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   481357篇
  免费   5026篇
  国内免费   1432篇
化学   242481篇
晶体学   7762篇
力学   22965篇
综合类   12篇
数学   57936篇
物理学   156659篇
  2021年   4196篇
  2020年   4555篇
  2019年   5125篇
  2018年   6924篇
  2017年   7012篇
  2016年   9889篇
  2015年   5839篇
  2014年   9521篇
  2013年   22581篇
  2012年   17559篇
  2011年   21043篇
  2010年   15234篇
  2009年   15111篇
  2008年   18945篇
  2007年   18990篇
  2006年   17789篇
  2005年   15561篇
  2004年   14488篇
  2003年   12847篇
  2002年   12719篇
  2001年   14875篇
  2000年   11211篇
  1999年   8721篇
  1998年   7255篇
  1997年   7084篇
  1996年   6637篇
  1995年   5864篇
  1994年   5745篇
  1993年   5538篇
  1992年   6179篇
  1991年   6336篇
  1990年   6092篇
  1989年   5858篇
  1988年   5703篇
  1987年   5826篇
  1986年   5491篇
  1985年   6976篇
  1984年   7225篇
  1983年   5966篇
  1982年   6193篇
  1981年   5945篇
  1980年   5803篇
  1979年   6096篇
  1978年   6221篇
  1977年   6220篇
  1976年   6274篇
  1975年   5848篇
  1974年   5822篇
  1973年   5978篇
  1972年   4082篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
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   
103.
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   
104.
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   
105.
Sybachin  A. V.  Stepanova  D. A. 《Colloid Journal》2021,83(4):531-531
Colloid Journal - An Erratum to this paper has been published: https://doi.org/10.1134/S1061933X21330024  相似文献   
106.
The synthesis of vinyl alcohol copolymers is limited due to the poor radical reactivity of vinyl acetate (VAc), the traditional precursor to polyvinyl alcohol (PVA). Main group monomers such as BN 2-vinylnaphthalene (BN2VN) have attracted attention as alternatives to VAc to form side chain hydroxyls via oxidation, but outstanding questions of molecular weight control remain. Herein we report systematic investigation of solvent, temperature, and initiator concentration as factors influencing BN2VN degree of polymerization. We find increased chain transfer to toluene, hypothesized to arise from differences in radical stabilization and reactivity by aromatic and BN aromatic rings. As a result of these combined efforts, high molecular weight (Mw ~ 105 g mol−1) BN2VN homopolymers and BN2VN-styrene copolymers were obtained.  相似文献   
107.
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   
108.
109.
110.
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