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   10828篇
  免费   946篇
  国内免费   202篇
电工技术   411篇
技术理论   1篇
综合类   276篇
化学工业   2473篇
金属工艺   442篇
机械仪表   416篇
建筑科学   482篇
矿业工程   116篇
能源动力   348篇
轻工业   1393篇
水利工程   94篇
石油天然气   258篇
武器工业   47篇
无线电   881篇
一般工业技术   2202篇
冶金工业   471篇
原子能技术   110篇
自动化技术   1555篇
  2024年   32篇
  2023年   155篇
  2022年   237篇
  2021年   436篇
  2020年   346篇
  2019年   313篇
  2018年   431篇
  2017年   458篇
  2016年   484篇
  2015年   434篇
  2014年   590篇
  2013年   994篇
  2012年   697篇
  2011年   798篇
  2010年   689篇
  2009年   603篇
  2008年   515篇
  2007年   419篇
  2006年   392篇
  2005年   276篇
  2004年   209篇
  2003年   184篇
  2002年   190篇
  2001年   154篇
  2000年   133篇
  1999年   139篇
  1998年   189篇
  1997年   135篇
  1996年   118篇
  1995年   97篇
  1994年   87篇
  1993年   81篇
  1992年   50篇
  1991年   45篇
  1990年   41篇
  1989年   42篇
  1988年   30篇
  1987年   34篇
  1986年   32篇
  1985年   63篇
  1984年   63篇
  1983年   52篇
  1982年   52篇
  1981年   55篇
  1980年   56篇
  1979年   44篇
  1978年   38篇
  1977年   38篇
  1976年   40篇
  1975年   29篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
This paper analyzes the performance of a switching architecture. The performance measures include the elapsed time of packet transfer and the waiting time to begin transfer. The architecture is partitioned depending on the type of network used and the expected traffic in the network. Every partition has a switch with a buffer that can absorb surges of bursty traffic within the network partition. The buffer size depends on the type of the network and incoming traffic. The partition size depends on the network bandwidth, network traffic, packet size and buffer size. Examples of different networks are used to show the applications of the model. The results show that the elapsed time of packet switch transfer depends exponentially on the number of partitions in the network.  相似文献   
22.
Summary Both preferential adsorption coefficient λ and intrinsic viscosity [η] for poly (di-o-alkylphenyl methacrylates) /Tetrahydrofuran (THF)/water have been determined. The results are discussed in relation to the steric effect of the ortho-substituent groups on the aromatic ring.  相似文献   
23.
共晶碳化物团球化对铸铁激光熔敷层抗裂性的影响   总被引:1,自引:1,他引:0  
为提高铸铁表面大面积激光熔敷层抗裂性问题,通过冶金因元素控制熔敷层组织形态在熔敷材料中加入碱金属元素钾,研究了在激光快速加热条件下钾对铸铁激光熔敷层组织团球化的影响,进而分析了该球状组织对熔敷层抗裂性的影响,结果表明随熔敷金属内钾含量增多熔敷层内共晶碳化物组织呈球状及孤岛状,这种组织明显提高了熔敷层抗裂性,此外大量的渗碳体组织确保了熔敷层具有较高的耐磨性;获得了无裂纹的大面积搭接熔敷层,其对应合金系统为Fe-C-Si-Ni-K。  相似文献   
24.
复合乳化沥青的粘附性试验方法研究   总被引:1,自引:1,他引:0  
鉴于目前使用的阳离子乳化沥青粘附性试验方法难以有效评价复合乳化沥青粘附性,通过试验研究并综合考虑乳化沥青施工和路用实际情况,提出了乳化沥青水煮法试验方法和采用该方法检验复合乳化沥青粘附性时的评定标准。  相似文献   
25.
26.
Although the notion of the parallelism in multidimensional applications has existed for a long time, it is so far unknown what the bound (if any) of inter-iteration parallelism in multirate multidimensional digital signal processing (DSP) algorithms is, and whether the maximum inter-iteration parallelism can be achieved for arbitrary multirate data flow algorithms. This paper explores the bound of inter-iteration parallelism within rate-balanced multirate multidimensional DSP algorithms and proves that this parallelism can always be achieved in hardware system given the availability of a large number of processors and the interconnections between them.  相似文献   
27.
This article is focused on the phase structure development in immiscible polymer blends during melt mixing. Nonuniformity of the phase structure, i.e., the coexistence of areas containing particles with markedly different size distribution, was detected in quenched and compression molded samples of a number of various blends prepared by long and intensive mixing in the chamber of a Plasticorder. The same effect was found also for polystyrene/polyamide blends prepared in a twin‐screw extruder. It was shown that neglecting nonuniformity of the phase structure can lead to considerable error in evaluation of the effect of system parameters on the blend morphology. The reasons for the effect were discussed and it was found that inhomogeneous flow field in mixers is a plausible explanation of the nonuniform phase structure. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers  相似文献   
28.
This study examined associations of temperament at ages 6 to 12 with body-mass index (BMI) and waist circumference (WC) at ages 24 to 30 years. The participants were 619 men and women derived from the population-based Cardiovascular Risk in Young Finns Study. Temperament was operationalized as (negative) emotionality, sociability, and activity. High emotionality predicted increased BMI, independently of WC, and independently of childhood and adulthood risk factors for adult obesity. None of the temperament dimensions had any associations with WC after controlling for BMI. The findings suggest that temperamental difficulty in childhood may be a useful risk indicator for general body mass in adulthood, and the mechanisms relating temperament with body mass should be further explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
29.
ZnO-based varistor samples were prepared by the direct mixing of the constituent phases (DMCP) and sintering at 1100 °C for 2 h. The influence of the starting powder mixture's composition – the amounts of the pre-reacted varistor compounds and their composition – and its preparation, either with or without mechano-chemical activation (MCA), on the microstructure, phase composition and electrical characteristics of the varistor samples was studied. It showed that MCA improved the density and microstructural homogeneity of the varistor samples. MCA strongly affected the grain growth: it enhanced the nucleation of inversion boundaries (IBs) in the ZnO grains and the IBs-induced grain-growth mechanism resulted in uniform grain growth and hence a microstructure with smaller ZnO grains and a narrower grain size distribution. The final phase composition of the samples prepared by the DMCP method mainly depended on the presence of varistor dopants that can prevent the formation of the pyrochlore phase, especially Cr2O3, while MCA can affect it mostly by providing a homogeneous distribution of those dopants. The DMCP varistor samples prepared with MCA had much better current–voltage characteristics than the samples of the same composition prepared from unactivated powders.  相似文献   
30.
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