全文获取类型
收费全文 | 1605篇 |
免费 | 51篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 80篇 |
地球物理 | 881篇 |
地质学 | 346篇 |
海洋学 | 14篇 |
天文学 | 276篇 |
综合类 | 3篇 |
自然地理 | 30篇 |
出版年
2021年 | 21篇 |
2020年 | 23篇 |
2018年 | 38篇 |
2017年 | 52篇 |
2016年 | 62篇 |
2015年 | 56篇 |
2014年 | 66篇 |
2013年 | 69篇 |
2012年 | 25篇 |
2011年 | 30篇 |
2010年 | 51篇 |
2009年 | 42篇 |
2008年 | 40篇 |
2007年 | 35篇 |
2006年 | 31篇 |
2004年 | 24篇 |
2003年 | 24篇 |
2002年 | 30篇 |
2001年 | 23篇 |
2000年 | 22篇 |
1999年 | 18篇 |
1998年 | 27篇 |
1996年 | 31篇 |
1995年 | 19篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1985年 | 15篇 |
1984年 | 28篇 |
1983年 | 29篇 |
1982年 | 34篇 |
1981年 | 23篇 |
1980年 | 21篇 |
1979年 | 36篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 23篇 |
1973年 | 23篇 |
1972年 | 24篇 |
1971年 | 24篇 |
1970年 | 15篇 |
1967年 | 16篇 |
排序方式: 共有1660条查询结果,搜索用时 15 毫秒
991.
V. Rušin 《Solar physics》2017,292(1):24
From observations of the solar white-light corona at 65 eclipses from 1851 to 2015 we confirm earlier findings that the flattening index of the white-light corona depends on the phase, rather than the magnitude of solar cycles, which is in contrast with behavior of other major solar activity indices like the sunspot number, the 2800 MHz radio flux, etc. This indicates that mechanisms responsible for creation and distribution of helmet streamers, the most essential coronal structures influencing the flattening index, could be of different magnetic nature from those of other manifestations of solar surface activity. 相似文献
992.
Mateja Dumbović Nandita Srivastava Yamini K. Rao Bojan Vršnak Andy Devos Luciano Rodriguez 《Solar physics》2017,292(8):96
Under the European Union 7th Framework Programme (EU FP7) project Coronal Mass Ejections and Solar Energetic Particles (COMESEP, http://comesep.aeronomy.be ), an automated space weather alert system has been developed to forecast solar energetic particles (SEP) and coronal mass ejection (CME) risk levels at Earth. The COMESEP alert system uses the automated detection tool called Computer Aided CME Tracking (CACTus) to detect potentially threatening CMEs, a drag-based model (DBM) to predict their arrival, and a CME geoeffectiveness tool (CGFT) to predict their geomagnetic impact. Whenever CACTus detects a halo or partial halo CME and issues an alert, the DBM calculates its arrival time at Earth and the CGFT calculates its geomagnetic risk level. The geomagnetic risk level is calculated based on an estimation of the CME arrival probability and its likely geoeffectiveness, as well as an estimate of the geomagnetic storm duration. We present the evaluation of the CME risk level forecast with the COMESEP alert system based on a study of geoeffective CMEs observed during 2014. The validation of the forecast tool is made by comparing the forecasts with observations. In addition, we test the success rate of the automatic forecasts (without human intervention) against the forecasts with human intervention using advanced versions of the DBM and CGFT (independent tools available at the Hvar Observatory website, http://oh.geof.unizg.hr ). The results indicate that the success rate of the forecast in its current form is unacceptably low for a realistic operation system. Human intervention improves the forecast, but the false-alarm rate remains unacceptably high. We discuss these results and their implications for possible improvement of the COMESEP alert system. 相似文献
993.
994.
Summary The rocks of the crystalline basement of the East European Craton in southern Estonia show effects of partial melting under
granulite facies conditions. Zircons extracted from partial melting products (tonalite from the Tapa Zone – 1824 ± 26, tonalite
from the South Estonian Zone – 1788 ± 16 Ma and charnockite from the Tapa Zone – 1761 ± 11 Ma) yield U–Pb crystallisation
ages that span over approximately 80 Ma, suggesting a prolonged high-grade metamorphism or several separate events. U–Pb zircon
age of one sample of charnockite is concordant with the Nd model age of partial melting of its host mafic granulite facies
gneiss (intercept at 1.76 Ga). Linear geochemical trends and similar initial Nd isotopic compositions of mafic granulites
and charnockites suggest their possible genetic relationship. From our new and previously published data it follows that the
peak granulite metamorphic conditions and formation of tonalites and charnockites (850 °C and 6 kbar) in the Estonian basement
occurred at 1788–1778 Ma. Then, the rocks cooled down, passing through the garnet closure temperature of approximately 650–700 °C
at 1728 ± 24 Ma. The age of metamorphism of the Estonian granulites is lower than the metamorphic ages known from southern
Finland, but it is similar to the age of metamorphism reported from the Belarus-Baltic Granulite Belt in Latvia. 相似文献
995.
D. Fidríková V. Greif P. Dieška V. Štofanik L. Kubičár J. Vlčko 《Environmental Earth Sciences》2013,69(4):1481-1489
Buildings are often composed of materials with a porous structure. Moisture in the masonry has a destructive impact caused by cycles of drying–wetting and freezing–thawing. A new sensor principle for monitoring moisture in the masonry is presented herein. This sensor utilizes changes in the thermal conductivity of porous structures when they are filled with moist air, water, or ice depending on the existing thermodynamic conditions. Herein, the “hot-ball” method is used to measure the thermal conductivity. The moisture sensor is prepared for porous material corresponding to the parent material, whether it is rock, brick, or concrete. This parent sample is taken from a borehole drilled into the wall. Methodology for moisture sensor calibration is also presented. Sensors were placed in the masonry walls of St. Martin’s Cathedral tower in the North, South, and West orientations. The sensors were placed in the plaster and bricks at depths up to 60 mm in the wall surface, just below the window sill. The temperature–moisture regime was monitored from August 19th, 2011 to March 30th, 2012. Changes in temperature and moisture were then correlated with meteorological data. 相似文献
996.
Summary The hydrothermal synthesis of kaolinite from various alumina and silica starting materials reacted at 200°C in aqueous solutions of oxalic acid and H2SO4 with the corresponding saturated water vapour pressure, in periods of time from 10 to 25 days, has been followed by X-ray diffraction measurements, scanning electron microscopy, and energy dispersive analysis of the products. The temperature and time periods of reactions were chosen on the basis of previously collected data on the effects of H4EDTA, a complex-forming agent, and of H2SO4, an inorganic acid, on the rate of formation of kaolinite. Aluminium-complexing acids increase the rate of formation or decrease the temperature of formation of kaolinite as shown by evidence from X-ray diffraction patterns. The influence of the starting materials as sources of aluminum, amorphous aluminum hydroxides, pseudoboehmite, allophane or gibbsite, has also been examined by X-ray diffraction, scanning electron microscopy, and by energy dispersive analysis. Scanning electron micrographs indicated that silica is a more mobile phase than alumina, based on the progressive formation of a thin coating on gibbsite during early reaction, then by growth of clusters of platy crystals of kaolin, and finally by production of pellets of stacked crystal flakes. Where gibbsite was used in the reaction mixture, boehmite was commonly observed as an intermediate phase.With 16 Figures 相似文献
997.
Dušan Němec 《Mineralogy and Petrology》1968,12(4):321-349
Summary The iron-ore skarns of the core of the Bohemian Massif is an old petrographic unit which is already doeply metamorphosed under conditions of an abyssal metamorphism. The paragenetical analysis as well as the chemical study of their mineral assemblages makes it clear that the amphibole occuring in subordinate quantities in these skarns is not a relic mineral (having not originated during the premetamorphic skarnization period). It appeared only in the course of the regional metamorphism in connection with the migmatization processes which took place in the rocks adjoining the skarn bodies and in connection with the injections of pegmatites traversing the skarn rocks.
Mit 11 Textabbildungen 相似文献
Mit 11 Textabbildungen 相似文献
998.
Caroline Aubry-Wake Lauren D. Somers Haley Alcock Aspen M. Anderson Amin Azarkhish Samuel Bansah Nicole M. Bell Kelly Biagi Mariana Castaneda-Gonzalez Olivier Champagne Anna Chesnokova Devin Coone Tasha-Leigh J. Gauthier Uttam Ghimire Nathan Glas Dylan M. Hrach Oi Yin Lai Pierrick Lamontagne-Hallé Nicolas R. Leroux Laura Lyon Sohom Mandal Bouchra R. Nasri Nataša Popović Tracy E. Rankin Kabir Rasouli Alexis Robinson Palash Sanyal Nadine J. Shatilla Brandon Van Huizen Sophie Wilkinson Jessica Williamson Majid Zaremehrjardy 《水文研究》2020,34(8):2001-2006
999.
Jaroslav Buša Miloš Rusnák Dávid Kušnirák Vladimír Greif Martin Bednarik René Putiška 《自然地理学》2020,41(2):169-194
ABSTRACTWe employed integrated methods to assess the landslide movement in Sv. Anton town in the Western Carpathians Neogene Volcanic Field (Central Slovakia). The integrated diagnostics required study of the landslide kinematic activity by a combination of Global Navigation Satellite Systems (GNSS) and Electrical Resistivity Tomography (ERT) imaging from November 2013 to March 2015. A topographic model with 2-cm accuracy was constructed from Unmanned Aerial Vehicles (UAV) photogrammetry. Continuous spatial datasets of movement and displacement field vectors were interpolated from the measured movements over the entire study period. Although deformation studies in Slovakia have a long-term tradition, complex interdisciplinary studies in urbanized areas are still lacking. This inspired our main objectives: to identify landslide kinematics and to reconstruct and define the rates of annual landslide movement obtained from geodetic measurement at the monitoring points. Our results demonstrate how landslide integrated diagnostics contribute to the detection of slope instability, with a maximum velocity of 60.82 mm/yr during the summer period. The precipitation effects are consistent with the Sv. Anton landslide displacement acceleration, and the following increases in total monthly precipitations are staggering compared to long-term monthly averages: July precipitation increased by 175.3%, August by 203.3%, and September by 198.1%. 相似文献
1000.
Thermochronological insights into the structural contact between the Tian Shan and Pamirs,Tajikistan
下载免费PDF全文
![点击此处可从《地学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gilby Jepson Stijn Glorie Dmitry Konopelko Jack Gillespie Martin Danišík Noreen J. Evans Yunus Mamadjanov Alan S. Collins 《地学学报》2018,30(2):95-104
Multi‐method thermochronology along the Vakhsh‐Surkhob fault zone reveals the thermotectonic history of the South Tian Shan–Pamirs boundary. Apatite U/Pb analyses yield a consistent age of 251 ± 2 Ma, corresponding to cooling below ~550–350°C, related to the final closure of the Palaeo‐Asian Ocean and contemporaneous magmatism in the South Tian Shan. Zircon (U–Th–Sm)/He ages constrain cooling below ~180°C to the end of the Triassic (~200 Ma), likely related either to deformation induced by the Qiangtang collision or to the closure of the Rushan Ocean. Apatite fission track thermochronology reveals two low‐temperature (<120°C) thermal events at ~25 Ma and ~10 Ma, which may be correlated with tectonic activity at the distant southern Eurasian margin. The late Miocene cooling is confirmed by apatite (U–Th–Sm)/He data and marks the onset of mountain building within the South Tian Shan that is ongoing today. 相似文献