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   481篇
  免费   3篇
  国内免费   1篇
电工技术   27篇
综合类   2篇
化学工业   52篇
金属工艺   14篇
机械仪表   18篇
建筑科学   27篇
能源动力   20篇
轻工业   25篇
石油天然气   1篇
无线电   81篇
一般工业技术   98篇
冶金工业   101篇
原子能技术   8篇
自动化技术   11篇
  2023年   1篇
  2022年   6篇
  2021年   9篇
  2020年   2篇
  2019年   4篇
  2018年   1篇
  2017年   2篇
  2016年   2篇
  2015年   1篇
  2014年   7篇
  2013年   20篇
  2012年   11篇
  2011年   14篇
  2010年   18篇
  2009年   22篇
  2008年   20篇
  2007年   20篇
  2006年   13篇
  2005年   14篇
  2004年   15篇
  2003年   23篇
  2002年   15篇
  2001年   12篇
  2000年   8篇
  1999年   15篇
  1998年   40篇
  1997年   43篇
  1996年   24篇
  1995年   19篇
  1994年   6篇
  1993年   13篇
  1992年   12篇
  1991年   8篇
  1990年   7篇
  1989年   4篇
  1988年   1篇
  1987年   3篇
  1986年   5篇
  1985年   3篇
  1984年   3篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   2篇
  1977年   5篇
  1976年   5篇
  1974年   2篇
排序方式: 共有485条查询结果,搜索用时 0 毫秒
31.
The thermal behavior of nitrocellulose (NC) containing diphenylamine (DPA), 2‐nitrodiphenylamine (2‐NO2‐DPA), N‐nitrosodiphenylamine (N‐NO‐DPA), ethyl centralite (EC), akardite II (AKII), 1,1,3‐tri‐(2‐methyl‐4‐hydroxy‐5‐tert‐butyl‐phenyl)‐butane (BPless), 3‐(3,5‐di‐tert‐butyl‐4‐hydroxy‐phenyl)‐propionic acid octadecyl ester (BPhin), and 3‐(3‐tert‐butyl‐4‐hydroxy‐5‐methyl‐phenyl)‐propionic acid 2‐(9‐{2‐[3‐(3‐tert‐butyl‐4‐hydroxy‐5‐methyl‐phenyl)‐propionyloxy]‐1,1‐dimethyl‐ethyl}‐2,4,8,10‐tetraoxa‐spiro [5.5] undec‐3‐yl)‐2‐methyl‐propyl ester (BPsemi) was observed during isothermal storage at 393 K using a C80 microcalorimeter. The results indicate that each stabilizer decreased NC's maximum heat release rate and increased the induction period of heat release. We also observed that the maximum heat release rate and the induction period were dependent on the amount of stabilizer. DPA decreased the maximum heat release rate to the greatest extent, with the other stabilizers having similar effects on the decrease of maximum heat release rate. AKII prolonged the induction period of heat release most. The order of prolongation of the induction period was AKII>2‐NO2‐DPA≈DPA>N‐NO‐DPA≈EC>BPless≈BPsemi≈BPhin.  相似文献   
32.
The reliability of InP-based HEMTs is studied, focussing on how it is affected by the doped layer material and gate recess structure. Bias-and-temperature stress tests reveal that fluorine-induced donor passivation in the recess region, formed adjacent to the gate electrode, causes the source resistance (Rs) to increase at large drain bias voltages. The increase in Rs can be prevented by using InP or InAlP as the carrier supply layer material instead of InAlAs. On the other hand, the increase in the drain resistance (Rd) does not depend on the material of the carrier supply layer, which suggests that a mechanism different from that in the case of Rs should be considered. It is also found that a deep gate recess suppresses the increase in Rd after long-term stressing.  相似文献   
33.
34.
This study measured air exchange rates, indoor concentrations of aldehydes and volatile organic compounds (VOCs), and radioactivity levels at 19 temporary houses in different temporary housing estate constructed in Minamisoma City following the Great East Japan Earthquake. The 19 surveyed houses represented all of the companies assigned to construct temporary houses in that Minamisoma City. Data were collected shortly after construction and before occupation, from August 2011 to January 2012. Mean air exchange rates in the temporary houses were 0.28/h, with no variation according to housing types and construction date. Mean indoor concentrations of formaldehyde, acetaldehyde, toluene, ethylbenzene, m/p‐xylene, o‐xylene, styrene, p‐dichlorobenzene, tetradecane, and total VOCs (TVOCs) were 29.2, 72.7, 14.6, 6.35, 3.05, 1.81, 7.29, 14.3, 8.32, and 901 μg/m3, respectively. The levels of acetaldehyde and TVOCs exceeded the indoor guideline (48 μg/m3) and interim target (400 μg/m3) in more than half of the 31 rooms tested. In addition to guideline chemicals, terpenes (α‐pinene and d‐limonene) and acetic esters (butyl acetate and ethyl acetate) were often detected in these houses. The indoor radiation levels measured by a Geiger–Müller tube (Mean: 0.22 μSv/h) were lower than those recorded outdoors (Mean: 0.42 μSv/h), although the shielding effect of the houses was less than for other types of buildings.  相似文献   
35.
36.
The inhibitory effect of chlorpromazine (CPZ), pentoxifylline (PTX) and dexamethasone (DEX) was investigated in a model of endotoxin shock in Holstein calves following an intravenous administration of Esherichia coli endotoxin (LPS). Initial correlations with its effects on the levels of tumor necrosis factor (TNF), a pivotal mediator of endotoxin shock, and clinical signs were obtained. The pretreatment of CPZ or DEX significantly decreased the serum levels of TNF, and reduced endotoxic shock. But the pretreatment of PTX hardly reduced the increase of serum TNF levels and endotoxin shock. The levels of serum endotoxin were not significantly different a minute of postinjection of LPS in calves. The results of this study indicate that pretreatment of CPZ or DEX inhibit various biological effects on endotoxin in calves.  相似文献   
37.
Chemical modification of zein by bifunctional polycaprolactone (PCL)   总被引:1,自引:0,他引:1  
Prepolymer was synthesized by use of PCL and hexamethylene diisocyanate (HDI), and then used to prepare modified zein-based polymers (ZPs). Solid-state 13C NMR results showed that at least four amino acids (Glu, Gln, Tyr and His) reacted with the prepolymer, and urea-urethane links were prominent. Thermal analysis indicated that micro-phase separation formed between zein matrix and PCL-HDI (PCLH) component in ZPs. With the increasing PCLH content, the melting point of PCL in ZP decreased, and the Tg of zein reduced due to plasticizer role of PCLH. The breaking elongation of modified zein containing 10% PCLH content, increased about 15 times while its strength at break only reduced by about 2 times than that of commercial zein. In addition, with the increasing PCLH content, the flexibility of modified zein sheet improved dramatically with negligible reduction in strength. This indicates that PCL was an elastic fraction in ZPs. Therefore, it is an effective way to improve the mechanical properties of zein by modification with PCL, showing a potential in the field of biodegradable polymers.  相似文献   
38.
We studied chest X rays of 911 patients with rheumatoid arthritis (RA). The findings showed interstitial shadow in 28 patients (3.1%), pleuritis in 13 patients (1.4%) and nodular shadow in 3 patients (0.3%). RA patients with interstitial pneumonia were commonly male and older. And they had significantly high levels of rheumatoid factor (RF), RAPA and IgG-RF in serum, but they were not associated with high score of Lansbary index. All patients with more than 1500 IU/ml in RF value had a complication of interstitial pneumonia. These results suggest the importance of chest X-ray in the management of RA patients with high titer in RF.  相似文献   
39.
Ohno  T. Sato  K. Iga  R. Kondo  Y. Yoshino  K. Furuta  T. Ito  H. 《Electronics letters》2003,39(19):1398-1400
An 80 GHz optical clock signal was successfully recovered from a 160 Gbit/s data stream using a regeneratively modelocking scheme of a semiconductor modelocked laser (MLLD). To handle an 80 GHz electrical signal, the MLLD integrated with a high-mesa electroabsorption modulator and a W-band UTC-PD module are used in this scheme.  相似文献   
40.
An optical electric-power sensor is presented that allows active and apparent powers to be measured simultaneously using one block of bismuth germanate (Bi/sub 4/Ge/sub 3/O/sub 12/) crystal as sensing element, which exhibits both the Faraday effect and the Pockels effect. It is based on the fact that the polarization-related intensity of the light wave passing through the crystal can be modulated by the product signal of applied electric and magnetic fields. When load current and voltage are simultaneously applied to the sensing crystal, the instantaneous electric power signal can be directly obtained from the intensity-modulated light wave. The simultaneous measurements of active power and apparent power, as well as the direction of power flow, have been carried out in experiments. Measurement uncertainty is theoretically analyzed. The potential applications of the proposed optical electric-power sensor are also discussed.  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