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   489847篇
  免费   14025篇
  国内免费   8245篇
化学   258773篇
晶体学   6952篇
力学   24691篇
综合类   578篇
数学   67357篇
物理学   153766篇
  2021年   4516篇
  2020年   5164篇
  2019年   5282篇
  2018年   13491篇
  2017年   14043篇
  2016年   12028篇
  2015年   7329篇
  2014年   9053篇
  2013年   18712篇
  2012年   20626篇
  2011年   30362篇
  2010年   19939篇
  2009年   19813篇
  2008年   26285篇
  2007年   28843篇
  2006年   16162篇
  2005年   20073篇
  2004年   15650篇
  2003年   14083篇
  2002年   12015篇
  2001年   12650篇
  2000年   9911篇
  1999年   7767篇
  1998年   6098篇
  1997年   5955篇
  1996年   6036篇
  1995年   5377篇
  1994年   5328篇
  1993年   4926篇
  1992年   5494篇
  1991年   5541篇
  1990年   5132篇
  1989年   4952篇
  1988年   4765篇
  1987年   4710篇
  1986年   4476篇
  1985年   5718篇
  1984年   5669篇
  1983年   4670篇
  1982年   4869篇
  1981年   4464篇
  1980年   4229篇
  1979年   4638篇
  1978年   4930篇
  1977年   4868篇
  1976年   4856篇
  1975年   4461篇
  1974年   4569篇
  1973年   4663篇
  1972年   3419篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
91.
92.
Russian Chemical Bulletin - Quantum chemical calculations and a comparative analysis of Raman spectra of 3,4,5-triphenyl-1-propyl-1,2-diphosphole (1),...  相似文献   
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.
Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research.  相似文献   
96.
Journal of Thermal Analysis and Calorimetry - In the present work, pyrolysis kinetic mechanism was studied for regenerated cellulosic fiber (RCF) and composite RCF containing silicon/nitrogen flame...  相似文献   
97.
Journal of Thermal Analysis and Calorimetry - Based on innovative design, a liquid–vapor separation plate condenser with excellent heat transfer performance is invented. It takes less time to...  相似文献   
98.
99.
100.
Applied Magnetic Resonance - The suggested approach allowed us to derive analytical expressions for modeling the shape of solid-echo signal and its time evolution for a system of three-spin groups...  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