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   127492篇
  免费   11408篇
  国内免费   6969篇
电工技术   8624篇
技术理论   11篇
综合类   9714篇
化学工业   19986篇
金属工艺   7479篇
机械仪表   8026篇
建筑科学   10344篇
矿业工程   3738篇
能源动力   3552篇
轻工业   11307篇
水利工程   2736篇
石油天然气   7286篇
武器工业   1222篇
无线电   14070篇
一般工业技术   14036篇
冶金工业   5513篇
原子能技术   1431篇
自动化技术   16794篇
  2024年   550篇
  2023年   2063篇
  2022年   3865篇
  2021年   5181篇
  2020年   4007篇
  2019年   3241篇
  2018年   3716篇
  2017年   4184篇
  2016年   3843篇
  2015年   5296篇
  2014年   6741篇
  2013年   7852篇
  2012年   9083篇
  2011年   9830篇
  2010年   8769篇
  2009年   8334篇
  2008年   8358篇
  2007年   7839篇
  2006年   7393篇
  2005年   6143篇
  2004年   4319篇
  2003年   3710篇
  2002年   3401篇
  2001年   3091篇
  2000年   2691篇
  1999年   2496篇
  1998年   1836篇
  1997年   1548篇
  1996年   1337篇
  1995年   1188篇
  1994年   943篇
  1993年   687篇
  1992年   522篇
  1991年   429篇
  1990年   383篇
  1989年   263篇
  1988年   198篇
  1987年   127篇
  1986年   126篇
  1985年   68篇
  1984年   50篇
  1983年   30篇
  1982年   37篇
  1981年   30篇
  1980年   34篇
  1979年   8篇
  1976年   5篇
  1973年   3篇
  1959年   10篇
  1951年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
讨论了石英晶体监控法在光学薄膜镀制过程中的应用原理。通过与常规的光学监控法镀制的膜层相比较.证实了石英晶体监控法有助于提高光学薄膜的光学品质。试验表明所镀膜层的光学性能优异,在光通信和激光器等领域具有广阔的应用前景。  相似文献   
112.
113.
This paper presents a computer-aided cloud-analysis approach by effectively modeling the integration of heterogeneous satellite-observed data and remote sensing images. First, automatic cloud detection and tracking methods are proposed to identify the georeferenced cloud objects in satellite remote sensing images. Then, a data integration modeling mechanism is designed to collect meaningful properties of those detected clouds by integrating the heterogeneous satellite-observed data and imaging into a unified cloud database. Finally, based on the integrated global data schema, a two-phase data mining method employing the decision tree algorithm is implemented to analyze and forecast the meteorological activities of all the cloud objects. Experimental results have shown that the proposed data integration model can effectively extract and synthesize all the useful information from heterogeneous data sources to generate a unified view of knowledge, on the basis of which the evolvement trends of clouds can be analyzed properly.  相似文献   
114.
车间调度下流水线制造系统的仿真研究   总被引:6,自引:0,他引:6  
在车间调度的基础上,采用事件调度法仿真策略,对流水线制造系统的仿真进行研究。  相似文献   
115.
116.
想象热刺激和实际热刺激脑功能成像研究   总被引:2,自引:0,他引:2  
本实验用功能性核磁共振成像技术(fMRI)对人想象热刺激和实际接受热刺激进行了研究。这是继想象冷刺激和实际接受冷刺激实验之后的另一个关于想象刺激与实际接受刺激的实验、实验结果发现想象热刺激与实际热刺激激活脑区既有相同之处也有不同之处。想象热刺激激活了初级体感区(SI)、左侧额上回、左侧额中回、运动区和扣带回。实际热刺激激活了初级体感区(SI)区、右侧额上回、右侧额中回、运动区。区别在于额叶和扣带回,这个结论与想象冷刺激和实际冷刺激实验的结论几乎相同,只是两种情况下在额叶的具体差别不同。  相似文献   
117.
In this paper, a feasibility study of a randomized space vector switching scheme for three-level inverters is reported. Based on the traditional space vector concept for pulse width modulation (PWM) inverters, the sequence of the space vector is randomized in this scheme. The overall vector, resulting from the randomization, is mathematically identical to that of the traditional space vector. It has been found that the randomized scheme can effectively spread the switching noise over a wide frequency range and at the same time keep the steady-state link capacitor voltage balanced. The proposed scheme has been implemented in real time in a digital controller and its features have been experimentally confirmed  相似文献   
118.
In-phase(IP) and out-of-phase(OP)thermal-mechanical fatigue(TMF) behavior of cast Ni-base superalloy K417 was studied.All experiments were carried out under total strain control with temperature cycling between 400-850℃.Both in-phase and out-of-phase TMF specimens exhibited cyclic hardening followed by cyclic softening at the minimum temperature.Besides,they cyclically hardened in the early stage of life followed by cyclic softening at the minimum temperature.Besides,they cyclically hardened in the early stage of life followed by cyclic softening at the maximum temperature.OP TMF life was longer than of IP TMF.Various damage mechanisms operating in different controlled strain ranges and phasing were discussed.A few life prediction methods for isothermal fatigue were used to handle TMF fatigue and their applicability to superalloy K417 was evaluated.The SEM analysis of the fracture surface showed that transgranular fracture was the principal cracking mode for both IP and OP TMF.Oxidation was the main damage mechanism in causing shorter fatigue life for IP TMF compared with OP TMF.  相似文献   
119.
Combined shape and sizing optimization of truss structures   总被引:1,自引:0,他引:1  
 In this paper, an evolutionary optimization method is presented for weight minimum problem of a 3-dimensional truss structure in terms of nodal coordinates and element cross-sectional areas. The structure is subject to stress, local buckling and displacement constraints. Two types of design variables with different natures are optimized separately: (1) a fully stressed design (FSD) and scaling techniques are applied to sizing variables and (2) the evolutionary node shift method is applied to shape variables. Alternating procedure is utilized to couple the two types of variables and to combine the results. The optimum solution is achieved gradually from the initial configuration design. Two typical truss structures are examined to illustrate the validity of the method. Received: 22 October 2001 / Accepted: 04 June 2002 This research work is supported by the National Natural Science Foundation of China under the guarantees no. 10072050 and 10172072, respectively.  相似文献   
120.
热力除氧器运行特性实验研究   总被引:2,自引:0,他引:2  
在热力除氧器实验装置上,对研制的新型除氧器进行了稳态运行特性和动态运行特性实验,得到了除氧器的各种运行特性曲线。研究结果表明,由于对喷嘴和填料进行改进,建立起有利于除氧的传热传质条件,使所研制的除氧器具有良好的稳态及动态运行特性,除氧效果优良。  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