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   9207篇
  免费   2086篇
  国内免费   2912篇
测绘学   1224篇
大气科学   1249篇
地球物理   2050篇
地质学   5492篇
海洋学   1665篇
天文学   308篇
综合类   926篇
自然地理   1291篇
  2024年   72篇
  2023年   199篇
  2022年   600篇
  2021年   713篇
  2020年   573篇
  2019年   654篇
  2018年   640篇
  2017年   570篇
  2016年   649篇
  2015年   654篇
  2014年   681篇
  2013年   789篇
  2012年   737篇
  2011年   710篇
  2010年   713篇
  2009年   648篇
  2008年   607篇
  2007年   577篇
  2006年   581篇
  2005年   464篇
  2004年   319篇
  2003年   244篇
  2002年   250篇
  2001年   254篇
  2000年   202篇
  1999年   198篇
  1998年   117篇
  1997年   120篇
  1996年   96篇
  1995年   94篇
  1994年   82篇
  1993年   73篇
  1992年   61篇
  1991年   40篇
  1990年   34篇
  1989年   39篇
  1988年   19篇
  1987年   21篇
  1986年   29篇
  1985年   23篇
  1984年   8篇
  1983年   9篇
  1982年   7篇
  1980年   7篇
  1979年   6篇
  1978年   3篇
  1965年   2篇
  1958年   4篇
  1957年   4篇
  1954年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
塔里木盆地库车坳陷盐下深部储层是天然气勘探的重要领域,白垩系储层岩盐广泛发育,储层含盐特征的精细表征和评价对该区勘探区带优选具有重要意义.以库车坳陷大北克深井区白垩系砂岩储层72件岩心样品为研究对象,通过薄片、扫描电镜、能谱分析与QEMSCAN(岩石矿物定量分析)等技术手段,对研究区白垩系砂岩储层的含盐特征、分布规律、形成条件及来源等进行研究.结果表明:岩盐晶体主要赋存在碎屑颗粒间、碎屑颗粒表面和溶蚀孔与裂缝中,呈格架状、晶粒状和团块状集合体等3种赋存状态,不同状态岩盐晶体Na和Cl等元素的原子分数存在差异;岩盐分布规律为,平面上表现出西高东低的特点,垂向上距上覆膏盐岩层越近,岩盐体积分数越高;不同的盐源供给条件、储层埋藏深度、砂岩粒级、分选性等制约岩盐晶体的集合体形态;岩盐来源主要为古近系膏盐类沉积物的溶蚀渗流,也可能与含盐流体沿构造断裂的侧向渗入有关.  相似文献   
983.
Feng  Peng  Zhao  Jiachen  Dai  Feng  Wei  Mingdong  Liu  Bo 《Acta Geotechnica》2022,17(5):1765-1784

Conjugate flaws widely exist in rock masses and play a significant role in their deformation and strength properties. Understanding the mechanical behaviors of rock masses containing conjugate flaws is conducive to rock engineering stability assessment and the related supporting design. This study experimentally investigates the mechanical properties of conjugate-flawed sandstone specimens under coupled static–dynamic compression, thereby providing insight into how conjugate fractures interact to produce tracing tensional joints. Results indicate that the coupled compressive strength and the dynamic elastic modulus of conjugate-flawed rock specimens show remarkable loading rate dependence. For a fixed strain rate, the specimen with a static pre-stress equal to 60% of its uniaxial compressive strength has the highest coupled strength. Besides, both higher static pre-stress and strain rate can induce smaller mean fragment size and greater fractal dimension of the specimen, corresponding to a more uniform distribution of the broken fragments with smaller sizes. When the static pre-stress is lower than 80%UCS, the flawed specimen under a higher strain rate is characterized by higher absorbed energy. However, when the pre-stress equals 80%UCS, the value of the energy absorbed by the specimen in the dynamic loading process is negative due to the release of the preexisting considerable elastic strain energy input from the static pre-loading. As for the failure modes, cracks always penetrate the preexisting ipsilateral flaw tips to form anti-wing cracks. Under dynamic loading, the conjugate-flawed specimen generally shows tensile failure at a low strain rate, while the shear failure dominates at a high strain rate. In addition, based on progressive failure processes of the conjugate-flawed rock specimens, the evolution of tracing tensional joints in the field is discussed.

  相似文献   
984.
Peng  Chen-Xin  Liu  Nian-Wu  Li  Ming-Guang  Zhen  Liang  Chen  Jin-Jian 《Acta Geotechnica》2022,17(6):2465-2479
Acta Geotechnica - This study investigates the effect of dewatering on wall deformations of deep excavations through numerical analyses. A hydro-mechanical coupled method...  相似文献   
985.
Zhang  Junxiang  Li  Bo  Liu  Yanwei  Li  Peng  Fu  Jiangwei  Chen  Liang  Ding  Pengchu 《Acta Geotechnica》2022,17(10):4699-4715
Acta Geotechnica - Air leakage in borehole not only seriously restricts the development and utilization of coal bed methane (CBM) but also affects gas disaster prevention and underground safety...  相似文献   
986.
Zhou  Peng  Liu  Hanlong  Zhou  Hang  Cao  Guangwei  Ding  Xuanming 《Acta Geotechnica》2022,17(12):5499-5519
Acta Geotechnica - In this paper, a simplified two-stage analysis method is introduced to predict the lateral response of the existing X-section Cast-in-place Concrete (XCC) pile caused by adjacent...  相似文献   
987.
Liu  Li  Li  Yucheng  Wu  Yongkang  Luo  Shengmin  Peng  Jing  Deng  Yongfeng  Zhang  Guoping 《Acta Geotechnica》2022,17(11):5113-5132
Acta Geotechnica - The macroscale mechanical properties of cement-stabilized soil have been widely reported, but the microscale behavior remains largely unexplored. This paper presents the first...  相似文献   
988.
Discrete fracture models are used for investigating precise processes of groundwater flow in fractured rocks,while a disc-shaped parallel-plates model for a single fracture is more reasonable and efficient for computational treatments.The flow velocity has a large spatial differentiation which is more likely to produce non-linear flow and additional head losses on and nearby intersections in such shaped fractures,therefore it is necessary to understand and quantify them.In this study,both laboratory experiments and numerical simulations were performed to investigate the total head loss on and nearby the intersections as well as the local head loss exactly on the intersections,which were not usually paid sufficient attention or even ignored.The investigation results show that these two losses account for 29.17%-84.97%and 0-73.57%of the entire total head loss in a fracture,respectively.As a result,they should be necessarily considered for groundwater modeling in fractured rocks.Furthermore,both head losses become larger when aperture and flow rate increase and intersection length decreases.Particularly,the ratios of these two head losses to the entire total head loss in a fracture could be well statistically explained by power regression equations with variables of aperture,intersection length,and flow rates,both of which achieved high coefficients of determination.It could be feasible through this type of study to provide a way on how to adjust the groundwater head from those obtained by numerical simulations based on the traditional linear flow model.Finally,it is practicable and effective to implement the investigation approach combining laboratory experiments with numerical simulations for quantifying the head losses on and nearby the intersections between disc-shaped fractures.  相似文献   
989.
Peng  Weilong  Liu  Quanyou  Zhang  Ying  Jia  Huichong  Zhu  Dongya  Meng  Qingqiang  Wu  Xiaoqi  Deng  Shang  Ma  Yongsheng 《中国科学:地球科学(英文版)》2022,65(5):874-881
Science China Earth Sciences - Helium gas is a scarce but important strategic resource, which is usually associated with natural gas. Presently, only one extra-large helium-rich gas field has been...  相似文献   
990.
Science China Earth Sciences - The onset of the South China Sea summer monsoon (SCSSM) heralds the establishment of the large-scale East Asian summer monsoon and the western North Pacific summer...  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