全文获取类型
收费全文 | 38294篇 |
免费 | 6273篇 |
国内免费 | 8827篇 |
专业分类
测绘学 | 3434篇 |
大气科学 | 4512篇 |
地球物理 | 6411篇 |
地质学 | 23232篇 |
海洋学 | 4408篇 |
天文学 | 3379篇 |
综合类 | 2429篇 |
自然地理 | 5589篇 |
出版年
2024年 | 270篇 |
2023年 | 705篇 |
2022年 | 1397篇 |
2021年 | 1586篇 |
2020年 | 1477篇 |
2019年 | 1817篇 |
2018年 | 1277篇 |
2017年 | 1535篇 |
2016年 | 1538篇 |
2015年 | 1726篇 |
2014年 | 2195篇 |
2013年 | 2134篇 |
2012年 | 2279篇 |
2011年 | 2390篇 |
2010年 | 2065篇 |
2009年 | 2600篇 |
2008年 | 2549篇 |
2007年 | 2595篇 |
2006年 | 2573篇 |
2005年 | 2404篇 |
2004年 | 2111篇 |
2003年 | 1994篇 |
2002年 | 1726篇 |
2001年 | 1557篇 |
2000年 | 1537篇 |
1999年 | 1366篇 |
1998年 | 1169篇 |
1997年 | 862篇 |
1996年 | 708篇 |
1995年 | 624篇 |
1994年 | 601篇 |
1993年 | 504篇 |
1992年 | 361篇 |
1991年 | 317篇 |
1990年 | 207篇 |
1989年 | 172篇 |
1988年 | 144篇 |
1987年 | 92篇 |
1986年 | 51篇 |
1985年 | 37篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 17篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
J. William Miller Jr. 《Mathematical Geology》1991,23(2):201-218
A computer simulation method has been developed to find efficient drilling grids for mineral deposits. A well-known ore deposit is used as a model to develop an efficient pattern for undiscovered ore bodies in the same area or in other prospects where similar geometry is suspected. The model for this study is the Austinville, Virginia deposit, a Mississippi Valley-type deposit composed of 17 ore bodies totaling 34 million short tons (30 million metric tons). The method employs a computer program that simulates drilling the model deposit with different patterns, including various levels of follow-up drilling. Follow-up holes are drilled in fences at one half the original spacing around holes in the grid that show ore-grade mineralization. Each pattern is drilled 100 times from random starting locations to provide a range of outcomes of drilling, including the best, worst, and most likely. For this study, patterns of 100 drill holes were composed of 10 fences spaced 1000–5000 feet (305–1524 m) apart, each with 10 holes spaced 200–1000 feet (61–305 m) apart. In all, 25 grids were used with zero to three levels of follow-up drilling. The 600/2000 grid, with drill holes spaced 600 feet (183 m) apart in fences spaced 2000 feet (610 m) apart, was compared with the 200/5000 grid because they represented contrasting outcomes. The 600/2000 grid penetrated many ore bodies consistently but with few multiple hits to individual ore bodies; whereas the 200/5000 grid inconsistently penetrated few ore bodies with many multiple hits. The 600/2000 grid was more efficient than the 200/5000 grid at hitting large ore bodies of 1,000,000 short tons or greater (900,000 metric tons or greater) and was made more effective by adding one cycle of follow-up drilling. The 600/2000 grid had a 97% chance of hitting one or more large ore bodies with at least one drill hole per ore body, and the 200/5000 grid had a 64% chance. Once hit, there was an 82% chance that the largest ore body would be penetrated by three or more holes when using the 600/2000 grid and an 88% chance using the 200/5000 grid. 相似文献
102.
103.
104.
105.
106.
107.
108.
109.
从胶东所处的板块构造位置和区域控热构造入手,根据地热传导理论,对胶东温泉的地热属性进行分析研究,认为胶东半岛温泉地热属性为毗邻板块边缘高温地热带的板内中低温地热系统,它以偏高的大地热流值为地热背景,以局部控热构造聚敛的大地热流为热源,以地形高差影响和相应的水力压差作用为动力,入渗的大气降水被岩石中的热量加热,并沿断裂出露形成温泉地热水。根据山东半岛温泉地热属性的特点和地热水开发中所面临的问题,提出保持胶东温泉可持续开发的相关对策。 相似文献
110.