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   376382篇
  免费   3572篇
  国内免费   1724篇
化学   173579篇
晶体学   4976篇
力学   20566篇
综合类   61篇
数学   74555篇
物理学   107941篇
  2021年   1888篇
  2020年   1973篇
  2019年   2105篇
  2018年   18882篇
  2017年   19419篇
  2016年   12337篇
  2015年   4076篇
  2014年   4204篇
  2013年   9719篇
  2012年   14761篇
  2011年   28907篇
  2010年   17660篇
  2009年   17870篇
  2008年   23783篇
  2007年   28581篇
  2006年   9116篇
  2005年   15130篇
  2004年   11510篇
  2003年   11037篇
  2002年   8291篇
  2001年   7157篇
  2000年   5669篇
  1999年   3881篇
  1998年   3304篇
  1997年   3190篇
  1996年   3367篇
  1995年   2848篇
  1994年   2897篇
  1993年   2768篇
  1992年   2963篇
  1991年   3043篇
  1990年   2834篇
  1989年   2766篇
  1988年   2712篇
  1987年   2649篇
  1986年   2665篇
  1985年   3467篇
  1984年   3517篇
  1983年   2948篇
  1982年   3198篇
  1981年   2953篇
  1980年   2755篇
  1979年   2933篇
  1978年   3144篇
  1977年   3088篇
  1976年   3141篇
  1975年   2858篇
  1974年   2967篇
  1973年   3065篇
  1972年   2372篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
41.
42.
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   
43.
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   
44.
45.
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions.  相似文献   
46.
We consider conformal gravity as a gauge natural theory. We study its conservation laws and superpotentials. We also consider the Mannheim and Kazanas spherically symmetric vacuum solution and discuss conserved quantities associated to conformal and diffeomorphism symmetries.  相似文献   
47.
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   
48.
Journal of Thermal Analysis and Calorimetry - In the present work, pyrolysis kinetic mechanism was studied for regenerated cellulosic fiber (RCF) and composite RCF containing silicon/nitrogen flame...  相似文献   
49.
50.
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