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31.
The results presented in this paper shows that high concentrations of sodium hydroxide causes abnormal changes on the volume
change behaviour of illite–smectite (interstratified mineral) soil due to mineralogical changes. The higher swell that occurs
is shown in the form of a new second stage of swelling. Increase in negative charges on soil particles and mineralogical changes
after interaction with soil, respectively, are responsible for the swelling in these two stages. However, potassium hydroxide
does not induce such high swelling in soils. This is mainly due to the fixation of potassium ions. Hence an attempt has been
made to control the swelling induced by sodium hydroxide by making used of potassium chloride as an additive. Potassium fixation
which is not substantial at neutral pH is favoured at higher pH Addition of potassium chloride salt solution (as 2 and 5%
solution) can reduce only the first stage of swelling by linking the unit layers of mineral by reducing development diffuse
double layer near clay surface. Potassium chloride is unable to prevent the formation of mineralogical alteration due to soil
alkali interaction and hence the swelling associated with mineralogical changes. X-ray diffraction studies have revealed that
mineralogical changes leading to formation of zeolite by soil alkali interaction is not inhibited by potassium ions. Morphological
changes studied by scanning electron microscope corroborate these observations. Also the compressibility of soil which is
increased in alkali solution is reduced in the presence of potassium salts. This reduction is due to reduction in the first
stage of swelling. 相似文献
32.
Using a laboratory gamma-ray spectrometer, 160 rock samples from different heat flow sites in India have been analysed for their U, Th and K contents. Heat generation has been estimated for the significant rock types. Of the six regions covered by this study, correction due to heat generation contrast and geologic structure was found necessary and has been applied in two regions. Heat flow/heat generation plots for two regions in the southernmost part of the shield follow the line characteristic of a normal continental heat flow province. The plots for the other four regions indicate a heat flow province with an intercept of 0.92 HFU and a slope of 14.8 km. From data available at present, these parameters are higher compared to those from the other shields. The higher parameters imply a higher temperature and heat flow at the Moho, indicating a region of “hotter” upper mantle in the Indian shield. 相似文献
33.
It has been demonstrated that VHF/UHF scintillation data can be used to evaluate important physical parameters such as scale sizes, strength, growth and decay of irregularities in the equatorial ionosphere. These parameters are important in constructing electroject models. It is shown that large scale irregularities are generated first which later break into smaller scale sizes. During the decay phase, the small scale irregularities disappear first after followed by large scale irregularities. The generation and destruction time of these irregularities has been estimated to be around 20 min. In addition these irregularities affect propagation of radio waves from HF to UHF range which suggests the existence of a wide spectrum of irregularities in the ionosphere. It has been found that the scale sizes of daytimeE-region irregularities are smaller than those in theF-region during night-time. The growth rate of the irregularities seems to be larger in theE-region than in theF-region of the ionosphere. 相似文献
34.
A new model of a Gaussian ionospheric irregularity with perturbation is studied. Analysis of two events of diffraction of ATS-6 radio signals on 40, 140 and 360 MHz by isolated ionospheric irregularities indicates that while one class of events is well described in terms of diffraction by a Gaussian irregularity, the other class of events necessitates the assumption of a more complex irregularity structure. General characteristics of diffraction patterns due to a minor Gaussian perturbation within a larger irregularity are discussed, and an attempt has been made to deduce the structure of the second observed irregularity on the basis of these characteristics. The result suggests the possibility of a distorted double-humped electron density distribution in the irregularity. 相似文献
35.
C. V. Srinivas R. Venkatesan N. V. Muralidharan Someshwar Das Hari Dass P. Eswara Kumar 《Journal of Earth System Science》2006,115(3):315-332
An operational atmospheric dispersion prediction system is implemented on a cluster supercomputer for Online Emergency Response
at the Kalpakkam nuclear site. This numerical system constitutes a parallel version of a nested grid meso-scale meteorological
model MM5 coupled to a random walk particle dispersion model FLEXPART. The system provides 48-hour forecast of the local weather
and radioactive plume dispersion due to hypothetical airborne releases in a range of 100 km around the site. The parallel
code was implemented on different cluster configurations like distributed and shared memory systems. A 16-node dual Xeon distributed
memory gigabit ethernet cluster has been found sufficient for operational applications. The runtime of a triple nested domain
MM5 is about 4 h for a 24 h forecast. The system had been operated continuously for a few months and results were ported on
the IMSc home page.
Initial and periodic boundary condition data for MM5 are provided by NCMRWF, New Delhi. An alternative source is found to
be NCEP, USA. These two sources provide the input data to the operational models at different spatial and temporal resolutions
using different assimilation methods. A comparative study on the results of forecast is presented using these two data sources
for present operational use. Improvement is noticed in rainfall forecasts that used NCEP data, probably because of its high
spatial and temporal resolution 相似文献
36.
Rotational Modulation of Microwave Solar Flux 总被引:1,自引:0,他引:1
Time series data of 10.7 cm solar flux for one solar cycle (1985–1995 years) was processed through autocorrelation. Rotation modulation with varying persistence and period was quite evident. The persistence of modulation seems to have no relation with sunspot numbers. The persistence of modulation is more noticeable during 1985–1986, 1989–1990, and 1990–1991. In other years the modulation is seen, but its persistence is less. The sidereal rotation period varies from 24.07 days to 26.44 days with no systematic relation with sunspot numbers. The results indicate that the solar corona rotates slightly faster than photospheric features. The solar flux was split into two parts, i.e., background emission which remains unaffected by solar rotation and the localized emission which produces the observed rotational modulation. Both these parts show a direct relation with the sunspot numbers. The magnitude of localized emission almost diminishes during the period of low sunspot number, whereas background emission remains at a 33% level even when almost no sunspots may be present. The localized regions appear to shift on the solar surface in heliolongitudes. 相似文献
37.
Hari Prasad PANDEY 《资源与生态学报(英文版)》2021,12(1):1-10
全球近四分之三的森林正在遭受人为干扰,尼泊尔三分之二以上的森林受到不同类型的干扰。在社区森林中,当地社区在生计的各个方面都依赖于森林提供的生态系统服务,这些服务以各种方式干扰森林的自然条件和生态系统的功能。本研究在尼泊尔中部丘陵区的两个社区管理森林中,研究了对植物物种多样性、更新(幼苗和树苗)、生物量、土壤有机碳(SOC)和总碳密度的主要干扰因子。以树桩数、断苗、砍伐和放牧践踏作为主要人为干扰的衡量指标,从89个随机选取的250 m2的样地中收集了必要的数据,利用广义线性模型(GLM)对人为干扰的响应进行了分析。结果表明,森林砍伐对生物量和总碳密度平衡的影响最大。森林砍伐程度越高,森林碳储量越低。SOC对上述类型的人为干扰均无显著反应。木本物种丰富度和幼树数量随着树桩数量的增加而增加,说明中间干扰是有益的。然而,较高的砍伐强度降低了幼树密度。放牧/践踏是抑制幼苗生长的最显著干扰,在践踏强度较高的森林地区,幼苗和树苗数量较少。这些结果将为尼泊尔多目标森林管理以及如何降低其他地区类似社会经济环境中的人为干扰的影响提供指南。 相似文献
38.
Wirasatriya Anindya Kawamura Hiroshi Helmi Muhammad Sugianto Denny Nugroho Shimada Teruhisa Hosoda Kohtaro Handoyo Gentur Putra Yoppik Disma Girindra Koch Magaly 《Ocean Dynamics》2020,70(6):771-786
Ocean Dynamics - The short-lived events of high SST are called hot events (HEs) and can only be generated under the conditions of large daily heat gain due to strong solar radiation and weak wind.... 相似文献
39.
Sea-breeze-initiated rainfall over the east coast of India during the Indian southwest monsoon 总被引:1,自引:0,他引:1
Matthew Simpson Hari Warrior Sethu Raman P. A. Aswathanarayana U. C. Mohanty R. Suresh 《Natural Hazards》2007,42(2):401-413
Sea-breeze-initiated convection and precipitation have been investigated along the east coast of India during the Indian southwest
monsoon season. Sea-breeze circulation was observed on approximately 70–80% of days during the summer months (June–August)
along the Chennai coast. Average sea-breeze wind speeds are greater at rural locations than in the urban region of Chennai.
Sea-breeze circulation was shown to be the dominant mechanism initiating rainfall during the Indian southwest monsoon season.
Approximately 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to convection
initiated by sea-breeze circulation. 相似文献
40.
Sensitivity of tropical cyclone intensification to boundary layer and convective processes 总被引:1,自引:1,他引:1
This study examines the role of the parameterization of convection, planetary boundary layer (PBL) and explicit moisture processes
on tropical cyclone intensification. A high-resolution mesoscale model, National Center for Atmospheric Research (NCAR) model MM5,
with two interactive nested domains at resolutions 90 km and 30 km was used to simulate the Orissa Super cyclone, the most
intense Indian cyclone of the past century. The initial fields and time-varying boundary variables and sea surface temperatures
were taken from the National Centers for Environmental Prediction (NCEP) (FNL) one-degree data set. Three categories of sensitivity
experiments were conducted to examine the various schemes of PBL, convection and explicit moisture processes. The results
show that the PBL processes play crucial roles in determining the intensity of the cyclone and that the scheme of Mellor-Yamada
(MY) produces the strongest cyclone. The combination of the parameterization schemes of MY for planetary boundary layer, Kain-Fritsch2
for convection and Mixed-Phase for explicit moisture produced the best simulation in terms of intensity and track. The simulated
cyclone produced a minimum sea level pressure of 930 hPa and a maximum wind of 65 m s−1 as well as all of the characteristics of a mature tropical cyclone with an eye and eye-wall along with a warm core structure.
The model-simulated precipitation intensity and distribution were in good agreement with the observations. The ensemble mean
of all 12 experiments produced reasonable intensity and the best track. 相似文献