全文获取类型
收费全文 | 258篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 4篇 |
教育与普及 | 1篇 |
理论与方法论 | 2篇 |
现状及发展 | 26篇 |
研究方法 | 18篇 |
综合类 | 173篇 |
自然研究 | 37篇 |
出版年
2022年 | 1篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2015年 | 1篇 |
2013年 | 5篇 |
2012年 | 11篇 |
2011年 | 56篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 9篇 |
2007年 | 13篇 |
2006年 | 18篇 |
2005年 | 27篇 |
2004年 | 25篇 |
2003年 | 26篇 |
2002年 | 24篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1972年 | 8篇 |
1971年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 31 毫秒
101.
Dennis D. Austin 《西北部美国博物学家》2011,60(2)
History and technical literature describing potential effects of livestock grazing on mule deer ( Odocoileus hemionus ) populations and winter range habitat are reviewed. Recommendations for livestock grazing on winter ranges within the Great Basin are advanced. 相似文献
102.
103.
Baldocchi D 《Nature》2005,437(7058):483-484
104.
Dennis P. Gordon Judy E. Sutherland Brenda A. Perez Andrea Waeschenbach Paul D. Taylor Emanuela Di Martino 《Journal of Natural History》2020,54(15-16):947-970
ABSTRACT The status of Conopeum Gray, 1848 in New Zealand is clarified, confirming the presence of three living species – one a naturalised alien, one new to science, and a third that is also known in the Pleistocene. Conopeum seurati (Canu, 1928), a Mediterranean-European species, is naturalised at three localities in New Zealand – Opua, Whangarei Harbour and Whanganui Inlet. Conopeum antipodum n. sp., previously confused with C. seurati, is an estuarine species distributed from Kaipara Harbour to Lyttelton Harbour and is also found in Te Whanga Lagoon at Chatham Island (all New Zealand localities). Conopeum oretiensis Uttley, 1951, first described from Foveaux Strait, is known as far north as Kaipara and Manukau Harbours and is known as a Pleistocene fossil from Napier, New Zealand. There is one other solely fossil New Zealand species – Plio-Pleistocene Electra ongleyi Brown, 1952 is transferred to Conopeum. Sequence data from the 18SrDNA locus confirm that Conopeum antipodum n. sp. is resolved within Conopeum and is distinct from C. seurati. http://www.zoobank.org/urn:lsid:zoobank.org:act:4FED6730-1C70-4420-B1DA-F1D9046221DF http://www.zoobank.org/urn:lsid:zoobank.org.pub:5C130A99-0869-44A2-885C-338005FBCE07 相似文献
105.
106.
107.
Stuber GD Sparta DR Stamatakis AM van Leeuwen WA Hardjoprajitno JE Cho S Tye KM Kempadoo KA Zhang F Deisseroth K Bonci A 《Nature》2011,475(7356):377-380
The basolateral amygdala (BLA) has a crucial role in emotional learning irrespective of valence. The BLA projection to the nucleus accumbens (NAc) is thought to modulate cue-triggered motivated behaviours, but our understanding of the interaction between these two brain regions has been limited by the inability to manipulate neural-circuit elements of this pathway selectively during behaviour. To circumvent this limitation, we used in vivo optogenetic stimulation or inhibition of glutamatergic fibres from the BLA to the NAc, coupled with intracranial pharmacology and ex vivo electrophysiology. Here we show that optical stimulation of the pathway from the BLA to the NAc in mice reinforces behavioural responding to earn additional optical stimulation of these synaptic inputs. Optical stimulation of these glutamatergic fibres required intra-NAc dopamine D1-type receptor signalling, but not D2-type receptor signalling. Brief optical inhibition of fibres from the BLA to the NAc reduced cue-evoked intake of sucrose, demonstrating an important role of this specific pathway in controlling naturally occurring reward-related behaviour. Moreover, although optical stimulation of glutamatergic fibres from the medial prefrontal cortex to the NAc also elicited reliable excitatory synaptic responses, optical self-stimulation behaviour was not observed by activation of this pathway. These data indicate that whereas the BLA is important for processing both positive and negative affect, the glutamatergic pathway from the BLA to the NAc, in conjunction with dopamine signalling in the NAc, promotes motivated behavioural responding. Thus, optogenetic manipulation of anatomically distinct synaptic inputs to the NAc reveals functionally distinct properties of these inputs in controlling reward-seeking behaviours. 相似文献
108.
Lepre CJ Roche H Kent DV Harmand S Quinn RL Brugal JP Texier PJ Lenoble A Feibel CS 《Nature》2011,477(7362):82-85
The Acheulian is one of the first defined prehistoric techno-complexes and is characterized by shaped bifacial stone tools. It probably originated in Africa, spreading to Europe and Asia perhaps as early as ~1?million years (Myr) ago. The origin of the Acheulian is thought to have closely coincided with major changes in human brain evolution, allowing for further technological developments. Nonetheless, the emergence of the Acheulian remains unclear because well-dated sites older than 1.4?Myr ago are scarce. Here we report on the lithic assemblage and geological context for the Kokiselei 4 archaeological site from the Nachukui formation (West Turkana, Kenya) that bears characteristic early Acheulian tools and pushes the first appearance datum for this stone-age technology back to 1.76?Myr ago. Moreover, co-occurrence of Oldowan and Acheulian artefacts at the Kokiselei site complex indicates that the two technologies are not mutually exclusive time-successive components of an evolving cultural lineage, and suggests that the Acheulian was either imported from another location yet to be identified or originated from Oldowan hominins at this vicinity. In either case, the Acheulian did not accompany the first human dispersal from Africa despite being available at the time. This may indicate that multiple groups of hominins distinguished by separate stone-tool-making behaviours and dispersal strategies coexisted in Africa at 1.76?Myr ago. 相似文献
109.
Dorner M Horwitz JA Robbins JB Barry WT Feng Q Mu K Jones CT Schoggins JW Catanese MT Burton DR Law M Rice CM Ploss A 《Nature》2011,474(7350):208-211
Hepatitis C virus (HCV) remains a major medical problem. Antiviral treatment is only partially effective and a vaccine does not exist. Development of more effective therapies has been hampered by the lack of a suitable small animal model. Although xenotransplantation of immunodeficient mice with human hepatocytes has shown promise, these models are subject to important challenges. Building on the previous observation that CD81 and occludin comprise the minimal human factors required to render mouse cells permissive to HCV entry in vitro, we attempted murine humanization via a genetic approach. Here we show that expression of two human genes is sufficient to allow HCV infection of fully immunocompetent inbred mice. We establish a precedent for applying mouse genetics to dissect viral entry and validate the role of scavenger receptor type B class I for HCV uptake. We demonstrate that HCV can be blocked by passive immunization, as well as showing that a recombinant vaccinia virus vector induces humoral immunity and confers partial protection against heterologous challenge. This system recapitulates a portion of the HCV life cycle in an immunocompetent rodent for the first time, opening opportunities for studying viral pathogenesis and immunity and comprising an effective platform for testing HCV entry inhibitors in vivo. 相似文献
110.
Atomic-resolution dynamics on the surface of amyloid-β protofibrils probed by solution NMR 总被引:1,自引:0,他引:1
Exchange dynamics between molecules free in solution and bound to the surface of a large supramolecular structure, a polymer, a membrane or solid support are important in many phenomena in biology and materials science. Here we present a novel and generally applicable solution NMR technique, known as dark-state exchange saturation transfer (DEST), to probe such exchange phenomena with atomic resolution. This is illustrated by the exchange reaction between amyloid-β (Aβ) monomers and polydisperse, NMR-invisible ('dark') protofibrils, a process of significant interest because the accumulation of toxic, aggregated forms of Aβ, from small oligomers to very large assemblies, has been implicated in the aetiology of Alzheimer's disease. The (15)N-DEST experiment imprints with single-residue-resolution dynamic information on the protofibril-bound species in the form of (15)N transverse relaxation rates ((15)N-R(2)) and exchange kinetics between monomers and protofibrils onto the easily observed two-dimensional (1)H-(15)N correlation spectrum of the monomer. The exchanging species on the protofibril surface comprise an ensemble of sparsely populated states where each residue is either tethered to (through other residues) or in direct contact with the surface. The first eight residues exist predominantly in a mobile tethered state, whereas the largely hydrophobic central region and part of the carboxy (C)-terminal hydrophobic region are in direct contact with the protofibril surface for a significant proportion of the time. The C-terminal residues of both Aβ40 and Aβ42 display lower affinity for the protofibril surface, indicating that they are likely to be surface exposed rather than buried as in structures of Aβ fibrils, and might therefore comprise the critical nucleus for fibril formation. The values, however, are significantly larger for the C-terminal residues of Aβ42 than Aβ40, which might explain the former's higher propensity for rapid aggregation and fibril formation. 相似文献