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   397307篇
  免费   8923篇
  国内免费   5477篇
化学   203794篇
晶体学   5047篇
力学   20122篇
综合类   330篇
数学   48494篇
物理学   133920篇
  2021年   4471篇
  2020年   5216篇
  2019年   5724篇
  2018年   7277篇
  2017年   7347篇
  2016年   9964篇
  2015年   6137篇
  2014年   9804篇
  2013年   19863篇
  2012年   16587篇
  2011年   19169篇
  2010年   14377篇
  2009年   14311篇
  2008年   16815篇
  2007年   16487篇
  2006年   15172篇
  2005年   13206篇
  2004年   12193篇
  2003年   10619篇
  2002年   10098篇
  2001年   12084篇
  2000年   8825篇
  1999年   6832篇
  1998年   5870篇
  1997年   5545篇
  1996年   5172篇
  1995年   4622篇
  1994年   4665篇
  1993年   4450篇
  1992年   4785篇
  1991年   5038篇
  1990年   4803篇
  1989年   4630篇
  1988年   4317篇
  1987年   4456篇
  1986年   4246篇
  1985年   5200篇
  1984年   5251篇
  1983年   4382篇
  1982年   4421篇
  1981年   4114篇
  1980年   4042篇
  1979年   4410篇
  1978年   4384篇
  1977年   4393篇
  1976年   4423篇
  1975年   4156篇
  1974年   4182篇
  1973年   4194篇
  1972年   3086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.
Crystallography Reports - The review presents the important unique results of the cycle of research led by M.V. Kovalchuk on the fundamental patterns of protein interactions and the protein...  相似文献   
5.
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   
6.
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   
7.
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   
8.
Journal of Analytical Chemistry - A review of works in developing optical multisensor systems, a new class of specialized spectroscopic analyzers, is presented. The development and use of such...  相似文献   
9.
Bo  Luo  Gao  Wei  Yu  Yuguo  Chen  Xiaojun 《Nonlinear dynamics》2022,110(1):281-311
Nonlinear Dynamics - The perovskite solar cell (PSC) is one of the most promising photovoltaic candidates along with the highly increasing demand for green electricity. One of the main concerns...  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