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   51篇
  免费   0篇
测绘学   3篇
大气科学   6篇
地球物理   9篇
地质学   28篇
海洋学   1篇
天文学   2篇
自然地理   2篇
  2021年   1篇
  2020年   2篇
  2019年   1篇
  2018年   2篇
  2017年   4篇
  2016年   1篇
  2015年   2篇
  2014年   3篇
  2013年   2篇
  2011年   4篇
  2010年   2篇
  2009年   3篇
  2008年   2篇
  2006年   1篇
  2005年   1篇
  2002年   1篇
  2000年   2篇
  1998年   1篇
  1995年   2篇
  1994年   1篇
  1989年   2篇
  1987年   2篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1973年   2篇
  1971年   1篇
  1968年   1篇
排序方式: 共有51条查询结果,搜索用时 875 毫秒
31.
Shoreline variation and river deltas are among the most dynamic systems in marine environments. The related different variations in spatial and temporal scales play significant roles in land planning and different management applications. Modeling the dynamics of seashore of Boujagh National Park (BNP) which is located on the southern coast of the Caspian Sea in the Sefidrud Delta (SD), considering natural and anthropogenic factors, was the main objective of the current study. To achieve this goal, a combination of remote sensing data, historical data, and numerical simulations was utilized. The BNP covers an area of 3,270 ha and includes two international wetlands, Boujagh and Kiashahr. In earlier periods, this area faced severe morphological changes whereas recently its shoreline has experienced gradual variations. Accordingly, at the first stage, the shoreline variation from 2006 to 2017 was extracted by processing and classifying Operational Land Imager (OLI) and Thematic Mapper (TM) images from Landsat satellites using the Maximum Likelihood approach. In the second stage, the two dimensional MIKE21 model was utilized to identify wave and coastal current patterns and parameters for the year 2015. Morphologically, the results showed that, the shoreline of the BNP is affected by several natural and anthropogenic factors. Seaward advancement of the shoreline occurred in zones A (east zone) and C (west zone) due to Caspian Sea Level drop and sedimentation while retreating occurred at Zone B (north zone) influenced by wave and current patterns and reduction of the Sefidrud River flows. Also, the results imply that maintaining the existing conditions results in the disappearance of a considerable part of the ecological area in the BNP. Hence, to manage and preserve the coastline of the BNP complying with the current anthropogenic and natural factors, it is vital to take necessary management measures.  相似文献   
32.
In the early 1780s, Nagakubo Sekisui, the first Japanese scientific geographer, published a world map containing latitudes and longitudes, based on Matteo Ricci's map of 1602. The map and its extensive explanatory text had a considerable impact on the educated classes of the late Edo Period (1603–1868) toward their new vision of the world. We are providing here an analysis of the map and the first complete English translation of Nagakubo Sekisui's most interesting, long explanatory text.  相似文献   
33.
A finite element model is developed to simulate the behaviour of an aquifer used as storage space for a compressed air energy storage (CAES) system. The governing equations describing a two-phase flow of air and water are coupled non-linear partial differential equations and are solved by the Galerkin approach. The resulting computer model is applied to a gas percolation problem. Upon verification of the numerical results, the model is employed to simulate the air-water displacement in a storage reservoir during daily air cycling. The corresponding saturation variations and the effects of reservoir permeability on the system are presented. The results obtained are essential in establishing storage design and stability criteria for long-term operation of compressed air energy storage systems.  相似文献   
34.
PEGASE is a mission dedicated to the exploration of the environment (including habitable zone) of young and solar-type stars (particularly those in the DARWIN catalogue) and the observation of low mass companions around nearby stars. It is a space interferometer project composed of three free flying spacecraft, respectively featuring two 40 cm siderostats and a beam combiner working in the visible and near infrared. It has been proposed to ESA as an answer to the first “Cosmic Vision” call for proposals, as an M mission. The concept also enables full-scale demonstration of space nulling interferometry operation for DARWIN.
M. OllivierEmail:
  相似文献   
35.
The baffling duality of the Carpathian Mountain Range and the Basin it surrounds is briefly discussed. The various attempts at solving the nature of this duality, including plate tectonics with its micro-plates are mentioned. The component ranges of the Carpathians and the structural belts are given, followed by the discussion of the Carpathian Basin System, the Interior, consisting of the Great Hungarian Plain, Transdanubia, the two groups of Central Mountains, also the Apuseni (Bihar) Mountains and the Banat Contact Belt. Economic ore deposits are featured in the relevant sections.  相似文献   
36.
Geological mapping of an unexposed area can be supported by indirect methods. Among these, the use of mushrooms as geobotanical indicators and the shallow-penetration electromagnetic VLF method proved to be useful in the Bükk Mountains. Mushrooms have not been applied to geological mapping before. Common species like Boletus edulis and Leccinum aurantiacum are correlated with siliciclastic and magmatic formations while Calocybe gambosa is correlated with limestone. The validity of this correlation observed in the eastern part of the Bükk Mts. was controlled on a site where there was an indicated (by the mushrooms only) but unexposed occurrence of siliciclastic rocks not mapped before. The extent and structure of this occurrence were explored with the VLF survey and a trial-and-error method was applied for the interpretation. This case study presented here demonstrates the effectiveness of the combination of these relatively simple and inexpensive methods.  相似文献   
37.
Garnets and clinopyroxenes, intergrown with diamonds in 37 diamondites (“bort”, “polycrystalline diamond aggregates”, “polycrystalline diamond”, “framesite”), presumably from southern Africa, were analyzed for trace element contents by LA-ICP-MS. The intimate diamond-silicate intergrowths suggest that both precipitated from the same fluids during the same crystallization events. In this study we distinguish 5 chemical garnet groups: “peridotitic” (P), intermediate (I) and 3 “eclogitic” groups (E1, E2 and E3). Chondrite-normalized trace element patterns for the garnet groups roughly correlate with major element abundances. Most of P garnets show complex, mildly sinusoidal REEN patterns with relatively flat HREEN-MREEN, a small hump at Sm-Nd and depleted LREEN, and have relatively high contents of Nb, Ta, U, and Th. The REEN abundance patterns of E garnets differ by showing a continuous increase from LREE to HREE and depletion in LREE and highly incompatible elements relative to the P garnets. Of all garnet groups, E3 garnets are the poorest in highly incompatible trace elements and in Mg. Model equilibrium fluids for P garnets suggest crystallization from magnesian carbonate-bearing fluids/melts, which were very rich in incompatible trace elements — similar to kimberlites. Hypothetical equilibrium melts for E1 and E2 garnets are also magnesian and poorer in LREE and highly incompatible elements relative to typical kimberlitic or carbonatitic melts. Fluids that crystallized the P and most of the E garnets have similar mg numbers indicating a peridotitic source for both. The differences in Cr and highly incompatible element contents can be the result of differences in fluid formation and/or evolution rather than different source rock. The positive correlation of Cr2O3 and mg with the abundances of highly incompatible elements in garnets indicate fluid-rock fractionation processes rather than igneous fractional crystallization processes being responsible for the evolution of the diamondite-forming fluids.  相似文献   
38.
An Archean age for Finnish rocks in the range 2500–3000 Ma has been determined north of the NW-striking Ladoga—Raahe shear belt. The Archean may be divided into two main units: the granitoid association and the greenstone-belt association. The complex is characterized by stockwork tectonics. The granitoid association forms the basement infrastructure and the greenston-belt association forms the suprastructure which is present in synforms between granitoid diapirs. The infrastructure has been subjected to ultrametamorphism, and the second and third generation palingenetic magmas so formed have intruded the suprastructure. The granitoid association contains widespread migmatized relicts of the greenstone-belt association, indicating that the latter originally covered much larger areas, but the granitoids are also thought to be partly transformed primitive ensialic crust on which rocks of the greenstone-belt association were deposited. The Archean rocks have been deformed in at least four subsequent phases, of which part developed in Proterozoic time. The youngest deformation is the overthrust of the granulite belt of Lapland towards SSW. NWSE striking transcurrent faults played a major role in Proterozoic time and affected cratonized Archean crust. On the whole the greenstone belts in eastern and northern Finland form a NNW-trending zone 750 km long. On a geochemical basis the volcanic rocks of the greenstone belts can be divided into two groups: tholeiites with a low potassium content and extremely low aluminium content and a calc-alkalic group with some alkalic affinities.  相似文献   
39.
Magnetotactic bacteria and their magnetofossils in sediments   总被引:1,自引:0,他引:1  
Living magnetotactic bacteria from freshwater environments show, under natural and laboratory conditions, a great variety of morphological appearances. Their magnetosomes vary in number, shape, and size. One species of bacteria yields up to 1000 magnetosomes per cell. Individual particles reach a size of up to 200 nm. As a rule, they form elongated chains. In bacteria which are held under laboratory conditions, loop-shaped arrangements and nearly unordered clusters are also found. During the laboratory experiments, different species of bacteria periodically dominated. Freshwater samples always exhibited a great variety of different magnetosomes. On the other hand, samples from marine environment clearly showed the preponderance of one type of particle. These observations may reflect specific properties of the physico-chemical milieu in which the bacteria grew. At the end of our experiments north- and south-seeking bacteria co-existed in roughly equal quantities.Quaternary unconsolidated sediments from the Ammersee (Bavaria) and the Antarctic, Quaternary to Tertiary deep-sea sediments from the Atlantic and Pacific, and Jurassic limestones from the Sonnwendgebirge (Tyrol, Austria) were analyzed for fossil magnetosomes. We found that fossil magnetosomes were morphologically similar to those from living bacteria, but seemed to be corroded in some cases.The observed differences in quantity, size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites, but are not determined by geographical latitude.  相似文献   
40.
The method of conformal mapping is applied to the analysis of transient flow toward parallel periodic drains in a semi-infinite aquifer taking into consideration the non-linear boundary conditions on the free surface. The mapping function is expressed as a power series in time and the seepage domain is mapped onto a domain of an auxiliary complex variable. Mapping is performed in such a manner that the free surface will always remain the real axis. Calculations are carried out for different ratios of drain depth to drain spacing using various drain diameter to depth ratios.  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