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   3911篇
  免费   666篇
  国内免费   1219篇
测绘学   487篇
大气科学   155篇
地球物理   1269篇
地质学   2942篇
海洋学   323篇
天文学   8篇
综合类   305篇
自然地理   307篇
  2024年   30篇
  2023年   108篇
  2022年   154篇
  2021年   171篇
  2020年   201篇
  2019年   238篇
  2018年   209篇
  2017年   181篇
  2016年   256篇
  2015年   228篇
  2014年   322篇
  2013年   299篇
  2012年   244篇
  2011年   254篇
  2010年   234篇
  2009年   278篇
  2008年   277篇
  2007年   270篇
  2006年   257篇
  2005年   200篇
  2004年   219篇
  2003年   173篇
  2002年   137篇
  2001年   144篇
  2000年   113篇
  1999年   109篇
  1998年   82篇
  1997年   78篇
  1996年   59篇
  1995年   44篇
  1994年   40篇
  1993年   27篇
  1992年   26篇
  1991年   15篇
  1990年   16篇
  1989年   19篇
  1988年   12篇
  1987年   13篇
  1986年   11篇
  1985年   14篇
  1984年   19篇
  1983年   5篇
  1982年   1篇
  1978年   2篇
  1976年   2篇
  1975年   1篇
  1973年   2篇
  1972年   2篇
排序方式: 共有5796条查询结果,搜索用时 15 毫秒
201.
场地震害预测需要考虑区域地震地质背景和具体的场地条件本史分析了抚顺钢厂场地对震害有影响的各个因素,并利用模糊数学的方法划分出强、中、弱三种场地类型.研究结果表明.钢厂的场地大部分是好的和比较好的.  相似文献   
202.
A swallow-tail type catastrophic model of earthquake process   总被引:1,自引:0,他引:1  
(殷有泉)(杜静)Aswallow-tailtypecatastrophicmodelofearthquakeprocess¥You-QuanYINandJingDU(PekingUniversdy,Beijing100871,China)(Nort...  相似文献   
203.
俞维贤  谷一山 《地震研究》1994,17(2):177-182
本文通过耿马县城1988年11月6日7.2级地震的宏观列度考察,结合县城区的地震地质及工程地质环境的综合调查研究表明:耿马县城北坡北西向断层的存在是造成耿马县城高烈度异常的主要原因;县城场地质因素的地震易损性指数的分区性是造成县城区建筑物破坏强度出于灶区性差异的重要因素。  相似文献   
204.
覃辉 《四川测绘》1994,17(3):110-114
本文把近似Bayes方基分量估计公式应用于矿区扩建网的虚拟权平差中,解决了具体计算中的一些实际问题,最后,通过一矿区扩建网平差实例验证了该方法的可行性.  相似文献   
205.
Lignosulfonate lyes, which had been deposited by a paper factory for about 50 years into Quaternary sediments and accumulated in a quasistagnant depression, became mobile when a depression cone caused by mine activity in a deeper aquifer reached the erosion window close to the disposal site. Their transport parameters in the karstic-fractured-porous carbonate aquifer are shown to be mainly governed by diffusion between the mobile water in karstic channels and fractures and the stagnant water in matrix, although the hydraulic conductivity is shown to depend mainly on the karstic system. The main transport velocity is, with a sufficient accuracy, related to the hydraulic conductivity by a simple model in which matrix porosity is the governing rock parameter. The dispersivity, although also governed by matrix diffusion, depends strongly on several parameters that are difficult to determine.  相似文献   
206.
淮河以北矿区地面沉降及其成因   总被引:1,自引:0,他引:1  
根据多年的高程实测资料,查明了淮河以北矿区(主要是潘集地区)地面沉降的幅度、速率及范围;分析了该区地面沉降的内因和外因,为区内地面沉降的防治提供了依据。  相似文献   
207.
南桐二井采区突水动态研究   总被引:1,自引:0,他引:1  
将南桐煤矿二井的突水动态划分为纯衰减型、波动衰减型、季节波动衰减型、波动稳定型和逐渐增大型5类,它们分别对应于采区与浅层长兴灰岩含水层、蒲河及大气降水的不同连通程度与方式。  相似文献   
208.
Tree stem (>2 m tall) mortality was assessed following a late dry‐season wildfire across a seasonally flooded elevation gradient at Workshop Jungle, near Darwin, in the Northern Territory of Australia. For all species combined, dead stems had significantly smaller diameter at breast height (dbh) than living stems. Assessment of tree‐stem damage following a tropical cyclone at Cobourg Peninsula, NT, revealed that damaged stems had significantly greater dbh than undamaged stems for all tree species sampled across a boundary between monsoon rainforest and savanna. A greater proportion of stems were damaged by the cyclone than by the fire (28 per cent as against 18 per cent), although there were considerable between‐community differences in the proportion of damaged stems at the two sites. The fire caused little impact (<10 per cent) on total basal area of three different forest communities on the elevation gradient at Workshop Jungle. The cyclone was found to cause >50 per cent damage to total basal area of three different communities on Cobourg Peninsula. It is suggested that the combination of a cyclone followed by an intense fire in storm debris could potentially destroy a monsoon rainforest through its impact on all tree‐size classes. This may explain why some monsoon rainforests rapidly contracted following Cyclone Tracy that destroyed the city of Darwin on Christmas Day, 1974.  相似文献   
209.
Summary This paper presents an analysis of causes of bump in a deep coal mine. The analysis consists of in-mine measurement determination, analysis of physical and mechanical properties of mine materials and simulation of mine layout and mining sequence. Major factors contributing to the causes of bump have been reviewed and those that are related to this case have been identified and simulated analytically using a three-dimensional finite element method.  相似文献   
210.
Summary A review of the benefits of assisting mechanical tools, notably drag bits, with moderate pressure waterjets suitably directed with respect to the bit is given. These benefits include reduced bit forces, especially the bit normal force, reduced bit wear, reduced dust make, and reduced incidence of frictional sparking. The research work that has been conducted to date to investigate this phenomenon has been empirical in nature. Experiments are described that extend the data bank of this empirical knowledge. In addition, experiments aimed at gaining a better understanding of the fundamentals of the rock fragmentation process with this hybrid cutting method are outlined.Results from the first of these experimental series are used to make recommendations as to the position of the jet with respect to the bit, the stand-off distance between the nozzle exit and the bit/rock interface, and the jet energy. In addition, preliminary findings are reported regarding the increase necessary in the jet energy when the bit velocity is increased. Results from the second test series are discussed in the context of rock fracture behaviour induced by mechanical bits acting alone. The likely influence of waterjets on these fracture processes is analysed. It is concluded that, in terms of the bit force reductions, a dominant influence of the jets when used in conjunction with sharp drag bits, is continuous removal of the rock debris that forms ahead of the advancing bit. The observed reductions in bit wear and incidence of frictional sparking are attributed to reduced heat loading of the bit during the cutting operation. Reductions in the dust make are attributed to effective wetting of the fine rock particles before they become entrained in the airstream.  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