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The threats posed by climate change make it important to expand knowledge concerning cold and heat tolerance in stenothermal species from habitats potentially threatened by temperature changes. Thermal limits and basal metabolism variations were investigated in Pseudodiamesa branickii (Diptera: Chironomidae) under thermal stress between ‐20 and 37 °C. Supercooling point (SCP), lower (LLTs) and upper lethal temperatures (ULTs), and oxygen consumption rate were measured in overwintering young (1st and 2nd instar) and mature (3rd and 4th instar) larvae from an Alpine glacier‐fed stream. Both young and mature larvae were freezing tolerant (SCPs = ‐7.1 °C and ‐6.4 °C, respectively; LLT100 <SCP and > ‐20 °C) and thermotolerant (ULT50 = 31.7 ± 0.4, 32.5 ± 0.3, respectively). However, ontogenetic differences in acute tolerance were observed. The LLT50 calculated for the young larvae (= ‐7.4 °C) was almost equal to their SCP (= ‐7.1 °C) and the overlapping of the proportion of mortality curve with the CPIF curve highlighted that the young larvae are borderline between freezing tolerance and freezing avoidance. Furthermore, a lower ULT100 in the young larvae (of ca. 1 °C), suggests that they are less thermotolerant than mature larvae. Finally, young larvae exhibit a higher oxygen consumption rate (mgO2/gAFDM/h) at any temperature tested and are overall less resistant to oxygen depletion compared to mature larvae at ≥10 °C. These findings suggest that mature larvae enter into a dormant state by lowering their basal metabolism until environmental conditions improve in order to save energy for life cycle completion during stressful conditions. 相似文献
134.
Aims We have two aims: (1) to examine the relationship between local population persistence, local abundance and regional occupancy of stream diatoms and (2) to characterize the form of the species–occupancy frequency distribution of stream diatoms. Location Boreal streams in Finland. There were three spatial extents: (1) across ecoregions in Finland, (2) within ecoregions in Finland, and (3) within a single drainage system in southern Finland. Methods Diatoms were sampled from stones (epilithon), sediment (epipelon) and aquatic plants (epiphyton) in streams using standardized sampling methods. To assess population persistence, diatom sampling was conducted monthly at four stream sites from June to October. The relationships between local population persistence, local abundance and regional occupancy were examined using correlation analyses. Results There was a significant positive relationship between local persistence and abundance of diatoms in epilithon, epipelon and epiphyton. Furthermore, local abundance and regional occupancy showed a significant positive relationship at multiple spatial extents; that is, across ecoregions, within ecoregions and within a drainage system. The relationships between occupancy and abundance did not differ appreciably among impacted and near pristine‐reference sites. The occupancy–frequency distribution was characterized by a large number of satellite species which occurred at only a few sites, whereas core species that occurred at most sites were virtually absent. Main conclusions The positive relationship between local population persistence and abundance suggested that a high local abundance may prevent local extinction or that high persistence is facilitated by a high local cell density. High local persistence and local abundance may also positively affect the degree of regional occupancy in stream diatoms. The results further showed that anthropogenic effects were probably too weak to bias the relationship between occupancy and abundance, or that the effects have already modified the distribution patterns of stream diatoms. The small number of core species in the species–occupancy frequency distribution suggested that the regional distribution patterns of stream diatoms, or perhaps unicellular microbial organisms in general, may not be fundamentally different from those described previously for multicellular organisms, mainly in terrestrial environments, although average global range sizes may differ sharply between these two broad groups of organisms. 相似文献
135.
Phylogeographic signal provided by the newly developed 23S plastid rRNA marker (universal plastid amplicon, UPA) and the cytochrome oxidase subunit I gene marker (COI) in the freshwater red alga Batrachospermum helminthosum, throughout its range in North America, was investigated. These markers were compared in individuals from a previous study using the cytochrome oxidase 2–3 spacer region ( cox 2–3), which has yielded the most useful data to date with 13 haplotypes among geographic locations. Five haplotypes were resolved for the UPA, differing by only one to two base pairs (bp), and we conclude that this marker may be more appropriate for studying interspecific variation. In contrast, the COI gene revealed 16 haplotypes, differing from one to 44 base pairs or up to 6.6% sequence variation. The intraspecific variation of COI in this taxon is much greater than that reported thus far for marine red algae (generally <5 bp). The intraspecific variation within B. helminthosum is in accord with levels shown in Batrachospermum macrosporum (48 bp within distant locations in Brazil). The COI gene is comparable to the cox 2–3 spacer for phylogeographic studies as the haplotype networks were similar and showed the same geographic patterns. To our knowledge, this is the first comparison of these three regions for phylogeographic research in the red algae. 相似文献
136.
Diatom floras were examined from geothermal environments in three contrasting tectonic settings. These included subduction-related
acid and alkaline springs in New Zealand; alkaline springs along a divergent plate boundary on Iceland; and alkaline springs
in the Kenya Rift. These shallow (<1 cm) aquatic environments vary considerably (e.g., temperature: 21.3–99°C; pH: 2.1–9.65;
56.41–643 mg l−1 SiO2). Diatoms form an important component of geothermal floras at temperatures of <45°C. The floras from New Zealand are distinguished
by the common occurrence of Pinnularia. Icelandic springs have a variety of Fragilariaceae. Navicula and Anomoeoneis are most common in the Kenyan springs. Statistical analyses suggest that the diatoms cluster into seven major groups. The
most common taxa include: Achnanthidium exiguum v. heterovalvum (Kras.) Czarn., Anomoeoneis sphaerophora (Ehrenb.) Pfitz, Brachysira brebissonii f. thermalis Grun., Caloneis bacillum (Grun.) Cl., Craticula cuspidata (Kütz.) Mann, Diadesmis confervacea Kütz., Epithemia argus (Ehrenb.) Kütz., Frustulia rhomboides (Ehrenb.) DeT., Hantzschia amphioxys (Ehrenb.) Grun., Navicula tenelloides Hust., Nitzschia amphibia Grun., Nitzschia inconspicua Grun., Nitzschia invisitata Hust., Nitzschia frustulum (Kütz.) Grun., Nitzschia sigma (Kütz.) W, Smith., Pinnularia chapmaniana Fog., Pinnularia appendiculata (Ag.) Cl., Pinnularia molaris (Grun.) Cl., Pinnularia acoricola Hust., Rhopalodia gibberula (Ehrenb.) O. Müll., Staurosira construens v. venter (Ehrenb.) Ham., Staurosira elliptica (Schum.) Will. & Round, and Staurosirella pinnata (Ehrenb.) Will. & Round. Canonical correspondence analysis shows clear correlations between species, alkalinity, pH, and
conductivity, with less strong correlations for silica and temperature. Other factors include substrate type, current velocity,
and light conditions. The preservation potential of host deposits varies considerably, being lowest for springs on clastic
deltas and highest where travertine or sinter is accumulating.
Handling editor: J. Padisak 相似文献
137.
Charles C. Ngugi Julius O. Manyala Murithi Njiru Chrisestom M. Mlewa 《African Journal of Ecology》2009,47(4):606-613
A study on some biological parameters of the mountain catfish, Amphilius uranoscopus Pfeffer 1889 (Silurifomes: Amphiliidae), was carried out in the Thego stream on the slopes of Mount Kenya from February to December 2002. Physical and chemical profiles of the Thego show that the water quality parameters is typical of high altitude streams with temperatures rarely exceeding 18°C, DO ranging from 7.9 to 8.2 mg l?1 and relatively high conductivity (97–137 μS cm?1) typical of perturbed lotic environments. A total of 1010 fish were caught by an electro‐fisher, with sizes ranging between 8 and 24 cm fork length. The population structure had a unimodal distribution with maxima at 14–16 cm. The length–weight relationship showed relatively narrow range in the slope ranging from 2.61 in April to 2.98 in February 2002, thereby suggesting isometric growth pattern. The fitted growth pattern of A. uranoscopus showed an asymptotic length (L∞) of 28.5 cm and a growth curvature (K) of 0.56 year?1 resulting in an estimated natural mortality coefficient (M) of 0.90 year?1. The Fulton’s condition factor (K) was also relatively stable with a peak in April (0.92 ± 0.21) and lowest value in June (0.86 ± 0.10). As A. uranoscopus is not under commercial exploitation, the seemingly depressed population is possibly attributed to the introduced exotic rainbow trout that heavily predates on the species and environmental perturbations arising from changes in land use. The implications of such changes on A. uranoscopus are discussed. 相似文献
138.
Dispersal can limit the ranges of species and the diversity of communities. Despite its importance, little is known about
its role in freshwater habitats and its relation to habitat type (lentic vs. lotic), especially for organisms with cryptic
dispersal methods such as plankton. Poor dispersers are expected to show more clumped distributions or greater spatial autocorrelation
(SA) in community composition than good dispersers. We examined patterns of SA across freshwater taxa with different dispersal
modes (active vs. passive) and their association with habitat type (lake vs. stream) using 18 spatially explicit community
composition data sets. We found significant relationships between SA and body size among taxa in lake habitats, but not in
streams. However, the increase in SA with body size in lakes was driven entirely by fishes—organisms ranging in size from
diatoms to macro-invertebrates showed equivalent levels of SA. These results support the idea that large organisms are less
effective dispersers in aquatic environments, resulting in greater SA in community structure over broad scales. Streams may
be effectively more connected than lakes as patterns of SA and body size were weaker in lotic habitats. Our data suggest that
the critical threshold where greater body size increases dispersal limitation seems to come at the juncture between invertebrates
and vertebrates rather than that between unicellular and multicellular organisms as has been previously suggested.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
139.
Janne Soininen Riku Paavola Janina Kwandrans Timo Muotka 《Biodiversity and Conservation》2009,18(1):79-89
As wholesale biodiversity assessment is often impractical, the use of surrogates that reflect the assemblage structure and
diversity of other taxa has attracted increased attention. We sampled 47 boreal streams for diatoms and macroalgae and examined
their assemblage patterns along major environmental gradients. Our main intention was to examine whether diatoms might be
useful surrogates for macroalgae in boreal streams. We also assessed whether taxon richness and community composition provided
similar insights into the patterns of cross-taxon concordance. According to canonical correspondence analysis, diatom distribution
was most strongly related to water pH, conductivity, latitude and longitude, and macroalgal distribution to water pH and iron
content, latitude and bed instability. In Mantel’s test, diatoms and macroalgae showed significant cross-taxon concordance.
However, there was no significant correlation between taxon richness of the two algal groups, likely reflecting their differing
responses to environmental variables. We found evidence that although diatoms and macroalgae are partly controlled by different
environmental factors, they are segregated rather similarly along latitude and a few environmental gradients such as water
pH and iron content. We conclude that, at least at broad geographical extents and in small streams, diatoms reflect the structure
of the macroalgal community and are therefore useful surrogates for cost-effective biomonitoring of algal communities in streams. 相似文献
140.