全文获取类型
收费全文 | 181篇 |
免费 | 3篇 |
专业分类
系统科学 | 4篇 |
教育与普及 | 1篇 |
理论与方法论 | 17篇 |
现状及发展 | 49篇 |
研究方法 | 30篇 |
综合类 | 83篇 |
出版年
2020年 | 1篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 4篇 |
2012年 | 13篇 |
2011年 | 15篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 13篇 |
2007年 | 14篇 |
2006年 | 14篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 1篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有184条查询结果,搜索用时 0 毫秒
61.
Beukelaers P Vandenbosch R Caron N Nguyen L Moonen G Malgrange B 《Cellular and molecular life sciences : CMLS》2012,69(9):1493-1503
The adult brain most probably reaches its highest degree of plasticity with the lifelong generation and integration of new
neurons in the hippocampus and olfactory system. Neural precursor cells (NPCs) residing both in the subgranular zone of the
dentate gyrus and in the subventricular zone of the lateral ventricles continuously generate neurons that populate the dentate
gyrus and the olfactory bulb, respectively. The regulation of NPC proliferation in the adult brain has been widely investigated
in the past few years. Yet, the intrinsic cell cycle machinery underlying NPC proliferation remains largely unexplored. In
this review, we discuss the cell cycle components that are involved in the regulation of NPC proliferation in both neurogenic
areas of the adult brain. 相似文献
62.
Grégoire Masliah Pierre Barraud Frédéric H. -T. Allain 《Cellular and molecular life sciences : CMLS》2013,70(11):1875-1895
The double-stranded RNA binding domain (dsRBD) is a small protein domain of 65–70 amino acids adopting an αβββα fold, whose central property is to bind to double-stranded RNA (dsRNA). This domain is present in proteins implicated in many aspects of cellular life, including antiviral response, RNA editing, RNA processing, RNA transport and, last but not least, RNA silencing. Even though proteins containing dsRBDs can bind to very specific dsRNA targets in vivo, the binding of dsRBDs to dsRNA is commonly believed to be shape-dependent rather than sequence-specific. Interestingly, recent structural information on dsRNA recognition by dsRBDs opens the possibility that this domain performs a direct readout of RNA sequence in the minor groove, allowing a global reconsideration of the principles describing dsRNA recognition by dsRBDs. We review in this article the current structural and molecular knowledge on dsRBDs, emphasizing the intricate relationship between the amino acid sequence, the structure of the domain and its RNA recognition capacity. We especially focus on the molecular determinants of dsRNA recognition and describe how sequence discrimination can be achieved by this type of domain. 相似文献
63.
Pierre A. Cholette 《Journal of forecasting》1982,1(4):375-383
Using the method of ARIMA forecasting with benchmarks developed in this paper, it is possible to obtain forecasts which take into account the historical information of a series, captured by an ARIMA model (Box and Jenkins, 1970), as well as partial prior information about the forecasts. Prior information takes the form of benchmarks. These originate from the advice of experts, from forecasts of an annual econometric model or simply from pessimistic, realistic or optimistic scenarios contemplated by the analyst of the current economic situation. The benchmarks may represent annual levels to be achieved, neighbourhoods to be reached for a given time period, movements to be displayed or more generally any linear criteria to be satisfied by the forecasted values. The forecaster may then exercise his current economic evaluation and judgement to the fullest extent in deriving forecasts, since the laboriousness experienced without a systematic method is avoided. 相似文献
64.
Weidenspointner G Skinner G Jean P Knödlseder J von Ballmoos P Bignami G Diehl R Strong AW Cordier B Schanne S Winkler C 《Nature》2008,451(7175):159-162
Gamma-ray line radiation at 511 keV is the signature of electron-positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511-keV line emission coming from the inner Galactic disk ( approximately 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies >20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron-positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511-keV line. For these models, our result implies that up to a few times 10(41) positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter. 相似文献
65.
66.
Gaspard N Bouschet T Hourez R Dimidschstein J Naeije G van den Ameele J Espuny-Camacho I Herpoel A Passante L Schiffmann SN Gaillard A Vanderhaeghen P 《Nature》2008,455(7211):351-357
The cerebral cortex develops through the coordinated generation of dozens of neuronal subtypes, but the mechanisms involved remain unclear. Here we show that mouse embryonic stem cells, cultured without any morphogen but in the presence of a sonic hedgehog inhibitor, recapitulate in vitro the major milestones of cortical development, leading to the sequential generation of a diverse repertoire of neurons that display most salient features of genuine cortical pyramidal neurons. When grafted into the cerebral cortex, these neurons develop patterns of axonal projections corresponding to a wide range of cortical layers, but also to highly specific cortical areas, in particular visual and limbic areas, thereby demonstrating that the identity of a cortical area can be specified without any influence from the brain. The discovery of intrinsic corticogenesis sheds new light on the mechanisms of neuronal specification, and opens new avenues for the modelling and treatment of brain diseases. 相似文献
67.
Continental erosion controls atmospheric carbon dioxide levels on geological timescales through silicate weathering, riverine transport and subsequent burial of organic carbon in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins is however limited by the organic carbon load capacity of the sediments and organic carbon oxidation in continental margins. At the global scale, previous studies have suggested that about 70 per cent of riverine organic carbon is returned to the atmosphere, such as in the Amazon basin. Here we present a comprehensive organic carbon budget for the Himalayan erosional system, including source rocks, river sediments and marine sediments buried in the Bengal fan. We show that organic carbon export is controlled by sediment properties, and that oxidative loss is negligible during transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the organic carbon is recent organic matter captured during transport, which serves as a net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon buried in oceanic sediments. High erosion rates in the Himalayas generate high sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the observed extreme organic carbon burial efficiency. Active orogenic systems generate enhanced physical erosion and the resulting organic carbon burial buffers atmospheric carbon dioxide levels, thereby exerting a negative feedback on climate over geological timescales. 相似文献
68.
TJ Pugh SD Weeraratne TC Archer DA Pomeranz Krummel D Auclair J Bochicchio MO Carneiro SL Carter K Cibulskis RL Erlich H Greulich MS Lawrence NJ Lennon A McKenna J Meldrim AH Ramos MG Ross C Russ E Shefler A Sivachenko B Sogoloff P Stojanov P Tamayo JP Mesirov V Amani N Teider S Sengupta JP Francois PA Northcott MD Taylor F Yu GR Crabtree AG Kautzman SB Gabriel G Getz N Jäger DT Jones P Lichter SM Pfister TM Roberts M Meyerson SL Pomeroy YJ Cho 《Nature》2012,488(7409):106-110
69.
A column generation based approach is proposed for solving the cluster-wise regression problem. The proposed strategy relies firstly on several efficient heuristic strategies to insert columns into the restricted master problem. If these heuristics fail to identify an improving column, an exhaustive search is performed starting with incrementally larger ending subsets, all the while iteratively performing heuristic optimization to ensure a proper balance of exact and heuristic optimization. Additionally, observations are sequenced by their dual variables and by their inclusion in joint pair branching rules. The proposed strategy is shown to outperform the best known alternative (BBHSE) when the number of clusters is greater than three. Additionally, the current work further demonstrates and expands the successful use of the new paradigm of using incrementally larger ending subsets to strengthen the lower bounds of a branch and bound search as pioneered by Brusco's Repetitive Branch and Bound Algorithm (RBBA). 相似文献
70.
Kaminsky R Ducray P Jung M Clover R Rufener L Bouvier J Weber SS Wenger A Wieland-Berghausen S Goebel T Gauvry N Pautrat F Skripsky T Froelich O Komoin-Oka C Westlund B Sluder A Mäser P 《Nature》2008,452(7184):176-180
Anthelmintic resistance in human and animal pathogenic helminths has been spreading in prevalence and severity to a point where multidrug resistance against the three major classes of anthelmintics--the benzimidazoles, imidazothiazoles and macrocyclic lactones--has become a global phenomenon in gastrointestinal nematodes of farm animals. Hence, there is an urgent need for an anthelmintic with a new mode of action. Here we report the discovery of the amino-acetonitrile derivatives (AADs) as a new chemical class of synthetic anthelmintics and describe the development of drug candidates that are efficacious against various species of livestock-pathogenic nematodes. These drug candidates seem to have a novel mode of action involving a unique, nematode-specific clade of acetylcholine receptor subunits. The AADs are well tolerated and of low toxicity to mammals, and overcome existing resistances to the currently available anthelmintics. 相似文献