全文获取类型
收费全文 | 87篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 9篇 |
地球物理 | 11篇 |
地质学 | 45篇 |
海洋学 | 5篇 |
天文学 | 14篇 |
综合类 | 2篇 |
出版年
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2005年 | 6篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有92条查询结果,搜索用时 15 毫秒
31.
Sumit R. Das 《Journal of Astrophysics and Astronomy》1999,20(3-4):131-148
We review some of the progress in understanding the statistical basis of black hole thermodynamics in string theory. The emphasis
is on the “derivation” of Hawking radiation from the unitary decay of near extremal D-brane states. We also review recent
progress in understanding Schwarzschild black holes by relating them to D-brane black holes via “boosts” in M-theory. 相似文献
32.
33.
Mg tracer diffusion in synthetic forsterite and San Carlos olivine as a function of P,T and fO2 总被引:1,自引:0,他引:1
Sumit Chakraborty John R. Farver Richard A. Yund David C. Rubie 《Physics and Chemistry of Minerals》1994,21(8):489-500
We present new experimental data on Mg tracer diffusion in oriented single crystals of forsterite (Fo100) and San Carlos olivine (Fo92) between 1000–1300° C. The activation energies of diffusion are found to be 400 (±60) kJ/mol (96 kcal/mol) and 275 (±25) kJ/mol (65 kcal/ mol) in forsterite and San Carlos olivine, respectively, along [001] at a fO2 of 10–12 bars. There is no change in activation energy of Mg tracer diffusion within this temperature range. Mg tracer diffusion in a nominally pure forsterite is found to be anisotropic (Dc > Da > D b) and a function of fO2. This fO2 dependence is different from that in olivine containing Fe as a major element, which suggests that the diffusion mechanism of Mg in forsterite is different from that in Fe-bearing olivine at least over some range of fO2. The diffusion mechanism in nominally pure forsterites may involve impurities present below the limits of detection or alternately, Si or Fe3+ interstitial defects, Fe being present as impurity (ppm level) in forsterite. Pressure dependence of Mg tracer diffusivity in forsterite measured to 10 GPa in a multianvil apparatus yields an activation volume of approximately 1–3.5 cm3/ mol. It is found that presence of small amounts of hydrogen bearing species in the atmosphere during diffusion anneal (fH2 0.2 bars, fH20 0.24 bars) do not affect Mg tracer diffusion in forsterite within the resolution of our measurement at a total pressure of 1 bar. The observed diffusion process is shown to be extrinsic; hence extrapolation of the diffusion data to lower temperatures should not be plagued by uncertainties related to change of diffusion mechanism from intrinsic to extrinsic. 相似文献
34.
Rajmal Jain Hemant Dave A. B. Shah N. M. Vadher Vishal M. Shah G. P. Ubale K. S. B. Manian Chirag M. Solanki K. J. Shah Sumit Kumar S. L. Kayasth V. D. Patel Jayshree J. Trivedi M. R. Deshpande 《Solar physics》2005,227(1):89-122
The first space-borne solar astronomy experiment of India, namely Solar X-ray Spectrometer (SOXS), was successfully launched on 08 May 2003 on board geostationary satellite GSAT-2 of India. The SOXS is composed of two independent payloads, viz. SOXS Low-Energy Detector (SLD) Payload and SOXS High-Energy Detector (SHD) Payload. The SOXS aims to study the full-disk integrated X-ray emission in the energy range from 4 keV to 10 MeV. In this paper we present the first report on the SLD instrumentation and its in-orbit performance. The SLD payload was designed and developed at the Physical Research Laboratory in collaboration with various centers of Indian Space Research Organisation (ISRO). The basic scientific aim of the SLD payload is to study solar flares in the energy range from 4 to 60 keV with high spectral and temporal resolution. To meet these requirements, the SLD payload employs state-of-the-art solid state detectors, the first time for a solar astronomy experiment, viz. Si PIN (4 –25 keV), and cadmium–zinc–telluride (4 –60 keV). With their superb high-energy resolution characteristics, SLD can observe iron and iron–nickel complex lines that are visible only during solar flares. In view of its 3.4 FOV, the detector package is mounted on a Sun Aspect System, for the first time, to get uninterrupted observations in a geostationary orbit. The SLD payload configuration, its in-flight operation, and the response of the detectors are presented. We also present the first observations of solar flares made by the SLD payload and briefly describe their temporal and spectral mode results. 相似文献
35.
36.
Sascha André Borinski Ulrich Hoppe Sumit Chakraborty Jibamitra Ganguly Santanu Kumar Bhowmik 《Contributions to Mineralogy and Petrology》2012,164(4):571-586
We have carried out a combined theoretical and experimental study of multicomponent diffusion in garnets to address some unresolved issues and to better constrain the diffusion behavior of Fe and Mg in almandine–pyrope-rich garnets. We have (1) improved the convolution correction of concentration profiles measured using electron microprobes, (2) studied the effect of thermodynamic non-ideality on diffusion and (3) explored the use of a mathematical error minimization routine (the Nelder-Mead downhill simplex method) compared to the visual fitting of concentration profiles used in earlier studies. We conclude that incorporation of thermodynamic non-ideality alters the shapes of calculated profiles, resulting in better fits to measured shapes, but retrieved diffusion coefficients do not differ from those retrieved using ideal models by more than a factor of 1.2 for most natural garnet compositions. Diffusion coefficients retrieved using the two kinds of models differ only significantly for some unusual Mg–Mn–Ca-rich garnets. We found that when one of the diffusion coefficients becomes much faster or slower than the rest, or when the diffusion couple has a composition that is dominated by one component (>75 %), then profile shapes become insensitive to one or more tracer diffusion coefficients. Visual fitting and numerical fitting using the Nelder-Mead algorithm give identical results for idealized profile shapes, but for data with strong analytical noise or asymmetric profile shapes, visual fitting returns values closer to the known inputs. Finally, we have carried out four additional diffusion couple experiments (25–35 kbar, 1,260–1,400 °C) in a piston-cylinder apparatus using natural pyrope- and almandine-rich garnets. We have combined our results with a reanalysis of the profiles from Ganguly et al. (1998) using the tools developed in this work to obtain the following Arrhenius parameters in D = D 0 exp{–[Q 1bar + (P–1)ΔV +]/RT} for D Mg* and D Fe*: Mg: Q 1bar = 228.3 ± 20.3 kJ/mol, D 0 = 2.72 (±4.52) × 10−10 m2/s, Fe: Q 1bar = 226.9 ± 18.6 kJ/mol, D 0 = 1.64 (±2.54) × 10−10 m2/s. ΔV + values were assumed to be the same as those obtained by Chakraborty and Ganguly (1992). 相似文献
37.
High-temperature cooling histories of migmatites from the High Himalayan Crystallines in Sikkim, India: rapid cooling unrelated to exhumation? 总被引:1,自引:0,他引:1
Nilanjana Sorcar Ulrich Hoppe Somnath Dasgupta Sumit Chakraborty 《Contributions to Mineralogy and Petrology》2014,167(2):1-34
The High Himalayan Crystallines (HHCs) provide an excellent natural laboratory to study processes related to crustal melting, crustal differentiation, and the tectonic evolution of mountain belts because partial melting in these rocks occurred under well-defined tectonic boundary conditions (N–S collision of the Indian and the Eurasian plates) and the rocks have not been modified by subsequent metamorphic overprinting. We have used petrogenetic grids, kinetically constrained individual thermobarometry, pseudosection calculations, and reaction histories constrained by textural evidence to determine that the migmatites in the HHC of Sikkim attained peak P–T conditions of 750–800 °C, 9–12 kbar, followed by steep isothermal decompression to 3–5 kbar, and then isobaric cooling to ~600 °C. There may be a trend where rocks to the north [closer to the South Tibetan detachment system (STDS)] attained somewhat higher maximum pressures. The decompression may have been triggered by a reduction in density due to the production of melt (~20 vol%); minor amounts of additional melt may have been produced in individual packages of rock during decompression itself, depending on the exact geometry of the P–T path and the bulk composition of the rock. The stalling of rapid, isothermal exhumation at depths of 10–18 km (3–5 kbar) is related to metamorphic reactions that occur in these rocks. Geospeedometry indicates that at least a two-stage cooling history is required to describe the compositional zoning in all garnets. Both of these stages are rapid (several 100’s °C/my between 800 and 600 °C, followed by several 10’s °C/my between 600 and 500 °C), but there appears to be a spatial discontinuity in cooling history: Rocks to the south (closer to main central thrust) cooled more slowly than rocks to the north (closer to STDS). The boundary between these domains coincides with the discontinuity in age found in the same area by Rubatto et al. (Contrib Mineral Petrol 165:349–372, 2013). Combined with the information on petrologic phase relations, the data reveal the remarkable aspect that the rapid cooling and change of cooling rates all occurred after, rather than during, the rapid exhumation. This result underscores that high-temperature (e.g., >550 °C) cooling is a result of several processes in addition to exhumation and a one-to-one correlation of cooling and exhumation may sometimes be misplaced. Moreover, average cooling rates inferred from the closure temperatures of two isotopic systems should be interpreted judiciously in such nonlinearly cooling systems. While many aspects (e.g., isothermal decompression, isobaric cooling, duration of metamorphism, and cooling rates) of the pressure–temperature history inferred by us are consistent with the predictions of thermomechanical models that produce midcrustal channel flow, the occurrence of blocks with two different cooling histories within the HHC is not explained by currently available models. It is found that while exhumation may be initiated by surface processes such as erosion, the course of exhumation and its rate, at least below depths of ~15 km, is mostly controlled by a coupling between mechanical (density gain/loss) and chemical (metamorphic reactions) processes at depth. 相似文献
38.
Kamal A. Ali Robert J. Stern William I. Manton Peter R. Johnson Sumit K. Mukherjee 《International Journal of Earth Sciences》2010,99(4):705-726
The Neoproterozoic Atud diamictite in Wadi Kareim and Wadi Mobarak in the Eastern Desert of Egypt and the Nuwaybah formation
in NW Saudi Arabia consist of poorly sorted, polymictic breccia, with clasts up to 1 m of granitoid, quartz porphyry, quartzite,
basalt, greywacke, marble, arkose, and microconglomerate in fine-grained matrix. Stratigraphic relations indicate that the
diamictite was deposited in a marine environment. Integrated field investigation, petrographic study and U–Pb SHRIMP zircon
ages demonstrate that the Atud and Nuwaybah are correlative. The distribution of zircon ages indicate that ~750 Ma ages are
dominant with a significant component of older materials, characterized by minor Mesoproterozoic and more abundant Paleoproterozoic
and Neoarchean ages. Some matrix and metasedimentary clast zircons yield ages that are a few 10s of Ma younger than the age
of the youngest clast (754 ± 15 Ma), suggesting Atud/Nuwaybah diamictite deposition ~750 Ma or slightly later, broadly consistent
with being deposited during the Sturtian glaciation (740–660 Ma). The Paleoproterozoic and Neoarchean clasts have no source
within the ensimatic Arabian–Nubian Shield. The distribution of the pre-Neoproterozoic ages are similar to the distribution
of the pre-Neoproterozoic ages in Yemen and Saharan Metacraton, suggesting that these clasts have been transported hundreds
of kilometers, maybe by ice-rafting. The Atud diamictite may represent important evidence for Cryogenian “Snowball Earth”
in the Arabian–Nubian Shield. 相似文献
39.
40.
Impact of Topography on Accuracy of Land Cover Spectral Change Vector Analysis Using AWiFS in Western Himalaya 总被引:1,自引:0,他引:1
J. K. Sharma V. D. Mishra R. Khanna 《Journal of the Indian Society of Remote Sensing》2013,41(2):223-235
The present paper discusses the impact of topography on accuracy for land cover classification and “from-to class change using improved spectral change vector analysis suggested by Chen et al. (2003). Two AWiFS sensor images of different dates are used. Double Window Flexible Pace Search (DFPS) is used to estimate threshold of change magnitude for change/no change classes. The topographic corrections show accuracy of 90% (Kappa coefficient 0.7811) for change/no change area as compared to 82% (Kappa coefficient 0.6512) in uncorrected satellite data. Direction cosines of change vector for determining change direction in n-dimensional spectral space is used for image classification with a minimum distance categorizing technique. The results of change detection are compared (i) Improved CVA with conventional two bands CVA and (ii) Improved CVA before and after topographic corrections. The improved CVA with topographic correction consideration using slope match show maximum accuracy of 90% (Kappa coefficient 0.83) as compared to conventional CVA which show maximum accuracy of 82% (Kappa coefficient 0.6624). The overall accuracy of ”from- to class using improved CVA increases from 86% (Kappa coefficient 0.7817) to 90% (Kappa coefficient 0.83) after topographic corrections. The improved CVA with proper topographic corrections is found to be effective for change detection analysis in the rugged Western Himalayan terrain. 相似文献