首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1742篇
  免费   410篇
  国内免费   511篇
测绘学   141篇
大气科学   9篇
地球物理   124篇
地质学   2124篇
海洋学   11篇
天文学   1篇
综合类   193篇
自然地理   60篇
  2024年   6篇
  2023年   21篇
  2022年   40篇
  2021年   71篇
  2020年   64篇
  2019年   83篇
  2018年   70篇
  2017年   45篇
  2016年   94篇
  2015年   110篇
  2014年   171篇
  2013年   111篇
  2012年   139篇
  2011年   163篇
  2010年   135篇
  2009年   152篇
  2008年   126篇
  2007年   141篇
  2006年   167篇
  2005年   103篇
  2004年   81篇
  2003年   78篇
  2002年   61篇
  2001年   73篇
  2000年   57篇
  1999年   55篇
  1998年   50篇
  1997年   47篇
  1996年   24篇
  1995年   14篇
  1994年   25篇
  1993年   16篇
  1992年   16篇
  1991年   5篇
  1990年   7篇
  1989年   7篇
  1988年   4篇
  1987年   9篇
  1986年   6篇
  1985年   4篇
  1984年   9篇
  1983年   1篇
  1980年   1篇
  1979年   1篇
排序方式: 共有2663条查询结果,搜索用时 46 毫秒
121.
着重讨论了如何利用人工智能技术进行矿岩界线的自动推断和连接,包括对所研制的基于知识的矿岩界线自动推连系统(AISMB)的措述,关于数据与知识的表示和组织、推理过程、策略以及系统实现等内容。  相似文献   
122.
Summary Dynamic programming is a technique which has been used to design the optimum final surface mining pit limit. In using dynamic programming there is a trade-off: if the geometric constraints are specified too strictly, the pit limit will not be the optimum, but if they are specified more loosely, then the computed pit contours must be smoothed. The smoothing process has usually been manual and is time consuming. In this paper a colour graphics computer routine is presented. This not only facilitates the smoothing but also has the following benefits: open-pit limits can be designed interactively on a personal computer; pit designs that are closer to the economic optimum can be obtained; and the engineer can bring his or her own experience and intuition to bear on the final open-pit design.  相似文献   
123.
Mine ventilation planning in the 1980s   总被引:1,自引:0,他引:1  
Conclusions In this paper, the author has attempted to trace the development of mine ventilation planning from the traditional, manual and largely empirical methods of the past to the numerate computer-based techniques of the 1980s.The computer revolution has changed the face of many engineering disciplines, not least mine environmental engineering. Nevertheless, the mining industries of the world have not all been equally progressive in adapting to the flexibility, power and practical utilization of the new methodologies. It is, for example, incongruous that current textbooks on mine ventilation separate completely the topics of network analysis and ventilation planning with very little cross-referencing. Many of the current generation of mine ventilation engineers recognize the need to know about computers but find difficulty in translating this into their daily work. The growing availability of self-teaching, friendly software for personal microcomputers, coupled with interactive graphics, will assist greatly in promoting uncomplicated but powerful usage of computers.Young engineers now graduating from universities and colleges have been brought up in a computer-oriented environment and are competent in interacting with these machines. Indeed, they wonder how the job was ever done without magnetic data bases and high-speed computation aid.  相似文献   
124.
Summary Recent mining literature on cutoff grade theory has come to reflect some viewpoints and analyses expressed earlier in the economic literature. Agreement is best when the cutoff grade policy is established by analysis in stages, starting from the limits of the deposit, and using the maximum net present value objective. In the derivation of the optimal cutoff grade policy a dynamic programming approach is then applied to solve the overall problem as a series of linked, nonlinear, stage optimization problems. A wholly satisfactory use of a dynamic programming methodology requires that two conditions be satisfied: the separability and optimality conditions. The former is, strictly, violated by a heap-leaching or dump-leaching process, the latter by possible forms of resource rent taxation. This paper considers the problem of including such a leaching process in a cutoff grade policy analysis along aforementioned lines. It concludes that a workable method of doing so may be found which, in particular, may be quite satisfactory in arid climates where, in addition, some practical leaching experience already exists.  相似文献   
125.
Summary Indian coal measures have widely varying caving characteristics. The maximum roof span of a longwall or depillaring panel at the time of nether roof collapse is shown to have a direct relation withRQD from a study of 12 case histories. A similar relation between maximum unsupported span of openings and rock mass quality as defined by theQ-system was also demonstrated. A simple nomogram is presented to predict the face advance required to cause roof collapse when theRQD or rock mass quality is known.  相似文献   
126.
本文解决大水矿床排供结合问题是国民经济建设中具有实际意义的重要课题。本文较系统地论述了解决排供矛盾和排供结合的办法。着重从地质一水文地质条件,从矿山排水前后矿床地下水的补给、迳流、排泄条件来论证对排供结合方案的选择,并以一个典型的矿床作为实例加以阐明。  相似文献   
127.
华北型煤田矿井突水灾害的防治   总被引:5,自引:2,他引:5       下载免费PDF全文
王明玉  张宝柱 《地质论评》1995,41(6):553-558
我国华北型煤田矿井中具有多层含水层,常发生底板突水事件,为了对突水灾害的防治,本文提出了切实可行的步骤,并利用水力学概念模型,研究了该类型矿井的突水量规律及其防治方法。  相似文献   
128.
本文基于三山岛金矿工程地质条件,针对设计所提出的采场和矿柱的尺寸,提出了分析矿柱稳定性的一种新的方法,并应用该方法分析了矿柱的稳定性;同时,提出了提高矿柱承载能力的一种有效途径。另外,还详细讨论了矿柱顶点的深度与长度之间存在的关系。  相似文献   
129.
北京地区地震、爆破和矿震的记录图识别   总被引:2,自引:7,他引:2  
以北京地区台网数据为例,讨论了天然地震、人工地震和矿山地震的区别,并对多重地震和不同地区的地震特征进行了分析。  相似文献   
130.
Conclusions Some bituminous coals, mostly of high volatile rank, sampled from various coalfields contained on average 0.5 m3 t–1 nitrogen and 0.13 m3 t–1.Nitrogen is released more readily than methane during coal winning but the volumes of nitrogen released are small compared with ventilation quantities and are only likely to be of significance for detailed oxygen deficiency studies.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号