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   751篇
  免费   26篇
  国内免费   3篇
化学   554篇
晶体学   17篇
力学   15篇
数学   60篇
物理学   134篇
  2023年   3篇
  2022年   3篇
  2021年   5篇
  2020年   12篇
  2019年   11篇
  2018年   7篇
  2016年   10篇
  2015年   17篇
  2014年   13篇
  2013年   48篇
  2012年   39篇
  2011年   35篇
  2010年   19篇
  2009年   22篇
  2008年   59篇
  2007年   48篇
  2006年   63篇
  2005年   64篇
  2004年   39篇
  2003年   21篇
  2002年   35篇
  2001年   11篇
  2000年   19篇
  1999年   7篇
  1998年   5篇
  1997年   7篇
  1996年   6篇
  1995年   14篇
  1994年   10篇
  1993年   9篇
  1992年   10篇
  1991年   4篇
  1990年   3篇
  1989年   8篇
  1988年   7篇
  1987年   4篇
  1985年   10篇
  1984年   8篇
  1983年   5篇
  1982年   12篇
  1981年   5篇
  1980年   3篇
  1979年   4篇
  1978年   7篇
  1977年   3篇
  1976年   2篇
  1974年   2篇
  1973年   8篇
  1965年   3篇
  1963年   2篇
排序方式: 共有780条查询结果,搜索用时 15 毫秒
71.
The influence of high-temperature annealing on the electrical properties and microstructure of tin-doped indium oxide (ITO) thin films was investigated as a function of oxygen gas flow ratio to argon gas during the sputtering deposition. The ITO thin films were annealed at 500 °C in air after the deposition. It was found that the ITO thin films, which were deposited in relatively low oxygen gas flow ratio, exhibited high Hall mobility and low-resistivity after the annealing. Furthermore, the X-ray reflectivity and diffraction measurement revealed that the ITO thin film with low-resistivity after annealing exhibited high packing density, smooth surface and low crystallization degree. It can be considered that the carrier electron scattering was suppressed with increasing in the packing density of the ITO thin film; as a result, the Hall mobility and resistivity were improved.  相似文献   
72.
The purpose of this article is to study an existence of p-bases and mainly to give some regularity criteria for semilocal rings essentially of finite type over fields.  相似文献   
73.
o-Ethynylbenzyl phenyl selenides regioselectively reacted with trifluoromethanesulfonic acid to afford the (Z)-1-methylidene-2-phenyl-1,3-dihydro-1H-benzo[c]selenophenium salts as the major products during the 5-exo-dig mode cyclization in good yields together with minor E isomers. The structure of the major (Z)-selenophenium salt was established by the single crystal X-ray crystallographic analysis using a tert-butyl derivative.  相似文献   
74.
75.
Under pathological conditions, morphological changes of the cells and tissues may differ from those of normal conditions, which can be reflected by changes in light scattering (LS). Consequently, LS has been recognized as a potential non-invasive tool for optical diagnosis of living tissue. This paper aimed to identify the basic properties of LS of isolated brain mitochondria in vitro under normoxic and anoxic conditions in the presence and absence of Mg2+. An increase in LS was observed during anoxia in both the presence and absence of Mg2+. In both cases, the changes in LS initiated by anoxia and reoxygenation started concomitantly with the reduction of heme aa3. The rates of LS changes were slower than those of heme aa3, particularly in the presence of Mg2+. Mg2+ inhibited the morphological responses of mitochondria caused by the addition of ADP and ATP, and significantly reduced the oxygen consumption rate in state 4. These results are due to modulation of the K+/H+ antiporter affected by Mg2+. In addition, the mitochondria were well coupled, although the basal level of LS fell after addition of Mg2+. Therefore, the observed responses of mitochondria at anoxia were physiological and independent of the presence or absence of Mg2+. The relationship between LS and redox state of cytochrome c oxidase, an anoxic indicator, provides a basis to assess the tissue conditions in vivo.  相似文献   
76.
A high density mark edge recording method on a phase change rewritable disk is reported. A carrier-to-noise ratio of 55 dB for a mark length of 0.55,μm is obtained by using a 680 nm, NA 0.6 head and a phase change rewritable disk. In mark edge recording, it is necessary to record each mark in correct length. A new laser power modulation pattern is proposed. This pattern consists of a first-pulse, a multi-pulse chain and a last-pulse. Both positions of the first-ptilse and the last-pulse are movable. By adjusting these positions, a jitter, σ/Tw (Tw is window margin), is improved to 6.5% in high density EFM (Eight to Fourteen Modulation) recording of 0.4 μm/bit.  相似文献   
77.
Let the finite, simple, undirected graph G = (V(G), E(G)) be vertex-colored. Denote the distinct colors by 1,2,…,c. Let Vi be the set of all vertices colored j and let <Vi be the subgraph of G induced by Vi. The k-path chromatic number of G, denoted by χ(G; Pk), is the least number c of distinct colors with which V(G) can be colored such that each connected component of Vi is a path of order at most k, 1 ? i ? c. We obtain upper bounds for χ(G; Pk) and χ(G; P) for regular, planar, and outerplanar graphs.  相似文献   
78.
79.
The effects of the homogeneity of precursor non-crystalline Pb---Ti---O gels on their transformation to crystalline PbTiO3 were studied. Hydrous gels were prepared via two different routes, i.e., (i) mixing two unitary sols (MS), and (ii) co-precipitation (CP). Mechanical pretreatment was also carried out, primarily for the purpose of homogenization. The local homogeneity was evaluated by elementary microanalysis using a transmission electron microscope. The process of ball-milling the MS gel for 3 h improved its homogeneity only slightly. However, the homogeneity of the ball-milled MS gel suddenly increased to that of the CP gel on subsequent heating to a temperature as low as 483 K. This type of thermal homogenization was not observed for the unground MS gel. The evaporation of lead monoxide on further heating to 1023 K was also suppressed by preliminary ball-milling. All these results suggest that the ionic migration and the formation of Pb---O---Ti bonds in the gels take place during the mechanical activation with the aid of OH groups.  相似文献   
80.
光折变法制备的As2S8条形波导的光阻断效应   总被引:5,自引:1,他引:4       下载免费PDF全文
实验研究了As2S8薄膜光折变现象.提出并采用紫外光激励的方法试制了As2S8条形波导,导模激励显示该波导具有良好的导波特性.在此基础上,考察了As2S8条波导的光阻断效应,实现了光-光效应的开关功能.  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