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   1702889篇
  免费   47472篇
  国内免费   17254篇
电工技术   48713篇
技术理论   31篇
综合类   23267篇
化学工业   311513篇
金属工艺   78137篇
机械仪表   57353篇
建筑科学   66391篇
矿业工程   20591篇
能源动力   57339篇
轻工业   117781篇
水利工程   19032篇
石油天然气   55749篇
武器工业   2368篇
无线电   221985篇
一般工业技术   300342篇
冶金工业   152549篇
原子能技术   36308篇
自动化技术   198166篇
  2022年   15832篇
  2021年   26135篇
  2020年   19519篇
  2019年   21005篇
  2018年   21496篇
  2017年   21768篇
  2016年   27548篇
  2015年   27655篇
  2014年   41473篇
  2013年   102476篇
  2012年   50050篇
  2011年   62375篇
  2010年   56315篇
  2009年   64221篇
  2008年   56259篇
  2007年   52577篇
  2006年   57885篇
  2005年   50390篇
  2004年   47847篇
  2003年   46837篇
  2002年   45565篇
  2001年   41715篇
  2000年   41037篇
  1999年   41104篇
  1998年   43714篇
  1997年   39776篇
  1996年   37383篇
  1995年   33023篇
  1994年   30789篇
  1993年   29600篇
  1992年   27446篇
  1991年   23971篇
  1990年   24068篇
  1989年   22886篇
  1988年   21143篇
  1987年   19290篇
  1986年   18485篇
  1985年   21679篇
  1984年   22060篇
  1983年   20004篇
  1982年   19162篇
  1981年   19197篇
  1980年   17733篇
  1979年   18272篇
  1978年   17524篇
  1977年   16805篇
  1976年   17030篇
  1975年   15793篇
  1974年   15321篇
  1973年   15392篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Ti-based amorphous metallic glasses have excellent mechanical, physical, and chemical properties, which is an important development direction and research hotspot of metal composite reinforcement. As a stable, simple, efficient, and large-scale preparation technology of metallic powders, the gas atomization process provides an effective way of preparing amorphous metallic glasses. In this study, the controllable fabrication of a Ti-based amorphous powder, with high efficiency, has been realized by using gas atomization. The scanning electron microscope, energy-dispersive spectrometer, and X-ray diffraction are used to analyze surface morphology, element distribution, and phase structure, respectively. A microhardness tester is used to measure the mechanical property. An electrochemical workstation is used to characterize corrosion behavior. The results show that as-prepared microparticles are more uniform and exhibit good amorphous characteristics. The mechanical test shows that the hardness of amorphous powder is significantly increased as compared with that before preparation, which has the prospect of being an important part of engineering reinforced materials. Further electrochemical measurement shows that the corrosion resistance of the as-prepared sample is also significantly improved. This study has laid a solid foundation for expanding applications of Ti-based metallic glasses, especially in heavy-duty and corrosive domains.  相似文献   
122.
Journal of Communications Technology and Electronics - Abstract—The matrix coefficients of projection models of strip lines obtained using the Chebyshev basis are presented as a sum of...  相似文献   
123.
Analog Integrated Circuits and Signal Processing - This paper presents the complete design of a phase locked loop-based clock synthesizer for reconfigurable analog-to-digital converters. The...  相似文献   
124.
Zhang  Qi  Wang  Yujing  Zhang  Xueling  Song  Jun  Li  Yinlei  Wu  Xuehong  Yuan  Kunjie 《Journal of Materials Science》2022,57(14):7208-7224
Journal of Materials Science - Form-stable composite phase change materials (C-PCMs) prepared by microencapsulation method and porous matrix adsorption method need for compression molding after...  相似文献   
125.
Catalysis Letters - An environmentally benign process for synthesizing 4-methoxyphenol through methylation of hydroquinone using polystyrene immobilized Bronsted acidic ionic liquid is presented....  相似文献   
126.
127.
128.
朱宏  张蔚翔  郭成英 《中州煤炭》2021,(11):239-243
为应对电力系统安全分析中的停机问题,基于概率法的方式,将常用的确定停机计算与加入了概率法的概率停机进行比较,研究了二者的区别与其在长期投资方向的不同。在进行电力系统停机分析时,通常会分别从确定停机与概率停机的角度出发,对其应急状态下的潮流进行计算。但前者的方法可能导致极低概率的停机事件被忽略,进而影响长期的资金投资。通过加入概率法的计算,使得对单个停机事件的判定由其具体的频率来确定,增加了系统运行的稳定性。  相似文献   
129.
Calmodulin (CaM) is an important intracellular protein that binds Ca2+ and functions as a critical second messenger involved in numerous biological activities through extensive interactions with proteins and peptides. CaM’s ability to adapt to binding targets with different structures is related to the flexible central helix separating the N- and C-terminal lobes, which allows for conformational changes between extended and collapsed forms of the protein. CaM-binding targets are most often identified using prediction algorithms that utilize sequence and structural data to predict regions of peptides and proteins that can interact with CaM. In this review, we provide an overview of different CaM-binding proteins, the motifs through which they interact with CaM, and shared properties that make them good binding partners for CaM. Additionally, we discuss the historical and current methods for predicting CaM binding, and the similarities and differences between these methods and their relative success at prediction. As new CaM-binding proteins are identified and classified, we will gain a broader understanding of the biological processes regulated through changes in Ca2+ concentration through interactions with CaM.  相似文献   
130.
Grass pea (Lathyrus sativus) is a leguminous plant of outstanding tolerance to abiotic stress. The aim of the presented study was to describe the mechanism of grass pea (Lathyrus sativus L.) photosynthetic apparatus acclimatisation strategies to salinity stress. The seedlings were cultivated in a hydroponic system in media containing various concentrations of NaCl (0, 50, and 100 mM), imitating none, moderate, and severe salinity, respectively, for three weeks. In order to characterise the function and structure of the photosynthetic apparatus, Chl a fluorescence, gas exchange measurements, proteome analysis, and Fourier-transform infrared spectroscopy (FT-IR) analysis were done inter alia. Significant differences in the response of the leaf and stem photosynthetic apparatus to severe salt stress were observed. Leaves became the place of harmful ion (Na+) accumulation, and the efficiency of their carboxylation decreased sharply. In turn, in stems, the reconstruction of the photosynthetic apparatus (antenna and photosystem complexes) activated alternative electron transport pathways, leading to effective ATP synthesis, which is required for the efficient translocation of Na+ to leaves. These changes enabled efficient stem carboxylation and made them the main source of assimilates. The observed changes indicate the high plasticity of grass pea photosynthetic apparatus, providing an effective mechanism of tolerance to salinity stress.  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