全文获取类型
收费全文 | 133篇 |
免费 | 3篇 |
专业分类
136篇 |
出版年
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 5篇 |
2007年 | 10篇 |
2004年 | 2篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1959年 | 1篇 |
1953年 | 1篇 |
1952年 | 1篇 |
1937年 | 2篇 |
1936年 | 1篇 |
1934年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有136条查询结果,搜索用时 15 毫秒
91.
Analysis of the community structure of planktonic ciliated protozoa relative to trophic state in Florida lakes 总被引:4,自引:0,他引:4
The planktonic ciliate populations of 30 Florida lakes constituting a broad trophic gradient were examined to determine the response of protozoan community structure to increasing eutrophication. Both ciliate abundance and biomass were strongly related to lake trophic state. Comparison of the Florida data base with a comparable north temperate lake group indicated that subtropical lakes generally possess higher ciliate abundance and biomass at a given trophic state than temperate lakes. However the equations derived for each data base were not significantly different. Community diversity and species richness increased with increasing lake productivity. Highly acidic lakes displayed significantly reduced diversity and numbers of species when contrasted with nonacidic oligotrophic lakes. Small-bodied (< 30 um) ciliates dominated all lakes but were proportionally less important in oligotrophic lakes. Presence-absence data produced three assemblages: an ubiquitous association of primarily small ciliate taxa, a group of large ciliates mainly restricted to eutrophic-hypereutrophic lakes, and a very large ciliate,Stentor niger, which dominated the protozoan communities of acidic oligotrophic lakes. 相似文献
92.
93.
Thermal regimes of Florida lakes 总被引:3,自引:3,他引:0
Water column temperatures were determined monthly for 24 lakes and bimonthly for 5 lakes in peninsular Florida during 1979. Three geographical groups (north, central, south) were delineated from mean monthly water column temperatures for individual lakes. On a monthly basis, northern lakes were least similar to southern lakes, while central Florida lakes displayed greater affinity to the southern than to the northern lake group. Temperature differences between lake groups broke down during late summer. Subtropical lakes have been defined tentatively as those Florida lakes south of 28° latitude which possess warm monomictic circulation and a mean annual temperature of 24.2 ± 4.8 °C with minimum water column temperature rarely less than 14 °C and summer maxima rarely exceeding 31 °C. While all lakes in Florida are clearly warm monomictic annual nutrient cycling and productivity patterns may be influenced by inter-group differences in the timing and duration of water column circulation. 相似文献
94.
Algal bioassays to determine toxicity of metal mixtures 总被引:1,自引:1,他引:0
The shortcomings of many established toxicity criteria for metals have resulted from a simplification of bioassays performed with single metals. A more comprehensive approach was needed to diagnose the effects of metal mixtures on aquatic organisms. Using Chlorella, Ankistrodesmus and Scenedesmus as test organisms, we experimented on a number of factors which affected metal toxicity bioassays. These included metal interactions, algal competitions, species sensitivities, the ratio of an excess metal to other metals and nutrient levels. An alternative technique was finally established which involved an evaluation of individual assays of Chlorella and Ankistrodesmus in separate media and a tissue-metal analysis on Chlorella. Chlorella fusca, commonly found in lakes with high metal concentrations, showed high tolerance to mixed-metal solutions, while Ankistrodesmus proved to be very sensitive. By determining the maximum yield ratio between Ankistrodesmus and Chlorella (i.e. the A/Ch ratio) it was possible to compare the toxic strength of harmful metals according to an established standard curve of A/Ch ratio versus mixed-metal concentrations. The levels of tissue-metal analysed in Chlorella also gave some indication as to which metals were responsible for the toxicity. 相似文献
95.
Seasonality of planktonic ciliated protozoa in 20 subtropical Florida lakes of varying trophic state 总被引:2,自引:0,他引:2
The planktonic ciliate populations of 20 Florida lakes ranging from oligotrophic to hypereutrophic were examined monthly for
one year. Oligotrophic lakes displayed abundance peaks during fall mixis and biomass peaks in late winter and fall. Mesotrophic
systems exhibited a spring-fall bimodality in ciliate abundance with a biomass maxima occurring during fall. Eutrophic/hypereutrophic
lakes had pronounced abundance and biomass maxima during summer, with the large ciliates Plagiopyla nasuta and Paramecium trichium often contributing heavily to the midsummer biomass peak. Members of the Oligotrichida numerically dominated abundance and
biomass peaks in oligotrophic lakes while the Scuticociliatida dominated the communities of higher trophic states. Total ciliate
abundance and biomass were strongly correlated with chlorophyll a concentrations as were various ciliate taxonomic groups. The relationship between ciliate seasonal distribution in these
subtropical lakes with lake thermal regimes and trophic state is discussed. 相似文献
96.
Havens Karl E. Ji Gaohua Beaver John R. Fulton Rolland S. Teacher Catherine E. 《Hydrobiologia》2019,829(1):43-59
Hydrobiologia - Analysis of an 18-year dataset from seven shallow lakes in Florida provides evidence of hydrologic factors controlling dynamics of cyanobacteria blooms. Depth was the most important... 相似文献
97.
Con-Struct Map is a graphical tool for the comparative study of protein structures. The tool detects potential conserved residue contacts shared by multiple protein structures by superimposing their contact maps according to a multiple structure alignment. In general, Con-Struct Map allows the study of structural changes resulting from, e.g. sequence substitutions, or alternatively, the study of conserved components of a structure framework across structurally aligned proteins. Specific applications include the study of sequence-structure relationship in distantly related proteins and the comparisons of wild type and mutant proteins. AVAILABILITY: http://pdbrs3.sdsc.edu/ConStructMap/viewer_argument_generator/singleArguments. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online. 相似文献
98.
John R. Beaver David E. Jensen Dale A. Casamatta Claudia E. Tausz Kyle C. Scotese Kristen M. Buccier Catherine E. Teacher Teodoro C. Rosati Alison D. Minerovic Thomas R. Renicker 《Hydrobiologia》2013,705(1):173-189
We assessed if the qualitative and quantitative aspects of plankton composition in reservoirs of the middle Missouri River were influenced by hydrologic variability. Phytoplankton and zooplankton communities in six reservoirs of this highly regulated system were sampled between 2004 and 2011 during historic drought, subsequent recovery, and a 100-year flood event. The reservoir system encompasses a broad latitudinal gradient of decreasing depth, decreasing water residence time and increasing trophic state. Phytoplankton communities of the upper three reservoirs were co-dominated by planktonic and meroplanktonic diatoms during the drought, recovery, and flood periods, but the proportion of more silicified meroplanktonic diatoms increased in the lower three reservoirs as water residence time decreased. Peak phytoplankton biovolume usually occurred during spring/early summer and was associated with increased hydrologic inflows and outflows. Zooplankton biomass of the reservoir system was dominated by Daphnia spp., but all zooplankton groups decreased as inflows and outflows accelerated during the recovery and flood periods. Rotifer abundances were higher under turbulent conditions associated with dam operations. Canonical correlation analyses suggested that temperature, water residence time, station depth, and water clarity explained more variance in the structures of phytoplankton and zooplankton communities than bioavailable nutrient parameters. 相似文献
99.
100.
Anaerobic threshold and respiratory gas exchange during exercise 总被引:28,自引:0,他引:28