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   3538篇
  免费   165篇
  国内免费   7篇
电工技术   57篇
综合类   7篇
化学工业   870篇
金属工艺   54篇
机械仪表   66篇
建筑科学   98篇
矿业工程   21篇
能源动力   111篇
轻工业   285篇
水利工程   26篇
石油天然气   19篇
无线电   363篇
一般工业技术   673篇
冶金工业   332篇
原子能技术   35篇
自动化技术   693篇
  2023年   41篇
  2022年   120篇
  2021年   138篇
  2020年   81篇
  2019年   97篇
  2018年   102篇
  2017年   95篇
  2016年   130篇
  2015年   88篇
  2014年   139篇
  2013年   236篇
  2012年   192篇
  2011年   236篇
  2010年   163篇
  2009年   149篇
  2008年   149篇
  2007年   147篇
  2006年   138篇
  2005年   112篇
  2004年   104篇
  2003年   94篇
  2002年   90篇
  2001年   49篇
  2000年   47篇
  1999年   59篇
  1998年   56篇
  1997年   56篇
  1996年   48篇
  1995年   41篇
  1994年   28篇
  1993年   33篇
  1992年   26篇
  1991年   17篇
  1990年   17篇
  1989年   22篇
  1988年   28篇
  1987年   22篇
  1986年   17篇
  1985年   25篇
  1984年   20篇
  1983年   20篇
  1982年   21篇
  1981年   12篇
  1980年   19篇
  1979年   22篇
  1978年   19篇
  1977年   17篇
  1976年   20篇
  1975年   18篇
  1973年   12篇
排序方式: 共有3710条查询结果,搜索用时 15 毫秒
81.
Through time domain observation, typical wireless signal strength values seems to exhibit some forms of mean-reverting and discontinuous “jumps” behaviour. Motivated by this fact, we propose a wireless link prediction and triggering (LPT) technique using a modified mean-reverting Ornstein–Uhlenbeck (OU) jump diffusion process. The proposed technique which we refer as OU-LPT is an integral component of wireless mesh network monitoring system developed by ICT FP7 CARrier grade wireless MEsh Network project. In particular, we demonstrate how this technique can be applied in the context of wireless mesh networks to support link switching or handover in the event of predicted link degradation or failure. The proposed technique has also been implemented and evaluated in a real-time experimental testbed. The results show that OU-LPT technique can significantly enhance the reliability of wireless links by reducing the rate of false triggers compared to a conventional linear prediction technique and therefore offers a new direction on how wireless link prediction, triggering and switching process can be conducted in the future.  相似文献   
82.
Focused ion beam was used to fabricate 2 mm-long, 4 μm-wide and 4 μm-deep multimode trench waveguides in InP/InGaAsP. An automated stitching method was developed to fabricate mm-long structures using alignment marks. The waveguides were sputtered or etched using I2 at room temperature and 150 °C stage temperature. The propagation losses induced by the different fabrication techniques were measured and ranged between 50 and 82 dB/cm. A damaged layer with implanted Ga and the sidewall roughness are identified to be the most important causes for the losses. FIB is shown to be a single-step fabrication technique for rapid-prototyping of photonic structures in InP/InGaAsP.  相似文献   
83.
本文旨在描述一种比利时冶金研究中心(CRM)研发的用于钢铁生产领域的传感器。这种以激光诱导击穿光谱(LIBS)技术为基础的传感器可以连续测量高炉流道中的化学成分和温度,其目的在于在线评估铁水的化学成分(主要包括铁,碳,硅和锰),以及其温度。这种传感器也可以测量炉渣中氧化钙、氧化镁、二氧化硅、氧化铝和氧化锰的浓度以及铁粒子的存在,这对于安全生产非常重要。这种传感器已用于比利时根特的阿塞洛米塔尔高炉的可行性测试。  相似文献   
84.
85.
The composition of various commercial tannin extracts were determined by liquid secondary ion mass spectrometry (LSIMS). Spectra were obtained directly from tannin extracts without any pre-separation. Eight different tannin powders were analysed: three gallotannins (Chinese, Turkish, tara), three ellagitannins (sweet chestnut, pendunculata oak, sessile oak), one mixed hydrolysable tannin (myrabolans) and one proanthocyanidin (grape seeds). This method enabled the main molecules in these powders to be identified.  相似文献   
86.
In humans, age-associated degrading changes, widely observed in molecular and cellular processes underly the time-dependent decline in spatial navigation, time perception, cognitive and psychological abilities, and memory. Cross-talk of biological, cognitive, and psychological clocks provides an integrative contribution to healthy and advanced aging. At the molecular level, genome, proteome, and lipidome instability are widely recognized as the primary causal factors in aging. We narrow attention to the roles of protein aging linked to prevalent amino acids chirality, enzymatic and spontaneous (non-enzymatic) post-translational modifications (PTMs SP), and non-equilibrium phase transitions. The homochirality of protein synthesis, resulting in the steady-state non-equilibrium condition of protein structure, makes them prone to multiple types of enzymatic and spontaneous PTMs, including racemization and isomerization. Spontaneous racemization leads to the loss of the balanced prevalent chirality. Advanced biological aging related to irreversible PTMs SP has been associated with the nontrivial interplay between somatic (molecular aging) and mental (psychological aging) health conditions. Through stress response systems (SRS), the environmental and psychological stressors contribute to the age-associated “collapse” of protein homochirality. The role of prevalent protein chirality and entropy of protein folding in biological aging is mainly overlooked. In a more generalized context, the time-dependent shift from enzymatic to the non-enzymatic transformation of biochirality might represent an important and yet underappreciated hallmark of aging. We provide the experimental arguments in support of the racemization theory of aging.  相似文献   
87.
88.
89.
Sewage sludge was used as precursor to develop a potential inexpensive adsorbent by both simple drying and pyrolysis. The resulting materials were evaluated as adsorbents for the removal of 4-chlorophenol (4-CP) from aqueous solution. The dried biosolids showed a BET surface area lower than 3 m2/g, which yield a maximum adsorption capacity of 0.73 mmol 4-CP/g at pH 5.0 and 15 °C. The carbonization of biosolids under relatively mild conditions allowed obtaining materials with BET surface area up to 45 m2/g, which led to a significant increase of the maximum adsorption capacity (1.36 mmol 4-CP/g). The high ash content of the starting material (23%, d.b.) limits the development of porosity on a total dry-weight basis. Adsorption data were well fitted to the Redlich–Peterson isotherm equation whereas the most commonly used Langmuir and Freundlich equations were less satisfactory probably because of the occurrence of summative adsorption phenomenon. A thermodynamic study of the adsorption showed the spontaneous and exothermic nature of the process. Thus, simple drying and carbonization provide two ways of valorization of sewage sludge through its conversion into inexpensive low-rank adsorbents potentially useful for the removal of some hazardous water pollutants, like chlorophenols and related compounds.  相似文献   
90.
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