全文获取类型
收费全文 | 301篇 |
免费 | 38篇 |
国内免费 | 114篇 |
专业分类
453篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 23篇 |
2013年 | 22篇 |
2012年 | 23篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 28篇 |
2008年 | 17篇 |
2007年 | 22篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 21篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 19篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有453条查询结果,搜索用时 15 毫秒
1.
2.
3.
1956-2009年内蒙古苏尼特左旗荒漠草原的降水格局 总被引:1,自引:0,他引:1
弄清全球变化背景下不同地区降水格局的变化对科学理解气候变化及其影响具有重要意义。苏尼特左旗荒漠草原是温带干旱半干旱地区的典型荒漠草原,对气候变化,特别是降水变化非常敏感。利用1956-2009年的日降水资料探讨了苏尼特左旗荒漠草原降水格局的变化规律,以为揭示气候变化的影响机制提供依据。结果表明,该地区年均降水量为191.9 mm,年际变化剧烈,变异系数达26.63%;年均降水日数为63.8 d,变异系数16.9%。生长季降水占全年的85%,但各月变异系数均>50%;降水日数占全年的63%。年和生长季的各月降水以中等降水量、弱降水日数为主,中等强度以上降水事件较少。近50 a来,年和生长季的降水量、降水日数与各等级降水事件均呈下降趋势,年降水减少的原因在于中等降水事件的减少、生长季降水减少的原因在于弱降水事件的减少。年降水减少将影响草地的土壤水分与植物返青;而生长季降水减少将直接影响草地固碳。气候变化背景下年与生长季降水的减少将进一步加剧该地区干旱程度并影响植物的生长发育,从而直接威胁到草地畜牧业的发展。 相似文献
4.
内蒙古达茂旗巴特敖包地区包尔汉图剖面牙形刺生物地层 总被引:6,自引:2,他引:6
内蒙古达茂旗(达尔罕茂明安联合旗)巴特敖包地区志留纪、泥盆纪碳酸岩相地层发育,本区珊瑚、腕足类、层孔虫等底栖大化石的研究工作已有一定基础。但志留纪、泥盆纪地层在时代确定和对比上还存在很多问题,必须用主导化石门类牙形刺加以解决。研究表明:包尔汉图剖面的顶部属泥盆系无疑,应归入阿鲁共组,而不是西别河组;巴特敖包地区的海侵,始于罗德洛统卢德福德阶(Ludfordian)早期。本剖面没有发现文洛克世和罗德洛世早期的海相沉积。本文描写了一个志留纪牙形刺新种:Ozarkodina uncrispa sp.nov.。 相似文献
5.
内蒙古道虎沟中侏罗世假古蝉属化石(同翅目,古蝉科) 总被引:4,自引:0,他引:4
描述古蝉科化石3新种,即多点假古蝉Pseudocossus punctulosus sp.nov.,美丽假古蝉P.bellus sp.nov.,弯脉假古蝉P.ancylivenius sp.nov..所有标本均采自内蒙古宁城道虎沟中侏罗世九龙山组,其中2个新种保存有完整的臀区.模式标本保存在首都师范大学生命科学学院. 相似文献
6.
啮齿动物群落结构可以反映生态环境特征。本研究对处于阿拉善荒漠区呈“孤岛”状态的内蒙古贺兰山国家级自然保护区内啮齿动物的种类、分布型及群落多样性进行系统研究。将内蒙古贺兰山划分为五种生境类型,于2013年春、夏、秋3季共布设有效铗日18748个,捕获啮齿动物235只,分属2目5科11属13种。在整体研究区域,阿拉善黄鼠(Spermophilus alashanicus)为优势种。明确了喜湿型是本研究区域的主要分布型,占捕获啮齿动物的54%,并且在中低海拔区域,随着海拔的升高,喜湿型所占比例增加。受“边缘效应”的影响,山地荒漠和荒漠草原生境以及山地草原灌丛生境的啮齿动物群落多样性指数高于其他生境,除环境因素外,啮齿动物群落的多样性受两种因素的影响,既可随群落内物种数量的增加而增大,同时又受制于群落内部物种分布的均匀程度。冗余分析结果表明,植被高度、植被盖度、灌木(乔木)高度和海拔4个环境因子是决定啮齿动物群落结构最主要的环境因子,其中植被盖度与群落多样性呈负相关,随着植被盖度的增加,多样性指数随之减低。 相似文献
7.
《Geobios》2021
Paleogene mammal localities of North China are particularly well represented in the Erlian Basin, Inner Mongolia. Among them, the locality of Bayan Ulan is most famous for its late Paleocene Gashatan fauna. However, the younger Arshantan fauna of the same site is not well known, since no extensive study has been done so far. Here, we present a small mammal assemblage based on dental and tarsal material from a new Arshantan collection retrieved from the red beds of the late early to early middle Eocene Arshanto Formation at Bayan Ulan. It consists of at least six different taxa: the basal lagomorph Dawsonolagus antiquus, the large pantodont Pantolambdodon sp., the tapiroid Schlosseria magister, and the rhinocerotoids Hyrachyus crista and Rhodopagus guoi nov. sp. The assemblage is dominated by perissodactyls, especially Lophialetidae and Hyracodontidae. For the first time, p4-m1 of Dawsonolagus antiquus, tarsal material from Pantolambdodon sp., and lower dentition and tarsals of Hyrachyus crista are described and illustrated. Unlike other described Arshantan faunas, the Bayan Ulan Arshantan mammal assemblage has been collected exclusively from a single locality, which contributes to the reassessment of the misunderstood Arshantan Asian Land Mammal Age. 相似文献
8.
Yanxin Gong Yuanqing Wang Yang Wang Fangyuan Mao Bin Bai Haibing Wang Qian Li Xun Jin Xu Wang Jin Meng 《Palaeontology》2020,63(4):547-564
Lophialetidae is an extinct group of endemic Asiatic tapiroids that are widely distributed in the Eocene sediments of Asia. Schlosseria magister and Lophialetes expeditus are the most abundant species in this family. However, their dietary and ecological characteristics are largely unknown. For the first time, we reconstruct the palaeodiet and habitat of these two lophialetids using a combination of mesowear and stable carbon isotope analysis of fossil teeth excavated from the Erlian Basin, China. Mesowear analysis (n = 141) suggests that the dietary structure of S. magister and L. expeditus shifted from less to more abrasive diets from ~52 to ~42 Ma. Stable carbon isotope analysis (n = 137) suggests that the habitats of S. magister and L. expeditus became drier and/or more open through time. The dietary shifts of the two lophialetids are consistent with evident changes in habitat. The changes in the diet and habitat were probably related to global climate change during that time period. The gradual drop in global temperatures during the early–middle Eocene led to a drier and more open terrestrial ecosystem in the Erlian Basin, probably resulting in changes in floral composition of the environment inhabited by S. magister and L. expeditus. Hence, herbivores highly susceptible to vegetation modification had to develop new resource exploitation strategies to adapt to these changes. Schlosseria magister, considered to be the sister-group of L. expeditus and with a low level of ecological flexibility, was unable to adapt to the habitat changes finally becoming extinct at ~45 Ma. 相似文献
9.
Abstract: Two new genera with six new species of hangingflies (Mecoptera: Raptipedia: Cimbrophlebiidae) are described. They were collected from the Middle Jurassic nonmarine sedimentary strata of the Jiulongshan Formation in Daohugou, Inner Mongolia, north‐eastern China. This report of Cimbrophlebiidae from the Yanliao Biota provides detailed morphological information and evidence of a broad diversity of Cimbrophlebiidae during the Middle Jurassic. A key to the known species of Cimbrophlebiidae is provided. 相似文献
10.
Lasiosynidae n. fam. is proposed for the genera Lasiosyne Tan, Ren & Chih 2007 (transferred from Archostemata to Polyphaga), Anacapitis Yan 2009 Tarsomegamerus Zhang 2005 (proposed in the superfamily Chrysomeloidea) and Bupredactyla n. gen. The new family is regarded in composition of the infraorder Elateriformia without a more detailed attribution, because it demonstrates a mixture of characters of different families and superfamilies, i.e. somehow an intermediate position between the superfamilies Dascilloidea, Elateroidea, Buprestoidea and Byrrhoidea with most resemblance to Dascillidae, Schizopodidae, Eulichadidae, Ptilodactylidae and Callirrhipidae and probable more close relationship to the last three families. Four new fossil species of the genus Lasiosyne: L. daohugouensis n. sp., L. fedorenkoi n. sp., L. gratiosa n. sp., L. quadricollis n. sp., and also Bupredactyla magna n. sp. are described from the Middle Jurassic Jiulongshan Formation of eastern Inner Mongolia, China. A probable generic composition of the new family is considered. The synonymy of generic names Anacapitis Yan 2009 and Brachysyne Tan & Ren 2009, n. syn. as well as synonymy of species names Lasiosyne euglyphea Tan, Ren & Chih 2007, Pappisyne eucallus Tan & Ren 2009, n. syn. and Pappisyne spathulata Tan & Ren 2009, n. syn. are proposed. 相似文献