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   469864篇
  免费   4630篇
  国内免费   1321篇
化学   236967篇
晶体学   7484篇
力学   23697篇
综合类   18篇
数学   57115篇
物理学   150534篇
  2021年   4418篇
  2020年   4639篇
  2019年   5370篇
  2018年   7478篇
  2017年   7654篇
  2016年   10426篇
  2015年   5728篇
  2014年   9798篇
  2013年   21869篇
  2012年   16954篇
  2011年   20257篇
  2010年   15307篇
  2009年   15380篇
  2008年   18497篇
  2007年   18356篇
  2006年   16717篇
  2005年   14637篇
  2004年   13704篇
  2003年   12230篇
  2002年   12231篇
  2001年   14175篇
  2000年   10495篇
  1999年   8113篇
  1998年   6833篇
  1997年   6737篇
  1996年   6246篇
  1995年   5460篇
  1994年   5509篇
  1993年   5291篇
  1992年   5908篇
  1991年   6197篇
  1990年   5841篇
  1989年   5855篇
  1988年   5561篇
  1987年   5693篇
  1986年   5353篇
  1985年   6803篇
  1984年   6957篇
  1983年   5777篇
  1982年   5813篇
  1981年   5587篇
  1980年   5350篇
  1979年   5896篇
  1978年   5840篇
  1977年   6017篇
  1976年   5993篇
  1975年   5659篇
  1974年   5547篇
  1973年   5660篇
  1972年   4143篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
113.
114.
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   
115.
116.
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   
117.
The microscopic Polymer Reference Interaction Site Model theory is employed to study, for the first time, the effective interactions, spatial organization, and miscibility of dilute spherical nanoparticles in non‐microphase separating, chemically heterogeneous, compositionally symmetric AB multiblock copolymer melts of varying monomer sequence or architecture. The dependence of nanoparticle wettability on copolymer sequence and chemistry results in interparticle potentials‐of‐mean force that are qualitatively different from homopolymers. An important prediction is the ability to improve nanoparticle dispersion via judicious choice of block length and monomer adsorption‐strengths which control both local surface segregation and chain connectivity induced packing constraints and frustration. The degree of dispersion also depends strongly on nanoparticle diameter relative to the block contour length. Small particles in copolymers with longer block lengths experience a more homopolymer‐like environment which renders them relatively insensitive to copolymer chemical heterogeneity and hinders dispersion. Larger particles (sufficiently larger than the monomer diameter) in copolymers of relatively short block lengths provide better dispersion than either a homopolymer or random copolymer. The theory also predicts a novel widening of the miscibility window for large particles upon increasing the overall molecular weight of copolymers composed of relatively long blocks. The influence of a positive chi‐parameter in the pure copolymer melt is briefly studied. Quantitative application to fullerenes in specific copolymers of experimental interest is performed, and miscibility predictions are made. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1098–1111  相似文献   
118.
119.
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   
120.
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   
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