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41.
Ecology and management of mahogany (Swietenia macrophylla King) in the Chimanes Forest, Bed, Bolivia
R.E. GULLISON S.N. PANFIL JJ. STROUSE S.P. HUBBELL 《Botanical journal of the Linnean Society. Linnean Society of London》1996,122(1):9-34
Mahogany ( Swietenia macrophylla King) regenerates in areas of erosion on high terraces and in forest killed by flooding and deposition of alluvial sediments in the Chimanes Forest, Bolivia. These hydrological disturbances are patchy, and only one of five stands of mahogany that we inventoried was regenerating. Mahogany survives these disturbances significantly better than the common tree species. The long time between disturbances appears to favour late maturation. Mahogany trees allocate little photosynthates to reproduction until they are very large emergents, at least 80 cm in diameter. The episodic nature of the regeneration sites means that mahogany stands are composed of one or a few cohorts, which are vulnerable to overharvesting, particularly with the current use of a minimum cutting diameter to regulate harvest. The delayed onset of fecundity means that the small trees that escape harvest are not very fecund, resulting in minimal seed input to logged forest. Only 7–9% of the gaps created by logging contain natural regeneration after 20 + yr. A successful management plan for mahogany would entail a monocyclic harvest, with a rotation age of 100 + years, the estimated time that it takes for trees to achieve commercial size in natural forest. Since the number of seed trees that will be left is small, they should be concentrated in sites that are likely to be conducive to natural regeneration, such as near rivers and flood damaged forest. Seed production will be maximized for a given basal area (opportunity cost to loggers) if trees c. 110 cm dbh are selected as seed trees. The mahogany stocks in the Chimanes Forest are nearly exhausted, but the findings of this study could be used to help rebuild the mahogany populations, or to design management plans for the commercial species that have similar ecologies to mahogany. 相似文献
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Stefanie Kirschner Bettina Mürle Manuela Felix Anna Arns Christoph Groden Frederik Wenz Andreas Hug Gerhard Glatting Martin Kramer Frank A. Giordano Marc A. Brockmann 《PloS one》2016,11(11)
PurposeThere is an increasing need for small animal in vivo imaging in murine orthotopic glioma models. Because dedicated small animal scanners are not available ubiquitously, the applicability of a clinical CT scanner for visualization and measurement of intracerebrally growing glioma xenografts in living mice was validated.ResultsTumor volumes (mean±SD mm3) were similar between both CT-modalities (micro-CT: 19.8±19.0, clinical CT: 19.8±18.8; Wilcoxon signed-rank test p = 0.813). Moreover, between reader analyses for each modality showed excellent agreement as demonstrated by correlation analysis (Spearman-Rho >0.9; p<0.01 for all correlations). Histologically measured tumor volumes (11.0±11.2) were significantly smaller due to shrinkage artifacts (p<0.05). CNR and SNR were 2.1±1.0 and 1.1±0.04 for micro-CT and 23.1±24.0 and 1.9±0.7 for the clinical CTscanner, respectively.ConclusionClinical CT scanners may reliably be used for in vivo imaging and volumetric analysis of brain tumor growth in mice. 相似文献
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Heterogeneous binding of high mobility group chromosomal proteins to nuclei 总被引:7,自引:5,他引:2
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A dramatic difference is observed in the intracellular distribution of the high mobility group (HMG) proteins when chicken embryo fibroblasts are fractionated into nucleus and cytoplasm by either mass enucleation of cytochalasin-B-treated cells or by differential centrifugation of mechanically disrupted cells. Nuclei (karyoplasts) obtained by cytochalasin B treatment of cells contain more than 90 percent of the HMG 1, while enucleated cytoplasts contain the remainder. A similar distribution between karyoplasts and cytoplasts is observed for the H1 histones and the nucleosomal core histones as anticipated. The presence of these proteins, in low amounts, in the cytoplast preparation can be accounted for by the small percentage of unenucleated cells present. In contrast, the nuclei isolated from mechanically disrupted cells contain only 30-40 percent of the total HMGs 1 and 2, the remainder being recovered in the cytosol fraction. No histone is observed in the cytosol fraction. Unike the higher molecular weight HMGs, most of the HMGs 14 and 17 sediment with the nuclei after cell lysis by mechanical disruption. The distribution of HMGs is unaffected by incubating cells with cytochalasin B and mechanically fractionating rather than enucleating them. Therefore, the dramatic difference in HMG 1 distribution observed using the two fractionation techniques cannot be explained by a cytochalasin-B-induced redistribution. On reextraction and sedimentation of isolated nuclei obtained by mechanical cell disruption, only 8 percent of the HMG 1 is released to the supernate. Thus, the majority of the HMG 1 originally isolated with these nuclei, representing 35 percent of the total HMG 1, is stably bound, as is all the HMGs 14 and 17. The remaining 65 percent of the HMGs 1 and 2 is unstably bound and leaks to the cytosol fraction under the conditions of mechanical disruption. It is suggested that the unstably bound HMGs form a protein pool capable of equilibrating between cytoplasm and stably bound HMGs. 相似文献
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Molecular evolution of rodent insulins 总被引:1,自引:0,他引:1
Several trees of amino acid sequences of rodent insulins were derived with
the maximum-parsimony procedure. Possible orthologous and paralogous
relationships were investigated. Except for a recent gene duplication in
the ancestor of rat and mouse, there are no strong arguments for other
paralogous relationships. Therefore, a tree in agreement with other
biological data is the most reasonable one. According to this tree, the
capacity to form zinc-binding hexamers was lost once in the ancestor of the
hystricomorph rodents, followed by moderately increased evolutionary rates
in the lineages to African porcupine and chinchilla but highly increased
rates in at least three independent lines to other taxa of this suborder:
guinea pig, cuis, and Octodontoidea (coypu and casiragua).
相似文献
49.
A downstream regulatory element located within the coding sequence mediates autoregulated expression of the yeast fatty acid synthase gene FAS2 by the FAS1 gene product 总被引:1,自引:0,他引:1
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Peter Wenz Sabine Schwank Ursula Hoja Hans-Joachim Schüller 《Nucleic acids research》2001,29(22):4625-4632
50.
Jorge J. Wenz Virginia Borroni Francisco J. Barrantes 《The Journal of membrane biology》2010,235(3):163-175
Extensive evidence supports the notion that the cytoskeleton participates in the immobilization and membrane clustering of
the nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. Stimulated emission depletion fluorescence microscopy
has revealed the supramolecular organization of AChR nanoclusters at the surface of CHO-K1/A5 cells with subdiffraction resolution
(Kellner et al., Neuroscience 144:135–143 2007). We studied the effect of two cytoskeletal-disrupting drugs (cytochalasin D and jasplakinolide) on the nanoscale distribution
of muscle-type AChR expressed in these cells by means of mathematical and statistical analysis of images obtained with the
same high-resolution microscopy. AChR nanoclusters were found to be randomly distributed in both controls and cells treated
with either drug for distances larger than 500 nm. Treatments altered the distribution of AChR nanoclusters according to their
brightness/size. Cytochalasin D and jasplakinolide produced a statistically significant increase in the proportion of medium-size
nanoclusters and a diminution of small nanoclusters, indicating higher disrupting activity on the latter. This was further
corroborated by the diminution of the brightness/diameter ratio of nanoclusters (a measure of the intracluster density of
AChR molecules) and by Ripley’s analysis applied to simulated patterns with intracluster aggregation of AChR molecules. The
combined analytical tools bring out subtle changes in the two-dimensional organization of the AChR nanoaggregates on disruption
of the cytoskeletal network and throw light on the possible link between the cytoskeleton and the distribution of the AChR
at the cell surface. 相似文献