全文获取类型
收费全文 | 2353篇 |
免费 | 2105篇 |
国内免费 | 549篇 |
专业分类
测绘学 | 133篇 |
大气科学 | 63篇 |
地球物理 | 627篇 |
地质学 | 3723篇 |
海洋学 | 211篇 |
天文学 | 31篇 |
综合类 | 163篇 |
自然地理 | 56篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 136篇 |
2021年 | 226篇 |
2020年 | 172篇 |
2019年 | 195篇 |
2018年 | 179篇 |
2017年 | 189篇 |
2016年 | 208篇 |
2015年 | 212篇 |
2014年 | 289篇 |
2013年 | 273篇 |
2012年 | 300篇 |
2011年 | 295篇 |
2010年 | 232篇 |
2009年 | 250篇 |
2008年 | 230篇 |
2007年 | 224篇 |
2006年 | 152篇 |
2005年 | 165篇 |
2004年 | 124篇 |
2003年 | 122篇 |
2002年 | 95篇 |
2001年 | 109篇 |
2000年 | 86篇 |
1999年 | 86篇 |
1998年 | 78篇 |
1997年 | 58篇 |
1996年 | 64篇 |
1995年 | 35篇 |
1994年 | 51篇 |
1993年 | 20篇 |
1992年 | 28篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有5007条查询结果,搜索用时 15 毫秒
111.
Signatures in flowing fluid electric conductivity logs 总被引:1,自引:0,他引:1
Flowing fluid electric conductivity logging provides a means to determine hydrologic properties of fractures, fracture zones, or other permeable layers intersecting a borehole in saturated rock. The method involves analyzing the time-evolution of fluid electric conductivity (FEC) logs obtained while the well is being pumped and yields information on the location, hydraulic transmissivity, and salinity of permeable layers. The original analysis method was restricted to the case in which flows from the permeable layers or fractures were directed into the borehole (inflow). Recently, the method was adapted to permit treatment of both inflow and outflow, including analysis of natural regional flow in the permeable layer. A numerical model simulates flow and transport in the wellbore during flowing FEC logging, and fracture properties are determined by optimizing the match between simulation results and observed FEC logs. This can be a laborious trial-and-error procedure, especially when both inflow and outflow points are present. Improved analyses methods are needed. One possible tactic would be to develop an automated inverse method, but this paper takes a more elementary approach and focuses on identifying the signatures that various inflow and outflow features create in flowing FEC logs. The physical insight obtained provides a basis for more efficient analysis of these logs, both for the present trial and error approach and for a potential future automated inverse approach. Inflow points produce distinctive signatures in the FEC logs themselves, enabling the determination of location, inflow rate, and ion concentration. Identifying outflow locations and flow rates typically requires a more complicated integral method, which is also presented in this paper. 相似文献
112.
Gadsaraporn Wannitikul 《Singapore journal of tropical geography》2005,26(1):102-118
Using a general statistical model, this study attempts to characterise the trend of deforestation in the northeast region (Isan) of Thailand between 1975 and 1991, a period when the kingdom had sustained high rates of economic growth and steady increases in population. Using data obtained directly from government bodies on the 17 provinces comprising this heavily deforested region, the study examines the correlations between forest area and a set of six variables: population density, agricultural area, real per capita income, accumulated irrigated area, agricultural credit levels, and distance from Bangkok, the national political and economic centre. It also considers the effect of the two logging bans instituted in 1979 and since 1989. The study found a negative correlation between forest area and population density in particular, followed in ranking by agricultural credit, per capita income, the logging bans and distance from Bangkok. Viewed together with more recent data showing that rates of deforestation in the kingdom as a whole have slowed and appear to be stabilising, these results also suggest the beginnings in the 1990s of a forest transition – from an industrial to a post‐industrial stage in forest utilisation – in Thailand. 相似文献
113.
Microcracks in the Cretaceous Ryoke-type granite in Japan were investigated by using deep drilling core samples collected in the Mizunami Underground Research Project of the Japan Nuclear Cycle Development Institute (JNC). The granite body suffered brittle deformation associated with Tertiary thrust movement. Based on core-scale and microscopic deformation features, the drill core from a depth of 300 to 700 m is divided into four domains, i.e. (A) undeformed granite, (B) granite intruded by cataclastic seams, (C) fractured granite in the fault damage zone, and (D) foliated cataclasite at the fault center. To characterize microcrack geometries in each domain, we employed the impregnation method using a low-viscous acrylic resin doped with fluorescent agents and captured the microcrack images by confocal laser scanning microscopy (CLSM). The CLSM image in the fault damage zone revealed anisotropic development of microcrack networks related to the fault movement. Both CLSM observation and porosity measurements reveal a drastic increase of micro-pores in the foliated cataclasite, possibly caused by fragmentation, and granulation and crack sealing in the fault zone. 相似文献
114.
在准噶尔盆地西北缘,寻找岩性圈闭油气藏已是至关重要的问题。但人们几乎还是用常规的手段来寻找岩性油气藏,没有实质性进展。本文是以利用宽方位角采集的地震数据为基础,对数据进行高保真资料处理和参考标准层的层拉平解释。利用前人的区域地质研究成果和钻井解释成果对侏罗系的沉积环境进行了精细的描述,确定了拐19井区在下侏罗统三工河组的出油层段附近的沉积环境由湖泊相-三角洲前缘相-河流相-湖泊相的演化过程。利用地震属性解释的结果也能较好地反映目标区的沉积环境变迁,并且与区域地质、测井解释结果相吻合,为寻找油气提供了很好的依据。由此得出利用地震属性可以进行沉积环境变迁分析,为油田寻找岩性圈闭及油气藏做出贡献。 相似文献
115.
旋挖钻进技术作为一种高效优质的钻进方法近年来广泛地被用于公路、铁路及大型水电站基础工程施工建设中,取得了良好的社会效益和经济效益。探讨了在卵砾石、漂石等复杂地层以及坚硬基岩中进行旋挖钻进所用钻头的结构及其施工工艺。 相似文献
116.
117.
118.
119.
120.
通过对近年来鄂北工区所施工井的钻井资料进行分析、对比,优选出了适合于各区块、各井段的钻头型号和钻井参数,提高了机械钻速,缩短了钻井周期,使鄂北工区的钻井技术上了一个新的台阶,加速了鄂北气田的建设。 相似文献