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   40569篇
  免费   4233篇
  国内免费   1575篇
电工技术   1908篇
综合类   2289篇
化学工业   5466篇
金属工艺   2045篇
机械仪表   2813篇
建筑科学   265篇
矿业工程   195篇
能源动力   854篇
轻工业   1010篇
水利工程   130篇
石油天然气   140篇
武器工业   209篇
无线电   16267篇
一般工业技术   9743篇
冶金工业   453篇
原子能技术   378篇
自动化技术   2212篇
  2025年   188篇
  2024年   850篇
  2023年   831篇
  2022年   725篇
  2021年   1018篇
  2020年   1141篇
  2019年   1090篇
  2018年   1106篇
  2017年   1437篇
  2016年   1403篇
  2015年   1546篇
  2014年   2017篇
  2013年   2525篇
  2012年   2634篇
  2011年   2955篇
  2010年   2181篇
  2009年   2187篇
  2008年   2188篇
  2007年   2531篇
  2006年   2331篇
  2005年   1954篇
  2004年   1705篇
  2003年   1652篇
  2002年   1330篇
  2001年   1311篇
  2000年   1054篇
  1999年   747篇
  1998年   637篇
  1997年   563篇
  1996年   447篇
  1995年   340篇
  1994年   312篇
  1993年   290篇
  1992年   256篇
  1991年   244篇
  1990年   182篇
  1989年   125篇
  1988年   66篇
  1987年   40篇
  1986年   36篇
  1985年   49篇
  1984年   30篇
  1983年   20篇
  1982年   18篇
  1981年   13篇
  1979年   9篇
  1978年   9篇
  1976年   10篇
  1975年   9篇
  1974年   15篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
介绍了一种新型的光纤传感器,采用热刻-酸蚀法在光纤上形成一些周期性刻纹结构,使得感受应变量的部分成为光纤本身的固有结构。这种光纤传感器具有线性、可重复的输入、输出响应且没有滞后效应,与其它传感器相比其最大的优点是灵敏度高、外形尺寸小。  相似文献   
72.
本文报道了PCVD法数据光纤的研制,包括光纤设计、工艺流程及关键工艺问题,还给出了该数据光纤产品性能的统计结果。  相似文献   
73.
关于光子学与光电子学   总被引:4,自引:0,他引:4  
本文论述了光了学和光电子学的有关情况,以及光子学与光电子学的讨论中出现的几中不同的观点,展望面向21世纪的光子学在我国信息产业中的重要意义。  相似文献   
74.
利用绝热扰动法研究了色散缓变光纤中Raman孤子自频移效应,得到了色散缓变光纤中Raman孤子自频移的表达式。结果表明:光纤色散变化率存在一个可以有效抑制孤子自频移的阈值,当光纤色散变化率大于这个阈值时,色散缓变光纤可以抑制孤子自频移,而当光纤色散变化率小于这个阈值时,色散缓变光纤不仅不能抑制孤子自频移,反而加剧孤子自频移。  相似文献   
75.
王劲松  毛庆和 《通信学报》1998,19(12):34-37
本文从理论上研究了四波混频在多级放大频分复用光通信系统中的特性,提出了一种消除四波混频串扰的新方法,该方法只需适当选择信道间隔,无需增添其它器件,因而更有利于在实际光通信系统当中的应用。  相似文献   
76.
The electrochemical bath used for growing device-quality CIS (CuInSe2) thin films by co-deposition as well as layer-by-layer (LBL) deposition was characterised and optimised with respect to the film properties. The bath composition was varied by changing the Cu, In and Se ion concentrations in specific ratios in both co-deposition and LBL deposition. The film properties were analysed using techniques such as SEM (scanning electron microscopy), EPMA (electron probe microanalysis), AES (Auger electron spectroscopy) and XRD (X-ray diffraction). The structural, morphological and compositional properties of the films were characterised and their variation is attributed to the bath composition and growth conditions. © 1998 John Wiley & Sons, Ltd.  相似文献   
77.
A new method to grow single crystals with stoichiometry close to 1:1:2 of CuInTe2, an important member of the Cu-III-VI2 family of semiconductors is described. This consists of tellurization in the liquid phase of stoichiometric Cu and In and later solidification under directional freezing. It is found from energy dispersive spectroscopy that the ingots obtained with the evaporation temperature (Tt) of Te at 590 and 635°C were very close to the ideal stoichiometry 1:1:2. Samples of all ingots obtained with Tt between 530 and 690°C, as studied by x-ray and differential thermal analysis, were of single phase having chalcopyrite structure and p-type conductivity. Optical and electrical characterization of different ingots were made. The acceptor ionization energy EA and the density of states effective mass m p * of the holes are estimated from the temperature dependence of the hole concentration p in samples of different ingots. m p * = (0.78 ± 0.02) me agrees quite well with the reported value. From a combined analysis of the variation of EA with p1/3 and the knowledge of molecularity and valence stoichiometry of each sample, it is established that the shallow acceptor level observed in different samples with EA (0) ⋍ 30 meV is due to VIn.  相似文献   
78.
CsLiB6O10 (CLBO) thin films are grown on Si (100) and (111) substrates using lower index SiO2 and CaF2 as buffer layers by pulsed KrF (248 nm) excimer laser ablation of stoichiometric CLBO targets over a temperature range of 425 to 725°C. A CaF2 buffer layer is grown on Si by laser ablation while SiO2 is prepared by standard thermal oxidation. From extended x-ray analysis, it is determined that CaF2 is growth with preferred orientation on Si (100) at temperatures lower than 525°C while on Si (111) substrate, CaF2 is grown epitaxially over the temperature range; this agrees well with observed reflection high energy electron diffraction patterns. X-ray 2θ-scans indicate that crystalline CLBO are grown on SiO2/Si and CaF2/Si (100). Analysis of reflectance spectra from CLBO/SiO2/Si yields the absorption edge at 182 nm. Surface roughness of the CaF2 and CLBO/CaF2/Si film are 19 and 15 nm, respectively. This relatively rough surface caused by the ablation of wide bandgap CaF2 and CLBO limits the application of CLBO for waveguiding measurement.  相似文献   
79.
The optical properties of hydrogenated amorphous silicon thin films prepared by a new thermocatalytic plasma enhanced chemical vapor deposition (PECVD) method are here reported for the first time. The transmission spectrum of the film, deposited at a rate of 1.5 nm/s, was measured between 500 and 1100 nm. The envelopes of the transmission spectrum interference maxima and minima were analyzed to reveal the absorption coefficient α(λ@#@), the refractive indexn(λ), the average thickness of the film (791 nm) and the variation of the thickness (11.4 nm), using an analysis which takes into account film inhomogeneity. The modified Newton's method of numerical analysis was used to obtain the optical parameters. The optical band gap ε0} was determined to be 1.69 eV from the absorption coefficient spectrum, commensurate with values quoted for lower deposition rate PECVD films. The value for ε0}, the small variation of the film thickness, and a value for the defect density of 3.7 x 1015}cm-3} determined for similar material in other work indicate that the thermocatalytic PECVD method can produce acceptable quality films at a high deposition rate.  相似文献   
80.
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