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排序方式: 共有160条查询结果,搜索用时 15 毫秒
71.
72.
The dynamics of a single impurity in an environment is a fundamental problem in many-body physics. In the solid state, a well known case is an impurity coupled to a bosonic bath (such as lattice vibrations); the impurity and its accompanying lattice distortion form a new entity, a polaron. This quasiparticle plays an important role in the spectral function of high-transition-temperature superconductors, as well as in colossal magnetoresistance in manganites. For impurities in a fermionic bath, studies have considered heavy or immobile impurities which exhibit Anderson's orthogonality catastrophe and the Kondo effect. More recently, mobile impurities have moved into the focus of research, and they have been found to form new quasiparticles known as Fermi polarons. The Fermi polaron problem constitutes the extreme, but conceptually simple, limit of two important quantum many-body problems: the crossover between a molecular Bose-Einstein condensate and a superfluid with BCS (Bardeen-Cooper-Schrieffer) pairing with spin-imbalance for attractive interactions, and Stoner's itinerant ferromagnetism for repulsive interactions. It has been proposed that such quantum phases (and other elusive exotic states) might become realizable in Fermi gases confined to two dimensions. Their stability and observability are intimately related to the theoretically debated properties of the Fermi polaron in a two-dimensional Fermi gas. Here we create and investigate Fermi polarons in a two-dimensional, spin-imbalanced Fermi gas, measuring their spectral function using momentum-resolved photoemission spectroscopy. For attractive interactions, we find evidence for a disputed pairing transition between polarons and tightly bound dimers, which provides insight into the elementary pairing mechanism of imbalanced, strongly coupled two-dimensional Fermi gases. Additionally, for repulsive interactions, we study novel quasiparticles--repulsive polarons--the lifetime of which determines the possibility of stabilizing repulsively interacting Fermi systems. 相似文献
73.
Ciocchi S Herry C Grenier F Wolff SB Letzkus JJ Vlachos I Ehrlich I Sprengel R Deisseroth K Stadler MB Müller C Lüthi A 《Nature》2010,468(7321):277-282
The central amygdala (CEA), a nucleus predominantly composed of GABAergic inhibitory neurons, is essential for fear conditioning. How the acquisition and expression of conditioned fear are encoded within CEA inhibitory circuits is not understood. Using in vivo electrophysiological, optogenetic and pharmacological approaches in mice, we show that neuronal activity in the lateral subdivision of the central amygdala (CEl) is required for fear acquisition, whereas conditioned fear responses are driven by output neurons in the medial subdivision (CEm). Functional circuit analysis revealed that inhibitory CEA microcircuits are highly organized and that cell-type-specific plasticity of phasic and tonic activity in the CEl to CEm pathway may gate fear expression and regulate fear generalization. Our results define the functional architecture of CEA microcircuits and their role in the acquisition and regulation of conditioned fear behaviour. 相似文献
74.
Recent decline in the global land evapotranspiration trend due to limited moisture supply 总被引:31,自引:0,他引:31
Jung M Reichstein M Ciais P Seneviratne SI Sheffield J Goulden ML Bonan G Cescatti A Chen J de Jeu R Dolman AJ Eugster W Gerten D Gianelle D Gobron N Heinke J Kimball J Law BE Montagnani L Mu Q Mueller B Oleson K Papale D Richardson AD Roupsard O Running S Tomelleri E Viovy N Weber U Williams C Wood E Zaehle S Zhang K 《Nature》2010,467(7318):951-954
More than half of the solar energy absorbed by land surfaces is currently used to evaporate water. Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate. Evapotranspiration changes may already be under way, but direct observational constraints are lacking at the global scale. Until such evidence is available, changes in the water cycle on land?a key diagnostic criterion of the effects of climate change and variability?remain uncertain. Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008, compiled using a global monitoring network, meteorological and remote-sensing observations, and a machine-learning algorithm. In addition, we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface models. Our results suggest that global annual evapotranspiration increased on average by 7.1?±?1.0?millimetres per year per decade from 1982 to 1997. After that, coincident with the last major El Ni?o event in 1998, the global evapotranspiration increase seems to have ceased until 2008. This change was driven primarily by moisture limitation in the Southern Hemisphere, particularly Africa and Australia. In these regions, microwave satellite observations indicate that soil moisture decreased from 1998 to 2008. Hence, increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend. Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science. 相似文献
75.
Characterization of murine non-adherent bone marrow cells leading to recovery of endogenous hematopoiesis 总被引:1,自引:1,他引:0
Stephan Fricke Christian Fricke Christopher Oelkrug Nadja Hilger Uta Sch?nfelder Manja Kamprad J?rg Lehmann Johannes Boltze Frank Emmrich Ulrich Sack 《Cellular and molecular life sciences : CMLS》2010,67(23):4095-4106
Non-adherent bone marrow-derived cells (NA-BMCs) are a mixed cell population that can give rise to multiple mesenchymal phenotypes
and that facilitates hematopoietic recovery. We characterized NA-BMCs by flow cytometry, fibroblast colony-forming units (CFU-f),
real-time PCR, and in in vivo experiments. In comparison to adherent cells, NA-BMCs expressed high levels of CD11b+ and CD90+ within the CD45+ cell fraction. CFU-f were significantly declining over the cultivation period, but NA-BMCs were still able to form CFU-f
after 5 days. Gene expression analysis of allogeneic NA-BMCs compared to bone marrow (BM) indicates that NA-BMCs contain stromal,
mesenchymal, endothelial cells and monocytes, but less osteoid, lymphoid, and erythroid cells, and hematopoietic stem cells.
Histopathological data and analysis of weight showed an excellent recovery and organ repair of lethally irradiated mice after
NA-BMC transplantation with a normal composition of the BM. 相似文献
76.
Genome-wide association study identifies multiple loci influencing human serum metabolite levels 总被引:1,自引:0,他引:1
Kettunen J Tukiainen T Sarin AP Ortega-Alonso A Tikkanen E Lyytikäinen LP Kangas AJ Soininen P Würtz P Silander K Dick DM Rose RJ Savolainen MJ Viikari J Kähönen M Lehtimäki T Pietiläinen KH Inouye M McCarthy MI Jula A Eriksson J Raitakari OT Salomaa V Kaprio J Järvelin MR Peltonen L Perola M Freimer NB Ala-Korpela M Palotie A Ripatti S 《Nature genetics》2012,44(3):269-276
Nuclear magnetic resonance assays allow for measurement of a wide range of metabolic phenotypes. We report here the results of a GWAS on 8,330 Finnish individuals genotyped and imputed at 7.7 million SNPs for a range of 216 serum metabolic phenotypes assessed by NMR of serum samples. We identified significant associations (P < 2.31 × 10(-10)) at 31 loci, including 11 for which there have not been previous reports of associations to a metabolic trait or disorder. Analyses of Finnish twin pairs suggested that the metabolic measures reported here show higher heritability than comparable conventional metabolic phenotypes. In accordance with our expectations, SNPs at the 31 loci associated with individual metabolites account for a greater proportion of the genetic component of trait variance (up to 40%) than is typically observed for conventional serum metabolic phenotypes. The identification of such associations may provide substantial insight into cardiometabolic disorders. 相似文献
77.
Melum E Franke A Schramm C Weismüller TJ Gotthardt DN Offner FA Juran BD Laerdahl JK Labi V Björnsson E Weersma RK Henckaerts L Teufel A Rust C Ellinghaus E Balschun T Boberg KM Ellinghaus D Bergquist A Sauer P Ryu E Hov JR Wedemeyer J Lindkvist B Wittig M Porte RJ Holm K Gieger C Wichmann HE Stokkers P Ponsioen CY Runz H Stiehl A Wijmenga C Sterneck M Vermeire S Beuers U Villunger A Schrumpf E Lazaridis KN Manns MP Schreiber S Karlsen TH 《Nature genetics》2011,43(1):17-19
Primary sclerosing cholangitis (PSC) is a chronic bile duct disease affecting 2.4-7.5% of individuals with inflammatory bowel disease. We performed a genome-wide association analysis of 2,466,182 SNPs in 715 individuals with PSC and 2,962 controls, followed by replication in 1,025 PSC cases and 2,174 controls. We detected non-HLA associations at rs3197999 in MST1 and rs6720394 near BCL2L11 (combined P = 1.1 × 10?1? and P = 4.1 × 10??, respectively). 相似文献
78.
Strauss J Zhang Q Verleyen P Huybrechts J Neupert S Predel R Pauwels K Dircksen H 《Cellular and molecular life sciences : CMLS》2011,68(20):3403-3423
We report identification of a beta-type pigment-dispersing hormone (PDH) identical in two water flea species, Daphnia magna and Daphnia pulex. It has been identified by cloning of precursors, chromatographic isolation from tissue extracts followed by immunoassays
and de novo-mass spectrometric sequencing. The peptide is restricted to a complex system of distinct interneurons in the brain
and visual ganglia, but does not occur in neurosecretory cells projecting to neurohemal organs as in decapod crustaceans.
Thirteen neuron types individually identified and reconstructed by immunohistochemistry were almost identical in terms of
positions and projection patterns in both species. Several neurons invade and form plexuses in visual ganglia and major brain
neuropils including the central body. Five neuron types show contralateral pathways and form plexuses in the lateral, dorsal,
or postlateral brain neuropils. Others are local interneurons, and a tritocerebral neuron connects the protocerebrum with
the neuropil of the locomotory second antenna. Two visual ganglia neuron types lateral to the medulla closely resemble insect
medulla lateral circadian clock neurons containing pigment-dispersing factor based upon positional and projectional criteria.
Experiments under 12:12 h light/dark cycles and constant light or darkness conditions showed significant circadian changes
in numbers and activities of one type of medulla lateral PDH neuron with an acrophase in the evening. This simple PDH system
shows striking homologies to PDH systems in decapod crustaceans and well-known clock neurons in several insects, which suggests
evolutionary conservation of an ancient peptidergic interneuronal system that is part of biological clocks. 相似文献
79.
Ludwig Heesen Michael Peitz Laura Torres-Benito Irmgard Hölker Kristina Hupperich Kristina Dobrindt Johannes Jungverdorben Swetlana Ritzenhofen Beatrice Weykopf Daniela Eckert Seyyed Mohsen Hosseini-Barkooie Markus Storbeck Noemi Fusaki Renata Lonigro Raoul Heller Min Jeong Kye Oliver Brüstle Brunhilde Wirth 《Cellular and molecular life sciences : CMLS》2016,73(10):2089-2104
80.