全文获取类型
| 收费全文 | 1462篇 |
| 免费 | 551篇 |
| 国内免费 | 247篇 |
学科分类
| 地球科学 | 2260篇 |
出版年
| 2025年 | 31篇 |
| 2024年 | 66篇 |
| 2023年 | 38篇 |
| 2022年 | 65篇 |
| 2021年 | 92篇 |
| 2020年 | 73篇 |
| 2019年 | 89篇 |
| 2018年 | 74篇 |
| 2017年 | 83篇 |
| 2016年 | 119篇 |
| 2015年 | 106篇 |
| 2014年 | 99篇 |
| 2013年 | 154篇 |
| 2012年 | 106篇 |
| 2011年 | 85篇 |
| 2010年 | 75篇 |
| 2009年 | 80篇 |
| 2008年 | 79篇 |
| 2007年 | 106篇 |
| 2006年 | 85篇 |
| 2005年 | 79篇 |
| 2004年 | 71篇 |
| 2003年 | 57篇 |
| 2002年 | 47篇 |
| 2001年 | 41篇 |
| 2000年 | 38篇 |
| 1999年 | 26篇 |
| 1998年 | 34篇 |
| 1997年 | 31篇 |
| 1996年 | 34篇 |
| 1995年 | 19篇 |
| 1994年 | 15篇 |
| 1993年 | 14篇 |
| 1992年 | 15篇 |
| 1991年 | 9篇 |
| 1990年 | 8篇 |
| 1989年 | 1篇 |
| 1988年 | 4篇 |
| 1987年 | 1篇 |
| 1986年 | 1篇 |
| 1985年 | 2篇 |
| 1984年 | 2篇 |
| 1983年 | 1篇 |
| 1981年 | 2篇 |
| 1979年 | 1篇 |
| 1978年 | 2篇 |
排序方式： 共有2260条查询结果，搜索用时 17 毫秒
31.
粉砂岩作为地球上广泛存在的岩石之一,在工程中经常被用到。泥质粉砂岩中含水量的增加会致使其强度降低和变形增加,从而导致洞室坍塌、边坡失稳等地质灾害。因此研究不同含水率下泥质粉砂岩破裂演化规律十分重要。本研究以龙游石窟围岩泥质粉砂岩为研究对象构建数值模型,基于实验室在位加载高能CT实时扫描试验获得的应力-应变曲线和裂纹形态修正模型参数,模拟不同含水率泥质粉砂岩在单轴压缩试验中的动态破裂演化过程,并通过声发射和矩张量反演技术来揭示不同含水率对泥质粉砂岩破裂的影响规律。研究结果表明：(1)从泥质粉砂岩强度方面,随着含水率的提高,泥质粉砂岩的强度逐渐降低,当含水率超过50%时,水对泥质粉砂岩强度弱化效应减弱;(2)从AE震级和b 值大小方面,随着含水率的增加,试样破坏时的b 值逐渐增加,这说明含水率的增加会使得泥质粉砂岩破裂过程产生的小事件数目增多,破坏渐进性增强,剧烈程度减弱,破坏释放的能量降低;(3)从破裂形态和AE失效源方面,随含水率的增加,AE剪切失效源的占比逐渐增加,泥质粉砂岩破坏模式由单斜面剪切破坏演变至Ⅹ状共轭斜面剪切破坏,含水率进一步增加趋近饱和状态,泥质粉砂岩的破坏表现为劈裂主导的外侧表皮剥落与内部剪切破坏。 相似文献
32.
全球导航卫星系统干涉反射测量（global navigation satellite system-interferometric reflectometry,GNSS-IR）技术能探测浅层地表的土壤湿度。针对多系统组合的土壤湿度反演问题,基于轨迹聚类方法,从全球定位系统(global positioning system,GPS)、北斗卫星导航系统（BeiDou satellite navigation system,BDS）、格洛纳斯(GLONASS)、伽利略（Galileo）导航系统的信噪比观测数据中提取多径干涉相位,利用经验模型求解轨迹聚类后的土壤湿度估计值,以加权平均方式得到系统组合后的估计结果。结果表明,BDS、Galileo反演精度相当且优于GPS、GLONASS,基于轨迹聚类的多系统组合土壤湿度估计方法的均方根误差为0.041 4 cm3/cm3,相比于单系统的综合反演精度提升约16.3%,相比于单系统的最佳频段反演精度提升约5.2%,所提方法能有效监测土壤湿度的变化。
相似文献33.
土壤水分作为全球水循环和能量循环的重要组成部分,在地球水循环、能量平衡以及气候变化中具有不可或缺的作用。传统的土壤水分实地测量方法难以获得大尺度、长时序的土壤湿度空间分布,且具有较高的测量成本。微波遥感信号源穿透能力强,具有全天时、全天候的特点,是获取长时序、大尺度土壤水分最有效的手段之一,特别是L波段的全球导航卫星系统反射测量(global navigation satellite system-reflectometry,GNSS-R)技术,其同时具有主动和被动微波遥感的优势,在土壤水分的测量中备受关注。分析了国内外基于GNSS-R技术的土壤水分遥感研究的现状和进展,系统性地介绍了GNSS-R技术获取土壤水分的原理与特征,分别从正演与反演两个角度详细说明了土壤水分测量的具体方法步骤,给出了主要困难与亟待解决的关键问题。以最新的基于旋风全球导航卫星系统（cyclone GNSS,CYGNSS）星载反演为主要介绍对象,深入阐述了基于CYGNSS数据反演土壤水分的理论模型与方法,并简要分析GNSS-R土壤水分遥感发展面临的机遇与挑战,以期为中国今后地基、空基和星载GNSS-R土壤水分遥感观测和应用提供参考和建议。 相似文献
34.
C. LOUMAGNE M. NORMAND M. RIFFARD A. WEISSE A. QUESNEY S. LE HÉGARAT-MASCLE 《水文科学杂志》2013,58(1):89-102
Abstract The purpose of this paper is to present the methodology set up to derive catchment soil moisture from Earth Observation (EO) data using microwave spaceborne Synthetic Aperture Radar (SAR) images from ERS satellites and to study the improvements brought about by an assimilation of this information into hydrological models. The methodology used to derive EO data is based on the appropriate selection of land cover types for which the radar signal is mainly sensitive to soil moisture variations. Then a hydrological model is chosen, which can take advantage of the new information brought by remote sensing. The assimilation of soil moisture deduced from EO data into hydrological models is based principally on model parameter updating. The main assumption of this method is that the better the model simulates the current hydrological system, the better the following forecast will be. Another methodology used is a sequential one based on Kalman filtering. These methods have been put forward for use in the European AIMWATER project on the Seine catchment upstream of Paris (France) where dams are operated to alleviate floods in the Paris area. 相似文献
35.
In this study, a capillary barrier system was designed and tested for an arid land environment. To simulate arid land conditions of high temperature and sub-irrigation systems, the barrier was subjected to thermal and hydraulic gradients in opposite directions; to test the barrier system under these severe conditions, an experimental apparatus was designed and fabricated. The multilayer capillary barrier consisted of three layers made of silica sand, a mixture of sand and bentonite in equal portions, and a mixture of clay (25%) and aggregate (75%). Several one dimensional coupled heat and moisture tests were performed. Temperature variations along the thickness of the barrier were recorded as a function of time, and at the end of each test, the barrier was sliced into small sections, for the determination of volumetric water content as a function of distance from the heat source. The experimental results were discussed in view of the barrier's intended purpose of its ability to store moisture for long time durations. Coupled heat and moisture flow equations were developed and solved numerically via a finite difference method. Diffusivity parameters were calculated by using experimental results, a numerical model, and Powell's conjugate directions method of nonlinear optimization. The model was calibrated and the results were discussed. Good agreement between calculated and experimental results was obtained. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
36.
Surface soil moisture has been extensively studied for various land uses and landforms. Although many studies have reported potential factors that control surface soil moisture over space or time, the findings have not always been consistent, indicating a need for identification of the main factors. This study focused on the static controls of topographic, soil, and vegetation features on surface soil moisture in a steep natural forested headwater catchment consisting of three hillslope units of a gully area, side slope, and valley‐head slope. Using a simple correlation analysis to investigate the effects of the static factors on surface soil moisture at depths of 0–20 cm at 470 points in 13 surveys, we addressed the characteristics of surface soil moisture and its main controlling factors. The results indicated that the mean of surface soil moisture was in the decreasing order of gully area > valley‐head slope > side slope. The relationship between the mean and standard deviation of surface soil moisture showed a convex‐upward shape in the headwater catchment, a negative curvilinear shape in the gully area, and positive curvilinear shapes at the side and valley‐head slopes. At the headwater catchment and valley‐head slope, positive contributions of soil porosity and negative contributions of slope gradient and saturated hydraulic conductivity were the main controlling factors of surface soil moisture under wetter conditions, whereas positive contributions of topographic wetness index and negative contributions of vegetation density were the main controlling factors of surface soil moisture under drier conditions. At the side slope underlain by fractured bedrocks, only saturated hydraulic conductivity and vegetation density were observed to be the controlling factors. Surface soil moisture in the gully area was mainly affected by runoff rather than were static features. Thus, using hillslope units is effective for approximately estimating the hydrological behaviours of surface moisture on a larger scale, whereas dependency between the main static factors and moisture conditions is helpful for estimating the spatial distributions of surface moisture on a smaller scale. 相似文献
37.
贺海超;南亚林;姚淼;薛君豪;王仲毅;郭鉴辉;李静;郭东欣;罗冬 《岩土工程技术》2025,39(2):167-176
为准确测量黄土古土壤互层下各土层的饱和程度,对黄土古土壤互层下黄土剖面含水率分布修正,用压力板法测得铜川地区黄土和古土壤的土壤水分特征曲线,进而用midas GTS NX软件进行非饱和渗流数值模拟,根据模拟数据建立含水率修正模型,并与现场浸水试验实测数据进行对比。研究表明：相同地质年代,不同古土壤受水分下渗的影响相对一致,但是不同地质时期,受影响的差异性变得明显;构建的含水率修正模型的计算值和实测值在黄土古土壤交接处等关键节点处的上下趋势基本一致,可以证明多层古土壤含水率模型计算的准确性和科学性。研究成果可为具有古土壤层的黄土地区含水率修正,进而提高黄土–古土壤互层地区湿陷性评价的精度提供参考。 相似文献
38.
盐溶液法测定非饱和膨润土的水分特征曲线 总被引：3，自引：0，他引：3
对于高放废物的最终处置，深地质处置被国内外公认为最合适的方法，而膨润土也被认为是高放废物处置库缓冲回填材料的良好基质。鉴于膨润土各项性质研究的重要性。本文介绍了利用盐溶液法进行非饱和膨润土水分特征曲线的测定工作，发现盐溶液法适合测定吸力极高的非饱和土，是一种值得推广的方法。 相似文献
39.
对2010年6月1—2日广西大暴雨天气的湿度场进行了分析。结果发现：暴雨前有一个高湿区的形成和维持过程,暴雨前一天预报的高湿区产生明显调整,导致暴雨出现,表明低层湿度场对暴雨发生有较好的指示意义。 相似文献
40.
There is little knowledge available about infiltration and evaporation processes in wadi channels in arid regions. This work was conducted to determine the actual evaporation from bare soils in wadi channels in the south-western region of the Kingdom of Saudi Arabia. The estimation of soil evaporation is highly dependent on the availability of moisture in the upper layers of alluvial wadis, in which the areal rainfall, flood hydrograph and soil properties play a significant part. The study was conducted by estimating the actual evaporation using soil moisture data, precipitation and runoff depths in a representative basin. The results are compared with potential rates. The actual rates were 1.5 mm/day immediately after a rainy day and then decreased to 0.42 mm/day. The minimum rate was about 0.1–0.2 mm/day during the dry season. The potential rates were about 9.5 mm/day in June and July, decreasing to 3.5 mm/day in December and January. 相似文献
