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   571720篇
  免费   6053篇
  国内免费   1659篇
化学   276219篇
晶体学   7833篇
力学   29331篇
综合类   13篇
数学   96936篇
物理学   169100篇
  2021年   3901篇
  2020年   4304篇
  2019年   4663篇
  2018年   20320篇
  2017年   20571篇
  2016年   16661篇
  2015年   7027篇
  2014年   9076篇
  2013年   20876篇
  2012年   21862篇
  2011年   36306篇
  2010年   23331篇
  2009年   23598篇
  2008年   30788篇
  2007年   34717篇
  2006年   16929篇
  2005年   21024篇
  2004年   17580篇
  2003年   16306篇
  2002年   13863篇
  2001年   13817篇
  2000年   10604篇
  1999年   8113篇
  1998年   6818篇
  1997年   6517篇
  1996年   6433篇
  1995年   5696篇
  1994年   5596篇
  1993年   5393篇
  1992年   5979篇
  1991年   6080篇
  1990年   5806篇
  1989年   5625篇
  1988年   5653篇
  1987年   5538篇
  1986年   5232篇
  1985年   6715篇
  1984年   6875篇
  1983年   5453篇
  1982年   5545篇
  1981年   5500篇
  1980年   5113篇
  1979年   5498篇
  1978年   5589篇
  1977年   5417篇
  1976年   5376篇
  1975年   4946篇
  1974年   4914篇
  1973年   4960篇
  1972年   3488篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
We consider conformal gravity as a gauge natural theory. We study its conservation laws and superpotentials. We also consider the Mannheim and Kazanas spherically symmetric vacuum solution and discuss conserved quantities associated to conformal and diffeomorphism symmetries.  相似文献   
94.
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   
95.
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   
96.
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures...  相似文献   
97.
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   
98.
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   
99.
Russian Journal of Organic Chemistry - Herein, we report the sulfonamide-functionalized covalent organic framework (COF-SO3H), prepared by condensation of melamine and terephthalaldehyde and...  相似文献   
100.
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