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   474篇
  免费   8篇
  国内免费   6篇
化学   250篇
晶体学   5篇
力学   28篇
数学   160篇
物理学   45篇
  2023年   2篇
  2022年   9篇
  2021年   15篇
  2020年   12篇
  2019年   6篇
  2018年   16篇
  2017年   10篇
  2016年   24篇
  2015年   12篇
  2014年   17篇
  2013年   45篇
  2012年   30篇
  2011年   25篇
  2010年   24篇
  2009年   37篇
  2008年   22篇
  2007年   17篇
  2006年   16篇
  2005年   26篇
  2004年   19篇
  2003年   16篇
  2002年   19篇
  2001年   7篇
  2000年   9篇
  1999年   2篇
  1998年   5篇
  1997年   1篇
  1995年   3篇
  1994年   1篇
  1993年   2篇
  1991年   2篇
  1990年   1篇
  1989年   4篇
  1988年   2篇
  1987年   2篇
  1986年   2篇
  1985年   7篇
  1984年   6篇
  1983年   3篇
  1981年   1篇
  1979年   2篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1966年   1篇
  1961年   1篇
  1940年   1篇
排序方式: 共有488条查询结果,搜索用时 0 毫秒
91.
Using a fixed point theorem by Kuo, Jeng and Huang, we obtain in G-convex spaces a very general intersection theorem concerning the values of three maps. From this result we derive successively alternative theorems concerning maximal elements, analytic alternatives and minimax inequalities.  相似文献   
92.
We consider the problem of thermal stresses in cylindrical elastic shells, modelled as Cosserat surfaces. In the theory of Cosserat shells, the thermal effects are described generally by means of two temperature fields. The problem consists in finding the equilibrium of the shell under the action of a given temperature distribution. The temperature fields are assumed to be general polynomial functions in the axial coordinate, whose coefficients depend on the circumferential coordinate.  相似文献   
93.
94.
We consider the connection between the thermal effect of a black hole and the restoration of a broken symmetry. It appears that the second law of thermodynamics could be violated in a special circumstance. It is shown that this does not happen if we impose some constraints on the Higgs field.This essay recieved Honorable Mention from the Gravity Research Foundation—Ed.  相似文献   
95.
Potential Analysis - We introduce and study the unconstrained polarization (or Chebyshev) problem which requires to find an N-point configuration that maximizes the minimum value of its potential...  相似文献   
96.
A tunnel diode non-linear transmission line has been investigated for second and third harmonic generation purposes. Design criteria are given and performance predictions have been obtained simulating the single diode behavior by means of a polynomial expression. An optimization of the non-linear transmission line as a harmonic generator has been obtained as a function of the number of diodes, their separation distances and the bias voltage.  相似文献   
97.
Using Pd-catalyzed Stille cross-coupling reactions, we report here the synthesis of various mono- or bis(tri-n-butylstannyl)diazines which were reacted with various halogenated diazines to access to various polyaza heterocyclic derivatives.  相似文献   
98.
A simple method for synthesis of polymers containing shape persistent imine macrocycles as nanohoops in the main chain is studied. It is based on the cyclocondensation reaction carried out in solution and room temperature of triphenylamine-based tetraaldehyde compounds with (R,R)-trans-1,2-diaminocyclohexane. The pristine polymer P1 bearing long alkyl groups is soluble during the synthesis but becomes insoluble after precipitation due to the strong and multiple C H/π and π-π stacking intermolecular interactions from arene–arene species and entanglement and interpenetrating of flexible alkyl groups inside of rigid macrocycle hollow. Polymer without any solubilizing groups ( P2 ) separates during the polymerization as an insoluble material. Both polymers are amorphous and have good thermal and environmental stability. They have a low surface area because discrete nanovoids introduced by macrocycles are disconnected in the amorphous polymers and non-accessible for gas adsorption. Polymers have inherent luminescent properties due to triphenylamine groups and chirality derived from (R,R)-conformation of the cyclohexane skeleton. In presence of picric acid (PA), the polymer fluorescence in solid state or suspension is strongly quenched, thus the polymers can work as efficient fluorescent probes toward nitrophenolic compounds. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2565–2573  相似文献   
99.
Spectroscopic investigation supported by molecular modeling methods has been used to describe the inclusion complex of β-cyclodextrin (β-CD) with 1-Methyl-1-({2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-4-yl}methyl) piperidinium chloride (1MPTMPC) in solution and in solid state. The formation of inclusion complex between the β-CD and the 1MPTMPC has been investigated both in solution and in the solid state. Solution-state complexation between the 1MPTMPC and β-CD was established using 1H NMR spectroscopy and isothermal titration calorimetry (ITC). From the 1H NMR spectroscopic studies, 1:1 complex stoichiometry was deduced with an association constant (K) of 925 M?1. Using an independent binding model, the ITC technique provides a K value of the same order with the one determined by NMR and the thermodynamic parameters ΔH, ΔS and ΔG which reveals driving forces involved during complex formation. The formation of the solid inclusion compound was confirmed by X-ray powder diffraction and differential scanning calorimetry. The most probable conformation of the inclusion complex obtained through a molecular docking investigation corroborates well to ROESY experiment.  相似文献   
100.
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