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61.
Philip L. Cadwallader 《新西兰海洋与淡水研究杂志》2013,47(1):27-34
Feeding of captive Galaxias vulgaris was found to be dependent on open‐water activity. It did not occur when fish remained beneath boulders. Pat'erns of spontaneous locornotory activity of individual fish were recorded to determine potential feeding times. The apparatus used to measure spontaneous locomotory activity is described. Fish were found to be active mainly at night for most of the year, but became predominantly diurnal during the spawning period. 相似文献
62.
Kota Katsuki Yasushi Miyamoto Kazuyoshi Yamada Hiroyuki Takata Keiko Yamaguchi Daisuke Nakayama Hugo Coops Hidenobu Kunii Ritsuo Nomura Boo-Keun Khim 《Journal of Paleolimnology》2008,40(4):1115-1125
Lake Nakaumi, southwest Japan, is an enclosed lagoon characterized by polyhaline and halocline conditions. Since the last
century, its ecological state has been altered by eutrophication. We used a paleolimnological approach and studied multiple
proxies, including chemical compounds, diatoms, foraminifera and molluscs, to infer the eutrophication history of the ecosystem.
Eutrophication in Lake Nakaumi was associated with several factors, including increased nutrient loading, input of herbicides,
and dike building since the 1920s. The ecological condition of this lake was divided into several stages that reflect the
eutrophication process after the 1940s. A catastrophic “regime shift” from a clear state with aquatic vegetation to a turbid
one with phytoplankton occurred in the early 1950s. Environmental degradation in the Honjo area, a part of Lake Nakaumi, was
attributed primarily to physical changes caused by the construction of an enclosing dike. Eutrophication occurred almost simultaneously
with the physical changes to the Honjo area in the 1970s. Until recently, no regime shift was observed in this area, though
the core-top sediments show possible symptoms of incipient change. 相似文献
63.
Shallow-water carbonates are invaluable archives of past global change. They hold the record of how neritic biologic communities reacted to palaeoenvironmental changes. However, attempts to decipher these geological archives are often severely hampered by the low stratigraphic resolution attained by biostratigraphy. This is particularly the case for the Upper Cretaceous carbonate platforms of the central Tethyan realm: their biostratigraphy suffers from very low resolution and poor correlation with the standard biochronologic scales based on ammonites, planktic foraminifers and calcareous nannoplankton.In this paper we show how this problem can be tackled by integrating biostratigraphy with isotope stratigraphy. We present a detailed record of the benthic foraminiferal biostratigraphy and carbon and strontium isotope stratigraphy of three upper Cenomanian-middle Campanian sections belonging to the Apennine Carbonate Platform of southern Italy. For the upper Cenomanian-Turonian interval, the carbon isotope curves of the studied sections are easily correlated to the reference curve of the English Chalk. The correlation is facilitated by the matching of the prominent positive excursion corresponding to the Oceanic Anoxic Event 2. For the Coniacian-middle Campanian interval, the correlation is mainly based on strontium isotope stratigraphy. We use the 87Sr/86Sr ratios of the low-Mg calcite of well preserved rudist shells to obtain accurate chronostratigraphic ages for many levels of the three studied sections. The ages obtained by Sr isotope stratigraphy are then used to better constrain the matching of the carbon isotope curves.From the high-resolution chronostratigraphic age-model stablished by isotope stratigraphy, we derive the chronostratigraphic calibration of benthic foraminiferal biostratigraphic events. For the first time the benthic foraminiferal biozones of the Apennine Carbonate Platform can be accurately correlated to the standard ammonite biozonation. This result is of great relevance because the biostratigraphic schemes of other carbonate platforms in the central and southern Tethyan realm are largely based on the same biostratigraphic events. 相似文献
64.
Afrobolivina afra, a Late Cretaceous bolivinid foraminifer, became extinct in the Early Paleocene. It was succeeded by the smaller, morphologically similar species Afrobolivina africana. Morphological variation in A. afra was in part correlated with environmental factors showing a pattern of random fluctuations about long-term ecological trends. A gradual, persistent and unbroken environmental trend, related to a eustatic fall in sea-level, is significantly correlated with the morphological evolution of the species. The micro-biogeography of A. afra at the time it was approaching extinction is consistent with its having given rise to A. afracana allopatrically in a manner which can be described by a fold-catastrophe adaptive model. This mode predicts that A. afra should undergo quantum evolution to A. africana in a restricted area in a near-shore environment.However, detailed study of borehole material reveals an apparent parabolic increase in the overall size of A. afra prior to extinction and it is argued that as a result, A. africana cannot be the direct descendant of A. afra without there having been some “discontinuity” in the environment or evolutionary process. This suggests that the sudden replacement of a species by a smaller, morphologically similar form may not be a straightforward succession. The apparent parabolic increase in size of A. afra can be modelled by the fold catastrophe of Thom theory if interpreted as representing the initial phase of a form of adaptive quantum evolution in which a gradual environmental change causes a fitness peak to be absorbed into the flank of a higher peak.In terms of such a model, the absence of a larger descendant species suggests that A. afra could have been replaced by A. africana before the quantum threshold had been reached. A possible cause for this could be that the changes in the environment might have lowered the height of the fitness function in the vicinity of the peak for A. afra to below that of the peak for A. africana, or vice versa. 相似文献
65.
Juliane Scheder Friederike Bungenstock Kristin Haynert Anna Pint Frank Schlütz Peter Frenzel Achim Wehrmann Helmut Brückner Max Engel 《第四纪科学杂志》2022,37(1):71-85
In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ? ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal bp. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment. 相似文献
66.
67.
钱塘江下游河段潮流和沉积特征 总被引:4,自引:0,他引:4
钱塘江下游河段水文泥沙测量、有孔虫和重矿物组合等的分析表明,涨潮流可以将海区沉积物向河口及其上游方向搬运,这为解释冰后期海进河床充填层序提供了对比依据。钱塘江河口沙坎主要物质来自长江和钱塘江。 相似文献
68.
Ian P. Wilkinson Peter M. Hopson 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(5):831-841
Ventnor No. 2 Borehole, located near Ventnor, Isle of Wight, penetrated the basal part of the Chalk Group and the Selborne Group before terminating in the upper part of the Lower Greensand Group (Sandrock Formation). The borehole was examined for Foraminifera, and although they were not seen in the Sandrock Formation and Monks Bay Sandstone Formation, the remainder of the borehole yielded moderately low diversity assemblages dominated by agglutinated species. Foraminiferal zones 3-6 (H dentatus to M. fallax/M. rostratum macrofaunal zones) were identified in the Gault Formation and zones 6 (lower) to 6a (M. fallax/M. rostratum to A. briacensis macrofaunal zones) were identified in the Upper Greensand Formation. Assemblages from the overlying West Melbury Marly Chalk Formation were used to identify foraminiferal zones BGS1-BGS3 (M. mantelli and M. dixoni macrofaunal zones). 相似文献
69.
In this study we compare the foraminifera of modern South San Francisco Bay with fossils from sediments of a previous estuary at 125 ka to provide a basis for interpreting the impact of natural and human change on the benthic ecosystem. All the species found in the Pleistocene sediments of this study are estuarine and/or shallow-water species occurring commonly in San Francisco Bay today, except for the introduced foraminifer Trochammina hadai, a native of Japan that was not found in samples taken in San Francisco Bay before 1983. The biodiversity and species composition of the fossil and modern assemblages before the introduction of T. hadai are nearly identical, suggesting that the environmental and physical changes in the 125,000-year-old and modern estuaries have not had a significant effect on the meiofauna of the Bay. In contrast, modern anthropogenic change in the form of species introductions has impacted the modern foraminiferal assemblage: T. hadai began to dominate the modern assemblage a decade after its introduction. Similar to the recorded impacts of introductions of marine metazoan invertebrate species, the dominance of T. hadai changed species proportions in the post-1980s foraminiferal assemblage, however no known extinctions in the native foraminiferal fauna occurred. 相似文献
70.
Andrew C. Kemp Benjamin P. Horton Stephen J. Culver Orson van de Plassche 《Quaternary Research》2009,71(1):9-21
Foraminifera and diatoms preserved in salt-marsh sediments have been used to produce high-resolution records of Holocene relative sea-level (RSL) change. To determine which of these microfossil groups is most appropriate for this purpose we investigated their relative utility from salt marshes in North Carolina, USA. Regional-scale transfer functions were developed using foraminifera, diatoms and a combination of both (multi-proxy) from three salt marshes (Oregon Inlet, Currituck Barrier Island and Pea Island). We evaluated each approach on the basis of transfer-function performance. Foraminifera, diatoms and multi-proxy-based transfer functions all demonstrated a strong relationship between observed and predicted elevations (r2jack > 0.74 and RMSEP < 0.05 m), suggesting that they have equal utility. Application of the transfer functions to a fossil core from Salvo to reconstruct former sea levels enabled us to consider relative utility in light of ‘paleo-performance’. Fossil foraminifera had strong modern analogues, whilst diatoms had poor modern analogues making them unreliable. This result reflects the high diversity and site-specific distribution of modern diatoms. Consequently, we used foraminifera to reconstruct RSL change for the period since ∼ AD 1800 using a 210Pb- and 14C-based chronology, and we were able to reconcile this with tide-gauge records. 相似文献