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   190076篇
  免费   20202篇
  国内免费   12183篇
化学   101641篇
晶体学   2040篇
力学   13786篇
综合类   667篇
数学   45025篇
物理学   59302篇
  2024年   270篇
  2023年   2301篇
  2022年   3407篇
  2021年   4104篇
  2020年   4746篇
  2019年   4563篇
  2018年   13278篇
  2017年   12847篇
  2016年   11164篇
  2015年   6099篇
  2014年   6797篇
  2013年   8918篇
  2012年   13900篇
  2011年   20782篇
  2010年   12519篇
  2009年   12551篇
  2008年   13651篇
  2007年   15049篇
  2006年   6452篇
  2005年   6539篇
  2004年   5413篇
  2003年   5073篇
  2002年   4015篇
  2001年   2733篇
  2000年   2437篇
  1999年   2611篇
  1998年   2319篇
  1997年   2119篇
  1996年   2367篇
  1995年   1858篇
  1994年   1723篇
  1993年   1394篇
  1992年   1265篇
  1991年   1186篇
  1990年   948篇
  1989年   704篇
  1988年   567篇
  1987年   489篇
  1986年   494篇
  1985年   406篇
  1984年   310篇
  1983年   215篇
  1982年   197篇
  1981年   154篇
  1980年   126篇
  1979年   88篇
  1978年   68篇
  1976年   53篇
  1974年   56篇
  1973年   56篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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   
92.
Journal of Radioanalytical and Nuclear Chemistry - In the present work the final products of coumarin radiation chemical transformation are investigated by chromatography. During radiolysis of...  相似文献   
93.
Journal of Thermal Analysis and Calorimetry - The fire behavior of one flame-retardant PVC cable used as building wire is investigated in this work. Bench scale tests were performed using a cone...  相似文献   
94.
95.
96.
97.
Transition Metal Chemistry - Two cubane-like complexes, namely [Ni4L4(HOEt)4] (1), [Co4L4(HOEt)4] (2) (H2L?=?(E)-2-((3-hydroxypropylimino)methyl)-6-methoxyphenol), were prepared under...  相似文献   
98.
Guided by the self-penetrating features can improve the stability of metal organic frameworks (MOFs), an unprecedented 3D self-penetrated framework, {[Zn (tptc)0.5(bimb)]·H2O}n ( NUC-6 , here NUC corresponding to North University of China), with 3D (4,4)-c {86} net, was designed. Benefit from the high chemical stability and excellent luminescent property, NUC-6 can be act as an efficient multi-response chemo-sensor in detecting dichloronitroaniline pesticide and nitrofuran antibiotics in water with the detection limits are 116 ppb for DCN pesticide, 16 ppb for NFT antibiotic, and 12 ppb for NTZ antibiotic. Besides, the mechanisms of luminescence quenching were revealed from the viewpoint of internal filter effect (IFE) and photo-induced electron transfer (PET), implied by the optical spectroscopy and quantum chemical calculation. This work provides a promising strategy to design stable MOFs by improving the self-penetrating features and to expand their practical applications in the detection of organic pollutants in aqueous medium.  相似文献   
99.
We propose a system of time-division multiplexing(TDM) and spatial frequency-division multiplexing(SFDM). Extrinsic Fabry–Perot interferometric sensors are applied to detect weak acoustic signals. The broadband source is employed, the light from it is modulated by a pulse signal sequence and is efficiently amplified by semiconductor optical amplifiers. Experimental results show that the equivalent noise pressure spectrum level is-97.2 d B re 1 rad/√Hz below 1250 Hz, and the cross talk between two sensors in one TDM channel is-32.7 d B with a cavity length difference of 60 μm. The number of sensors in this multiplexing system can theoretically reach 160.  相似文献   
100.
A single-polarization filter comprising a gold-coated photonic crystal fiber based on surface plasmon resonance is designed and investigated. The pattern matching and coupled polarization characteristics analyzed by the full-vector finite element method (FEM) and losses at 1,540 nm are achieved to 1,016.01739 dB/cm (x-pol core mode) and 33.81917 dB/cm (y-pol core mode). The crosstalk (CT) value of the 1,540 nm band is ?853.12653 dB for fiber length L=1,000μm and the bandwidth is 850 nm. The working wavelength of the filter ranges from 1,280 nm to 1,540 nm by varying the diameter of outer air holes (d1), the diameter of inner air holes (d4), the metal film thickness (t), as well as the liquid refractive index (n).  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