全文获取类型
收费全文 | 1207篇 |
免费 | 252篇 |
国内免费 | 888篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 3篇 |
地球物理 | 194篇 |
地质学 | 1821篇 |
海洋学 | 10篇 |
天文学 | 2篇 |
综合类 | 96篇 |
自然地理 | 210篇 |
出版年
2024年 | 8篇 |
2023年 | 8篇 |
2022年 | 38篇 |
2021年 | 69篇 |
2020年 | 82篇 |
2019年 | 123篇 |
2018年 | 103篇 |
2017年 | 87篇 |
2016年 | 95篇 |
2015年 | 102篇 |
2014年 | 109篇 |
2013年 | 128篇 |
2012年 | 121篇 |
2011年 | 136篇 |
2010年 | 123篇 |
2009年 | 115篇 |
2008年 | 98篇 |
2007年 | 119篇 |
2006年 | 101篇 |
2005年 | 74篇 |
2004年 | 81篇 |
2003年 | 66篇 |
2002年 | 54篇 |
2001年 | 67篇 |
2000年 | 44篇 |
1999年 | 33篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 20篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 4篇 |
排序方式: 共有2347条查询结果,搜索用时 46 毫秒
151.
基于数值模拟的汾河二库对晋祠泉岩溶水系统渗漏补给作用研究 总被引:1,自引:0,他引:1
汾河二库的下闸蓄水,改变了晋祠泉域汾河地表水对岩溶水的渗漏补给条件,对区域岩溶水流场变化有着长远的影响。本研究通过系统梳理库区水文地质条件,勾画地表水渗漏补给岩溶水范围,考虑地层岩性、蓄水高度等因素,确定二库不同蓄水水位下晋祠泉域获渗漏量占比;构建晋祠泉三维岩溶地下水流模型,研究二库渗漏对泉域岩溶地下水补给作用,并预测不同蓄水情景下晋祠泉口水位变化趋势。结果表明:晋祠泉域获渗漏量占比随二库蓄水位非线性变化,最低为92.8%,在二库蓄水位达902 m后稳定在93.7%,而渗漏量与二库蓄水高度呈正相关;泉域岩溶水径流区受渗漏补给作用最显著,其次为排泄区、北部补给区;渗漏补给作用下,地下水位回升值受二库水位和补水距离影响;维持设计水位(905.7 m)和2017年水位(895.9~902.4 m)时,预计晋祠泉口水位分别在2021年7月和2023年1月达到泉口高程。 相似文献
152.
岩溶断陷盆地不同海拔植物水分利用效率分析 总被引:1,自引:0,他引:1
为探讨不同海拔高度的养分、环境要素与植物水分利用效率变化的关系,以岩溶断陷盆地云南小江流域的乔木、灌木、草本为研究对象,分析水分利用效率和叶片养分浓度随海拔的变化情况。结果表明:(1)研究区内海拔2 000 m处的草本植物的叶片δ13C值最高,2 200 m处的乔木的叶片δ13C值最低;(2)海拔高度对乔木、灌木的植物水分利用效率影响大于草本植物,草本植物的水分利用效率随海拔高度的变化甚微,两者之间的拟合度较小;高值区出现在海拔为2 200 m处的乔木;低值区出现在海拔为2 000 m处的草本植物;(3)不同海拔水分利用效率与叶片N、P浓度的相关性较弱(与叶片的N浓度呈弱正相关,与叶片的P浓度呈弱负相关);(4)不同海拔水分利用效率与各气候因子的相关性较弱,与多年平均气温、多年平均降雨量、多年平均日照时数均呈弱正相关。 相似文献
153.
王克林 《中国地理科学(英文版)》1998,(3)
I.INTRODUCTIONItisgeneralyacceptedthatthedegradationofrenewableresourcesandfragileenvironmentsindevelopingcountriesisbecomin... 相似文献
154.
信息量法在西宁市斜坡稳定性评价中的应用 总被引:11,自引:1,他引:10
毕海良 《水文地质工程地质》1998,25(4):25-27
本文选定西宁市东川弱侧丘陵前缘做为评价对象,采用二态变量信息法,对斜皮稳定性进行试评价。通过本次尝试性计算评价,与实际情况对比检验,其准确率达到89%。故本方法在斜坡稳定性评价中较为实用。 相似文献
155.
综合物探在南昆线岩溶复查工作中的应用 总被引:5,自引:0,他引:5
阐述了以综合物探为主要手段探测地下隐伏岩溶的工作原理及过程。针对岩溶勘探的特点,通过采用多种物探方法、布置高密度测网、勾绘高密度资料定性解释图性、剔除非可溶岩地层干扰影响以及总结一套简单实用的定性及准定量资料判释方法等5项措施,在南昆线岩溶复查工作中取得了良好的效果。 相似文献
156.
清江神女洞岩溶洞穴沉积物的磁学研究 总被引:3,自引:0,他引:3
通过对清江神女洞岩溶沉积物的磁学研究,得出有关该洞沉积物形成环境的下列判断:岩溶洞穴沉积物形成于早更新世至中更新世;岩溶洞穴沉积物形成于湿暖、干冷交替的环境;岩溶洞穴沉积物形成于NE56°流向的古水流中。 相似文献
157.
黔中地区是岩溶作用发育的喀斯特区域.1993年秋和1994年春末采自该地区不同类型水样的水化学分析表明:碳酸盐岩裂隙泉水呈中偏碱性,为[C]Ca-Ⅱ型;秋季离子总量、HCO3-及Ca2+浓度大于春季.裂隙泉水流经地表一定距离后,HCO3-降低,pH及SO42-、Cl-、K+、Na+明显增高.黄果树的天星桥、水帘洞及落水潭三个部位河水的SO42-、Na+以及Fe3+、NO3-等浓度的季节性变化也更加明显.春季因瀑布暴气,CO2的逸出,钙华生成更强烈一些.红枫湖作为喀斯特区域地表水的汇集地,HCO3-与SO42-的当量比值仅2.1~2.4;Ca2+与Mg2+比值上升为2.4~4.2,Cl-浓度较碳酸盐岩裂隙泉水增高1倍;Na+浓度增高一个数量级.说明流域内地表土层溶蚀及人为污染影响的增强.土层孔隙水属强矿化水,而湖水呈现过渡特征.碳酸盐沉淀作用、硫酸盐矿化作用及固氮氨化作用,导致水质组成的显着差异. 相似文献
158.
Jing Wu Jian Yin Yonghong Hao Yan Liu Yonghui Fan Xueli Huo Youcun Liu Tian‐Chyi J. Yeh 《水文研究》2015,29(13):2855-2866
The traditional hydrological time series methods tend to focus on the mean of whichever variable is analysed but neglect its time‐varying variance (i.e. assuming the variance remains constant). The variances of hydrological time series vary with time under anthropogenic influence. There is evidence that extensive well drilling and groundwater pumping can intercept groundwater run‐off and consequently induce spring discharge volatility or variance varying with time (i.e. heteroskedasticity). To investigate the time‐varying variance or heteroskedasticity of spring discharge, this paper presents a seasonal autoregressive integrated moving average with general autoregressive conditional heteroskedasticity (SARIMA‐GARCH) model, whose the SARIMA model is used to estimate the mean of hydrological time series, and the GARCH model estimates its time‐varying variance. The SARIMA‐GARCH model was then applied to the Xin'an Springs Basin, China, where extensive groundwater development has occurred since 1978 (e.g. the average annual groundwater pumping rates were less than 0.20 m3/s in the 1970s, reached 1.20 m3/s at the end of the 1980s, surpassed 2.0 m3/s in the 1990s and exceeded 3.0 m3/s by 2007). To identify whether human activities or natural stressors caused the heteroskedasticity of Xin'an Springs discharge, we segmented the spring discharge sequence into two periods: a predevelopment stage (i.e. 1956–1977) and a developed stage (i.e. 1978–2012), and set up the SARIMA‐GARCH model for the two stages, respectively. By comparing the models, we detected the role of human activities in spring discharge volatility. The results showed that human activities caused the heteroskedasticity of the Xin'an Spring discharge. The predicted Xin'an Springs discharge by the SARIMA‐GARCH model showed that the mean monthly spring discharge is predicted to continue to decline to 0.93 m3/s in 2013, 0.67 m3/s in 2014 and 0.73 m3/s in 2015. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
159.
Water samples were collected from cold and warm karst springs for stable isotopes (δ18O and δD) and 3H from SE of Kashmir valley (western Himalayas) to distinguish the sources of recharge and infer their recharge areas. The spring water samples were most depleted in heavier isotopes in May (average δ18O: ?8.87‰ and δD: ?50.3‰) and enriched in September (average δ18O: ?7.58‰ and δD: ?48.1‰). The depleted 18O and 2H of spring waters bear the signatures of winter precipitation while as the enriched 18O and 2H of spring waters bear the signature of summer rainfall. D‐excess and 3H corroborate with the stable isotope results that the spring flow in spring season (May) and autumn (September) is dominantly controlled by the melting of winter snowmelt and summer rainfall, respectively. The results showed that unlike δD, the δ18O value in the karst spring waters decreases in January suggesting δ18O shift. The spring water samples also fall above the Local Meteoric Water Line and Global Meteoric Water Line indicating the δ18O shift due to interaction of groundwater with the host carbonate rocks during its traverse. The mean elevation of the recharge areas of the springs using δ18O and δD tracers was also estimated. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
160.
In our previous study, we developed the Stokes–Darcy (SD) model was developed for flow in a karst aquifer with a conduit bedded in matrix, and the Beavers–Joseph (BJ) condition was used to describe the matrix–conduit interface. We also studied the mathematical well‐posedness of a coupled continuum pipe flow (CCPF) model as well as convergence rates of its finite element approximation. In this study, to compare the SD model with the CCPF model, we used numerical analyses to validate finite element discretisation methods for the two models. Using computational experiments, simulation codes implementing the finite element discretisations are then verified. Further model validation studies are based on the results of laboratory experiments. Comparing the results of computer simulations and experiments, we concluded that the SD model with the Beavers–Joseph interface condition is a valid model for conduit–matrix systems. On the other hand, the CCPF model with the value of the exchange parameter chosen within the range suggested in the literature perhaps does not result in good agreement with experimental observations. We then examined the sensitivity of the CCPF model with respect to the exchange parameter, concluding that, as has previously been noted, the model is highly sensitive for small values of the exchange parameter. However, for larger values, the model becomes less sensitive and, more important, also produces results that are in better agreement with experimental observations. This suggests that the CCPF model may also produce accurate simulation results, if one chooses larger values of the exchange parameter than those suggested in the literature. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献