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   511027篇
  免费   4144篇
  国内免费   1165篇
化学   240037篇
晶体学   6274篇
力学   28001篇
综合类   14篇
数学   75028篇
物理学   166982篇
  2021年   3968篇
  2020年   4435篇
  2019年   5138篇
  2018年   12620篇
  2017年   13178篇
  2016年   12471篇
  2015年   5866篇
  2014年   9383篇
  2013年   20797篇
  2012年   18806篇
  2011年   27303篇
  2010年   19233篇
  2009年   19517篇
  2008年   24487篇
  2007年   26752篇
  2006年   16097篇
  2005年   17845篇
  2004年   14934篇
  2003年   13824篇
  2002年   11955篇
  2001年   13561篇
  2000年   10049篇
  1999年   7521篇
  1998年   6410篇
  1997年   6204篇
  1996年   5848篇
  1995年   5345篇
  1994年   5285篇
  1993年   5145篇
  1992年   5530篇
  1991年   5962篇
  1990年   5687篇
  1989年   5661篇
  1988年   5371篇
  1987年   5567篇
  1986年   5205篇
  1985年   6600篇
  1984年   6669篇
  1983年   5622篇
  1982年   5710篇
  1981年   5421篇
  1980年   5227篇
  1979年   5725篇
  1978年   5874篇
  1977年   5854篇
  1976年   5957篇
  1975年   5561篇
  1974年   5506篇
  1973年   5702篇
  1972年   4233篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Crystallography Reports - Fluoride crystals K2(Ta0.9I0.1)F7 (sp. gr. Р21/c) complementary to the K2TaF7 and K2NbF7 fluoride family have been obtained by hydrothermal synthesis. Their...  相似文献   
2.
Gaponov  S. A. 《Fluid Dynamics》2022,57(5):587-596
Fluid Dynamics - The problem of stability of a subsonic boundary layer is solved under the conditions of heat supply inside the boundary layer with injection of a homogeneous gas through a porous...  相似文献   
3.
Awad  A. M.  Askar  S. S.  Elsadany  A. A. 《Nonlinear dynamics》2022,107(4):3983-3999
Nonlinear Dynamics - In this paper, an economic competition between two firms that want to maximize the weighted-average social welfare and own profits is proposed. This kind of competition is...  相似文献   
4.
Journal of Applied Mechanics and Technical Physics - A method for determining the empirical dependence of the rheological properties of rocks on stresses has been developed and tested in...  相似文献   
5.
Pomogaev  V. A.  Lee  H. J.  Goh  E.  Tchaikovskaya  O. N.  Kononov  A. I.  Avramov  P. V. 《Russian Physics Journal》2022,64(11):2076-2081
Russian Physics Journal - Theoretical calculations of excited states in the complexes of gold and silver three-atom nanoclusters with carbon quantum nanodots are performed using the M062X...  相似文献   
6.
Russian Journal of General Chemistry - On the basis of 4-(thien-2-yl)-3-aminopyridine-2(1H)-one, the corresponding chloroacetamide and condensed 1H-pyrido[2,3-b][1,4]oxazine-2(3H)-one were...  相似文献   
7.
A new series of azomethine-functionalized compounds was synthesized from the condensation of 2-hydroxy-1,3-propanediamine and 2-thienylcarboxaldehydes in the presence of a drying agent. The derivatives were spectroscopically characterized by NMR, LC-MS, UV/Vis, IR and elemental analysis. Variable temperature 1H-NMR (−60 to +60 °C) was performed to investigate the effect of solvent polarity; the capability of solvent to form H-bond was found to dramatically influencing the tautomerization process of the desired structures. The calculated thermochemical parameters (ΔH298, ΔG298 and ΔS298) at DFT and MP2 levels of theory explained that 3 b exists in equilibrium with two tautomers. The basis of the electronic absorptions was pursued through Time-Dependent Density-Functional Theory (TD-DFT). Analysis of the structural surfaces was inspected and the molecular electrostatic potential (MEP) demonstrated that the three functionalized compounds were relatively analogous in the electronic distributions. Furthermore, the electrophilic and nucleophilic centers lying on the molecular surfaces were probably playing a key-role in stabilizing the compounds through the nonclassical C−H⋅⋅⋅π interactions and hydrogen bonding. The impact of solvent polarity on absorption spectra were investigated via solvatochromic shifts. For instance, compound 3 c displayed a gradual shift of the maximum absorption to the red area when the solvent polarity was increased, recording a 21 nm of bathochromic shift. In contrast, no significant solvent-effect on 3 a and 3 b was observed. The solvation relation was pursued between Gutmann's donicity numbers the experimental λmax; exhibited almost positive linear performance with a minor oscillation, that ascribe to the possible weak interface between the molecules of solute and designated solvents. The bandgap energy of all products were assessed experimentally using optical absorption spectra following Tauc approach, giving −4.050 ( 3 a ), −3.900 ( 3 b ) and −3.210 ( 3 c ) eV. However, the ΔE were computationally figured out from TD-DFT simulation to be −4.258 ( 3 a ), −4.022 ( 3 b ) and −3.390 ( 3 c ) eV.  相似文献   
8.
Physics of the Solid State - Using the X-ray diffraction and electron microscopy methods, the structure and the elemental and phase compositions of hypereutectic alloy Al86Ni2Co6Gd6 (hereinafter,...  相似文献   
9.
Russian Physics Journal - The results of a study of the dislocation structure evolution in polycrystals of homogeneous solid solutions in low-stability states in Cu-Mn-based alloys with FCC crystal...  相似文献   
10.
The European Physical Journal A - The goal of the present paper is twofold. First, a novel expansion many-body method applicable to superfluid open-shell nuclei, the so-called Bogoliubov in-medium...  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