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81.
In this study,we evaluate the forecast skill of the subseasonal-to-seasonal(S2S)prediction model of the Beijing Climate Center(BCC)for the boreal summer intraseasonal oscillation(BSISO).We also discuss the key factors that inhibit the BSISO forecast skill in this model.Based on the bivariate anomaly correlation coefficient(ACC)of the BSISO index,defined by the first two EOF modes of outgoing longwave radiation and 850-hPa zonal wind anomalies over the Asian monsoon region,we found that the hindcast skill degraded as the lead time increased.The ACC dropped to below 0.5for lead times of 11 days and longer when the predicted BSISO showed weakened strength and insignificant northward propagation.To identify what causes the weakened forecast skill of BSISO at the forecast lead time of 11 days,we diagnosed the main mechanisms responsible for the BSISO northward propagation.The same analysis was also carried out using the observations and the outputs of the four-day forecast lead that successfully predicted the observed northward-propagating BSISO.We found that the lack of northward propagation at the 11-day forecast lead was due to insufficient increases in low-level cyclonic vorticity,moistening and warm temperature anomalies to the north of the convection,which were induced by the interaction between background mean flows and BSISO-related anomalous fields.The BCC S2S model can predict the background monsoon circulations,such as the low-level southerly and the northerly and easterly vertical shears,but has limited capability in forecasting the distributions of circulation and moisture anomalies. 相似文献
82.
《The Journal of geography》2012,111(4):150-162
Abstract This article presents research on evaluating problem-based learning using GIS technology in a Singapore secondary school. A quasi-experimental research design was carried to test the PBL pedagogy (PBL-GIS) with an experimental group of students and compare their learning outcomes with a control group who were exposed to PBL but not GIS. The results show significant differences in the learning outcomes between the two groups. Specifically, students in the control group show more memorization skill while students in the experimental group demonstrate more analytical and evaluation skills. The conclusion is that learning with PBL-GIS pedagogy can result in higher-order learning outcomes. 相似文献
83.
关于避免中国交通建设过度超前的建议 总被引:3,自引:0,他引:3
这里发表的是经过2009-2010年间大量调查研究和分析写成的咨询报告全文(原文)。“报告”于2010年9月由有关部门上报到国家。“报告”对近年来交通建设成就和交通运输业发展已经达到的水平进行了概括性评价,集中而系统地揭示了近年来全国范围内交通运输建设中出现的过度扩张、重复建设、能力浪费、不合理竞争以及各种运输方式之间... 相似文献
84.
85.
煤层气渗流理论及其研究进展 总被引:1,自引:0,他引:1
综述了煤层气渗流研究的现状及取得的研究进展,包括线性渗透、线性扩散、扩散—渗透以及非线性渗流等基本理论,基于各种地球物理场效应影响的渗流理论及其修正模型,以及多煤层瓦斯越流相关的研究;并介绍了新兴的数值计算方法(格子Boltzmann方法与分子动力学方法)在煤层瓦斯渗流模拟中的应用;展望了其发展趋势及尚需深入研究的问题。 相似文献
86.
本文对广东省西部沿海高速公路新会四标段管涵的反开挖施工中常见问题进行了探讨,提出了判定开挖时间的方法,并论述了开挖边坡坡度,基底承载力大小以及反开挖施工合理性问题。 相似文献
87.
The present study describes an analysis of Asian summer monsoon forecasts with an operational general circulation model (GCM)
of the European Centre for Medium Range Weather Forecasts (ECMWF), U.K. An attempt is made to examine the influence of improved
treatment of physical processes on the reduction of systematic errors. As some of the major changes in the parameterization
of physical processes, such as modification to the infrared radiation scheme, deep cumulus convection scheme, introduction
of the shallow convection scheme etc., were introduced during 1985–88, a thorough systematic error analysis of the ECMWF monsoon
forecasts is carried out for a period prior to the incorporation of such changes i.e. summer monsoon season (June–August)
of 1984, and for the corresponding period after relevant changes were implemented (summer monsoon season of 1988).
Monsoon forecasts of the ECMWF demonstrate an increasing trend of forecast skill after the implementation of the major changes
in parameterizations of radiation, convection and land-surface processes. Further, the upper level flow is found to be more
predictable than that of the lower level and wind forecasts display a better skill than temperature. Apart from this, a notable
increase in the magnitudes of persistence error statistics indicates that the monsoon circulation in the analysed fields became
more intense with the introduction of changes in the operational forecasting system.
Although, considerable reduction in systematic errors of the Asian summer monsoon forecasts is observed (up to day-5) with
the introduction of major changes in the treatment of physical processes, the nature of errors remain unchanged (by day-10).
The forecast errors of temperature and moisture in the middle troposphere are also reduced due to the changes in treatment
of longwave radiation. Moreover, the introduction of shallow convection helped it further by enhancing the vertical transports
of heat and moisture from the lower troposphere. Though, the hydrological cycle in the operational forecasts appears to have
enhanced with the major modifications and improvements to the physical parameterization schemes, certain regional peculiarities
have developed in the simulated rainfall distribution over the monsoon region. Hence, this study suggests further attempts
to improve the formulations of physical processes for further reduction of systematic forecast errors. 相似文献
88.
1993年,我国金属矿地球物理工作继续缩减。航空物探工作量仅及1988年的1/3.油气地球物理工作持续增长,其中陆上三维地震年工作量已超过9000km2.水文、工程、环境地球物理市场保持兴旺,推动了有关技术的发展,众多单位不断推出新型号的多功能浅层地震仪式工程检测仪。较少受经费制约的室内计算机处理、解释、模拟、显示方法及软件研究,以及某些理论研究保持前进势头,又有一些引人注意的成果。承担国际市场项目有所增多,但总规模仍然很小。 相似文献
89.
Quantitative precipitation forecasting (QPF) has been attempted over the Narmada Catchment following a statistical approach.
The catchment has been divided into five sub-regions for the development of QPF models with a maximum lead-time of 24 hours.
For this purpose the data of daily rainfall from 56 raingauge stations, twice daily observations on different surface meteorological
parameters from 28 meteorological observatories and upper air data from 11 aerological stations for the nine monsoon seasons
of 1972–1980 have been utilized. The horizontal divergence, relative vorticity, vertical velocity and moisture divergence
are computed using the kinematic method at different pressure levels and used as independent variables along with the rainfall
and surface meteorological parameters. Multiple linear regression equations have been developed using the stepwise procedure
separately with actual and square root and log-transformed rainfall using 8-year data (1972–1979). When these equations were
verified with an independent data for the monsoon season of 1980, it was found that the transformed rainfall equations fared
much better compared to the actual rainfall equations. The performance of the forecasts of QPF model compared to the climatological
and persistence forecasts has been assessed by computing the verification scores using the forecasts for the monsoon season
of 1980. 相似文献
90.
Between 1973 and 1986 a group at the University of Wisconsin worked on the use of the periodic portion of climatic time series
with the aim of exploring the potential for year-or-more in advance forecasting. This paper reports on the real time verification
of the last sets of forecasts made by the group.
From spectra of temperature and cube-rooted precipitation the dominant frequencies were chosen. These were usually related
to tidal frequencies. A Fourier series of these dominant terms was then fitted to the dependent data set and future values
calculated. These were analyzed for forecast skill, and the skillful Fourier series retained. Real time forecasts were then
made. Verification shows a low probability that the forecast skills were obtained by chance. It is suggested that the periodic
term might be a useful addition to more standard approaches to long range forecasting. 相似文献