全文获取类型
收费全文 | 7032篇 |
免费 | 1213篇 |
国内免费 | 1128篇 |
专业分类
测绘学 | 141篇 |
大气科学 | 624篇 |
地球物理 | 2550篇 |
地质学 | 3710篇 |
海洋学 | 875篇 |
天文学 | 56篇 |
综合类 | 295篇 |
自然地理 | 1122篇 |
出版年
2024年 | 37篇 |
2023年 | 113篇 |
2022年 | 196篇 |
2021年 | 269篇 |
2020年 | 282篇 |
2019年 | 279篇 |
2018年 | 255篇 |
2017年 | 292篇 |
2016年 | 276篇 |
2015年 | 285篇 |
2014年 | 415篇 |
2013年 | 553篇 |
2012年 | 339篇 |
2011年 | 397篇 |
2010年 | 366篇 |
2009年 | 441篇 |
2008年 | 509篇 |
2007年 | 429篇 |
2006年 | 461篇 |
2005年 | 337篇 |
2004年 | 316篇 |
2003年 | 288篇 |
2002年 | 271篇 |
2001年 | 246篇 |
2000年 | 228篇 |
1999年 | 227篇 |
1998年 | 195篇 |
1997年 | 173篇 |
1996年 | 144篇 |
1995年 | 122篇 |
1994年 | 107篇 |
1993年 | 107篇 |
1992年 | 90篇 |
1991年 | 69篇 |
1990年 | 68篇 |
1989年 | 44篇 |
1988年 | 43篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1978年 | 16篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有9373条查询结果,搜索用时 15 毫秒
841.
图们江流域中更新世火山泥石流仅分布在残留的Ⅲ阶地上,碎屑物的粒级范围很广,具正粒序层理,分选差,是在冰川作用或冰雪融化作用下快速搬运、沉积形成的,具有浊积岩的沉积模式。 相似文献
842.
There are many arguments on energy sources and main controlling factors of geothermal fields, so a systematic study on the distribution of ground temperature fields shall be necessary. In this paper the thermal conduction forward method of geothermal field is used to simulate cooling rate of abnormal heat sources and heat transfer of the paleo-uplift model. Combined with a large number of geothermal field exploration cases and oil exploration well temperature curves of domestic and foreign, the following conclusions are drawn: (1) According to the magmatic activity time, the magmatism activities are divided into two categories: Magma active areas (activity time < 500 000 years) and weak/magma inactive areas (activity time > 500 000 years). The latter has a fast cooling rate (the cooling time of the magma pocket buried around 10 km is less than 200 000 years) after it has intruded into the shallow layer and it has no direct contribution to modern geothermal fields; (2) China belongs to a weak/magma inactive area such as Tengchong region and Qinghai-Tibet region because the chronological data of these regions show that its magma activity time is more than 500 000 years; (3) The temperature of most geothermal fields can be obviously divided into three segments in the vertical direction: A high geothermal gradient segment (Segment H) at the surface, then a low geothermal gradient segment (Segment L) at a secondary depth, and finally a lower temperature segment (Segment D) at a deeper depth. The temperature isoline presents a mirror reflection relation on the temperature profile, indicating that geothermal field is dominated by heat conduction, rather than having an abnormally high temperature “heat source” to provide heat; (4) Near-surface (0-5 km) materials’ lateral heterogeneity caused by tectonic movement shall probably be the main controlling factor of ground temperature fields. 相似文献
843.
盆地热体制及深部温度估算对油气和区域地热能资源评估具有重要意义。南方上扬子区是海相油气勘探的重要区块,近年来更是我国页岩气勘探的主要选区。然而,由于数据不足及研究目标的分散,该区的盆地热体制特征还有待深化。结合前人已有地热数据,并整合新近开展的稳态测温数据,我们揭示了上扬子区现今地温梯度、大地热流分布特征,继而估算了1000~6000m埋深处的深部地层温度和2套主要古生界海相烃源岩底界面处的温度。结果表明,上扬子区具有中-低温的地热状态,其现今地温梯度和大地热流的范围(平均值)分别为10~74℃/km(24℃/km)和27~118mW/m2(64mW/m2),整体上从东北向西南方向递增,呈现出"东北低、西南高"的分布趋势。1000~6000m埋深处估算温度的分布格局与地温梯度及热流的分布趋势基本一致。东北部的鄂西-湘北地区为低温区,中部的四川盆地其大部分为中温区,西南的云南地区为高温区。上扬子区现今地热分布格局受区域差异构造和岩浆作用控制。结合储层温度估算并综合其他油气地质资料,提出川东的石柱-涪陵、川南的威远-自贡-泸州和宜宾-长宁等区的下... 相似文献
844.
长江三峡工程正常蓄水位为175m,在蓄水过程中随着库水位的抬升,必然会引起库岸边坡地下水渗流场的变化。运用3D-Modflow软件模拟了三峡工程的蓄水过程中奉节库段边坡岩土体内部地下水位的动态变化,为长江三峡工程奉节库区段移民迁建地质灾害预测与防治提供科学依据。 相似文献
845.
846.
Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico 总被引:1,自引:0,他引:1
Roger González-Herrera Ismael Sánchez-y-Pinto José Gamboa-Vargas 《Hydrogeology Journal》2002,10(5):539-552
The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens
floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so
the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer
modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled
using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following
hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of
sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward
the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The
model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head
values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered
despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge,
and the well-developed karst system of the region has a very high hydraulic conductivity.
Electronic Publication 相似文献
847.
Review of Earth Critical Zone Research 总被引:2,自引:0,他引:2
Since the Earth Critical Zone put forward by National Research Council of America in 2001, it has got a lot of attention and some significant progresses have been made. This paper summarized those Earth Critical Zone projects and related research plans organized and implemented by the United States of America, Germany, Australia, France, China and the European Union, as well as main scientific problems and future development direction in the study of Earth Critical Zone. According to research status of China, the four main research contents should be strengthened including structure, formation and evolution mechanism of Earth Critical Zone, the coulpling interaction mechanism between migration and transformation of material and multi-processes, sevice function and evolution features of Earth Critical Zone and its support and effect on sustainable development, model simulation of process and system of Earth Critical Zone. In addition, our country should actively conduct cooperation and communication with the advanced countries, and enhance our involvement in international key research plans. 相似文献
848.
岩体通常是以孔隙岩石为基质并包含各种成因的裂隙和溶隙的复杂多空隙组合地质材料。为研究孔隙-裂隙-溶隙多空隙组合介质的渗流特性,在简要介绍多孔介质渗流Darcy定律、平板窄缝流Poiseuille定律和圆形管道流Darcy-Weibach理论的基础上,分析了几种孔隙-裂隙-溶隙组合情况的多空隙介质渗流特性,推导出相应组合的等效渗透系数KE,给出了描述多空隙组合介质KE的一般表达式,讨论了影响各种空隙组合KE的主要因素。以普通砖模拟岩石基质,通过砖身钻孔填充及砖间缝隙填充,试验模拟了岩溶岩体和裂隙岩体中溶孔和裂隙填充后的渗透情况。试验结果与所推求理论公式计算出的KE在同一量级且误差很小,很好地验证了所推导的多空隙组合介质渗透系数表达式的有效性。 相似文献
849.
850.
剪切带的流体-岩石相互作用 总被引:5,自引:1,他引:5
作为大陆岩石圈中的应变局部化带,剪切带中一般都渗透着大量流体。流体的来源与剪切带所处的构造背景、流变域和水文条件有关,而剪切带中流体的流动则受岩石的渗透率、孔隙度、孔隙性质、流体的扩散和渗透能力、环境的温压条件、应力或载荷的梯度等因素所制约。剪切带中流体的成分、通量及赋存状态或流动方式,直接影响着岩石的流变。由应变局部化及力学失稳所引起的化学不平衡和由流体与岩石的相互作用,使剪切带岩石的矿物成分和化学成分发生调整,其变异程度取决于原岩的性质、剪切的温压条件和流体的成分及通量等。由于流体的渗透流动和流体与岩石的相互作用使剪切带的体积有所变化,体积变化过程是一种自组织行为。较大的体积亏损,意味着剪切带中渗透过大量的流体,这对剪切带的流变行为、化学行为和成矿作用都有深刻的影响。 相似文献