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   2705篇
  免费   2044篇
  国内免费   966篇
测绘学   127篇
大气科学   273篇
地球物理   279篇
地质学   3321篇
海洋学   1330篇
天文学   18篇
综合类   242篇
自然地理   125篇
  2024年   14篇
  2023年   51篇
  2022年   188篇
  2021年   264篇
  2020年   209篇
  2019年   246篇
  2018年   232篇
  2017年   217篇
  2016年   234篇
  2015年   251篇
  2014年   323篇
  2013年   326篇
  2012年   303篇
  2011年   303篇
  2010年   225篇
  2009年   262篇
  2008年   249篇
  2007年   230篇
  2006年   191篇
  2005年   204篇
  2004年   160篇
  2003年   138篇
  2002年   113篇
  2001年   135篇
  2000年   115篇
  1999年   106篇
  1998年   83篇
  1997年   47篇
  1996年   58篇
  1995年   47篇
  1994年   42篇
  1993年   26篇
  1992年   26篇
  1991年   24篇
  1990年   16篇
  1989年   12篇
  1988年   8篇
  1987年   6篇
  1986年   8篇
  1985年   9篇
  1984年   6篇
  1979年   3篇
  1977年   4篇
  1972年   1篇
排序方式: 共有5715条查询结果,搜索用时 15 毫秒
141.
夏建国  乌效鸣  胡郁乐 《探矿工程》2005,32(9):46-48,51
利用特殊植物纤维KWS作为泥浆处理剂的新型充气钻井液,不仅具有常规充气钻井液低密度、排粉能力强、节约用水等优点,还可以不受钠、钙离子的影响,提高钻井泡沫稳定性和钻井液抗盐能力。通过采用此种新型充气钻井液,利用其低密度特性、特殊泥饼、泡沫的群体封堵作用和泡沫的疏水屏蔽作用,成功解决了裂隙地层的漏失问题,恢复了钻探生产。在我国西部干旱缺水漏失地区具有良好的应用前景。  相似文献   
142.
介绍了钻探施工中,利用膨胀材料充填、堵漏的新工艺,其具有经济、高效、安全的特点。  相似文献   
143.
李德红 《探矿工程》2005,32(8):50-54
通过对近年来鄂北工区所施工井的钻井资料进行分析、对比,优选出了适合于各区块、各井段的钻头型号和钻井参数,提高了机械钻速,缩短了钻井周期,使鄂北工区的钻井技术上了一个新的台阶,加速了鄂北气田的建设。  相似文献   
144.
This paper presents a novel dynamical model to analyze the long‐term response of a percussive drilling system. This departs from existing approaches that usually consider a single activation and bit/rock interaction cycle for the analysis of the process performance. The proposed model integrates the axial dynamics of an elastic piston and an elastic drill bit, a motion‐dependent pressure law to drive the piston, and a generalized bit/rock interaction law representative of the dynamic indentation taking place at the bit/rock interface. It applies to down‐the‐hole percussive drilling as well as top‐hole, with minor modifications. The model does not account for the angular motion or the hole cleaning, however. The model is first formulated mathematically; then, a finite‐dimensional approximation is proposed for computations. Numerical analyses of the model response, for a low‐size down‐the‐hole percussive system, follow. The period‐1 stationary response for the reference configuration is studied in detail, and parametric analyses assessing the influence on the rate of penetration of the bit/rock interaction parameters, the feed force, and the percussive activation parameters are conducted. These analyses reveal that the multiscale nature of the process is well captured by the model and recover expected trends for the influence of the parameters. They also suggest that a significant increase of the penetration rate can be achieved by increasing the percussive frequency. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
145.
正20141864 Deng Mengchun(Institute of Exploration Technology,CAGS,Chengdu 611734,China);Huang Shenghui Rock Sample Collection and Division Technologies for Air Reverse Circulation Sampling Drilling(Exploration Engineering,ISSN1672-7428,CN11-5063/TD,40(7),2013,p.73-76,80,16 illus.,5 refs.)  相似文献   
146.
正20141900Lan Xianhong(Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology,Ministry of Land and Resources,Qingdao 266071,China);Zhang Zhixun Geochemical Characteristics of Trace Elements of Sediments from Drillhole SFK-1  相似文献   
147.
This paper describes how measurements of the movement of identifiable features at the edge of a turbulent plume can be interpreted to determine the properties of the mean flow and consequently, using plume theory, can be used to make estimates of the fluxes of volume (mass), momentum, and buoyancy in a plume. This means that video recordings of smoke rising from a chimney or buoyant material from a source on the sea bed can be used to make accurate estimates of the source conditions for the plume. At best we can estimate the volume flux and buoyancy flux to within about 5% and 15% of the actual values, respectively. Although this is restricted to the case of a plume rising in a stationary and unstratified environment, we show that the results may be of practical use in other more complex situations. In addition, we demonstrate that large-scale (turbulent) coherent structures at the plume edge form on a scale approximately 40% of the local (mean) plume half-width and travel at almost 60% of the average local (mean) velocity in the plume.  相似文献   
148.
郑文龙 《地质与勘探》2016,52(5):931-936
CCSD-SK2井是一口钻穿松辽盆地白垩纪陆相沉积地层的中国大陆科学钻探井。二开段先以216mm口径钻至2806.20m,然后进行444.5mm口径扩孔。泥页岩地层大井眼钻进过程中粘土矿物含量高且易造浆,砂砾岩层渗透性强易粘卡,井壁稳定控制与钻屑携带难度大。选用了钾铵聚合物钻井液体系和聚磺钻井液体系,通过正交实验确定了钻井液配方。将钻井液控制在合适的密度、较低的失水量以及较强的封堵性,有效实现了井壁稳定;保持适当的环空返速、较高的动塑比以及定期打稠塞举砂等措施,有效实现了井眼净化。1086.45m~1147.56m与1182.74m~1256.01m井段累计收获岩心130.90m,取心率达到97.41%,平均机械钻速为0.84m/h;最终顺利钻至2806.20m。  相似文献   
149.
We report 40Ar–39Ar laser step-heating age determinations on 15 stratigraphically controlled lava flows and intrusive rocks from Heard Island, Central Kerguelen Plateau (Indian Ocean). The island history began with uplift of pelagic limestone intruded by 22 Ma gabbro sills. Subaerial and wave erosion levelled the early island, producing an unconformity onto which pillow lavas, tuffaceous sediments and shallow-water, fossiliferous marine siltstone (Drygalski Formation) were deposited, beginning in late Miocene time. Two volcanic systems then formed in the late Quaternary. Big Ben dominates the larger southeast part of the island, while Mount Dixon occupies the northwest Laurens Peninsula. Feeder dykes and the early lava flows in both systems are 400–200 ka. Lava flows with evolved compositions (trachytes, trachyandesites) erupted 100–20 ka. Well-preserved parasitic cones exposed at low elevations are 15–10 ka and younger. Mawson Peak, near the summit of Big Ben, has erupted lava flows as recently as 2007. Heard Island, and nearby active McDonald Island, are subaerial features of a larger Neogene volcanic region of Central Kerguelen Plateau that includes several large sea knolls and recently identified submarine fields of small cones. This broadly distributed volcanic activity is linked to incubation of plume material at the base of the nearly stationary overlying Central Kerguelen Plateau.  相似文献   
150.
利用1979—2012年逐月Hadley中心海表温度、欧洲中期天气预报中心次表层海温、NCEP/NCAR风场再分析资料,对两类中太平洋(CP)El Nio及耦合的大气环流特征进行分析。结果表明,第一类CP El Nio(CP-ⅠEl Nio)增暖中心位于Nio4区且关于赤道对称;第二类CP El Nio(CP-ⅡEl Nio)的Nio4区与热带东北太平洋区域(NEP,130~110°W、15~25°N)同位相变化,冬季成熟后形成关于赤道非对称的带状增暖结构。进一步的研究表明,两类CP El Nio次表层结构存在差异:CP-ⅠEl Nio冬季次表层海温异常(SOTA)在中东太平洋与西太平洋呈显著偶极分布;CP-ⅡEl Nio在中、西太平洋位相相反但东太平洋异常较弱,且经向异常主要在赤道及其以北。两类CP El Nio耦合的大气环流特征不同:CP-ⅠEl Nio冬季异常Walker环流上升中心位于赤道上空,经向风向赤道辐合,低纬地区Hadley环流加强;CP-ⅡEl Nio冬季低层向北越赤道气流加强,Walker环流上升中心移到赤道以北,低纬地区Hadley环流减弱。  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