全文获取类型
收费全文 | 185篇 |
免费 | 12篇 |
出版年
2021年 | 2篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 10篇 |
2013年 | 9篇 |
2012年 | 9篇 |
2011年 | 8篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 2篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1971年 | 8篇 |
1970年 | 2篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1966年 | 5篇 |
1965年 | 2篇 |
1960年 | 1篇 |
1954年 | 1篇 |
1951年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有197条查询结果,搜索用时 15 毫秒
151.
The conditions for continuous cultivation of Bacillus megaterium on a collagen-derived substrate (SP-100) were determined. The optimum conditions of temperature, pH, and dilution rate were 34 C, pH 7.0, and 0.25/hr, respectively. Increasing the substrate concentration in plain tap water resulted in proportional increases in the productivity of cell mass from 0.6 g per liter per hr at 1% substrate to 1.8 g per liter per hr at 10% substrate; however, the protein content of the biomass decreased from 60 to 36%, and the protein yield decreased from 91 to 50% at substrate concentrations of 1 and 10%, respectively. These effects (decreases) were reversed up to 7.5% substrate by mineral supplementation of the medium. The productivity of biomass increased from 0.6 to 1.9 per liter per hr; the protein content of the biomass, from 43 to 54%; and the protein yield, from 60 to 93%, respectively, as the substrate concentration (with mineral supplementation of the medium) was increased from 1 to 7.5%. Spent medium could be refortified and recycled as often as five times. The amino acids in the substrate protein appeared to be utilized for growth and metabolism more or less uniformly. Analysis of the B. megaterium biomass indicated considerable enrichment of the essential amino acids and reduction of proline, glycine, and hydroxyproline as compared to the collagen-derived substrate. The Protein Efficiency Ratios obtained on the collagen-derived substrate (SP-100) and on the B. megaterium biomass, expressed as percentages of the casein reference protein, were 14 and 74%, respectively. Thus, considerable improvement in nutritional value was effected by bacterial conversion of the collagen-derived substrate into single-cell protein. 相似文献
152.
In Arbacia punctulata and Strongylocentrotus purpuratus, two species of sea urchins, collagen synthesis begins during gastrulation and increases many-fold before reaching a plateau in the late pluteus stage. A collagen extraction method involving treatment with 0.1 M NaOH and hot 10% trichloroacetic acid provided the basis for a sensitive assay of collagen synthesis. 相似文献
153.
The critical electrolyte concentration principle was applied to the Alcian Blue staining of rat epiphyseal cartilage proteoglycans for electron microscopy. The distribution and structure of material in glutaraldehyde-fixed cartilage stained at pH 5.8 without MgCl2 and in the presence of 0.05, 0.4, 0.5, 0.9 and 1.0 M MgCl2 was compared with that produced by simultaneous staining and fixation at neutral pH. Both methods resulted in staining of intracellular material within vacuoles as well as staining of non-collagenous matrix material. The structure and distribution of Alcian Blue-positive matrix material consisted of rounded or polygonal granules which accumulated around cells in the proliferative and hypertrophied zones. A similar pattern of distribution was observed in samples stained in the presence of 0.4 or 0.5 M MgCl2. In these cases, however, the stained material exhibited a ribbon-like configuration and granules were few in number. Increasing the MgCl2 concentration to 1.0 M resulted in a marked reduction of Alcian Blue stained material. No ribbon-like structures were observed, and matrix granules were reduced in both number and size. The decreased staining associated with increased electrolyte concentration lends support to the concept that epiphyseal cartilage matrix granules are composed primarily of chondroitin sulphate, and suggest that this same material is present in vacuoles associated with the Golgi apparatus in chondrocytes of the proliferative and hypertrophying zones. 相似文献
154.
Morphological studies of bone and tendon 总被引:2,自引:0,他引:2
155.
Differential sensitivity of tongue areas and palate to electrical stimulation: a suprathreshold cross-modal matching study 总被引:2,自引:1,他引:1
A cross-modal matching procedure was used, in twelve subjects,to evaluate regional differences in suprathreshold sensitivityof the oral cavity to electrogustometric stimulation. Stimulationof five loci on each side of the oral cavity was performed:tongue tip (one cm from the midline), anterior tongue side (2.5cm from tip on lateral margin), posterior tongue side (regionof the foliate papillae), posterior medial tongue (one cm frommidline on circumvallate papillae), and soft palate (one cmfrom midline, one cm above superior pole of anterior palatinearch). The tip of the tongue was significantly more sensitivethan the other areas to electric stimulation, as evidenced bythe slope and absolute position of the psychophysical powerfunctions. Strong correlations were observed in the sensitivitymeasures across tongue loci and between tongue and palate sides.No effects of subject gender or mouth side were found. 相似文献
156.
Light microscopy, electron microscopy, and enzyme histochemistry were used to study the effects of spaceflight on metaphyseal and cortical bone of the rat tibia. Cortical cross-sectional area and perimeter were not altered by a 12.5-day spaceflight in 3-month-old male rats. The endosteal osteoblast population and the vasculature near the periosteal surface in flight rats compared with ground controls showed more pronounced changes in cortical bone than in metaphyseal bone. The osteoblasts demonstrated greater numbers of transitional Golgi vesicles, possibly caused by a decreased cellular metabolic energy source, but no difference in the large Golgi saccules or the cell membrane-associated alkaline phosphatase activity. The periosteal vasculature in the diaphysis of flight rats often showed lipid accumulations within the lumen of the vessels, occasional degeneration of the vascular wall, and degeneration of osteocytes adjacent to vessels containing intraluminal deposits. These changes were not found in the metaphyseal region of flight animals. The focal vascular changes may be due to ischemia of bone or a developing fragility of the vessel walls as a result of spaceflight. 相似文献
157.
The gun cells which develop from germinating cysts in Haptoglossa produce a specialized infection apparatus, the injection tube. Upon eversion this tube fires a missile-like projectile which penetrates the host cuticle and then forms an infective sporidium within the body cavity of the nematode host. The temporal assembly of this complex cell organelle has been determined by serial-section reconstructions of maturing gun cells in a previously undescribed Haptoglossa species. The differentiation of the partially walled inverted injection tube is an unusual example of internal tube growth, in which membrane and wall assembly are temporally separated. There is no evidence that the shape of this inverted tube, which coils around the nucleus until it doubles back on itself, is dictated by the disposition of cytoplasmic microtubules. However, actin-like material was associated with the delimiting membrane of the differentiating tube, particularly in the regions of extension. From these studies it seems likely that the "head and buttress" structures previously depicted as the barbed tip of the "harpoon-like" penetration missile are part of a separate, structurally complex system which we suggest locks the "missile" into position in the invaginated injection tube. From this detailed account of cell architecture, models for the likely mechanism of infection cell firing are discussed, and unresolved questions relating to the cell biology and biochemistry of these complex organelles are highlighted. Copyright 1998 Academic Press. 相似文献
158.
Lee A. Newman Sharon L. Doty Katrina L. Gery Paul E. Heilman Induluis Muiznieks Tanya Q. Shang 《Soil & Sediment Contamination》1998,7(4):531-542
As overwhelmingly positive results have become available regarding the ability of plants to degrade compounds such as trichloroethylene, phytoremediation studies are expanding. Studies to determine the potential for phytoremediation of fully chlorinated compounds, such as carbon tetrachloride and tetrachloroethylene, brominated compounds, such as ethylene dibromide and dibromochloropropane, and nonhalogenated compounds, such as methyl-t-butyl ether (MTBE), are underway. When using phytoremediation, it is important to select not only a plant that is capable of degrading the pollutant in question, but also one that will grow well in that specific environment. In ecologically sensitive areas, such as the Hawaiian Islands, only plants native to the area can be used. One way to supplement the arsenal of plants available for remedial actions is to utilize genetic engineering tools to insert into plants those genes that will enable the plant to metabolize a particular pollutant. Hybrid technologies, such as using plants in pumping and irrigation systems, also enable plants to be used as a remedial method when the source of the pollutant is beyond the reach of plant roots, or when planting space directly over the pollutant is unavailable or restricted. Thus, the potential uses of phytoremediation are expanding as the technology continues to offer new, low-cost remediation options. 相似文献
159.
Trichloroethylene (TCE) is a widespread and persistent environmental contaminant. Recently, plants, poplar trees in particular, have been investigated as a tool to remove TCE from soil and groundwater. The metabolism of TCE in plants is being investigated for two reasons: one, plant uptake and metabolism represent an important aspect of the environmental fate of the contaminant; two, metabolism pattern and metabolite identification will help assess the applicability of phytoremediation. It was previously shown that TCE metabolites in plants are similar to ones that result from cytochrome P450-mediated oxidation in mammals: trichloroethanol, trichloroacetate and dichloroacetate. Our measurements indicate that one of these metabolites, trichloroethanol, is further glycosylated in tobacco and poplar. The glycoside was detected in all tissues (roots, stems and leaves) in comparable levels, and was at least 10 fold more abundant than free trichloroethanol. The glycoside in tobacco was identified as the ss-D-glucoside of trichloroethanol by comparison of the mass spectra and the chromatographic retention time of its acetylation product to that of the synthesized standard. Trichloroethanol and its glucoside did not persist in plant tissue once plants are removed from TCE contaminated water, indicating further metabolism. 相似文献
160.
Replication process of the parvovirus H-1. VIII. Partial denaturation mapping and localization of the replication origin of H-1 replicative-form DNA with electron microscopy. 总被引:7,自引:5,他引:2
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Partial denaturation mapping, restriction endonuclease digestion, and electron microscopy were used to determine which end of the linear duplex replicative-form (RF) DNA molecule contains the origin of RF replication for the parvovirus H-1. This origin was localized within approximately 300 base pairs of the arbitrarily designated right end of the RF DNA, in the EcoRI or HaeII-A fragment. Based on denaturation behavior in formamide, the right end was also found to have a relatively high guanine plus cytosine content, whereas the region adjacent to the left terminus of the RF DNA molecule was adenine plus thymine rich. 相似文献