全文获取类型
收费全文 | 181篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 18篇 |
地球物理 | 38篇 |
地质学 | 75篇 |
海洋学 | 5篇 |
天文学 | 26篇 |
综合类 | 2篇 |
自然地理 | 3篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 22篇 |
2015年 | 5篇 |
2014年 | 20篇 |
2013年 | 13篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 4篇 |
2007年 | 9篇 |
2006年 | 3篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1997年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 10篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有192条查询结果,搜索用时 15 毫秒
81.
Port Okha coast, which is known for its luxuriant growth of a diverse assemblage of seaweeds on Saurashtra coast, is found
to have abundant quantities of seaweeds being drifted and washed ashore every year. Studies conducted for quantifying the
stranded seaweeds from May 2004 to April 2005 showed an average biomass value of 3.10 kg fresh wt/m2/month with maximum being 6.60 kg fresh wt/m2 in April. The stranded weeds constituted a total of 62 species during the entire study period. Of this, Rhodophyta ranked
high with 26 species followed by Chlorophyta with 22 species and Phaeophyta with 14 species. The stranded seaweeds that were
washed ashore provide valuable floristic information about the intertidal and near shore sub-tidal algae of the respective
regions. Although natural senescence of seaweeds is one of the major factors, strong currents primarily forced by tides, also
contribute to the uprooting and subsequent drifting of seaweeds on to the beach. This ultimately causes changes in floristic
features of the existing algal beds. 相似文献
82.
83.
84.
Modeling of tide–aquifer interaction plays a vital role in the management of coastal aquifer systems. A novel and robust methodology is presented in this paper for estimating aquifer parameters of coastal aquifers from tide–aquifer interaction data using tide–aquifer interaction model and genetic algorithm (GA). Two stand-alone computer programs were developed to optimize hydraulic diffusivities of unconfined and confined coastal aquifers at multiple sites using GA technique and tide–aquifer interaction model and considering two approaches (‘lumped tidal component approach’ and ‘multi-tidal component approach’). Five sets of real-world tide–aquifer interaction data at two sites of an unconfined aquifer and one set of tide–aquifer interaction data at three sites of a confined aquifer were used to demonstrate the efficacy of the methodology. The analysis of the GA-based inverse modeling results indicated that the ‘multi-tidal component approach’ yields more accurate and reliable hydraulic diffusivities for the unconfined aquifer (RMSE = 0.0129–0.0521 m, NSE = 0.70–0.97, and d1 = 0.91–0.99) as well as for the confined aquifer (RMSE = 0.0204–0.0545 m, NSE = 0.95–0.97, and d1 = 0.99) compared with the ‘lumped tidal component approach’. A comparative evaluation of data-size revealed that the short-duration datasets of the unconfined aquifer provide more reliable estimate of hydraulic diffusivity than the long-duration datasets. Further, it was found that the spring and neap tidal data yield unreasonable values of hydraulic diffusivity with considerably high values of RMSE and very low values of r 2, NSE, and d1, thereby suggesting that spring and neap tidal data are not suitable for aquifer parameter estimation. Overall, it is concluded that the GA-based tide–aquifer interaction model following ‘multi-tidal component approach’ is the most efficient tool for estimating aquifer parameters of unconfined and confined aquifers from tide–aquifer interaction data. The developed methodology is also applicable to other coastal basins of the world irrespective of hydrogeological settings. 相似文献
85.
Abstract— A simple granular flow model is used to investigate some of the conditions under which ejecta may flow as a granular media. The purpose of this investigation is to provide some bounds as to when either volatiles or an atmosphere are required to explain the fluid‐like morphology of many Martian ejecta deposits. We consider the ejecta deposition process from when an ejecta curtain first strikes a target surface via ballistics and possibly flows thereafter. A new finding is that either hard‐smooth surfaces or slightly erodible surfaces allow ejecta to flow readily as a granular medium. Neither volatiles nor an atmosphere are required to initiate flow. A low friction coefficient between ejecta grains can also generate flow and would be analogous to adding volatiles to the ejecta. The presence of either a rough or a densely packed erodible surface does not permit easy ejecta flow. High friction coefficients between ejecta grain also prevent flow, while changes in the coefficient of restitution (a measure of how much energy is retained after collisions between particles) plays a minor role in the flow dynamics of ejecta. A hard smooth or a somewhat erodible surface could be generated by past fluvial activity on Mars, which can either indurate a surface, erode and smooth a surface, or generate sedimentary terrains that are fairly easy to erode. No ramparts or layered ejecta morphologies are generated by our model, but this may be because several simplifying assumptions are used in our model and should not be construed as proof that either volatiles or an atmosphere are required to form fluidized ejecta morphologies. 相似文献
86.
We report the discovery of Early Permian (late Asselian, ∼280–275 Ma) plant fossils and associated palynomorphs from a marine sedimentary sequence of the eastern Karakoram plate, in northern India. These specimens show affinities with those found in marine Lower Gondwana sediments of the Indian subcontinent. This supports the contention that during the Early Permian Period, the Karakoram plate was Peri-Gondwanan. It is suggested to have had an intermediate position between the Indian plate and the Qiangtang–Lhasa microcontinents, at a latitude of about 35° south. 相似文献
87.
Contrasts between cloud condensation nuclei (CCN) spectral volatility (thermal fractionation) measurements in two aircraft
field projects provide insight into the relative contribution of sea salt. During the much more cloudy Rain in Cumulus over
the Ocean (RICO) project there was a high correlation coefficient (R) between refractory (non-volatile) CCN concentrations
(NCCN) and horizontal wind speed (U), especially for low supersaturation (S) NCCN, whereas this R was significantly lower in the nearly cloud free Pacific Aerosol Sulfur Experiment (PASE) project. Volatile
NCCN at all S were uncorrelated with U. Ambient particle concentrations over a broad range of large sizes displayed consistently
high R with U in both projects that was similar to the R of refractory NCCN with U in RICO. The size range of this high R extended down to 0.2 μm in RICO but only down to 9 μm in PASE. In both projects
particle concentrations smaller than these respective sizes were highly correlated with NCCN, at all S in PASE, but mainly with NCCN at high S in RICO. In each project NCCN at all S was uncorrelated with all ambient particle concentrations larger than these same respective sizes. NCCN at all S was also uncorrelated with U in both projects. The contrast in cloudiness between the two projects was responsible
for many of the differences noted between the two projects. The results indicate that the effects of clouds on NCCN play a major role in the relative influence of sea salt on NCCN and ultimately on climate. Sea salt is a minor component of maritime CCN except at high wind speeds especially at low S. 相似文献
88.
Neerja Jha K. Pauline Sabina N. C. Mehrotra 《Journal of the Geological Society of India》2011,77(2):167-174
High fluoride content in the groundwater is reported from parts of the Gad River Basin, Sindhudurg district, coastal Maharashtra,
India. The fluoride content of up to 5 mg/l has been found in the groundwater in laterite, basalt and the Precambrian basement
(gneiss) aquifers in the region. The presence of high fluoride in groundwater well above the permissible levels for consumption
poses a serious health threat to the rural populace in the region. The presence of tourmaline bearing pegmatites in the Precambrian
basement is considered as a potential fluorine source. Deep circulation of fluoride rich groundwater between the latetritised
basalts and the underlying crystalline basement could be responsible for the occurrence of fluoride in both the shallow and
deeper aquifers of the region. 相似文献
89.
The Effects of Attenuation and Site on the Spectra of Microearthquakes in the Shillong Region of Northeast India 总被引:1,自引:0,他引:1
Rajib Biswas Santanu Baruah Dipok K. Bora Aditya Kalita Saurabh Baruah 《Pure and Applied Geophysics》2013,170(11):1833-1848
Microearthquake spectra from the Shillong region are analyzed to observe the effect of attenuation and site on these spectra. The spectral ratio method is utilized to estimate the Q values for both P- and S-waves in the subsurface layer, wherein the ratio of spectral amplitudes at lower and higher frequencies are taken into consideration for three stations at varying epicentral distances. Average estimates of Q P and Q S are 178 and 195. The ratio of Q S to Q P is estimated to be greater than 1 in major parts of the Shillong area, which can be related to the dry crust prevailing in the Shillong region. Typically, the variation in corner frequencies for these spectra is inferred to be characteristic of the site. Simultaneously, observations from spectral content of local earthquakes recorded at two different stations with respect to the reference site yield greater amplification of incoming seismic signals in the frequency range of 2–5 Hz, which is found to be well supported by the existing local lithology pertinent to that region. 相似文献
90.
Sunny Aggarwal Jagjit Singh A. K. S. Jha Man Mohan 《Journal of Astrophysics and Astronomy》2012,33(3):291-301
Semi-relativistic calculations are performed for the photoionization of Fe X (an important coronal ion) from its ground state 3s23p $^{5}(^{2}P^{0}_{3/2})$ and the first two excited states 3s23p $^{5}(^{2}P^{0}_{1/2})$ and 3s3p $^{6}(^{2}S_{1/2})$ using the Breit?CPauli R-matrix method. A lowest 41 state eigenfunction expansion for Fe XI is employed to ensure an extensive treatment of auto ionizing resonances that affect the effective cross-sections. In the present calculations, we have considered all the important physical effects like channel coupling, exchange and short range correlation. The present calculations using the lowest 41 target levels of Fe XI in the LSJ coupling scheme are reported and we expect that the present results should enable more accurate modelling of the emission spectrum of highly excited plasma from the optical to the far UV region. 相似文献