首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   172篇
  免费   3篇
  国内免费   5篇
测绘学   26篇
大气科学   7篇
地球物理   18篇
地质学   80篇
海洋学   9篇
天文学   30篇
综合类   3篇
自然地理   7篇
  2024年   1篇
  2022年   4篇
  2021年   6篇
  2020年   1篇
  2019年   5篇
  2018年   11篇
  2017年   10篇
  2016年   13篇
  2015年   10篇
  2014年   7篇
  2013年   13篇
  2012年   8篇
  2011年   8篇
  2010年   6篇
  2009年   7篇
  2008年   4篇
  2007年   8篇
  2006年   5篇
  2005年   6篇
  2004年   1篇
  2002年   1篇
  2001年   2篇
  2000年   1篇
  1999年   3篇
  1996年   1篇
  1995年   2篇
  1994年   1篇
  1993年   2篇
  1992年   3篇
  1991年   1篇
  1990年   3篇
  1989年   1篇
  1988年   3篇
  1987年   1篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1982年   5篇
  1981年   2篇
  1980年   3篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1974年   2篇
  1973年   1篇
  1964年   1篇
排序方式: 共有180条查询结果,搜索用时 95 毫秒
51.
In the present study, behavior of the SARAL/AltiKa (Satellite with ARgos and ALtiKa) waveforms over Maithon Reservoir (~65 km2 of surface area), Jharkhand, India, has been studied. The estimated water level has been compared with the in situ measurements at hydro-gauging station at the dam site. The problem of minimization of errors in the water level retrieval from AltiKa measurements has been resolved by improvement of the retracking method. A real retracking gate detection algorithm based on statistical analysis harnessing various physical parameters of the waveform has been developed, which has been applied to SARAL/AltiKa waveforms over the Maithon reservoir. Comparing the in-situ measurements with altimetry data (from cycle 1, 19 March 2013 to cycle 12, 8 April 2014) showed that it is crucial to improve the retracking method. Results showed accuracy of water level monitoring increased by nearly 76% by the newly developed waveform retracking algorithm over non-retracked water level. We also compared this new method with the existing ice-1 algorithm and found that with the new method there is improvement of ~27% over ice-1 retracked water level. The correlation coefficient values and root mean square values without retracking, with ice-1 algorithm and with newly developed retracking algorithm were 0.87, 0.91, and 0.95, and 8.12 cm, 2.08 cm, and 1.42 cm, respectively. This shows the proposed retracker performed better than ice-1. The retracking procedure helped in outliers' identification and substitution and with waveform fitting and waveform parameter extraction. This algorithm should have good performance capability for retrieving water level over inland water bodies like Maithon reservoir.  相似文献   
52.
Summary Mineralogical characteristics of eclogite xenoliths from three kimberlite pipes (KL2, P2 and P10) of the Proterozoic Wajrakarur kimberlite field of southern India have been studied. In a rare sample of enstatite eclogite from the KL2 pipe garnet contains microscopic triangular arrays of needles or blebs of omphacite, enstatite and rutile consistent with an origin by exsolution parallel to the isometric form {111}. Discrete omphacite grains in the sample contain exsolved needles or blebs of enstatite and garnet. Kyanite eclogites are abundant in the KL2 pipe which occasionally show a secondary ring of pure celsian around kyanite grains. Omphacite Na2O contents in the eclogites of the KL2 and P2 pipes are typically between 3 and 6 wt%, and garnet has widely variable composition with end member ranges of Prp22-81Grs0-47Alm10-30Sps0-1Adr0-5Uv0-3. Eclogites of the P10 pipe comprise chromian omphacite and garnet. Phase relations in the ACF projection exhibit systematic increase of the Ca-Tschermak’s component in omphacite from enstatite eclogite through biminerallic eclogite to kyanite eclogite. Garnet-clinopyroxene Fe–Mg geothermometry yields temperatures mostly in the range of 900–1100 °C. A formerly supersilicic nature of garnet in enstatite eclogite as inferred from exsolution mineralogy indicates minimum peak pressure of 5 GPa.  相似文献   
53.
The aerial remote sensing data can be reliable source to obtain an estimate of urban population. A study was carried out in the city of Coimbatore (municipal area) using aerial photoghraphs of scale 1:4000 taken by a metric camera of 300 mm. focal length in the year 1979. The findings obtained by photo-interpretation compared very favourably with the interpolated population census figures for the year 1979, for the municipal area of the city Coimbatore. Dwelling units counted on the aerial photograph for different types of residential areas classified on the basis of size, shape and pattern are the physical indicators of population. Occupancy rate of dwelling units was determined by sampling survey carried out during field visit itself in this particular study.  相似文献   
54.
Abundance ratios in QSOs Q 1246-057, 0453-423, PKS 0528-250, Q 0002-422, and PKS 2126-158 have been calculated by the method of curve of growth. Relative abundance of carbon with respect to silicon has been calculated in the QSOs Q 1246-057, PKS 0528-250, Q 0002-422, and PKS 2126-158. Relative abundance of aluminium with respect to silicon has been calculated in the QSOs PKS 0528-250 and PKS 2126-158. Relative abundance of iron with respect to magnesium has been also calculated in the QSOs Q 0453-423 and Q 0002-422. The ratiosN(C)/N(Si) andN(Al)/N(Si) andN(Fe)/N(Mg) in QSOs considered as a class are 3.45±2.33, 0.063±0.054, and 1.08±0.70, respectively.The ratiosN(C)/N(Si) andN(Al)/N(Si) show a mild trend of increase with decreasing emission redshift. On the other hand, the ratioN(Fe)/N(Mg) shows a mild trend of decrease with decreasing emission redshift. This suggests the possibility of the chemical evolution of QSOs.The comparison ofN(C)/N(Si), the relative abundance of carbon-one of the four most plentiful elements — with respect to silicon in QSOs and normal galaxies suggests that QSOs might belong to an early phase in the evolutionary sequence of galaxies and that they evolve chemically into normal galaxies in course of time.Mrs. Alpana Gangopadhyaya after marriage.  相似文献   
55.
This study presents a novel contrast-based classification algorithm for Synthetic Aperture Radar image. The proposed algorithm primarily analyses homogeneous and non-homogeneous patterns within the moving window. The points which are either significantly brighter or darker than the central pixel are considered as non-homogeneous patterns. While the points, moderately equal to central pixel are described as homogeneous patterns. The mean intensity values of homogeneous and non-homogeneous regions are used thereafter for measuring the contrast around the central pixel of the moving window. The ISODATA algorithm is used to classify the contrast transformed image. The importance of this method is that it is computationally simple, works with minimum human interaction and robust to speckle noise. The validation of the method is done on RISAT (Radar Imaging Satellite) data.  相似文献   
56.
Sponges alter the proportion of structural and morphological components such as spicule skeleton and number of oscula in response to environment, development and growth. Such mechanisms indicate morphological and physiological variations within populations. We measured the pumping rate of different sized specimens of contractile sponge Cinachyrella cf. cavernosa present in the intertidal rock pools, during morning and afternoon low tides along the central west coast of India. Additionally, we measured the exhalant opening (oscular cross‐sectional area—OSA), tissue density, spicule skeleton weight and the abundance of choanocyte chambers to assess the morphological variations. Water temperature and sponge size showed a significant positive effect on pumping rate. OSA and the number of oscula increased with sponge size, but the sponge volume‐specific pumping rate did not increase (0.029 ± 0.020 ml/s ml‐1). Histological sections showed the abundance of chaonocyte chambers increased marginally with the sponge size, but the contraction state affected the count. Both tissue density and spicule skeleton weight were positively correlated with sponge size, particularly the increase in the size and number of spicule bundles radiating from the centre indicated a denser core in larger specimens. The subcortical lacunae and the peripheral choanosome with high abundance of canals appear to be the major volume reduction zones during contraction events. Our results indicate that the size and number of spicule bundles increase with sponge volume and the variation in temperature, contraction state, and size and number of oscula influence the pumping rate of C. cf. cavernosa.  相似文献   
57.
58.
In the hilly region due to scarcity of the plain area, buildings like set back-step back are more often used and also as a big surge in the telecommunication industries, rooftop tower adaptation is very common story nowadays. In the present study an analogy has been drawn to find out the influence of the rooftop telecommunication tower on the setback-step back building resting on ground at 20° and 30° slopes. A dynamic analysis has been performed and compared on the 4 legged angled section telecommunication tower which is located on the roof top of set back-step back building by varying positions of tower with the existing host structure built up on ground slope of 20° and 30° in both directions(X and Y).  相似文献   
59.
This report examines the problem involving the pumping of groundwater from a group of 90 existing wells along the banks of the Yamuna River, northwest of Delhi (India), underlain with geologically occurring saline water. It is known that unregulated pumping will lead to upconing of saline water and therefore it is necessary to determine optimal rates and associated well locations (from an existing group of candidate wells that supply drinking water to the city of Delhi) that will minimize the total salinity. The nonlinear, non-convex problem is solved by embedding the calibrated groundwater model within a simulation-optimisation (S/O) framework. Optimisation is accomplished by using simulated annealing (SA), a search algorithm. The computational burden is primarily managed by replacing the numerical model with a surrogate simulator-artificial neural network (ANN). The model is applied to the real system to determine the optimal pumping schedule. The results of the operational model suggest that the skimming wells must be operated from optimal locations such that they are staggered in space and time to obtain the least saline water.  相似文献   
60.
Forecasting of rainfall and subsequent river runoff is important for many operational problems and applications related to hydrology. Modeling river runoff often requires rigorous mathematical analysis of vast historical data to arrive at reasonable conclusions. In this paper we have applied the stochastic method to characterize and predict river runoffofthe perennial Kulfo River in southem Ethiopia. The time series analysis based auto regressive integrated moving average (ARIMA) approach is applied to mean monthly runoff data with 10 and 20 years spans. The varying length of the input runoff data is shown to influence the forecasting efficiency of the stochastic process. Preprocessing of the runoff time series data indicated that the data do not follow a seasonal pattern. Our forecasts were made using parsimonious non seasonal ARIMA models and the results were compared to actual 10-year and 20-year mean monthly runoff data of the Kulfo River. Our results indicate that river runoff forecasts based upon the 10-year data are more accurate and efficient than the model based on the 20-year time series.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号