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   164910篇
  免费   879篇
  国内免费   315篇
化学   64079篇
晶体学   2612篇
力学   10414篇
综合类   8篇
数学   30022篇
物理学   58969篇
  2022年   531篇
  2021年   478篇
  2020年   447篇
  2019年   436篇
  2018年   10083篇
  2017年   10960篇
  2016年   5250篇
  2015年   1591篇
  2014年   1131篇
  2013年   2645篇
  2012年   6919篇
  2011年   16303篇
  2010年   9854篇
  2009年   10005篇
  2008年   14099篇
  2007年   17757篇
  2006年   2680篇
  2005年   9651篇
  2004年   5770篇
  2003年   5433篇
  2002年   3188篇
  2001年   3194篇
  2000年   2497篇
  1999年   1605篇
  1998年   1138篇
  1997年   1082篇
  1996年   1080篇
  1995年   902篇
  1994年   808篇
  1993年   713篇
  1992年   1038篇
  1991年   1031篇
  1990年   932篇
  1989年   841篇
  1988年   836篇
  1987年   894篇
  1986年   746篇
  1985年   987篇
  1984年   947篇
  1983年   677篇
  1982年   663篇
  1981年   629篇
  1980年   599篇
  1979年   743篇
  1978年   778篇
  1977年   696篇
  1976年   648篇
  1975年   541篇
  1974年   577篇
  1973年   549篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
We summarize the results of our recent work on Bäcklund transformations (BTs), particularly focusing on the relation between BTs and infinitesimal symmetries. We present a BT for an associated Degasperis–Procesi (aDP) equation and its superposition principle and investigate the solutions generated by applying this BT. Following our general methodology, we use the superposition principle of the BT to generate the infinitesimal symmetries of the aDP equation.  相似文献   
15.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
16.
17.
18.
Su  X. F.  Zhang  Y. L.  Maximov  A. L.  Zhang  K.  Xin  Q.  Feng  C. Q.  Bai  X. F.  Wu  W. 《Russian Journal of Applied Chemistry》2020,93(1):127-136
Russian Journal of Applied Chemistry - Nanoscale ZSM-5 (AlZ5-D) and Ga-substituted ZSM-5 zeolites ((Al,Ga)Z5-D and GaZ5-D) were synthesized by a green dry-gel conversion strategy. For comparison,...  相似文献   
19.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
20.
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   
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