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   408434篇
  免费   6546篇
  国内免费   1373篇
电工技术   7634篇
综合类   349篇
化学工业   60046篇
金属工艺   14250篇
机械仪表   11742篇
建筑科学   11487篇
矿业工程   866篇
能源动力   11101篇
轻工业   43116篇
水利工程   3304篇
石油天然气   1621篇
武器工业   13篇
无线电   55289篇
一般工业技术   76458篇
冶金工业   74964篇
原子能技术   5568篇
自动化技术   38545篇
  2021年   2624篇
  2019年   2434篇
  2018年   3836篇
  2017年   3902篇
  2016年   4143篇
  2015年   3425篇
  2014年   5714篇
  2013年   19282篇
  2012年   10202篇
  2011年   14681篇
  2010年   11283篇
  2009年   12885篇
  2008年   13916篇
  2007年   14285篇
  2006年   12779篇
  2005年   11962篇
  2004年   11575篇
  2003年   11280篇
  2002年   10914篇
  2001年   11134篇
  2000年   10271篇
  1999年   10769篇
  1998年   24018篇
  1997年   17503篇
  1996年   13221篇
  1995年   10861篇
  1994年   9668篇
  1993年   9255篇
  1992年   7001篇
  1991年   6676篇
  1990年   6309篇
  1989年   5984篇
  1988年   5742篇
  1987年   4807篇
  1986年   4756篇
  1985年   5906篇
  1984年   5521篇
  1983年   4763篇
  1982年   4432篇
  1981年   4391篇
  1980年   4130篇
  1979年   4029篇
  1978年   3724篇
  1977年   4503篇
  1976年   6056篇
  1975年   3084篇
  1974年   2973篇
  1973年   2851篇
  1972年   2291篇
  1971年   1965篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
21.
In this study, the hydraulic reactivity and cement formation of baghdadite (Ca3ZrSi2O9) was investigated. The material was synthesized by sintering a mixture of CaCO3, SiO2, and ZrO2 and then mechanically activated using a planetary mill. This leads to a decrease in particle and crystallite size and a partial amorphization of baghdadite as shown by X-ray powder diffraction (XRD) and laser diffraction measurements. Baghdadite cements were formed by the addition of water at a powder to liquid ratio of 2.0 g/ml. Maximum compressive strengths were found to be ~2 MPa after 3-day setting for a 24-h ground material. Inductively coupled plasma mass spectrometry (ICP-MS) measurements showed an incongruent dissolution profile of set cements with a preferred dissolution of calcium and only marginal release of zirconium ions. Cement formation occurs under alkaline conditions, whereas the unground raw powder leads to a pH of 11.9 during setting, while prolonged grinding increased pH values to approximately 12.3.  相似文献   
22.
Multimedia Tools and Applications - The design of robots capable of operating autonomously in changing and unstructured environments, requires using complex software architectures in which,...  相似文献   
23.
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic...  相似文献   
24.
The main drawback of bioglasses is their restricted use in load bearing applications and the consequent need to develop stronger glassy materials. This has led to the consideration of oxynitride glasses for numerous biomedical applications. This paper investigated two different types of glasses at a constant cationic ratio, with and without nitrogen (a N containing and a N-free glass composition) to better understand the effect of N on the biological properties of glasses. The results revealed that the addition of N increased the glass transition temperature, isoelectric point (IEP) and slightly increased wettability. Moreover, compared to N including glass, N-free glass exhibited better anti-bacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), two key bacteria that infect implants. In summary, these in vitro results indicated that amine functional groups existing in N containing glasses which are missing in N-free glasses, caused a slight difference in wetting behavior and a more obvious change in isoelectric point and in bacterial response. N-free glasses exhibited better inhibitory results both against E. coli and S. aureus compared to N including glass suggesting that oxygen rich glasses should be further studied for their novel antibacterial properties.  相似文献   
25.
The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm2h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC.  相似文献   
26.
The corrosion mechanisms of T24, T92, VM12, and AISI 304 steels are studied under the influence of NaCl–KCl, NaCl–Na2SO4, and KCl–K2SO4 salt mixtures in a dry air atmosphere at 650°C for 15 days. NaCl–KCl was the most aggressive deposit and AISI 304 stainless steel exhibited the highest corrosion resistance. There was no relation between the Cr content of the ferritic steels and their corrosion resistance in NaCl–KCl. In contrast, the resistance of high-Cr steels was better when exposed to NaCl–Na2SO4 and KCl–K2SO4. The high-Cr and the low-Cr steels were more susceptible to NaCl–Na2SO4 and to KCl–K2SO4, respectively.  相似文献   
27.
Treating neuroinflammation-related injuries and disorders through manipulation of neuroinflammation functions is being heralded as a new therapeutic strategy. In this study, a novel pectic galactan (PG) polysaccharide based gene therapy approach is developed for targeting reactive gliosis in neuroinflammation. Galectin-3 (Gal-3) is a cell protein with a high affinity to β-galactoside sugars and is highly expressed in reactive gliosis. Since PG carries galactans, it can target reactive gliosis via specific carbohydrate interaction between galactan and Gal-3 on the cell membrane, and therefore can be utilized as a carrier for delivering genes to these cells. The carrier is synthesized by modifying quaternary ammonium groups on the PG. The resulting quaternized PG (QPG) is found to form complexes with plasmid DNA with a mean diameter of 100 nm and have the characteristics required for targeted gene therapy. The complexes efficiently condense large amounts of plasmid per particle and successfully bind to Gal-3. The in vivo study shows that the complexes are biocompatible and safe for administration and can selectively transfect reactive glial cells of an induced cortical lesion. The results confirm that this PG-based delivery system is a promising platform for targeting Gal-3 overexpressing neuroinflammation cells for treating neuroinflammation-related injuries and neurodegenerative diseases.  相似文献   
28.
JOM - Refractory high-entropy alloys (RHEAs) are potential candidate materials for use in next-generation nuclear reactors due to their excellent mechanical performance at high temperatures. Here,...  相似文献   
29.
Polymer Bulletin - In this study, we synthesized a new ion-imprinted polymer (IIP) based on introduction of amidoxime groups in acrylonitrile, complexation with Cd2+ ions and polymerization with...  相似文献   
30.
Debittered trub (brewing waste) is an important source of protein source (70.26%). Trub and whey protein were used for 5% protein enrichment of ice cream frozen by liquid nitrogen. Three formulations were elaborated: ice cream standard (ICS), ice cream with whey protein (ICW) and ice cream with trub (ICT). Chemical composition, rheological properties, texture, overrun, melting rate, scanning electron microscopy and a sensorial test were performed. Results showed that ICT presented a higher viscosity, obtained on the upward curve up to 6.76 Pa s−1, consistency index (22.96 (Pa s−1)n), hysteresis area (140.40 mPa s−1) and hardness (31113.33 g) but a lower melting rate (0.38 g min−1), overrun (13.92%) and sensorial acceptability than the other formulations. The addition of trub debittered for protein enrichment improved ice cream properties and demonstrated that it could be used as a food ingredient.  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