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   4911篇
  免费   1058篇
  国内免费   1219篇
测绘学   168篇
大气科学   718篇
地球物理   696篇
地质学   4069篇
海洋学   901篇
天文学   98篇
综合类   280篇
自然地理   258篇
  2024年   24篇
  2023年   91篇
  2022年   176篇
  2021年   198篇
  2020年   182篇
  2019年   236篇
  2018年   215篇
  2017年   248篇
  2016年   267篇
  2015年   243篇
  2014年   331篇
  2013年   312篇
  2012年   357篇
  2011年   336篇
  2010年   280篇
  2009年   349篇
  2008年   307篇
  2007年   341篇
  2006年   348篇
  2005年   304篇
  2004年   243篇
  2003年   230篇
  2002年   243篇
  2001年   175篇
  2000年   202篇
  1999年   158篇
  1998年   163篇
  1997年   130篇
  1996年   103篇
  1995年   75篇
  1994年   76篇
  1993年   61篇
  1992年   40篇
  1991年   24篇
  1990年   27篇
  1989年   11篇
  1988年   25篇
  1987年   8篇
  1986年   20篇
  1985年   7篇
  1984年   8篇
  1983年   1篇
  1982年   6篇
  1981年   5篇
  1978年   1篇
  1977年   1篇
排序方式: 共有7188条查询结果,搜索用时 359 毫秒
71.
Two widely-used techniques to estimate the volume of remaining oil and gas resources are discovery process modeling and geologic assessment. Both were used in a recent national assessment of oil and gas resources of the United States. Parallel estimates were obtained for 27 provinces. Geological-based estimates can typically see into areas not available to discovery process models (that is areas with little or no exploration history) and thus, on average, yield higher estimates. However, a linear relation does exist between the mean estimates obtained from these two methods. In addition, other variables were found in a multiple regression model that explained much of the difference. Thus, it is possible to perform discovery process modeling and adjust the estimates to yield results that might be expected from geological-based assessments.  相似文献   
72.
西江主洼是珠江口盆地一个低勘探程度洼陷,油气差异聚集特征明显,但其机理不清。本文在断陷盆地油气成藏理论指导下,利用研究区地质、地球物理和地球化学等资料,开展了烃源岩、断盖组合、储集体系和运聚模式等方面的研究。结果表明,裂陷期沉降、沉积中心有序迁移,造成主力烃源岩自东向西由文四段迁移至文三段、文一+二段,控制东、西部油气差异分布。恩平组区域性泥岩发育且晚期断裂缺乏,导致油气纵向上更易聚集于下构造层;区域泥岩减薄尖灭或晚期断裂切开盖层的区域,上构造层有一定油气分布。"源-汇"类型从宏观上控制储层优劣,影响下构造层油气富集程度;"仓储"运移是控制上构造层油气规模聚集的主要模式。下构造层古近系应作为重点部署方向,东部围绕文四段、西部围绕文三段、文一+二段烃源岩构成的含油气系统展开;上构造层勘探需关注珠海组,在隆起周边寻找具备"仓储"运移模式的有利区带。  相似文献   
73.
The American whaling industry rose from humble beginnings off Long island to become an international giant. In its peak year, 1846, 735 ships and 70,000 people served the industry. As whale stocks and reserves decreased, whalers were forced to go farther and farther from their New England home ports. Voyages became longer, and risks on required return-on-investment became higher. The easy money of Atlantic and Pacific whaling was no more: the only remaining profitable ventures were to Arctic and Antarctic waters. Many ships returned empty, if at all. in 1871, most of the Arctic whaling fleet was crushed by early winter ice and lost. This calamity, in conjunction with the long-term diminishing whale stocks, the diversion of investment capital to more profitable ventures, and the discovery, development, and refinement of abundant petroleum crude oil, struck the death blow to the American whaling industry. By 1890, only 200 whaling vessels were at work, and by 1971, no American commercial whaling ship sailed the world's oceans.It is apparent that no single event caused the final, rapid decline. However, a single calamity, in an already stressed industry, that was self-insured and commercially interlinked, precipitated the end. Today's American petroleum industry, although adopting some principles of the American whaling industry, also has embraced other activities such as work process reengineering and customer alliances, which may preempt, or postpone, a similar catastrophic demise.  相似文献   
74.
The EGO method, developed by Egozcue et al. and the SRAMSC method, originally developed by Cornell and later programmed by McGuire, to assess the seismic hazard, are compared for the low seismicity area Belgium, The Netherlands, and NW Germany. Using the same input data, the results of the EGO method without the majority criterion and the SRAMSC method with upper bound XII agree very well. The influence of the zoning is investigated for the EGO method. It is not necessary to define the zones for the EGO method so strictly as for the SRAMSC method, but too wide zones can give bad results.  相似文献   
75.
浅变质岩区地层特征及地层单位探讨   总被引:2,自引:0,他引:2  
袁鄂荣 《地球科学》1990,15(2):137-144,T001
  相似文献   
76.
以吉林省境内红星构造带(已发现油田)和杨柳青构造带(未发现油田)为试验区,首先利用地震地层学方法,研究间接参数特征,确定有利相带和有效圈闭,并在有效圈闭上选择了39个2×2cm时窗。在时窗内提取与地震波动力学有关的信息,即频率、振幅、频谱能量等,然后对这种信息进行统计计算,获得振幅方差等九个参数并对其进行综合分析,从已知油气藏出发,对未知圈闭油气状况进行了三级预测,指出了最有利的勘探靶区。  相似文献   
77.
利用中国西北五省(区)1960-2004年129个台站逐日最低、最高温度资料,从中统计出年极端高温发生频次、年极端低温发生频次、年极端高温强度、年极端低温强度以及年极端高温和低温开始和结束日期,分析了它们近45 a来的变化情况。结果表明:近45 a来中国西北年极端高温发生频次的增加趋势是明显的,而年极端低温发生频次的减少趋势更显著;中国西北近45 a来年极端高温的强度在不断增强,而极端低温的强度在不断减弱;近45 a来中国西北年极端高温开始日期逐渐提前,结束日期逐渐推迟,而年极端低温的开始日期在逐渐推迟,结束日期在逐渐提前;年极端低温发生频次的减少对于西北区域增暖的响应比年极端高温发生频次增加更显著,而年极端低温强度的减弱要比年极端高温强度的增强对西北区域性增暖的响应偏弱,年极端高温发生频次的增加同年极端高温强度的增强对西北区域性增暖的响应程度基本相当。  相似文献   
78.
Low molecular weight organic acids (LMWOAs) are important components of root exudates. They play an important role in immobilizing and remobilizing contaminants in rhizospheric soil. Effects of four LMWOAs on the sorption and desorption behavior of p-chlorophenol by yellow earth was studied in batch mode. The results showed that the previous application of LMWOAs to enhanced adsorption capacity of p-chlorophenol of the soil in the order of maleic acid〉malic acid〉oxalic acid〉citric acid. However, when LMWOAs were applied to soil where p-chlorophenol had been previously adsorbed, substantial p-chlorophenol was desorbed from soil by oxalic acid, whereas citric acid, malic acid and maleic acid didn't desorb as much p-chlorophenol from soil as deionized water.  相似文献   
79.
In the process of steam stimulation exploitation of viscous crude oil, the injected water, at high temperature and under high pressure, reacts intensively with the host rock. This kind of water–rock interaction in Liaohe Shuguang Oil Field was studied on the basis of analysis of water composition changes, laboratory experiments, mineral saturation indices analysis, and mass balance calculation. Compared with the injected water, the changes of the composition of discharged water are mainly the distinct decrease of pH, Na+, SiO2 and Cl, as well as the increase of K+, Ca2+, Mg2+, SO 4 2− and HCO 3 . Laboratory experiments under field conditions showed: the dissolution sequence of minerals quantitatively is quartz>potassium feldspar>albite, and the main change of clay minerals is the conversion of kaolinite to analcime. Mass balance calculation indicated during the process of steam stimulation, large quantities of analcime are precipitated with the dissolution of large amounts of quartz, kaolinite, potassium feldspar, and CO2. These results correlated very well with the experimental results. The calculated results of Liaohe Shuguang Oil Field showed that during the steam stimulation for viscous crude oil, the amounts of minerals dissolved (precipitated) are huge. To control the clogging of pore spaces of oil reservoirs, increased study of water–rock interaction is needed.  相似文献   
80.
油页岩综合利用对周围环境的影响——以抚顺矿区为例   总被引:3,自引:0,他引:3  
世界能源日益减少的局面为油页岩的开发应用带来广阔的前景,但油页岩工业所带来的环境影响亦不容忽视。以抚顺油页岩为例,从油页岩综合利用和油页岩工业对环境的影响等方面系统讨论了在我国发展油页岩工业时,如何本着节约能源、保护环境、实现可持续发展的观念,利用现有先进技术,科学发展油页岩工业,降低生产过程中的固、液、气污染物对环境的危害。  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