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   591818篇
  免费   4959篇
  国内免费   1346篇
化学   288212篇
晶体学   8368篇
力学   31204篇
综合类   28篇
数学   86994篇
物理学   183317篇
  2021年   5215篇
  2020年   5659篇
  2019年   6456篇
  2018年   13246篇
  2017年   13616篇
  2016年   14402篇
  2015年   6897篇
  2014年   11007篇
  2013年   24389篇
  2012年   21470篇
  2011年   29518篇
  2010年   21019篇
  2009年   21021篇
  2008年   27179篇
  2007年   29139篇
  2006年   19292篇
  2005年   20253篇
  2004年   17358篇
  2003年   16205篇
  2002年   14983篇
  2001年   14951篇
  2000年   11830篇
  1999年   8917篇
  1998年   7800篇
  1997年   7663篇
  1996年   7146篇
  1995年   6396篇
  1994年   6371篇
  1993年   6111篇
  1992年   6465篇
  1991年   6949篇
  1990年   6652篇
  1989年   6580篇
  1988年   6424篇
  1987年   6220篇
  1986年   5958篇
  1985年   7510篇
  1984年   7876篇
  1983年   6625篇
  1982年   6913篇
  1981年   6423篇
  1980年   6098篇
  1979年   6612篇
  1978年   6848篇
  1977年   6662篇
  1976年   6651篇
  1975年   6361篇
  1974年   6177篇
  1973年   6512篇
  1972年   4741篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data.  相似文献   
132.
Development of biocompatible porous supports is a promising strategy in the field of tissue engineering for the repair and regeneration of bone tissues with severe damage. Graphene oxide aerogels (GOAs) are excellent candidates for the manufacture of these systems due to their porosity, ability to imitate bone structure, and mechanical resistance, and according to their surface chemical reactivity, they can facilitate osseointegration, osteogenesis, osteoinduction and osteoconduction. In this review, synthesis of GOAs from the most primary source is described, and recent studies on the use of these functionalized carbonaceous foams as scaffolding for bone tissue regeneration are presented.  相似文献   
133.
Russian Journal of Organic Chemistry - Binder-free iron- and nickel-containing micro-, meso-, and macroporous zeolites FeHY and NiHY were found to effectively catalyze Knoevenagel condensation of...  相似文献   
134.
Russian Journal of General Chemistry - Some new fluoro-heterocyclic compounds containing thiazole and pyridine moities have been synthesized and studied for their antiproliferative activity....  相似文献   
135.
In this research article, we describe the synthesis and characterization of mononuclear and dinuclear Cu complexes bound by a family of tridentate redox-active ligands with tunable H-bonding donors. The mononuclear Cu-anion complexes were oxidized to the corresponding “high-valent” intermediates by oxidation of the redox-active ligand. These species were capable of oxidizing phenols with weak O−H bonds via H-atom abstraction. Thermodynamic analysis of the H-atom abstractions, which included reduction potential measurements, pKa determination and kinetic studies, revealed that modification of the anion coordinated to the Cu and changes in the H-bonding donor did not lead to major differences in the reactivity of the “high-valent” CuY complexes (Y: hydroxide, phenolate and acetate), which indicated that the tridentate ligand scaffold acts as the H+ and e acceptor.  相似文献   
136.
Sybachin  A. V.  Stepanova  D. A. 《Colloid Journal》2021,83(4):531-531
Colloid Journal - An Erratum to this paper has been published: https://doi.org/10.1134/S1061933X21330024  相似文献   
137.
Journal of Thermal Analysis and Calorimetry - This article considers viscoelastic effects on the enhancement of transportation of heat in thin-film flow when the relaxation time phenomenon is...  相似文献   
138.
Journal of Computer-Aided Molecular Design - Accurate predictions of acid dissociation constants are essential to rational molecular design in the pharmaceutical industry and elsewhere. There has...  相似文献   
139.
Journal of Thermal Analysis and Calorimetry - Coal O2/CO2 combustion is a promising carbon capture and storage technology for coal-fired power plant. Char consumption rate prediction is essential...  相似文献   
140.
This mini-review highlights key structural features that should be taken into account when creating ambipolar redox-active closed-shell metal-free molecules. This type of compound is strongly required for the fabrication of all-organic ‘poleless’ batteries and semiconductors. The suggested strategies aimed at stabilization of both oxidized (cationic) and reduced (anionic) redox-states are based on the comprehensive analysis of the most successful structures taken from the recent publications.  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