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   21576篇
  免费   1772篇
  国内免费   992篇
电工技术   1412篇
综合类   1730篇
化学工业   1626篇
金属工艺   3636篇
机械仪表   4595篇
建筑科学   1234篇
矿业工程   992篇
能源动力   463篇
轻工业   549篇
水利工程   236篇
石油天然气   1264篇
武器工业   278篇
无线电   950篇
一般工业技术   2292篇
冶金工业   1284篇
原子能技术   236篇
自动化技术   1563篇
  2024年   29篇
  2023年   311篇
  2022年   493篇
  2021年   621篇
  2020年   631篇
  2019年   559篇
  2018年   564篇
  2017年   722篇
  2016年   694篇
  2015年   719篇
  2014年   1112篇
  2013年   1238篇
  2012年   1384篇
  2011年   1533篇
  2010年   1077篇
  2009年   1140篇
  2008年   962篇
  2007年   1541篇
  2006年   1432篇
  2005年   1177篇
  2004年   1039篇
  2003年   844篇
  2002年   634篇
  2001年   640篇
  2000年   606篇
  1999年   491篇
  1998年   420篇
  1997年   355篇
  1996年   331篇
  1995年   260篇
  1994年   193篇
  1993年   112篇
  1992年   112篇
  1991年   84篇
  1990年   59篇
  1989年   54篇
  1988年   51篇
  1987年   25篇
  1986年   12篇
  1985年   14篇
  1984年   13篇
  1983年   6篇
  1982年   10篇
  1980年   6篇
  1963年   2篇
  1961年   5篇
  1959年   5篇
  1958年   4篇
  1957年   3篇
  1956年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
基于现场试验,采用Abaqus有限元软件对等截面桩及变截面桩单桩竖向承载力测试实验过程进行数值模拟。结果表明:弹性变形阶段,竖向荷载-沉降曲线呈线性变化趋势,等截面桩比变截面桩桩身沉降较小;塑性屈服阶段,等截面桩与变截面桩单桩承载力几乎一致。变截面位置对桩侧摩阻力沿深度的分布有一定影响,最大侧摩阻力位置根据变截面的位置而变化。变截面桩的平均侧摩阻力较等截面桩的平均侧摩阻力大,变截面桩侧摩阻力效果较等截面桩更有优势。在相同承载力条件下,变截面桩所耗费的材料较等截面少,对于竖向承载特性,变截面桩与等截面桩表现基本一致,因此使用变截面桩能节约工程成本。  相似文献   
2.
Fiber production from inorganic industrial solid wastes is an effective waste management strategy. Because of cost considerations, most enterprises generally use local solid wastes as raw materials to produce fibers. In this study, we explored the feasibility of producing fibers using fly ash and magnesium slag. The results show that the melting temperature of the blends composed of fly ash, magnesium slag, and a small amount of calcined dolomite first decreased and then increased with an increase in acidity coefficient (Mk) from 1.0 to 2.4. The samples could form a eutectic system in the Mk range of 1.4–1.8, and therefore have a relatively low melting temperature in this Mk range. Fly ash could react with magnesium slag and calcined dolomite to form akermanite, gehlenite-magnesium, and anorthite at temperatures close to the melting temperature; therefore, these crystalline phases were the main reaction products formed in the samples with Mk values lower than 1.80. Anorthite reacted further with some Na-containing and Si-containing spieces to produce labradorite. Thus, the content of anorthite and labradorite rapidly increased and they became the major crystal phases in the blend samples with Mk values greater than 1.80. MAS-NMR spectroscopic analysis revealed that the network structure of the melts depended on the ratio of bridging oxygen to non-bridging oxygen; a high ratio of bridging oxygen to non-bridging oxygen could lead to the formation of a dense network structure in the melt. The blends of fly ash and magnesium slag can be used to produce wool fibers and continuous fibers. In addition, the suitable temperature ranges for the production of both types of fibers were determined. The drawing temperature for continuous fiber production depended on the degree of polymerization and structure of the melt.  相似文献   
3.
液压驱动是目前船用舵机的主要驱动方式,其振动噪声不仅会影响系统的平稳运行、人员的健康舒适,还会对设备和元件的寿命产生影响,因此,振动噪声水平是现代船舶装备设计的关键指标之一。针对双柱塞缸对称驱动及单柱塞缸非对称驱动典型船用舵机,通过容积控制和节流控制两种方式,进行了两种舵机系统振动噪声的对比试验,探讨了不同驱动方式、不同驱动速度等因素对船用舵机振动噪声的影响。结果表明:采用阀控双柱塞缸对称驱动可有效降低舵机系统的振动噪声。  相似文献   
4.
当带孔的塑件由侧抽型芯和动模型芯配合成型时,侧抽型芯与动模的相对运动造成模具零件磨损,导致生产的塑件不合格,设计了防止型芯滑动磨损的浮动镶件,避免了模具零件的磨损。  相似文献   
5.
Diamond-like carbon (DLC) possesses brilliant and excellent properties, including excellent corrosion resistance as well as outstanding wear resistance. Ni and B co-doped DLC films were deposited on AZ91D magnesium alloy by electrodeposition under mild conditions (300 V and 25°C). Uniform and dense morphology of co-doped DLC films were observed, and Ni and B were uniformly incorporated into the carbon-based films. Among all the electrodeposits, the appearance of D and G peaks near 1330 and 1570 cm−1 revealed that the as-deposited films were typical DLC films. As the addition of Ni was increased to 0.05 g, the highest microindentation hardness, the lowest friction coefficient, and wear loss were achieved to be 164.5 HV, 0.3, and 0.6 × 10−5 kg/m, respectively. The amorphous carbon films fabricated at 0.05 g Ni had the lowest corrosion current density and the most positive corrosion potential, which was mainly due to the small and dense granular structure effectively hindering the penetration of corrosion media.  相似文献   
6.
庄勋桐 《中国园林》2021,37(11):121
泉州“生态连绵带”规划建设作为一种新的生态网 络空间形式出现,虽然已经在生态空间连续、居民日常可达、 功能构成复合、景观形式优美、经济效益显著等方面取得一定 的成效,但仍然存在较多可以优化提升的空间。为更好地开展 “生态连绵带”项目实施,通过深入调查研究,并运用AHP 分析法和李克特量表双重科学的评估体系,对已完成的若干泉 州“生态连绵带”示范项目加以评估,确定出示范项目中规划 建设效果最佳的项目,再从其生态保护修复、园林景观营造、 可持续发展理念及历史文化展示等方面的关键技术和难点重点 进行研究分析,为泉州“生态连绵带”后续规划建设提供理论 依据与技术支撑。  相似文献   
7.
Ultra-high molecular weight polyethylene (UHMWPE) is extensively used in frictional applications due to its advanced wear resistance. This advanced polymer is reinforced with hard particulate fillers for further developments against wear conditions. Since elevated temperatures prevail in the service conditions, wear behavior of UHMWPE composites is an important issue for the engineering applications. In the present work, UHMWPE-based composites including silicon carbide (SiC) fillers were fabricated in a compression molding chamber. In the specimen preparation stage, molding pressure, filler amount, and filler particle size were varied to investigate the influence of these variables. Upon deciding the optimum parameters from the wear tests conducted at room temperature, the wear experiments were repeated for the optimum specimen at elevated temperatures, such as 40 and 60°C. According to the results, the wear behavior of the SiC/UHMWPE composites is heavily changed by the effect of elevated temperature. Adhesive effect is pronounced at elevated temperatures while the wear characteristics possess the abrasive effect in the sliding path. In addition, the composites exhibit an accelerated material loss as temperature increases during the frictional system.  相似文献   
8.
In this work, a novel graphene oxide (GO)-fly ash cenospheres (FACs) hybrid fillers was introduced to improve the wear and corrosive resistance of epoxy resin (ER) composite coatings. The tribological behavior and the corrosion performance of three kinds of coatings (pure ER, GO/ER and GO-FACs/ER coatings) were studied and the reinforced mechanisms of coatings filled by different fillers were analyzed. The friction coefficient and wear rate of the ER coatings were decreased with the addition of GO-FACs hybrids. The scanning electron microscope images showed that the dispersibility and compatibility of GO-FACs hybrids were effectively improved compared with that of GO sheet. The water contact angle examination indicated that the hydrophobicity of the GO-FACs/ER coatings increased. The electrochemical impedance spectroscopy (EIS) results demonstrated that the GO-FACs/ER coatings have better anticorrosion performance compared with the pure ER coatings and the GO/ER coatings. The hydrophobic surface and the well dispersed fillers constitute the dual barrier to resist the corrosion medium.  相似文献   
9.
采用ABAQUS软件对牵引绳用调控式往复密封装置在高压环境下的密封性能进行有限元分析,获得密封组件与牵引绳的应力分布及变形情况,分析调控压力与介质压力对密封泄漏率及摩擦力的影响规律。设计搭建主密封试验装置并进行试验验证。结果表明:采用合理的调控压力与密封结构设计可以实现较好的接触应力分布,显著地减少密封泄漏;随着调控压力的增加,密封泄漏率先迅速下降,而后缓慢下降并逐渐趋于稳定,当调控压力大于介质压力的1.3倍时,泄漏率接近于0;增加调控压力导致摩擦力呈现先缓后急的增长趋势;介质压力对密封环具有开启作用,能够降低流体膜压力而减小摩擦力;工程应用中,维持调控压力比介质压力高出0.2~0.5 MPa时密封效果最好。  相似文献   
10.
In order to determine the effect of heat treatment on the mechanical and wear properties of Zn–40Al– 2Cu–2Si alloy, different heat treatments including homogenization followed by air-cooling (H1), homogenization followed by furnace-cooling (H2), stabilization (T5) and quench–aging (T6 and T7) were applied. The effects of these heat treatments on the mechanical and tribological properties of the alloy were studied by metallography and, mechanical and wear tests in comparison with SAE 65 bronze. The wear tests were performed using a block on cylinder type test apparatus. The hardness, tensile strength and compressive strength of the alloy increase by the application of H1 and T6 heat treatments, and all the heat treatments except T6, increase its elongation to fracture. H1, T5 and T6 heat treatments cause a reduction in friction coefficient and wear volume of the alloy. However, this alloy exhibits the lowest friction coefficient and wear volume after T6 heat treatment. Therefore, T6 heat treatment appears to be the best process for the lubricated tribological applications of this alloy at a pressure of 14 MPa. However, Zn–40Al–2Cu–2Si alloy in the as-cast and heat-treated conditions shows lower wear loss or higher wear resistance than the bronze.  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