首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1354篇
  免费   51篇
  国内免费   15篇
  2023年   10篇
  2022年   14篇
  2021年   25篇
  2020年   45篇
  2019年   39篇
  2018年   38篇
  2017年   36篇
  2016年   33篇
  2015年   65篇
  2014年   60篇
  2013年   134篇
  2012年   53篇
  2011年   49篇
  2010年   48篇
  2009年   38篇
  2008年   74篇
  2007年   51篇
  2006年   65篇
  2005年   71篇
  2004年   53篇
  2003年   46篇
  2002年   39篇
  2001年   41篇
  2000年   40篇
  1999年   29篇
  1998年   14篇
  1997年   9篇
  1996年   15篇
  1995年   18篇
  1994年   15篇
  1993年   24篇
  1992年   28篇
  1991年   19篇
  1990年   5篇
  1989年   8篇
  1988年   3篇
  1987年   8篇
  1986年   11篇
  1985年   11篇
  1984年   10篇
  1982年   4篇
  1981年   1篇
  1979年   1篇
  1978年   5篇
  1977年   4篇
  1976年   4篇
  1975年   2篇
  1972年   4篇
  1971年   1篇
排序方式: 共有1420条查询结果,搜索用时 156 毫秒
71.
Pareiasaurs were important medium‐ to large‐sized herbivores in the Middle and Late Permian, some 268–252 Ma. They are best known from abundant remains of several taxa found in South Africa and Russia, with isolated finds from other parts of the world. Six genera and species of pareiasaurs have been described from China, and yet they have not been reviewed. Of these six, Tsiyuania may be a synonym of Honania, but this taxon is not further considered here. The other four, which were named for separate finds from the Sunjiagou Formation (Changhsingian, 254–252 Ma), show considerable similarities. Despite earlier suggestions, there are no convincing anatomical characters to distinguish Shihtienfenia, Shansisaurus, and Huanghesaurus, and these three genera are synonymized as Shihtienfenia permica Young & Yeh, 1963. The fourth taxon, Sanchuansaurus pygmaeus Gao, 1989, shows distinctly different teeth from those of Huanghesaurus (= Shihtienfenia), and was about one‐third of the size, so it is retained as a second valid pareiasaur from the Chinese latest Permian. Phylogenetic analysis confirms the validity of these two taxa, with Sanchuansaurus belonging among the derived forms, close to Elginiidae, and with Shihtienfenia associated with Pumiliopareiasauria and Pareiasuchus.  相似文献   
72.
73.
Polymeroid trilobite fauna from two stratigraphic sections (Godbondar and Kuhbanan) of the Kuhbanan Formation in northern Kerman (central Iran) were studied and subjected to biostratigraphic analysis. Eleven genera and species are recognised from the latest Early Cambrian and Middle Cambrian Peri-Gondwanian successions of the study sections. The recognised fauna includes Afghanocare lategenatum, Blountia blountia, Iranoleesia sp., Iranoleesia pisiformis, Kermanella kuhbananensis, Kermanella lata lata, Kermanella lata minuta, Kermanella sp., Redlichia chinensis, Redlichia noetlingi and Redlichia sp. Based on trilobite distribution, three trilobite biozones were recognised in the study sections, namely Redlichia noetlingi biozone, Kermanella kuhbananensis biozone and Iranoleesia pisiformis biozone. The age of the study sections is late Early Cambrian to late Middle Cambrian based on the recognised trilobite biozones. The recognised late Early Cambrian trilobite assemblages (especially Redlichia and Kermanella) from northern Kerman are similar to those found from some other parts of Gondwana or Peri-Gondwana terrains (north India, Pakistan, northwestern Kashmir, Tajikistan, South Australia, South China and Afghanistan) and show affinities with fauna found in some other parts of Iran (Alborz, northern Iran; Tabas, eastern Iran; southeast Karman).  相似文献   
74.
A dinosaur tracksite in the Lower Jurassic Ziliujing Formation of Sichuan Province, China consists of a spectacular sub-vertical exposure, with multiple track-bearing levels and trackways showing parallel and bimodal orientations. Based on well-preserved material, the new ichnogenus and ichnospecies, Liujianpus shunan ichnogen. nov. ichnosp. nov. is erected to accommodate distinctive sauropodomorph trackways occurring in this assemblage. Liujianpus has a unique combination of features, some relating to the early Jurassic basal sauropodomorph (prosauropod in traditional usage) ichnogenus Otozoum, others to the sauropod ichnogenus Brontopodus. Despite such a mix of basal sauropodomorph- and sauropod-like features, the trackmaker of Liujianpus is likely a basal sauropodomorph. This identification is consistent with the occurrence of basal sauropodomorph skeletons from geographically and chronologically close localities. The other distinct morphotype from the tracksite is linked to a sauropod trackmaker. As such, the ichnofauna consisting of two distinct foot morphotypes reflects the diversity of sauropodomorph dinosaurs in the Early Jurassic of Asia.  相似文献   
75.
76.
77.
Madtsoiids constitute a successful group of extinct snakes widely distributed across Gondwana and the European archipelago during Late Cretaceous times, surviving in reduced numbers to the Pleistocene. They are renowned for including some of the largest snakes that have ever crawled on earth, yet diverse small madtsoiids are also known. Uncovering the evolutionary trends that led these snakes into disparate body sizes has been hampered mainly by the lack of phylogenetic consensus and the paucity of taxa with novel combinations of features. Here we describe a new large madtsoiid snake based on isolated vertebrae from the La Colonia Formation (Maastrichtian–Danian) of Patagonia, Argentina. A comprehensive phylogenetic analysis recovers Madtsoiidae as a basal ophidian lineage and the new snake as sister to a clade of mostly big-to-gigantic taxa, providing insights into early stages and evolutionary trends towards madtsoiid gigantism.  相似文献   
78.
《Palaeoworld》2022,31(4):570-581
Rhynchonelliform brachiopods made their first appearance in early Cambrian, and became a major group within the palaeozoic evolutionary fauna since late Cambrian. Exceptionally preserved fossils from the early Cambrian Lagerstätten provide valuable chances to investigate their phylogeny and ecology. Longtancunella is one of the most interesting early rhynchonelliforms, and has been mainly recovered from the Chengjiang Lagerstätte (Series 2, Stage 3). Here, we report a new rhynchonelliform Longtancunella xiazhuangensis n. sp. from the lower Hongjingshao Formation (upper Stage 3) in Yunnan Province, China. These specimens were well preserved with soft parts, including pinnate mantle canal system and a pedicle. It is identified as a new species based mainly on its difference in shell ornamentations, pinnate mantle canals and pedicle morphology from the type species. Its pedicle looks unusually stout with distinct annulated lamellae on the surface, and reveals crucial evidence in illustrating its ecology and settling strategy as an early marine epifauna. The ecological interaction between L. xiazhuangensis and other marine animals also provides insights into the food web structure in the early Cambrian.  相似文献   
79.
Fluorescence properties of Early Cambrian acritarchs were investigated using Leica das Mikroskop (DM) microscopy with a mercury lamp. Well-preserved autoflurescence properties show a correlation between acritarchs morphology and the intensity of emitted fluorescence. In accordance with the fluorescence intensity of organic cell walls, two groups of microfossils were distinguished. Results of observation in this study, which are consistent with those of the previous foreign studies, are in good agreement with regular difference in autofluorescence intensity among palynomorphs reported by McPhilemy (1998). Spores and algae, including Botryococcus, have very bright fluorescence while acritarchs often show less intense fluorescence. Dark brown microfossils have been reworked, and have little or no fluorescence. __________ Translated from Acta Micropalaeontologica Sinica, 2006, 23(3): 309–312 [译自: 微体古生物学报]  相似文献   
80.
Fluorescence properties of Early Cambrian acritarchs were investigated using Leica das Mikroskop (DM)microscopy with a mercury lamp.Well-preserved autoflurescence properties show a correlation between acritarchs morphology and the intensity of emitted fluorescence.In accordance with the fluorescence intensity of organic cell walls,two groups ofmicrofossils were distinguished.Results of observation in this study,which are consistent with those of the previous foreign studies,are in good agreement with regular difference in autofluorescence intensity among palynomorphs reported by McPhilemy (1998).Spores and algae,including Botryococcus,have very bright fluorescence while acritarchs often show less intense fluorescence.Dark brown microfossils have been reworked,and have little or no fluorescence.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号