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   339112篇
  免费   5336篇
  国内免费   1089篇
电工技术   5813篇
综合类   845篇
化学工业   52292篇
金属工艺   12820篇
机械仪表   10160篇
建筑科学   8091篇
矿业工程   2275篇
能源动力   8052篇
轻工业   28444篇
水利工程   3910篇
石油天然气   7311篇
武器工业   24篇
无线电   34579篇
一般工业技术   63501篇
冶金工业   69775篇
原子能技术   7807篇
自动化技术   29838篇
  2021年   2967篇
  2019年   2787篇
  2018年   5451篇
  2017年   5499篇
  2016年   5898篇
  2015年   3790篇
  2014年   5398篇
  2013年   13729篇
  2012年   9723篇
  2011年   12540篇
  2010年   8819篇
  2009年   9955篇
  2008年   9907篇
  2007年   9747篇
  2006年   8636篇
  2005年   11595篇
  2004年   9950篇
  2003年   9014篇
  2002年   7561篇
  2001年   7287篇
  2000年   6506篇
  1999年   6817篇
  1998年   19886篇
  1997年   14217篇
  1996年   10692篇
  1995年   7749篇
  1994年   6841篇
  1993年   6761篇
  1992年   4716篇
  1991年   4665篇
  1990年   4507篇
  1989年   4457篇
  1988年   4414篇
  1987年   3728篇
  1986年   3738篇
  1985年   4244篇
  1984年   3970篇
  1983年   3639篇
  1982年   3492篇
  1981年   3671篇
  1980年   3555篇
  1979年   3364篇
  1978年   3505篇
  1977年   4416篇
  1976年   6164篇
  1975年   3204篇
  1974年   3004篇
  1973年   3026篇
  1972年   2654篇
  1971年   2465篇
排序方式: 共有10000条查询结果,搜索用时 232 毫秒
1.
Multimedia Tools and Applications - Remote Sensing categorical signature classification has gained significant implications on spatial resolution image analysis due to differences in the...  相似文献   
2.
3.
Journal of Materials Science - Chitosan is one of the natural cationic polymers with unique properties such as non-toxicity, biodegradability, biocompatibility, environmentally friendly that has...  相似文献   
4.
Theoretical Foundations of Chemical Engineering - On the basis of the classic concepts of the theory of solid-phase combustion, for the first time, a model with a detailed scheme of chemical...  相似文献   
5.
Journal of Inorganic and Organometallic Polymers and Materials - Immobility of copper on magnetic nanoparticles was performed using surface rectification of Fe3O4 with Agar. The magnetic...  相似文献   
6.
International Journal of Control, Automation and Systems - In this paper, a new controllable simulator is proposed and modeled by which, experimental tests of the aircraft’s models can be...  相似文献   
7.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses.  相似文献   
8.
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   
9.
Catalysis Letters - In the present paper, an efficient Cu-catalyzed regioselective acylation of indoles with phenylglyoxals was developed which is the first example of indolyl diketones synthesis...  相似文献   
10.
This work evaluated the synergistic effects of combined high-intensity ultrasound (HIU) with β-cyclodextrin (β-CD) treatments on inhibiting browning of apple juice and explored the mechanism through simulation system. The combined treatment of 300 W HIU with 0.006 g mL−1 β-CD had a synergistic impact on maintaining juice colour, resulting in a 39.06% reduction in browning degree, only a 36.64% decrease in total phenolic content, and a 17.82% reduction in PPO activity. The inhibition of enzymatic browning in simulated system revealed that HIU suppressed the enzyme (Polyphenol oxidase, PPO) and β-CD inhibited enzyme (PPO) and embedded substrate (polyphenol). The results of spectroscopic analysis showed that the particle-size distribution of PPO narrowed, the content of α-helix in the secondary structure increased, the fluorescence intensity increased, and the maximum wavelength was red-shifted after HIU and β-CD treatment. Changes in structure could further result in PPO activity loss. Hence, the combined treatment could synthetically alleviate the browning of apple juice.  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