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   484720篇
  免费   9308篇
  国内免费   2587篇
电工技术   9306篇
技术理论   5篇
综合类   1376篇
化学工业   75975篇
金属工艺   18120篇
机械仪表   14126篇
建筑科学   13063篇
矿业工程   2252篇
能源动力   12074篇
轻工业   50450篇
水利工程   4747篇
石油天然气   7635篇
武器工业   248篇
无线电   56327篇
一般工业技术   90962篇
冶金工业   87760篇
原子能技术   8402篇
自动化技术   43787篇
  2021年   4248篇
  2020年   3093篇
  2019年   3699篇
  2018年   6008篇
  2017年   5982篇
  2016年   6618篇
  2015年   5127篇
  2014年   8129篇
  2013年   22707篇
  2012年   13802篇
  2011年   18914篇
  2010年   14965篇
  2009年   16300篇
  2008年   17521篇
  2007年   17614篇
  2006年   15735篇
  2005年   13928篇
  2004年   12886篇
  2003年   12456篇
  2002年   12031篇
  2001年   12321篇
  2000年   11335篇
  1999年   11711篇
  1998年   26871篇
  1997年   19322篇
  1996年   14745篇
  1995年   11224篇
  1994年   10067篇
  1993年   9789篇
  1992年   7329篇
  1991年   6951篇
  1990年   6880篇
  1989年   6614篇
  1988年   6349篇
  1987年   5281篇
  1986年   5186篇
  1985年   6216篇
  1984年   5838篇
  1983年   5339篇
  1982年   4791篇
  1981年   5070篇
  1980年   4614篇
  1979年   4673篇
  1978年   4435篇
  1977年   4820篇
  1976年   6171篇
  1975年   3874篇
  1974年   3649篇
  1973年   3730篇
  1972年   3030篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
1.
2.
Journal of Materials Science -  相似文献   
3.
Journal of Communications Technology and Electronics - A quantitative comparison of the spectral characteristics of the human visual system and matrix photodetectors is carried out. Criteria for a...  相似文献   
4.
Xiao  Zhu  Chen  Yanxun  Jiang  Hongbo  Hu  Zhenzhen  Lui  John C. S.  Min  Geyong  Dustdar  Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of...  相似文献   
5.
6.
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized...  相似文献   
7.
Forschung im Ingenieurwesen - Das Arbeitsmittel in Wärmepumpen unterliegt einer Vielzahl von Anforderungen, welche für einen effizienten und sicheren Betrieb eingehalten werden...  相似文献   
8.
While protein medications are promising for treatment of cancer and autoimmune diseases, challenges persist in terms of development and injection stability of high-concentration formulations. Here, the extensional flow properties of protein-excipient solutions are examined via dripping-onto-substrate extensional rheology, using a model ovalbumin (OVA) protein and biocompatible excipients polysorbate 20 (PS20) and 80 (PS80). Despite similar PS structures, differences in extensional flow are observed based on PS identity in two regimes: at moderate total concentrations where surface tension differences drive changes in extensional flow behavior, and at small PS:OVA ratios, which impact the onset of weakly elastic flow behavior. Undesirable elasticity is observed in ultra-concentrated formulations, independent of PS identity; higher PS contents are required to observe these effects than in analogous polymeric excipient solutions. These studies reveal novel extensional flow behaviors in protein-excipient solutions, and provide a straightforward methodology for assessing the extensional flow stability of new protein-excipient formulations.  相似文献   
9.
Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi4P4 and IrSi3P3 are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and 29Si and 31P magic angle spinning NMR. In agreement with previous report RuSi4P4 crystallizes in NCS space group P1, while IrSi3P3 is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi4P4 and IrSi3P3 to be wide bandgap (Eg) semiconductors, Eg = 1.9 and 1.8 eV, respectively. RuSi4P4 and IrSi3P3 outperform the current state-of-the-art infrared SHG material, AgGaS2, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi4P4 and IrSi3P3 are promising candidates for longer wavelength NLO materials.  相似文献   
10.
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   
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