全文获取类型
收费全文 | 333篇 |
免费 | 12篇 |
国内免费 | 7篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 16篇 |
2012年 | 11篇 |
2011年 | 7篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 28篇 |
2005年 | 14篇 |
2004年 | 7篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1992年 | 1篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 13篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有352条查询结果,搜索用时 15 毫秒
91.
CHAD W. HARGRAVE RAUL RAMIREZ MELODY BROOKS MICHAEL A. EGGLETON KATHERINE SUTHERLAND RAELYNN DEATON HEATHER GALBRAITH 《Freshwater Biology》2006,51(10):1901-1910
1. We tested the hypothesis that indirect food web interactions between some common, invertivorous fishes and their prey would positively affect growth of an algivorous fish species. Specifically, we predicted that orangethroat darter (Etheostoma spectabile) would increase periphyton biomass via a top‐down pathway, indirectly enhancing growth of the algivorous central stoneroller minnow (Campostoma anomalum). Moreover, we predicted that sand shiner (Notropis stramineus) would increase periphyton biomass via a bottom‐up pathway and indirectly enhance growth of the stoneroller minnow. 2. In an 83‐day experiment in large, outdoor, stream mesocosms, we stocked two fish species per mesocosm (stoneroller and either darter or shiner), estimated the effects of the invertivorous and grazing fishes on periphyton biomass and estimated growth of the algivorous fish. 3. The darter consumed grazing invertebrates, indirectly increasing periphyton biomass. The shiner consumed terrestrial insects as predicted, but it did not affect periphyton biomass. 4. In support of our hypothesis, the darter indirectly enhanced stoneroller growth. As predicted, stonerollers consumed the increased periphyton in streams with darters, resulting in greater growth, condition and gut fullness compared to streams without darters. No indirect interaction was observed between stonerollers and shiners. 5. Our study suggests that some invertivorous fish species can positively affect growth of algivorous fishes through indirect food web interactions. Thus, in stream communities, it is possible that the loss of a single, invertivorous fish taxon could have negative consequences on algivorous fish populations via the removal of positive indirect food web interactions. 相似文献
92.
Chemical-diffusing substrates were designed to allow delivery of toxicants to mature periphyton communities under natural
conditions without contaminating the surrounding environment. Artificial stream validation studies were conducted in which
the effects of substrate-released copper (Cu) on periphyton communities were compared to those generated in a more conventional
manner (via water column additions). Effects of copper on the following community parameters were assessed: total community
biomass (measured as ash-free dry mass), relative chlorophyll a (chl a and adenosine triphosphate contents, and relative biomass of heterotrophic bacteria. Exposure of more laboratory periphyton
communities to substrate-released Cu generated dose-response relationships and recovery models that were indistinguishable
from those generated by the conventional route of exposure. The results of this study demonstrate the utility of chemical-diffusing
substrates in field validations of laboratory toxicity tests and in investigations of the effects of stress history on periphyton
tolerance to toxicants.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
93.
Community composition and sensitivity of periphyton to atrazine in flowing waters: the role of environmental factors 总被引:4,自引:0,他引:4
Helena Guasch Núria Ivorra Volker Lehmann Maria Paulsson Montserrat Real Sergi Sabater 《Journal of applied phycology》1998,10(2):203-213
The relationship between environmental variables, community composition and the sensitivity of periphyton on artificial substrata
to the herbicide atrazine (EC50 values obtained by concentration-effect curves of photosynthesis to atrazine) was studied for 20 stream and river sites on
a latitudinal across Europe (Sweden, The Netherlands, Spain). Sensitivity to atrazine was higher in Swedish than in the Spanish
or Dutch sites. Direct gradient analyses were used to relate diatom taxa and algal groups with environmental variables. A
first redundancy analysis (RDA) based on diatom taxa showed a pollution gradient (atrazine and nutrient concentration) associated
to diatom taxa that are indicators of different degrees of pollution. A second RDA based on algal groups showed that diatom-dominated
communities corresponded both to sites at higher altitudes and less industrialized areas and to sites with higher atrazine
concentration; Cyanobacteria were the most common in industrial areas, whereas Chlorophyceae dominated in sites with high
water temperature and alkalinity. Linear regression analyses were applied to find the relationship between the ordination
axes obtained and the EC50 values. First axes of both RDA showed significant or marginally significant relationship with atrazine sensitivity. Regression
analyses for the Spanish sites indicated that the sensitivity to atrazine was related with light conditions (EC50 was positively correlated with light) and the percentage of different algal groups (EC50 was positively correlated with the percentage of diatoms and negatively correlated with the percentage of green algae). The
results indicating that differences in sensitivity are related to environmental variables such as light, nutrients or atrazine
concentration, permitted us to identify biological indicators of sensitivity to atrazine in lotic systems: Bacillariophyceae-dominated
periphyton communities were more tolerant than Chlorophyceae and Chrysophyceae-dominated communities. In addition, diatom
taxa found to be tolerant to atrazine in this study have been considered in the literature to be tolerant to organic pollution.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
94.
Effects of the water discharge on periphyton abundance and diversity in a large river (River Danube,Hungary) 总被引:4,自引:2,他引:2
This paper examines the relevance of intermediate disturbance theory in the context of in a large river the algal flora attaching to artificial substrata. It was observed that the theory is in good agreement with most of the communities analysed, however, with different frequency intervals compared to phytoplankton. Floods provided the most significant disturbances. As a rough generalization, we can say that in case of floods following each other in 8–14 days, respectively, the disturbance is of medium frequency. In case of 8 days, high frequency is more typical while in case of 14 days, low frequency is more characteristic. Owing to the fact that riverine periphytic algal organisms are attached in different ways and with differing efficiencies, the changes in the total mass occurring as a result of changes in water discharge lead to changes in diversity. The analysis of individual numbers can help in investigating the intensity of the disturbing effect on the algal communities. Negative correlation was found between water discharge and numbers of individuals, that is, the numbers of algae increase with low water discharge and decrease with high water level in the river. This second observation is valid only within a certain range of discharges (in this case up to 100 m3 s–1), which will be specific to particular rivers and individual reaches. Below the upper limit of the range, the increased water flows carry more nutrients to the organisms but with no severe wash-off effect. Beyond the upper limit (in this case in range 100–400 m3 s–1) the numbers of individuals is roughly in inverse proportion to the wash-off effect of the current, and the community is in equilibrium. In cases when discharge surpasses 400 m3 s–1 decrease in individual numbers is general. We suggest that in the environments similar to the study area, the periphyton of the artificial substrata (e.g., pontoons) undergo similar processes. In respect of the periphyton formed on the surface of the riverbeds in large rivers with considerable changes in water level, a more complex system can be supposed where part of the periphyton is periodically dried and flooded alternately. 相似文献
95.
Biofilms were allowed to develop on wooden slides of the River Red Gum (Eucalyptus camaldulensis Dehnh., Myrtaceae) submerged in two billabongs of south-eastern Australia. The slides were placed in the photic zone and the aphotic zone, and the biofilms sampled after eight week's growth over the summer of 1989–1990 and winter of 1990. Bacterial numbers, estimated with epifluorescence microscopy, ranged from 4–78 × 106 cells cm–2. Bacteria were more abundant in the photic zone than the aphotic zone, and more abundant in summer than winter. Fewer than 0.5% of the bacteria could be cultivated on nutrient agar plates. Concentrations of phospholipids ranged from 8–79 ng cm–2, which corresponded to bacterial abundances of 2–17 × 106 cells cm–2. Fifty five phospholipid fatty acids (PLFA) were identified, of which 16:0 (13–29% of total PFLA) was the most common. Other abundant PFLA included 16:17c (6–28%), 18:26 (3–16%), 18:33 (4–12%), 18:19c (3–5%), 18:l7c (5–11%) and 18:0 (2–8%). Minor PLFA included 14:0, i and a 15:0, 15:0, 16:l5c, 16:113c, 18:36, 18:43, 20:46 and 20:53. The PLFA profiles of the biofilms were quite different from those of the sediments and plankton. There was a clear distinction between the PLFA profiles of summer and winter biofilms, but less evidence for unequivocal site or light-regime effects. 相似文献
96.
A quantitative comparison of the grazing behaviour of young Oreochromis niloticus feeding on the planktonic cyanobacterium Microcystis aeruginosa and a periphytic community dominated by the cyanobacterium Oscillatoria sp., determined that biomass ingestion rates of fish filter-feeding on planktonic cyanobacteria were significantly lower than those surface-grazing on periphyton. Comparisons of published laboratory data on filter-feeding with field data on algal ingestion rates suggest that filter-feeding may be a relatively unimportant method of ingesting algae. 相似文献
97.
Algal response to a thermal effluent: study of a power station on the provo river,Utah, USA 总被引:3,自引:3,他引:0
The effect of a thermal effluent on the attached algae of the Provo River, Utah, USA, was studied from 1975 to 1977. Data for macroscopic and microscopic algae were collected and analyzed. Diatoms, Cladophora glomerata, and Hydrurus foetidus dominated the flora. The thermal effluent significantly affected the algal flora in a section of river 100 to 135 meters long immediately below the discharge point. Cladophora growth was increased and Hydrurus was absent in this area. In addition, diatom production was often higher and diversity lower than in the rest of the river. Community structure was unique from all other adjacent areas. Small temperature increases which occured as effluent and river waters mixed farther downstream were apparently not as important to the algal flora as other environmental factors. 相似文献
98.
DAVID W. BOWKER PATRICK DENNY 《Biological journal of the Linnean Society. Linnean Society of London》1978,10(1):49-65
The periphyton communities established in Nyumba ya Mungu were investigated between July and September 1974.
One hundred and ninety-two taxa were identified. One hundred and fifteen taxa were collected in the southern end of the lake, where 97 taxa were non-selectively distributed in the littorine epiphytic, epilithic, and epixylic environments. The offshore epixylon supported only 53 taxa. The epipelon and epipsammon were poorly developed at the southern end of the lake but were well developed in the northern inflow regions.
Diatoms and cyanophytes were the dominant phyla which contributed over 80% of the algal numbers. Chlorophytes were not common. Taxonomic compositions of periphyton on artificial and natural surfaces were similar, but artificial substrata accumulated greater proportional representations of diatoms.
The mean net production rates of periphyton on artificial substrata located at depths from 0-0.65 m for 28 days ranged from 140 mg organic dry weight m-2 day-1 on shoots in the macrophyte zone to 820 mg organic dry weight m-2 day-1 on glass surfaces on a rocky shore. The epiphytic environments produced the least standing crops of less than 250, 000 individuals cm-2 , but maximum densities of over 2,000,000 individuals cm-2 were recorded in the epilithon. 相似文献
One hundred and ninety-two taxa were identified. One hundred and fifteen taxa were collected in the southern end of the lake, where 97 taxa were non-selectively distributed in the littorine epiphytic, epilithic, and epixylic environments. The offshore epixylon supported only 53 taxa. The epipelon and epipsammon were poorly developed at the southern end of the lake but were well developed in the northern inflow regions.
Diatoms and cyanophytes were the dominant phyla which contributed over 80% of the algal numbers. Chlorophytes were not common. Taxonomic compositions of periphyton on artificial and natural surfaces were similar, but artificial substrata accumulated greater proportional representations of diatoms.
The mean net production rates of periphyton on artificial substrata located at depths from 0-0.65 m for 28 days ranged from 140 mg organic dry weight m
99.
R. Christian Jones 《Hydrobiologia》1978,59(3):165-180
Algal biomass during colonization of polyurethane foam islands (5.1 cm × 7.6 cm × 7.6 cm) was approximated by measuring chlorophyll a levels on islands after exposure periods of 1, 2, 3, 4, and 6 weeks at six locations in a small lake in central Tennessee, USA. Chlorophyll, ash-free dry weight, and concurrent environmental data were collected for two colonization periods: one in late winter and spring (Set 1), a second in summer (Set 2).During Set 1 algal biomass levels, as indicated by chlorophyll a, showed a sharp rise initially, but Set 2 islands exhibited a lag period of 7 to 12 days before a rapid increase in algal biomass was noted. Equilibrium chlorophyll a values were similar for both sets. High levels of phaeopigments were found at Stations 2, 3, and 4 during Set 2 resulting in large corrections in chlorophyll a readings. Ash-free dry weight values increased steadily through each colonization period.A model of biomass accumulation during colonization was constructed postulating three major processes — photosynthesis, respiration, and passive accumulation — which were modulated by three environmental factors — light, temperature, and plankton chlorophyll a levels. For simulations parameter values were taken from the literature where possible. Additional parameter values were set and literature values adjusted when the model was tuned to Set 2 data. A simulation with the tuned model using Set 1 environmental input resulted in a good prediction of equilibrium values, but a misinterpretation of initial values. The discrepancy between model predictions and data was alleviated when the passive accumulation rate was increased demonstrating the dependence of biomass values early in colonization on passive accumulation from the plankton. 相似文献
100.
Periphyton production in an Appalachian river 总被引:3,自引:3,他引:0
Periphyton primary production was measured by 14C uptake on natural substrates in two sections of the New River, Virginia, U.S.A. Production ranged from 6.71 ± 0.43 mg C g–1 h–1 in summer to 1.47 ± 0.22 mg C g–1 h–1 in late autumn in the hardwater reach and from l.90 ± 0.10 mg C g–1 h–1 to 0.12 ± 0.08 mg C g–1 h–1 in the softwater reach. Production in the hardwater reach was 3–5 times greater than in the softwater reach and significantly correlated with dissolved inorganic carbon (DIC) concentration (r2 = 0.506). No significant correlation was found between periphyton production and photosynthetically active radiation (PhAR). Extrapolation of periphyton production to a 135 km reach of the New River yielded an estimated annual input of 2 252 T AFDW from this source. Estimates of allochthonous (excluding upstream contributions) and aquatic macrophyte inputs to this same reach were 64 T AFDW and 2 001 T AFDW, respectively. While periphyton is not a large source of organic matter, its high food quality and digestibility make it an important component of the New River energy dynamics. 相似文献