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   307514篇
  免费   3723篇
  国内免费   638篇
化学   166167篇
晶体学   4376篇
力学   12587篇
综合类   10篇
数学   37535篇
物理学   91200篇
  2020年   2670篇
  2019年   2844篇
  2018年   3950篇
  2017年   3887篇
  2016年   5985篇
  2015年   3897篇
  2014年   5468篇
  2013年   13371篇
  2012年   10524篇
  2011年   12191篇
  2010年   8640篇
  2009年   8187篇
  2008年   11371篇
  2007年   11336篇
  2006年   10512篇
  2005年   9737篇
  2004年   8871篇
  2003年   7913篇
  2002年   7710篇
  2001年   8073篇
  2000年   6443篇
  1999年   4931篇
  1998年   4314篇
  1997年   4216篇
  1996年   4101篇
  1995年   3690篇
  1994年   3931篇
  1993年   3601篇
  1992年   4082篇
  1991年   4028篇
  1990年   3990篇
  1989年   3780篇
  1988年   3888篇
  1987年   3757篇
  1986年   3576篇
  1985年   4753篇
  1984年   4964篇
  1983年   4157篇
  1982年   4289篇
  1981年   4221篇
  1980年   4161篇
  1979年   4121篇
  1978年   4421篇
  1977年   4331篇
  1976年   4410篇
  1975年   4053篇
  1974年   4110篇
  1973年   4282篇
  1972年   2983篇
  1971年   2484篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
63.
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   
64.
65.
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   
66.
67.
68.
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   
69.
The synthesis and characterisation of a family of block codendrimers consisting of highly versatile mesogenic and carbazole‐containing 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) dendrons are reported. The liquid‐crystal behaviour was investigated by means of differential scanning calorimetry, polarised‐light optical microscopy and X‐ray diffraction. Depending on the chemical structure of the constituent dendrons, the codendrimers show lamellar or columnar mesophases. On the basis of the experimental results, models both at the molecular level and in the mesophase are proposed. The physical properties of the block codendrimers derived from the presence of the carbazole moiety in their structure were investigated: photoluminescence in solution and in the mesophase, electrochemical behaviour and hole transport. Electrodeposition of carbazole dendrons afforded a globular supramolecular conformation in which the mesogenic molecular side plays a key role.  相似文献   
70.
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