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   1306202篇
  免费   29673篇
  国内免费   7597篇
化学   636528篇
晶体学   14700篇
力学   75007篇
综合类   102篇
数学   243224篇
物理学   373911篇
  2021年   12732篇
  2020年   15900篇
  2019年   16023篇
  2018年   15152篇
  2017年   13833篇
  2016年   28894篇
  2015年   21066篇
  2014年   30403篇
  2013年   74298篇
  2012年   37813篇
  2011年   35967篇
  2010年   38655篇
  2009年   41249篇
  2008年   35276篇
  2007年   31491篇
  2006年   34253篇
  2005年   29310篇
  2004年   29601篇
  2003年   27831篇
  2002年   25359篇
  2001年   24117篇
  2000年   20880篇
  1999年   19322篇
  1998年   18429篇
  1997年   19066篇
  1996年   19072篇
  1995年   18435篇
  1994年   17996篇
  1993年   17473篇
  1992年   17058篇
  1991年   17421篇
  1990年   16632篇
  1989年   16740篇
  1988年   16319篇
  1987年   16380篇
  1986年   15183篇
  1985年   21777篇
  1984年   23196篇
  1983年   19365篇
  1982年   21146篇
  1981年   20388篇
  1980年   19682篇
  1979年   19852篇
  1978年   21288篇
  1977年   20898篇
  1976年   20572篇
  1975年   19263篇
  1974年   18876篇
  1973年   19412篇
  1972年   13917篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
ABSTRACT

Using density functional theory calculations, we investigate the gas sensing performance of B-, N-doped and BN-codoped C60 fullerenes towards NO and NO2 molecules. The calculated adsorption energies and net charge-transfer values indicate that NO and NO2 molecules have a stronger interaction with the BN-codoped fullerenes compared to the B- or N-doped ones. It is also found that the electronic properties of the BN-codoped C60 exhibit a larger sensitivity towards NO and NO2 molecules. An increase in the concentration of doped/co-doped B and N atoms tends to weaken the gas sensing ability of these systems.  相似文献   
992.
Torsional states caused by vibrations of hydroxyl groups in the methanediol molecule and its two deuterated analogues – DO(CH2)OH and DO(CH2)OD were analysed at MP2/cc-pVTZ and CCSD(T)/cc-pVQZ levels of theory. In the first case, 2D PES and 2D surfaces of kinematic coefficients were calculated with geometry optimisation for all other geometric parameters, and in the second case, only the energy of optimised configurations at the MP2/cc-pVTZ level of theory was determined. Then 2D PES was recounted to the complete basis set (CBS) limit by extrapolating the results of calculations at the MP2/cc-pVTZ and MP2/cc-pVQZ levels of theory The calculated values were then averaged over four equivalent points on the coordinate plane. Hamiltonian matrices were constructed using DVR and Fourier methods. After their subsequent diagonalization, the energies of the stationary torsional states were computed. Their classification by C2V(M) and CS(M) molecular symmetry groups has been performed. The splitting values due to the tunnelling of the thirty most deeply located torsional states in the three studied molecules were also determined. The torsional states, internal rotation barriers, and tunnelling frequencies in the molecules of methanediol and hydrogen trioxide were compared.  相似文献   
993.
Optics and Spectroscopy - A method that allows modeling the scattering characteristics of bodies of arbitrary geometry has been proposed on the basis of the method of continued boundary conditions....  相似文献   
994.
Optics and Spectroscopy - The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical...  相似文献   
995.
Petrin  A. B. 《Optics and Spectroscopy》2020,128(11):1809-1827
Optics and Spectroscopy - A rigorous theory of radiation of an elementary dipole that is located either on the boundary of a plane-layered structure or inside it is considered. For a particular...  相似文献   
996.
Putilin  A. N.  Morozov  A. V.  Kopenkin  S. S.  Dubynin  S. E.  Borodin  Yu. P. 《Optics and Spectroscopy》2020,128(11):1828-1836
Optics and Spectroscopy - Main properties of holographic waveguide periscopic multiplexors of the exit pupil of optical systems of augmented reality displays are considered. Limitations in the...  相似文献   
997.
Tkachev  V. G.  Ivanov  A. I. 《Optics and Spectroscopy》2020,128(11):1707-1714
Optics and Spectroscopy - The influence of symmetry breaking caused by charge transfer in excited quadrupole molecules of the D-π-A-π-D or A-π-D-π-A type, where A and D are the...  相似文献   
998.
Optics and Spectroscopy - We investigated the morphology and luminescent properties of ZnO tetrapod powders with copper and gold admixtures, obtained by carbothermal pyrolysis. A broad band in the...  相似文献   
999.
Optics and Spectroscopy - Methods of preparation of single-crystal 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST) films with a thickness of several micrometers, designed...  相似文献   
1000.
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar...  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