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   33836篇
  免费   2548篇
  国内免费   4910篇
化学   27969篇
晶体学   1189篇
力学   366篇
综合类   375篇
数学   4403篇
物理学   6992篇
  2023年   282篇
  2022年   666篇
  2021年   857篇
  2020年   728篇
  2019年   746篇
  2018年   567篇
  2017年   764篇
  2016年   823篇
  2015年   1068篇
  2014年   1406篇
  2013年   2420篇
  2012年   1808篇
  2011年   1949篇
  2010年   1868篇
  2009年   2137篇
  2008年   2172篇
  2007年   2262篇
  2006年   2097篇
  2005年   1846篇
  2004年   1855篇
  2003年   1514篇
  2002年   1303篇
  2001年   1015篇
  2000年   1766篇
  1999年   1306篇
  1998年   1222篇
  1997年   616篇
  1996年   556篇
  1995年   544篇
  1994年   488篇
  1993年   430篇
  1992年   408篇
  1991年   299篇
  1990年   196篇
  1989年   206篇
  1988年   168篇
  1987年   115篇
  1986年   87篇
  1985年   97篇
  1984年   108篇
  1983年   37篇
  1982年   62篇
  1981年   95篇
  1980年   77篇
  1979年   59篇
  1978年   50篇
  1977年   38篇
  1976年   20篇
  1975年   18篇
  1973年   18篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Let G be a 2-connected graph with minimum degree at least 3. We prove that there exists an even circuit C in G with factorization F={F1,F2} such that GE(F1) is 2-connected.  相似文献   
83.
The authors study the bifurcation problems of rough heteroclinic loop connecting three saddle points for the case β1 > 1, β2 > 1, β3 < 1 and β1β2β3 < 1. The existence, number, coexistence and incoexistence of 2-point-loop, 1-homoclinic orbit and 1-periodic orbit are studied. Meanwhile, the bifurcation surfaces and existence regions are given.  相似文献   
84.
The questions raised by A. M. Turing in his paper on thought and machines are discussed. Human thought is considered in turn as a concept of normal language usage, as a basic concept of psychology, and as the basis of intellectual activity. It is concluded that neither of these notions of thought identifies something specific that a human being can or cannot do. The imitation game proposed by Turing for deciding whether a machine can think is found to result from an arbitrary empoverishment of the channel of communication between the interrogator and the item under investigation. Turing's notions of thinking are shown to lead to logical difficulties. An alternative view of consciousness, that would place it beyond the reach of any finite test, is finally discussed.  相似文献   
85.
86.
In [5] Phillips proved that one can obtain the additive group of any nonstandard model *? of the ring ? of integers by using a linear mod 1 function h : F ?, where F is the α-dimensional vector space over ? when α is the cardinality of *?. In this connection it arises the question whether there are linear mod 1 functions which are neither addition nor quasi-linear. We prove that this is the case.  相似文献   
87.
同步荧光法测定食品中维生素B1   总被引:7,自引:0,他引:7  
本文研究了食品中维生素B1的同步荧光法测定条件,采用氯化钾-乙醇作柱层析洗脱液,碱性介质中氧化后立即调为中性,并加入表面活性剂OP对体系增稳增敏,取代丁醇萃取,经济方便,用于几种粮食样品的测定,结果满意。  相似文献   
88.
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields . Received: 11 November 1997 / Revised in final form: 28 November 1997 / Accepted: 28 November 1997  相似文献   
89.
We have observed a remarkable two-armed spiral in the collapse process of a floating monolayer at the air-water interface by phase contrast microscopy. This demonstrates that the floating monolayer as a form of soft condensed matter reorganizes itself due to a certain kind of macroscopic or collective behavior of molecules as it collapses. This pattern formation is caused by the breakdown of a critical dynamical balance between the deformation of solid domain and the applied surface pressure. The fragility as well as the flexibility of the floating monolayer can be associated with the observed pattern growth. There are also observed interesting, periodically arranged collections of molecules in numerous collapsed regions. Received: 8 July 1997 / Accepted: 4 November 1997  相似文献   
90.
Several α-ketoalcohols of synthetic value were resolved using lipase as a catalyst. Lipoprotein lipase (LPL) provided the best rate of hydrolysis and kinetic differentiation. One of these optically pure α-ketoalcohol was converted to (5)-ibuprofen in good optical purity. The stereospecific inversion of (R)-alcohol to (S)-alcohol is described.  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