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   391543篇
  免费   1997篇
  国内免费   556篇
化学   182724篇
晶体学   5844篇
力学   22395篇
综合类   9篇
数学   56158篇
物理学   126966篇
  2020年   4174篇
  2019年   5064篇
  2018年   7462篇
  2017年   7620篇
  2016年   9546篇
  2015年   4448篇
  2014年   8450篇
  2013年   15881篇
  2012年   12932篇
  2011年   15157篇
  2010年   12632篇
  2009年   12825篇
  2008年   14608篇
  2007年   14402篇
  2006年   12896篇
  2005年   11223篇
  2004年   10857篇
  2003年   10036篇
  2002年   10340篇
  2001年   10478篇
  2000年   8124篇
  1999年   6197篇
  1998年   5693篇
  1997年   5483篇
  1996年   5017篇
  1995年   4468篇
  1994年   4516篇
  1993年   4512篇
  1992年   4596篇
  1991年   5079篇
  1990年   5006篇
  1989年   5059篇
  1988年   4706篇
  1987年   4778篇
  1986年   4467篇
  1985年   5357篇
  1984年   5554篇
  1983年   4730篇
  1982年   4976篇
  1981年   4641篇
  1980年   4292篇
  1979年   4925篇
  1978年   5106篇
  1977年   5298篇
  1976年   5452篇
  1975年   5058篇
  1974年   4887篇
  1973年   5135篇
  1972年   4305篇
  1971年   3945篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
The system of linearized Einstein and Maxwell equations and a kinetic equation with model collision integral for the cosmological plasma are used to calculate the magnetic field generated by solenoidal perturbations in the radiation-dominated stage of expansion of the universe. The magnetic field is generated by two effects — the Harrison effect and a new effect due to kinetic processes. The second effect contributes to the magnetic field if solenoidal gravitational perturbations exist from the very beginning of the radiation-dominated stage.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 122–126, January, 1992.  相似文献   
982.
The energy levels and oscillator strengths for dipole transitions between the levels of low-lying configurations are calculated for ions of the KI isoelectronic sequence. The calculations are based on the energy approach to the effective potential method with the most important polarization effects taken into account, including core polarization by the outer electron. The results, some of which are obtained here for the first time for potassium-like ions, can be useful in a number of related fields, such as laser physics, plasmas, and so on.Odessa Hydrometeorological Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–9, November, 1992.  相似文献   
983.
984.
Novosibirsk. Translated from Sibirskii Matematicheskii Zhurnal, Vol. 33, No. 1, pp. 205–207, January–February, 1992.  相似文献   
985.
986.
987.
988.
Necessary and sufficient conditions for the isomorphism of two groups, each defined by a single relation of the type a–1bma=bn, are obtained.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 12, pp. 1684–1686, December, 1991.  相似文献   
989.
Summary The results of local meteorology, solar radiation and ground-level ozone measurements taken in Antarctica during the second Italian expedition (December 86–February 87) at Terra Nova Bay are presented. During the summer months the site of the Italian base camp is characterized by a thin strip of deglaciated ground, along which the temperature measurements close to the ground and up to 6 m high show a strongly superdiabatic profile. This irregular trend of the temperature in the surface layer is mainly due to the notable incoming amounts of radiation and to the extreme transparency of the atmosphere. This is also shown by the low values of the ratio between total radiation and diffuse radiation. The ground is thus subjected to intense heating, especially in the warmer hours of the day, while the surface layer of the atmosphere will be characterized by strong upward heat fluxes and by turbulent convective movements. Vertical-temperature-profile measurements show an almost forced persistence in the superdiabatic trend, which tends towards isothermic values only as a resultof rapid variations in the direction and intensity of the wind, connected to the downward flux of cold air masses, shown also by the simultaneous increases in ground-level ozone concentrations which would support the presence of dry-deposition processes in the lower layer. However, the complex local orography and the horizontal discontinuity (sea, deglaciated coast, snow-covered surfaces) do not permit a correct application of profile flux relations, normally used in studies on groundlevel dry-deposition. Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome.  相似文献   
990.
Both a mode-locked argon-ion laser and synchrotron radiation were used as excitation sources to obtain time-resolved polarized fluorescence of the two FAD cofactors in electron transferring flavoprotein fromMegasphaera elsdenii. Red-edge excited and blue-edge detected fluorescence anisotropy decay curves did not contain a fast relaxation process which was observed upon mainband excitation and detection. This relaxation was assigned to homo-energy transfer between the two FAD cofactors. Failure of energy transfer as observed with edge spectroscopy on this protein excludes restricted reorientational motion of the flavins as a possible mechanism of depolarization. From the global analysis of the fluorescence anisotropy decay surface obtained at multiple excitation and detection wavelengths, the distance between and the relative orientation of the flavins could be estimated. The methodology described has general applicability in other multichromophoric biopolymers and has the potential to acquire accurate geometrical parameters in these systems.  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