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   340486篇
  免费   8264篇
  国内免费   3338篇
电工技术   8870篇
技术理论   6篇
综合类   4629篇
化学工业   49194篇
金属工艺   18225篇
机械仪表   16169篇
建筑科学   11235篇
矿业工程   4383篇
能源动力   7904篇
轻工业   22637篇
水利工程   4300篇
石油天然气   10560篇
武器工业   468篇
无线电   37157篇
一般工业技术   67606篇
冶金工业   46367篇
原子能技术   6790篇
自动化技术   35588篇
  2022年   2300篇
  2021年   4347篇
  2020年   3299篇
  2019年   3450篇
  2018年   13060篇
  2017年   13871篇
  2016年   9409篇
  2015年   4990篇
  2014年   6564篇
  2013年   13138篇
  2012年   11907篇
  2011年   19873篇
  2010年   17457篇
  2009年   16858篇
  2008年   16577篇
  2007年   18491篇
  2006年   9398篇
  2005年   12104篇
  2004年   9167篇
  2003年   8553篇
  2002年   7017篇
  2001年   6341篇
  2000年   6487篇
  1999年   6756篇
  1998年   13087篇
  1997年   9484篇
  1996年   7518篇
  1995年   5798篇
  1994年   5196篇
  1993年   4767篇
  1992年   3726篇
  1991年   3475篇
  1990年   3151篇
  1989年   3152篇
  1988年   3009篇
  1987年   2495篇
  1986年   2380篇
  1985年   2771篇
  1984年   2519篇
  1983年   2338篇
  1982年   2090篇
  1981年   2203篇
  1980年   2025篇
  1979年   2107篇
  1978年   2098篇
  1977年   2350篇
  1976年   3170篇
  1975年   1819篇
  1974年   1738篇
  1973年   1757篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
3.
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   
4.
5.
A digital light processing (DLP) technology has been developed for 3D printing lead-free barium titanate (BTO) piezoelectric ceramics. By comparing the curing and rheological properties of slurries with different photosensitive monomer, a high refractive index monomer acryloyl morpholine (ACMO) was chosen, and a design and preparation method of BTO slurry with high solid content, low viscosity and high curing ability was proposed. By further selecting the printing parameters, the single-layer exposure time was reduced and the forming efficiency has been greatly improved. Sintered specimens were obtained after a nitrogen-air double-step debinding and furnace sintering process, and the BTO ceramics fabricated with 80 wt% slurry shows the highest relative density (95.32 %) and piezoelectric constant (168.1 pC/N). Furthermore, complex-structured BTO ceramics were prepared, impregnated by epoxy resin and finally assembly made into hydrophones, which has significance for the future design and manufacture of piezoelectric ceramic-based composites that used in functional devices.  相似文献   
6.
7.
Sun  Junli  Wang  Huaibin  Li  Yang  Zhao  Min 《Journal of Porous Materials》2021,28(3):889-894
Journal of Porous Materials - Co3O4 has been widely investigated as a promising candidate anode material for lithium-ion batteries. We report on the porous Co3O4 column synthesized via a simple...  相似文献   
8.
A set of novel hydrazone derivatives were synthesized and analyzed for their biological activities. The compounds were tested for their inhibitory effect on the phosphorylating activity of the protein kinase CK2, and their antioxidant activity was also determined in three commonly used assays. The hydrazones were evaluated for their radical scavenging against the DPPH, ABTS and peroxyl radicals. Several compounds have been identified as good antioxidants as well as potent protein kinase CK2 inhibitors. Most hydrazones containing a 4-N(CH3)2 residue or perfluorinated phenyl rings showed high activity in the radical-scavenging assays and possess nanomolar IC50 values in the kinase assays.  相似文献   
9.
Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO3-xBi(Ni2/3Nb1/3)O3(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni0·5Nb0.5)O3 boosts the insulation ability, thus obtaining a high breakdown strength (Eb) of 440 kV/cm in xBNN ceramics. A high energy storage density (Wtotal) of 4.09 J/cm3, recoverable energy storage density (Wrec) of 3.31 J/cm3, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of Wrec ≤ 0.4% over 5–100 Hz and Wrec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm3) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.  相似文献   
10.
B4C-TiB2 ceramics (TiB2 ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B4C-TiB2 without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB2 grains. The interface of the rim between TiB2 and B4C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B4C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B2 rim around the TiB2 core may occur as a result of the solid solution and dissolution-precipitation between TiB2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB2 content increased, alongside the decreased hardness. B4C-30 vol% TiB2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m1/2.  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