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   228092篇
  免费   26864篇
  国内免费   21054篇
化学   103746篇
晶体学   1707篇
力学   9040篇
综合类   1099篇
数学   18817篇
物理学   55714篇
综合类   85887篇
  2024年   726篇
  2023年   3640篇
  2022年   5617篇
  2021年   6570篇
  2020年   6752篇
  2019年   6007篇
  2018年   5778篇
  2017年   5438篇
  2016年   7960篇
  2015年   8584篇
  2014年   11290篇
  2013年   13630篇
  2012年   16144篇
  2011年   16731篇
  2010年   12651篇
  2009年   12577篇
  2008年   13717篇
  2007年   12695篇
  2006年   11459篇
  2005年   10253篇
  2004年   8027篇
  2003年   6993篇
  2002年   7113篇
  2001年   6457篇
  2000年   5545篇
  1999年   7298篇
  1998年   6005篇
  1997年   5837篇
  1996年   5499篇
  1995年   4816篇
  1994年   4427篇
  1993年   3630篇
  1992年   3245篇
  1991年   2919篇
  1990年   2464篇
  1989年   2141篇
  1988年   1641篇
  1987年   1128篇
  1986年   892篇
  1985年   514篇
  1984年   286篇
  1983年   244篇
  1982年   181篇
  1981年   129篇
  1980年   79篇
  1979年   37篇
  1978年   25篇
  1976年   27篇
  1975年   24篇
  1957年   35篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
121.
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.  相似文献   
122.
Guo  Yan  Li  Zhuang  Wei  Yuxi  Zhang  Xinxu  Shi  Kexin 《Journal of Solid State Electrochemistry》2022,26(4):1051-1065
Journal of Solid State Electrochemistry - Polyvinylpyrrolidone (PVP) and graphene (G)-modified iron oxides (Fe2O3-PVP-G) are prepared by a simple hydrothermal reaction. Their morphology and...  相似文献   
123.
In this paper, we analyze the concentration behavior of a positive solution to an evolution equation with critical exponential growth on a closed Riemann surface, and particularly derive an energy identity for such a solution. This extends a result of Lamm-Robert-Struwe and complements that of Yang.  相似文献   
124.
125.
The Ramanujan Journal - Inspired by Andrews and Merca’s recent work on the number of even parts over all partitions into distinct parts, we introduce a new kind of Beck type identities, which...  相似文献   
126.
The design and exploration of efficient, stable and environmentally compatible organic emitters for an electrochemiluminescence (ECL) sensor is a promising topic. Herein, a novel environmentally-friendly luminophore, ZnBCBTP@MWCNTs, were fabricated via self-assembly of porphyrin molecules (ZnBCBTP) onto multi-walled carbon nanotubes (MWCNTs). The resulting luminophore ZnBCBTP@MWCNTs displayed not only the highly ECL property and but also the good accelerated electron mobility. Then, a label-free ECL biosensor based ZnBCBTP@MWCNTs was constructed for the ultrasensitive detection of uric acid. Excitingly, this proposed ECL biosensor performed a good linear relationship in the range of 0–300 μM with a low detection limit of 1.4 μM, thus offering another reliable and feasible sensing platform for clinical bioanalysis with good selectivity, stability, and repeatability.  相似文献   
127.
通过post李超代数的定义, 讨论post李超代数结构的基本性质, 给出post李超代数的一些存在性结果, 并利用post李超代数可构造LR超代数和左对称超代数, 给出交换post李超代数结构的相关结果.  相似文献   
128.
129.
Au@Cu_2O core-shell nanorods with tunable thickness of Cu_2O shell were synthesized and their linear and nonlinear optical responses were investigated. Two transverse plasmon resonance peaks were observed when the Au nanorods were coated with Cu_2O shells, which were adjusted by the Cu_2O shell thickness. The nonlinear absorption of the Au@Cu_2O nanorods is enhanced by 5 times at the longitudinal plasmon resonance wavelength compared with that of bare Au nanorods. More intriguingly, largely enhanced nonlinear refraction and suppressed nonlinear absorption at the transverse plasmon resonance wavelength were observed in the Au@Cu_2O nanorods. Our findings indicate the existence of strong local field enhancement at the interface between the Au core and the Cu_2O shell, which would provide a promising strategy in designing plasmonic nonlinear nanodevices with good nonlinear figures of merit.  相似文献   
130.
Let L be an additive map between (real or complex) matrix algebras sending n×n Hermitian idempotent matrices to m×m Hermitian idempotent matrices. We show that there are nonnegative integers p,q with n(p+q)=rm and an m×m unitary matrix U such thatL(A)=U[(Ip?A)(Iq?At)0m?r]U?,for any n×n Hermitian A with rational trace. We also extend this result to the (complex) von Neumann algebra setting, and provide a supplement to the Dye-Bunce-Wright Theorem asserting that every additive map of Hermitian idempotents extends to a Jordan ?-homomorphism.  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