全文获取类型
收费全文 | 247篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 20篇 |
大气科学 | 25篇 |
地球物理 | 40篇 |
地质学 | 95篇 |
海洋学 | 8篇 |
天文学 | 55篇 |
综合类 | 4篇 |
自然地理 | 6篇 |
出版年
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 12篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 13篇 |
2013年 | 17篇 |
2012年 | 5篇 |
2011年 | 14篇 |
2010年 | 8篇 |
2009年 | 17篇 |
2008年 | 6篇 |
2007年 | 6篇 |
2006年 | 11篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有253条查询结果,搜索用时 453 毫秒
171.
Pramoda Kumar Samal Rajib Saha Pankaj Jain John P. Ralston 《Monthly notices of the Royal Astronomical Society》2009,396(1):511-522
Recently, a symmetry-based method to test for statistical isotropy of the cosmic microwave background was developed. We apply the method to template-cleaned 3- and 5-years Wilkinson Microwave Anisotropy Probe - Differencing Assembly maps. We examine a wide range of angular multipoles from 2 < l < 300 . The analysis detects statistically significant signals of anisotropy inconsistent with an isotropic cosmic microwave background in some of the foreground-cleaned maps. We are unable to resolve whether the anomalies have a cosmological, local astrophysical or instrumental origin. Assuming the anisotropy arises due to residual foreground contamination, we estimate the residual foreground power in the maps. For the W -band maps, we also find a highly improbable degree of isotropy we cannot explain. We speculate that excess isotropy may be caused by faulty modelling of detector noise. 相似文献
172.
D. P. K. Banerjee R. K. Das N. M. Ashok 《Monthly notices of the Royal Astronomical Society》2009,399(1):357-368
We present near-infrared photospectroscopy in the H and K bands of the 2006 outburst of the recurrent nova RS Ophiuchi. The observations cover the period between 1 and 94 d after the eruption. The near-infrared light curve is presented. An extensive set of spectra is presented, lines identified and the general characteristics of the spectra discussed. Analysis of the H i line profiles shows the presence of broad wings on both flanks of a strong central component indicating the presence of a bipolar velocity flow in the ejecta. Such a flow is kinematically consistent with the bipolar structure that the object displays in high-resolution spatial images. We discuss the behaviour and origin of the Fe ii lines at 1.6872 and 1.7414 μm that are prominently seen throughout the span of the observations. It is examined and shown that Lyman α and Lyman continuum fluorescence are viable mechanisms to excite these lines. We draw upon the result, that collisional excitation can also contribute in exciting and significantly enhancing the strength of these Fe ii lines, to propose that these lines originate from a site of high particle density. Such a likely site could be the high-density, low-temperature contact surface that should exists in the shock front in between the shocked ejecta and red giant wind. Recombination analysis of the H i lines indicates deviations from case B conditions during most of the span of our observations indicating optical depth effects. It appears likely that the breakout of the shock front had not yet occurred till the end of our observations. An analysis is made of the temporal evolution of the [Si vi ] 1.9641 μm coronal line and another coronal line at 2.0894 μm which is attributed to [Mn xiv ]. Assuming collisional effects to dominate in the hot coronal gas, estimates are made of the ion temperature in the gas. 相似文献
173.
The Kachchh region of Western India is a pericratonic basin experiencing periodic high magnitude earthquakes events. In 2001 a catastrophic seismic event occurred at Bhuj measuring Mw = 7.7. The epicenters of both the 1956 and 2001 earthquakes were along the Kachchh Mainland Fault (KMF), proximal to the eastern end of the Northern Hill Range (NHR). The latter is a topographic expression of an active fault related fold on the hanging wall, and is controlled by a south dipping blind thrust.The present study deals with the eastern sector of NHR and uses optical dating to reconstruct the chronology of tectonically caused incisions. Along the backlimb of the NHR, incision ages on, channel fills and valley fill terraces progressively decrease from 12 ka to 4.3 ka. This age progression along with geomorphic evidences (decrease in topographic relief, drainage capture and drainage migration across the fold nose) suggests an active vertical and lateral fold growth along the KMF. Optical ages suggest that during the Late Holocene, the average uplift rate along the eastern NHR was 10 ± 1 mm/a. Recent GPS based estimates on crustal shortening are 12 mm/a.The KMF and the South Wagad Fault (SWF) represent the bounding faults of a transtensional basin that formed during the initial rifting. This basin is termed as the Samakhiali basin. The compressive stresses on account of structural inversion from normal to reverse phase resulted in lobate-shaped anticlines along KMF and SWF zone. These anticlines subsequently coalesced and formed linked and overlap segments. The present study suggests that eastward lateral deformation across the eastern portion of KMF has continued and has now resulted in its interaction with a left step over transfer fault called the South Wagad Master Fault (SWMF). This implies an increasing transpersional deformation of the Samakhiali basin. We therefore, suggest that the eastward NHR ridge propagation along KMF resulted in the thrust faulting on the south dipping SWMF resulting in the Bhuj 2001 event. The increasing strain on this basin may cause enhanced seismicity in the future along the eastern KMF and Wagad region. 相似文献
174.
P. Vethamony V. M. Aboobacker K. Sudheesh M. T. Babu K. Ashok Kumar 《Natural Hazards》2009,49(2):411-420
The Ministry of Shipping desires to revise the inland vessels’ limit (IVL) notification based on scientific rationale to improve
the safety of vessels and onboard personnel. The Mormugao port region extending up to the Panaji was considered for this pilot
study. Measured winds and wave parameters (AWS and moored buoy) as well as NCEP re-analysis and NCMRWF winds were used for
the analysis and input to regional and local models. The results of wave model were validated with measured significant wave
heights (SWHs) and the comparison shows a good match. The analysis indicates that SWHs do not exceed 2.0 m during non-monsoon
months, and in monsoon months exceed 5.0 m, and even 7.0 m, especially during extreme events. In order to draw IVL contours
for Goa coastal region, local model was set up and nearshore waves were simulated for the period May 2004–May 2005. Based
on the nearshore SWH distribution, IVL contours have been fixed for the Mormugao port and Panaji coastal regions. 相似文献
175.
Changes in soil quality indicators under long-term sewage irrigation in a sub-tropical environment 总被引:3,自引:0,他引:3
Reginald Ebhin Masto Pramod K. Chhonkar Dhyan Singh Ashok K. Patra 《Environmental Geology》2009,56(6):1237-1243
Though irrigation with sewage water has potential benefits of meeting the water requirements, the sewage irrigation may mess
up to harm the soil health. To assess the potential impacts of long-term sewage irrigation on soil health and to identify
sensitive soil indicators, soil samples were collected from crop fields that have been irrigated with sewage water for more
than 20 years. An adjacent rain-fed Leucaena leucocephala plantation system was used as a reference to compare the impact of sewage irrigation on soil qualities. Soils were analyzed
for different physical, chemical, biological and biochemical parameters. Results have shown that use of sewage for irrigation
improved the clay content to 18–22.7%, organic carbon to 0.51–0.86% and fertility status of soils. Build up in total N was
up to 2,713 kg ha−1, available N (397 kg ha−1), available P (128 kg ha−1), available K (524 kg ha−1) and available S (65.5 kg ha−1) in the surface (0.15 m) soil. Long-term sewage irrigation has also resulted a significant build-up of DTPA extractable Zn
(314%), Cu (102%), Fe (715%), Mn (197.2), Cd (203%), Ni (1358%) and Pb (15.2%) when compared with the adjacent rain-fed reference
soil. Soils irrigated with sewage exhibited a significant decrease in microbial biomass carbon (−78.2%), soil respiration
(−82.3%), phosphatase activity (−59.12%) and dehydrogenase activity (−59.4%). An attempt was also made to identify the sensitive
soil indicators under sewage irrigation, where microbial biomass carbon was singled out as the most sensitive indicator. 相似文献
176.
The tandem operation of draglines is in use in some of the major Indian opencast coalmines owing to the favourable geo-mining
conditions, technical suitability, efficiency and economic viability. In view of the importance of tandem operation, the present
study has been undertaken in a large Indian opencast coalmine in order to critically investigate the horizontal and vertical
tandem operation of draglines on moderately strong and high sandstone benches (35–42 m), overlying a 15–18 m thick coal seam.
The study has revealed that although the preparation of balancing diagram for planning of dragline operations is the first
and the most important step, its actual implementation is equally important. Marked discrepancies in the productivity parameters
as envisaged by the balancing diagram and as observed in the field studies, have been investigated and reported. The study
also propounds the importance of appraisal of dragline productivity parameters, such as, cycle time, swing angle, seating
position, availability, utilization, etc., in the field scale. Irrespective of the mode of operation (horizontal or vertical
tandem), the study moots the concept of computation of the weighted cycle time and overall cycle time vis-à-vis swing angle
variation for the draglines operating in field. The results drawn from the case study have been discussed in terms of cycle
time computations, annual output computation and evaluation of earthmoving efficiency for the horizontal and vertical tandem
modes of operation. 相似文献
177.
Antony Joseph R. G. Prabhudesai Prakash Mehra V. Sanil Kumar K. V. Radhakrishnan Vijay Kumar K. Ashok Kumar Yogesh Agarwadekar U. G. Bhat Ryan Luis Pradhan Rivankar Blossom Viegas 《Natural Hazards》2011,57(2):293-312
Response of the coastal regions of eastern Arabian Sea (AS) and Kavaratti Island lagoon in the AS to the tropical cyclonic storm `Phyan??, which developed in winter in the south-eastern AS and swept northward along the eastern AS during 9?C12 November 2009 until its landfall at the northwest coast of India, is examined based on in situ and satellite-derived measurements. Wind was predominantly south/south-westerly and the maximum wind speed (U10) of ~16 m/s occurred at Kavaratti Island region followed by ~8 m/s at Dwarka (Gujarat) and ~7 m/s at Diu (located south of Dwarka) as well as two southwest Indian coastal locations (Mangalore and Malpe). All other west Indian coastal sites recorded maximum wind speed of ~5?C6 m/s. Gust factor (i.e., gust-to-speed ratio) during peak storm event was highly variable with respect to topography, with steep hilly stations (Karwar and Ratnagiri) and proximate thick and tall vegetation-rich site (Kochi) exhibiting large values (~6), whereas Island station (Kavaratti) exhibiting ~1 (indicating consistently steady wind). Rainfall in association with Phyan was temporally scattered, with the highest 24-h accumulated precipitation (~60 mm) at Karwar and ~45 mm at several other west Indian coastal sites. Impact of Phyan on the west Indian coastal regions was manifested in terms of intensified significant waves (~2.2 m at Karwar and Panaji), sea surface cooling (~5°C at Calicut), and moderate surge (~50 cm at Verem, Goa). The surface waves were south-westerly and the peak wave period (T p) shortened from ~10?C17 s to ~5?C10 s during Phyan, indicating their transition from the long-period `swell?? to the short-period `sea??. Reduction in the spread of the mean wave period (T z) from ~5?C10 s to a steady period of ~6 s was another manifestation of the influence of the cyclone on the surface wave field. Several factors such as (1) water piling-up at the coast supported by south/south-westerly wind and seaward flow of the excess water in the rivers due to heavy rains, (2) reduction of piling-up at the coast, supported by the upstream penetration of seawater into the rivers, and (3) possible interaction of upstream flow with river run-off, together resulted in the observed moderate surge at the west Indian coast. Despite the intense wind forcing, Kavaratti Island lagoon experienced insignificantly weak surge (~7 cm) because of lack of river influx and absence of a sufficiently large land boundary required for the generation and sustenance of wave/wind-driven water mass piling-up at the land?Csea interface. 相似文献
178.
Trace fossils namely, Planolites, Planolites montanus, Thalassinoides and stuff burrows belonging to the Lameta Formation of Central India are reported for the first time from two new localities, i.e., Salbardi and Belkher area. Both the exposures are well represented by the typical marker lithounits as of Jabalpur, Nand-Dongargaon area of central India, i.e., greenish yellow sandstone, clays of various shades, chertified and brecciated limestones, etc. These successions are devoid of megaforal remains, therefore, these biogenic structures play a significant role in the interpretation of palaeoenvironment and palaeoecology during the deposition of the Lameta sediments. The trace fossils assemblage shows that the benthonic community was mainly polychaetes and crustaceans. 相似文献
179.
Blesson Mathew Watson P. Varricatt Annapurni Subramaniam N. M. Ashok D. P. K. Banerjee 《中国天文和天体物理学报》2014,(9)
We present optical and infrared photometric and spectroscopic studies of two Be stars in the 70–80-Myr-old open cluster NGC 6834. NGC 6834(1) has been reported as a binary from speckle interferometric studies whereas NGC 6834(2) may possibly be a γ Cas-like variable. Infrared photometry and spectroscopy from the United Kingdom Infrared Telescope(UKIRT), and optical data from various facilities are combined with archival data to understand the nature of these candidates.High signal-to-noise near-IR spectra obtained from UKIRT have enabled us to study the optical depth effects in the hydrogen emission lines of these stars. We have explored the spectral classification scheme based on the intensity of emission lines in the H and K bands and contrasted it with the conventional classification based on the intensity of hydrogen and helium absorption lines. This work also presents hitherto unavailable UBV CCD photometry of NGC 6834, from which the evolutionary state of the Be stars is identified. 相似文献
180.
The Hydrologic Simulation Programme‐Fortran (HSPF), a hydrologic and water quality computer model, was employed for simulating runoff and sediment yield during the monsoon months (June–October) from a small watershed situated in a sub‐humid subtropical region of India. The model was calibrated using measured runoff and sediment yield data for the monsoon months of 1996 and was validated for the monsoon months of 2000 and 2001. During the calibration period, daily‐calibrated runoff had a Nash‐Sutcliffe efficiency (ENS) value of 0·68 and during the validation period it ranged from 0·44 to 0·67. For daily sediment yield ENS was 0·71 for the calibration period and it ranged from 0·68 to 0·90 for the validation period. Sensitivity analysis was performed to assess the impact of important watershed characteristics. The model parameters obtained in this study could serve as reference values for model application in similar climatic regions, with practical implications in watershed planning and management and designing best management practices. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献