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   544篇
  免费   16篇
化学   339篇
晶体学   1篇
力学   13篇
数学   125篇
物理学   82篇
  2023年   11篇
  2022年   6篇
  2021年   15篇
  2020年   28篇
  2019年   17篇
  2018年   10篇
  2017年   7篇
  2016年   17篇
  2015年   9篇
  2014年   17篇
  2013年   24篇
  2012年   34篇
  2011年   27篇
  2010年   14篇
  2009年   15篇
  2008年   31篇
  2007年   22篇
  2006年   16篇
  2005年   12篇
  2004年   16篇
  2003年   20篇
  2002年   14篇
  2001年   10篇
  2000年   3篇
  1999年   4篇
  1998年   5篇
  1997年   3篇
  1996年   9篇
  1995年   5篇
  1994年   5篇
  1993年   7篇
  1992年   5篇
  1991年   4篇
  1990年   5篇
  1989年   7篇
  1987年   6篇
  1986年   4篇
  1985年   3篇
  1984年   6篇
  1983年   7篇
  1981年   5篇
  1980年   4篇
  1979年   6篇
  1978年   4篇
  1977年   9篇
  1973年   5篇
  1966年   3篇
  1937年   3篇
  1915年   3篇
  1911年   3篇
排序方式: 共有560条查询结果,搜索用时 281 毫秒
1.
The phenomenon of roll-waves occurs when shallow water flows down open inclined channels. This flow is described by the Saint Venant’s equations with a friction term due to Chezy. In the case of a flat bottom, their existence (as entropic and periodic travelling waves) follows from a classical work due to DRESSLER [6]. The aim of this paper is to prove the existence of roll-waves when the bottom is modulated by a small periodic perturbation. Following JIN and KATSOULAKIS [15], we first compute a Burgers-type equation which possesses “pulsating” roll-waves (the wave speed oscillates around an average velocity). We prove, in a mathematically rigorous fashion, the existence of these solutions.  相似文献   
2.
In this article, we will describe the results of a study of 6th grade students learning about the mathematics of change. The students in this study worked with software environments for the computer and the graphing calculator that included a simulation of a moving elevator, linked to a graph of its velocity vs. time. We will describe how the students and their teacher negotiated the mathematical meanings of these representations, in interaction with the software and other representational tools available in the classroom. The class developed ways of selectively attending to specific features of stacks of centimeter cubes, hand-drawn graphs, and graphs (labeled velocity vs. time) on the computer screen. In addition, the class became adept at imagining the motions that corresponded to various velocity vs. time graphs. In this article, we describe this development as a process of learning to see mathematical representations of motion. The main question this article addresses is: How do students learn to see mathematical representations in ways that are consistent with the discipline of mathematics? This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
3.
4.
The previously synthesised (1–37), (38–75), (76–93), (94–104), (105–117) and (118–129) fragments of the analogue were combined making extensive use of the DCCI/HONSu method. The final coupling involved the (1–75) and (76–129) sub-fragments. Aggregation of the latter fragment caused problems in purification by routine gel filtration methods employing Enzacryl K2 or Sephadex LH60. The fully protected (1–129) product was partially purified by washing, then deprotectcd and purified by gel filtration and ion exchange chromatography. Satisfactory removal of the acetamidomethyl group used for cysteine protection could not be achieved.  相似文献   
5.
In this paper, we investigate {1,2,3}-semiaffine planes. All such planes of order n >51 shall be classified. It turns out that they are embeddable into projective planes of the same order n in the most natural way.Work supported by National Research Project on Strutture Geometriche Combinatoria, loro applicazioni of Italian M.P.I. and G.N.S.A.G.A. of C.N.R.  相似文献   
6.
7.
The complexes Ru(L1-CH3)(CO)3Cl, RuL2(CO)2Cl2, and RuL3(CO)2Cl2 (L1= 6-methoxy-5,8-quinolinedione, L2 = 7-amino-6-methoxy-5,8-quinolinedione, L3 = 6,6'-dimethoxycarbonyl-2,2'-bipyridine) were prepared by reaction of L1-L3 with the tricarbonyldichlororuthenium(II) dimer. L1-L3 act as bidentates through the ortho oxygen atoms, the pyridyl nitrogen and the adjacent quinone oxygen, and the bipyridyl nitrogens, respectively. RuL3(CO)2Cl2 is characterized by X-ray crystallography. 15N NMR correlation spectra give upfield shifts of around 60 ppm for the pyridyl nitrogens that are coordinated to the metal, while 13C NMR correlation spectra give a downfield shift of 10 ppm for the quinone carbonyl group that is coordinated to the metal. The electrochemistry of RuL2(CO)2Cl2 is examined, and the implications for the formation of metal complexes of the antitumor antibiotic streptonigrin, which cleaves DNA in the presence of metal ions, are discussed.  相似文献   
8.
A tungsten neopentylidene complex has been found to decompose to yield a heterochiral dimer that contains a W=W double bond and no bridging ligands. Decompositions of related bisalkoxide complexes also yield compounds that contain an "unsupported" W=W double bond, while a sample of [Mo(NAr)(CH2-t-Bu)(OC6F5)]2 has been found to be a homochiral species related to [W(NAr)(CH2-t-Bu)(OC6F5)]2.  相似文献   
9.
The Stark splittings and rotational asymmetry splittings of a number of levels of the Ã1A″ excited state of HNO have been measured using the sub-Doppler technique of optical—optical double resonance, μa is found to be 1.08 ± 0.01 D for the 100 vibronic state, and 1.05 ± 0.01 D for the 020 vibronic state. These values are to be compared with a recently determined ground state value of μa = 0.996 D. The asymmetry splittings of some of the levels studied are considerably larger than predicted from the known rotational constants, indicating minor rotational perturbations.  相似文献   
10.
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