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   62147篇
  免费   1443篇
  国内免费   719篇
化学   29919篇
晶体学   906篇
力学   3402篇
综合类   44篇
数学   5051篇
物理学   24987篇
  2022年   487篇
  2021年   576篇
  2020年   593篇
  2019年   588篇
  2018年   716篇
  2017年   620篇
  2016年   1098篇
  2015年   806篇
  2014年   1207篇
  2013年   2802篇
  2012年   2643篇
  2011年   3364篇
  2010年   2359篇
  2009年   2405篇
  2008年   3007篇
  2007年   2818篇
  2006年   2697篇
  2005年   2341篇
  2004年   2144篇
  2003年   1868篇
  2002年   1711篇
  2001年   3071篇
  2000年   2161篇
  1999年   1577篇
  1998年   1105篇
  1997年   1068篇
  1996年   854篇
  1995年   835篇
  1994年   751篇
  1993年   650篇
  1992年   988篇
  1991年   953篇
  1990年   867篇
  1989年   749篇
  1988年   741篇
  1987年   800篇
  1986年   671篇
  1985年   893篇
  1984年   834篇
  1983年   571篇
  1982年   568篇
  1981年   543篇
  1980年   497篇
  1979年   624篇
  1978年   647篇
  1977年   660篇
  1976年   575篇
  1975年   482篇
  1974年   525篇
  1973年   449篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
21.
Two new octahedral [Ni(phen)2(dppz-idzo)]2+ and [Co(phen)2(dppz-idzo)]3+ complexes have been synthesized and characterized by CHN analysis, electrospray ionization-MS, nuclear magnetic resonance, and UV–Vis spectra. The DNA-binding ability of these complexes was spectrophotometrically, hydrodynamically, and electrophoretically evaluated which indicated that they strongly intercalate into the DNA double helix, and that both induced severe DNA damage in the presence of peroxide. The complexes also showed strong antiproliferative effect against HepG2 and MDA-MB-231 cells. By contrast, they were found to be inactive against the MCF-7 cell line. The ligand itself was found to be inactive against the cells tested.  相似文献   
22.
Bimetallic AgPd nanoparticles have been synthesized before, but the interfacial electronic effects of AgPd on the photocatalytic performance have been investigated less. In this work, the results of hydrogen evolution suggest that the bimetallic AgPd/g-C3N4 sample has superior activity to Ag/g-C3N4 and Pd/g-C3N4 photocatalysts. The UV/Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, CO adsorption diffuse reflectance FTIR spectroscopy, and FTIR results demonstrate that in the AgPd/g-C3N4, the surface electronic structures of Pd and Ag are changed, which is beneficial for faster photogenerated electron transfer and greater H2O molecule adsorption. In situ ESR spectra suggest that, under visible light irradiation, there is more H2O dissociation to radical species on the AgPd/g-C3N4 photocatalyst. Furthermore, DFT calculations confirm the interfacial electronic effects of AgPd/g-C3N4, that is, Pdδ−⋅⋅⋅Agδ+, and the activation energy of H2O molecule dissociation on AgPd/g-C3N4 is the lowest, which is the main contributor to the enhanced photocatalytic H2 evolution.  相似文献   
23.
A multivariate calibration method was applied to improve the accuracy of the determination of cadmium in the presence of potassium by total reflection X-ray fluorescence (TXRF). Due to TXRF's relatively low resolution, a particular interference caused by potassium at line Kα 3.31 keV as interference can compromise the cadmium determination at line Lα 3.13 keV, respectively. The method is based on the hypothesis that the application of a multivariate calibration method, for example, partial least squares, could reduce variations due to interference and, consequently, improve the selectivity and accuracy in Cd determination. In this work, this strategy was evaluated on the X-ray fluorescence emission signals between 2.50 and 3.90 keV for a set of 26 different synthetic calibration mixtures and eight different mixtures for external calibration. Based on a certified reference material (Clay 2—CRM051) with high potassium levels, a significant improvement of accuracy for cadmium determination was observed, overcoming the problems associated with spectral interferences by potassium.  相似文献   
24.
High pressure can effectively control the phase transition of MoTe2 in experiment, but the mechanism is still unclear. In this work, we show by first-principles calculations that the phase transition is suppressed and 1T phase becomes more stable under high pressure, which originates from the pressure-induced change of the interlayer band occupancies near the Fermi energy. Specifically, the interlayer states of 1T phase tend to be fully occupied under high pressure, while they keep partially occupied for the Td phase. The increase of the band occupancies makes the 1T phase more favorable in energy and prevents the structure changing from 1T to Td phase. Moreover, we also analyze the superconductivity under high pressure based on BCS theory by calculating the density of states and phonon spectra. Our results may shed some light on understanding the relationship between the interlayer band occupancy and crystal stability of MoTe2 under high pressures.  相似文献   
25.
Elahi  S. A.  Connesson  N.  Chagnon  G.  Payan  Y. 《Experimental Mechanics》2019,59(2):251-261
Experimental Mechanics - Simulating the deformations of soft tissues has gained importance in recent years due to the development of 3D patient-specific biomechanical models in the context of...  相似文献   
26.
Xu  Wu  Zhang  Yuanya  Achi  Oliver Y.  Knierim  Kathleen D.  Hanks  Justin G.  Wang  Yingchun 《Structural chemistry》2019,30(4):1459-1470
Structural Chemistry - ERK1 is an important kinase in Ras–Raf–MEK signaling. We have recently demonstrated by mass spectrometry that Tyr210 of ERK1 can be nitrated, and the nitration...  相似文献   
27.
Guo  J.  Dadashi  S.  Bender  M.  Paruchuri  S. T.  Powell  N.  Sharma  Y.  Kurdila  H.  McGlothlin  J. W.  Kurdila  A. J. 《Nonlinear dynamics》2019,98(1):195-213
Nonlinear Dynamics - In contrast to many systems studied in the field of classical mechanics, models of animal motion are often distinguished in that they are both highly uncertain and evolve in a...  相似文献   
28.
29.
Chang  Mingning  Wang  He  Zheng  Yonglei  Li  Ningning  Chen  Siheng  Wan  Yong  Yuan  Feng  Shao  Weiquan  Xu  Sheng 《Journal of Solid State Electrochemistry》2019,23(2):607-613
Journal of Solid State Electrochemistry - Li1.2Ni1/3Co1/3Mn1/3O2 was synthesized as a cathode material for lithium-ion batteries and coated with various amounts of CoAl2O4 (0–5 wt%)...  相似文献   
30.
Journal of Radioanalytical and Nuclear Chemistry - A castable polyurethane (PUR) with soft segment made by polytetrahydrofuran polyol (or polytretramethylene ether glycol?=?PTMEG)...  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