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   233篇
  免费   4篇
  国内免费   1篇
测绘学   10篇
大气科学   9篇
地球物理   41篇
地质学   110篇
海洋学   18篇
天文学   34篇
综合类   1篇
自然地理   15篇
  2022年   1篇
  2021年   4篇
  2020年   8篇
  2019年   8篇
  2018年   12篇
  2017年   10篇
  2016年   11篇
  2015年   5篇
  2014年   12篇
  2013年   10篇
  2012年   10篇
  2011年   7篇
  2010年   10篇
  2009年   14篇
  2008年   11篇
  2007年   8篇
  2006年   13篇
  2005年   8篇
  2004年   9篇
  2003年   6篇
  2002年   8篇
  2001年   3篇
  2000年   4篇
  1999年   2篇
  1997年   5篇
  1996年   3篇
  1995年   4篇
  1994年   3篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1989年   2篇
  1987年   1篇
  1984年   1篇
  1983年   1篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   3篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1970年   2篇
  1965年   1篇
  1962年   1篇
  1914年   2篇
  1912年   1篇
  1911年   1篇
排序方式: 共有238条查询结果,搜索用时 31 毫秒
41.
In this study, single crystals of pure enstatite (Mg2Si2O6) were synthesised under water-saturated conditions at 4 and 8 GPa and 1,150°C with variable silica activity, leading to phase assemblages enstatite + forsterite, enstatite or enstatite + coesite. Run products were investigated using an FTIR spectrometer equipped with a focal plane array detector enabling IR imaging with a lateral pixel resolution of 2.7 μm. IR spectra within the OH-absorption region show two different groups of absorption bands: group 1 (wavenumbers at 3,592 and 3,687 cm?1) shows strongest absorptions for E||n β, whereas group 2 (wavenumbers at 3,067 and 3,362 cm?1) shows strongest absorptions for E||n γ. The groups are related to different defect types, group 1 to tetrahedral defects (T-site vacancies) and group 2 to octahedral defects (M-site vacancies). The intensity ratio of the bands within one group (i.e. A 3067/A 3362 and A 3592/A 3687) and the intensity ratio of E||n γ and E||n α in group 2 bands remain constant within error. In contrast, the intensity ratio of group 2 to group 1 absorption bands [e.g. (A 3362)/(A 3687)] is sensitive to the SiO2 activity and pressure. On the basis of the results of this and previous studies, a barometer for pure orthoenstatite coexisting with forsterite can be formulated:\( P\,[{\text{GPa}}] = 1.056 + \sqrt {{\frac{{1.025 - A_{{\left( {3362} \right)/\left[ {(3362) + (3687)} \right]}} }}{0.009}}} , \) where A (3362) and A (3687) are the integral absorbances of the component E||n γ of the absorption bands at 3,362 cm?1 and the component E||n β of the absorption band at 3,687 cm?1, respectively.  相似文献   
42.
Coastal erosion vs riverine sediment discharge in the Arctic Shelf seas   总被引:8,自引:0,他引:8  
This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45᎒6 t a-1) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10᎒6 t a-1, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4᎒6 t a-1) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6᎒6 t a-1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.  相似文献   
43.
On the basis of the results of simultaneous observations of parameters of currents, attenuation factor of light, and temperature performed aboard a moving vessel, we established the main characteristics and features of the circulation of waters and the structure of transparency and temperature fields in the surface layer of the northwest part of the Black Sea. We investigate the correlation between the variability of fluid dynamics and redistribution of transparency and temperature fields. The measured currents are compared with those calculated using the actual field of atmospheric pressure during the time of observation. It is shown that the results obtained in the areas of steady currents in the west and central regions are in good agreement. Translated by Peter V. Malyshev and Dmitry V. Malyshev  相似文献   
44.
For the Quaternary and Neogene, aragonitic biogenic and abiogenic carbonates are frequently exploited as archives of their environment. Conversely, pre‐Neogene aragonite is often diagenetically altered and calcite archives are studied instead. Nevertheless, the exact sequence of diagenetic processes and products is difficult to disclose from naturally altered material. Here, experiments were performed to understand biogenic aragonite alteration processes and products. Shell subsamples of the bivalve Arctica islandica were exposed to hydrothermal alteration. Thermal boundary conditions were set at 100°C, 175°C and 200°C. These comparably high temperatures were chosen to shorten experimental durations. Subsamples were exposed to different 18O‐depleted fluids for durations between two and twenty weeks. Alteration was documented using X‐ray diffraction, cathodoluminescence, fluorescence and scanning electron microscopy, as well as conventional and clumped isotope analyses. Experiments performed at 100°C show redistribution and darkening of organic matter, but lack evidence for diagenetic alteration, except in Δ47 which show the effects of annealing processes. At 175°C, valves undergo significant aragonite to calcite transformation and neomorphism. The δ18O signature supports transformation via dissolution and reprecipitation, but isotopic exchange is limited by fluid migration through the subsamples. Individual growth increments in these subsamples exhibit bright orange luminescence. At 200°C, valves are fully transformed to calcite and exhibit purple‐blue luminescence with orange bands. The δ18O and Δ47 signatures reveal exchange with the aqueous fluid, whereas δ13C remains unaltered in all experiments, indicating a carbonate‐buffered system. Clumped isotope temperatures in high‐temperature experiments show compositions in broad agreement with the measured temperature. Experimentally induced alteration patterns are comparable with individual features present in Pleistocene shells. This study represents a significant step towards sequential analysis of diagenetic features in biogenic aragonites and sheds light on reaction times and threshold limits. The limitations of a study restricted to a single test organism are acknowledged and call for refined follow‐up experiments.  相似文献   
45.
This study focuses on the relevance of accurate surface parameters, in particular soil moisture, and of parameterizations for heterogeneous land surfaces, for the prediction of sensible and latent heat fluxes by a mesoscale weather forecast model with horizontal grid resolution of 7 km. The analysis is based on model integrations for a 30-day period, which are compared both to flux measurements obtained from the LITFASS-2003 field experiment and to high-resolution-model (1-km grid spacing) results. At first, the relevance of improved parameter sets and input data compared to usual operational practice for an accurate prediction of near-surface fluxes is shown and discussed. It is demonstrated that an observation-based land-surface assimilation scheme leads to an improved soil moisture analysis, which is shown to be essential for the realistic simulation of surface fluxes. Secondly, the implementation of two efficient parameterization strategies for subgrid-scale variability of the surface, the mosaic and the tile approach, is presented. Using these methods, the simulations are in better agreement with measurements than simulations with simple aggregation methods that use effective surface parameters. Integrations with the mosaic approach reproduce high resolution simulations very well and more accurately than simulations with the tile method. Finally, the high resolution simulations are analyzed to justify and discuss the approximations underlying both methods.  相似文献   
46.
The existence of intra-plate deformation of the Sundaland platelet along its eastern edge in North Borneo, South-East Asia, makes it an interesting area that still is relatively understudied. In addition, the motion of the coastal area of North-West Borneo is directed toward a frontal fold-and-thrust belt and has been fueling a long debate on the possible geophysical sources behind it. At present this fold-and-thrust belt is not generating significant seismic activity and may also not be entirely active due to a decreasing shelfal extension from south to north. Two sets of Global Positioning System (GPS) data have been used in this study; the first covering a time period from 1999 until 2004 (ending just before the Giant Sumatra–Andaman earthquake) to determine the continuous Sundaland tectonic plate motion, and the second from 2009 until 2011 to investigate the current deformations of North Borneo. Both absolute and relative positioning methods were carried out to investigate horizontal and vertical displacements. Analysis of the GPS results indicates a clear trend of extension along coastal regions of Sarawak and Brunei in North Borneo. On the contrary strain rate tensors in Sabah reveal that only insignificant and inconsistent extension and compression occurs throughout North-West Borneo. Moreover, station velocities and rotation rate tensors on the northern part of North Borneo suggest a clockwise (micro-block) rotation. The first analysis of vertical displacements recorded by GPS in North-West Borneo points to low subsidence rates along the western coastal regions of Sabah and inconsistent trends between the Crocker and Trusmadi mountain ranges. These results have not been able to either confirm or reject the hypothesis that gravity sliding is the main driving force behind the local motions in North Borneo. The ongoing Sundaland–Philippine Sea plate convergence may also still play an active role in the present-day deformation (crustal shortening) in North Borneo and the possible clockwise rotation of the northern part of North Borneo as a micro-block. However, more observations need to be collected to determine if the northern part of North Borneo indeed is (slowly) moving independently.  相似文献   
47.
Summary A method of numerical simulation of the coefficient of reflection of the ionospheric transition layer as a function of frequency is applied to the experimental data related to several series of pearl-type pulsations Pc1 (f = 0.2 – 2 Hz) recorded at the observatories of Kerguelen, Sogra and Nurmijarvi. The inverse problem of modelling, i.e. determining the vertical profiles of ionospheric electron concentration corresponding to the actual experimental situations, was solved approximately. The initial assumption for interpreting the specific nature of the series of Pc1 micropulsations parallel in time was their resonance origin under reflection of the signal at magnetically conjugate ionospheres, Alfvén's resonators, in both of the Earth's hemispheres.  相似文献   
48.
49.
50.
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