全文获取类型
收费全文 | 167篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 24篇 |
地球物理 | 24篇 |
地质学 | 57篇 |
海洋学 | 8篇 |
天文学 | 33篇 |
自然地理 | 3篇 |
出版年
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 13篇 |
2016年 | 11篇 |
2015年 | 2篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 5篇 |
2011年 | 8篇 |
2010年 | 4篇 |
2009年 | 8篇 |
2008年 | 4篇 |
2007年 | 9篇 |
2006年 | 9篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有173条查询结果,搜索用时 31 毫秒
61.
Priyabrata Santra Bhabani Sankar Das Debashish Chakravarty 《Environmental Earth Sciences》2012,65(7):2051-2061
Surface map of soil properties plays an important role in various applications in a watershed. Ordinary kriging (OK) and regression
kriging (RK) are conventionally used to prepare these surface maps but generally need large number of regularly girded soil
samples. In this context, REML-EBLUP (REsidual Maximum Likelihood estimation of semivariogram parameters followed by Empirical
Best Linear Unbiased Prediction) shown capable but not fully tested in a watershed scale. In this study, REML-EBLUP approach
was applied to prepare surface maps of several soil properties in a hilly watershed of Eastern India and the performance was
compared with conventionally used spatial interpolation methods: OK and RK. Evaluation of these three spatial interpolation
methods through root-mean-squared residuals (RMSR) and mean squared deviation ratio (MSDR) showed better performance of REML-EBLUP
over the other methods. Reduction in sample size through random selection of sampling points from full dataset also resulted
in better performance of REML-EBLUP over OK and RK approach. The detailed investigation on effect of sample number on performance
of spatial interpolation methods concluded that a minimum sampling density of 4/km2 may successfully be adopted for spatial prediction of soil properties in a watershed scale using the REML-EBLUP approach. 相似文献
62.
Surface layer atmospheric and ocean observations have been collected along the cruise track from a special scientific expedition to Antarctica. Bulk estimates of surface momentum flux, sensible heat flux and latent heat flux have been computed applying bulk algorithms from the data collected along cruise track during the time period January 27 to March 31, 2006, and compared the results with National Centre for Environmental Prediction (NCEP) reanalysis. Underestimation of surface momentum flux in roaring forties (40°S–50°S) area of Indian Ocean is seen from NCEP reanalysis. Systemic differences in sensible and latent heat fluxes between observed and NCEP reanalysis have been found. Along the cruise track, the average sensible (latent) heat flux was 9.45 Wm?2 (67.46 Wm?2) and 3.75 Wm?2 (64.45 Wm?2) from the direct measurement and NCEP reanalysis, respectively. The NCEP reanalysis is being widely used in numerical modeling studies, and the discrepancies shown in the NCEP reanalysis in present study will be of immense use to the modeling community of the Indian Ocean in general and Southern Indian Ocean in particular. 相似文献
63.
Microtremor survey in Talchir, India to ascertain its basin characteristics in terms of predominant frequency by Nakamura's ratio technique 总被引:2,自引:0,他引:2
M. Yanger Walling William K. Mohanty Sankar K. Nath Supriyo Mitra Ajesh John 《Engineering Geology》2009,106(3-4):123-132
The Talchir Basin, one of India's oldest basins, has been a subject of interest because of its rich coal deposits. The maximum thickness of the basin is about 1500 m. Beyond the basin is the hard metamorphic rocks of Precambrian age. The ambient noise survey data have been analyzed for the Talchir Basin using Nakamura's technique of horizontal–vertical-spectral-ratio (HVSR) to ascertain the basin structure in terms of the predominant frequency. The predominant frequency varies from 0.25 Hz to 7.8 Hz but a major portion of the basin comes under the range of 0.3 Hz–2.4 Hz while on the metamorphic rocks it is as high as 7.8 Hz. The variation in predominant frequency shows a good correlation with the sediment thickness of the basin. The results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin. The present study has also been compared with the results of the synthetic seismogram that was performed for the Talchir Basin. The predominant frequency obtained from HVSR technique complements well with the frequency at which the peak response spectra ratio is observed. The present study of the predominant frequency identifies quite well the characteristics of Talchir Basin and is in good agreement with the synthetic ground motion modeling of the region. 相似文献
64.
Ajoy K. Bhaumik Joydeep Paikray Jagadish Dutta Arijit Mitra Devleena Tiwari Dattatray J. Patil 《Journal of the Geological Society of India》2017,90(4):437-446
Baripada Marine Beds (BMB) have been studied extensively in terms of its mega fossil content. However, not much has been discussed about the foraminiferal content and the organic matter assemblage in these beds. The fossiliferous sequence of BMB consists of sandstone, shale and limestone units. The present study is persued on the limestone unit of BMB. Foraminiferal, thin section and rock-eval pyrolysis studies were performed on the 33 surface samples collected from five sections of Jamdapal and Mukurmatia region along the Budhabalang river bank. Foraminifera are less abundant in the samples of Jamdapal, whereas Mukurmatia is comparatively rich. First appearance datum of Globorotalia menardii[ranges since middle Miocene (12.6 Ma); FAD at planktic foraminiferal zone N12] and last appearance datum of Neogloboquadrina continuosa [ranges between early Miocene (23.2 Ma) to late Miocene (8.3 Ma); FAD at planktic foraminiferal zone N4B and LAD at N16] together suggest that the limestone unit was deposited in between 12.6 to 8.3 Ma within the upper Miocene. Also, the association of shallow water benthic foraminifera (Species of Ammonia, Asterorotalia, Bolivina, Buliminella, Cibicides, Challengerella, Criboelphidium, Cribononion, Elphidium, Hanzawaia, Nonionella) and planktic foraminifera (Globigerina falcoensis, Globigerina woodi, Globorotalia menardii, Neogloboquadrina continuosa) together with oyster bank and shark teeth suggest deposition of limestone within well oxygenated, tropical, shallow water, open marine condition (within 40m water depth). Lithological and thin section studies together with global sea level fluctuation history advocate that upper Miocene marine transgression promoted the formation of this unit. Bulk organic geochemical data obtained by the rock-eval pyrolysis studies on selected samples indicate a low total organic carbon (TOC), with low hydrogen index (HI), high oxygen index (OI). The organic facies is characterised by type-IV kerogen with major contribution from near shore terrestrial plants. This also suggests deposition in shallow, oxygenated environments that did not promote significant accumulation and preservation of organic content in sediments. 相似文献
65.
Ines Hoog Subir K. Mitra Karoline Diehl Stephan Borrmann 《Journal of Atmospheric Chemistry》2007,57(1):73-84
In laboratory experiments the interactions of ammonia with ice crystals were studied within the temperature range between
0 and −20°C. In a first series of experiments dendritic ice crystals were grown from water vapor in presence of ammonia gas
in various concentrations between 4 and 400 ppbv. In a second series of experiments pure ice crystals were exposed to a humidified
ammonia–air mixture inside a horizontal flow tube. The influence of temperature, ammonia gas concentration (0.6, 1.5, and
10 ppmv), exposure time, and the presence of impurities such as sulfate on the ammonia uptake by the ice surface was investigated
by determining the ammonium content in the melt water of the ice crystals by ion chromatography. During the growth of ice
crystals significant amounts of ammonia (around 200 μg/l) were taken up even at small gas concentrations. In contrast, even
at high gas concentrations the uptake of ammonia by non-growing ice crystals was lower by approximately one order of magnitude.
The presence of sulfate on the ice surface affected an enhanced uptake of ammonia by a factor of 5–10. A model is presented
which describes the uptake of ammonia by ice considering the chemical processes occurring in the ice surface layer and simultaneous
diffusion of ammonia into bulk ice. Even the increased uptake of ammonia by growing ice is rather small compared to the uptake
by water droplets; thus, the major process for scavenging of ammonia from the atmosphere via the ice phase might not be the
direct uptake by ice crystals but the riming involving super-cooled droplets containing ammonia. 相似文献
66.
S. Santra J. S. Sanders A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2007,382(2):895-902
We present a study of the X-ray emission from the nuclei of galaxies observed in the core of the Perseus cluster in a deep exposure with Chandra . Point sources are found coincident with the nuclei of 13 early-type galaxies, as well as the central galaxy NGC 1275. This corresponds to all galaxies brighter than M B > −18 in the Chandra field. All of these sources have a steep power-law spectral component and four have an additional thermal component. The unabsorbed power-law luminosities in the 0.5–7.0 keV band range from 8 × 1038 to 5 × 1040 erg s−1 . We find no simple correlations between the K -band luminosity, or the FUV and NUV AB magnitudes of these galaxies and their X-ray properties. We have estimated the black hole masses of the nuclei using the K -band M BH – L K bol relation and again find no correlation between black hole mass and the X-ray luminosity. Bondi accretion on to the black holes in the galaxies with minihaloes should make them much more luminous than observed. 相似文献
67.
Abhas Mitra 《Journal of Astrophysics and Astronomy》1994,15(2):179-186
Recent accelerator data based parameterization of the inclusive cross section (c −s) forπ0 production in hadronic collisions and an explicit incorporation of the finiteness of the relevant projectile hadron spectrum
suggest a significant steepening in the spectrum (by as much as 0.4 in the spectral index) of the secondaryγ-ray towards the end of the spectrum. We emphasize here that this spectral steepening in conjunction with the possibility
that in the bright X-ray binaries the maximum energy to which theγ-ray producing progenitor protons may be accelerated is only ∼ l0 PeV, may imply an effective efficiency forγ-ray production,ε, as reckoned by the PeV arrays, one or two orders smaller than the previous estimates. To explain the genesis of a given
PeV photon flux from an X-ray binary, one, therefore, has to. accordingly consider a much higher value of the progenitor proton
beam luminosity,L
p
. This requirement may raise further questions regarding the actual genesis of PeVγ-rays in X-ray binaries, or alternatively, on the veracity of the high values of the PeV photon fluxes reported by earlier
experiments. 相似文献
68.
69.
Debdatta?PalEmail author Subrata?Kumar?Mitra 《Theoretical and Applied Climatology》2018,131(1-2):69-76
This study used a quantile autoregressive distributed lag (QARDL) model to capture asymmetric impact of rainfall on food production in India. It was found that the coefficient corresponding to the rainfall in the QARDL increased till the 75th quantile and started decreasing thereafter, though it remained in the positive territory. Another interesting finding is that at the 90th quantile and above the coefficients of rainfall though remained positive was not statistically significant and therefore, the benefit of high rainfall on crop production was not conclusive. However, the impact of other determinants, such as fertilizer and pesticide consumption, is quite uniform over the whole range of the distribution of food grain production. 相似文献
70.