全文获取类型
收费全文 | 946篇 |
免费 | 77篇 |
国内免费 | 78篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 25篇 |
2021年 | 18篇 |
2020年 | 35篇 |
2019年 | 41篇 |
2018年 | 32篇 |
2017年 | 31篇 |
2016年 | 28篇 |
2015年 | 46篇 |
2014年 | 40篇 |
2013年 | 104篇 |
2012年 | 28篇 |
2011年 | 43篇 |
2010年 | 39篇 |
2009年 | 41篇 |
2008年 | 50篇 |
2007年 | 55篇 |
2006年 | 51篇 |
2005年 | 49篇 |
2004年 | 29篇 |
2003年 | 29篇 |
2002年 | 41篇 |
2001年 | 31篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 17篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 14篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有1101条查询结果,搜索用时 390 毫秒
111.
Microfacies of the Early to Middle Norian reefal limestone of the Sambosan Accretionary Complex (SAC) at Kamase locality,
southwest Japan, are classified into seven major facies types in stratigraphic order: peloidal grainstone-packstone, unfossiliferous
lime-mudstone, tubular problematica-rich wackestone, sponge-coral floatstone, sponge bafflestone, coral rudstone, and peloidal-bioclastic
packstone-grainstone. The SAC records patch reef development on a mid-oceanic seamount in the Panthalassa Ocean. Because most
examples of Triassic reefs come from the former Tethys, counterparts such as those from the SAC are pivotal in resolving paleogeographic
issues as well as clarifying the depositional patterns between the eastern Tethys and adjacent western Pacific (Panthalassa).
We also reveal that the primary stratigraphy of the reefal limestone was disrupted by submarine landslides of the seamount
in an open-ocean realm during the late Middle to Late Jurassic time. 相似文献
112.
塔里木河流域下游地区植物有30科80属122种。以双子叶植物类群占优势,其中多年生草本植物在塔里木河流域下游植物中占多数。显示了物种形成是年轻的进化类型。生态类型以旱生植物为主。占总种数的52%,这足长期适应比较干旱的自然环境的结果。该区系的温带成分占优势。地中海成分也占有一定地位。这些区系成分的植物都是干旱区荒漠植物的代表。区系地理反映了物种演化过程的历史气候、地质变化动态。查清塔里木河流域下游植物资源的数量和分布区的变迁,为该地区的植物资源保护提供科学依据。 相似文献
113.
贵州兴义中三叠世 Nothosaurus一新种 总被引:12,自引:4,他引:8
记述了贵州兴义法郎组竹竿坡段幻龙一新种———Nothosaurusyoungisp .nov .。新种以眶后弓窄 ,上颌骨和眶后骨在轭骨之后相连 ,外翼骨形成明显的腹向凸缘 ,下颌具清晰的冠状突 ,和夹板骨前端进入下颌缝合部等特征区别于幻龙的其他种。支序分析的结果表明N .youngi的原始性仅次于N .juvenilis。新种N .youngi具有Nothosaurus中的一些原始特征 ,短的下颌缝合部 ,短的上颌齿列和窄的眶后弓 ,新种在法郎组竹杆坡段的发现支持含化石地层为中三叠世拉丁期的结论。 相似文献
114.
黑河下游河岸绿洲区包气带土壤水分与植被生长状况的研究 总被引:8,自引:1,他引:7
黑河下游荒漠平原区近年来由于河水流入量的持续减小,致使依赖河水补给来源的地下水呈减少趋势,造成区域性地下水位下降,从而引起一系列生态环境问题。通过研究黑河下游河岸绿洲区非饱和带的含水量、地下潜水埋深、土壤类型结构等与河岸绿洲植被生长状况之间的关系,发现土壤结构、地下水位埋深和土壤盐分是决定研究区植被生长状况的3个主要因素,而土壤结构是不可改变的,土壤盐分又与地下水关系密切,因此,地下水是极端干旱区植被生长状况的决定因素。 相似文献
115.
The trace fossil Zoophycos has been described from the Middle Triassic carbonates of the German Basin for the first time. It occurs in a calcilutite bed at the top of a shallowing-upward cycle (parasequence) in the transgressive systems tract of the Middle to Upper Muschelkalk sequence of Thuringia (Germany). Based on sedimentological and palaeontological features, the studied interval is interpreted as deposited in a marine nearshore environment with proximal storm deposits (tempestites). Zoophycos occurs in a very simple planar form with lobate spreiten, which were most likely produced by a worm-like animal by strip mining. The upper tier of the ichnofabric consists of Zoophycos, whereas the lower tier is occupied by cylindrical trace fossils of unknown taxonomic affiliation and with decreasing size towards the bottom. Associated trace fossils such as Rhizocorallium, Balanoglossites and Trypanites indicate a partly firm to hard substrate. No mixed layer is developed at the top of the trace fossil bearing succession. The ichnofabric together with the sedimentological features (disseminated pyrite, blue-grey colour) and palaeontological circumstances (poor benthic fauna, meiofauna with a small body size) support an interpretation of a dysaerobic environment. In the view of evolutionary change, Palaeozoic Zoophycos occurs in both deep and shallow marine deposits, whereas Mesozoic and Cenozoic Zoophycos is only common in shelfal and deeper-marine deposits. The new finding from the shallow-marine Middle Triassic represents the first reliable occurrence of Zoophycos after the end-Permian mass extinction and shows close similarities to its Palaeozoic precursors. It demonstrates that the producer survived the end-Permian mass extinction, became re-established in the nearshore realm and progressively colonized deeper-marine environments during the Mesozoic and Cenozoic. 相似文献
116.
A new galesaurid cynodont, Progalesaurus lootsbergensis gen. et sp. nov., is described on the basis of a well-preserved skull, lower jaw, right scapula and left atlantal neural arch. Autapomorphies of Progalesaurus include postcanine teeth bearing numerous mesial and distal accessory cusps that flank a recurved main cusp, a post-temporal fenestra bordered by the squamosal ventrally and a large external naris. Progalesaurus is similar to Galesaurus in possessing a poorly defined masseteric fossa on the dentary, a strongly recurved main cusp of the postcanine dentition, an incomplete secondary palate and a similar basisphenoid-parasphenoid morphology. A cladistic analysis of ten early cynodont genera resolves a monophyletic Galesauridae encompassing Cynosaurus , Progalesaurus and Galesaurus , although support for this clade is weak. Procynosuchus and Dvinia are placed at the base of Cynodontia whereas Thrinaxodon and Platycraniellus are positioned higher, but outside of Eucynodontia. The holotype and only known specimen of Progalesaurus was collected during systematic prospecting of Permo/Triassic boundary strata at New Lootsberg Pass, Graaff-Reinet District, South Africa. The discovery of Progalesaurus increases the number of valid Early Triassic cynodonts to four and sheds light on the tempo of early cynodont diversification after the end-Permian mass extinction. 相似文献
117.
A diverse Late Triassic (Late Norian) gastropod fauna is described from the Mission Creek Limestone of the Wallowa terrane
(Idaho, USA). Sample standardization by rarefaction analysis indicates that the fauna is even more diverse than the Late Triassic
gastropod fauna from the Pucara Formation (Peru) which represents the most diverse gastropod fauna from South America. The
gastropod fauna consists of 66 species; several genera are reported for the first time from North America. A high percentage
of the species are highly ornamented and several have distinct siphonal canals. This suggests that the appearance of truly
Mesozoic elements among the gastropods began before the Mesozoic Marine Revolution in other clades. The fauna is dominated
by high-spired strongly ornamented procerithiids, a group more characteristic for the Jurassic. Comparison of the present
fauna and the Iranian Nayband Formation gastropod fauna show that the procerithiids underwent a first global radiation in
the Late Triassic. The high number of new species in this fauna suggests that sampling of Late Triassic gastropod faunas is
still incomplete and hinders palaeobiogeographic considerations. Previous suggesions that gastropod faunas from the Wallowa
and Wrangellia terranes resemble each other and are distinct from those of Alexander, Chulitna, and Farewell terranes are
basically corroborated. The gastropod fauna of the Mission Creek Limestone differs considerably from that of the western and
central Tethys but shares several taxa with the Late Triassic gastropod fauna of the Pucara Formation in Peru. Thus, the Hispanic
corridor was probably not present in the Norian but opened only in the Early Jurassic.
The subfamily Andangulariinae is introduced and placed in the Zygopleuridae. The generaSpiniomphalus, Nodoconus, Gudrunella, Blodgettella, Idahospira, andSiphonilda and the subgenusCryptaulax (Wallowax) are introduced. 27 species are erected. A lectotype is designated forCryptaulax rhabdocolpoides
Haas, 1953.
相似文献
118.
119.
长江下游水生动物群落生物多样性变动趋势初探 总被引:20,自引:0,他引:20
对1990-1999年间长江下游江段生物多样性的变动趋势进行了研究,并就群落稳定性与多样性的关系进行了探讨,结果表明,物种多样性指数量大值为1.1112,最小值为0.0327,反映物种均匀度,丰盛度的指数都有不同程度的下降,而反映优势度的指数却有一定程度的上升,优势度指数最大值为1,最小值为0.34046,优势种前6位分别为杂虾,青虾,餐条,吻Qu,蛇Qu,黄颡,表明长江下游江段的生物多样性正在逐步丧失,经济鱼类数量趋减,小型野杂鱼类数量趋增。 相似文献
120.
天山和昆仑—秦岭造山带志留系、石炭系和三叠系复理石相遗迹化石 总被引:2,自引:0,他引:2
在天山志留系,石炭系和东昆仑-西秦岭三叠系浊积岩系中遗迹化石发育,经研究计有:Helminthopsis hieroglyphica,Neonerietes biserialis.,N,uniserialis,palaeophycus isp.,P.serratus,P.striatus.P.tubularis,Paleodictyon imperfectum,Phycodes circinnatum,Phycosiphon incertum,Planolites annularis,P.beverleyensis,P.Montanus,Rhizocorallium ips.,Scalarituba missourensis,Skolithos ips.,?Spirorhaphe isp.,sublorenzinia ips.Tambia isp.,Taphrhelminthopsis auricularis,Teichichnus isp.,Thalassinoides isp.它们构成4种遗迹化石组合:Phycosiphon-Palaeophycus组合,Neonereites-Scalarituba组合,Paleodictyon组合和Phycodes Skolithos组合,分别代表局限缺氧深海盆地浊流沉积,半深海环境中-上扇沉积,多岛洋环境的中-下扇沉积,半深海环境的中扇浊流沉积。 相似文献