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   147篇
  免费   9篇
  国内免费   21篇
测绘学   1篇
大气科学   9篇
地球物理   15篇
地质学   120篇
海洋学   6篇
天文学   2篇
综合类   11篇
自然地理   13篇
  2024年   1篇
  2023年   1篇
  2022年   4篇
  2021年   1篇
  2020年   1篇
  2019年   5篇
  2018年   1篇
  2017年   18篇
  2016年   12篇
  2015年   12篇
  2014年   6篇
  2013年   4篇
  2012年   3篇
  2011年   6篇
  2010年   6篇
  2009年   11篇
  2008年   8篇
  2007年   11篇
  2006年   6篇
  2005年   6篇
  2004年   3篇
  2003年   5篇
  2002年   4篇
  2001年   5篇
  2000年   3篇
  1999年   6篇
  1998年   1篇
  1997年   2篇
  1996年   4篇
  1995年   3篇
  1994年   5篇
  1993年   3篇
  1992年   1篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1988年   1篇
  1986年   2篇
  1983年   1篇
排序方式: 共有177条查询结果,搜索用时 15 毫秒
101.
102.
辽宁西部中生代地层发育,在国内外同期地层研究中占有重要地位。辽西中生代鸟化石的发现,具有重要的科学价值。含鸟层位包括上侏罗统义县组含鸟层和下白垩统九佛堂组含鸟层。现共鉴定出鸟类化石11个属14个种,其中义县组鸟化石4个属6个种,地位最为重要。鉴于此,将义县组下部的沉积层划分出来,并建立了四合屯组,该组对寻找鸟类的祖先具有重要的意义。原土城子组一段具有组级岩石地层单位意义称为蒙古营子组。  相似文献   
103.
The paper reports sunthetically the Cocene fauna of the Messel Pit Fossil site of Germany, in detail, including its rich taxanomic composttions, geological and paleogeographic backgroud, and the studying and applying history.  相似文献   
104.
A new Late Pennsylvanian species of gymnospermous fossil wood, Zalesskioxylon xiaheyanense sp. nov. is described from the Lower Taiyuan Formation (Stephanian B-C) near the village of Xiaheyan, Ningxia Hui Autonomous Region, northwestern China. The specimen consists only of silicified secondary xylem. The tracheids are pycnoxylic with 2–3 seriate bordered pits, arranged in subcircular or hexagonal alternate (araucaroid) pattern. The pores of the pits are small, linear, and regularly tilted. Xylem rays are homogeneous, uniseriate, 1–25 cells high. Cross-fields are filled with numerous mixed simple pits of various sizes. Growth rings, axial parenchymatous elements and resin canals are absent. The geographic distribution of Zalesskioxylon woods is reviewed. Zalesskioxylon xiaheyanense sp. nov. grew at low latitudes, and because of the lack of growth rings, probably lived under relatively uniform climatic conditions. Our new species supplements the poorly known distribution of Carboniferous wood in China.  相似文献   
105.
华东白垩纪鸭嘴龙类恐龙蛋化石的发现   总被引:1,自引:1,他引:1       下载免费PDF全文
浙江天台白垩纪地层中最常见的蛋化石类型之一是赤城山组地层(锆石U-Pb法同位素年龄约92Ma)的树枝树枝蛋(Dendroolithus dendriticus)。对比河南西峡含恐龙胚胎的蛋化石,确定其为鸭嘴龙类(Hadrosaurs)恐龙所产。鸭嘴龙类恐龙在系统分类上归鸟脚亚目(Ornithopoda Marsh,1881)鸭嘴龙超科(Hadrosauroidea Cope,1869)鸭嘴龙科(Hadrosauridae Cope,1869),建议树枝蛋化石也相应归入圆形蛋化石亚目(Spheroolithineae账oosubord.nov.)树枝蛋化石超科(Dendroolithoidea oosuperfam.nov.)树枝蛋化石科(Dendroolithidae Zhaoand Li 1988),以便对应研究。从已知的鸭嘴龙类恐龙产蛋尺寸推算,浙江天台的树枝树枝蛋(Dendroolithus dendriticus)为身长不超过7m的恐龙所产,个体大小类似东北一蒙古发现的萨哈林日本龙(Nipponosaurus sachaIinensis)、李氏黑龙江龙(Amurosaurus riabinini)和姜氏巴克龙(Bactrosaurus johnsoni)。该蛋在巢穴里,无序放置,至少3层,常超过20枚,蛋壳具韧性,重力作用下呈扁球形。  相似文献   
106.
The Eutheiini includes over 90 extant species classified in seven genera and distributed predominantly in the Northern Hemisphere. So far only one extinct genus and species unambiguously placed in this tribe has been known, Archeutheia, from Albian of Spain. We report the discovery of Eutheia, a member of the largest extant genus of Eutheiini, in Santonian of northern Siberia. Extant species of Eutheia are primarily defined on the basis of male genital characters, and the specimen discovered in Taimyr amber is a female; consequently it is described as Eutheia sp. The new finding remarkably extends the known range of Eutheiini during Cretaceous over the area of about 6 thousand kilometers, from the Iberian Plate to northern Siberia. A long morphological stasis in Eutheia suggests that this genus was associated with stable mesic microhabitats of the upper soil layers or rotten wood for at least 83 my.  相似文献   
107.
陈军  尹勇前  李涛  金利勇 《地质通报》2016,35(6):872-878
猛犸象-披毛犀动物群是晚更新世时期北半球最具代表性的典型哺乳动物群,该动物群的化石在中国东北地区广泛分布,其演化、发展乃至灭绝与古人类文明的发展有密切的关系。综述猛犸象-披毛犀动物群的概况,从动物组合、古地理分布、古生态环境等方面介绍了该生物群之全貌。以吉林省大布苏国家重点化石产地为例,对该产地出土的猛犸象-披毛犀动物群化石标本进行了最新的统计(分属6目13科21属23种),对其化石组合特征进行了分析,并对在东北地区深入开展该动物群研究的意义进行了探讨。  相似文献   
108.
胡绍锦 《云南地质》2005,24(3):321-327
记述滇池盆地含煤层中首次发现的上新世剑齿象化石,包括脊棱齿象属的一个新种昆明脊棱齿象(Stegolophodon kunm ingensissp..nov.)、似元谋剑齿象(Stegodonaff.yuan-m ouensis)、玉溪剑齿象、师氏剑齿象等。这一剑齿象化石组合的发现,对研究新生代象类和滇池盆地的演化史,重新划分盆地煤系地层具有重要意义。  相似文献   
109.
Two closely associated egg types occur at the same locality in the Upper Cretaceous (Maastrichtian) St. Mary River Formation in north central Montana. These specimens represent the first fossil eggs described from this formation. At least fifteen small ovoid eggs or egg portions are scattered through a 25 cm interval of rock. Five significantly larger, round eggs overlie these smaller eggs and are in close proximity to one another on a single bedding plane. The best preserved egg of the smaller size measures 36 mm × 62 mm and exhibits the prismatic, two-layered eggshell structure of a theropod egg. The dispersed distribution and inconsistent angles of these small eggs likely resulted from disturbance by subsequent nesting activity and/or possibly nest predation. At least twelve additional small prismatic eggs also occur at this site. We assign the small eggs as a new oogenus and oospecies, Tetonoolithus nelsoni, within the Prismatoolithidae. The large round eggs measure 130 mm in diameter and the eggshell displays substantial diagenetic alteration. These eggs likely belonged to a hadrosaur due to their similarity in egg size, shape, and eggshell thickness to Maiasaura eggs from the stratigraphically lower Two Medicine Formation. Eggs at different stratigraphic levels at this site indicate that conditions favorable to both dinosaur species persisted for an extended period of time. However, determining whether these dinosaurs occupied the nesting site at the same or different years remains beyond the resolution of the rock record.  相似文献   
110.
A new, highly specialized family, Rafaelidae, is proposed for two new lacewing-like species from the Lower Cretaceous Crato Formation in the Araripe Basin, Brazil. They have body and wing venation characters that are unique within the neuropterid insects, i.e., head, ovipositor, organization of the radial and median veins and structure of the subcostal vein. This new family cannot be attributed to any known insect order with certainty. These discoveries support the hypothesis of a considerable morphological disparity between neuropterid insects during the Early Cretaceous, as for the Odonatoptera.  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