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   721324篇
  免费   8847篇
  国内免费   1667篇
电工技术   13255篇
综合类   596篇
化学工业   112637篇
金属工艺   32463篇
机械仪表   24081篇
建筑科学   16636篇
矿业工程   5073篇
能源动力   17928篇
轻工业   57461篇
水利工程   8588篇
石油天然气   16783篇
武器工业   42篇
无线电   77126篇
一般工业技术   147385篇
冶金工业   121534篇
原子能技术   17084篇
自动化技术   63166篇
  2021年   6253篇
  2019年   5983篇
  2018年   14633篇
  2017年   14957篇
  2016年   13683篇
  2015年   7250篇
  2014年   11931篇
  2013年   31384篇
  2012年   19879篇
  2011年   29380篇
  2010年   24283篇
  2009年   25932篇
  2008年   26452篇
  2007年   27264篇
  2006年   19498篇
  2005年   19587篇
  2004年   18098篇
  2003年   17441篇
  2002年   16406篇
  2001年   15645篇
  2000年   15004篇
  1999年   14736篇
  1998年   34633篇
  1997年   25110篇
  1996年   19605篇
  1995年   15045篇
  1994年   13418篇
  1993年   13172篇
  1992年   10164篇
  1991年   9767篇
  1990年   9640篇
  1989年   9382篇
  1988年   9087篇
  1987年   8171篇
  1986年   7968篇
  1985年   9027篇
  1984年   8218篇
  1983年   7769篇
  1982年   7029篇
  1981年   7190篇
  1980年   6850篇
  1979年   6987篇
  1978年   6889篇
  1977年   7651篇
  1976年   9666篇
  1975年   6148篇
  1974年   5920篇
  1973年   6071篇
  1972年   5176篇
  1971年   4853篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
12.
While protein medications are promising for treatment of cancer and autoimmune diseases, challenges persist in terms of development and injection stability of high-concentration formulations. Here, the extensional flow properties of protein-excipient solutions are examined via dripping-onto-substrate extensional rheology, using a model ovalbumin (OVA) protein and biocompatible excipients polysorbate 20 (PS20) and 80 (PS80). Despite similar PS structures, differences in extensional flow are observed based on PS identity in two regimes: at moderate total concentrations where surface tension differences drive changes in extensional flow behavior, and at small PS:OVA ratios, which impact the onset of weakly elastic flow behavior. Undesirable elasticity is observed in ultra-concentrated formulations, independent of PS identity; higher PS contents are required to observe these effects than in analogous polymeric excipient solutions. These studies reveal novel extensional flow behaviors in protein-excipient solutions, and provide a straightforward methodology for assessing the extensional flow stability of new protein-excipient formulations.  相似文献   
13.
Water Resources Management - The water evaluation and planning (WEAP) approach and the invasive weed optimization algorithm (IWOA) are herein employed to determine the optimal operating policies in...  相似文献   
14.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
15.
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically...  相似文献   
16.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is...  相似文献   
17.
Glass and Ceramics - Ceramic bricks based on low-melting clay and ferro-dust from self-disintegrating, low-carbon, ferrochrome slags, graded from M100 to M175, respectively, were obtained in the...  相似文献   
18.
Automation and Remote Control - A linear-quadratic positional differential game of three persons is considered. Coefficient criteria are established under which there is no Nash equilibrium...  相似文献   
19.
20.
Cell temperature and water content of the membrane have a significant effect on the performance of fuel cells. The current-power curve of the fuel cell has a maximum power point (MPP) that is needed to be tracked. This study presents a novel strategy based on a salp swarm algorithm (SSA) for extracting the maximum power of proton-exchange membrane fuel cell (PEMFC). At first, a new formula is derived to estimate the optimal voltage of PEMFC corresponding to MPP. Then the error between the estimated voltage at MPP and the actual terminal voltage of the fuel cell is fed to a proportional-integral-derivative controller (PID). The output of the PID controller tunes the duty cycle of a boost converter to maximize the harvested power from the PEMFC. SSA determines the optimal gains of PID. Sensitivity analysis is performed with the operating fuel cell at different cell temperature and water content of the membrane. The obtained results through the proposed strategy are compared with other programmed approaches of incremental resistance method, Fuzzy-Logic, grey antlion optimizer, wolf optimizer, and mine-blast algorithm. The obtained results demonstrated high reliability and efficiency of the proposed strategy in extracting the maximum power of the PEMFC.  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