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   233558篇
  免费   2508篇
  国内免费   659篇
化学   125766篇
晶体学   3601篇
力学   11021篇
综合类   10篇
数学   27184篇
物理学   69143篇
  2021年   2368篇
  2020年   2501篇
  2019年   3034篇
  2018年   4016篇
  2017年   4026篇
  2016年   5612篇
  2015年   3043篇
  2014年   5082篇
  2013年   10252篇
  2012年   8624篇
  2011年   10262篇
  2010年   7547篇
  2009年   7597篇
  2008年   9532篇
  2007年   9510篇
  2006年   8569篇
  2005年   7660篇
  2004年   7122篇
  2003年   6449篇
  2002年   6362篇
  2001年   5978篇
  2000年   4512篇
  1999年   3471篇
  1998年   3017篇
  1997年   3094篇
  1996年   2995篇
  1995年   2538篇
  1994年   2604篇
  1993年   2477篇
  1992年   2779篇
  1991年   2868篇
  1990年   2747篇
  1989年   2819篇
  1988年   2753篇
  1987年   2745篇
  1986年   2588篇
  1985年   3368篇
  1984年   3432篇
  1983年   2831篇
  1982年   2866篇
  1981年   2835篇
  1980年   2625篇
  1979年   2978篇
  1978年   2913篇
  1977年   3086篇
  1976年   3070篇
  1975年   2867篇
  1974年   2804篇
  1973年   2912篇
  1972年   2168篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
A model of an expanding and rotating universe is constructed in the framework of general relativity. The parameters of the model are compared with the fundamental observables and shown to be in good agreement.Kaluzhsk Branch, N. É. Bauman Moscow State Technical University (MGTU). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 71–77, June, 1993.  相似文献   
952.
We look at the recently proposed scheme of approximating a sine-Gordon soliton by an expression derived from two dimensional instantons. We point out that the scheme of Sutcliffe in which he uses two dimensional instantons can be generalised to higher dimensions and that these generalisations produce even better approximations than the original approximation. We also comment on generalisations to other models.  相似文献   
953.
Raman mechanical spectroscopy was used to examine interfacial effects on the stress distribution in model polydiacetylene fiber/epoxy composites. Epoxy release agents were coated on fiber surfaces to modify the interfacial adhesion properties. The modified fiber surfaces were then characterized by scanning electron microscopy and x-ray photoelectron spectroscopy as well as optical microscopy. No difference in the maximum stress value or stress distribution was observed for the two types of fibers, coated or uncoated, used in composites. This suggests that adhesion properties at the composite interface do not affect tensile stress transfer efficiency nor, therefore, the composite tensile modulus along the fiber axis direction in uniaxial composites. Experimental data were also compared with theoretical calculations assuming perfect bonding between fiber and matrix, and idealized frictional force transfer mechanism at the fiber–matrix interface.  相似文献   
954.
The reaction of CH3 with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 1013 cm3/mol-s was measured for removal of OH by CH3. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (?75%) for the removal of OH by CH3 at these conditions is their combination to form CH3OH. Rate coefficients of (5.3 ± 0.8) × 1012 and (9.0 ± 1.4) × 1012 cm3/mol-s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure.  相似文献   
955.
Translated from:Problemy Ustoichivosti Stokhasticheskikh Modelei, Trudy Seminara, 1989, pp. 20–26.  相似文献   
956.
957.
958.
It is shown that a completely ionized, classical, Coulombian plasma, placed in an adiabatic enclosure, possesses a stationary state. At the same time, a plasma placed in a thermostat recombines through triple collisions, with a velocity satisfactorily accounted for by well-known theoretical results. The results obtained by numerical modeling have shown that, for a plasma placed in an adiabatic enclosure, the ergodic assumption is not valid. Various possible kinetic mechanisms, ensuring the existence of a stationary state of the adiabatically enclosed plasma, are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–34, November, 1991.  相似文献   
959.
The process γγ→π+π? was measured using the detector MD-1 at VEPP-4. The two-photon reactionse + e ?, μ+ μ? and π+ π? pair production were separated using scintillation counters, Cherenkov counters and shower-range chambers. A radiation widthГ γγ(f 2(1270))=3.1±0.35±0.35 keV was obtained.  相似文献   
960.
The existence of bound states and resonances of the Hamiltonian of a system ofN different quantum lattice particles with nonvanishingN-particle short-range interaction is proved. The dependence of the bound states and the resonances on the coupling constant and the quasimomentum is studied.Samarkand State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 91, No. 1, pp. 51–65, April, 1992.  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