全文获取类型
收费全文 | 664篇 |
免费 | 11篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 113篇 |
地球物理 | 119篇 |
地质学 | 260篇 |
海洋学 | 29篇 |
天文学 | 125篇 |
综合类 | 3篇 |
自然地理 | 20篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 11篇 |
2013年 | 24篇 |
2012年 | 22篇 |
2011年 | 21篇 |
2010年 | 38篇 |
2009年 | 31篇 |
2008年 | 43篇 |
2007年 | 37篇 |
2006年 | 27篇 |
2005年 | 28篇 |
2004年 | 25篇 |
2003年 | 26篇 |
2002年 | 17篇 |
2001年 | 15篇 |
2000年 | 23篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1972年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有681条查询结果,搜索用时 15 毫秒
211.
The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data
Tsvetanov ZI Golimowski DA Zheng W Geballe TR Leggett SK Ford HC Davidsen AF Uomoto A Fan X Knapp GR Strauss MA Brinkmann J Lamb DQ Newberg HJ Rechenmacher R Schneider DP York DG Lupton RH Pier JR Annis J Csabai I Hindsley RB Ivesic Z Munn JA Thakar AR Waddell P 《The Astrophysical journal》2000,531(1):L61-L65
We report the discovery of a second field methane brown dwarf from the commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS J134646.45-003150.4 (hereafter SDSS 1346-00), was selected because of its very red color and stellar appearance. Its spectrum between 0.8 and 2.5 μm is dominated by strong absorption bands of H2O and CH4 and closely mimics those of Gliese 229B and SDSS 162414.37+002915.6 (hereafter SDSS 1624+00), two other known methane brown dwarfs. SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that it lies about 11 pc from the Sun. The ratio of flux at 2.1 μm to that at 1.27 μm is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which suggests that SDSS 1346-00 has a slightly higher effective temperature than the others. Based on a search area of 130 deg2 and a detection limit of z*=19.8, we estimate a space density of 0.05 pc-3 for methane brown dwarfs with Teff approximately 1000 K in the 40 pc3 volume of our search. This estimate is based on small-sample statistics and should be treated with appropriate caution. 相似文献
212.
Earth observation relies heavily on imaging. Extraction of informationin turn relies on image processing and analysis. A new and powerfulmethodology has come to the fore in recent years, based on the waveletand other multiscale transforms. Of the many possible application areaswe describe in this paper some approaches for object and feature findingin images', noise filtering of synthetic aperture radar (SAR) images, andthe automatic geometrical registration of different images. 相似文献
213.
O. Esper K. A. F. Zonneveld C. Höll B. Karwath H. Kuhlmann R. R. Schneider A. Vink I. Weise-Ihlo H. Willems 《International Journal of Earth Sciences》2000,88(4):680-693
Despite the increasing interest in the South Atlantic Ocean as a key area of the heat exchange between the southern and the
northern hemisphere, information about its palaeoceanographic conditions during transitions from glacial to interglacial stages,
the so-called Terminations, are not well understood. Herein we attempt to increase this information by studying the calcareous
dinoflagellate cysts and the shells of Thoracosphaera heimii (calcareous cysts) of five Late Quaternary South Atlantic Ocean cores. Extremely high accumulation rates of calcareous cysts
at the Terminations might be due to a combined effect of increased cyst production and better preservation as result of calm,
oligotrophic conditions in the upper water layers. Low relative abundance of Sphaerodinella albatrosiana compared with Sphaerodinella tuberosa in the Cape Basin may be the result of the relatively colder environmental conditions in this region compared with the equatorial
Atlantic Ocean with high relative abundance of S. albatrosiana. Furthermore, the predominance of S. tuberosa during glacials and interglacials at the observed site of the western Atlantic Ocean reflects decreased salinity in the upper
water layer.
Received: 9 November 1998 / Accepted: 26 October 1999 相似文献
214.
R. Schneider A. Ferrara B. Ciardi V. Ferrari S. Matarrese † 《Monthly notices of the Royal Astronomical Society》2000,317(2):385-390
We study the gravitational wave emission from the first stars, which are assumed to be very massive objects (VMOs). We take into account various feedback (both radiative and stellar) effects regulating the collapse of objects in the early Universe and thus derive the VMO initial mass function and formation rate. If the final fate of VMOs is to collapse, leaving very massive black hole remnants, then the gravitational waves emitted during each collapse would be seen as a stochastic background. The predicted spectral strain amplitude in a critical density cold dark matter (CDM) universe peaks in the frequency range ν ≈5×10−4 –5×10−3 Hz, where it has a value in the range ≈10−20 –10−19 Hz−1/2 , and might be detected by the Laser Interferometer Space Antenna ( LISA ). The expected emission rate is roughly 4000 event yr−1 , resulting in a stationary discrete sequence of bursts, i.e. a shot-noise signal. 相似文献
215.
216.
Benjamin M. C. Fischer Michael Rinderer Philipp Schneider Tracy Ewen Jan Seibert 《水文研究》2015,29(26):5321-5336
Mountainous headwaters consist of different landscape units including forests, meadows and wetlands. In these headwaters it is unclear which landscape units contribute what percentage to baseflow. In this study, we analysed spatiotemporal differences in baseflow isotope and hydrochemistry to identify catchment‐scale runoff contribution. Three baseflow snapshot sampling campaigns were performed in the Swiss pre‐alpine headwater catchment of the Zwäckentobel (4.25 km2) and six of its adjacent subcatchments. The spatial and temporal variability of δ2H, Ca, DOC, AT, pH, SO4, Mg and H4SiO4 of streamflow, groundwater and spring water samples was analysed and related to catchment area and wetland percentage using bivariate and multivariate methods. Our study found that in the six subcatchments, with variable arrangements of landscape units, the inter‐ and intra catchment variability of isotopic and hydrochemical compositions was small and generally not significant. Stream samples were distinctly different from shallow groundwater. An upper spring zone located near the water divide above 1,400 m and a larger wetland were identified by their distinct spatial isotopic and hydrochemical composition. The upstream wetland percentage was not correlated to the hydrochemical streamflow composition, suggesting that wetlands were less connected and act as passive features with a negligible contribution to baseflow runoff. The isotopic and hydrochemical composition of baseflow changed slightly from the upper spring zone towards the subcatchment outlets and corresponded to the signature of deep groundwater. Our results confirm the need and benefits of spatially distributed snapshot sampling to derive process understanding of heterogeneous headwaters during baseflow. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
217.
Determination of the aromaticity and the degree of aromatic condensation of a thermosequence of wood charcoal using NMR 总被引:1,自引:0,他引:1
Anna V. McBeath Ronald J. SmernikMaximilian P.W. Schneider Michael W.I. SchmidtEmma L. Plant 《Organic Geochemistry》2011,42(10):1194-1202
Quantifying the role of black carbon (BC) in geochemical processes is difficult due to the heterogeneous character of its chemical structure. Chestnut wood charcoal samples produced at heat treatment temperatures (HTT) from 200-1000 °C were analysed using two different solid state 13C NMR techniques. First, aromaticity was determined as the percentage of total signal present in the aromatic region of 13C direct polarisation (DP) spectra. This was found to increase through the low temperature range of 200-400 °C; at higher temperatures, aromaticity was found to be >90%. Second, aromatic condensation was determined through the measurement of the chemical shift of 13Cbenzene sorbed to the charcoals, which is influenced by the presence of “ring currents” in the aromatic domains of the charcoals. This technique was less sensitive to molecular changes through the lower temperature range, but showed there was a smooth increase in the degree of condensation of the aromatic structures with increasing temperature through the temperature range 400-1000 °C. Ab initio molecular modelling was used to estimate the size of aromatic domains in the charcoals based on the strength of the ring currents detected. These calculations indicated that charcoals produced at temperatures below 500 °C contain aromatic domains no larger than coronene (7 ring). At higher temperatures the size of these domains rapidly increases, with structures larger than a 19 ring symmetrical PAH being predominant in charcoals produced at temperatures above 700 °C. Data from this study were found to be generally consistent with previously published measurements using the benzenepolycarboxylic acid (BPCA) molecular marker method on the same set of samples. 相似文献
218.
The Teggiolo zone is the sedimentary cover of the Antigorio nappe, one of the lowest tectonic units of the Penninic Central
Alps. Detailed mapping, stratigraphic and structural analyses, and comparisons with less metamorphic series in several well-studied
domains of the Alps, provide a new stratigraphic interpretation. The Teggiolo zone is comprised of several sedimentary cycles,
separated by erosive surfaces and large stratigraphic gaps, which cover the time span from Triassic to Eocene. At Mid-Jurassic
times it appears as an uplifted, partially emergent block, marking the southern limit of the main Helvetic basin (the Limiting
South-Helvetic Rise LSHR). The main mass of the Teggiolo calcschists, whose base truncates the Triassic–Jurassic cycles and
can erode the Antigorio basement, consists of fine-grained clastic sediments analogous to the deep-water flyschoid deposits
of Late Cretaceous to Eocene age in the North-Penninic (or Valais s.l.) basins. Thus the Antigorio-Teggiolo domain occupies a crucial paleogeographic position, on the boundary between the Helvetic
and Penninic realms: from Triassic to Early Cretaceous its affinity is with the Helvetic; at the end of Cretaceous it is incorporated
into the North-Penninic basins. An unexpected result is the discovery of the important role played by complex formations of
wildflysch type at the top of the Teggiolo zone. They contain blocks of various sizes. According to their nature, three different
associations are distinguished that have specific vertical and lateral distributions. These blocks give clues to the existence
of territories that have disappeared from the present-day level of observation and impose constraints on the kinematics of
early folding and embryonic nappe emplacement. Tectonics produced several phases of superimposed folds and schistosities,
more in the metasediments than in the gneissic basement. Older deformations that predate the amplification of the frontal
hinge of the nappe generated the dominant schistosity and the km-wide Vanzèla isoclinal fold. 相似文献
219.
本文的工作区域是按中国地矿部和德国下萨克森州科学和艺术部之间科学台作协议而提供的。在唐家湾地区的中上泥盆统碳酸盐岩中可以见到以下8种微相类型:泥岩、具纹层球粒-颗粒岩/泥粒岩、无纹层球粒-颗粒岩/泥粒岩、介形虫-颗粒岩/泥粒岩、枝状层孔虫-粒泥岩、枝状层孔虫-棘皮类-粒泥岩、生物碎屑-粒泥岩和骨架岩。这些微相类型可指示不同的能量指数及水深。同欧文(Irwin,1965)浅水碳酸盐沉积模式对比,唐家湾泥盆纪(吉维特期和弗拉斯期)属于Y带和Z带沉积,并可分出发育生物丘-生物层的正常海环境、局限浅水沉积环境和潮坪沉积环境。最大水深估计为10m—20m。
唐家湾剖面碳酸盐岩经历了三种早成岩环境:海水成岩环境、大气水成岩环境和混合水成岩环境。其后又经历了晚成岩阶段的压溶、重结晶和交代作用。白云石化部分为混合水成因,部分为晚成岩期交代成因。 相似文献
唐家湾剖面碳酸盐岩经历了三种早成岩环境:海水成岩环境、大气水成岩环境和混合水成岩环境。其后又经历了晚成岩阶段的压溶、重结晶和交代作用。白云石化部分为混合水成因,部分为晚成岩期交代成因。 相似文献
220.