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   571106篇
  免费   94218篇
  国内免费   58668篇
电工技术   49072篇
技术理论   54篇
综合类   47299篇
化学工业   88027篇
金属工艺   44595篇
机械仪表   31436篇
建筑科学   43254篇
矿业工程   25110篇
能源动力   18795篇
轻工业   46119篇
水利工程   14771篇
石油天然气   36106篇
武器工业   6713篇
无线电   70799篇
一般工业技术   72202篇
冶金工业   26952篇
原子能技术   5371篇
自动化技术   97317篇
  2024年   3979篇
  2023年   9860篇
  2022年   14981篇
  2021年   19908篇
  2020年   19235篇
  2019年   26069篇
  2018年   28796篇
  2017年   31179篇
  2016年   30037篇
  2015年   33178篇
  2014年   36096篇
  2013年   39066篇
  2012年   40593篇
  2011年   39971篇
  2010年   35663篇
  2009年   31440篇
  2008年   29596篇
  2007年   28101篇
  2006年   27770篇
  2005年   24721篇
  2004年   20581篇
  2003年   17799篇
  2002年   16630篇
  2001年   14831篇
  2000年   14387篇
  1999年   14684篇
  1998年   11980篇
  1997年   10342篇
  1996年   9798篇
  1995年   8636篇
  1994年   7128篇
  1993年   5507篇
  1992年   4801篇
  1991年   3605篇
  1990年   2854篇
  1989年   2484篇
  1988年   2005篇
  1987年   910篇
  1986年   727篇
  1985年   506篇
  1984年   344篇
  1983年   266篇
  1982年   284篇
  1981年   216篇
  1980年   191篇
  1976年   253篇
  1975年   209篇
  1972年   242篇
  1971年   134篇
  1960年   207篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
现今国内的数字集群网络发展存在局限性、差异性,还远没有达到“网”状分布的程度,因此,共网数字集群发展空间巨大、前景广阔。通过列举共网数字集群系统在龙嘉国际机场和长春雷锋车队的成功应用案例,探讨了我国共网数字集群系统应用的可行性和必要性。  相似文献   
13.
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels.  相似文献   
14.
15.
16.
Removal of imidacloprid and acetamiprid in tea infusions by microfiltration membrane using dead‐end model was investigated in the present study. The results showed that microfiltration significantly promoted the removal of both pesticides (P < 0.05) in tea infusions. Furthermore, the extent of removal was strongly influenced by the pore size of membrane, operational pressure and the concentrations of tea infusions. The initial concentration of imidacloprid and acetamiprid showed no significant effect on their removal rates. The maximum removal rates were 79.7% for imidacloprid and 81.9% acetamiprid. The changes in major chemical components of tea infusions after microfiltration were evaluated. The results indicated that microfiltration caused no considerable changes in total polyphenols and total free amino acids, and small but statistically significant losses (6.3–18.0%) of eight catechins and three methylxanthines when filtration volume reached to 200 mL. The present study validated the application of microfiltration as a potentially feasible and promising method for the removal of imidacloprid and acetamiprid residues from tea infusions.  相似文献   
17.
18.
We investigate the effect of dopant random fluctuation on threshold voltage and drain current variation in a two-gate nanoscale transistor. We used a quantum-corrected technology computer aided design simulation to run the simulation (10000 randomizations). With this simulation, we could study the effects of varying the dimensions (length and width), and thicknesses of oxide and dopant factors of a transistor on the threshold voltage and drain current in subthreshold region (off) and overthreshold (on). It was found that in the subthreshold region the variability of the drain current and threshold voltage is relatively fixed while in the overthreshold region the variability of the threshold voltage and drain current decreases remarkably, despite the slight reduction of gate voltage diffusion (compared with that of the subthreshold). These results have been interpreted by using previously reported models for threshold current variability, load displacement, and simple analytical calculations. Scaling analysis shows that the variability of the characteristics of this semiconductor increases as the effects of the short channel increases. Therefore, with a slight increase of length and a reduction of width, oxide thickness, and dopant factor, we could correct the effect of the short channel.  相似文献   
19.
20.
本文提出了将智能全站仪这种精密测量仪器广泛应用于田赛项目测量中,并结合其他科技元素用于解决田赛项目中跳远、投掷等项目的测量及数据管理问题,实现实时、自动、准确地裁定和报告比赛成绩。  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