全文获取类型
收费全文 | 525篇 |
免费 | 73篇 |
国内免费 | 121篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 81篇 |
地球物理 | 167篇 |
地质学 | 206篇 |
海洋学 | 69篇 |
天文学 | 4篇 |
综合类 | 73篇 |
自然地理 | 86篇 |
出版年
2024年 | 5篇 |
2023年 | 15篇 |
2022年 | 36篇 |
2021年 | 42篇 |
2020年 | 43篇 |
2019年 | 32篇 |
2018年 | 63篇 |
2017年 | 54篇 |
2016年 | 51篇 |
2015年 | 39篇 |
2014年 | 38篇 |
2013年 | 37篇 |
2012年 | 39篇 |
2011年 | 49篇 |
2010年 | 14篇 |
2009年 | 45篇 |
2008年 | 19篇 |
2007年 | 25篇 |
2006年 | 18篇 |
2005年 | 16篇 |
2004年 | 5篇 |
2003年 | 14篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有719条查询结果,搜索用时 31 毫秒
661.
针对某些地勘单位干部选拔及用人过程中存在的任人唯亲等不正之风问题,从“考察失真、关系利益、任用随意、责任层次不清”四个方面进行了根源剖析,并着重在“强化责任意识、严格考察程序、规范领导行为、完善监督机制”等方面提出了整改措施。 相似文献
662.
2007年9月26日,中国地震局监测预报司在北京主持召开了“超宽频带观测应用研讨会”。出席研讨会的监测预报司领导有监测预报司司长李克,处长余书明,余书明处长主持会议。中国工程院院士许绍燮到会演讲。会议承办方中国地震局地震研究所所长姚运生到会致词,龚平副所长到会。出席 相似文献
663.
The inherent heterogeneity of geological media often results in anomalous dispersion for solute transport through them, and how to model it has been an interest over the past few decades. One promising approach that has been increasingly used to simulate the anomalous transport in surface and subsurface water is the fractional advection–dispersion equation (FADE), derived as a special case of the more general continuous time random walk or the stochastic continuum model. In FADE, the dispersion is not local and the solutes have appreciable probability to move long distances, and thus reach the boundary faster than predicted by the classical advection–dispersion equation (ADE). How to deal with different boundaries associated with FADE and their consequent impact is an issue that has not been thoroughly explored. In this paper we address this by taking one-dimensional solute movement in soil columns as an example. We show that the commonly used FADE with its fractional derivatives defined by the Riemann–Liouville definition is problematic and could result in unphysical results for solute transport in bounded domains; a modified method with the fractional dispersive flux defined by the Caputo derivatives is presented to overcome this problem. A finite volume approach is given to numerically solve the modified FADE and its associated boundaries. With the numerical model, we analyse the inlet-boundary treatment in displacement experiments in soil columns, and find that, as in ADE, treating the inlet as a prescribed concentration boundary gives rise to mass-balance errors and such errors could be more significant in FADE because of its non-local dispersion. We also discuss a less-documented but important issue in hydrology: how to treat the upstream boundary in analysing the lateral movement of tracer in an aquifer when the tracer is injected as a pulse. It is shown that the use of an infinite domain, as commonly assumed in literature, leads to unphysical backward dispersion, which has a significant impact on data interpretation. To avoid this, the upstream boundary should be flux-prescribed and located at the upstream edge of the injecting point. We apply the model to simulate the movement of Cl− in a tracer experiment conducted in a saturated hillslope, and analyse in details the significance of upstream-boundary treatments in parameter estimation. 相似文献
664.
空间关联规则可以从空间数据库中发现空间对象之间的隐含的、不明确的空间关系。空间数据库中空间关联规则挖掘研究是空间数据挖掘和知识发现(SDMKD)的主要内容,其主要问题是多层,多关系的规则发现问题。本文把元模式与空间关联规则挖掘相结合介绍了挖掘地理信息系统(GIS)中空间数据库关联规则的常用步骤方法。 相似文献
665.
666.
The features of climate change and their effects on glacier snow melting in the past 50 years (1961–2010) in Xinjiang were studied. Regional climate data for 49 meteorological stations in the Tianshan Mountains and the northern and southern areas of Xinjiang were collected with the aid of techniques such as climatological statistical diagnosis, regional climate models, remote sensing, and geographic information system. The annual average temperature displayed a rising trend across the Tianshan mountainous area and both areas of Xinjiang. The trend was particularly apparent in winter and autumn with the rate of increase in the annual average minimum temperature being significantly higher than that of the maximum temperature. Rainfall also tended to increase in all three areas over the 50-year period, with the magnitude of change being highest in the mountainous area followed by northern Xinjiang and then southern Xinjiang. As a result of the rising temperatures, there was a negative material balance among the region's glaciers, of which the year 1982/1983 was the key year for the development of Tianshan mountain glacier snow. After this date, glacial ablation intensified with an annual change increase in average temperature of 1 °C, leading to a glacier material balance change of about 300 mm. To establish rainfall and temperature sequences for three regional climate change scenarios in the 2011–2050 period, we adopted the delta method using actual measurements during the 1961–2000 period against corrected data from rainfall and temperature simulations. All three scenarios indicated that temperatures will continue to increase, that the increase in rainfall may decrease in mountainous regions but will increase in the basin, and that the speed of glacial ablation in Xinjiang will continue to accelerate. 相似文献
667.
668.
三江源地区位于青海南部,是中国三大主要河流长江、黄河和澜沧江的源头汇水区,是中国海拔最高的天然湿地和面积最大的自然保护区。三江源地区生态环境脆弱,评估地下水蒸散量对该地区水循环和水资源量评价有重要作用,对生态环境保护也具有一定意义。基于中等分辨率的MODIS数据,利用表面能量平衡系统对三江源地区2001—2017年的区域蒸散量进行估算,并采用Sen+Mann-Kendall法分析其连续时间序列内的时空变化趋势,讨论其影响因素。结果表明:研究区蒸散量从2001年到2017年总体呈增长趋势;三个源区多年年平均蒸散量值表现为澜沧江源>黄河源>长江源的变化规律;三江源区超过62.62%的地区蒸散量变化呈显著增长趋势,轻微显著增长地区占28.03%,显著减小地区占比极少;蒸散量的变化主要受气候影响,与气温、降水量呈明显正相关关系,其确定系数分别为0.80、0.89;蒸散量与植被指数及土壤湿度也均呈明显正相关关系。 相似文献
669.
六九铜矿床位于黑龙江省大兴安岭成矿带中段,龙江铜、金、钼成矿亚带.为了探讨矿床的形成时代和研究该地区岩浆活动,本次对侵入矿体的英云闪长斑岩采用电感耦合等离子体质谱仪LA-ICP-MS锆石U-Pb定年,结果为122.96±0.93 Ma,由此可限定成矿时代上限,结合区域铜成矿规律,推测六九铜矿的成矿时代为晚侏罗世—早白垩世,成矿背景是蒙古—鄂霍茨克洋俯冲闭合有关的造山—造山后环境.对区内出露的绢英岩进行锆石U-Pb定年,结果为303.7±1.6 Ma,代表其原岩花岗闪长岩的结晶年代为晚石炭世晚期,结合区域地质调查成果,表明研究区自华力西晚期以来存在多期次岩浆活动. 相似文献
670.
Natural Hazards - Landslide is a global environmental geological hazard caused by natural or human activities. Since the impoundment of the Three Gorges reservoir area, the geological disasters... 相似文献