全文获取类型
收费全文 | 489篇 |
免费 | 39篇 |
国内免费 | 56篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 108篇 |
地球物理 | 128篇 |
地质学 | 156篇 |
海洋学 | 62篇 |
天文学 | 61篇 |
综合类 | 11篇 |
自然地理 | 36篇 |
出版年
2024年 | 4篇 |
2023年 | 6篇 |
2022年 | 12篇 |
2021年 | 9篇 |
2020年 | 16篇 |
2019年 | 27篇 |
2018年 | 23篇 |
2017年 | 25篇 |
2016年 | 30篇 |
2015年 | 18篇 |
2014年 | 26篇 |
2013年 | 28篇 |
2012年 | 24篇 |
2011年 | 29篇 |
2010年 | 19篇 |
2009年 | 30篇 |
2008年 | 26篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 25篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有584条查询结果,搜索用时 15 毫秒
11.
Rural Hong Kong contains culturally protected enclaves of remnant woodlands that provide sanctuary for vegetation, wildlife and soil. This study focuses on the influence of natural and cultural factors on soil properties in woodlands with different human activities. At each of the nine selected sites, two pits were dug to collect soil samples for analysis of 24 physical and chemical properties. Analyses of variance between soil attributes and site factors suggest the prominence of woodland size, and important contribution of topography, aspect and parent material. Soil indicators of human impacts and the tenacity of woodland soil towards anthropogenic disturbance were demonstrated. 相似文献
12.
斑井岩体位于徐淮推覆体中北部皇藏峪复背斜北段西翼,由于研究重点和关注度不同,对其成因类型及年代学特征研究较少。故此,本次研究将依托于钻孔XZK01中的7个岩石样品,通过大量的主微量元素地球化学分析及锆石U-Pb年代学分析,深入探讨斑井岩体的成因机制、形成年代及其地质意义。LA-ICP-MS锆石U-Pb年代学分析结果揭示斑井岩体的结晶年龄为126.4Ma±2.1Ma,侵位时代为中生代早白垩世,为地球动力学背景转变期间形成的岩体。本次6个样品的主量元素分析结果中w(SiO2)变化范围为56.54%~59.29%,全碱w(Na2O+K2O)变化范围为4.98%~5.68%,为中性岩;里特曼组合指数σ介于1.77~1.98之间,σ<3.3,属于钙碱性岩。其次,该组样品微量元素w(Sr)介于589×10^-6~728×10^-6之间,平均值为659×10^-6;w(Y)介于11.3×10^-6~12.8×10^-6之间,平均值为12.1×10^-6;w(Yb)介于1.13×10^-6~1.4×10^-6之间,平均值为1.23×10^-6;w(Cr)介于100×10^-6~660×10^-6之间,平均为377×10^-6;Mg#值介于47.17~68.14之间,平均值为58.21。该结果指示斑井岩体具富Sr,Sr/Y,贫Y,Yb的特征,指示其源区具有高压的环境,Mg#的变化特征揭示斑井岩体并非来自下地壳镁铁质岩石部分熔融,且w(Cr)的变化特征指示地幔橄榄岩也可能参与其中。此外,LREE/HREE介于6.91~10.98之间,平均值为8.895;LaN/YbN值在7.68~12.95之间,平均值为10.17,为轻稀土较强富集;大离子亲石元素Rb(23.9×10^-6~44.8×10^-6),K(11373×10^-6~14610.6×10^-6),Ba(513×10^-6~694×10^-6),Th(1.5×10^-6~2.5×10^-6),U(0.51×10^-6~0.79×10^-6)相对富集;高场强元素Nb(3.2×10^-6~4.7×10^-6),Ti(3056.7×10^-6~3536.2×10^-6)等表现出明显负异常。 相似文献
13.
Influencing domain of peripheral sources in the urban heavy pollution process of Beijing 总被引:1,自引:0,他引:1
Multiple cities in a diveloped economic area may consist of a city cluster,and the difusion and mixing of its pollutants result in the effect of pollutants plume between cities and the large-scale regional pollution diffusion phenomenon.The distant transfer and diffusion of pollutants occurs when massive aerosols are affected by the dynamic porcess of large-scale circulations.Research suggesten that the life span of aerosol particles whose diameters are about 1 um is the longest.The longevity … 相似文献
14.
1. Introduction In recent decades, extreme weather events seem to be growing in frequency and risk due to water-related disasters. According to the World Meteorological Or- ganization report (ISDR and WMO, 2004) on World Water Day, 22 March 2004, the economic losses caused by water-related disasters, including floods, droughts and tropical cyclones, are on an increasing trend as follows: the yearly mean in the 1970s was about 131 billion US dollars, 204 billion dollars in the 1980s, and … 相似文献
15.
André Lyra Pablo Imbach Daniel Rodriguez Sin Chan Chou Selena Georgiou Lucas Garofolo 《Climatic change》2017,141(1):93-105
Tropical rainforest plays an important role in the global carbon cycle, accounting for a large part of global net primary productivity and contributing to CO2 sequestration. The objective of this work is to simulate potential changes in the rainforest biome in Central America subject to anthropogenic climate change under two emissions scenarios, RCP4.5 and RCP8.5. The use of a dynamic vegetation model and climate change scenarios is an approach to investigate, assess or anticipate how biomes respond to climate change. In this work, the Inland dynamic vegetation model was driven by the Eta regional climate model simulations. These simulations accept boundary conditions from HadGEM2-ES runs in the two emissions scenarios. The possible consequences of regional climate change on vegetation properties, such as biomass, net primary production and changes in forest extent and distribution, were investigated. The Inland model projections show reductions in tropical forest cover in both scenarios. The reduction of tropical forest cover is greater in RCP8.5. The Inland model projects biomass increases where tropical forest remains due to the CO2 fertilization effect. The future distribution of predominant vegetation shows that some areas of tropical rainforest in Central America are replaced by savannah and grassland in RCP4.5. Inland projections under both RCP4.5 and RCP8.5 show a net primary productivity reduction trend due to significant tropical forest reduction, temperature increase, precipitation reduction and dry spell increments, despite the biomass increases in some areas of Costa Rica and Panama. This study may provide guidance to adaptation studies of climate change impacts on the tropical rainforests in Central America. 相似文献
16.
Kristie?L.?EbiEmail author Jessica?Hartman Nathan?Chan John?Mcconnell Michael?Schlesinger John?Weyant 《Climatic change》2005,73(3):375-393
Climate is one factor that determines the potential range of malaria. As such, climate change may work with or against efforts
to bring malaria under control. We developed a model of future climate suitability for stable Plasmodium falciparum malaria transmission in Zimbabwe. Current climate suitability for stable malaria transmission was based on the MARA/ARMA
model of climatic constraints on the survival and development of the Anopheles vector and the Plasmodium falciparum malaria parasite. We explored potential future geographic distributions of malaria using 16 projections of climate in 2100.
The results suggest that, assuming no future human-imposed constraints on malaria transmission, changes in temperature and
precipitation could alter the geographic distribution of malaria in Zimbabwe, with previously unsuitable areas of dense human
population becoming suitable for transmission. Among all scenarios, the highlands become more suitable for transmission, while
the lowveld and areas with low precipitation show varying degrees of change, depending on climate sensitivity and greenhouse
gas emission stabilization scenarios, and depending on the general circulation model used. The methods employed can be used
within or across other African countries. 相似文献
17.
A western North Pacific tropical cyclone (TC) intensity prediction scheme (WIPS) is developed based on TC samples from 1996
to 2002 using the stepwise regression technique, with the western North Pacific divided into three sub-regions: the region
near the coast of East China (ECR), the South China Sea region (SCR), and the far oceanic region (FOR). Only the TCs with
maximum sustained surface wind speed greater than 17.2 m s−1 are used in the scheme. Potential predictors include the climatology and persistence factors, synoptic environmental conditions,
potential intensity of a TC and proximity of a TC to land. Variances explained by the selected predictors suggest that the
potential intensity of a TC and the proximity of a TC to land are significant in almost all the forecast equations. Other
important predictors include vertical wind shear in ECR, 500-hPa geopotential height anomaly at the TC center, zonal component
of TC translation speed in SCR, intensity change of TC 12 or 24 h prior to initial time, and the longitude of TC center in
FOR. 相似文献
18.
Summary Analysis of ozonesonde data shows that in the lower troposphere above Hong Kong, there is a relative maximum with respect to height in all seasons except winter. In the upper troposphere, there is with respect to height a relative minimum in the seasonally averaged ozone mixing ratio in winter. Ozone mixing ratios in the upper troposphere in winter and spring can be significantly enhanced by stratospheric intrusions associated with the passage of cold fronts and upper cut-off lows.For Hong Kong, the seasonally averaged total ozone has the highest value in spring, and the lowest in winter. The seasonally averaged total tropospheric ozone also has the highest value in spring, but the lowest in summer. In a relative sense, total tropospheric ozone contributes most to the total ozone in spring and the least in summer.The phase of the total ozone anomaly above Hong Kong is influenced by the Quasi-Biennial Oscillation (QBO), with the positive anomaly associated with the easterly phase of QBO, and the negative anomaly the westerly phase. 相似文献
19.
Ho-Jeong Shin Chan Joo Jang Il-Ung Chung 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(4):411-419
Recently we have had abnormal weather events worldwide that are attributed by climate scientists to the global warming induced by human activities. If the global warming continues in the future and such events occur more frequently and someday become normal, we will have an unprecedented climate. This study intends to answer when we will have an unprecedented warm climate, focusing more on the regional characteristics of the timing of unprecedented climate. Using an in-situ observational data from weather stations of annual-mean surface air temperature in Korea from 1973 to 2015, we estimate a timing of unprecedented climate with a linear regression method. Based on the in-situ data with statistically significant warming trends at 95% confidence level, an unprecedented climate in Korea is projected to occur first in Cheongju by 2043 and last in Haenam by 2168. This 125-year gap in the timing indicates that a regional difference in timing of unprecedented climate is considerably large in Korea. Despite the high sensitivity of linear estimation to the data period and resolution, our findings on the large regional difference in timing of unprecedented climate can give an insight into making policies for climate change mitigation and adaptation, not only for the central government but for provincial governments. 相似文献
20.
The axisymmetric formulation of the governing equations for geomechanics in the framework of smoothed particle hydrodynamics (SPH) is presented in this study. Two forms of SPH discretization for the motion equations, which are labeled as form I and form II, are proposed, and the methods to compute the hoop stress and strain terms including hoop strain rate and the acceleration introduced by the hoop stress are compared. To avoid possible singularity problem near the axis of symmetry, a perfectly smooth contact along with ghost particles are applied to prevent the real particles from overly approaching the axis of symmetry to remove this potential singularity. In addition, the Mohr–Coulomb constitutive model is implemented into the SPH formulation in describing soil behavior. Four numerical tests are carried out to validate and compare the accuracy and stability of the proposed algorithms, and their results are compared with analytical solutions and results from FEM analysis. The performance in these comparisons suggests that SPH II with hoop terms computed through direct hoop method is more stable than the others, and the adoption of contact for the symmetric axis is efficient in eliminating the singularity problem. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献