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   274篇
  免费   37篇
  国内免费   62篇
地球物理   26篇
地质学   183篇
海洋学   117篇
综合类   17篇
自然地理   30篇
  2023年   2篇
  2022年   3篇
  2021年   2篇
  2020年   8篇
  2019年   3篇
  2018年   4篇
  2017年   3篇
  2016年   11篇
  2015年   7篇
  2014年   12篇
  2013年   10篇
  2012年   14篇
  2011年   18篇
  2010年   14篇
  2009年   21篇
  2008年   23篇
  2007年   19篇
  2006年   16篇
  2005年   19篇
  2004年   12篇
  2003年   14篇
  2002年   14篇
  2001年   4篇
  2000年   11篇
  1999年   4篇
  1998年   9篇
  1997年   10篇
  1996年   12篇
  1995年   7篇
  1994年   10篇
  1993年   5篇
  1992年   11篇
  1991年   8篇
  1990年   6篇
  1989年   2篇
  1988年   3篇
  1987年   2篇
  1985年   4篇
  1984年   3篇
  1983年   3篇
  1982年   6篇
  1981年   4篇
排序方式: 共有373条查询结果,搜索用时 15 毫秒
91.
贵州毕节发现的巨猿牙齿化石及其意义   总被引:3,自引:0,他引:3       下载免费PDF全文
文章报道了发现于贵州毕节的一枚巨猿牙齿化石,介绍了巨猿化石发现的历史过程及与之相关的毕节扒耳岩早更新世哺乳动物化石。贵州毕节巨猿化石的发现,填补并扩大了巨猿化石的地史分布范围,对研究巨猿演化及云贵高原地质环境变化等相关问题有着重要意义。  相似文献   
92.
2010年冬季与2011年春夏季,采用样线法对位于豫鄂交界处的信阳南湾湖鸟类多样性进行调查。结合历史资料,南湾湖共记录到鸟类16目40科110种,其中4目5科9种均为国家重点Ⅱ级保护野生动物;特有种或主要分布在我国的鸟类2目2科2种。留鸟40种,夏候鸟38种,冬候鸟9种,旅鸟23种。古北界鸟类42种,东洋界鸟类35种,广布种33种。研究区具有古北界种与东洋界种混杂的特点,古北界种鸟类占优势,分布型以北方鸟类为主。基于科属水平上的G-F指数计算结果显示,南湾湖的F指数、G指数与F-G指数分别是29.26、4.57、0.84,低于邻近的伏牛山鸟类各指数,显示南湾湖在鸟纲科属水平上与伏牛山鸟类多样性相异,且具有相对较低的鸟类多样性。  相似文献   
93.
The species of Ophiuroidea that commonly occur on coral reefs can be found on different substrates and associated with other organisms including algae, sponges, and corals. This study evaluated the temporal variability of the ophiuroid fauna associated with the alga Amphiroa fragilissima on the Ponta Verde coral reef on the coast of Maceió in Alagoas, Northeastern Brazil. Replicate samples of algal substrate were collected at low tide during in the dry and rainy seasons, over a 10‐year period, from 1998–2007. Eight species of Ophiuroidea were identified, with a total of 8736 individuals associated with A. fragilissima. The most dominant and frequent species of Ophiuroidea were Amphipholis squamata and Ophiactis savignyi; all other species were rare. Cluster analysis and nMDS detected four groups, with two groups each occurring only in summer or winter periods, as well as other groups occurring in both periods.  相似文献   
94.
Biological Traits Analysis (BTA) is a method for addressing ecological functioning based on traits exhibited by members of biological assemblages. This study explores and compares species and biological trait patterns on either side (landward and seaward) of coastal breakwater structures in northwestern Adriatic Sea (Italy), with the aim of giving insights and knowledge for management of sandy beach systems affected by coastal development. Eight ecological traits of 96 benthic species were considered. Taxon composition evidenced differences in benthic assemblages across time and exposure: landward and seaward communities shared less than 50% of the total number of species. BTA suggested a no-management effect in the functioning of benthic assemblages. Dominant traits modalities were deposit-feeding, short life, small body size, short life span, iteroparity, gonocorism, with plankto-planktotrophic larvae. The results of BTA highlighted similarities and stability in trait composition contrary to species composition, suggesting a possible persistence in benthic functioning despite the occurrence of species replacements. To best of my knowledge, this study is one of the first attempts to investigate the effects of a management measure (submerged shore-parallel barriers with groynes) in a shallow marine system by means of BTA.  相似文献   
95.
To explore the spatial pattern of macrobenthic communities and their response to environmental factors in the Prydz Bay,samples were collected using a 0.25-m2 box corer at 10 stations from November 2012 to April 2013.A total of 50 species of macrobenthos belonging to 8 phyla and 33 families were identified,of which polychaetes(e.g.,Maldane sarsi)and sponges(e.g.,Halichondria sp.and Leucosolenia sp.)were the most prominent groups.The macrobenthos in study area were categorized into five functional groups based on the feeding type,and the detritivorous group represented by polychaetes showed the highest average abundance,while the planktophagous group represented by sponges showed the highest average biomass.Macrobenthos abundance(0–592 ind./m2)and biomass(0–1155.5 g/m2)in the Prydz Bay were relatively lower than those of other Antarctic shelf soft-bottom waters,although the compositions of the dominant species and functional feeding groups were similar.The results of the Spearman rank correlation analysis indicated that the average biomass of the macrobenthos and the biomass of the planktophagous group in the study area were negatively correlated with the water depth,sediment grain size and silt percentage.However,these variables were clearly not strong determinants of macrobenthos assemblage structure.Many factors not measured in the study,e.g.,sediment organic matter and iceberg interference,have probably influenced the spatial distribution of macrobenthic community structure in the Prydz Bay.  相似文献   
96.
The investigation of a limestone cave on the Ryonggok-ri of Sangwon County, North Hwanghae Province, DPRK, has yielded many faunal remains including Late Pleistocene deer, brown bears and horses. Uranium series dating of fossil teeth yielded dates of ~72ka at the base of Layer 2 – the bone-bearing unit – and ~44ka at the top. The rich and diverse mammal remains of Ryonggok Cave No. 1 are indicative of warm and humid temperate conditions during the Late Pleistocene, and reflect the presence of both dense forests and open grassland. In addition, pollen and spores from the site include two families and 24 genera of trees, six families and a genus of grasses and herbs, and two families and six genera of ferns, corroborating the environments inferred from the faunal remains.  相似文献   
97.
讨论晚三叠世卡尼期早期关岭生物群的生存环境和死亡埋葬特点,认为该生物群分布于裂谷地区;生物群的群体死亡并被迅速埋葬的原因是地震;贵州龙生物群与关岭生物群是同期生物群;"S形带"是一构造断陷带,在卡尼期早期是裂谷。  相似文献   
98.
The macrobenthic animal biomass of the intertidal area of the Sembilang peninsula of South Sumatra, Indonesia, has been studied in 2004. Each month (March–August) 21 core samples were taken at each of six sampling stations. Macrobenthic fauna were identified at the lowest taxonomical level possible and counted. Biomass was measured as ash-free dry mass (afdm). The average biomass over all stations and months was 3.62 g afdm m−2, the highest biomass (47.45 g afdm m−2) found at a station in one month was due to abundant occurrence of the bivalve Anadara granosa. Low biomass of macrobenthic fauna at Sembilang peninsula cannot easily be explained but is in line with low biomasses found elsewhere in the tropics. For that reason we analyzed a data set of 268 soft-bottom intertidal biomasses collected world-wide to look for a relationship with latitude. It was shown that average biomass of intertidal macrobenthic fauna in the tropics was significantly (p < 0.05) lower than that at non-tropical sites. A significant second-order relationship between biomass of macrobenthic fauna and latitude was established.  相似文献   
99.
100.
Abstract. Seven harpacticoid species were found to be associated with sea ice collected during 5 Antarctic cruises of the RV Polarstern. Their distribution within the fast ice and pack ice zones of the Weddell Sea is presented. Whereas some individuals probably become entrapped into the ice only accidentally, at least 4 species arc genuinely sympagic. These have evolved remarkable adaptations, as evidenced by field and laboratory studies of Dresclieriella glacialis , which is by far the most abundant. Such adaptations include: the ability to penetrate deep into ice; a comparatively high salinity tolerance allowing it to endure large salinity fluctuations associated with ice crystal formation and melting; good swimming ability, necessary both for horizontal dispersal and for a planktonic intermezzo after annual melting of the sea ice. D. glacialis is the first polar non-vertebrate mctazoan to be cultivated through its entire life cycle. Its life history suggests an r-stratcgy; this would be the first indication of such a trait in the polar environment. A new species of Drescheriella , on the other hand, exhibits resting stages (C IV-V) known to date only for Calanoidu but not reported for Harpacticoida.  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