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   1486401篇
  免费   27574篇
  国内免费   6922篇
电工技术   33935篇
综合类   6362篇
化学工业   255419篇
金属工艺   64211篇
机械仪表   42668篇
建筑科学   42868篇
矿业工程   11474篇
能源动力   49930篇
轻工业   108355篇
水利工程   15357篇
石油天然气   36885篇
武器工业   132篇
无线电   196298篇
一般工业技术   283298篇
冶金工业   170849篇
原子能技术   34188篇
自动化技术   168668篇
  2021年   14599篇
  2020年   11879篇
  2019年   14654篇
  2018年   16915篇
  2017年   16390篇
  2016年   21872篇
  2015年   17457篇
  2014年   28738篇
  2013年   87923篇
  2012年   35902篇
  2011年   49056篇
  2010年   43411篇
  2009年   51759篇
  2008年   45363篇
  2007年   42768篇
  2006年   44606篇
  2005年   39777篇
  2004年   41728篇
  2003年   40965篇
  2002年   38259篇
  2001年   34982篇
  2000年   32814篇
  1999年   32642篇
  1998年   45525篇
  1997年   38605篇
  1996年   33791篇
  1995年   30657篇
  1994年   28646篇
  1993年   28567篇
  1992年   25629篇
  1991年   22837篇
  1990年   23272篇
  1989年   22178篇
  1988年   20720篇
  1987年   19040篇
  1986年   18477篇
  1985年   21795篇
  1984年   21981篇
  1983年   19879篇
  1982年   18929篇
  1981年   19048篇
  1980年   17666篇
  1979年   18168篇
  1978年   17460篇
  1977年   17211篇
  1976年   18126篇
  1975年   15745篇
  1974年   15263篇
  1973年   15378篇
  1972年   12865篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
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   
992.
Glass and Ceramics - The effect of diopside on the sintering temperature, structure, and properties of low-temperature electrotechnical porcelain was investigated. Diopside concentrate in the...  相似文献   
993.
In this paper the microstructure and mechanical properties of two different Cf/ZrB2-SiC composites reinforced with continuous PyC coated PAN-derived fibres or uncoated pitch-derived fibres were compared.Pitch-derived carbon fibres showed a lower degree of reaction with the matrix phase during sintering compared to PyC/PAN-derived fibres. The reason lies in the different microstructure of the carbon. The presence of a coating for PAN-derived fibres was found to be essential to limit the reaction at the fibre/matrix interface during SPS. However, coated bundles were more difficult to infiltrate, resulting in a less homogeneous microstructure.As far as the mechanical properties are concerned, specimens reinforced with coated PAN-derived fibres provided higher strengths and damage tolerance than uncoated pitch-derived fibres, due to the higher degree of fibre pull-out. On the other hand, the weaker fibre/matrix interface resulted in lower interlaminar shear, off-axis strength and ablation resistance.  相似文献   
994.
A series of rare earth zirconates (RE2Zr2O7) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La2Zr2O7 and Yb2Zr2O7, the smaller “rattling” ions (Yb3+, Er3+, Y3+) have been incorporated into pyrochlore lattice in (La0.2Nd0.2Y0.2Er0.2Yb0.2)2Zr2O7 (LNYEY) while larger ions (La3+, Nd3+, Sm3+, Eu3+) incorporated into fluorite lattice in (La0.2Nd0.2Sm0.2Gd0.2Yb0.2)2Zr2O7 (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb3+, Er3+, and Y3+, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m-1 K-1, 100-600℃) than LNSGY (1.74-1.75 W m-1 K-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, Hv = 11.47 ± 0.41 GPa; LNSGY, Hv = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10-6 K-1, 1000℃; LNSGY, 11.02 × 10-6 K-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings.  相似文献   
995.
为了提高公司综合经济效益,充分发挥目前现有的水泥半终粉磨系统生产能力大、电耗低的特点,利用水泥销售淡季间隔生产经济效益较好的矿渣粉。经过调整和部分改造,半终粉磨系统运行情况良好,效果显著。  相似文献   
996.
Sanjay  Prasad  B.  Vohra  A. 《Semiconductors》2021,55(12):936-942
Semiconductors - In this work, drain current ID for 5-nm gate length with dual-material (DM) double-surrounding gate (DSG) inversion mode (IM) and junctionless (JL) silicon nanotube (SiNT) MOSFET...  相似文献   
997.
Multidimensional Systems and Signal Processing - Filter banks are the major signal processing blocks that dissipate large amount of power in a portable digital hearing aid device. The power...  相似文献   
998.
The Journal of Supercomputing - Data aggregation is an effective mechanism to prolong lifetime in the wireless sensor networks by preventing extra data transmission. However, it may have some...  相似文献   
999.
1000.
Materials Science - We solve the plane problem of the theory of elasticity for a circular disk weakened by an arbitrarily located internal radial crack subjected to the action of a model contact...  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