全文获取类型
收费全文 | 158篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
164篇 |
出版年
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2013年 | 5篇 |
2012年 | 2篇 |
2011年 | 7篇 |
2010年 | 21篇 |
2009年 | 13篇 |
2008年 | 8篇 |
2007年 | 6篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1931年 | 1篇 |
排序方式: 共有164条查询结果,搜索用时 0 毫秒
111.
112.
113.
Temperature and the metabolic balance of streams 总被引:1,自引:0,他引:1
BENOÎT O.L. DEMARS J. RUSSELL MANSON JON S. ÓLAFSSON GÍSLI M. GÍSLASON RAKEL GUDMUNDSDÓTTIR GUY WOODWARD JULIA REISS DORIS E. PICHLER JES J. RASMUSSEN NIKOLAI FRIBERG 《Freshwater Biology》2011,56(6):1106-1121
1. It is becoming increasingly clear that fresh waters play a major role in the global C cycle. Stream ecosystem respiration (ER) and gross primary productivity (GPP) exert a significant control on organic carbon fluxes in fluvial networks. However, little is known about how climate change will influence these fluxes. 2. Here, we used a ‘natural experiment’ to demonstrate the role of temperature and nutrient cycling in whole‐system metabolism (ER, GPP and net ecosystem production – NEP), in naturally heated geothermal (5–25 °C) Icelandic streams. 3. We calculated ER and GPP with a new, more accurate method, which enabled us to take into account the additional uncertainties owing to stream spatial heterogeneity in oxygen concentrations within a reach. ER ranged 1–25 g C m?2 day?1 and GPP 1–10 g C m?2 day?1. The median uncertainties (based on 1 SD) in ER and GPP were 50% and 20%, respectively. 4. Despite extremely low water nutrient concentrations, high metabolic rates in the warm streams were supported by fast cycling rates of nutrients, as revealed from inorganic nutrient (N, P) addition experiments. 5. ER exceeded GPP in all streams (with average GPP/ER = 0.6) and was more strongly related to temperature than GPP, resulting in elevated negative NEP with warming. We show that, as a first approximation based on summer investigations, global stream carbon emission to the atmosphere would nearly double from 0.12 Pg C year?1 at 13 °C to 0.21 (0.15–0.33) Pg C year?1 with a 5 °C warming. 6. Compared to previous studies from natural systems (including terrestrial ecosystems), the temperature dependence of stream metabolism was not confounded by latitude or altitude, seasonality, light and nutrient availability, water chemistry, space availability (water transient storage), and water availability. 7. Consequently, stream nutrient processing is likely to increase with warming, protecting downstream ecosystems (rivers, estuaries, coastal marine systems) during the summer low flows from nutrient enrichment, but at the cost of increased CO2 flux back to the atmosphere. 相似文献
114.
GUY CHARMANTIER MIREILLE CHARMANTIER-DAURES 《Invertebrate reproduction & development.》2013,57(2-3):273-287
Summary This review deals with the studies which have been conducted for the past 30 years on the endocrine and neuroendocrine regulations in embryos and larvae of crustaceans, mostly in decapods. Y-organs, mandibular organs and the X-organ sinus gland complex of the eyestalks are present in the first post-embryonic instar of most investigated species. Y-organs, the X-organs and the sinus glands have also been located in embryos of a few species. Larval molting appears to be regulated in a way similar to that in adults involving a MIH-ecdysteroid system. Evidence points to a control of metamorphosis through the eyestalks. Experimental evidence points to a neuroendocrine control of changes in pigmentation and of osmoregulation. Progress in the isolation and characterization of the hormones and neurohormones controlling these metabolic changes in adults should help and promote further research on regulation during the embryonic and early postembryonic development. 相似文献
115.
Temporal and spatial environmental variability in the Upper Rhône River and its floodplain 总被引:1,自引:1,他引:0
BERNARD CELLOT † MARIE JOSÉ DOLE-OLIVIER GUDRUN BORNETTE GUY PAUTOU‡ 《Freshwater Biology》1994,31(3):311-325
- 1 This paper develops a framework of spatial and temporal variability for a habitat typology of the Upper Rhône River (France) and its alluvial floodplain that is based on about 17 years of data collection and analysis. The aim was to provide a scale of spatial-temporal variability for river habitat templet predictions on trends in species traits and species richness.
- 2 In developing this framework, eight physical-chemical variables were available and could be considered for twenty-two habitat types: seventeen superficial (surface) and five interstitial (0.5 m below the substrate surface). These habitat types were selected in two areas (Jons and Brégnier-Cordon) after geomorphological considerations and because of differences in their biological characteristics.
- 3 The data sets used were processed by a ‘fuzzy coding’ method using, for each variable, the frequency distribution (by modalities = categories) of all measurements and monthly means over an annual scale. Two tables were produced; the first corresponded to an expression of the total variability, and the second represented an evaluation of the temporal variability.
- 4 Each of these tables was analysed by correspondence analysis, which provided factorial scores that were used to calculate, by habitat type and by variable, a total variability and a temporal variability in terms of cumulated variability of factorial scores for the eight physical–chemical variables. The rationale in describing variability from these two tables is that total variability equals temporal variability plus spatial variability. The spatial variability was then determined by the difference between total and temporal variability. From this procedure, a positioning of the twenty-two habitat types on the spatial and temporal variability axes was obtained.
- 5 The estimate of spatial variability did not consider any error term that may have occurred in the above model; it was then tested by an independent assessment of the spatial variability using thirteen variables in nine major habitat types. A high correlation between the two ways of assessing spatial variability (r = 0.85, P < 0.004) underscored the reliability of the spatial variability that was calculated previously.
- 6 The river habitat templet obtained for the Upper Rhône and its alluvial floodplain appears to be appropriate to test the predictions on patterns of species traits and species richness in the framework of spatial and temporal variability.
116.
JAMES J. GILROY GUY Q. A. ANDERSON PHILIP V. GRICE JULIET A. VICKERY & WILLIAM J. SUTHERLAND 《Ibis》2010,152(1):90-104
Declines in habitat quality through the breeding season within a bird's home-range can limit overall productivity. In environments where multiple breeding opportunities arise during the course of a season, these effects can be buffered by a shift to different breeding sites or habitats. We studied the distribution and habitat associations of a crop-nesting farmland bird, the Yellow Wagtail Motacilla flava , across an arable-dominated farming region in eastern England using both field-scale territory mapping and large-scale transect surveys. Surveys were repeated at monthly intervals to measure changes in both distribution and habitat use during the course of the season. The distribution of breeding birds changed markedly at both regional and field-scales, coinciding with a shift in crop preference. Initially, most territorial birds were recorded in autumn-sown cereal fields, but this crop was subsequently abandoned in favour of potato crops, which were more patchily distributed. Other habitat features influencing Yellow Wagtail distribution included local crop diversity, hedgerow presence and soil type, with organic soils supporting higher abundance than alluvial clays or silts. The mid-season switch in habitat associations might allow individuals to maximize the number of breeding attempts made in a single year by using multiple habitats sequentially. The use of multiple habitats could influence population regulation by buffering the effects of local within-season declines in habitat suitability. Seasonal habitat switching may be more prevalent than is currently recognized in seasonal environments. 相似文献
117.
D. R. GEORGE O. A. E. SPARAGANO G. PORT E. OKELLO R. S. SHIEL J. H. GUY 《Medical and veterinary entomology》2010,24(1):9-15
Seven essential oils with potential as acaricides for use against the poultry red mite, Dermanyssus gallinae (De Geer) (Acari: Dermanyssidae), were selected for study. These products (essential oils of manuka, cade, pennyroyal, thyme, garlic, clove bud and cinnamon bark) were deployed against different life stages of D. gallinae in laboratory tests at the (lethal concentration) LC50 level for adult mites. For all essential oils tested, toxicity to D. gallinae juveniles was as high as toxicity to adults, if not higher. However, at the LC50 level determined for adults, some oils were ineffective in preventing hatching of D. gallinae eggs. The essential oils were also tested under laboratory conditions at their LC90 levels for D. gallinae adults on two model non‐target species, the brine shrimp, Artemia salina (L.), and the mealworm beetle, Tenebrio molitor (L.). Results showed that not all essential oils were as toxic to A. salina and T. molitor as they were to D. gallinae, suggesting that it may be possible to select certain oils for development as acaricides against D. gallinae that would have minimal impact on non‐target organisms. However, the level of toxicity to A. salina and T. molitor was not consistent across the selected essential oils. 相似文献
118.
GUY MIDGLEY 《Journal of Biogeography》2002,29(7):971-972
119.
Abstract Shifts in ?13C of the graminaceous C3 halophyte Puccinellia nuttalliana (Schultes) Hitch. can be induced by salinization. To investigate this phenomenon, three approaches were taken: assay of carboxylases, CO2-enrichment studies, and gas exchange analysis. Although ribulose-1,5-bisphosphate carboxylase activity decreased with salinity, phosphoenolpyruvate carboxylase activity did not increase and its levels were not atypical of C3 plants. When plants were grown at four NaCl concentrations under atmospheres of 310 and 1300 cm3 m?3 CO2, the CO2-enrichment enhanced the effects of salinity on ?13C. This is consistent with a biophysical explanation for salt-induced shifts in ?13C, whereby there is a steepening of the CO2 diffusion gradient into the leaf. Gas exchange analysis indicated that intercellular CO2 concentrations were depressed in the leaves of salt-affected plants. This resulted from a greatly decreased stomatal conductance coupled with only small effects on intrinsic photosynthetic capacity. Water-use efficiency was enhanced. 相似文献
120.
Salt activation and inhibition of membrane ATPase from roots of the halophyte Atriplex nummularia 总被引:1,自引:0,他引:1
H. R. LERNER LEONORA REINHOLD RACHEL GUY YAEL BRAUN MIRIAM HASIDIM ALEXANDRA POLJAKOFF-MAYBER 《Plant, cell & environment》1983,6(6):501-506
Abstract Salt-stimulated ATPase activity in membrane preparations obtained from roots of Atriplex nummularia Lindl. at pH 5 was not suscep-tible to inhibition by KC1 or NaCl up to 450 mol m-3 but showed a broad peak of activity between 150 and 300 mol m?3. At pH 8 stimulation occurred at 50 mol m?3 but concentrations above 100 mol m?3 depressed activity below the level of the MgATPase activity. By contrast, preparations from roots of Pisum sativum L. at pH 5 showed maximal stimulation at 25 to 50 mol m?3 of NaCl or KC1; concentrations higher than 150 mol m?3 depressed activity below that of MgATPase activity. At pH 8 maximal stimulation was observed at 5 to 10 mol m?3 NaCl or KC1 while the threshold for inhibition was reduced to 15 mol m?3. With increasing salt concentrations the pH profiles for NaCl stimulation of Atriplex ATPase activity (expressed as the difference between treatment and control) showed a progressive displacement of the apparent optimum towards lower pH. The shift was not apparent when stimulation was expressed as a percentage of MgATPase activity. This shift may be accounted for if NaCl stimulated the monovalent salt-activated ATPase activity but simultaneously inhibited MgATPase activity. 相似文献