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   1483篇
  免费   27篇
  国内免费   28篇
电工技术   38篇
综合类   71篇
化学工业   263篇
金属工艺   204篇
机械仪表   165篇
建筑科学   79篇
矿业工程   74篇
能源动力   79篇
轻工业   122篇
水利工程   14篇
石油天然气   58篇
武器工业   12篇
无线电   73篇
一般工业技术   106篇
冶金工业   35篇
原子能技术   17篇
自动化技术   128篇
  2024年   3篇
  2023年   14篇
  2022年   21篇
  2021年   22篇
  2020年   25篇
  2019年   20篇
  2018年   20篇
  2017年   22篇
  2016年   32篇
  2015年   24篇
  2014年   45篇
  2013年   64篇
  2012年   66篇
  2011年   99篇
  2010年   58篇
  2009年   63篇
  2008年   63篇
  2007年   87篇
  2006年   103篇
  2005年   83篇
  2004年   82篇
  2003年   76篇
  2002年   78篇
  2001年   47篇
  2000年   44篇
  1999年   49篇
  1998年   43篇
  1997年   30篇
  1996年   32篇
  1995年   31篇
  1994年   31篇
  1993年   12篇
  1992年   13篇
  1991年   9篇
  1990年   7篇
  1989年   3篇
  1988年   6篇
  1987年   2篇
  1986年   3篇
  1985年   3篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
排序方式: 共有1538条查询结果,搜索用时 15 毫秒
1.
甫沙4井位于塔里木盆地塔西南坳陷昆仑山前冲断带的柯东构造带上,北部和东部分别发育有柯克亚和柯东1井油气田。为研究甫沙4井原油来源与充注过程,对原油样品和连续抽提后的含油砂样各组分(游离态、束缚态、包裹体)进行GC、GC?MS和 GC?IRMS分析,与柯克亚凝析油气田油样进行油—油对比。结果表明:甫沙4井晚期充注原油组分具有C29?32重排藿烷、重排甾烷和Ts相对含量高,C27?29甾烷ααα 20R分布呈反“L”型,以及正构烷烃单体碳同位素值较低等特征,与柯克亚凝析油气田来源于二叠系普司格组(P2?3p)烃源岩的主体原油(I类)地球化学特征一致。而早期充注的原油组分具有重排藿烷、重排甾烷和Ts相对含量较低,C27?29甾烷ααα 20R分布呈“V”型,以及正构烷烃单体碳同位素值较高等特征,与柯克亚凝析油气田来源于中—下侏罗统湖相泥岩的II类原油地球化学特征一致。甫沙4井经历3个阶段成藏过程:①在上新世,二叠系烃源岩于生油晚期阶段生成的I类原油运移至柯克亚构造带或柯东构造带深部形成油藏;②在更新世早期,侏罗系烃源岩于生油早—中期生成的II类原油运移至甫沙4井白垩系储层;③在第四纪,强烈的构造作用使深部I类原油沿断裂调整进入甫沙4井白垩系储层。最终造成甫沙4井白垩系储层II类原油先充注,I类原油后充注的特殊现象。  相似文献   
2.
A wide range of dangerous and special tasks have witnessed the applications of wall-climbing robots, but they still cannot adapt well torough or sloping walls. This paper proposes a 6-DOF (degree of freedom) humanoid wall-climbing robot (HWCR) based on the principle of negative pressure suction. HWCR has the advantages of flexible adsorption feet, strong adaptability, strong anti-subversion performance, and high friction to the wall. We deduce mechanics formulas and carry out a parametric design of the foot structure so that it can meet the requirement of robot wall climbing. We use Fluent to analyze the flow field of the adsorption foot and determine the motor speed that can provide a reliable adsorption force. Using the D-H matrix to plan gait, we also design a compound cycloid-based foot trajectory to reduce the impact between the HWCR and the wall. Experiments on the uneven wall and sloping wall show that the vehicle can walk with an ideal gait, and the resistance value of the servo on each joint is much lower than the critical value, which ensures the smooth movement of the HWCR.  相似文献   
3.
《Ceramics International》2022,48(16):23111-23118
Porous alumina microspheres have attracted significant attention owing to their high mechanical strength and excellent chemical and thermal stability. The emulsion method is considered as a simple and controllable method for the preparation of inorganic microspheres. However, preparing alumina microspheres with the emulsion method is challenging because the emulsification of the precursor is inhibited by the rapid hydrolysis of aluminum alkoxide. Herein, we report a new emulsion method for the preparation of high-porosity alumina microspheres using a combination of ionic and non-ionic surfactants; in this method, the compound surfactants act as a template agent to guide aluminum alkoxide to form a lamellar structure through self-assembly. The decomposition of the templating agent and transformation of the alumina crystal at a high temperature result in structural collapse and formation of lamellar pores. Compound surfactants increased the spheroidization rate of the emulsion from 47% to 63% after hydrolysis, whereas the particle size was decreased by almost half. Additionally, the morphology and porosity of the alumina microspheres were changed. With increasing anionic surfactant content, the porosity increased initially and then decreased. The porosity of the alumina microspheres reached a maximum value of 76% at the 1:1 mass ratio of the non-ionic to anionic surfactants. Heat treatment was found to change the size of lamellar pores, with the pore diameter reaching maximum value at 1300 °C. The compound surfactants also increased the compressive stress and specific surface area of the porous alumina microspheres.  相似文献   
4.
ABSTRACT

Multiple-material products are characterised by a complex property profile which is achieved by combining the particular advantages of at least two different materials. Bimetal casting is an energy- and material-efficient technology for the production of multi-metallic objects. This paper describes the development of a semi-continuous casting process for the formation of a rotationally symmetric bimetal with a cohesive bonding character at the interface of a copper–tin alloy (CuSn6) and pure copper (Cu99.5). Initial experiments are conducted by static casting to evaluate the thermal process window. Based on the results of the initial experiments, a vertical semi-continuous compound casting process is developed. A stable cohesive bond between the joining partners is accomplished by forming a solid solution at the interface.

This paper is part of a Thematic Issue on Copper and its Alloys.  相似文献   
5.
Construction of this 67 m high RSS was completed in December 2006. After seven years in-service, a tension crack was observed at the top of the slope. In March 2015 this RSS structure catastrophically collapsed. This RSS structure collapsed in a compound failure mode; as the failure plane passed beneath, partially behind, and partially through the reinforced soil mass. The failure plane beneath the RSS was along a shale-claystone interface. The failure surface partially behind the RSS was along sandstone bedrock with water-seeping bedding planes dipping out of the rock mass. The failure surface through the upper portion of the RSS is where the geogrid reinforcement was overwhelmed by stresses originating from underlying deformation. The RSS collapse occurred after 8.3 years in-service as the shear strength along the shale-claystone interface decreased and approached the fully softened strength. The primary causative factors of this failure are: (i) an insufficient subsurface investigation program and interpretation of data for design and detailing; (ii) insufficient specifications and construction plan details for both foundation preparation and rock backcut benching; (iii) insufficient foundation preparation and rock backcut benching during construction; and (iv) adaptations to the design made during construction.  相似文献   
6.
This essay tells the story of the conception of the Two-State Reactivity (TSR) notion. Since scientific career is part of life's flow, the story blends sub-stories of scientific colleagues and events. This is also a story of a beguiling paradigm, which has started from a puzzling reactivity of the diatomic oxidant FeO+, has continued to larger oxidants, like the active species of Cytochrome P450 and of nonheme enzymes, and its extension to reductive processes. Finally, the essay discusses prospects of experimental probing of the reactive spin-state, and of the transition state constitution for these reactions by means of tunneling-augmented kinetic isotope effects.  相似文献   
7.
《工程爆破》2022,(2):12-15
通过简化爆破荷载的形式,对爆破振动作用下地基位移方程进行了推导,在此基础上给出了爆破作用下影响地基位移的诸要素,并提出了地基位移幅值在爆破作用下的变化规律,这对结构抗震工作的开展有着重要意义。  相似文献   
8.
李本仁 《矿山机械》2006,34(4):26-27,28
复摆颚式破碎机上装有两对轴承:一对轴承装在机架与偏心轴之问,通常称为机架轴承,机象军田泵支承偏心轴作叫转运动;另一对轴承装在动颚与偏心轴之间,通常称为动颚轴承,支承动颚在偏心轴回转时作摆动运动。阿对轴承将破碎机运行时的破碎物料负荷传递到机架上.是颚破机重要的零部件之一。  相似文献   
9.
为满足国家“八五”重点项目——新建调军台选厂设备大型化需要研制的CFB-1230永磁中磁机,以降低强磁机给矿磁性铁含量,避免其磁性堵塞。通过在原矿性质相同且生产工艺相近的齐大山选厂-选工业试验表明,该设备连续运行3000h,运行平稳可靠,与现用的CTB-1024中磁机相比较,处理量提高1倍,分级效率高,其尾矿(强磁机给矿)中的磁性铁含量成倍降低。工业试验成功后在调军台选厂推广使用,设备处理能力和分选效果超过设计要求,并取得可观经济效益。  相似文献   
10.
通过对大量测试数据的整理和分析讨论,得出玻璃微球与气泡复合敏化的乳化炸药爆速与炸药密度、敏化剂含量等因素的关系。由显著性分析可知,复合敏化剂中的任何一种组分都对乳化炸药的爆速有显著影响。  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