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81.
The myelin-associated glycoprotein (MAG) mediates cell-cell interactions between myelinating glial cells and neurons. Here we describe the extracellular matrix glycoprotein fibronectin as a binding partner of MAG. It has been identified by affinity precipitation with MAG-Fc from NG108-15 cells and by microsequencing of two peptides derived from a 210-kDa protein band. Western blot analysis showed that fibronectin is also present in MAG binding partners isolated from N(2)A (murine neuroblastoma) cells, rat brain and rat spinal cord. Different fibronectin isoforms have been isolated from brains of young and adult rats, indicating that the expression of MAG binding fibronectin changes during development. 相似文献
82.
M. Wurster S. Mundt E. Hammer F. Schauer U. Lindequist 《Journal of applied phycology》2003,15(2-3):171-176
Investigations of the unicellular marine cyanobacterium Synechococcus PCC 7002 revealed its ability to metabolize phenol under non-photosynthetic conditions up to 100 mg L–1. Under continuous light, photoautotrophic growth was reduced only slightly in the presence of this phenol concentration, but no transformation was observed. However neither under photoautotrophic nor heterotrophic conditions were the cells able to use phenol for growth. During the degradation of phenol in the dark cis,cis-muconic acid was produced as the major product, which was identified by gas chromatography/mass spectrometry. This result was confirmed by an identical absorption spectrum and an identical retention time in high performance liquid chromatographic analysis with authentic muconic acid as standard. This provides the first record for an ortho-fission of a phenolic substance by cyanobacteria. Further investigations of the breakdown mechanism of phenol have shown that the transformation is an extracellular process inhibited by heat, proteases and metal ions and is probably catalyzed by a protein. 相似文献
83.
84.
Methylotrophic bacteria on the surfaces of field-grown sunflower plants: a biogeographic perspective
Plant-associated methylobacteria of the genus Methylobacterium colonize the foliage and roots of embryophytes, living on the volatile compound methanol emitted from the cells of their
host organism. In this study we analyzed these surface-dwelling pink-pigmented epiphytes in three contrasting habitats of
field-grown sunflower plants (Helianthus annuus). Using the methanol–ammonium salts agar surface impression method and a polymerase chain reaction (PCR)-based assay, we
document the occurrence and characterize the composition of the methylobacteria in these epiphytic habitats. In both the sun-exposed
phylloplane (yellow ligulate florets; green leaves) and the moist, dark rhizoplane pink-pigmented methylobacteria were detected
that are assigned to the taxa M. mesophilicum, M. extorquens, M. radiotolerans and M. sp. (un-identifiable by our methods). Considerable differences in relative species compositions were found. These data are
discussed with respect to a biogeographic model of the plant surface and microbial population dynamics on leaves. In addition,
methylobacteria were analyzed by microscopic techniques. We document that in sedentary colonies extracellular polymers are
secreted. However, flagella, which were observed in single cells maintained in liquid cultures, are absent in these bacterial
aggregates. 相似文献
85.
86.
C.-T. Lai J. R. Ehleringer A. J. Schauer P. P. Tans† D. Y. Hollinger‡ K. T. Paw U§ J. W. Munger¶ S. C. Wofsy¶ 《Global Change Biology》2005,11(4):633-643
The δ13C values of atmospheric carbon dioxide (CO2) can be used to partition global patterns of CO2 source/sink relationships among terrestrial and oceanic ecosystems using the inversion technique. This approach is very sensitive to estimates of photosynthetic 13C discrimination by terrestrial vegetation (ΔA), and depends on δ13C values of respired CO2 fluxes (δ13CR). Here we show that by combining two independent data streams – the stable isotope ratios of atmospheric CO2 and eddy‐covariance CO2 flux measurements – canopy scale estimates of ΔA can be successfully derived in terrestrial ecosystems. We also present the first weekly dataset of seasonal variations in δ13CR from dominant forest ecosystems in the United States between 2001 and 2003. Our observations indicate considerable summer‐time variation in the weekly value of δ13CR within coniferous forests (4.0‰ and 5.4‰ at Wind River Canopy Crane Research Facility and Howland Forest, respectively, between May and September). The monthly mean values of δ13CR showed a smaller range (2–3‰), which appeared to significantly correlate with soil water availability. Values of δ13CR were less variable during the growing season at the deciduous forest (Harvard Forest). We suggest that the negative correlation between δ13CR and soil moisture content observed in the two coniferous forests should represent a general ecosystem response to the changes in the distribution of water resources because of climate change. Shifts in δ13CR and ΔA could be of sufficient magnitude globally to impact partitioning calculations of CO2 sinks between oceanic and terrestrial compartments. 相似文献
87.
To characterize synchronisation strategies in the tracking of auditory rhythm with rhythmic finger tapping, the adaptation
process after unexpected step changes of an interstimulus interval (ISI) of 500 ms was investigated. Step changes of 2% (10
ms), 4% (20 ms), and 10% (50 ms) of ISI were applied to the stimulus sequence. Synchronisation patterns of 5 subjects were
analyzed based on synchronisation error (SE) and interresponse intervals (IRI). A strategy shift contigent upon the size of
the introduced step change was detected. After small ISI changes, rapid IRI matching to the new ISI was accompanied by temporarily
enlarged SE values, which slowly returned to preferred SE values before the step change. Large ISI changes showed quick SE
adaptations accompanied by a temporary overcorrection of IRI. Response asymmetry between ISI decreases and increases emerged,
showing a stronger adaptation during ISI increases. A two-dimensional difference equation was formulated to simulate the time
series of intertap intervals and explain the control process during IRI and SE adjustments. The system constants were optimized
to minimalize the deviations between the computed and the observed response trajectories, consisting of the time series of
SE and IRI. It was shown that a successful model fit using a linear two-dimensional difference equation was based on the size
and direction of the ISI changes. MANOVA procedures showed that differences in equation parameters during small and large
step changes were statistically significant (P<0.05). It is therefore suggested that a uniform model accounting for synchronization responses to all step changes would
require the introduction of nonlinear system properties.
Received: 20 August 1997/Accepted in revised form: 9 June 1998 相似文献
88.
89.
90.
Hui Liu Loranne Magoun Steve Luperchio David B. Schauer & John M. Leong 《Molecular microbiology》1999,34(1):67-81
Enterohaemorrhagic Escherichia coli (EHEC) has emerged as an important agent of diarrhoeal disease. Attachment to host cells, an essential step during intestinal colonization by EHEC, is associated with the formation of a highly organized cytoskeletal structure containing filamentous actin, termed an attaching and effacing (A/E) lesion, directly beneath bound bacteria. The outer membrane protein intimin is required for the formation of this structure, as is Tir, a bacterial protein that is translocated into the host cell and is thought to function as a receptor for intimin. To understand intimin function better, we fused EHEC intimin to a homologous protein, Yersinia pseudotuberculosis invasin, or to maltose-binding protein. The N-terminal 539 amino acids of intimin were sufficient to promote outer membrane localization of the C-terminus of invasin and, conversely, the N-terminal 489 amino acids of invasin were sufficient to promote the localization of the C-terminus of intimin. The C-terminal 181 residues of intimin were sufficient to bind mammalian cells that had been preinfected with an enteropathogenic E. coli strain that expresses Tir but not intimin. Binding of intimin derivatives to preinfected cells correlated with binding to recombinant Tir protein. Finally, the 181-residue minimal Tir-binding region of intimin, when purified and immobilized on latex beads, was sufficient to trigger A/E lesions on preinfected mammalian cells. 相似文献