全文获取类型
收费全文 | 1515篇 |
免费 | 240篇 |
国内免费 | 516篇 |
专业分类
测绘学 | 103篇 |
大气科学 | 269篇 |
地球物理 | 497篇 |
地质学 | 903篇 |
海洋学 | 148篇 |
天文学 | 9篇 |
综合类 | 85篇 |
自然地理 | 257篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 28篇 |
2021年 | 56篇 |
2020年 | 62篇 |
2019年 | 70篇 |
2018年 | 65篇 |
2017年 | 59篇 |
2016年 | 77篇 |
2015年 | 81篇 |
2014年 | 111篇 |
2013年 | 136篇 |
2012年 | 92篇 |
2011年 | 105篇 |
2010年 | 91篇 |
2009年 | 101篇 |
2008年 | 112篇 |
2007年 | 123篇 |
2006年 | 100篇 |
2005年 | 96篇 |
2004年 | 88篇 |
2003年 | 41篇 |
2002年 | 56篇 |
2001年 | 62篇 |
2000年 | 58篇 |
1999年 | 51篇 |
1998年 | 48篇 |
1997年 | 46篇 |
1996年 | 37篇 |
1995年 | 39篇 |
1994年 | 32篇 |
1993年 | 32篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 16篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有2271条查询结果,搜索用时 531 毫秒
941.
郭屯矿井井筒基岩富水性分析 总被引:2,自引:0,他引:2
根据山东郭屯矿建井前施工的井筒检查钻孔钻探取心、简易水文观测、地球物理测井(包括流量测井)及结合郭屯矿井精查地质报告资料,对井筒的含、隔水层进行了划分;通过抽水试验、流量测井方法求解了风氧化带含水层、风氧化带下含水层及其各含水层分层的水文地质参数,分别预算了主井、副井、风井井筒的涌水量,并分析了郭屯矿各井筒基岩涌水量大于邻近煤矿井筒基岩涌水量的主要影响因素。 相似文献
942.
晋西北某矿井位于吕梁山黄土塬区,为年产500万t的特大型在建矿井,为查明首采区煤层赋存条件、地质构造情况、以及奥灰与主要含水层的富水性,对该区进行了三维地震及电法综合勘探。其中三维地震勘探查明了勘探区内4#、9#煤层的埋藏深度和起伏形态,解释断层18条,陷落柱4个,褶曲1条,煤层倾角大于15°的区段1处;运用瞬变电磁法结合直流电测深法查明K6、K5砂岩富水异常29处、4#、7#、9#煤顶板岩层富水异常51处,奥灰顶界面-100m富水异常18处。三维地震及电法的综合勘探,不仅解释了该区主要煤层的厚度变化趋势及基岩面和奥灰顶界面深度变化情况,还对落差大于5m断层、直径大于25m陷落柱、煤层、奥灰水以及主要含水层的富水情况、导通关系及相互间的水力联系进行了分析,其结论为解决矿井建设和开采中的地质难题,提供了可靠的地质信息。 相似文献
943.
Xiaobo Wang Shaoqiang Wang Jinghua Chen Huijuan Cui Yijin Wu N H Ravindranath Atiq Rahman 《地理学报(英文版)》2018,28(7):1020-1036
In this study, information is collected on the weather, soils, field management and agricultural statistics in the Bangladesh, India and Myanmar (BIM) region. Crop growth parameters within the EPIC (Environmental Policy Integrated Climate) model are calibrated using cultivar data and regional experimental records of indica hybrid rice Fyou498 and Fengliangyou4 in China. Potential yields of rice are then simulated in the BIM region from 1996 to 2005. The effects of local irrigation and fertilization levels on super hybrid rice yield are examined. The potential yields of Chinese hybrid rice at local irrigation and fertilization levels in 2000 and at full irrigation and rational fertilization levels are found to be 10.22 t/ha and 11.33 t/ha, respectively. The potential for increasing monsoon rice production in the study region is 227.71 million tons. The eastern Indo-Gangetic Plain in India, the southeast coast of India Peninsula and the Ayeyarwady Delta in Myanmar have the largest potentials for monsoon rice production. The northeastern and southwestern areas of the Deccan Plateau and the northwestern region of the Indo-Gangetic Plain need to improve irrigation equipment to meet the water-use requirements of high-yield rice. The central and southern plains in Myanmar and northeastern India need greater access to nitrogen fertilization for high-yield rice. 相似文献
944.
为加快碳达峰、碳中和进程,中国正探索碳总量控制制度,而省域碳配额分配是落实总量控制目标的重要抓手。从分配准则、分配方法和分配结果3个环节对关于中国省域碳配额分配的研究开展综述。结果表明,兼顾公平和效率原则是各方研究共识,但对于公平原则的解读和测度尚存争议。指标法和优化法在省域碳配额分配中被广泛采用,前者能兼顾多方利益,后者能提升分配效率;混合法因具备多方法优势而具有较大发展潜力;博弈法因缺乏透明度而较为罕见。既有分配结果对各省分配的减排责任与各省实情间尚有差距,并仅关注某一特定年份当期或者某一时间区间内累计的碳配额分配,缺乏对逐年碳配额分配的关注。建议后续研究进一步关注兼顾公平与效率、考虑区域异质性与消费端排放责任、采用多方法组合、兼容个案特殊性的跨期动态分配方法学的构建过程。 相似文献
945.
针对传统GM(1,1)+AR组合模型的缺点,提出一种可及时更新建模序列和增强数据间相关性的循环式钟差预报模型,在预报过程中根据预报时刻的不同实时调整AR模型阶数。考虑到原始钟差建模序列长度会对预报精度造成影响,分别使用2 h、6 h、12 h和24 h的钟差序列构建模型。实验结果表明,改进模型的预报精度较传统方法有一定提高,且预报结果更稳定;使用不同长度的钟差序列构建模型对预报结果有一定影响,其中二次多项式模型受原始序列长度的影响较大,改进模型受影响较小。 相似文献
946.
947.
The Glendhu experimental catchment study,upland east Otago,New Zealand: 34 years of hydrological observations on the afforestation of tussock grasslands
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper presents results from 34 years of the Glendhu Experimental Catchment Study, established in 1979 by the former New Zealand Forest Service in upland east Otago in New Zealand's South Island to determine the hydrological consequences of converting indigenous tussock grassland to plantation forestry. A traditional paired catchment approach was adopted; after a 2.5‐year pretreatment period, one catchment (GH2, 310 ha) was planted over two thirds of its area in Pinus radiata, and an adjacent catchment (GH1, 216 ha) was left in tussock as a control. The average annual reduction in water yield from the planted catchment between canopy closure in 1991 and 2013, compared with that in tussock, was 273 mm (33%). Annual water yields from the planted catchment continued to decline relative to the tussock catchment until 2010. Since then, the difference in annual water yields between the two catchments has narrowed. Ripping before planting caused some redistribution of the total streamflow from stormflow to baseflow. Following canopy closure, afforestation has reduced the low flow (Q95) by an average of 26% compared with the tussock catchment. Average peak flows for small events (2–5 L/s/ha) were reduced by 78%, but only by 37% for larger, less frequent storms (>15 L/s/ha), suggesting that peak flows during high magnitude storms are less dependent on the prevailing land cover. 相似文献
948.
Thomas R. Cianciolo Jacob S. Diamond Daniel L. McLaughlin Robert A. Slesak Anthony W. D'Amato Brian J. Palik 《水文研究》2021,35(4):e14014
Black ash (Fraxinus nigra) wetlands are widespread, forested landscape features in the western Great Lakes region. However, the future of these ecosystems is threatened due to impending spread of the invasive emerald ash borer (EAB), which results in tree mortality, decreased transpiration, and potential shifts to wetter, non-forested conditions. The vulnerability to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site-dependent vulnerability and our ability to predict it is unknown. Here, we assessed vulnerability potential as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. Further, we used high-resolution (1-cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Although we observed similar ET and groundwater exchange rates among settings, lowland sites were generally drier because of elevated landscape position and greater water level drawdowns (via lower specific yield). We predict that such drier sites will exhibit greater water level increases following EAB-induced ash mortality, compared to wetter sites where open water evaporation and shallow-rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibited minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss. These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, we assessed the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts. 相似文献
949.
An approach based on the category of limiting equilibrium analysis is proposed to consider the reinforcing effect of one row of vertical piles on slope under seismic conditions. The approach is based on an uncoupled formulation in which the pile response and slope stability are considered separately. Closed‐form equations are derived, allowing the yield acceleration coefficient to be determined for giving pile characteristics. Results were compared with those obtained using another limit equilibrium method. The effects of pile location on the effectiveness of increasing seismic stability of the slope–pile system were elucidated. It was found out that the piles should be installed in the middle–upper part of the slope to achieve greatest safety, but the pile length and other possible failure modes should be checked carefully in design. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
950.
The cohesive‐frictional nature of cementitious geomaterials raises great interest in the discrete element method (DEM) simulation of their mechanical behavior, where a proper bond failure criterion is usually required. In this paper, the failure of bond material between two spheres was investigated numerically using DEM that can easily reproduce the failure process of brittle material. In the DEM simulations, a bonded‐grain system (composed of two particles and bond material in between) was discretized as a cylindrical assembly of very fine particles connecting two large end spheres. Then, the bonded‐grain system was subjected to compression/tension, shear, rolling and torsion loadings and their combinations until overall failure (peak state) was reached. Bonded‐grain systems with various sizes were employed to investigate bond geometry effects. The numerical results show that the compression strength is highly affected by bond geometry, with the tensile strength being dependent to a lesser degree. The shear, rolling and torsion strengths are all normal force dependent; i.e., with an increase in the normal force, these strengths first increase at a declining rate and then start to decrease upon the normal force exceeding a critical value. The combined actions of shear force, rolling moment and torque lead to a spherical failure envelope in a normalized loading space. The fitted bond geometry factors and bond failure envelopes obtained numerically in this three‐dimensional study are qualitatively consistent with those in previous two‐dimensional experiments. The obtained bond failure criterion can be incorporated into a future bond contact model. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献