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   755篇
  免费   24篇
  国内免费   15篇
测绘学   17篇
大气科学   41篇
地球物理   171篇
地质学   298篇
海洋学   84篇
天文学   103篇
综合类   8篇
自然地理   72篇
  2023年   5篇
  2022年   9篇
  2021年   11篇
  2020年   12篇
  2019年   21篇
  2018年   23篇
  2017年   26篇
  2016年   28篇
  2015年   22篇
  2014年   23篇
  2013年   43篇
  2012年   29篇
  2011年   44篇
  2010年   30篇
  2009年   31篇
  2008年   48篇
  2007年   35篇
  2006年   30篇
  2005年   31篇
  2004年   24篇
  2003年   22篇
  2002年   12篇
  2001年   18篇
  2000年   6篇
  1999年   11篇
  1998年   10篇
  1997年   6篇
  1996年   9篇
  1995年   9篇
  1994年   12篇
  1993年   7篇
  1992年   9篇
  1991年   5篇
  1989年   4篇
  1988年   4篇
  1987年   9篇
  1986年   5篇
  1985年   10篇
  1984年   9篇
  1982年   8篇
  1981年   8篇
  1980年   4篇
  1979年   8篇
  1978年   8篇
  1976年   10篇
  1975年   4篇
  1974年   9篇
  1971年   6篇
  1969年   3篇
  1963年   4篇
排序方式: 共有794条查询结果,搜索用时 15 毫秒
731.
The possibilities of recent advantages in Geographical Information Systems (GIS) technology as a tool for multidisciplinary coastal zone research are discussed. International education in the new high technologies is one of the most urgent tasks for the University GIS Network.  相似文献   
732.
The North Atlantic craton in southern West Greenland mainly consists of a tectonic collage of Mesoarchean continental crustal terranes, which were amalgamated at c. 2.7 Ga and are currently exposed at mid-crustal amphibolite to granulite facies levels. Tonalitic orthogneisses predominate, intercalated with slightly older tholeiitic to andesitic metavolcanic rocks and associated gabbro-anorthosite intrusive complexes. The North Atlantic craton also contains enclaves of Eoarchean, c. 3.86-3.6 Ga orthogneisses and supracrustal rocks including the Isua greenstone (or supracrustal) belt. This is the oldest known assemblage of rocks deposited at the surface of the Earth, comprising mafic pillow lavas, banded iron formations and metasedimentary schists with local disseminated graphite of possible biogenic origin. Eoarchean rocks have not been found in Kola and Karelia in Fennoscandia where most rocks are 2.9-2.7 Ga tonalitic-trondhjemitic-granodioritic orthogneisses with intercalated coeval greenstone belts and amphibolites. Mesoarchean 3.0-3.2 Ga rocks are found in the eastern and western parts of the Karelian province. Subduction-related rocks like the Iringora supra-subduction type ophiolite and basalt-andesite-dacite-rhyolite series volcanic rocks in many greenstone belts, as well as eclogites are found in the Archean of Fennoscandia. A clear distinction between Greenland and Fennoscandia is the abundance of 2.75-2.65 Ga igneous rocks in Fennoscandia which indicates that these two cratons had a separate evolution during the Neoarchean.  相似文献   
733.
We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope ratios are reported as δ65Cu‰ = ((65Cu/63Cusample/65Cu/63CuNIST 976 standard) − 1) ? 103. Errors for all the analyses are ± 0.14‰ (determined by multiple analyses of the samples) and mass bias was corrected through standard-sample-standard bracketing. The overall isotopic variability measured in these samples range from − 16.96‰ to 9.98‰.  相似文献   
734.
Vulture volcano displays a wide range of mafic to alkaline, carbonate-, and/or CaO-rich volcanic rocks, with subvolcanic and plutonic rocks together with mantle xenoliths in pyroclastic ejecta. The roles of magmatic volatiles such as CO2, S, and Cl have been determined from compositions and trapping temperatures of inclusions in phenocrysts, which include the Na-K-Ca-carbonate nyerereite within melilite. We surmise that this alkali carbonate crystallised from an appropriate carbonatitic melt at relatively high temperature. Carbonatitic metasomatic features are traceable throughout many of the mantle xenoliths, and various carbonatitic components are found in the late stage extrusive suite. There is no evidence that alkali carbonatite developed as a separate magma, but it may have been an important evolutionary stage. We compare the rare occurrence of nyerereite at Vulture with other carbonatites and with an unaltered kimberlite from the Udachnaya pipe. We review the evidence at Vulture for associated carbonatitic metasomatism in the mantle, and we suggest that low viscosity alkali carbonatitic melts may have a primary and much deeper origin than previously considered.  相似文献   
735.
Marked, 19th‐century kiln bricks and rocks from Caledonia Springs (CS) have black glass coatings that can easily be mistaken for glass produced at the elusive CS glassworks (c. 1844–1846). The glass‐on‐brick material, however, is more aluminous (nearly 20% Al2O3) than virtually any analyzed historical glass, and the glass‐on‐rock is compositionally similar to the rock itself, which shows clear signs of having undergone extensive melting. Mineral thermometry (Cpx‐Ol, Pl‐melt) indicates that parts of the kiln‐achieved temperatures of approximately 1200–1300°C. The CS samples show that caution must be exercised when identifying seemingly obvious waste glass near defunct glassworks sites. © 2005 Wiley Periodicals, Inc.  相似文献   
736.
737.
Paleotsunami remains have been studied in Middle/Late Holocene peat bogs and lacustrine deposits on Shikotan I. We determined the age of the events, the inundation areas, and the distance the tsunami waves traveled on shores of varying structures. The frequency of tsunami occurrence was nonuniform; these events were the most frequent in the middle of the Late Holocene. Data are provided for specific areas of the island’s coast, sequences have been identified containing numerous interbeds of tsunamigenic sand, which can be used as markers. The composition of the tsunamigenic sand has been analyzed to reveal its similarities with and differences to other coastal marine facies and to determine the sources of the material. These data could serve as a basis for compiling a highly detailed geological record of these events for the southern Kuril region during the last 6000 years.  相似文献   
738.
A study of the geomagnetic storm of November 20–21, 2003, is presented using Solar X-rays data, solar wind parameters and magnetic index, Dst. The results suggest that very large X class flares may not cause very intense geomagnetic storms, as flares of M importance would do. Furthermore, the results suggest that the solar wind structure that was responsible for this storm is of the shock-driver gas configuration in which the sheath is the most geoeffective element. Presently it is shown that an intense storm can be driven by two successive southward B z structures without a resultant “double dip” at the boundary of these structures within the corresponding interval of the main phase. Furthermore, this study confirms earlier results that show that pressure enhancement does not cause the direct injection of new particles into the ring current region; rather it causes a local adiabatic energization of the particles already within the ring current region.  相似文献   
739.
The near-field expression of the tsunami produced by the 15 November 2006 Kuril earthquake (Mw 8.1–8.4) in the middle Kuril Islands, Russia, including runup of up to 20 m, remained unknown until we conducted a post-tsunami survey in the summer of 2007. Because the earthquake occurred between summer field expeditions in 2006 and 2007, we have observations, topographic profiles, and photographs from three months before and nine months after the tsunami. We thoroughly surveyed portions of the islands of Simushir and Matua, and also did surveys on parts of Ketoi, Yankicha, Ryponkicha, and Rasshua. Tsunami runup in the near-field of the middle Kuril Islands, over a distance of about 200 km, averaged 10 m over 130 locations surveyed and was typically between 5 and 15 m. Local topography strongly affected inundation and somewhat affected runup. Higher runup generally occurred along steep, protruding headlands, whereas longer inundation distances occurred on lower, flatter coastal plains. Sediment transport was ubiquitous where sediment was available—deposit grain size was typically sand, but ranged from mud to large boulders. Wherever there were sandy beaches, a more or less continuous sand sheet was present on the coastal plain. Erosion was extensive, often more extensive than deposition in both space and volume, especially in areas with runup of more than 10 m. The tsunami eroded the beach landward, stripped vegetation, created scours and trim lines, cut through ridges, and plucked rocks out of the coastal plain.  相似文献   
740.
Bucharest is one of the cities most affected by earthquakes in Europe. Situated at 150–170 km distance from Vrancea epicentral zone, Bucharest had suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8–12 levels, while more than 150 old buildings with 6–9 levels were seriously damaged. The studies done after this earthquake had shown the importance of the surface geological structure upon ground motion parameters. New seismic measurements are performed in Bucharest area aiming at defining better elastic and dynamic properties of the shallow sedimentary rocks. Down-hole seismic measurements were performed in a number of 10 cased boreholes drilled in the Bucharest City area. Processing and interpretation of the data lead to the conclusion that shallow sedimentary rocks can be considered weak in the area, down to 150–200 m depth. Seismic wave velocity values and bulk density values presented in the paper associated with local geology are useful primary data in the seismic microzonation of Bucharest City. They are used as 1D models to derive transfer functions and response spectra for the stack of sedimentary rocks in several parts of Bucharest area, leading to a better knowledge of the local site amplification and associated frequency spectra. In a recent study the H/V spectral ratio using Nakamuras method was applied on the seismic noise measurements in 22 sites in Bucharest City in order to derive the fundamental period associated with these sites. The values confirm the previous results, showing a dominant resonance in the period range of 1.25–1.75 s. The fundamental periods obtained with Nakamuras method are in good agreement with those computed on the basis of geological and geotechnical data in boreholes, which show an increase of the fundamental period in the Bucharest area from south to north, in the same direction as the increase of the thickness of the Quaternary deposits above the Fratesti layer which is considered the bedrock in the area.  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