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   65798篇
  免费   7551篇
  国内免费   3538篇
电工技术   5585篇
技术理论   8篇
综合类   5095篇
化学工业   9587篇
金属工艺   4064篇
机械仪表   4271篇
建筑科学   5468篇
矿业工程   2308篇
能源动力   2019篇
轻工业   4148篇
水利工程   1616篇
石油天然气   3300篇
武器工业   797篇
无线电   7842篇
一般工业技术   7272篇
冶金工业   2703篇
原子能技术   914篇
自动化技术   9890篇
  2024年   190篇
  2023年   1227篇
  2022年   2481篇
  2021年   3452篇
  2020年   2657篇
  2019年   2021篇
  2018年   2348篇
  2017年   2505篇
  2016年   2317篇
  2015年   3283篇
  2014年   3938篇
  2013年   4646篇
  2012年   5234篇
  2011年   5526篇
  2010年   4721篇
  2009年   4403篇
  2008年   4250篇
  2007年   3850篇
  2006年   3615篇
  2005年   2971篇
  2004年   1998篇
  2003年   1453篇
  2002年   1314篇
  2001年   1043篇
  2000年   980篇
  1999年   902篇
  1998年   681篇
  1997年   551篇
  1996年   567篇
  1995年   402篇
  1994年   335篇
  1993年   243篇
  1992年   206篇
  1991年   118篇
  1990年   101篇
  1989年   79篇
  1988年   74篇
  1987年   43篇
  1986年   32篇
  1985年   28篇
  1984年   13篇
  1983年   12篇
  1982年   14篇
  1981年   10篇
  1980年   10篇
  1979年   7篇
  1976年   9篇
  1975年   3篇
  1959年   9篇
  1951年   6篇
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
1.
2.
Mobile Networks and Applications - In order to effectively identify the pattern of personalized adaptive learning in online education and improve the recommendation satisfaction of personalized...  相似文献   
3.
4.
5.
The effects of cellulose microfibres (CMFs, Average size: 100 ± 5 μm) and cellulose nanofibres (CNFs, Average size: 60 ± 3 nm) on the properties of myofibrillar protein (MP) gels from duck breast meat were studied. The results demonstrated that CMFs and CNFs were mostly connected to MP by non-covalent bonds, the diffusion and cross-linking of MP molecules was promoted, and a denser and more complete gel network was formed. With the increases of CMFs and CNFs concentration (0–10%), the hardness was increased by 13.15% and 19.78% for CMFs10% and CNFs10% gels, respectively, and the elasticity was increased by 40% and 80%, respectively. At the same concentration (0–10%), the increase in gel hardness, viscoelasticity and immobilised water content was greater in the CNFs-MP group than in the CMFs-MP group. The CNFs-MP group had a tighter gel network, and CNFs had a better potential to improve the gelation performance of MP.  相似文献   
6.
Corrosion and salt deposition problems severely restrict the industrialization of supercritical water oxidation. Transpiring wall reactor can effectively weaken these two problems by a protective water film. In this work, methanol was selected as organic matter, and the influences of vital structural parameters on water film properties and organic matter removal were studied via numerical simulation. The results indicate that higher than 99% of methanol conversion could be obtained and hardly affected by transpiration water layer, transpiring wall porosity and inner diameter. Increasing layer and porosity reduced reactor center temperature, but inner diameter's influence was lower relatively. Water film temperature reduced but coverage rate raised as layer, porosity, and inner diameter increased. Notably, the whole reactor was in supercritical state and coverage rate was only approximately 85% in the case of one layer. Increasing reactor length affected slightly the volume of the upper supercritical zone but enlarged the subcritical zone.  相似文献   
7.
Song  Na  Wang  Pei  Cao  Donglei  Wang  Zhifeng  Ding  Peng 《Journal of Materials Science》2022,57(4):2540-2549
Journal of Materials Science - Currently, polymeric composites with good thermal conductivity and simple preparation method are in the rapid increment of demand. In this work,...  相似文献   
8.
This study investigated the effects of l -lysine (Lys) and l -histidine (His) on the oxidative characteristics and gel properties of porcine myofibrillar proteins (MP). Results showed that Lys and His had a strong ferrous ion-chelating ability and hydroxyl radical-scavenging activity. Moreover, Lys and His inhibited the protein carbonyl formation and MP aggregation at 0.2 M and 0.6 M NaCl, respectively, in a dose-dependent manner. Furthermore, 2 and 4 mg mL−1 Lys and His decreased the oxidation-induced loss of the tertiary structure of MP accompanied by the lower surface hydrophobicity. The water-holding capacity and gel strength of MP gels increased with increasing Lys and His concentrations due to more regular and lamellar structures with smaller and homogeneous pores at 0.6 M NaCl and more orderly crosslinking via fibrous filament at 0.2 M NaCl. In summary, Lys and His chelated the ferrous ions and scavenged hydroxyl radicals, decreased the oxidation-induced physicochemical changes, thus preventing oxidative damage during the formation of a three-dimensional gel network, which resulted in better gel quality.  相似文献   
9.
10.
High-efficiency Yb:Y2O3 laser ceramics were fabricated using the vacuum-sintering plus hot isostatic pressing (HIP) without sintering additives. High-purity well-dispersed nanocrystalline Yb:Y2O3 powder was synthesized using a modified co-precipitation method in-house. The green bodies were first vacuum sintered at a temperature as low as 1430°C and then HIPed at 1450°C. Finally, the samples were air annealed at 800°C for 10 h. Although no sintering aids were used, full density of the samples with excellent optical homogeneity and an inline transmission of 80% at 400 nm could be obtained. Moreover, photodarkening phenomenon was not detected in the ceramics. Preliminary laser experiment with the fabricated ceramics in a two-mirror cavity has demonstrated 32 W continuous-wave (CW) output at ∼1077 nm with an optical-to-optical conversion efficiency of 58.2%. To the best of our knowledge, this is so far the highest CW output power and optical-to-optical conversion efficiency achieved with the Yb3+-doped sesquioxide ceramics in a simple two-mirror cavity.  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