosis. Injection of oligodendroglia-derived exosomes into the mouse brain results in functional retrieval of exosome cargo in neurons. Supply of cultured neurons with oligodendroglial exosomes improves neuronal viability under conditions of cell stress. These findings indicate that oligodendroglial exosomes participate in a novel mode of bidirectional neuron-glia communication contributing to neuronal integrity. 相似文献