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   331925篇
  免费   2990篇
  国内免费   662篇
化学   165376篇
晶体学   4633篇
力学   15564篇
综合类   6篇
数学   50287篇
物理学   99711篇
  2021年   2067篇
  2020年   2469篇
  2019年   2713篇
  2018年   11478篇
  2017年   12158篇
  2016年   9064篇
  2015年   3996篇
  2014年   4877篇
  2013年   11264篇
  2012年   12966篇
  2011年   21980篇
  2010年   13700篇
  2009年   13484篇
  2008年   19564篇
  2007年   22827篇
  2006年   9364篇
  2005年   14388篇
  2004年   10401篇
  2003年   9745篇
  2002年   7636篇
  2001年   6600篇
  2000年   5437篇
  1999年   3851篇
  1998年   3317篇
  1997年   3243篇
  1996年   3295篇
  1995年   2622篇
  1994年   2708篇
  1993年   2781篇
  1992年   2887篇
  1991年   2877篇
  1990年   2763篇
  1989年   2744篇
  1988年   2684篇
  1987年   2649篇
  1986年   2551篇
  1985年   3296篇
  1984年   3447篇
  1983年   2768篇
  1982年   3025篇
  1981年   2896篇
  1980年   2677篇
  1979年   2916篇
  1978年   3047篇
  1977年   2981篇
  1976年   2980篇
  1975年   2813篇
  1974年   2774篇
  1973年   2976篇
  1972年   1925篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
51.
52.
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   
53.
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   
54.
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   
55.
56.
57.
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   
58.
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   
59.
60.
Physics of Atomic Nuclei - We have studied the mechanisms influencing production of cumulative pions and protons in the fragmentation of the incident deuterons into cumulative pions and protons...  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