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   49篇
  免费   7篇
  国内免费   3篇
大气科学   2篇
地球物理   16篇
地质学   20篇
海洋学   4篇
天文学   11篇
自然地理   6篇
  2023年   1篇
  2022年   1篇
  2020年   1篇
  2019年   3篇
  2018年   6篇
  2017年   2篇
  2016年   5篇
  2015年   5篇
  2014年   3篇
  2013年   1篇
  2012年   5篇
  2011年   2篇
  2010年   6篇
  2009年   2篇
  2007年   1篇
  2006年   3篇
  2005年   2篇
  2003年   1篇
  1999年   1篇
  1998年   1篇
  1995年   3篇
  1993年   1篇
  1990年   1篇
  1981年   1篇
  1974年   1篇
排序方式: 共有59条查询结果,搜索用时 31 毫秒
41.
Fossil anguine lizard specimens from several Turkish localities are described in this paper. The material comes from ten different localities, spanning a large geographic area consisting of both parts of the European Turkey and Anatolia, and ranging in age from the Oligocene to the Late Miocene. In certain cases, the generic determination was possible and, accordingly, members of Ophisaurus and Anguis were identified and described in detail. The specimens of Anguis, found in different, Middle and Late Miocene localities from Anatolia, represent two of only a few fossil occurrences of this taxon. Moreover, the material reported herein represents the oldest occurrences of anguine lizards, not only from Turkey, but from southeastern Europe and the Eastern Mediterranean basin as a whole. These rare records provide important information about the dispersal routes of anguines from Europe to Asia and significantly enhance our understanding of their biogeography.  相似文献   
42.
The city of Ljubljana is located in one of the three areas with the highest seismic hazard in Slovenia, and it is also the most densely populated. Site effects due to Quaternary sediments, which fill the up to 200 m-deep basin, are characteristic of the whole city area, but they can be especially strong in the southern part of Ljubljana, which is built on very soft lacustrine deposits. Existing microzonation studies of the city are inadequate, since there is a lack of borehole, geophysical and earthquake data. The microtremor horizontal-to-vertical spectral ratio (HVSR) method was therefore applied to a 200 m dense grid of free-field measurements over an area of 45 km2 (1,223 measuring points) in order to assess the fundamental frequency of the sediments. The main difficulties in microtremor measurement arose from high levels of traffic and industrial noise, and from underground structures. Experimental conditions which can influence data quality, such as strong wind and water saturation of soil, were analysed. Very clear HVSR peaks were obtained in the entire southern part of the city, whereas in the northern part the site response is in general lower due to lower impedance contrast of gravel with the bedrock. The iso-frequency map of sediments shows a distribution in the range of 0.9–10 Hz. In the southern part of Ljubljana, sediment frequency correlates well with the thickness of soft sediments known from geophysical investigations and sparse drilling. Average amplitude of the HVSR peaks is considerably higher in the southern part (6.7 ± 2.4) than in the northern part (4.0 ± 2.0) of the city, indicating a high impedance contrast of lacustrine sediments with the bedrock. Microtremor measurements were also performed inside 122 buildings of various heights. We focused on important public buildings and selected blocks of flats and houses. To assess the longitudinal and transverse fundamental frequencies of each building, amplitude spectra and the spectral ratio between the upper floor and the basement were analysed for both directions. When one of these frequencies is close to a nearby free-field fundamental frequency, a potential soil-structure resonance is present. This was found in 12 of the measured buildings. Three of them are tall residential buildings (from 10 to 15 floors) with a fundamental frequency of 2–3 Hz, and nine of them are low-rise buildings (from 3 to 5 floors) with a fundamental frequency ranging from 3 to 4.5 Hz. Using the relationship between fundamental frequency and height, the typical height of buildings that might cause soil-structure resonance can be estimated at a given sediment frequency obtained from free-field measurements.  相似文献   
43.
This paper investigates the structural properties of a model fluid dictated by an effective inter-particle oscillatory potential by grand canonical ensemble Monte Carlo (GCEMC) simulation and classical liquid state theories. The chosen oscillatory potential incorporates basic interaction terms used in modeling of various complex fluids which is composed of mesoscopic particles dispersed in a solvent bath, the studied structural properties include radial distribution function in bulk and inhomogeneous density distribution profile due to influence of several external fields. The GCEMC results are employed to test the validity of two recently proposed theoretical approaches in the field of atomic fluids. One is an Ornstein--Zernike integral equation theory approach; the other is a third order + second order perturbation density functional theory. Satisfactory agreement between the GCEMC simulation and the pure theories fully indicates the ready adaptability of the atomic fluid theories to effective model potentials in complex fluids, and classifies the proposed theoretical approaches as convenient tools for the investigation of complex fluids under the single component macro-fluid approximation.  相似文献   
44.
Extreme heterogeneity of karst systems makes them very challenging to study. Various processes within the system affect its global response, usually measured at karst springs. Research conducted in caves provides a unique opportunity for in situ analysis of separate processes in karst underground. The aim of the present study was to research the water and air dynamics within a deep karst system. Air and water basic physical parameters across the Lukina jama–Trojama cave system (?1,431 m) were continuously monitored during a 1‐year period. Recorded hydrograph of the siphon lake at the bottom of the cave was used to interpret the characteristics of an unexplored phreatic/epiphreatic conduit network. Water origin in the siphon was determined based on temperature and electrical conductivity. Air temperature and humidity monitoring revealed a strong inflow of air of sub‐zero temperature into the upper portion of the cave during winter. Cave passage morphology was interpreted as the main determinant of air dynamics, which caused ice to accumulate extensively in the upper portions of the cave and caused the temperature on the top of the homothermic zone to be significantly below the mean outside temperature. Air dynamics also lowered the temperature of water flowing through the cave vadose zone and feeding the phreatic zone of the massif. The pronounced temperature difference between the phreatic zone and the top of the homothermic zone probably contributed to the thermal gradient observed in the cave, which is steeper than in ice‐free caves in the area. Our results enabled the development of a conceptual model that describes coupling between air and water dynamics in the cave system and its surroundings.  相似文献   
45.
Small mountain lakes are natural archives for understanding long-term natural and anthropogenic impact on the environment. This study focused on long-term (last ca. 13 000 years) vegetation changes and sedimentary processes in the catchment area of Lake Planina pri jezeru (1430 m a.s.l.) by using mineralogical, geochemical and palynological methods. Palynological results suggest that regional vegetation between 12 900 and 11 700 cal a bp was a herbaceous–forest tundra (Pinus, Artemisia, Poaceae ). Climate warming at the beginning of the Holocene (ca. 11 700 cal a bp ) caused the transition from a wetland (Cyperaceae) to an eutrophic lake with alternating anoxic (pyrite) and oxic conditions (gypsum). In addition, the surrounding area became forested (Picea, Larix, Ulmus). Fagus expanded at 10 200 cal a bp and Abies at 8200 cal a bp. Between 7500 and 4300 cal a bp , human impact on the environment was barely noticeable and mostly limited to grazing. During 4300–430 cal a bp human impact became more evident and gradually increased. The greatest influence was observed from 430 cal a bp onwards, when excessive exploitation of the surrounding area (logging and grazing) severely eutrophicated the lake.  相似文献   
46.
Results of nondestructive gamma‐ray analyses of cosmogenic radionuclides (7Be, 22Na, 26Al, 46Sc, 48V, 54Mn, 56Co, 57Co, 58Co, and 60Co) in 19 fragments of the Ko?ice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic‐ray particles in the space affecting radionuclides with different half‐lives. Monte Carlo simulations of the production rates of 60Co and 26Al compared with experimental data indicate that the pre‐atmospheric radius of the meteoroid was 50 ± 5 cm. In two Ko?ice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble‐gas cosmic‐ray exposure age of the Ko?ice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Ko?ice is a regolith breccia. The agreement between the simulated and observed 26Al activities indicate that the meteoroid was mostly irradiated by a long‐term average flux of galactic cosmic rays of 4.8 particles cm?2 s?1, whereas the short‐lived radionuclide activities are more consistent with a flux of 7.0 protons cm?2 s?1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall.  相似文献   
47.
Molluscs are a diverse and ubiquitous group of organisms which contribute to the formation of biogenic sediments and are one of the major prey taxa for the neritic‐stage loggerhead sea turtles (Caretta caretta) worldwide. Here we investigated to what degree molluscs contribute to the diet of individual turtles, and what role the feeding strategy of loggerheads might play in bioturbation, one of the key processes in nutrient transport in marine ecosystems. We performed a detailed analysis of benthic molluscs from the digestive tracts of 62 loggerhead sea turtles (curved carapace length: 25.0–85.4 cm) found in the Northern Adriatic Sea. From 50 of the turtles that contained benthic molluscs, we identified 87 species representing 40 families and three classes (Gastropoda, Bivalvia and Scaphopoda), including 72 new dietary records for loggerhead turtle. Most of the identified molluscs were small‐sized species (shell length ≤ 3 cm) and were often found in a subfossil condition. Their intake may be considered a byproduct of infaunal mining, while larger molluscs were mainly found crushed into smaller fragments. Through such foraging behaviour loggerheads actively rework sediments, increase the surface area of shells and the rate of shells disintegration, acting as bioturbators in this system. We conservatively estimate that loggerheads in the neritic zone of the Adriatic Sea bioturbate about 33 tonnes of mollusc shells per year, and hypothesize about the possible effects of bioturbation reduction on environmental changes in the Northern Adriatic ecosystem.  相似文献   
48.
Andrej Kranjc 《中国岩溶》2011,30(2):157-162
对于术语"karst"的起源和演化,不少文献(包括手册、教科书、字典等)仍有不准确、不一致甚至错误的论述。鉴于此,本文不仅重述了众所周知的关于"karst"起源的事实,而且介绍了"karst"起源和演化的最新语言学研究结果。"karst"是由喀尔斯(Kras)高地的名称演化而来的。喀尔斯位于亚得里亚海的里雅斯特湾(Gulf of Trieste)达尔马提亚(Dal matia)海岸地区,其大部分属于斯洛文尼亚。喀尔斯是一处海拔150~450 m,覆盖面积550 km2(长约40 km,宽约13 km)的碳酸盐岩高地。斯洛文尼亚语、意大利语和德语分别称之为Kras、Carso和Karst。喀尔斯高地表面大致平坦,但从局部看,喀斯特洼地遍布,各种典型的喀斯特地貌形态随处可见,包括坡立谷、大小溶斗(包括大的塌陷溶斗)、喀斯特干谷和溶洞。这些形态规模较小,起伏平缓。喀尔斯高地的名称起源于前罗马时期,其古典拉丁语名称(也是目前已知最早的名称)为Carsus。该词的词根*kar(u)s-是由意思为"石头或岩石"的词根*kar-演化而来。从欧洲众多文献中可以发现有许多名词来自前印欧语系的词根kar(r)a/gar(r)a。这些词根最初意思指石头或岩石,而后发展为石头筑成的遮盖物——一间房屋,一座城堡,甚至一个村落,这些词根还演化成喀斯特相关术语。由Carsus的宾格形式Carsum演变成现代意大利语名称Carso;同样的宾格依据前斯洛文尼亚语言规则(即r或l出现在元音和辅音字母之间时,须将其移至元音字母之前。)演变成Kras;德语Karst则是由意大利语Carso依据德语变化规则(以s结束的单词末尾须添加t)演变而来。由此可见,Kras、Karst和Carso均源于古拉丁文Carsus,该词含有词根*kar(u)s-。印刷技术的改进和新大陆的发现,带动了地图和地图集的出版。喀尔斯高地的名称不仅出现在地方性地图上,而且被大尺度区域性地图所标示出来,德文Karst甚至被用作区域地图的标题,足见喀尔斯高地的重要性。喀尔斯高地之所以比其它更大的地区重要且较早为人们所认识,与历史的地缘政治形势有关。16至19世纪,地中海东海岸大多由威尼斯共和国管辖,的里雅斯特港口和内陆地区则隶属于奥地利和土耳其帝国。对于奥地利帝国的公民,大部分中欧人和小部分东欧人来说,通向地中海唯一可行的途径就是从维也纳穿过卢布尔雅那市(Lju-bljana),经喀尔斯高地,至的里雅斯特镇。1719年,当的里雅斯特港宣布成为自由港后,这条道路变得更为重要。与此同时,喀尔斯高地不寻常的地貌和恶劣的自然环境给途经的旅行者和学者留下了深刻的印象。在他们的旅行记录中对Kras有近乎相同的描述:"碳酸盐岩裸露,岩洞繁多,没有水和土壤,夏暑冬寒,冬季强烈的冷风暴有时让高地无法通行......"。此后,当描述其他喀斯特地区时,作者们往往会将其与Kras(Karst)相类比。1830年F.J.H.Hohenwart在《Postojna岩洞导游手册》中,第一次确切地写道"喀斯特地貌不仅存在于Karst高地,它从Friuli平原一直延伸至希腊岛……"。十九世纪上半叶,地质、地理和水文学者开始了对喀尔斯高地的详细研究,出版了喀斯特地质地貌方面的著作,并开始使用一些喀斯特术语。自1830年起,由于这些记述性的文字和专业著作大多用德语撰写,德语名称Karst逐渐为更多地区的人们所了解。19世纪末20世纪初,可以说"karst"已经成为国际科技术语。对"karst"加入国际术语行列影响最大的可能是毕业于维也纳大学的Jovan Cviji′c教授,他是最重要的学者之一,也是著名地形学教授A.Penck的学生。他最重要的喀斯特著作"Das Karstphanomen"(The phenomenon of Karst)的书名中就使用了"karst"。"karst"就这样由一个地名逐渐演变为学术名词,然后成为国际科技术语。  相似文献   
49.
50.
We herein review the Adriatic opisthobranch fauna, provide an updated checklist of 223 species and assess their distribution at regional and country levels. New Adriatic records are provided for 67 opisthobranch taxa, adding three new records for the Italian coastline, five new records for Albania, eight for Croatia and 15 for Montenegro. The presence of Hermaea bifida (Montagu, 1815), Hermaea variopicta (Costa A., 1869) and Facelina annulicornis (Chamisso & Eysenhardt, 1821) is reported for the first time from anywhere in the Adriatic Sea. Including the new findings, our inventory includes 28 species from Albania, 163 from Croatia, 178 from the Italian coastline of the Adriatic, 41 from Montenegro and 74 from Slovenia. No records were available from Bosnia and Hercegovina. Ninety species (40.4%) are widespread, and were recorded from all three main divisions (Northern, Western and Eastern Adriatic), whilst 79 species (35.4%) were reported from only one of them. At sub‐division levels, the Albanian inventory is the most dissimilar to the other country/regional lists, presumably because of the lack of targeted field surveys. The highest similarity is observed amongst the Western Adriatic, Croatia and the Italian Ionian coastline. Seven alien, one possible alien and three cryptogenic opisthobranchs were reliably recorded from the Adriatic Sea. The first Mediterranean records of five species were in the Adriatic Sea, of which four species have not been found elsewhere in the Mediterranean. Shipping and aquaculture are the probable pathways for most of the alien species. A steady rate of one to two alien introductions per decade since the 1970s was evident. The Northern Adriatic coasts are the most affected by alien invasions, probably due to repeated local introductions along with shellfish transfers (oysters, mussels, Manila clams), and heavy maritime transport.  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