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91.
Summary This study presents sedimentological and micropaleontological data on ostracods from a cold-temperate inner shelf setting
in the Troms District, northern Norway. The coarse fraction analyses carried out on sediment surface samples from coastal
platforms and adjacent outer fjord troughs reveal a considerable contribution from ostracods to the accumulation of skeletal
carbonates in distinct depositional settings. Ostracod accumulation is highest along wave-sheltered areas of coastal platforms
where fleshy seaweed and coralline algal communities thrive in 10 to 30 m water depth. Current-exposed slopes of outer fjord
troughs show a highly mixed ostracod assemblage consisting of imported species from the shallow coastal platform which is
mixed with the trough assemblage. The hydrodynamic transport of ostracods into deeper areas results from the strong tidal
current regime. Because of this mixing process, only the end members, the coastal platform and the fjord trough assemblages
can be defined. The former is characterized byBaffinicythere emarginata, Cythere lutea, Finmarchinella angulata, Hemicytherura clathrata, Robertsonites tuberculatus, Sclerochilus
rudjakovi, Semicytherura undata andXestoleberis cf.depressa. The outer fjord trough assemblage is characterized byCluthia cluthae, Cytherella abyssorum, Cytheropteron alatum, Krithe cf.adelspergi, Muellerina abyssicola, Cytherella cf.vulgatella andCytheropteron testudo. Members of the northern Norwegian trough assemblage are known to occur in deeper open shelf environments of the NE-Atlantic. 相似文献
92.
新疆准噶尔盆地西北缘三叠纪孢粉组合 总被引:18,自引:5,他引:13
本文对新疆准噶尔盆地西北缘红山咀区拐114井和百口泉区38井的下克拉玛依组、上克拉玛组、下白碱滩组层段13块样品中所含的孢子花粉进行了系统的分析研究,共获得孢粉77属170种,描述了31种,其中包括1新属21新种,根据陷粉组合特征,详细地讨论了上述地层的时代,认为下克拉玛依组属中三叠世,上克拉玛依组及下白碱滩组属晚三叠世。 相似文献
93.
《Palaeoworld》2023,32(2):266-286
Middle and Late Ordovician strata in the nearshore area of the western Yangtze Platform are investigated. In total, 241 δ13Ccarb samples and 108 conodont samples from the Songliang and Tuanjie sections in the northeastern Yunnan Province were collected for chemostratigraphic and biostratigraphic studies. Altogether, 21 species belonging to 16 conodont genera were recovered from the two sections, among which Ansella jemtlandica, Drepanoistodus basiovalis, Hamarodus brevirameus, and Microzarkodina hagetiana are important age indicators within the Dapingian to early Katian interval. Four carbon isotope shifts are recognized in the studied sections: a negative shift in the early Darriwilian, the middle Darriwilian carbon isotope excursion (MDICE), the early Katian Guttenberg carbon isotope excursion (GICE), and a further positive carbon isotope shift later in the early Katian which is a new record of this event in South China. Integrated carbon chemostratigraphy and conodont biostratigraphy indicate early Darriwilian and early Katian ages for the base and top, respectively, of the Huadan Formation at the Songliang section, and a Darriwilian to early Katian age for the Shihtzupu Formation at the Tuanjie section. 相似文献
94.
Summary The Asselian-Sakmarian strata of the Fosheim-Hamilton subbasin represent a distinct 15 000 km2 depocentre located at the northeast margin of the main Sverdrup Basin in the Canadian Arctic Archipelago. Approximately 35
high-frequency cycles composed mainly of platformal carbonates with subaqueous evaporites accumulated at a time of renewed
rifting activity in this subbasin.
A general depositional model based on the facies analysis of the Asselian-Sakmarian strata shows that the carbonate platforms
surrounding the Fosheim-Hamilton subbasin were segmented by the position of critical interfaces including the: 1) base of
the fairweather wave abrasion zone; 2) base of the storm wave abrasion zone; and 3) base of the photic zone. The base of the
fairweather wave abrasion zone divided the platforms into two broad parts; an inner shelf with a relatively quiet, semi-restricted
lagoon and more agitated, open marine barries and shoals and an open marine mid-shelf with numerous reefal and non-reefal
subenvironments extending from the base of fairweather wave abrasion zone to below the photic zone. Outer shelf and associated
slope and basin were not present within the Fosheim-Hamilton subbasin but were present farther west along the margin of the
main Sverdrup Basin. 相似文献
95.
Adam J. Friedman George Han Mahantesh S. Navati Manju Chacko Leslie Gunther Alan Alfieri Joel M. Friedman 《Nitric oxide》2008,19(1):12-20
A new platform using biocompatible materials is presented for generating powders comprised of nanoparticles that release therapeutic levels of nitric oxide (NO) in a controlled and sustained manner. The capacity of these particles to retain and gradually release NO arises from their having combined features of both glassy matrices and hydrogels. This feature allows both for the generation of NO through the thermal reduction of added nitrite by glucose and for the retention of the generated NO within the dry particles. Exposure of these robust biocompatible nanoparticles to moisture initiates the sustained release of the trapped NO over extended time periods as determined both fluorimetrically and amperometrically. The slow sustained release is in contrast to the much faster release pattern associated with the hydration-initialed NO release in powders derived from glassy matrices. These glasses are prepared using trehalose and sucrose doped with either glucose or tagatose as the source of thermal electrons needed to convert nitrite to gNO. Significantly, the release profiles for the NO in the hydrogel/glass composite materials are found to be an easily tuned parameter that is modulated through the specific additives used in preparing the hydrogel/glass composites. The presented data raise the prospect that these new NO releasing nanoparticles can be easily formulated for use under a wide range of therapeutic circumstances. 相似文献
96.
Extensive information has been acquired on the occurrence of Lower Cambrian Small Shelly Fossils (SSF) in the shallow water sediments of the western fringe of the Yangtze Platform (eastern Yunnan and central Sichuan Provinces) during the last two decades. However, less is known on the temporal and spatial distribution of SSFs on the northern margin of the Yangtze Platform. Here we report SSF associations from Kuanchuanpu (Ningqiang County, southern Shaanxi Province), Shatan, and Xinli (both Nanjiang County, northern Sichuan Province) representing the Southwest Shaanxi region and from Sanlangpu, and Xiaowan (Xixiang County, southern Shaanxi Province) of the Southeast Shaanxi - Northwest Hubei region. The thickness of the Lower Cambrian SSF-bearing strata strongly decreases in this region from West to East and the stratigraphic hiatus increases. An earliest Cambrian hiatus is widely distributed on the northern margin of the Yangtze Platform. At the same time, a syngenetic brecciation occurred in wide shallow shelf settings. A tectonic mobilization, possibly related to the assembly of Gondwana following the breakup of Rodinia, may be responsible for this. In sections near Kuanchuanpu (Ningqiang County), the Meishucunian (equivalent to the Nemakit-Daldynian to Tommotian of Siberia) succession comprises ca. 55 m of dark phosphatic carbonates, siltstones, and cherts. The SSF associations are similar to those of East Yunnan and, in ascending order, can be discriminated into the Anabarites trisulcatus - Protohertzina anabarica Zone, the Watsonella yunnanensis Zone (previously mentioned as Heraultipegma yunnanensis Zone), and the Sinosachites flabelliformis - Tannuolina zhangwentangi Zone. The Siphogonuchites triangularis - Paragloborilus subglobosus Zone cannot be unambiguously detected in the Southwest Shaanxi region. The occurrence of embryos and eggs within the Anabarites trisulcatus - Protohertzina anabarica Zone, which has been reported earlier, is remarkable. The previously reconstructed life cycle and taxonomic treatment of Olivooides / Punctatus are re-discussed. The earliest SSF associations (Anabarites trisulcatus - Protohertzina anabarica Zone to Watsonella yunnanesis Zone) are missing in the Southeast Shaanxi - Northwest Hubei region and the Ninella tarimensis - Cambroclavus fangxianensis Assemblage Zone and Rhombocorniculum cancellatum Taxon Range Zone are introduced herein. 相似文献
97.
Tvrtko Korbar Ladislav Fuček Antun Husinec Igor Vlahović Nenad Oštrić Dubravko Matičec Vladimir Jelaska 《Facies》2001,45(1):39-58
Summary The island of Cres is located in the northern part of the Adriatic Sea. The island is built up of predominantly Cretaceous
carbonates deposited in north-western part of extensive and long-lasting Adriatic Carbonate Platform. Owing to the influence
of synsedimentary tectonics supported by eustatic changes during the latest Albian/Early Cenomanian, different sedimentary
environments were established: from shallow intraplatform basin and related slope, across basin margin to protected shallow-platform.
During the Early to Middle Cenomanian rudist communities (ichthyosarcolitid/caprinid/radiolitid)flourished along a relatively
high-energy intraplatform basin margin. Fair amounts of coarse-grained bioclasts, derived almost exclusively from broken rudist
shells, were deposited over a marginal depocenter. Contemporaneously, pithonellid wackestone-packstones containing microbioclasts
and planktonic foraminifera were deposited basinward while marginal bioclastic sediments and limestone blocks of the basin
margin origin were sporadically deposited within the basin. The opening of the Cres intraplatform basin was aborted and the
basin was finally filled up during the Late Cenomanian. Since the Cres intraplatform basin was established at the beginning
of the Cenomanian it probably represented the initiation phase in the north-western extension of the later Adriatic Trough
development. 相似文献
98.
西伯利亚地台早寒武世钙藻的发育特征 总被引:1,自引:0,他引:1
VALUCHININA AATERLEEV 《微体古生物学报》2003,20(1):31-38
西伯利亚地台的新元古代到早寒武世间的钙藻化石特别丰富,为研究钙藻化石的发育历史提供了模式。在几次演化事件背景下记录了演化的两次转折,其中一个是藻类的普遍钙化,还有一个是Botomian晚期到Toyonian早期之间在西伯利亚地台缺失钙藻化石记录,而在其它地区包括西伯利亚地台的边缘(Altay—Sayan地区),钙藻的丰度却达到了最大。 相似文献
99.
底栖藻对扬子地台西缘晚奥陶世生态危机的改善作用 总被引:1,自引:0,他引:1
晚奥陶世的冈瓦纳大陆冰川导致全球性海退和两幕生物灭绝事件,第一幕,也是高潮幕,发生于Rawtheyan期末;第二幕发生于Hirnantian期末。在经历第一幕事件的过程中,扬子地台西缘的四川汉源地区大渡河组浅水相灰岩和硅质灰岩中出现了极其繁盛的底栖藻类,局部层位中可达到造礁的程度。大量底栖藻通过光合作用改善、缓冲了这一浅海地区的低温、缺氧的灾变环境,并成为生态系统重建的先驱群落。局部浅海环境的正常化为后生动物腕足类、三叶虫和海百合在Hirnantian期南郑组的短暂复苏创造了生存条件。当后生动物再度成为生态系统的主体时,啃食压力的增大使底栖藻的居群数量骤然减低。始于Hirnantian后期冰川消融的海进造成第二幕Hirnantia动物群的灭绝。 相似文献
100.
扬子台地西北缘志留纪笔石Oktavites spiralis (Geinitz, 1842)发育过程研究 总被引:1,自引:0,他引:1
Oktavites spiralis(Geinitz,1842)是志留系特列奇阶(Telychian)的笔石带化石,其形态特征明显,在全球范围内广泛分布,地层对比意义较强。然而,该种宽泛的化石定义以及缺乏居群变异研究,造成了对该化石延限的争议,不利于地层的精确对比。笔者对产自陕西紫阳、岚皋地区特列奇阶Oktavites spiralis带至Cyrtograptus lapworthi笔石带的45个Oktavites spiralis不同发育阶段的幼体标本进行研究,建立了较完整的发育序列,从而对该种的始部特征有了更为深入的了解,增加了描述的精确性。同时,通过始部特征的对比研究,可将Oktavites spiralis和与之共生的Oktavites contortus(Perner,1897)明确区分为2个独立的种。此外,对Oktavites spiralis和Oktavites contortus发育过程的研究,也可成为该属进一步精确厘定的主要依据之一。 相似文献