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   293865篇
  免费   23974篇
  国内免费   12927篇
电工技术   16411篇
技术理论   25篇
综合类   20768篇
化学工业   48856篇
金属工艺   16760篇
机械仪表   18704篇
建筑科学   22215篇
矿业工程   9026篇
能源动力   8179篇
轻工业   19425篇
水利工程   4989篇
石油天然气   19049篇
武器工业   2155篇
无线电   32964篇
一般工业技术   34043篇
冶金工业   15655篇
原子能技术   3170篇
自动化技术   38372篇
  2024年   1192篇
  2023年   4437篇
  2022年   7784篇
  2021年   10898篇
  2020年   8533篇
  2019年   7240篇
  2018年   8109篇
  2017年   9136篇
  2016年   8344篇
  2015年   11106篇
  2014年   14338篇
  2013年   17045篇
  2012年   18649篇
  2011年   20260篇
  2010年   18028篇
  2009年   17234篇
  2008年   16932篇
  2007年   16231篇
  2006年   16617篇
  2005年   14337篇
  2004年   10272篇
  2003年   8942篇
  2002年   8743篇
  2001年   7749篇
  2000年   7351篇
  1999年   7764篇
  1998年   6276篇
  1997年   5167篇
  1996年   4820篇
  1995年   4059篇
  1994年   3216篇
  1993年   2272篇
  1992年   1777篇
  1991年   1419篇
  1990年   1092篇
  1989年   843篇
  1988年   637篇
  1987年   412篇
  1986年   309篇
  1985年   248篇
  1984年   179篇
  1983年   145篇
  1982年   142篇
  1981年   117篇
  1980年   88篇
  1979年   50篇
  1978年   34篇
  1977年   32篇
  1976年   50篇
  1974年   17篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
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   
82.
83.
84.
85.
86.
The evaluation of cell's weatherability is of practical interest. To further improve the soluble lead flow battery's weatherability, physiochemical properties of electrolytes containing fluoborate, perchlorate, methanesulfonate and trifluoromethanesulfonate are investigated from ?60 to 50 °C. Activities of CF3SO3H and HClO4 are poor in trifluoromethanesulfonate and perchlorate solutions due to common anion effect. The solubility of lead salt can be improved by increasing temperature, but worsened by increasing acid's content. With the temperature increasing, the conductivity is enhanced, and the viscosity is lowered for four solutions. The same results have been found by increasing acid's content except for CF3SO3H. The high energy efficiency can be achieved for cells over ?40–0 °C using fluoborate and perchlorate solutions, 73.2% at ?40 °C and 78.1% at ?30 °C respectively. Over the temperature range of 20–50 °C, the cells with methanesulfonate and trifluoromethanesulfonate solutions have good performance, 77.4% and 73.7% at 50 °C respectively.  相似文献   
87.
We investigated some properties of the hydride Mg2FeH6 substituted with yttrium by a first principles calculation. Some experimental results showed that 4d transition metal, yttrium serves as a good catalyst for magnesium based hydrogen storage alloys, but there are a few theoretical studies about magnesium based hydrides substituted with it. Mg2FeH6 is regarded as a cheaper material than pure MgH2, while it is crystalized into Fm3m structure (space group 225). Although it has high hydrogen storage capacity, many investigations have not been devoted to it due to its extremely high thermodynamic stability. The yttrium substituted Mg2FeH6 exhibits very low energy of formation, and its desorption temperature, 75 °C is very suitable for practical hydrogen storage applications. Our results showed that Mg2FeH6 is destabilized effectively by yttrium substitution and introducing vacancy defects has additive effect to the improvement of dehydrogenation performance.  相似文献   
88.
陈国亮  李宏  朱旭 《纺织器材》2015,42(1):61-62
为了解决钢丝圈挂花问题,阐述了LH001新型钢丝圈清洁器的特点和应用效果;通过试验说明使用新型钢丝圈清洁器断头率低,基本无挂花,纺纱效果好。指出:新型钢丝圈清洁器是普通钢丝圈清洁器的更新换代产品,值得推广。  相似文献   
89.
90.
Journal of Mechanical Science and Technology - This study delivers equations useful for low-height pleated fibrous filter design: two pressure drop equations and one set of optimum design equations...  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