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   305篇
  免费   3篇
  2024年   1篇
  2023年   2篇
  2022年   5篇
  2021年   6篇
  2020年   13篇
  2019年   5篇
  2018年   7篇
  2017年   5篇
  2016年   4篇
  2015年   11篇
  2014年   5篇
  2013年   10篇
  2012年   16篇
  2011年   26篇
  2010年   22篇
  2009年   35篇
  2008年   18篇
  2007年   24篇
  2006年   20篇
  2005年   30篇
  2004年   6篇
  2003年   8篇
  2002年   6篇
  2001年   9篇
  2000年   7篇
  1999年   1篇
  1998年   1篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1993年   1篇
排序方式: 共有308条查询结果,搜索用时 31 毫秒
1.
Monitoring is deemed crucial for the incentivization of a decentralized organization, but its function relies on information transparency between the central authority and the delegated individuals. We test this hypothesis by considering changes in the fiscal behavior of Chinese county governments following an exogenous fiscal reform in 2004/2005 that removed information obstacles between provinces and counties. Employing data on 590 Chinese counties from 2000 to 2009, we find that counties in the reform provinces adopt a more proactive fiscal policy after the reform, suggesting that they become more incentivized in the political competition for economic growth. Such effects are stronger in counties with fewer competing peers and counties with either high or low ranks in the records of economic growth among peers. The increase in counties' productive spending leads to higher economic growth in later years.  相似文献   
2.
Shear walls are important lateral force-resistant components of tall buildings. Hence, a reliable numerical model that can accurately represent the mechanical characteristics and large deformations of shear walls is critical for realistic collapse simulation of tall buildings. Based on the theory of generalized conforming element, a high-performance quadrilateral flat shell element, NLDKGQ, accounting for the large deformation using the updated Lagrangian formulation, is proposed herein and implemented in OpenSees. The reliability of NLDKGQ is validated using classical benchmark problems and reinforced concrete specimens. In addition, its capability in simulating the collapse of a tall building is also demonstrated.  相似文献   
3.
Pan, Z., Zhu, M., Zhu, Y. &; Jia, L., August 2017. A new antiarch placoderm from the Emsian (Early Devonian) of Wuding, Yunnan, China. Alcheringa 42, 10–21. ISSN 0311-5518.

Wufengshania magniforaminis, a new genus and species of the Euantiarcha (Placodermi: Antiarcha), is described from the late Emsian (Early Devonian) of Wuding, Yunnan, southwestern China. The referred specimens were three-dimensionally preserved in black shales, allowing a high-resolution computed tomography reconstruction of anatomical details. The new euantiarch is characterized by a large orbital fenestra, an arched exoskeletal band around the orbital fenestra and a developed obtected nuchal area of the skull roof. Maximum parsimony analysis, using a revised data-set of antiarchs with 44 taxa and 66 characters, resolves Wufengshania gen. nov. as a member of the Bothriolepididae, which is characterized by the presence of the infraorbital sensory canal diverging on the lateral plate, and the nuchal plate with orbital facets. New analysis supports a sister group relationship between Dianolepis and the Bothriolepididae. Luquanolepis, a coeval euantiarch from the neighboring site of the new form, is referred to the Asterolepidoidei and represents the basalmost and earliest member of the Asterolepidoidei.

Zhaohui Pan* [], Min Zhu* [], You’an Zhu? [] and Liantao Jia [] Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, PR China. *Also affiliated with University of Chinese Academy of Sciences, Beijing, 100049, PR China. ?Also affiliated with Uppsala University, PO Box 256, 751 05 Uppsala, Sweden.  相似文献   
4.
L. Jiang  W. Pan  C. Cai  L. Jia  L. Pan  T. Wang  H. Li  S. Chen  Y. Chen 《Geofluids》2015,15(3):483-498
Permian hydrothermal activity in the Tarim Basin may have been responsible for the invasion of hot brines into Ordovician carbonate reservoirs. Studies have been undertaken to explain the origin and geochemical characteristics of the diagenetic fluid present during this hydrothermal event although there is no consensus on it. We present a genetic model resulting from the study of δ13C, δ18O, δ34S, and 87Sr/86Sr isotope values and fluid inclusions (FIs) from fracture‐ and vug‐filling calcite, saddle dolomite, fluorite, barite, quartz, and anhydrite from Ordovician outcrops in northwest (NW) Tarim Basin and subsurface cores in Central Tarim Basin. The presence of hydrothermal fluid was confirmed by minerals with fluid inclusion homogenization temperatures being >10°C higher than the paleo‐formation burial temperatures both in the NW Tarim and in the Central Tarim areas. The mixing of hot (>200°C), high‐salinity (>24 wt% NaCl), 87Sr‐rich (up to 0.7104) hydrothermal fluid with cool (60–100°C), low‐salinity (0 to 3.5 wt% NaCl), also 87Sr‐rich (up to 0.7010) meteoric water in the Ordovician unit was supported by the salinity of fluid inclusions, and δ13C, δ18O, and 87Sr/86Sr isotopic values of the diagenetic minerals. Up‐migrated hydrothermal fluids from the deeper Cambrian strata may have contributed to the hot brine with high sulfate concentrations which promoted thermochemical sulfate reduction (TSR) in the Ordovician, resulting in the formation of 12C‐rich (δ13C as low as ?13.8‰) calcite and 34S‐rich (δ34S values from 21.4‰ to 29.7‰) H2S, pyrite, and elemental sulfur. Hydrothermal fluid mixing with fresh water in Ordovician strata in Tarim Basin was facilitated by deep‐seated faults and up‐reaching faults due to the pervasive Permian magmatic activity. Collectively, fluid mixing, hydrothermal dolomitization, TSR, and faulting may have locally dissolved the host carbonates and increased the reservoir porosity and permeability, which has significant implications for hydrocarbon exploration.  相似文献   
5.
在植物对土遗址作用的研究中,鲜有就真实的遗址来展开调查,以及讨论植物给土遗址带来的负作用及其机理。为此,本研究选取西安地区大型土遗址秦阿房宫为研究对象,利用现场调查结合样带法、图像分析法并采集土样,开展对遗址区植物分布、根系产生的裂隙和土壤环境的研究。结果表明:造成土遗址病害现象的主要原因为植物根系作用,加之雨蚀、风化作用及人为破坏的叠加作用,使遗址保存面临严重威胁;其中酸枣、臭椿等萌生树种所产生的根劈裂隙及植物根系对土壤环境的影响十分明显。现存土遗址由植物以及风雨作用而引发的主要病害,其类型包含了边缘夯土的基础掏蚀、洞穴遗存、开裂坍塌、冲沟发育、表面剥蚀,这些是阿房宫遗址面临的主要威胁,也是半干旱地区土遗址存在的特有问题。研究结果既有助于揭示植被对土遗址的作用机理,又能为土遗址保护的植物选择提供理论依据和技术支撑。  相似文献   
6.
光绪二十一年三月二十三日李鸿章在《马关条约》上签字画押。①条约规定,从签画到换约,限期二十一日,即截止四月十四日夜十二点钟,“两帝国政府彼此不允批准和约,无庸告知,即将此约作为废止”②。这短暂的21天为清政府的换约决策提供了思考的时间。其间,清廷一度谕令前敌主帅刘  相似文献   
7.
(2006年8月21日)同志们:中国地方志协会年鉴工作专业委员会首届学术年会今天在乌鲁木齐市召开了。这次学术年会,中国地方志指导小组办公室非常重视,年鉴工作专业委员会做了认真的组织和筹备,新疆维吾尔自治区地方志编委会和乌鲁木齐市委、市政府给予了大力支持,承办会议的乌鲁木齐市党史地方志办公室的同志们,为会议的顺利召开,做了大量的、周密的准备工作,付出了辛勤劳动。在此,我谨代表中国地方志指导小组办公室、中国地方志协会年鉴工作专业委员会,向新疆维吾尔自治区地方志编委会、乌鲁木齐市委、市政府的领导同志及乌鲁木齐市党史地方…  相似文献   
8.
贾一凡 《江汉考古》2020,(1):88-95,80
近年来追缴的小邾国青铜器中,邾寿父鼎、邾眉父匜被盗于距东江小邾国墓地仅1.5千米的横岭埠遗址,器主是小邾国宗室贵族。郳公戈被盗于大韩墓地,年代为春秋晚期偏晚,是小邾国君郳公克父的自作器,综合文献记载和郳公镈铭文,推知克父应即小邾国春秋末期的国君恭公或惠公。两件邾季簠是小邾国君之幼弟为其妻仲娸作的媵器。  相似文献   
9.
徐兆奎是一位在历史地理学、地名学、地理学史及地理教育上做出重要贡献的历史地理学家。本文梳理了徐兆奎的生平,分析了其在上述领域的主要贡献,希冀引起学界的重视,以此缅怀这位前辈知名学者。  相似文献   
10.
受北京艺术博物馆的委托,对两件香色地四合如意云寸蟒纹织金妆花缎进行保护修复。两件妆花织物质地柔软、组织结构紧凑、纹样细腻、设色庄重。但经长期自然和人为因素的影响,织物多处破损、开裂、脱丝、破洞、污渍等,圆金和片金纹纬上的金片大量脱落,整体污染较为严重,质地脆弱,无法研究和展出。本文通过研究妆花所承载的历史文化信息、综合织物的质地、组织结构、纹样形态、设色特征等诸多因素,将其定为清早期织物。应用三维视频显微镜和电子丝绸尺软件对织物组织结构、破损程度进行了分析。在此基础上,制定了保护修复工作目标和方案。修复后的两件织物基本恢复了原貌,效果较好,可以作为研究中国丝织品的实物根据。  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