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   74649篇
  免费   9505篇
  国内免费   4379篇
电工技术   6466篇
技术理论   4篇
综合类   5468篇
化学工业   11395篇
金属工艺   4567篇
机械仪表   4968篇
建筑科学   6271篇
矿业工程   2439篇
能源动力   2171篇
轻工业   5337篇
水利工程   1739篇
石油天然气   3808篇
武器工业   851篇
无线电   9361篇
一般工业技术   8822篇
冶金工业   2929篇
原子能技术   792篇
自动化技术   11145篇
  2025年   5篇
  2024年   1308篇
  2023年   1972篇
  2022年   3401篇
  2021年   4638篇
  2020年   3361篇
  2019年   2502篇
  2018年   2642篇
  2017年   2862篇
  2016年   2605篇
  2015年   3426篇
  2014年   4066篇
  2013年   4741篇
  2012年   5331篇
  2011年   5505篇
  2010年   4862篇
  2009年   4548篇
  2008年   4384篇
  2007年   4107篇
  2006年   3758篇
  2005年   3402篇
  2004年   2211篇
  2003年   1784篇
  2002年   1701篇
  2001年   1406篇
  2000年   1404篇
  1999年   1309篇
  1998年   995篇
  1997年   817篇
  1996年   787篇
  1995年   625篇
  1994年   520篇
  1993年   371篇
  1992年   305篇
  1991年   209篇
  1990年   141篇
  1989年   133篇
  1988年   105篇
  1987年   66篇
  1986年   67篇
  1985年   27篇
  1984年   26篇
  1983年   13篇
  1982年   21篇
  1981年   13篇
  1980年   19篇
  1979年   12篇
  1969年   1篇
  1959年   7篇
  1951年   7篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
The HUB-CI model is investigated in a telerobotic system in a client/server network to manage the lifecycle of engineering design and prototyping. The purpose of this platform is to support collaborative engineering design and proof of concept to enhance distributed team collaboration and resource utilization. The suggested platform is exemplified in two collaboration support tools and a physical prototyping platform. Structured Co-Insight Management is developed to support innovative idea exchanges and the consensus decision-making during the design process. Conflict/error detection management helps preventing conflicts and errors during the lifecycle of design and development. Physical collaboration over the network occurs when a team controls the telerobot operation during prototyping and testing in design cycles. A pilot system is implemented with a group project for the design of an electronic circuit (including both hardware and software designs). The functional assessment method is used to compare this platform to other collaborative design tools. The system presented offers unique qualitative advantages as an integrated collaboration support system.  相似文献   
33.
1 率值控制工艺结构 衡量生料质量的标准是水泥的三个率值.石灰石饱和系数KH、硅酸率SM、铝氧率IM,即在出磨生料中,、Fe2O3、Al2O3、SiO2诸氧化物的百分比含量必须满足以下二三式:  相似文献   
34.
Three-dimensionally ordered long-range macroporous carbon structures were prepared using commercially available phenolic resin by utilizing sacrificial colloidal silica crystalline arrays as templates that were subsequently removed by HF etching after pyrolysis in an argon atmosphere. SEM, TEM, and BET were employed to characterize the morphology and the surface area of the porous carbon structures. The pore size (150–1000 nm) and BET surface area, which reflect pore volume (298.6 m2/g (1.32 cm3/g) ∼ 93.7 m2/g (0.12 cm3/g)), of the macroporous carbon structures produced were approximately proportional to the size (150–1000 nm) of the sacrificial silica sphere templates used (annealing temp. 550°C). The achieved 550 nm porous carbon structures were examined to function as potential catalyst carriers and were successfully impregnated with Ag or Pt-Ru on their inner walls after borohydride reduction at room temperature. In addition, porous carbon patterns were fabricated using the ‘micromolding in capillary’ technique, which has potential applications in the microreaction technology.  相似文献   
35.
Lithium manganese oxides LiMn2O4 and rare earth elements doped LiNd0.01Mn1.99O4 were synthesized by microwave method. The structure and the electrochemical performances of the samples were characterized. XRD data shows both samples exhibit the same pure spinel phase. But due to the introduction of Nd3+ ion into the unit cell, the lattice parameter of the Nd-doped spinel was larger than that of the undoped one. The two samples had a similar morphology including small particle size and homogeneous particle distribution as tested by SEM. The cyclic voltammmetry and constant-current charge-discharge tested that Nd-doped spinel displayed a better reversibility and cycleability.  相似文献   
36.
The structure of benzoxazines is similar to that of phenolic resin through thermal self‐curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn–Wall–Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn–Wall–Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 730–737, 2005  相似文献   
37.
心理资本前因变量研究   总被引:5,自引:0,他引:5  
采用心理资本问卷对分别属于医药、建筑、水利工程、电信、通讯运营和服务行业的6家企业的员工进行了调查.根据对回收的283份有效问卷的统计分析,认为员工的性别、受教育程度和所在企业的性质对员工心理资本不会产生显著性影响,而员工年龄的影响显著,50岁以上员工的总体心理资本水平高于其他年龄段员工.  相似文献   
38.
Silver powder was fabricated by spray pyrolysis, using 2%–20% AgNO3 solution, 336–500 mL/h flux of AgNO3 solution, 0.28–0.32 MPa flux of carrier gas and in the 620–820 °C temperature range. The effects of furnace set temperature, concentration of AgNO3 aqueous solution, flux of AgNO3 aqueous solution as well as carrier gas on the morphology and particle size distribution of silver powder, were investigated. The experimental results showed that with the high concentration of AgNO3 aqueous solution, the average grain size of silver decreased with the increasing of furnace set temperature. But the gain size distribution was not homogenous, the discontinuous grain growth occurred. With the low concentration of AgNO3 aqueous solution, the higher furnace set temperature made the nano sliver grains sintered together to grow. Nano silver powder about 100 nm was fabricated by spray pyrolysis, using 2wt% AgNO3 solutions, 336 mL/h flux of AgNO3 aqueous solution, 0.32 MPa flux of carrier gas at 720 °C furnace set temperature.  相似文献   
39.
The zonal disintegration phenomenon (ZDP) is a typical phenomenon in deep block rock masses. In order to investigate the mechanism of ZDP, an improved non-linear Hock-Brown strength criterion and a bi-linear constitutive model of rock mass were used to analyze the elasto-plastic stress field of the enclosing rock mass around a deep round tunnel. The radius of the plastic region and stress of the enclosing rock mass were obtained by introducing dimensionless parameters of radial distance. The results show that tunneling in deep rock mass causes a maximum stress zone to appear in the vicinity of the boundary of the elastic and the plas-tic zone in the surrounding rock mass. Under the compression of a large tangential force and a small radial force, the rock mass in the maximum stress zone was in an approximate uniaxial loading state, which could lead to a split failure in the rock mass.  相似文献   
40.
为解决传统病房有线呼叫系统存在的布线复杂、易出故障、维修不便、不能在现有床位基础上及时增加新床位信息等问题,提出了无线呼叫系统设计。采用STC89C52系列单片机作为主控芯片,nRF905作为无线收发的核心芯片,并配以相应的LCD显示屏和声光报警器,设计出了无线病房呼叫系统。结果表明,该系统可靠传输距离达90 m以上,具有一定的抗干扰性,且可以临时方便增加床位显示信息,能够满足医院的临时实际需求。该系统性能稳定,操作简便,可以有效代替传统有线呼叫系统。  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