全文获取类型
收费全文 | 593篇 |
免费 | 33篇 |
国内免费 | 15篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 12篇 |
2017年 | 20篇 |
2016年 | 24篇 |
2015年 | 16篇 |
2014年 | 12篇 |
2013年 | 45篇 |
2012年 | 11篇 |
2011年 | 15篇 |
2010年 | 10篇 |
2009年 | 38篇 |
2008年 | 37篇 |
2007年 | 34篇 |
2006年 | 40篇 |
2005年 | 16篇 |
2004年 | 18篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1997年 | 20篇 |
1996年 | 16篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
排序方式: 共有641条查询结果,搜索用时 31 毫秒
91.
Aquatic biodiversity under anthropogenic stress: an insight from the Archipelago Sea (SW Finland) 总被引:1,自引:0,他引:1
Erkki Leppäkoski Harri Helminen Jari Hänninen Minna Tallqvist 《Biodiversity and Conservation》1999,8(1):55-70
The Archipelago Sea in the northern Baltic has been subjected to large-scale cultural, economic and ecological changes, especially during the last three decades. Environmental threats originate from both basin-wide sources, affecting the whole Baltic Sea, and from local sources, such as nutrient loading from nearby river outflows, intense agriculture, fish farming, ships' traffic, boating, and man's physical impacts on the landscape and seascape. Both the Åland archipelago and the Archipelago Sea have been listed as hot-spots by HELCOM, Baltic Marine Environment Protection Commission, eutrophication being the main threat to the aquatic environment. In this study we review how biological communities have reacted to an increase in man-induced multisource stresses. Changes in plankton, benthic animals, macroalgal assemblages and fish communities have been documented in most parts of the Baltic Sea since the 1970s. What remains to be understood is the importance of these structural changes for the functioning of the Archipelago Sea ecosystem under various levels of human impact. 相似文献
92.
Organisms are facing global climate change and other anthropogenic pressures, but most research on responses to such changes only considers effects of single drivers. Observational studies and physiological experiments suggest temperature increases will lead to faster growth of small fish. Whether this effect of warming holds in more natural food web settings with concurrent changes in other drivers, such as darkening water color (“browning”) is, however, unknown. Here, we set up a pelagic mesocosm experiment with large bags in the Baltic Sea archipelago, inoculated with larval Eurasian perch (Perca fluviatilis) and zooplankton prey and varying in temperature and color, to answer the question how simultaneous warming and browning of coastal food webs impact body growth and survival of larval perch. We found that browning decreased body growth and survival of larval perch, whereas warming increased body growth but had no effect on survival. Based on daily fish body growth estimates based on otolith microstructure analysis, and size composition and abundance of available prey, we explain how these results may come about through a combination of physiological responses to warming and lower foraging efficiency in brown waters. We conclude that larval fish responses to climate change thus may depend on the relative rate and extent of both warming and browning, as they may even cancel each other out. 相似文献
93.
Future warming and acidification effects on anti‐fouling and anti‐herbivory traits of the brown alga Fucus vesiculosus (Phaeophyceae) 下载免费PDF全文
Human‐induced ocean warming and acidification have received increasing attention over the past decade and are considered to have substantial consequences for a broad range of marine species and their interactions. Understanding how these interactions shift in response to climate change is particularly important with regard to foundation species, such as the brown alga Fucus vesiculosus. This macroalga represents the dominant habitat former on coastal rocky substrata of the Baltic Sea, fulfilling functions essential for the entire benthic community. Its ability to withstand extensive fouling and herbivory regulates the associated community and ecosystem dynamics. This study tested the interactive effects of future warming, acidification, and seasonality on the interactions of a marine macroalga with potential foulers and consumers. F. vesiculosus rockweeds were exposed to different combinations of conditions predicted regionally for the year 2100 (+?5°C, +?700 μatm CO2) using multifactorial long‐term experiments in novel outdoor benthic mesocosms (“Benthocosms”) over 9–12‐week periods in four seasons. Possible shifts in the macroalgal susceptibility to fouling and consumption were tested using consecutive bioassays. Algal susceptibility to fouling and grazing varied substantially among seasons and between treatments. In all seasons, warming predominantly affected anti‐fouling and anti‐herbivory interactions while acidification had a subtle nonsignificant influence. Interestingly, anti‐microfouling activity was highest during winter under warming, while anti‐macrofouling and anti‐herbivory activities were highest in the summer under warming. These contrasting findings indicate that seasonal changes in anti‐fouling and anti‐herbivory traits may interact with ocean warming in altering F. vesiculosus community composition in the future. 相似文献
94.
Kristiina Vuorio Annika Lagus Jaana M. Lehtimäki Harri Helminen 《Journal of experimental marine biology and ecology》2005,322(1):39-52
The impact of nutrient enrichment on the phytoplankton community structure, and particularly cyanobacteria, was studied in a 3-week mesocosm experiment conducted in August 2001 in the Archipelago Sea, a part of the northern Baltic Sea. The factorial design experiment included daily additions of nitrogen (N) and phosphorus (P) at two mass ratios, 1N:1P and 7N:1P, respectively, additions of iron (Fe) and a synthetic chelator, ethylenediaminetetraacetic acid (EDTA). The floating enclosures (400 l) were sampled for analyses of phytoplankton biomass and community structure, phytoplankton primary production, chlorophyll a, nutrients, and hepatotoxins. Chlorophyll a concentration, phytoplankton biomass and primary production increased most in the 7N:1P treatment. The increase was mainly due to an abundant growth of chlorophytes (Dictyosphaerium subsolitarium, Kirchneriella spp., Monoraphidium contortum, and Oocystis spp.), pennate diatoms (especially Nitzschia spp.), dinophytes and the chroococcalean cyanobacterium Synechococcus sp. The nutrient enrichments had no effect on the total biomass of N2-fixing cyanobacteria. Nevertheless, the biomass of Anabaena spp. was highest in the enrichments with a low N/P ratio. Chlorophyll a concentration and total phytoplankton biomass were not affected by Fe or EDTA, but Fe alone had a positive effect on the chlorophyte Kirchneriella sp. The N2-fixing cyanobacteria Aphanizomenon sp. responded positively to Fe alone and to both Fe and EDTA added together. The hepatotoxin concentration increased during the experiment, but no clear responses to nutrient enrichments were found. Our study showed species-specific responses to nutrient enrichments among the N2-fixing cyanobacteria. Although the total phytoplankton production was not Fe-limited; the availability of Fe clearly affected the phytoplankton community structure. 相似文献
95.
In this study, one of the major bloom-forming cyanobacteria in the Gulf of Gdańsk (Southern Baltic Sea), Aphanizomenon Morren ex Bornet et Flahaut has been characterized using a polyphasic approach by comparing phenotypic and molecular characteristics.
The phenotypic analysis dealt with cell and filament morphology as well as ultrastructure. The molecular phylogenetic analyses
were based on sequences of the 16S rRNA gene and the adjacent intergenic transcribed spacer (ITS). We have found the Aphanizomenon population from the Gulf of Gdańsk to be significantly different in ultrastructure, morphology from freshwater A. flos-aquae and according to the traditional approach; it could be assigned to different taxonomic units. However, genetic relationship
with regard to sequences of the 16S rRNA gene, showed an high overall sequence identity (97.5–99%) to freshwater isolates.
Similarly, ITS sequence identity among populations from the Baltic Sea and different freshwater isolates was as high as 90.3–97.7%
suggesting one and the same species.
Handling editor: D. Hamilton
An erratum to this article can be found at 相似文献
96.
Ralf Thiel Philip Riel Renate Neumann Helmut M. Winkler Uwe Böttcher Tomas Gröhsler 《Hydrobiologia》2008,602(1):161-177
The status of twaite shad was investigated within the Southern Baltic Sea (ICES subdivision 22–27) and transitional area between
the Baltic and North Seas (division IIIa). The following sources of data were analysed: (i) commercial catch statistics and
relevant publications, (ii) records from ichthyological museum collections, (iii) records from recent commercial and recreational
fisheries, (iv) research fisheries with trawls. A total of 476 records of twaite shad including more than 16 million individuals
were obtained for the time between the years 1836 and 2005. About 72.9% of all records originated from commercial catch statistics
and publications, whereas 18.9% were received from ichthyological collections. Research fisheries provided 6.3%, and 1.9%
of the records were obtained from recent commercial and recreational fisheries. Most records of twaite shad were estimated
for subdivisions 24 (45.2%) and 26 (35.5%). From 1836 to 1959, 29.6% of the records date from the period until 1899. 70.4%
of the records of twaite shad originate from the twentieth century until 1959. The mean annual catch of twaite shad between
1891 and 1959 amounted to 86,674 kg within subdivisions 24–26 of the Southern Baltic Sea. Catch data show an approximately
20-year-cyclicity of maximum yields and minimum catches, respectively. The maximum annual yield of twaite shad in subdivisions
24–26 (474,700 kg) was registered in 1940, the minimum annual yield was estimated in 1958 (10 kg). In the 1950s, the annual
catches of twaite shad declined sharply. Until 1960 twaite shad catches and records originated mainly from the Pommeranian
Bay/Pommeranian Coast and adjacent waters including the Szczecin Lagoon (subdivision 24), the Bay of Gdańsk, Vistula Lagoon
and Vistula Spit (subdivision 26) and from the Curonian Lagoon and Curonian Spit (subdivision 26). The highest catches of
twaite shad originated from the area of Curonian Lagoon/Curonian Spit from 1941 to 1960. Seasonal catches of twaite shad showed
maximum values from May to July. From 1960 to 1989, only four records of A. fallax were registered in the Southern Baltic Sea which originated from German coastal waters in subdivisions 22 and 24. A total
of 107 records of twaite shad was obtained in subdivisions 20–27 from 1990 to 2005. Most of these recent records originate
from a twaite-shad stock in subdivisions 24, 25 and 26. There are indications which suggest a separate stock of twaite shad
in subdivisions 20 and 21. Disappearance and recovery of twaite shad stocks were probably caused by the following factors:
construction of barriers in rivers with spawning sites of twaite shad; habitat destruction in those rivers as consequence
of gravel extraction and reengineering scheme to improve navigation and for flood defence purposes, water pollution in the
lagoons of the Southern Baltic and in their tributaries, commercial fishery in the Southern Baltic and climatic variation
in the Baltic Sea basin south of the latitude of 60° N.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot
Fish and diadromy in Europe (ecology, management, conservation) 相似文献
97.
With the aim of elaborating a breeding plan on a captive stock of the highly endangered Adriatic sturgeon (Acipenser naccarii), a total of 10 polymorphic microsatellite loci were isolated from an enriched library. The results of cross amplification
of additional 8 loci previously isolated from A. oxyrinchus, A. fulvescens and Scaphyrinchus platorhynchus are also reported. Given the tetraploid condition of the species the genetic variability was estimated basing on the number
of alleles per individuals and the average band sharing. 相似文献
98.
The aims of the present study were to develop a parameterization of a one-year-long observed PAR time-series, apply the PAR parameterization in a primary production relation, and compare calculated and observed time-series of primary production. The PAR parameterization was applied in the generally used relation for the primary production (P d): P d = a(BI 0 Z 0) + b with observed photic depth (Z 0) and Chl-a concentrations (B). It was tested whether the PAR parameterization in combination with this simple relation for primary production was able to describe the actual measured primary production. The study is based on a one year long time-series of PAR, CTD-casts (n = 45), and primary production measurements (n = 24) from Århus Bay (56°09′ N; 10°20′ E), south west Kattegat. Results showed a high and positive correlation between observed and calculated primary production in the bay, as based on the present PAR parameterization combined with the simple primary production relation. The developed PAR parameterization, which calculates total daily surface irradiance per day (M photons m?2 d?1), can be applied in any ecological application taking into account that it was developed for the latitude of 56° N. 相似文献
99.
Helen Orav-Kotta Jonne Kotta Kristjan Herkül Ilmar Kotta Tiina Paalme 《Biological invasions》2009,11(3):597-608
Mesograzers are known to reduce the biomass of their host plant and modify the structure of the whole macrophyte community
in many ecosystems. Thus, the introduction of an efficient mesograzer may destabilize macrophyte community and also affect
the native grazers. We estimated how large proportion of macrophyte production are consumed by the alien gammarid G. tigrinus and the native gammarid G. salinus in the species poor ecosystem of the northern Baltic Sea. We analysed whether G. tigrinus consumes different diet as the native G. salinus and whether the effect of G. tigrinus on the survival of the native G. salinus is macrophyte species specific. Grazing experiments showed that there was a clear difference in the grazing rates of gammarids
among the studied macrophyte species in summer and autumn but not in spring. The grazing rates were significantly higher in
the prevailing macrophyte Pilayella littoralis as compared to other macrophytes. The grazing was inversely related to the diurnal net photosynthetic values of macrophytes.
The gammarid amphipods potentially removed only a minor part of plant primary production except for summer and autumn when
grazing of a few perennial species exceeded macrophyte production. Macrophyte species and presence of G. salinus had no effect on the survival of G. tigrinus. The presence of G. tigrinus, however, reduced the survival of the native gammarids within P. littoralis in summer. To conclude it is likely that both native and alien gammarid amphipods do not exert significant pressure on the
macroalgal communities in the northern Baltic Sea. Competitive interactions between G. tigrinus and G. salinus within the prevailing macrophyte P. littoralis is the likely explanation of the decline of the native gammarid amphipods after the establishment of G. tigrinus in the northern Baltic Sea. 相似文献
100.
Camilla Gustafsson Christoffer Boström 《Journal of experimental marine biology and ecology》2009,382(1):8-17
Studies conducted in terrestrial ecosystems have shown that increasing plant diversity enhances ecosystem processes such as primary production. In marine systems, knowledge of how plant diversity influences ecosystem processes and higher trophic levels is still limited. To examine how plant richness and composition influence recruitment and colonization processes, defaunated eelgrass (Zostera marina), sago pondweed (Potamogeton pectinatus) and perfoliate pondweed (Potamogeton perfoliatus) were planted on an unvegetated, sandy bottom in all possible combinations in July and August. Both field experiments lasted 1 week. Our results showed that in these plant assemblages plant richness had a negative effect on faunal diversity (H′) and evenness (J′), while total abundance showed strong temporal variation with weak, positive relationships with plant species richness in both August and July. Plant species composition had strong effects on amphipods (Gammarus spp.), thus both the abundance and biomass were higher in treatments containing P. perfoliatus. The colonization process was significantly influenced by the numerical dominance of a few faunal species, e.g. the settlement of lagoon cockles (Cerastoderma glaucum), and by the timing of the experiments. The results indicate that faunal colonization in these communities is rapid and significantly influenced by the traits of particular plant species. 相似文献