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   2693篇
  免费   171篇
  国内免费   62篇
化学   2088篇
晶体学   11篇
力学   132篇
数学   290篇
物理学   405篇
  2024年   1篇
  2023年   11篇
  2022年   43篇
  2021年   106篇
  2020年   167篇
  2019年   140篇
  2018年   192篇
  2017年   135篇
  2016年   226篇
  2015年   149篇
  2014年   214篇
  2013年   339篇
  2012年   227篇
  2011年   204篇
  2010年   172篇
  2009年   139篇
  2008年   138篇
  2007年   90篇
  2006年   53篇
  2005年   31篇
  2004年   30篇
  2003年   29篇
  2002年   19篇
  2001年   10篇
  2000年   9篇
  1999年   3篇
  1998年   2篇
  1997年   4篇
  1996年   2篇
  1995年   3篇
  1994年   2篇
  1993年   5篇
  1992年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1985年   4篇
  1984年   1篇
  1983年   2篇
  1982年   5篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1978年   2篇
  1975年   4篇
  1972年   2篇
排序方式: 共有2926条查询结果,搜索用时 695 毫秒
51.
Cellulose - The electrical conductivity of cotton fabrics was enhanced using an in situ synthesis of graphene or polymerization of conductive polymer. The impact of conductive materials...  相似文献   
52.
53.
54.
Catalytic one‐pot condensation of benzil, aldehyde and ammonium acetate have been successfully carried out using 2‐hydroxyethylammonium formate (HEAF) grafted on a magnetic nanoparticles as a new heterogeneous catalyst. The as‐prepared catalyst was characterized by FT‐IR, TEM, FESEM, VSM, TGA and XRD. This catalyst indicated significant advantages, such as excellent yields, shorter reaction time, reusability of the catalyst and easy workup process.  相似文献   
55.
A hybrid meshless technique based on composition of meshless local Petrov–Galerkin method (for spatial variables) and Newmark finite difference method (for time domain) is developed for natural frequencies analysis of thick cylinder made of functionally graded materials (FGMs). The FG cylinder is assumed to be under suddenly thermal loading, axisymmetric and plane strain conditions. The dynamic behaviors and time history of displacements are obtained in time domain using Green–Naghdi (GN) theory of coupled thermo-elasticity (without energy dissipation). Using fast Fourier transform (FFT) technique, the displacements are transferred to frequency domain and all natural frequencies are illustrated for various grading patterns of FGMs. The variations of mechanical properties in FG thick hollow cylinder are considered to be in nonlinear volume fraction law through radial direction. The presented hybrid meshless technique furnishes a ground to analyze the effects of various grading patterns of FGMs on natural frequencies, which are obtained employing GN coupled thermo-elasticity governing equations. Also, the frequency history and natural frequencies are illustrated for various grading patterns at several points across thickness of cylinder.  相似文献   
56.
57.
A new and efficient method has been developed for the one-pot synthesis of novel 2,9-dihydro-2-oxo-4-aryl-1H-pyrido[2,3-b]indole-3-carbonitrile derivatives by condensation of substituted (triethoxymethyl)arene, 1-methyl-1H-indol-2-ol and cyanoacetamide in the presence of a catalytic amount of crosslinked poly(2-acrylamido-2-methyl propane sulfonic acid) (AMPS) as an efficient and heterogeneous catalyst. This polymeric solid acid catalyst is stable and can be easily recovered and reused without significant change in its activity.  相似文献   
58.
Structural Chemistry - In this work, the hydrogenation of acetylene on the Pd2/g-C3N4 catalyst is investigated by the density functional theory (DFT) and quantum theory of atoms in molecules...  相似文献   
59.
We propose that spectral intensity of superconductor based random lasers can be made tunable by changing temperature. The two fluid model and wavelength dependent dispersion formula have been employed to describe the optical response of the superconducting materials. Random laser characteristics have been calculated using the one dimensional FDTD method. Our simulation results reveal that the emission spectrum can be manipulated through the ambient temperature of the system. It is observed that transition from metal phase to pure superconducting phase leads to the enhancement of the laser emission. Furthermore, spatial distribution of the fields in one dimensional disordered media is very sensitive to the system temperature.  相似文献   
60.
Chemistry of Heterocyclic Compounds - This microreview describes recent approaches to the synthesis of thieno[2,3-b]pyridine derivatives. Selected works published in 2015–2019 are reviewed.  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