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   333715篇
  免费   24131篇
  国内免费   12578篇
电工技术   17987篇
技术理论   56篇
综合类   19737篇
化学工业   56680篇
金属工艺   18584篇
机械仪表   21195篇
建筑科学   25775篇
矿业工程   10973篇
能源动力   9783篇
轻工业   18760篇
水利工程   5281篇
石油天然气   22999篇
武器工业   2605篇
无线电   36703篇
一般工业技术   39879篇
冶金工业   18392篇
原子能技术   3224篇
自动化技术   41811篇
  2024年   1298篇
  2023年   5238篇
  2022年   8920篇
  2021年   12600篇
  2020年   9865篇
  2019年   8033篇
  2018年   9237篇
  2017年   10417篇
  2016年   9317篇
  2015年   12274篇
  2014年   15913篇
  2013年   19243篇
  2012年   20232篇
  2011年   22512篇
  2010年   19259篇
  2009年   18376篇
  2008年   18009篇
  2007年   17415篇
  2006年   18298篇
  2005年   16146篇
  2004年   10353篇
  2003年   9135篇
  2002年   8141篇
  2001年   7474篇
  2000年   8004篇
  1999年   9653篇
  1998年   8156篇
  1997年   6769篇
  1996年   6365篇
  1995年   5340篇
  1994年   4378篇
  1993年   3089篇
  1992年   2492篇
  1991年   1961篇
  1990年   1504篇
  1989年   1232篇
  1988年   1019篇
  1987年   681篇
  1986年   536篇
  1985年   342篇
  1984年   243篇
  1983年   204篇
  1982年   196篇
  1981年   129篇
  1980年   131篇
  1979年   67篇
  1978年   33篇
  1977年   38篇
  1976年   55篇
  1975年   20篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
132.
前言 近20年来,随着改革开放和国民经济的飞速发展,我国建筑卫生陶瓷行业也得到快速发展,产量连年增长,成为世界上建筑卫生陶瓷的最大生产国和消费国,也是出口大国.2007年全国卫生陶瓷的产量达到15 000万件,占世界产量的40%,出口量达到5 525万件,占产量的40%.  相似文献   
133.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters.  相似文献   
134.
135.
A novel cholesterol‐imprinted polymer (CMIP‐H) was prepared by a hybrid method of covalent imprinting and non‐covalent imprinting. This approach involves the copolymerization of a template‐containing monomer, cholesteryl 2‐hydroxyethyl methacrylate carbonate, and a cross‐linker, followed by hydrolysis to afford a flexible guest‐binding site accompanied with the easy and efficient removal of a ‘sacrificial spacer’. The effect of solvent on the binding capacity of CMIP‐H towards cholesterol was studied, indicating that a good binding capacity towards cholesterol could be achieved in a less‐polar solvent. The binding experiments of CMIP‐H towards a series of structural analogues of cholesterol, including cholesterol acetate, progesterone and stigmasterol, were carried out in hexane. The results showed that CMIP‐H almost did not bind cholesterol acetate at all because the hydrogen‐bonding site is blocked. It exhibited a similar binding towards both cholesterol and stigmasterol, but much higher binding towards progesterone. Copyright © 2005 Society of Chemical Industry  相似文献   
136.
137.
Colour Centres and Energy Transfer in BaF2-xClx:Eu2+ Phosphors   总被引:1,自引:1,他引:0  
The optical absorption spectra of BaF2-xClx:Eu2 after ultraviolet (UV) light excitation were investigated.The differences between the absorption spectra after and before excitation (DAS) were observed.The DAS increase at both the high and the low energy side of F band in BaF2-xClx:Eu2 after 245 nm UV light excitation.The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres (association of F(Cl-) centres), whose absorption band matches the HeNe laser better, may explain the latter.In the write-in process, the transfer of electrons is via tunneling.In the readout process, the transfer of electrons captured in F(F-) and Fa centres is more likely via tunneling, and that of F(Cl-) centres is more likely via conduction band.  相似文献   
138.
Using the concept of loss compensation, novel broad-band monolithic microwave integrated circuits (MMICs), including an amplifier and an analog multiplier/mixer, with LC ladder matching networks in a commercial 0.35-mum SiGe BiCMOS technology are demonstrated for the first time. An HBT two-stage cascade single-stage distributed amplifier (2-CSSDA) using the modified loss-compensation technique is presented. It demonstrates a small-signal gain of better than 15 dB from dc to 28 GHz (gain-bandwidth product=157 GHz) with a low power consumption of 48 mW and a miniature chip size of 0.63 mm2 including testing pads. The gain-bandwidth product of the modified loss-compensated CSSDA is improved approximately 68% compared with the conventional attenuation-compensation technique. The wide-band amplifier achieves a high gain-bandwidth product with the lowest power consumption and smallest chip size. The broad-band mixer designed using a Gilbert cell with the modified loss-compensation technique achieves a measured power conversion gain of 19 dB with a 3-dB bandwidth from 0.1 to 23 GHz, which is the highest gain-bandwidth product of operation among previously reported MMIC mixers. As an analog multiplier, the measured sensitivity is better than 3000 V/W from 0.1 to 25 GHz, and the measured low-frequency noise floor and corner frequency can be estimated to be 20 nV/sqrt(Hz) and 1.2 kHz, respectively. The mixer performance represents state-of-the-art result of the MMIC broad-band mixers using commercial silicon-based technologies  相似文献   
139.
利用引进的制造技术和设备,制作出了 APT(STLRI)—1.78型系列化光纤连接器。  相似文献   
140.
in-situ transmission electron microscopy (TEM) tensile tests on as-cast and aged 63Sn37Pb solder alloys were conducted, and the fracture behavior in nanometer scale ahead of the crack tip was inspected and discussed. Results show that the fracture was completed by connecting the discontinuous cracks or voids. Dislocation behavior was concentrated along the grain boundaries for as-cast samples, and displayed mainly as dislocation climb. The crack was intergranular dominated under the lower strain rate. While remarkable mutual dislocation emission was detected in the aged solder. Transgranular cracks were dominant in the fractured area, and they propagated by linking up with the nanometer scale cracks ahead of the crack tips under the effective promotion of the inverse dislocation emission. At the same time, the partial interphase or intergranular cracks in the thinned area were also found. Under this condition, a new critical stress intensity factor K c to define the mutual dislocation emission was proposed.  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