全文获取类型
收费全文 | 73篇 |
免费 | 11篇 |
出版年
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 3篇 |
2012年 | 4篇 |
2011年 | 2篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1957年 | 1篇 |
1953年 | 2篇 |
1952年 | 3篇 |
1951年 | 2篇 |
1949年 | 1篇 |
排序方式: 共有84条查询结果,搜索用时 31 毫秒
11.
12.
Growth of Anopheles mosquito larvae on dietary microbiota in aquatic surface microlayers 总被引:1,自引:0,他引:1
R. S. WOTTON D. T. CHALONER C. A. YARDLEY R. W. MERRITT 《Medical and veterinary entomology》1997,11(1):65-70
Abstract. Hydrophobic organic matter accumulates under the surface film of water bodies to form the surface microlayers. Heterotrophic microorganisms use this organic matter for growth, and they, in turn, are fed upon by Anopheles mosquito larvae and other animals. From laboratory experiments we show that two species of mosquito larvae, Anopheles gambiae and An.quadrimaculatus , grew most rapidly where surface micro-layers were present and, especially, where labile dissolved organic matter was added to promote growth of microorganisms. The importance of microorganisms was confirmed by the addition of gentamicin antibiotic, which suppressed the microbiota and reduced the growth of larvae feeding on surface microlayers. Anopheles larvae grew well on a suspension of finely ground fish food to which the antibiotic had been added, showing that reduced growth was not due to gentamicin itself. Because sub-surface microorganisms are the components of the larval diet that most affect growth, we discuss their relevance to strategies for larval control of Anopheles mosquitoes. 相似文献
13.
JW Santo Domingo J C Radway E W Wilde P Hermann T C Hazen 《Journal of industrial microbiology & biotechnology》1997,18(6):389-395
Immobilization of the trichloroethylene-degrading bacterium Burkholderia cepacia was evaluated using hydrophilic polyurethane foam. The influence of several foam formulation parameters upon cell retention
was examined. Surfactant type was a major determinant of retention; a lecithin-based compound retained more cells than pluronic-
or silicone-based surfactants. Excessive amounts of surfactant led to increased washout of bacteria. Increasing the biomass
concentration in the foam from 4.8 to 10.5% dry weight per wet weight of foam resulted in fewer cells being washed out. Embedding
at reduced temperature did not significantly affect retention, while the use of a silane binding agent gave inconsistent
results. The optimal formulation retained all but 0.2% of total embedded cells during passage of 2 L of water through columns
containing 2 g of foam. All foam formulations tested reduced the culturability of embedded cells by several orders of magnitude,
but O2 consumption and CO2 evolution rates of embedded cells were never less than 50% of those of free cells. Nutrient amendments stimulated an increase
in cell volume and ribosomal activity in immobilized cells as indicated by hybridization studies using fluorescently labeled
ribosomal probes. These results indicate that, although immobilized cells were mostly nonculturable, they were metabolically
active and thus could be used for biodegradation of toxic compounds.
Received 23 December 1996/ Accepted in revised form 13 March 1997 相似文献
14.
Restriction-map variation associated with the G6PD polymorphism in natural populations of Drosophila melanogaster 总被引:10,自引:0,他引:10
Restriction-map variation was studied in 126 copies of the G6pd region in X
chromosome lines of Drosophila melanogaster from North America, Europe, and
Africa. Special attention was focused on the distribution of variation
relative to the geographically variable polymorphism for two
electrophoretic variants. Nucleotide heterozygosity as determined by eight
six-cutter restriction enzymes for the 13-kb region is estimated, on the
basis of the worldwide sample, to be 0.065%, which is the lowest value
reported for any comparable region in the D. melanogaster genome.
Significant linkage disequilibrium between electrophoretic alleles and
restriction-site variation is observed for several sites. In contrast to
published studies of other genetic regions, there are large insertions that
reach significant frequencies and are found across considerable geographic
distances. There is a clustering of this variation inside the first large
intervening sequence of the G6PD gene.
相似文献
15.
HUMAN α-amylase (α-1,4-glucan 4-glucanohydrolase, E.C. 3.2.1.1) is primarily in the pancreas and salivary glands and can be detected in serum and urine (UAmy) as well as in saliva (SaAmy) and duodenal secretions. The SaAmy locus (Amy1) has at least three mutant alleles with the combined frequency of electrophoretic variant phenotypes totalling approximately 0.01 in Caucasian Americans1. Subsequently, UAmy was shown to be a convenient source of pancreatic amylase. The pancreatic amylase locus (Amy2) has at least two mutant alleles in Caucasian and Afro-Americans2. The variant UAmy Ss is common in Caucasians whereas UAmy Sp has been found only in Afro-Americans; the frequency of variant phenotypes is 0·086 in each population2. 相似文献
16.
17.
Aartjan JW te Velthuis Jeroen F Admiraal Christoph P Bagowski 《BMC evolutionary biology》2007,7(1):129
Background
Development, differentiation and physiology of metazoans all depend on cell to cell communication and subsequent intracellular signal transduction. Often, these processes are orchestrated via sites of specialized cell-cell contact and involve receptors, adhesion molecules and scaffolding proteins. Several of these scaffolding proteins important for synaptic and cellular junctions belong to the large family of membrane-associated guanylate kinases (MAGUK). In order to elucidate the origin and the evolutionary history of the MAGUKs we investigated full-length cDNA, EST and genomic sequences of species in major phyla. 相似文献18.
Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska 总被引:2,自引:0,他引:2
JENNIFER W. HARDEN KRISTEN L. MANIES MERRITT R. TURETSKY† JASON C. NEFF‡ 《Global Change Biology》2006,12(12):2391-2403
The influence of discontinuous permafrost on ground‐fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four‐way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground‐fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5 cm depth was about 0.5°C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems. 相似文献
19.
20.
The growth and division of mitochondria during the cell cycle was investigated by a morphometric analysis of electron micrographs of synchronized HeLa cells. The ratio of total outer membrane contour length to cytoplasmic area did not vary significantly during the cell cycle, implying a continuous growth of the mitochondrial outer membrane. The mean fraction of cytoplasmic area occupied by mitochondrial profiles was likewise found to remain constant, indicating that the increase in total mitochondrial volume per cell occurs continuously during interphase, in such a way that the mitochondrial complement occupies a constant fraction( approximately 10-11(percent)) of the volume of the cytoplasm. The mean area, outer membrane contour length, and axis ratio of the mitochondrial profiles also did not vary appreciably during the cell cycle; furthermore, the close similarity of the frequency distributions of these parameters for the six experimental time-points suggested a stable mitochondrial shape distribution. The constancy of both the mean mitochondrial profile area and the number of mitochondrial profiles per unit of cytoplasmic area was interpreted to indicate the continuous division of mitochondria at the level of the cell population. Furthermore, no evidence was found for the occurrence of synchronous mitochondrial growth and division within individual cells. Thus, it appears that, in HeLa cells, there is no fixed temporal relationship between the growth and division of mitochondria and the events of the cell cycle. A number of statistical methods were developed for the purpose of making numerical estimates of certain three-dimensional cellular and mitochondrial parameters. Mean cellular and cytoplasmic volumes were calculated for the six time-points; both exhibited a nonlinear, approx. twofold increase. A comparison of the axis ratio distributions of the mitochondrial profiles with theoretical distributions expected from random sectioning of bodies of various three-dimensional shapes allowed the derivation of an "average" mitochondrial shape. This, in turn, permitted calculations to be made which expressed the two-dimensional results in three-dimensional terms. Thus, the estimated values for the number of mitochondria per unit of cytoplasmic volume and for the mean mitochondrial volume were found to remain constant during the cell cycle, while the estimated number of mitochondria per cell increase approx. twofold in an essentially continuous manner. 相似文献