全文获取类型
收费全文 | 2606篇 |
免费 | 48篇 |
国内免费 | 27篇 |
专业分类
测绘学 | 251篇 |
大气科学 | 167篇 |
地球物理 | 533篇 |
地质学 | 916篇 |
海洋学 | 62篇 |
天文学 | 629篇 |
综合类 | 21篇 |
自然地理 | 102篇 |
出版年
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 35篇 |
2019年 | 29篇 |
2018年 | 141篇 |
2017年 | 116篇 |
2016年 | 154篇 |
2015年 | 78篇 |
2014年 | 132篇 |
2013年 | 152篇 |
2012年 | 107篇 |
2011年 | 116篇 |
2010年 | 101篇 |
2009年 | 111篇 |
2008年 | 89篇 |
2007年 | 62篇 |
2006年 | 59篇 |
2005年 | 56篇 |
2004年 | 33篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 36篇 |
2000年 | 39篇 |
1999年 | 45篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 28篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 31篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 41篇 |
1988年 | 48篇 |
1987年 | 52篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 61篇 |
1983年 | 58篇 |
1982年 | 34篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1976年 | 12篇 |
1974年 | 11篇 |
1973年 | 13篇 |
1972年 | 15篇 |
1971年 | 10篇 |
排序方式: 共有2681条查询结果,搜索用时 46 毫秒
991.
Trace metals in antifouling paint particles and their heterogeneous contamination of coastal sediments 总被引:4,自引:0,他引:4
Nimisha Singh 《Marine pollution bulletin》2009,58(4):559-564
Antifouling paint residues collected from the hard-standings of a marine leisure boat facility have been chemically characterised. Scanning electron microscopy revealed distinct layers, many containing oxidic particles of Cu and Zn. Quantitative analysis indicated concentrations of Cu and Zn averaging about 300 and 100 mg g−1, respectively, and small proportions of these metals (<2%) in organometallic form as pyrithione compounds. Other trace metals present included Ag, Cd, Cr, Ni, Pb and Sn, with maximum concentrations of about 330, 75, 1200, 780, 1800 and 25,000 μg g−1, respectively. Estuarine sediment collected near a boatyard contained concentrations of Cu and Zn an order of magnitude greater than respective concentrations in “background” sediment, and mass balance calculations suggested that the former sample was contaminated by about 1% by weight of paint particles. Clearly, antifouling residues represent a highly significant, heterogeneous source of metallic contamination in the marine environment where boating activities occur. 相似文献
992.
S. T. G. Raghu Kanth Konjengbam Darunkumar Singh Kumar Pallav 《Pure and Applied Geophysics》2009,166(4):641-672
In this article, the spatial variation of ground motion in Imphal City has been estimated by the finite-fault seismological
model coupled with site response analysis. The important seismic sources around Imphal City have been identified from the
fault map and past seismicity data. The rock level acceleration time histories at Imphal City for the 1869 Cachar (Mw 7.5) earthquake and a hypothetical Mw 8.1 event in the Indo-Burma subduction zone have been estimated by a stochastic finite-fault model. Soil investigation data
of 122 boreholes have been collected from several construction projects in Imphal City. Site response analysis has been carried
out and the surface level ground motion has been determined for Imphal City for these two earthquake events. The results are
presented in the form of peak ground acceleration (PGA) contour map. From the present study it has been ascertained that the
maximum amplification for PGA over Imphal City is as high as 2.5. The obtained contour maps can serve as guidelines for identifying
vulnerable areas and disaster mitigation in Imphal City. 相似文献
993.
994.
995.
Lu Chen Vijay P. Singh Shenglian Guo Jianzhong Zhou Lei Ye 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1755-1767
The rainfall–runoff relationship is not only nonlinear and complex but also difficult to model. Artificial neural network (ANN), as a data-driven technique, has gained significant attention in recent years and has been shown to be an efficient alternative to traditional methods for hydrological modeling. However, for different input combinations, ANN models can yield different results. Therefore, input variables and ANN types need to be carefully considered, when using an ANN model for stream flow forecasting. This study proposes the copula-entropy (CE) theory to identify the inputs of an ANN model. The CE theory permits to calculate mutual information (MI) and partial MI directly which avoids calculating the marginal and joint probability distributions. Three different ANN models, namely multi-layer feed (MLF) forward networks, radial basis function networks and general regression neural network, were applied to predict stream flow of Jinsha River, China. Results showed that the inputs selected by the CE method were better than those by the traditional linear correlation analysis, and the MLF ANN model with the inputs selected by CE method obtained the best predicted results for the Jinsha River at Pingshan gauging station. 相似文献
996.
Fourier spectral- and duration models for the generation of response spectra adjustable to different source-, propagation-, and site conditions 总被引:3,自引:2,他引:1
Sanjay Singh Bora Frank Scherbaum Nicolas Kuehn Peter Stafford 《Bulletin of Earthquake Engineering》2014,12(1):467-493
One of the major challenges related with the current practice in seismic hazard studies is the adjustment of empirical ground motion prediction equations (GMPEs) to different seismological environments. We believe that the key to accommodating differences in regional seismological attributes of a ground motion model lies in the Fourier spectrum. In the present study, we attempt to explore a new approach for the development of response spectral GMPEs, which is fully consistent with linear system theory when it comes to adjustment issues. This approach consists of developing empirical prediction equations for Fourier spectra and for a particular duration estimate of ground motion which is tuned to optimize the fit between response spectra obtained through the random vibration theory framework and the classical way. The presented analysis for the development of GMPEs is performed on the recently compiled reference database for seismic ground motion in Europe (RESORCE-2012). Although, the main motivation for the presented approach is the adjustability and the use of the corresponding model to generate data driven host-to-target conversions, even as a standalone response spectral model it compares reasonably well with the GMPEs of Ambraseys et al. (Bull Earthq Eng 3:1–53, 2005), Akkar and Bommer (Seismol Res Lett 81(2):195–206, 2010) and Akkar and Cagnan (Bull Seismol Soc Am 100(6):2978–2995, 2010). 相似文献
997.
An entry in the Tarikh-i-Hassan records that in 883 AD during the reign of King Avantivarman (855–883) an earthquake in Kashmir triggered a landslide that impounded the River Jhelum and flooded the Kashmir Valley. Kalhana’s Rajatarangini provides abundant details about how the ninth century engineer Suyya both cleared the natural dam, drained the valley and instituted numerous irrigation works. We identify the landslide(s) responsible for this Medieval flood and from twentieth century discharge statistics of the Jhelum calculate that it would have taken at least 2 years to flood the Kashmir Valley to near Anantnag. This presents a chronological difficulty, for the causal earthquake could not have occurred in the last 4 months of Avantivarman’s rule, and we conclude that it must have occurred much earlier, perhaps before the start of his reign. The flood occurred during a period of widespread temple building using massive uncemented limestone megablocks, capped by monolithic multi-ton roofs. Many of these magnificent temples, now in ruinous condition, are located close to the shores of the inferred Medieval flood level, suggesting that the transport of construction materials for these temples may have been ferried by barge from distant quarries. Historians and archaeologists have attributed the partial collapse of these temples to malicious damage by subsequent occupants of the valley, but the misalignment of blocks at lower levels within each edifice in recent earthquakes suggests that their lateral offsets are the result of jostling during prolonged shaking in historical earthquakes. From the serendipitous entrapment of datable materials beneath fallen blocks from Kashmir’s ninth century temples we can, in principle, identify the times of historical earthquakes. We chose the ruined Sugandhesa temple near Patan to test this hypothesis. Preliminary results indicate collapse in the tenth or eleventh century, and significant damage in 1885, with at least one intervening earthquake possibly in the seventieth century. 相似文献
998.
Comparative evaluation of performances of two versions of NCEP climate forecast system in predicting Indian summer monsoon rainfall 总被引:1,自引:0,他引:1
Nachiketa Acharya Makarand A. Kulkarni Uma C. Mohanty Ankita Singh 《Acta Geophysica》2014,62(1):199-219
The operational prediction of climatic variables in monthly-to-seasonal scales has been issued by National Centers for Environmental Prediction (NCEP) through Climate Forecast System model (CFSv1) since 2004. After incorporating significant changes, a new version of this model (CFSv2) was released in 2011. The present study is based on the comparative evaluation of performances of CFSv2 and CFSv1 for the southwest monsoon season (June-July-August-September, JJAS) over India with May initial condition during 1982–2009. It was observed that CFSv2 has improved over CFSv1 in simulating the observed monsoon rainfall climatology and inter annual variability. The movement of the cell of Walker circulation in years of excessive and deficient rainfall is better captured in CFSv2, as well. The observed teleconnection pattern between ISMR-sea surface temperature (SST) is also better captured in CFSv2. The overall results suggest that the changes incorporated in CFSv1 through the development of CFSv2 have resulted in an improved prediction of ISMR.21 相似文献
999.
Prashant Patil Sarnam Singh V. K. Dadhwal 《Journal of the Indian Society of Remote Sensing》2012,40(1):37-46
Spectral modeling of above ground biomass (AGB) with field data collected in 48 field sites representing moist deciduous forest
in Surat district is reported. Models were generated using LISS-III and MODIS data. The plot-wise field data was aggregated
to MODIS pixel (250 m) using area weightages of forest/vegetation. The study reports that above ground phytomass varied from
6.13 t/ha to 389.166 t/ha while AGB phytomass estimated using area-weights for sites of 250×250 m, ranged from 5.534 t/ha
to 134.082 t/ha. The contribution of bamboo in AGB has been found very high. The analysis indicated that the highest correlation
between AGB phytomass and red band (R) of MODIS satellite data of October was (R2=0.7823) and R2=0.6998 with both NDVI of October data as well as NDVImax. High correlation (R2=0.402) with IR band of February month was also found. The phytomass range obtained by using MODIS data varies from 0.147 t/ha
to 182.16 t/ha. The mean biomass is 40.50 t/ha. Total biomass is 31.44 Mt. The mean Carbon density is 19.44 tC/ha in forest
areas. The study is validation of region-wise spectral modeling approach that will be adopted for mapping vegetation carbon
pool of the India under National Carbon Project of ISRO-Geosphere Biosphere Programme. 相似文献
1000.
Mehul R. Pandya Raghavendra Pratap Singh Sushma Panigrahy Jai Singh Parihar 《Journal of the Indian Society of Remote Sensing》2012,40(2):215-223
Quantitative remote sensing involving accurate estimation of vegetation properties relies greatly on the measurements of the
near infrared (NIR) channel because of unique interaction property between light and leaf. It is generally assumed that the
NIR measurements are made in the absence of atmospheric absorption. However, relatively weak water vapour absorption features
still persist in the NIR channel, which has bearing on the quantitative estimates of the vegetation properties and long-term
data series. This paper reports the results of a study that was carried out to infer the possible influence of the atmospheric
water vapour (WV) on the NIR measurements (0.77–0.86 μm) of Indian Remote Sensing (IRS) satellite sensors through radiative
transfer simulations using MODTRAN model. The study also suggests and evaluates the alternate band-positions for the NIR channel
to improve the IRS NIR measurements. It was observed that the water absorption features present around 0.810 μm reduces the
WV transmission of IRS NIR channel from 1 to 0.91 when atmospheric WV content increased from 0 to 6 g/cm2 and thus hampered the NIR reflectance by 14% as compared to reference signal. A significant improvement of the order of 6.5
to 12% in the NIR reflectance and 4.2 to 7% in NDVI was observed, when IRS NIR channel was split into NIR1 (0.775–0.805 μm)
and NIR2 (0.845–0.875 μm) channels by avoiding the WV absorption features. The companion paper in this issue (Pandya et al.
2011) will support results of this simulation study through the EO1-Hyperion data analysis. 相似文献