全文获取类型
收费全文 | 609篇 |
免费 | 31篇 |
国内免费 | 3篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 30篇 |
2015年 | 15篇 |
2014年 | 10篇 |
2013年 | 86篇 |
2012年 | 13篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 32篇 |
2008年 | 34篇 |
2007年 | 29篇 |
2006年 | 43篇 |
2005年 | 15篇 |
2004年 | 14篇 |
2003年 | 17篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 13篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 4篇 |
排序方式: 共有643条查询结果,搜索用时 15 毫秒
631.
The chemical character and burial of phosphorus in shallow coastal sediments in the northeastern Baltic Sea 总被引:1,自引:0,他引:1
The chemical composition and vertical distribution of sediment phosphorus (P) in shallow coastal sediments of the northeastern
Baltic Sea (BS) were characterized by sequential extraction. Different P forms were related to chemical and physical properties
of the sediments and the chemistry of pore water and near-bottom water. Sediment P composition varied among the sampling sites
located in the Archipelago Sea (AS) and along the northern coast of the Gulf of Finland (GoF): the organic rich sites were
high in organic P (OP), while apatite-P dominated in the area affected by sediment transportation. Although the near-bottom
water was oxic, the sediments released P. Release of P was most pronounced at the site with high sediment OP and reduced conditions
in the sediment-water interface, indicating that P had its origins in organic sources as well as in reducible iron (Fe) oxyhydroxides.
The results suggest that even though these coastal areas are shallow enough to lack salinity stratification typical for the
brackish BS, they are vulnerable to seasonal oxygen (O2) depletion and P release because of their patchy bottom topography, which restricts mixing of water. Furthermore, coastal
basins accumulate organic matter (OM) and OP, degradation of which further diminishes O2 and creates the potential for P release from the sediment. In these conditions, an abundance of labile OP may cause marked
efflux of P from sediment reserves in the long-term. 相似文献
632.
Louise Forsblom Andreas Lindn Jonna Engstrm
st Maiju Lehtiniemi Erik Bonsdorff 《Ecology and evolution》2021,11(9):4035
Benthic species and communities are linked to pelagic zooplankton through life‐stages encompassing both benthic and pelagic habitats and through a mutual dependency on primary producers as a food source. Many zooplankton taxa contribute to the sedimentary system as benthic eggs. Our main aim was to investigate the nature of the population level biotic interactions between and within these two seemingly independent communities, both dependent on the pelagic primary production, while simultaneously accounting for environmental drivers (salinity, temperature, and oxygen conditions). To this end, we applied multivariate autoregressive state‐space models to long (1966–2007) time series of annual abundance data, comparing models with and without interspecific interactions, and models with and without environmental variables included. We were not able to detect any direct coupling between sediment‐dwelling benthic taxa and pelagic copepods and cladocerans on the annual scale, but the most parsimonious model indicated that interactions within the benthic community are important. There were also positive residual correlations between the copepods and cladocerans potentially reflecting the availability of a shared resource or similar seasonal dependence, whereas both groups tended to correlate negatively with the zoobenthic taxa. The most notable single interaction within the benthic community was a tendency for a negative effect of Limecola balthica on the amphipods Monoporeia affinis and Pontoporeia femorata which can help explain the observed decrease in amphipods due to increased competitive interference. 相似文献
633.
Eocene forest ecosystems can be considered as rich biodiversity hotspots regarding soldier beetles (family Cantharidae). Paleogene European ambers, for instance, comprised many genera that are still extant in Europe, but also extinct forms and lineages such as the tribe established herein, or the tribe Mimoplatycini Kazantsev, 2013 that mimics the lycids. In this note, the authors describe Cacomorphocerus wiszniewskii sp. nov., and the new tribe Cacomorphocerini tri. nov. is proposed for Cacomorphocerus Schaufuss, 1892 and Sucinocantharis Ku?ka and Kania, 2010. The new tribe is characterized by antennae with 12 or 16 articles, with saucer-shaped or dilated central antennomeres and is distributed in Eocene Baltic and Rovno amber. Furthermore, Cacomorphocerus is transferred from the subfamily Dysmorphocerinae Brancucci, 1980 to Cantharinae Imhoff, 1856. 相似文献
634.
《Comptes Rendus Palevol》2019,18(6):589-597
Examination of fossil ant specimens from various private and institutional German collections of Baltic amber has revealed a new genus and species of Myrmicinae, described here as Thanacomyrmex hoffeinsorum gen. et sp. nov. The new worker morphotype shares some similarities with the coeval extinct genus Parameranoplus Wheeler, also from Baltic amber, and the extant genera Pristomyrmex Mayr and Acanthomyrmex Emery, suggesting placement of the new fossil in the Myrmecina genus-group within the tribe Crematogastrini. The new genus highlights the tremendous diversity of ants that evolved in the Palaeogene European forests and composed the first major radiation of crown-group ants. 相似文献
635.
636.
Peter Torstensson 《Plant Ecology》1987,68(3):169-172
The population dynamics of the annual Spergularia marina was studied during four years on three different sites on a Baltic seashore meadow. The population density varied significantly both between years and between sites. At one of the sites the average population density was higher than at the two other sites. Both differences in reproductive capacity and in density-independent mortality caused differences in population size. Variation in population seed yield or loss of seed or both, between years, to a large extent determined the variation in the population density between years. 相似文献
637.
Benthic processes were measured at a coastal deposition area in the northern Baltic Sea, covering all seasons. The N2 production rates, 90–400 μmol N m−2 d−1, were highest in autumn-early winter and lowest in spring. Heterotrophic bacterial production peaked unexpectedly late in
the year, indicating that in addition to the temperature, the availability of carbon compounds suitable for the heterotrophic
bacteria also plays a major role in regulating the denitrification rate. Anaerobic ammonium oxidation (anammox) was measured
in spring and autumn and contributed 10% and 15%, respectively, to the total N2 production. The low percentage did, however, result in a significant error in the total N2 production rate estimate, calculated using the isotope pairing technique. Anammox must be taken into account in the Gulf
of Finland in future sediment nitrogen cycling research.
Handling editor: J. Cole 相似文献
638.
639.
Martin Fikáček Shûhei Yamamoto Keita Matsumoto Rolf G. Beutel David R. Maddison 《Systematic Entomology》2023,48(2):233-249
Sphaeriusidae (Coleoptera: Myxophaga) is a group of shiny, blackish and hemispherical riparian beetles, known for their miniaturized bodies. They are worldwide in distribution, but very limited information is available about taxonomic and morphological diversity, and natural and evolutionary history. The aim of this study is to help fill in these gaps. We examined the external morphology of modern representatives using scanning electron microscopy (SEM), and reconstructed the phylogeny of the family using five DNA markers (cytochrome oxidase I, 18S rRNA, 28S rRNA, CAD and wingless). Our results suggest a larger morphological diversity than previously expected, corresponding to the deep genetic divergences of principal lineages. We also examined two inclusions in 99-million-year-old Burmese amber. The integration of all evidence allows us to recognize three genera: the extinct genus †Burmasporum Kirejtshuk, the newly defined genus Bezesporum gen.nov. preserved in Burmese amber (B. burmiticum sp.nov. ) and present in the modern fauna of Southeast Asia, and the genus Sphaerius Waltl with a world-wide distribution. Sphaerius species are morphologically highly uniform, with the exception of species from Australia and South Africa, which share some characteristics with Bezesporum gen.nov. despite being resolved as deeply nested lineages of Sphaerius by DNA data. The presence of Bezesporum gen.nov. in Burmese amber and in recent fauna indicates that Sphaeriusidae largely maintained their specific morphology and specialized riparian lifestyle for at least 100 million years. Therefore, they can be considered an exceptionally conserved group, with a minimum of evolutionary changes over a long period. Our study also demonstrates that the species numbers and fine-scale morphological diversity of Sphaeriusidae are larger than expected in both the past and present-day faunas. Both were apparently underestimated due to the minute body size and cryptic habits of these beetles. 相似文献
640.
In the shallow eutrophic waters of the Darss-Zingst-ecosystem (Baltic Sea) wind induced mixing of the water column, and resuspension
of sediment is an important phenomenon. Incubation experiments (7 days) with natural water were performed in the laboratory
under simulated mixing conditions in order to assess the effects on abundance, biomass and activity of bacteria, heterotrophic
nanoflagellates and ciliates in the water column and upper bottom layers.
Under calm mixing conditions a bottom layer developed, rich in organic aggregates. Bacterial biomass increased through increase
of bacteria abundance and doubled cell volume. Consequently, biomass of flagellates and, more pronounced, of ciliates increased.
The bottom layer, comprising only 15% of the incubated volume, containedca. 60% of the bacterial biomass and ca. 55% of production, 75 and 95% of flagellate biomass, and ca. 70% of ciliate biomass.
It is concluded that bottom layers rich in organic aggregates, although not being present permanently, play an important role
in the shallow Darss-Zingst-ecosystem. 相似文献