全文获取类型
收费全文 | 1417篇 |
免费 | 300篇 |
国内免费 | 421篇 |
专业分类
测绘学 | 133篇 |
大气科学 | 322篇 |
地球物理 | 363篇 |
地质学 | 805篇 |
海洋学 | 176篇 |
天文学 | 37篇 |
综合类 | 143篇 |
自然地理 | 159篇 |
出版年
2024年 | 3篇 |
2023年 | 26篇 |
2022年 | 46篇 |
2021年 | 61篇 |
2020年 | 63篇 |
2019年 | 75篇 |
2018年 | 86篇 |
2017年 | 74篇 |
2016年 | 76篇 |
2015年 | 83篇 |
2014年 | 98篇 |
2013年 | 68篇 |
2012年 | 99篇 |
2011年 | 95篇 |
2010年 | 89篇 |
2009年 | 79篇 |
2008年 | 87篇 |
2007年 | 90篇 |
2006年 | 69篇 |
2005年 | 66篇 |
2004年 | 49篇 |
2003年 | 42篇 |
2002年 | 45篇 |
2001年 | 51篇 |
2000年 | 55篇 |
1999年 | 67篇 |
1998年 | 51篇 |
1997年 | 55篇 |
1996年 | 62篇 |
1995年 | 49篇 |
1994年 | 29篇 |
1993年 | 24篇 |
1992年 | 28篇 |
1991年 | 13篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1958年 | 1篇 |
排序方式: 共有2138条查询结果,搜索用时 281 毫秒
151.
基于资源环境压力与经济发展的相互耦合关系视角,基于脱钩理论构建了资源环境与经济增长的脱钩状态评价指标体系,引入生态足迹法并结合改进的弹性脱钩分析方法,探讨了沈阳市2002~2009年资源环境与经济发展的脱钩程度、时序演变及其综合脱钩程度等.研究结果表明:2002 ~ 2005年研究区经济增长导致资源环境压力逐渐增大,2005~2009年资源环境压力趋缓;整个时段内研究区资源环境与经济发展脱钩状态以相对脱钩为主,呈“相对脱钩4—强耦合—相对脱钩4—相对脱钩1”的演变趋势. 相似文献
152.
GPU accelerated marine data visualization method 总被引:1,自引:0,他引:1
The study of marine data visualization is of great value. Marine data, due to its large scale, random variation and multiresolution in nature, are hard to be visualized and analyzed. Nowadays, constructing an ocean model and visualizing model results have become some of the most important research topics of ‘Digital Ocean'. In this paper, a spherical ray casting method is developed to improve the traditional ray-casting algorithm and to make efficient use of GPUs. Aiming at the ocean current data, a 3D view-dependent line integral convolution method is used, in which the spatial frequency is adapted according to the distance from a camera. The study is based on a 3D virtual reality and visualization engine, namely the VV-Ocean. Some interactive operations are also provided to highlight the interesting structures and the characteristics of volumetric data. Finally, the marine data gathered in the East China Sea are displayed and analyzed. The results show that the method meets the requirements of real-time and interactive rendering. 相似文献
153.
In this study, the temporal and spatial variations of observed global oceanic precipitation during 1979–2010 are investigated. It is found that the global trend in precipitation during this period varies at a rate of 1.5%/K of surface warming while the rate is 6.6%/K during 2006–2010. The precipitation is highly correlated with Sea Surface Temperature(SST) in both the temporal and the spatial patterns since the strong 1997–98 El Nino event. Considering the distributions of precipitation and SST, seven oceanic regions are classified and presented using the observed Global Precipitation Climatology Project(GPCP) data and Extended Reconstructed Sea Surface Temperatures, version 3(ERSST.v3) data. Further examining the mechanisms of the classified oceanic precipitation regions is conducted using the Tropical Rainfall Measuring Mission(TRMM) satellite, GFDL-ESM-2G model precipitation and SST data and Hadley Center sea ice and SST version 1(Had ISST1) data. More than 85% of global oceanic precipitations are controlled by either one or both of the warmer-get-wetter mechanism and wet-get-wetter mechanism. It is estimated that a 0.5 SST signal-to-noise ratio, representing the trend of SST time series to the standard deviation, is a criterion to distinguish the mechanism of a region. When the SST ratio is larger than 0.5, the precipitation of this region is controlled by the warmer-get-wetter mechanism. SST, rather than the humidity, is the pivotal factor. On the other hand, when the SST ratio is less than 0.5, the precipitation is controlled by the wet-get-wetter mechanism. The SST variability is a significant factor contributing to the precipitation variation. 相似文献
154.
从20世纪50年代以来,度日数一直作为气候变化与供暖关系的一个综合评价指标。基于全球变暖可能对我国供暖天数和温度产生深刻的影响,本文采用绵阳市1946~2005年共49年的日最低、最高气温资料,分析了绵阳市度日数年变化特征,并对其进行了趋势分析。结果表明:绵阳市历年供暖度日数最小值处于1998年,比1976年最大值低93.5%,10a年均供暖度日数变化趋势为二次曲线;制冷度日数波动性很大,1960~1979年在1500℃·d左右波动,1979~1990年在1400℃·d左右波动,1990年以后基本处于1500℃·d以上,10a年均制冷度日数拟合趋势曲线为三次曲线。基于Mann-Kendall(M-K)检验法,在α=0.05水平下,对绵阳市供暖和制冷度日数进行检验,研究发现:供暖度日数明显减少,1992年为突变起始年份;制冷度日数波动增长,且自1997年起突变。 相似文献
155.
A Dipole Pattern of Summer Precipitation over Mid-high Latitude Asia and Related Snow Cover Anomalies in the Preceding Spring 下载免费PDF全文
A dipole pattern of summer precipitation over the mid-high latitudes of Asia, which is characterized by opposing summer precipitation variations between the Mongolian and Northeast China (MNC) region and the West Siberian Plain (WSP), is found to be clear and stable on both interdecadal and interannual scales during 1981- 2011. Spring snow cover anomalies over a small region within the WSP and the Heilongjiang River (HR) region are closely related to the variation of this dipole mode during the subsequent summer, and they can therefore be considered as forecasting factors. Our statistical results imply a potential process explaining the relationship between the spring snow anomalies and the summer rainfall dipole. Corresponding to the snow anomalies, Rossby waves propagate along a path from the WSP region, via the Mongolian Plateau, to the Stanovoy Range during summer. At the same time, Rossby-wave energy divergences and convergences along this path maintain and reinforce an anomalous cyclone and anticyclone pairing over the Asian continent, which is significantly linked to opposite summer precipitation anomalies between the MNC and WSP regions. Numerical experiments are need- ed to further confirm the above conjecture and demonstrate the detailed physical mechanisms linking the spring snow cover anomalies and summer precipitation dipole. 相似文献
156.
157.
The arrival-time-difference approach is the dominant source location approach used in the microseismic source location area. Multiple solutions problem is one of the major concerns in microseismic source location, which is closely related to the microseismic network. This paper categorizes the multiple solutions into two types based on the origin times when using the arrival-time-difference approach. Type I multiple solutions are those which have the same origin time; type II multiple solutions are those with different origin times. The sufficient and necessary conditions to produce type I multiple solutions are that all sensors are located in a straight line for two-dimensional cases and on a plane for three-dimensional cases. The sufficient and necessary conditions to produce type II multiple solutions are that all sensors are located on a hyperbola for two-dimensional cases and on a hyperboloid for three-dimensional cases. Furthermore, the proofs indicate that type I multiple solutions are preventable, while a microseismic network consisting of the minimum number of sensors can never be free of type II multiple solutions. It means, besides the minimum number of sensors, at least one more sensor which is not on this hyperbola or hyperboloid is needed to uniquely determine a source. The results from field tests and applications indicate that when the sensors of a network lie on a hyperbola, the type II multiple solutions may not be the necessary outcome under the influence of errors in real data. However, the accuracy of the microseismic source location is affected significantly by this kind of networks. The results also show that not only the multiple solutions problem can be avoided effectively, but more importantly, the accuracy of the source location will be greatly improved by the optimization of network based on the characteristics of the microseismic network and field conditions. 相似文献
158.
新疆西天山哈勒尕提-木祖克铁铜铅锌矿床地质特征及成矿条件分析 总被引:1,自引:0,他引:1
哈勒尕提-木祖克铁铜铅锌矿床是近年来在新疆西天山博罗科努成矿带内发现的一处典型的矽卡岩型铜多金属矿床,目前为中型规模,有达到大型矿床的潜力。矿体赋存于大瓦布拉克岩体与上奥陶统呼独克达坂组(O3h)大理岩、大理岩化灰岩的接触带。成矿受岩浆岩、地层岩性和接触带构造"三位一体"联合控制。大瓦布拉克岩体主要岩性为二长花岗岩和花岗闪长岩,岩石地球化学显示高硅、准铝、低镁、富碱、富钾,为I型花岗岩,富集大离子亲石元素,相对亏损高场强元素,具俯冲带岩浆岩的地球化学特点。呼独克达坂组(O3h)碳酸盐岩地球化学性质活泼且富含铜、锌,有利于含矿热液交代成矿,是区域找矿的优势层位。接触带构造既是成矿地球化学障,又是良好的成矿热液运移通道,直接控制着矿体的产出。 相似文献
159.
160.
The social impact of global climate change is one of the hotspots in the current research. To deal with the challenges from climate change, it could be learned from the adapting experiences and lessons to climate change in the history. The main achievements of cognition on the historical impacts of climatic change in China and on coping with the climate changes in the future based the published papers in recent years is summarized. The followings are the main conclusions. ①The general characteristics of the impacts of climatic change in the history was negative in the cold periods and positive in the warm periods, but there were regional differences in the impact and responses. ②The cooling trend on centurial scale and the social economic decline run concurrently. The rapid development supported by better resources and environment in the warm period could lead to the increase of the social vulnerability when the climate turned to the cold period. ③Strategies and policies to cope with the climate change in the history were adopted according to the temporal and spatial circumstances and the subjects. Initiative adaptation promoted by governments was an effective way. 相似文献