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   7695篇
  免费   1378篇
  国内免费   737篇
化学   5388篇
晶体学   43篇
力学   461篇
综合类   56篇
数学   944篇
物理学   2918篇
  2024年   27篇
  2023年   145篇
  2022年   260篇
  2021年   295篇
  2020年   363篇
  2019年   275篇
  2018年   251篇
  2017年   244篇
  2016年   365篇
  2015年   403篇
  2014年   444篇
  2013年   555篇
  2012年   696篇
  2011年   737篇
  2010年   470篇
  2009年   443篇
  2008年   482篇
  2007年   436篇
  2006年   429篇
  2005年   304篇
  2004年   276篇
  2003年   180篇
  2002年   205篇
  2001年   123篇
  2000年   140篇
  1999年   152篇
  1998年   130篇
  1997年   156篇
  1996年   131篇
  1995年   121篇
  1994年   103篇
  1993年   102篇
  1992年   72篇
  1991年   61篇
  1990年   59篇
  1989年   36篇
  1988年   34篇
  1987年   33篇
  1986年   13篇
  1985年   26篇
  1984年   10篇
  1983年   6篇
  1982年   4篇
  1981年   6篇
  1980年   1篇
  1979年   2篇
  1959年   2篇
  1957年   1篇
  1916年   1篇
排序方式: 共有9810条查询结果,搜索用时 0 毫秒
21.
22.
23.
Based on the studies on the source regions of a group of coronal mass ejections, we have identified two types of large-scale magnetic structures, and suggested that they are intrinsic components of solar magnetism, their destabilization, expansion, and eruption into the interplanetary space are the basic physical processes which lead to the coronal mass ejections. These two types of large-scale structures are giant magnetic loops connecting the two active belts on the opposite hemispheres of the Sun, and the giant filaments (filament channels) and their related magnetic structures. The latter often appear as two parallel rows of sunspots and plage fields, which align side by side in the full disk daily and synoptic magnetograms. The magnetic neutral lines of these large-scale structures are usually longer than 50 heliographic degrees. We name this type of structure “super A configuration”. Sometimes, they are shown as very long filaments and related large-scale magnetic fields. As these magnetic structures are of very large scale, they extend to a great altitude into the corona, they are not easily recognized in magnetic field observations which are usually aimed at solar flare studies. To identify these large-scale structures becomes a key to understanding and predicting coronal mass ejections.  相似文献   
24.
In this paper, using a modified Poisson kernel in an upper half-space, we prove that a harmonic function u(z) in a upper half space with its positive part u+(x)=max{u(x),0} satisfying a slowly growing condition can be represented by its integral in the boundary of the upper half space, the integral representation is unique up to the addition of a harmonic polynomial, vanishing in the boundary of the upper half space and that its negative part u(x)=max{−u(x),0} can be dominated by a similar slowly growing condition, this improves some classical result about harmonic functions in the upper half space.  相似文献   
25.
Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4′-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA.  相似文献   
26.
关于不完全双二次非协调板元的误差估计   总被引:1,自引:0,他引:1  
邓庆平 《应用数学》1992,5(4):61-65
本文在[1,2]的基础上,对不完全双二次板元作了进一步的讨论,不仅得到了最优的L~2—误差估计,改进了[1]的相应结果,而且利用“辅助元技巧”并结合正则Green函数法,得到了拟最优的L~∞—误差估计.  相似文献   
27.
本利用矩阵对的标准相关分解,得到了矩阵方程(A^TXB,B^TXB)=(C,D)反对称解存在的充分必要条件及通解表达式,同时给出了解关于已知矩阵的最佳逼近.  相似文献   
28.
29.
Lanthanide Complexes for Oligomerization of Phenyl Isocyanate   总被引:1,自引:0,他引:1  
IntroductionThestudyonthereactivitiesoflanthanidecomplexesto wardisocyanateshasattractedmuchattention .Ithasbeenre portedthatlanthanidealkoxides,1anddivalentdiaza pentadi enyllanthanidecomplexes2 canbeusedasthesinglecompo nentinitiatorsforisocyanatespolymerization .Recentlyourre searchgrouphasalsofoundthatlanthanoceneamide ,3diva lentaryloxideofsamarium4 ,5anddivalentsamarocene6 areallactivefortheoligomerizationofphenylisocyanate,andtheactivespeciesforthesethreesystemswereallsuccessfullyisolat…  相似文献   
30.
Apparatus integrating a Fourier transform-infrared (FT-IR) spectrometer and a mid-infrared difference frequency generation (DFG) laser spectrometer was built for the study of the matrix isolation spectrum in solid molecular hydrogen. A 3-cm-long molecular hydrogen crystal was grown in a liquid-helium Dewar, and its infrared absorption spectrum in the 1-5 μm region was recorded to test the system. The W0(0) (ν=0←0, J=6←0) line around 2410 cm−1 of solid hydrogen was investigated with the DFG laser spectroscopy. High-resolution matrix isolation spectrum of CO2 co-deposited with hydrogen on a BaF2 cold plate at liquid-helium temperature was studied.  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