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   19022篇
  免费   1663篇
  国内免费   807篇
电工技术   1177篇
综合类   1037篇
化学工业   3203篇
金属工艺   1041篇
机械仪表   1177篇
建筑科学   1234篇
矿业工程   504篇
能源动力   628篇
轻工业   1220篇
水利工程   272篇
石油天然气   1015篇
武器工业   145篇
无线电   2480篇
一般工业技术   2439篇
冶金工业   1046篇
原子能技术   155篇
自动化技术   2719篇
  2024年   39篇
  2023年   333篇
  2022年   500篇
  2021年   856篇
  2020年   579篇
  2019年   474篇
  2018年   560篇
  2017年   616篇
  2016年   561篇
  2015年   763篇
  2014年   990篇
  2013年   1240篇
  2012年   1202篇
  2011年   1339篇
  2010年   1184篇
  2009年   1064篇
  2008年   1103篇
  2007年   1018篇
  2006年   999篇
  2005年   915篇
  2004年   582篇
  2003年   497篇
  2002年   427篇
  2001年   380篇
  2000年   373篇
  1999年   446篇
  1998年   415篇
  1997年   320篇
  1996年   296篇
  1995年   228篇
  1994年   210篇
  1993年   163篇
  1992年   133篇
  1991年   106篇
  1990年   98篇
  1989年   77篇
  1988年   57篇
  1987年   27篇
  1986年   43篇
  1985年   30篇
  1984年   25篇
  1983年   19篇
  1982年   34篇
  1981年   26篇
  1980年   17篇
  1979年   17篇
  1978年   10篇
  1977年   14篇
  1976年   20篇
  1975年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Reconstruction of spectral information based on multi‐channel image system is a significant problem in color reproduction, detection, and recognition. A spectral radiance reconstruction from trichromatic digital camera responses is researched in this article. The mapping relationship between the trichromatic imaging system response and the incident spectral radiance is analyzed. Then, in order to remove the ill‐posedness of the problem, a regularized constraint solution model of spectral radiance reconstruction matrix is established. And the spectral radiance can be reconstructed by spectral radiance reconstruction matrices and trichromatic imaging system response. Finally, the spectral radiance reconstruction matrix is estimated by the system radiometric calibration experiment. The input radiance is offered by a LCD display. A 3‐factor and 9‐level orthogonal test is designed for the calibration experiment, and a test set of 24 colors is used for precision analysis. The results show that the average relative mean error of our method is 8.69%, it is lower than that of Wiener filtering method by 2.84%. The method can reconstruct spectral radiance information effectively.  相似文献   
2.
The main scope of this comprehensive study is to investigate the effects of poly(p-benzophenoneoxycarbonylphenyl acrylate), poly(BPOCPA), which presenting as only graft units or both graft and ungrafted units in the matrix, on the fundamental features of isotactic polypropylene (IPP). The graft copolymerization of BPOCPA onto IPP was performed with the aid of bulk melt polymerization at varying monomer content levels ranging from 5% to 40%. The thermal behavior, crystal quality, mechanical performance, and surface morphology of the samples were investigated by means of differential scanning calorimeter, X-ray diffractometer (XRD), universal mechanical test, and scanning electron microscope (SEM) techniques. Thermal analyses depicted that there existed the noteworthy enhancements in both crystalline melting temperatures and percent crystallinities of matrix polymers. Furthermore, according to XRD results, a and b parameters increased significantly at low percentages of the graft units, while the parameter c decreased in all products in consistence with the content. As for the mechanical characterization, the grafting led to remarkable improvements in modulus, tensile and impact strength of the products. SEM micrographs indicated that the samples were completely homogeneous without any phase separation and the products exhibited brittle nature with some ductility.  相似文献   
3.
The joining of liquid-phase sintered SiC (LPS-SiC) ceramics was conducted using spark plasma sintering (SPS), through solid state diffusion bonding, with Ti-metal foil as a joining interlayer. Samples were joined at 1400 °C, under applied pressures of either 10 or 30 MPa, and with different atmospheres (argon, Ar, vs. vacuum). It was demonstrated that the shear strength of the joints increased with an increase in the applied joining pressure. The joining atmosphere also affected on both the microstructure and shear strength of the SiC joints. The composition and microstructure of the interlayer were examined to understand the mechanism. As a result, a SiC-SiC joining with a good mechanical performance could be achieved under an Ar environment, which in turn could provide a cost-effective approach and greatly widen the applications of SiC ceramic components with complex shape.  相似文献   
4.
Suspension plasma spraying (SPS) as a potential technique to prepare thermal barrier coatings (TBCs) has been attracting more and more attention. However, most reports on SPS were carried out in the atmosphere. Given the unique features of in-flight particles and plasma jets under low pressure, the resulting coatings are expected to be different from those under atmospheric pressure. In this article, yttria-stabilized zirconia (YSZ) thermal barrier coatings were prepared using suspension plasma spraying under different environmental pressures. The results show that as the environmental pressure decreased, the column-like structural coating turned into a vertical crack segmented structure, as well as a dramatic decrease in surface roughness. More nanoparticle agglomerates were formed in the coating under lower environmental pressures. The real porosity of the coating increased with a decrease in environmental pressure.  相似文献   
5.
针对旅行商问题适用范围存在的局限性,结合实际的仓库拣货作业优化实例开展研究.考虑仓库内各货位点之间的相对位置关系以及拣货员可能行走的路线,设计出关于拣货员行走路线的分类算法;提出虚拟点的概念来解决旅行商问题求解时起点、终点不一致的问题;利用虚拟点,根据任务单要求找出拣货员所有的最优位置访问顺序;比较每一种情况,得到拣货员的最优路径,以实现缩短拣货总时间、减少人力和物力的总目标,较好地提高拣货效率.  相似文献   
6.
Ma  Yonghong  Yang  Xiaomeng  Qu  Sen  Kong  Lingkai 《Scientometrics》2022,127(3):1273-1294
Scientometrics - The purpose of the present paper is to investigate the formation mechanism of big data technology cooperation networks by considering the combined effect of three key factors,...  相似文献   
7.
Yang  Ning  Wang  Zhelong  Zhao  Hongyu  Shi  Xin  Qiu  Sen 《Multimedia Tools and Applications》2022,81(13):17595-17614
Multimedia Tools and Applications - Human-human interactions recognition has high potential to have a big impact on enabling robots being able to interact with people. Recently, body sensor...  相似文献   
8.
以红花菜籽油中亚油酸为原料,偏铁酸钠为催化剂,在单因素试验的基础上,选取反应温度、反应时间、催化剂用量为考察因素,以异构化产物共轭亚油酸(CLA)转化率为响应值,通过响应面分析法对异构化反应进行优化,并建立相应的回归模型,试验结果表明,红花菜籽油中亚油酸异构化为CLA的最佳工艺为:反应温度195℃、反应时间4.7 h、催化剂用量0.6 g,在此条件下得到CLA转化率为92.90%,与预测值93.92%相比,误差为1.02%.然后再通过脲素包合纯化、经2%的H2SO4-CH3OH溶液甲酯化后,用气相色谱-质谱联用仪检测CLA含量为64.27%.  相似文献   
9.
向森 《电子测试》2021,(6):125-126
电路板在我们的日常生活中非常常见,这就使得印刷电路板的缺陷检测显得尤为重要。AOI作为新兴的检测PCB板缺陷的系统,在生产实际中正在被大家熟知并且应用。相较于传统的检测方式,AOI系统比较灵活,无论是在检测时间还是系统运算上,或者是对相关技术人员的要求相较于传统方式都比较有优势,本文就AOI系统在实际中的应用展开讨论,分析并且介绍了在实际应用中的具体细则。  相似文献   
10.
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