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   607篇
  免费   21篇
化学   377篇
晶体学   1篇
力学   28篇
数学   96篇
物理学   126篇
  2023年   13篇
  2022年   3篇
  2021年   19篇
  2020年   21篇
  2019年   25篇
  2018年   15篇
  2017年   16篇
  2016年   26篇
  2015年   26篇
  2014年   11篇
  2013年   26篇
  2012年   38篇
  2011年   42篇
  2010年   20篇
  2009年   22篇
  2008年   30篇
  2007年   41篇
  2006年   29篇
  2005年   23篇
  2004年   21篇
  2003年   15篇
  2002年   12篇
  2001年   8篇
  2000年   7篇
  1999年   6篇
  1998年   4篇
  1997年   4篇
  1996年   5篇
  1995年   4篇
  1994年   11篇
  1993年   6篇
  1992年   4篇
  1990年   5篇
  1987年   2篇
  1986年   5篇
  1985年   7篇
  1984年   7篇
  1983年   5篇
  1982年   2篇
  1981年   6篇
  1979年   2篇
  1977年   2篇
  1975年   2篇
  1974年   2篇
  1966年   2篇
  1956年   2篇
  1954年   4篇
  1909年   2篇
  1887年   1篇
  1884年   1篇
排序方式: 共有628条查询结果,搜索用时 15 毫秒
601.
The determination of the parameters of the deconfining transition in N f = 2 QCD and its relevance to the understanding of the mechanism of color confinement are discussed.  相似文献   
602.
We derive the optimal universal broadcasting for mixed states of qubits. We show that the no-broadcasting theorem cannot be generalized to more than a single input copy. Moreover, for four or more input copies it is even possible to purify the input states while broadcasting. We name such purifying broadcasting superbroadcasting.  相似文献   
603.
The preparation of 8-substituted guanines using a new phosphorus(III)-mediated cyclisation of 4-acylamino-5-nitrosopyrimidines as the key step is described.  相似文献   
604.
We define a continuous Gabor transform for strong hypergroups and prove a Plancherel formula, an L 2 inversion formula and an uncertainty principle for it. As an example, we show how these techniques apply to the Bessel–Kingman hypergroups and to the dual Jacobi polynomial hypergroups. These examples have an interpretation in the setting of radial functions on R d and zonal functions on compact two-point homogeneous spaces, where they provide a new transform which possesses many properties of the classical Gabor transform.  相似文献   
605.
The reactions of the cluster complexes [Pt3(-CO)3L3], where L=PPh3 1a, PPh2Bz 1b and PCy3 1c, with activated mono-olefins have been studied under preparative and equilibrium conditions. At low temperature the olefins react quantitatively giving the adducts [Pt3(-CO)3L3(olefin)] (olefin=trans-dicyanoethene, DCE 2a–2c, maleic anhydride, MA 3a–3c). The stereo-chemistry of these unstable clusters has been deduced from low temperature 31P, 13C, 195Pt-NMR and I.R. spectra. At higher temperature these adducts in presence of excess of olefin convert quantitatively to stable mononuclear Pt(0) complexes [Pt(CO)L(olefin)] (olefin=DCE 4a–4c, MA 5a–5c, maleimide, MI 6a–6c and 1–4-naphthoquinone, NQ 7a, 7c).  相似文献   
606.
Phenolic compounds in Sicilian olive oils were analyzed by GC-MS and GC-MS/MS after extraction with methanol:water 80:20 and derivatization with bis(trimethylsilyl)trifluoracetamide and trimethylchlorosilane (BSTFA:TMCS 99:1). Numerous compounds were detected and 23 were identified. Tyrosol, hydroxytyrosol and the decarbomethoxy ligstroside and oleuropein aglycons in the dialdehydic forms were the most abundant compounds. 4-(Acetoxyethyl)-1-hydroxybenzene, 3,4-dihydroxyphenylacetaldehyde, syringaldehyde and the cis form of ferulic acid were identified: these compounds were not found in olive oils before. The presence of the dialdehydic form of elenolic acid (without carbomethoxy group) linked to 3-methoxy-4-hydroxyphenylethanol was hypothesized. There were quantitative differences in oils from the varieties Nocellara del Belice, Santagatese and Cerasuola; these differences could depend on the olive varieties and ripeness.  相似文献   
607.
A method for the reconstruction of boundary points of convex sets is provided starting from three X-ray pictures in two orthogonal directions and from a point.  相似文献   
608.
The quantity G = (α/π) Σa,μνGμνaGμνa is extracted from Monte Carlo data for SU(2) lattice gauge theory We find G = 0.015 ± 0.002 GeV4.  相似文献   
609.
Tri-o-thymotide (TOT) clathrates are enantiomorphous and enantioselective (chiral cages). It was shown that an external molecular reactant can diffuse into the TOT host crystal lattice and reacts with the included molecule (guest) in characteristic ways, differing from those occurring in liquid solutions. Several aspects of the action of hydrogen halides (HCl, HBr) on the chemical behavior of included oxiranes were investigated for solid-gas and solid-liquid (aqueous) systems. Under well established experimental conditions, these reactions gave regiospecifically one target product and were asymmetric. The included substrate underwent first an acid-catalyzed allylic isomerization that is cage-specific and mostly quantitative. In sheer contrast, strong basic conditions were required to promote, in reduced yield, the analogous transformation in solution. The regiospecificity and enantioselectivity of several intra-crystalline conversions allowed the accurate determination of the absolute configuration of several guest molecules. Kinetic measurements were achieved that disclosed some striking features of this new type of heterogeneous reactions. Tentative models for the cage stereoselective mechanisms are briefly discussed.  相似文献   
610.
ABSTRACT

Eight N,N´-diarylisophthalamide/dipicolineamide derivatives have been synthesised and fully characterised, both in solution and in the solid state. The transmembrane anion transport properties of these compounds have been studied by chloride-selective electrode and fluorescence experiments. The substitution pattern of the aromatic moieties determines the transport properties of these systems, with those containing electron-withdrawing groups in their structures being the most active ones of the series.  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