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   849篇
  免费   29篇
  国内免费   4篇
化学   636篇
晶体学   3篇
力学   12篇
数学   52篇
物理学   179篇
  2021年   4篇
  2020年   7篇
  2019年   16篇
  2018年   11篇
  2017年   4篇
  2016年   13篇
  2015年   12篇
  2014年   22篇
  2013年   31篇
  2012年   29篇
  2011年   47篇
  2010年   22篇
  2009年   30篇
  2008年   40篇
  2007年   62篇
  2006年   32篇
  2005年   42篇
  2004年   46篇
  2003年   36篇
  2002年   25篇
  2001年   21篇
  2000年   18篇
  1999年   12篇
  1998年   9篇
  1997年   6篇
  1996年   11篇
  1995年   11篇
  1994年   8篇
  1993年   9篇
  1992年   12篇
  1991年   11篇
  1990年   16篇
  1989年   12篇
  1988年   13篇
  1987年   12篇
  1986年   8篇
  1985年   22篇
  1984年   15篇
  1983年   8篇
  1982年   12篇
  1981年   10篇
  1980年   8篇
  1979年   12篇
  1978年   9篇
  1977年   4篇
  1976年   15篇
  1975年   17篇
  1974年   5篇
  1973年   4篇
  1972年   4篇
排序方式: 共有882条查询结果,搜索用时 46 毫秒
31.
A novel class of supramolecular assemblies in organic media consisting of a molecular wire of a halogen-bridged platinum complex [Pt(en)2][PtCl2(en)2]4+ (en = 1,2-diaminoethane) and anionic amphiphiles is developed. When double-chained phosphates or sulfonates are employed, the resultant [Pt(en)2][PtCl2(en)2](4+)-lipid complexes displayed intervalence charge transfer (CT) absorption bands in the crystalline state. They are soluble in organic solvents because of the amphiphilic superstructure, in which the solvophobic one-dimensional platinum complex is surrounded by solvophilic alkyl chains. CT absorption bands of halogen-bridged linear complexes are maintained in organic media, with varied colors that depend on the chemical structure of constituent amphiphiles. Monoalkylated phosphates failed to form colored, halogen-bridged ternary complexes probably because of their coordination to the axial position of PtII(en)2. Formation of mesoscopic supramolecular assemblies in organic media was confirmed for the [Pt(en)2][PtCl2(en)2] complexes by electron microscopy. Interestingly, a supramolecular complex consisting of dihexadecyl sulfosuccinate and [Pt(en)2][PtCl2(en)2]4+ displayed clear, indigo solutions that are distinct from the yellow color observed for those of [Pt(en)2][PtCl2(en)2]/dialkyl phosphate complexes. The indigo color of the former complex disappeared upon heating the solution to 60 degrees C, whereas it reappeared reversibly by cooling the solution to room temperature. In electron microscopy, rodlike nanostructures with a minimum width of 18 nm and lengths of 700-1700 nm were observed after cooling, though not at elevated temperatures. Apparently, the lipid-[Pt(en)2][PtCl2(en)2]4+ complex undergoes reversible dissociation and reassembly processes in chloroform, and it becomes better dispersed after the reassembling process. The present finding opens a general route to solution chemistry of low-dimensional inorganic complexes and enables rational design and control of self-assembling inorganic molecular wires.  相似文献   
32.
33.
Reaction of α-nitro olefins with secondary amines in the presence of palladium(O) catalyst affords allylic amines.  相似文献   
34.
Oda T  Nakashima S  Okuda T 《Inorganic chemistry》2003,42(17):5376-5383
The effects of cation symmetry and packing on the mixed-valence state of binuclear ferrocene derivatives are discussed separately by using chiral isomers and racemic modification of 1',1' "-bis(2-phenylbutyl)-1,1' '-biferrocenium pentaiodide. The pentaiodide anion has a polymeric structure and is composed of triiodide anion and iodine molecule units. The (R,S) isomer having an inversion center shows a detrapped-valence state even at 78 K. On the other hand, the (R,R) and the (S,S) isomers having no inversion center show a trapped-valence state at room temperature. The racemic modification, however, consisting of the (R,R) and the (S,S) isomers shows a perfect detrapped-valence state at room temperature. This finding shows that the packing effect overcomes the effect of cation asymmetry.  相似文献   
35.
Photolysis of the N-[ω-(cycloalken-1-yl)alkyl]phthalimides 6b-e in each case gave a pair of stereoisomers of spiro-nitrogen multicyclic systems (9b-e) in moderate yields, whose stereochemistry was determined by means of chemical and spectroscopic analyses. Similarly, in N-[ω-(inden-3-yl)alkyl]-phthalimides (8), spiro-nitrogen macrocycles up to 13-membered 13a-c were obtained in good yields  相似文献   
36.
A new force approach is reported in which we improve the wavefunction so that the Hellmann-Feynman theorem is satisfied. A sufficient condition for the Hellmann-Feynman theorem to be satisfied is that the basis set includes AO derivatives ?xr/?xrfor any basis xr. Here we test a procedure in which only the first derivative AOs are added to the “parent” AOs. The results are very encouraging.  相似文献   
37.
The efficient and novel bifunctional organocatalyst for the enantioselective aza-Morita-Baylis-Hillman (aza-MBH) reaction has been established with (S)-3-(N-isopropyl-N-3-pyridinylaminomethyl)BINOL for the first time. The reaction proved to be deeply influenced by the position of the Lewis base attached to BINOL. The acid-base-mediated functionalities for the activation of the substrate and the fixing of conformation of the organocatalyst are harmoniously performed to promote the reaction with high enantiocontrol.  相似文献   
38.
Fluoroalkanoyl peroxides were reacted with adamantane in the presence of radical polymerizable monomers such as acrylic acid, acryloylmorpholine, and N,N‐dimethylacrylamide to afford fluoroalkyl end‐capped oligomers having adamantane units in the main chains via a radical process under very mild conditions. Thermal stability of these new fluorinated adamantane co‐oligomers thus obtained became higher than that of the corresponding fluorinated homo‐oligomers having no adamantane units. Interestingly, these fluorinated adamantane co‐oligomers exhibited good solubility in traditional organic solvents such as methanol, ethanol, tetrahydrofuran, chloroform, benzene, dimethylsulfoxide and N,N‐dimethylformamide including water, although the parent adamantane exhibited no solubility in water, methanol and dimethylsulfoxide. Furthermore, these adamantane co‐oligomers were able to reduce the surface tension effectively to form the nanometer size‐controlled self‐assembled fluorinated molecular aggregates. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
39.
In the first section we summarize some properties of Jordan pairs. Then we state some results about some groups defined by Jordan pairs.In the next section we construct a Lie algebra to a Jordan pair. This construction is a generalization of the wellknown Koecher-Tits-construction. We calculate the radical of this Lie algebra in terms of the given Jordan pair.In the last section we prove a Wedderburn decomposition theorem for Jordan pairs in the characteristic zero case. Some special cases in arbitrary characteristic have been shown by R. Carlson (see [5]). Also we show that any two such decompositions are conjugate under a certain group of automorphism. Analogous theorems will be shown for Jordan Triples.  相似文献   
40.
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