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   501287篇
  免费   5383篇
  国内免费   1191篇
化学   250772篇
晶体学   5991篇
力学   24088篇
综合类   12篇
数学   69741篇
物理学   157257篇
  2021年   3359篇
  2020年   4184篇
  2019年   4518篇
  2018年   12386篇
  2017年   12906篇
  2016年   11805篇
  2015年   6167篇
  2014年   8620篇
  2013年   20248篇
  2012年   18904篇
  2011年   28646篇
  2010年   19057篇
  2009年   18925篇
  2008年   25598篇
  2007年   28042篇
  2006年   16206篇
  2005年   19644篇
  2004年   16003篇
  2003年   14349篇
  2002年   11853篇
  2001年   13102篇
  2000年   9711篇
  1999年   7316篇
  1998年   6018篇
  1997年   5887篇
  1996年   5739篇
  1995年   5381篇
  1994年   5356篇
  1993年   5133篇
  1992年   5751篇
  1991年   5860篇
  1990年   5607篇
  1989年   5421篇
  1988年   5449篇
  1987年   5365篇
  1986年   5040篇
  1985年   6552篇
  1984年   6700篇
  1983年   5305篇
  1982年   5400篇
  1981年   5379篇
  1980年   4956篇
  1979年   5395篇
  1978年   5534篇
  1977年   5374篇
  1976年   5354篇
  1975年   4923篇
  1974年   4893篇
  1973年   4932篇
  1972年   3469篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
1.
Different strategies for the preparation of efficient and robust immobilized biocatalysts are here reviewed. Different physico-chemical approaches are discussed.i.- The stabilization of enzyme by any kind of immobilization on pre-existing porous supports.ii.- The stabilization of enzymes by multipoint covalent attachment on support surfaces.iii.- Additional stabilization of immobilized-stabilized enzyme by physical or chemical modification with polymers.These three strategies can be easily developed when enzymes are immobilized in pre-existing porous supports. In addition to that, these immobilized-stabilized derivatives are optimal to develop enzyme reaction engineering and reactor engineering. Stabilizations ranging between 1000 and 100,000 folds regarding diluted soluble enzymes are here reported.  相似文献   
2.
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   
3.
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   
4.
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   
5.
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   
6.
Journal of Solid State Electrochemistry - The addition of nanocrystalline titanium dioxide (P90) to a cathode of Li/S cell enhances its voltammetric charge capacity by 19%, from which only a small...  相似文献   
7.
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   
8.
Carnicer  J. M.  Khiar  Y.  Peña  J. M. 《Numerical Algorithms》2022,90(4):1691-1713
Numerical Algorithms - An inverse central ordering of the nodes is proposed for the Newton interpolation formula. This ordering may improve the stability for certain distributions of nodes. For...  相似文献   
9.
Syrovatka  R. A.  Lipaev  A. M.  Naumkin  V. N.  Klumov  B. A. 《JETP Letters》2022,116(12):869-874
JETP Letters - A quasi-two-dimensional plasma crystal in (3 + 1) dimensions has been experimentally observed for the first time; i.e., three spatial coordinates of each microparticles of the...  相似文献   
10.
Physics of the Solid State - The discovery of extreme magnetoresistance (MR) in nonmagnetic materials attracted attention to WTe2 semimetal. We studied MR in a single crystal of tungsten...  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