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91.
Abstract. The temperatures at which liposomes prepared from membrane phospholipids begin to phase separate were compared to the temperatures at which intact plants were damaged. Woody perennials tolerated temperatures below which their membrane phospholipids began to phase separate. By contrast, rye and wheat seedlings were damaged about 25°C above their phase separation temperature. Differences in tolerance among cultivars pre-hardened to frost were reflected by changes of the phase separation temperature. The results support the notion that alterations in membrane lipid composition are associated with frost hardening. A correlation between the temperature of phase separation and frost tolerance suggests that lipid properties may influence freezing tolerance of cereals; however, the lethal event is apparently not phase separation of the membrane phospholipids.  相似文献   
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ABSTRACT. The composition and incorporation of lipids in two marine ciliates, Pleuronema sp. and Fabrea salina, was examined following growth on either an algal or bacterial diet. When allowed to feed on a natural bacterial community, Pleuronema sp. synthesized the triterpenoid alcohol gammaceran-3β-ol (tetrahymanol) and two hopanoids (hopan-3β-ol and one uncharacterized hopanoid). When fed the marine alga Isochrysis galbana, F. salina contained the major algal sterol 24-methylcholesta-5, 22-dien-3β-ol and several long chain ketones specific to the alga. In both ciliates, fatty acids composition showed a general correspondence to that of the diet. Using a series of antibiotic treatments to alter the bacterial prey community, and thus fatty acid composition of the ciliate's diet, promoted changes in the fatty acid composition of Pleuronema sp. to resemble that of the bacterial prey. The addition of a mixture of algal sterols to a bacterized culture of another scuticociliate, Parauronema acutum, inhibited tetrahymanol synthesis and resulted in the incorporation of sterols into the ciliate.  相似文献   
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Effects of oil-based fungicides on plant surfaces were studiedby assessing water loss from excised sprayed leaves or petalsand by microscopy. Two fungicides (Turbair Zineb Fungicide andTurbair Copper Fungicide) were sprayed, using a Potter tower,onto the adaxial surfaces of excised leaves or petals, and weightloss was determined as a measure of water loss. Doses of approximately4–9 g m–2 significantly increased water loss fromPelargonium hybrid petals and leaves of Coleus blumei Benth.The fungicides, their supernatants and the carrier oil increasedwater loss from the petals but effects of the supernatants andthe carrier oil on C. blumei leaves were less conclusive. LowTemperature Scanning Electron Microscopy (LTSEM) did not revealany scoring or marked erosion of the adaxial surface of leavesor petals 24 h after application of the fungicides. Coleus blumei Benth., Pelargonium hybrid, cuticle, fungicides, oils, LTSEM, water loss  相似文献   
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1. We measured NH4+ and PO4?3 uptake length (Sw), uptake velocity (Vf), uptake rate (U), biofilm respiration and enzyme activity and channel geomorphology in streams draining forested catchments in the northwestern (Northern California Coast Range and Cascade Mountains) and southeastern (Appalachian and Ouachita mountains) regions of the United States. Our goal was to use measures of biofilm enzyme activity and nutrient uptake to assess nutrient limitation in forested streams across broad regional scales. 2. Geomorphological attributes, biofilm enzyme activity and NH4+ uptake were significantly different among streams in the four study units. There was no study unit effect on PO4?3 uptake. The proportion of the stream channel in pools, % woody debris, % canopy closure, median substrate size (d50), stream width (w), stream velocity (v), discharge (Q), dispersion coefficient (D) and transient storage (As/A) were correlated with biofilm enzyme activity and nutrient uptake in some study units. 3. Canonical correlation analyses across study units revealed significant correlations of NH4Vf and PO4Vf with geomorphological attributes (w, d50, D, % woody debris, channel slope and % pools) and biofilm phosphatase activity. 4. The results did not support our expectation that carbon processing rates by biofilm microbial assemblages would be governed by stream nutrient availability or that resulting biofilm enzyme activity would be an indicator of nutrient uptake. However, the relative abundances of peptidases, phosphatase and glycosidases did yield insight into potential N‐, P‐ and C‐limitation of stream biofilm assemblages, and our use of biofilm enzyme activity represents a novel application for understanding nutrient limitations in forested streams. 5. Regressions of Vf and U against ambient NH4+ and PO4?3 indicated that none of our study streams was either NH4+ or PO4?3 saturated. The Appalachian, Ouachita and Coastal streams showed evidence of NH4+ limitation; the Ouachita and Coastal streams were PO4?3 limited. As a correlate of nutrient limitation and saturation in streams, ratios of total aminopeptidase and phosphatase activities and the ratio of NH4U to PO4U indicate these forested streams are predominantly N‐limited, with only the streams draining Ouachita and Coastal catchments demonstrating appreciable levels of P‐limitation. 6. Our results comparing the stoichiometry of microbial enzyme activity with nutrient uptake ratios and with the molar ratios N and P in stream waters suggest that biological limitations are not strictly the result of stream chemistry and that the assessments of nutrient limitations in stream ecosystems should not be based on chemistry alone. 7. Our present study, along with previous work in streams, rivers and wetlands, suggests that microbial enzyme activities, especially the ratios of total peptidases to phosphatase, are useful indicators of nutrient limitations in aquatic ecosystems.  相似文献   
99.

Background  

Helicobacter pylori infection is one of the most common infections worldwide and is associated with gastric cancer and peptic ulcer. Bacterial virulence factors such as CagA have been shown to increase the risk of both diseases. Studies have suggested a causal role for CagA EPIYA polymorphisms in gastric carcinogenesis, and it has been shown to be geographically diverse. We studied associations between H. pylori CagA EPIYA patterns and gastric cancer and duodenal ulcer, in an ethnically admixed Western population from Brazil. CagA EPIYA was determined by PCR and confirmed by sequencing. A total of 436 patients were included, being 188 with gastric cancer, 112 with duodenal ulcer and 136 with gastritis.  相似文献   
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