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   1289371篇
  免费   30477篇
  国内免费   8145篇
化学   638366篇
晶体学   14130篇
力学   73939篇
综合类   119篇
数学   238913篇
物理学   362526篇
  2021年   13235篇
  2020年   16070篇
  2019年   16192篇
  2016年   27465篇
  2015年   20737篇
  2014年   30581篇
  2013年   74537篇
  2012年   36546篇
  2011年   31834篇
  2010年   35895篇
  2009年   38453篇
  2008年   31548篇
  2007年   26760篇
  2006年   34545篇
  2005年   25976篇
  2004年   28031篇
  2003年   26825篇
  2002年   28235篇
  2001年   27665篇
  2000年   24319篇
  1999年   19853篇
  1998年   18653篇
  1997年   19273篇
  1996年   19193篇
  1995年   18570篇
  1994年   18062篇
  1993年   17561篇
  1992年   17539篇
  1991年   17771篇
  1990年   17097篇
  1989年   17102篇
  1988年   16678篇
  1987年   16701篇
  1986年   15587篇
  1985年   22134篇
  1984年   23400篇
  1983年   19501篇
  1982年   21204篇
  1981年   20446篇
  1980年   19741篇
  1979年   20083篇
  1978年   21365篇
  1977年   21059篇
  1976年   20769篇
  1975年   19476篇
  1974年   19108篇
  1973年   19642篇
  1972年   14139篇
  1968年   12223篇
  1967年   12585篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Drichko  I. L.  Smirnov  I. Yu.  Bakarov  A. K.  Bykov  A. A.  Dmitriev  A. A.  Galperin  Yu. M. 《JETP Letters》2020,112(1):45-52
JETP Letters - The DC and AC conductivities of the n-GaAs/AlAs heterostructure with two filled size quantization levels are studied within a wide magnetic field range. The electron spectrum of such...  相似文献   
992.
Mavrogordatos  Th. K. 《JETP Letters》2020,112(5):274-282

We calculate the steady-state and first-order time varying atom—field correlation functions in the weak-excitation limit of absorptive optical bistability from a linearized theory of quantum fluctuations. We formulate a Fokker—Planck equation in the positive P representation following the phase-space analysis in [H. J. Carmichael, Phys. Rev. A 33, 3262 (1986)], which is suitable for the determination of cross-correlations as it does not resort to adiabatic elimination. Special emphasis is placed on the limit of collective strong coupling as attained from a vanishing photon-loss rate. We compare to the cavity-transmission spectrum with reference to experimental results obtained for macroscopic dissipative systems, discussing the role of anomalous correlations arising as distinct nonclassical features.

  相似文献   
993.
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   
994.
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   
995.
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   
996.
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   
997.
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   
998.
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   
999.
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   
1000.
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   
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