全文获取类型
收费全文 | 178篇 |
免费 | 16篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 18篇 |
地球物理 | 60篇 |
地质学 | 52篇 |
海洋学 | 9篇 |
天文学 | 52篇 |
综合类 | 4篇 |
自然地理 | 13篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 11篇 |
2020年 | 4篇 |
2019年 | 11篇 |
2018年 | 21篇 |
2017年 | 17篇 |
2016年 | 12篇 |
2015年 | 12篇 |
2014年 | 15篇 |
2013年 | 8篇 |
2012年 | 11篇 |
2011年 | 13篇 |
2010年 | 22篇 |
2009年 | 7篇 |
2008年 | 8篇 |
2007年 | 11篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有217条查询结果,搜索用时 89 毫秒
41.
This paper lists difficult railway construction conditions that are typical for the northern areas of the Russian Far East. Permafrost-bound issues of railway and highway construction and operation are described. Some of the authors'' developments for subgrade stabilization in the foregoing conditions are given as examples. 相似文献
42.
Alexey P. Kuklin Gazhit Ts. Tsybekmitova Evgenia P. Gorlacheva Balzhit B. Bazarova Alexey V. Afonin 《中国海洋湖沼学报》2016,34(3):507-516
Present-day conditions of the Lake Kenon ecosystem are determined by a combination of natural and anthropogenic factors.We have estimated the effects of a complex of factors on the condition of the abiotic environment and on specific biological components in the lake ecosystem.Change in biogenic load has caused an increase in the role of phytoplankton in the general balance of organic matter during the high-water period.Charophytes are the main dominants of bottom vegetation.Anthropogenic load has caused a decrease in both fish species and fish capacity.The lake application as a water reservoir-cooler has influenced the average annual water mineralization(from 420 mg/L to 530.0 mg/L with a maximum 654 mg/L in 1993) and fluctuations in its hydrochemical composition.The present composition of the lake is sulfate-hydrocarbonate-chloride calcium-sodic-magnesium in character.SO 4 – content is twice as much as the maximum permissible concentration in fishery waters.Water drainage from an ash disposal area to the lake has caused an increase in chemical-element concentrations including the heavy metals.Hg concentration in Perca fluviatilis muscles is 0.5 μg/g dry wt.Thus,understanding directions in the ecosystem of the water reservoir-cooler under changing hydrological conditions will let us forecast the consequences of new combined heat and power plant operation. 相似文献
43.
Abstract. The dependence of the vertical distribution of sessile macrobenthos upon environmental physical factors was studied in a community inhabiting rocky substrata at 2 to 15 m depth near the Rimsky‐Korsakov Islands (Peter the Great Bay, Sea of Japan). Three separate groups of species were distinguished within this community. The main dominant species are the anthozoan Metridium senile and the mussel Crenomytilus grayanus. Water movement, bottom inclination and topographic position of the studied sites in respect to prevailing water flows influence the spatial structure of sessile invertebrates. No vertical zonation in the scale of the studied sublittoral area below the 2 m depth level was observed. The studied factors are believed to condition the observed mosaic of patches characterized by specific composition, with a single species being dominant. 相似文献
44.
Gennady G. Boeskorov Peter A. Lazarev Andrei V. Sher Sergei P. Davydov Nadezhda T. Bakulina Marina V. Shchelchkova Jonas Binladen Eske Willerslev Bernard Buigues Alexey N. Tikhonov 《Quaternary Science Reviews》2011,30(17-18):2262-2272
A nearly complete frozen mummy of a woolly rhinoceros (Coelodonta antiquitatis Blum., 1799) was discovered in a gold mine on the lower reaches of the Kolyma River, north–eastern Siberia. This is the first find of the whole body of woolly rhino in permafrost. A large part of the mummified body was preserved, including the left part of the body, covered by skin, including skin of the head and ear, fore and hind legs. The skull with 2 horns and the lower jaw were also preserved. Most of the internal organs were lost, except the intestines, stomach, and their contents. A rib fragment from this individual was dated by AMS-radiocarbon method to 39,140 ± 390 years BP (OxA-18755). Spore and pollen analyses of the stomach contents indicate that grasses and sagebrushes formed the main part of the diet of C. antiquitatis in this region of Arctic Siberia. 相似文献
45.
46.
M. Yu. Piotrovich Yu. N. Gnedin N. A. Silant'ev T. M. Natsvlishvili S. D. Buliga 《Astronomische Nachrichten》2015,336(10):1013-1016
Magnetic fields in an accretion disk around the central black hole can modify the size of the innermost stable circular orbit (ISCO) and can produce a difference to the classical Novikov‐Thorne radius. We estimated the ISCO magnetic field strength from the polarimetric observations of the accretion‐disk radiation. This estimate is obtained taking into account the effect of the Faraday rotation of the polarization plane at the distance of the mean free path of photons between successive electron scattering events. We present the new method for estimating the ISCO radius in the accretion disk, i.e. in the nearest vicinity of a central black hole. Our estimates confirmed the Frolov, Shoom & Tzounis (2014) and Ranea‐Sandoval & Garcia (2015) conclusion that the magnetic field in the accretion disk decreases the size of the innermost stable circular orbit. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
47.
Atmospheric water vapor abundances in Mars’ north polar region (NPR, from 60° to 90°N) are mapped as function of latitude and longitude for spring and summer seasons, and their spatial, seasonal, and interannual variability is discussed. Water vapor data are from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and the Viking Orbiter (VO) Mars Atmospheric Water Detector (MAWD). The data cover three complete northern spring-summer seasons in 1977-1978, 2000-2001 and 2002-2003, and shorter periods of spring-summer seasons during 1975, 1999 and 2004. Long term interannual variability in the averaged NPR abundances may exist, with Viking MAWD observations showing twice as much water vapor during summer as the MGS TES observations more than 10 martian years (MY) later. While the averaged abundances are very similar in TES observations for the same season in different years, the spatial distributions in the early summer season do vary significantly year over year. Spatial and temporal variabilities increase between Ls ∼ 80-140°, which may be related to vapor sublimation from the North Polar Residual Cap (NPRC), or to changes in circulation. Spatial variability is observed on scales of ∼100 km and temporal variability is observed on scales of <10 sols during summer. During late spring the TES water vapor spatial distribution is seen to correlate with the low topography/low albedo region of northern Acidalia Planitia (270-360°E), and with the dust spatial distribution across the NPR during late spring-early summer. Non-uniform vertical distribution of water vapor, a regolith source or atmospheric circulation ‘pooling’ of water vapor from the NPRC into the topographic depression may be behind the correlation with low topography/low albedo. Sublimation winds carrying water vapor off the NPRC and lifting surface dust in the areas surrounding the NPRC may explain the correlation between the water vapor and dust spatial distributions. Correlation between water vapor and dust in MAWD data are only observed over low topography/low albedo area. Maximum water vapor abundances are observed at Ls = 105-115° and outside of the NPRC at 75-80°N; the TES data, however, do not extend over the NPRC and thus, this conclusion may be biased. Some water vapor appears to be released in plumes or ‘outbursts’ in the MAWD and TES datasets during late spring and early summer. We propose that the sublimation rate of ice varies across the NPRC with varying surface winds, giving rise to the observed ‘outbursts’ at some seasons. 相似文献
48.
M. Yu. Piotrovich Yu. N. Gnedin T. M. Natsvlishvili N. A. Silant’ev 《Astronomy Letters》2010,36(6):389-395
We analyze the spectropolarimetric observations of 12 candidates for quasars from the spectroscopic database of the SDSS Catalog.
The magnetic fields of these objects are estimated in the context of a theory that includes the Faraday rotation of the polarization
plane on the mean free path of a photon in the outflow from an accretion disk. As a result, we have determined the column
density in the outflow, N
H ∼ 6 × 1023 cm−2, and the radial, B ∼ 1 G, and toroidal, B ∼ 600 G, magnetic fields. 相似文献
49.
Yu. N. Gnedin M. Yu. Piotrovich T. M. Natsvlishvili 《Monthly notices of the Royal Astronomical Society》2007,374(1):276-281
The birefringent effects of photon–pseudo-scalar boson (Goldstone) particle mixing in intergalactic magnetic field are calculated for cosmological objects. We use the recent results of PVLAS collaboration that reported recently the observation of a rotation of the polarization plane of light propagating through a transverse static magnetic field. Such result was interpreted as arising due to conversion of photon into pseudo-scalar with coupling strength g aγ ∼ 4 × 10−6 GeV−1 . This result contradicts to data of stellar evolution that excluded standard axion model and seems to claim existence of supersymmetry (SUSY) pseudo-scalars. We estimate the intergalactic magnetic field magnitude as ∼10−16 G based on Hatsemekers et al. observations of extreme-scale alignments of quasar polarization vectors. We analysed some additional results of astronomical observations that could be explained by axion interpretation of the PVLAS data: a sharp steepening of the quasi-stellar object (QSO) continuum shortward of ≃1100 Å, observed circular polarization of active galactic nuclei (AGNs) and QSOs, discrepancy between observed intrinsic polarization of stars in the Local Bubble and stellar spectral classification. The observed polarization of stars in the Local Bubble cannot be explained by interstellar origin. 相似文献
50.
Magnetic resonance sounding applied to aquifer characterization 总被引:3,自引:0,他引:3
Legchenko A Baltassat JM Bobachev A Martin C Robain H Vouillamoz JM 《Ground water》2004,42(3):363-373
Magnetic resonance sounding (MRS) is distinguished from other geophysical tools used for ground water investigation by the fact that it measures a magnetic resonance signal generated directly from subsurface water molecules. An alternating current pulse energizes a wire loop on the ground surface and the MRS signal is generated; subsurface water is indicated, with a high degree of reliability, by nonzero amplitude readings. Measurements with varied pulse magnitudes then reveal the depth and thickness of water saturated layers. The hydraulic conductivity of aquifers can also be estimated using boreholes for calibration. MRS can be used for both predicting the yield of water supply wells and for interpolation between boreholes, thereby reducing the number of holes required for hydrogeological modeling. An example of the practical application of MRS combined with two-dimensional electrical imaging, in the Kerbernez and Kerien catchments area of France, demonstrates the efficiency of the technique. 相似文献