全文获取类型
| 收费全文 | 2062篇 |
| 免费 | 578篇 |
| 国内免费 | 454篇 |
专业分类
| 测绘学 | 104篇 |
| 大气科学 | 45篇 |
| 地球物理 | 596篇 |
| 地质学 | 1370篇 |
| 海洋学 | 198篇 |
| 天文学 | 8篇 |
| 综合类 | 128篇 |
| 自然地理 | 645篇 |
出版年
| 2024年 | 9篇 |
| 2023年 | 40篇 |
| 2022年 | 101篇 |
| 2021年 | 132篇 |
| 2020年 | 125篇 |
| 2019年 | 122篇 |
| 2018年 | 153篇 |
| 2017年 | 119篇 |
| 2016年 | 142篇 |
| 2015年 | 144篇 |
| 2014年 | 146篇 |
| 2013年 | 174篇 |
| 2012年 | 157篇 |
| 2011年 | 142篇 |
| 2010年 | 125篇 |
| 2009年 | 121篇 |
| 2008年 | 115篇 |
| 2007年 | 113篇 |
| 2006年 | 144篇 |
| 2005年 | 128篇 |
| 2004年 | 109篇 |
| 2003年 | 66篇 |
| 2002年 | 67篇 |
| 2001年 | 58篇 |
| 2000年 | 62篇 |
| 1999年 | 54篇 |
| 1998年 | 44篇 |
| 1997年 | 37篇 |
| 1996年 | 29篇 |
| 1995年 | 20篇 |
| 1994年 | 21篇 |
| 1993年 | 15篇 |
| 1992年 | 15篇 |
| 1991年 | 14篇 |
| 1990年 | 10篇 |
| 1989年 | 4篇 |
| 1988年 | 5篇 |
| 1987年 | 5篇 |
| 1986年 | 3篇 |
| 1985年 | 4篇 |
排序方式： 共有3094条查询结果，搜索用时 15 毫秒
31.
概述了我国地质找矿钻探市场现状及前景，分析研究了地质取样钻探传统的立轴钻机及全液压动力头钻机的优缺点及综合效能，针对国家提出加强地质工作的形势及中国的实际状况，提出了完善和改进我国现有钻探设备、提高我国地质找矿取样钻探效率、降低能耗及成本的观点及建议。 相似文献
32.
Risk and uncertainty assessments for waste containment systems employing clay barriers often include spatial variability in
the hydraulic conductivity as part of the analysis. The two-parameter log-normal distribution is often used to describe the
spatial variability, but for compacted clays the three-parameter form can be more appropriate. A statistical hypothesis test
was developed that can be used to determine if the two- or three-parameter form of the log-normal distribution is more appropriate.
The test is based on a likelihood ratio, comparing likelihood functions for the two- and three-parameter forms at their maximums.
Likelihood functions are used assuming that a data set can be segregated into a set of distinct groups of hydraulic conductivities.
A step-by-step calculation procedure is described and the test is applied to data collected from 45 sites. 相似文献
33.
34.
35.
Driving forces of tropical deforestation: The role of remote sensing and spatial models 总被引：2，自引：0，他引：2
Rinku Roy Chowdhury 《Singapore journal of tropical geography》2006,27(1):82-101
Remote sensing technologies are increasingly used to monitor landscape change in many parts of the world. While the availability of extensive and timely imagery from various satellite sensors can aid in identifying the rates and patterns of deforestation, modelling techniques can evaluate the socioeconomic and biophysical forces driving deforestation processes. This paper briefly reviews some emerging spatial methodologies aimed at identifying driving forces of land use change and applies one such methodology to understand deforestation in Mexico. Satellite image classification, change analysis and econometric modelling are used to identify the rates, hotspots and drivers of deforestation in a case study of the southern Yucatán peninsular region, an enumerated global hotspot of biodiversity and tropical deforestation. In particular, the relative roles of biophysical and socioeconomic factors in driving regional deforestation rates are evaluated. Such methodological approaches can be applied to other regions of the forested tropics and contribute insights to conservation planning and policy. 相似文献
36.
Abdullah Al-Khanbashi Shihab W. Abdalla 《Geotechnical and Geological Engineering》2006,24(6):1603-1625
This study reports on waterborne polymer emulsion systems that were used for structural modification of sandy soils. The first
emulsion used was a styrene-acrylic, copolymer emulsion; the second and third were vinyl-acrylic, copolymer-based emulsions.
Specimens were prepared by adding different polymer emulsions to the sand and water in prescribed amounts. The performance
of the different emulsion systems as sand stabilizers was estimated through measurement of the hydraulic conductivity and
compressive strength. Measurements of hydraulic conductivity were conducted in a flexible membrane test apparatus. The hydraulic
conductivity for the three emulsions decreased at different rates, with an increase in polymer content up to 3 wt. (i.e.,
% by weight). Additional increase of polymer content did not introduce significant decrease in hydraulic conductivity, and,
at 5 wt.%, the three emulsions had essentially the same effect. Measurements made on dry cylindrical specimens disclosed remarkable
enhancement in the mechanical behavior of the system. The compressive strength and modulus of elasticity of the examined emulsions
increased with a higher concentration of polymer. Scanning electron microscope (SEM) revealed that the reduction in the permeability
and the improved mechanical properties can be attributed to three dominant structural changes: the development of interconnecting
ties between the sand particles, the development of adhesion between neighboring sand particles in contact, and the covering
of the sand particles with a thin polymer film. 相似文献
37.
1 IntroductionFracturing plays an important role in increasingthe production and injection and enhancing the final re-covery of oil and gas. At present, the use of ahydroxypropyl guar gum, borate-crosslinked, hydraulicfracturing fluid systemhas become ext… 相似文献
38.
39.
40.