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   355篇
  免费   17篇
化学   227篇
晶体学   1篇
数学   9篇
物理学   135篇
  2023年   3篇
  2022年   10篇
  2021年   7篇
  2020年   25篇
  2019年   14篇
  2018年   3篇
  2017年   2篇
  2016年   8篇
  2015年   7篇
  2014年   12篇
  2013年   17篇
  2012年   22篇
  2011年   23篇
  2010年   10篇
  2009年   11篇
  2008年   24篇
  2007年   21篇
  2006年   8篇
  2005年   16篇
  2004年   8篇
  2003年   7篇
  2002年   7篇
  2001年   11篇
  1999年   3篇
  1997年   5篇
  1996年   4篇
  1994年   11篇
  1993年   5篇
  1992年   5篇
  1990年   4篇
  1988年   2篇
  1987年   2篇
  1986年   5篇
  1985年   3篇
  1979年   2篇
  1978年   2篇
  1977年   5篇
  1976年   2篇
  1975年   7篇
  1974年   2篇
  1973年   5篇
  1969年   1篇
  1968年   1篇
  1967年   4篇
  1966年   1篇
  1965年   1篇
  1964年   1篇
  1936年   2篇
  1931年   1篇
  1888年   2篇
排序方式: 共有372条查询结果,搜索用时 15 毫秒
281.
Fermilab experiment E835 has observed (-)pp annihilation production of the charmonium state chi(c0) and its subsequent decay into pi(0)pi(0). Although the resonant amplitude is an order of magnitude smaller than that of the nonresonant continuum production of pi(0)pi(0), an enhanced interference signal is evident. A partial wave expansion is used to extract physics parameters. The amplitudes J=0 and 2, of comparable strength, dominate the expansion. Both are accessed by L=1 in the entrance (-)pp channel. The product of the input and output branching fractions is determined to be B((-)pp-->chi(c0))xB(chi(c0)-->pi(0)pi(0))=(5.09+/-0.81+/-0.25)x10(-7).  相似文献   
282.
Growth mode, surface morphology, crystal perfection and growth rate of siliconmolecular beam epitaxy films were observed as function of temperature (450°–950°C), silicon flux density (8×1014–8×1015cm2/s) and surface orientation (111, 110, 100). Within the varied parameters growth proceeds by the two-dimensional growth mode via the lateral motion of atomic steps originating from the slight misorientation of commercially available substrates (typically 0.25°). Single crystalline films with high lattice perfection and smooth surfaces result from this growth mode. The growth rate — linearly dependent on Si-flux density and independant of temperature and orientation — indicates a condensation coefficient near unity. An atomic step flow model on the basis of the Burton-Cabrera-Frank theory explains this behaviour by mobile adatoms with low activation energy of diffusion.  相似文献   
283.
We have studied dielectric spectra of the glass-forming liquid metafluoroaniline under hydrostatic pressure up to 700 MPa. Its glass transition pressure p(g) increases approximately linearly with temperature. Above p(g)(T), a well pronounced secondary relaxation, the Johari beta peak, is observed showing activated behavior. The activation energy rises proportionally to pressure and, consequently, proportionally to the glass transition temperature T(g)(p). The activation volume is independent of temperature but exhibits different values for pressures higher and lower than the pressure where the liquid left the ergodic regime. The activation volumes are about 1/10 and 1/6 of the molecular volume of fluoroaniline, respectively, suggesting that there are two different species of clusters.  相似文献   
284.
A high statistics measurement of the D(s)+ lifetime from the Fermilab fixed-target FOCUS photoproduction experiment is presented. We describe the analysis of the two decay modes, D(s)+ --> phi(1020)pi+ and D(s)+ -->K*(892)0K+, used for the measurement. The measured lifetime is 507.4 +/- 5.5(stat) +/- 5.1(syst) fs using 8961 +/- 105 D(s)+ --> phi(1020)pi+ and 4680 +/- 90 D(s)+ --> K*(892)0K+ decays. This is a significant improvement over the present world average.  相似文献   
285.
The optical conductivity of the heavy fermions UPd(2)Al(3) and UPt(3) has been measured in the energy range from 0.04 to 5 meV. In both compounds a well pronounced pseudogap of less than 1 meV develops in the optical response at low temperatures; we relate this to the antiferromagnetic ordering. From the energy dependence of the effective mass and scattering rate we conclude that the enhancement of the mass mainly occurs below the energy which is related to magnetic correlations between the local magnetic moments and the itinerant electrons. This implies that the magnetic order in these compounds is the prerequisite to the formation of the heavy quasiparticles and eventually to superconductivity.  相似文献   
286.
287.
288.
289.
290.
Zusammenfassung Im System ZnO–Sb2O5 existieren zwei Spinellphasen (I) und (III) gleicher Zusammensetzung Zn7Sb2O12. Außerdem konnte noch eine weitere Modifikation (II) mit einer niedrigsymmetrischen Struktur aufgefunden werden.In (II) und (III) wurden Cu2+, Ni2+ und Co2+ als farbgebende Kationen eingebaut. Die spektralphotometrische Untersuchung ergab, daß Zn2+ in (II) sowohl oktaedrisch als auch tetraedrisch koordiniert ist. Im Spinell (III) wird Cu2+ sowohl in Tetraeder-und Oktaederlücken, Ni2+ nur in Oktaeder- und Co2+ vorwiegend in Oktaederlücken eingebaut.In the system ZnO–Sb2O5 exist two phases (I) and (III) with the spinel structure and the same composition Zn7Sb2O12. Besides these another modification (II) with a structure of lower symmetry could be found.The colouring cations Cu2+, Ni2+, Co2+ have been incorporated in (II) and (III). The spectrophotometrical investigation shows that Zn2+ occupies in (II) octahedral and tetrahedral sites. In the spinel (III) Cu2+ is incorporated tetrahedrally and octahedrally, Ni2+ only octahedrally and Co2+ predominantly octahedrally.Mit 4 Abbildungen1. Mitt.:H. Kasper, Z. anorg. allgem. Chem. (im Druck).  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