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   553538篇
  免费   12229篇
  国内免费   4078篇
电工技术   13257篇
技术理论   6篇
综合类   4824篇
化学工业   83162篇
金属工艺   23934篇
机械仪表   22405篇
建筑科学   18054篇
矿业工程   4014篇
能源动力   13896篇
轻工业   49436篇
水利工程   5351篇
石油天然气   8573篇
武器工业   473篇
无线电   69263篇
一般工业技术   103921篇
冶金工业   83939篇
原子能技术   7392篇
自动化技术   57945篇
  2022年   3483篇
  2021年   5471篇
  2020年   3908篇
  2019年   4294篇
  2018年   14401篇
  2017年   15341篇
  2016年   10685篇
  2015年   6584篇
  2014年   9160篇
  2013年   23386篇
  2012年   16973篇
  2011年   27549篇
  2010年   23123篇
  2009年   23454篇
  2008年   23940篇
  2007年   26097篇
  2006年   16539篇
  2005年   18880篇
  2004年   15594篇
  2003年   14766篇
  2002年   13299篇
  2001年   12772篇
  2000年   12153篇
  1999年   12774篇
  1998年   25683篇
  1997年   18917篇
  1996年   15249篇
  1995年   12114篇
  1994年   10703篇
  1993年   10040篇
  1992年   7644篇
  1991年   7209篇
  1990年   6700篇
  1989年   6343篇
  1988年   6077篇
  1987年   5012篇
  1986年   4930篇
  1985年   6058篇
  1984年   5654篇
  1983年   4864篇
  1982年   4537篇
  1981年   4467篇
  1980年   4228篇
  1979年   4091篇
  1978年   3774篇
  1977年   4553篇
  1976年   6104篇
  1975年   3118篇
  1974年   3012篇
  1973年   2891篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Wireless Personal Communications - In this article compact multiple input multiple output (MIMO) antenna with triple notch at the ultra-wideband application having two identical monopole antennas...  相似文献   
103.
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research.  相似文献   
104.
The family of NAD(P)H-dependent short-chain dehydrogenases/reductases (SDRs) comprises numerous biocatalysts capable of C=O or C=C reduction. The highly homologous noroxomaritidine reductase (NR) from Narcissus sp. aff. pseudonarcissus and Zt_SDR from Zephyranthes treatiae, however, are SDRs with an extended imine substrate scope. Comparison with a similar SDR from Asparagus officinalis (Ao_SDR) exhibiting keto-reducing activity, yet negligible imine-reducing capability, and mining the Short-Chain Dehydrogenase/Reductase Engineering Database indicated that NR and Zt_SDR possess a unique active-site composition among SDRs. Adapting the active site of Ao_SDR accordingly improved its imine-reducing capability. By applying the same strategy, an unrelated SDR from Methylobacterium sp. 77 (M77_SDR) with distinct keto-reducing activity was engineered into a promiscuous enzyme with imine-reducing activity, thereby confirming that the ability to reduce imines can be rationally introduced into members of the “classical” SDR enzyme family. Thus, members of the SDR family could be a promising starting point for protein approaches to generate new imine-reducing enzymes.  相似文献   
105.
Wei  Mengnan  Ban  Boyuan  Li  Jingwei  Sun  Jifei  Li  Feifei  Jiang  Xuesong  Chen  Jian 《SILICON》2020,12(2):327-338
Silicon - A novel green cationic surfactant Poly (propylene glycol) bis (2-aminopropyl ether) (PEA) with multiple amine groups was utilized as a collector for flotation separation of quartz from...  相似文献   
106.
107.
High‐performance adhesives require mechanical properties tuned to demands of the surroundings. A mismatch in stiffness between substrate and adhesive leads to stress concentrations and fracture when the bonding is subjected to mechanical load. Balancing material strength versus ductility, as well as considering the relationship between adhesive modulus and substrate modulus, creates stronger joints. However, a detailed understanding of how these properties interplay is lacking. Here, a biomimetic terpolymer is altered systematically to identify regions of optimal bonding. Mechanical properties of these terpolymers are tailored by controlling the amount of a methyl methacrylate stiff monomer versus a similar monomer containing flexible poly(ethylene glycol) chains. Dopamine methacrylamide, the cross‐linking monomer, is a catechol moiety analogous to 3,4‐dihydroxyphenylalanine, a key component in the adhesive proteins of marine mussels. Bulk adhesion of this family of terpolymers is tested on metal and plastic substrates. Incorporating higher amounts of poly(ethylene glycol) into the terpolymer introduces flexibility and ductility. By taking a systematic approach to polymer design, the region in which material strength and ductility are balanced in relation to the substrate modulus is found, thereby yielding the most robust joints.  相似文献   
108.
JOM - Alpha-radiation damage in metals is a concern for long-term radioactive storage and systems that produce nuclear energy. Accurate prediction of irradiated material properties and failure...  相似文献   
109.
110.
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