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   200267篇
  免费   2321篇
  国内免费   586篇
化学   118399篇
晶体学   2366篇
力学   7428篇
综合类   7篇
数学   19950篇
物理学   55024篇
  2020年   1654篇
  2019年   1721篇
  2018年   1848篇
  2017年   1769篇
  2016年   3295篇
  2015年   2260篇
  2014年   3294篇
  2013年   7951篇
  2012年   6829篇
  2011年   8421篇
  2010年   5502篇
  2009年   5360篇
  2008年   7523篇
  2007年   7545篇
  2006年   7209篇
  2005年   6619篇
  2004年   5850篇
  2003年   4985篇
  2002年   5030篇
  2001年   4935篇
  2000年   3925篇
  1999年   3057篇
  1998年   2698篇
  1997年   2648篇
  1996年   2489篇
  1995年   2311篇
  1994年   2368篇
  1993年   2220篇
  1992年   2436篇
  1991年   2455篇
  1990年   2258篇
  1989年   2252篇
  1988年   2255篇
  1987年   2195篇
  1986年   2069篇
  1985年   2808篇
  1984年   2892篇
  1983年   2204篇
  1982年   2515篇
  1981年   2356篇
  1980年   2472篇
  1979年   2542篇
  1978年   3470篇
  1977年   3081篇
  1976年   2576篇
  1975年   2370篇
  1974年   2446篇
  1973年   2407篇
  1972年   1611篇
  1971年   1417篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We have investigated the low-lying collective states and electromagnetic transitions in 94Mo within the framework of the interacting boson model. The influence of model parameters on the energy levels and electromagnetic properties has been investigated. The analysis of the obtained results and the parameter values predict that the 23+state is the lowest mixed symmetry state with pure F = Fmax - 1 in this nucleus. The calculated results predicate that the 25+ (two-Q-phonon) mixed symmetry state is closed to the J = 2+ at 2.870 MeV in the experimental data, and the 2.965 MeV state is the lowest mixed symmetry with J = 3+.  相似文献   
82.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 41, No. 8, pp. 1054–1058, August, 1989.  相似文献   
83.
84.
The low-temperature reaction of magnesium with fluorobenzene has been investigated. Joint condensation of magnesium and fluorobenzene vapours at low temperatures quantitatively gave phenylmagnesium fluoride in one stage.  相似文献   
85.
86.
87.
The possibility of usage of the spontaneous electrooptical (EO) effect in strontium barium niobate (SBN) crystals for the creation of controlled electroholographic elements is studied. It is found that unipolar EO properties of these crystals with respect to switching their spontaneous polarization make it possible to devise field-controlled holographic elements with reversible energy-independent memory for spatial position of an optical beam.  相似文献   
88.
89.
For a graph A and a positive integer n, let nA denote the union of n disjoint copies of A; similarly, the union of ?0 disjoint copies of A is referred to as ?0A. It is shown that there exist (connected) graphs A and G such that nA is a minor of G for all n??, but ?0A is not a minor of G. This supplements previous examples showing that analogous statements are true if, instead of minors, isomorphic embeddings or topological minors are considered. The construction of A and G is based on the fact that there exist (infinite) graphs G1, G2,… such that Gi is not a minor of Gj for all ij. In contrast to previous examples concerning isomorphic embeddings and topological minors, the graphs A and G presented here are not locally finite. The following conjecture is suggested: for each locally finite connected graph A and each graph G, if nA is a minor of G for all n ? ?, then ?0A is a minor of G, too. If true, this would be a far‐reaching generalization of a classical result of R. Halin on families of disjoint one‐way infinite paths in graphs. © 2002 Wiley Periodicals, Inc. J Graph Theory 39: 222–229, 2002; DOI 10.1002/jgt.10016  相似文献   
90.
Cavity ring-down spectroscopy (CRDS) is used to measure the NO mole fraction formed in the burnt gases of low-pressure premixed flames. It is shown that the line-of-sight absorption is greatly increased by the contribution of the NO molecules surrounding the burner. This contribution has been quantified by developing a mathematical procedure taking into account the spatial and spectral features of the CRDS measurement. Calculations have been undertaken in the general case of a stable species not consumed in the flame. The most sensitive parameter is the temperature both in the flame and outside the flame. Simulations allow the selection of the best spectroscopic transitions for a given flame (i.e. a given temperature profile), ensuring the weakest influence of the inaccuracy affecting the temperature determination. High quantum states belonging to the A–X (0–1) band of NO have been found to be the most valuable and have led to a NO mole fraction determination with an accuracy of ±13%. NO absorption in the flame was completely masked using the A–X (0–0) band. Finally, the prompt-NO mole fraction formed in a methane/air flame stabilized at 33 Torr is obtained by combining CRDS and laser induced fluorescence techniques. Received: 12 October / Revised version: 1 February 2002 / Published online: 14 March 2002  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