全文获取类型
收费全文 | 436篇 |
免费 | 84篇 |
国内免费 | 30篇 |
专业分类
测绘学 | 84篇 |
大气科学 | 22篇 |
地球物理 | 249篇 |
地质学 | 96篇 |
海洋学 | 35篇 |
天文学 | 4篇 |
综合类 | 25篇 |
自然地理 | 35篇 |
出版年
2024年 | 2篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 7篇 |
2017年 | 18篇 |
2016年 | 17篇 |
2015年 | 11篇 |
2014年 | 19篇 |
2013年 | 22篇 |
2012年 | 18篇 |
2011年 | 21篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 20篇 |
2007年 | 27篇 |
2006年 | 34篇 |
2005年 | 22篇 |
2004年 | 23篇 |
2003年 | 19篇 |
2002年 | 20篇 |
2001年 | 17篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 16篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有550条查询结果,搜索用时 15 毫秒
31.
32.
33.
设计了在接近实际储层温压条件下,流体介质为纯原油时在冰洲石中合成烃类包裹体的实验。合成样品的显微观察及荧光分析证实实验成功合成了烃类包裹体,实验证明油气对晶体生长和包裹体的形成有抑制作用,但不会终止其形成,纯油条件晶体仍能生长捕获包裹体,水并不是矿物生长捕获烃类包裹体的必须条件。结合矿物润湿性实验及前人研究将碳酸盐岩烃类包裹体捕获机制归纳为3种情况:油水共存(水润湿)、油水共存(油润湿)及纯油条件。水润湿条件下由水溶液提供矿物质来源,较易形成包裹体; 油润湿条件下由水溶液和油中的极性组分共同提供矿物质来源; 纯油条件下由原油中的极性组分和裂解产生的有机酸提供物源,形成烃类包裹体较少,晶体生长受到抑制。 相似文献
34.
物元可拓法在地下水水质评价中的应用 总被引:31,自引:1,他引:31
可以从定性、定量两个角度解决问题的物元可拓法已被广泛应用于各个领域,本文对物元可拓法进行了改进,并应用于地下水水质评价,同时采用模糊综合评判方法进行了验证。Piper-三线图显示,研究区地下水主要为HCO3—Na和HCO3—Ca·Na型水,水质本底条件较好。水质评价结果表明,上第三系馆陶组地下水水质显著优于明化镇组,1984~1999年间明化镇组和馆陶组的地下水水质均有变坏趋势,前者趋势较为明显。物元可拓法采用综合关联度与可拓指数判断地下水水质级别,不仅能反映其相对性,也能反映绝对性,可延拓连续的特点使其更有说服力。 相似文献
35.
lvaro Gonzlez Miguel Vzquez-Prada Javier B. Gmez Amalio F. Pacheco 《Tectonophysics》2006,424(3-4):319
Numerical models are starting to be used for determining the future behaviour of seismic faults and fault networks. Their final goal would be to forecast future large earthquakes. In order to use them for this task, it is necessary to synchronize each model with the current status of the actual fault or fault network it simulates (just as, for example, meteorologists synchronize their models with the atmosphere by incorporating current atmospheric data in them). However, lithospheric dynamics is largely unobservable: important parameters cannot (or can rarely) be measured in Nature. Earthquakes, though, provide indirect but measurable clues of the stress and strain status in the lithosphere, which should be helpful for the synchronization of the models.The rupture area is one of the measurable parameters of earthquakes. Here we explore how it can be used to at least synchronize fault models between themselves and forecast synthetic earthquakes. Our purpose here is to forecast synthetic earthquakes in a simple but stochastic (random) fault model. By imposing the rupture area of the synthetic earthquakes of this model on other models, the latter become partially synchronized with the first one. We use these partially synchronized models to successfully forecast most of the largest earthquakes generated by the first model. This forecasting strategy outperforms others that only take into account the earthquake series. Our results suggest that probably a good way to synchronize more detailed models with real faults is to force them to reproduce the sequence of previous earthquake ruptures on the faults. This hypothesis could be tested in the future with more detailed models and actual seismic data. 相似文献
36.
Geostatistical analysis of soil moisture measurements and remotely sensed data at different spatial scales 总被引:1,自引:0,他引:1
The European remote sensing satellite (ERS-2) synthetic aperture radar (SAR) data was used for temporal monitoring of soil moisture at Sukhothai, Thailand. Higher correlations were found between the observed soil moisture and the radar backscattering coefficient. The soil moisture distribution shows great variation in space and time due to its stochastic nature. In order to obtain a better understanding of the nature and causes of spatial variation of soil moisture, the extensive soil moisture measurements observed in Thailand and also remotely sensed ERS-2 SAR data were used for geostatistical analysis. The observed soil moisture shows seasonal variations with mean varying from 3.33 %v/v (dry season) to 33.44 %v/v (wet season). The spatial geostatistical structure also shows clear seasonal variations in the geostatistical characteristics such as range and sill. The sills vary from 1.00 (%v/v)2 for the driest day to 107.57 (%v/v)2 for one of the wet days. The range or the correlation lengths varies between 46.5 and 149.8 m for the wettest and driest periods. The nugget effect does not show strong seasonal pattern or trend but the dry periods usually have a smaller nugget effect than the wet periods. The spherical variogram model fits the sample variograms very well in the case of soil moisture observations while the exponential model fits those of the remotely sensed data. The ranges observed from the observed soil moisture data and remotely sensed data at the same resolution are very similar. Resolution degradation affects the geostatistical structure of the data by reducing the sills, and increasing the ranges. 相似文献
37.
本文以对营前特大桥桥位区的砂土液化的综合评判为例子,提出砂土液化必须运用定值准则的概念与方法并结合各种宏观液化势判定手段进行综合评判,文中还针对水下孔的水位取值进行了讨论。 相似文献
38.
利用1961—2013年大连地区3测站逐日地面雷暴观测资料及1948—2016年NCEP/NCAR再分析月平均资料,采用线性趋势估计和合成分析方法分析了大连地区雷暴日数的时间和空间分布规律,并进一步探讨雷暴严重年5—9月平均大气环流背景特征。结果表明:大连地区雷暴具有明显的地域特征,空间分布主要呈现北部内陆地区多,南部沿海地区少的特点;除2月外,各地其余月份均可发生雷暴,7月和8月达到高峰值,雷暴集中发生在5—9月,雷暴具有较强的季节性,夏季6—8月最多,冬季很少出现雷暴;年平均雷暴日数总体呈减少趋势,其中北部的减少趋势尤为显著;雷暴初日多出现在4月,终日多出现在10月,初日较终日稳定,无论初日和终日均以北部地区较南部地区稳定,各地雷暴初日显著提前,终日推迟不显著,但仅有大连终日推迟趋势显著;雷暴初日和终日北部地区对应的候平均气温阈值分别为-1℃和10℃,南部(东部)地区对应的候平均气温阈值分别为6℃(-1℃)和3℃(8℃);多雷暴年,高层500 hPa蒙古低涡异常偏强,副热带高压偏西偏北,低层850 hPa偏南风水汽输送和大连上空整层垂直上升运动均异常偏强,这些有利于雷暴日数的增多,而少雷暴年与多雷暴年特征基本相反。 相似文献
39.
陕西强连阴雨天气个例的综合分析 总被引:10,自引:3,他引:10
利用T213客观分析资料,对陕西2003年8月24日~9月7日强连阴雨天气过程的综合分析表明,连阴雨发生在欧亚稳定的环流形势下,乌拉尔山阻塞高压的建立和稳定使东亚中纬度纬向环流得以长时间维持。偏北、偏西、偏强的西太平洋副热带高压,不仅使冷空气受阻于秦岭山脉附近,同时其外围的偏南气流也为雨区提供了丰富的水汽,而乌拉尔山阻塞高压的崩溃引导冷空气大举南下,西太平洋副热带高压的东移南退则预示着持续的降水天气的结束。东亚合成环流的垂直结构表明,连阴雨期间秦岭邻近地区始终处于锋区中,并存在低空辐合、高空辐散的垂直结构。水汽条件分析表明连阴雨期间水汽的输送主要在对流层底部。热力学条件分析显示连阴雨期间河套始终为高潜热能区和位势不稳定区,偏南气流对热量的输送与高潜热能的维持有密切的关系,而低层偏东气流的加强促使了潜热能的释放,并导致了秦巴山区强降水天气的产生。 相似文献
40.
Steven M. Babin Todd D. Sikora Nathaniel S. Winstead 《Boundary-Layer Meteorology》2003,106(3):527-546
A case study of a particularly intense cold air outbreak over the northAtlantic Ocean extending from the northeast coast of the UnitedStates to the Gulf Stream is described. A RADARSAT satellite synthetic apertureradar (SAR) image of this outbreak dramatically illustrates the spatialevolution of convection. Nearly coincident images from the National Oceanic and Atmospheric Administration's Advanced Very HighResolution Radiometer are used to compare many interesting features.In addition, National Weather Service rawinsonde data, National Data Buoy Center buoy data, and Woods Hole Oceanographic Institute Coastal Mixing and Optics mooring data arepresented. We use these data to help describe the spatial evolution of the atmospheric boundary-layer processes involved in this outbreak.Rows of cellular convective clouds begin to appear some distance offshore and then slowly increase in horizontal diameter and wavelength in the downwind direction, with a subsequent jump in cloud diameter downwind of the Gulf Stream North Wall (GSNW). The SAR image shows a similar evolution of sea-surface footprints of these boundary-layer features. This change in boundary-layer structure is attributed to corresponding changes in static stability. About 300 km south of the GSNW in the SAR image, an even larger jump in cell diameter appears and the cells becomenon-uniform with bright crescents and filled semi-circles on thedownwind sides of the cells. These are believed to be surface effectsof gust fronts induced by the mesoscale cellular convection and enhanced by the overall northwesterly flow. 相似文献