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   456篇
  免费   28篇
化学   297篇
晶体学   1篇
力学   21篇
数学   66篇
物理学   99篇
  2023年   5篇
  2022年   3篇
  2021年   14篇
  2020年   21篇
  2019年   7篇
  2018年   18篇
  2017年   11篇
  2016年   19篇
  2015年   27篇
  2014年   27篇
  2013年   26篇
  2012年   49篇
  2011年   47篇
  2010年   24篇
  2009年   18篇
  2008年   28篇
  2007年   29篇
  2006年   25篇
  2005年   22篇
  2004年   14篇
  2003年   16篇
  2002年   10篇
  2001年   1篇
  1999年   1篇
  1998年   1篇
  1996年   2篇
  1995年   3篇
  1994年   3篇
  1992年   2篇
  1989年   1篇
  1987年   1篇
  1984年   1篇
  1982年   2篇
  1980年   2篇
  1979年   1篇
  1977年   1篇
  1976年   2篇
排序方式: 共有484条查询结果,搜索用时 234 毫秒
31.
In this paper we present the room temperature synthesis of a novel serie of 1,4-disubstituted-1,2,3-triazoles 4a-l by employing the (3+2) cycloaddition reaction of pyrimidinones containing alkyne functions with different model azides in the presence of copper sulphate and sodium ascorbate. To obtain the final triazoles, we also synthesized the major precursors 6-amino-5-cyano-1,4-disubstituted-2(1H)-pyrimidinones 3a-r from ethyl 2,2-dicyanovinylcarbamate derivatives 2a-c and various primary aromatic amines containing an alkyne group. The triazoles were prepared in good to very good yields.  相似文献   
32.
We report on a new, original and efficient method for π‐stacking functionalization of single‐wall carbon nanotubes. This method is applied to the synthesis of a high‐yield light‐harvesting system combining single‐wall carbon nanotubes and porphyrin molecules. We developed a micelle‐swelling technique that leads to controlled and stable complexes presenting an efficient energy transfer. We demonstrate the key role of the organic solvent in the functionalization mechanism. By swelling the micelles, the solvent helps the non‐water‐soluble porphyrins to reach the micelle core and allows a strong enhancement of the interaction between porphyrins and nanotubes. This technique opens new avenues for the functionalization of carbon nanostructures.  相似文献   
33.
This paper introduces LocalSolver 1.x, a black-box local-search solver for general 0-1 programming. This software allows OR practitioners to focus on the modeling of the problem using a simple formalism, and then to defer its actual resolution to a solver based on efficient and reliable local-search techniques. Started in 2007, the goal of the LocalSolver project is to offer a model-and-run approach to combinatorial optimization problems which are out of reach of existing black-box tree-search solvers (integer or constraint programming). Having outlined the modeling formalism and the main technical features behind LocalSolver, its effectiveness is demonstrated through an extensive computational study. The version 1.1 of LocalSolver can be freely downloaded at and used for educational, research, or commercial purposes.  相似文献   
34.
We consider a multidimensional diffusion XX with drift coefficient b(α,Xt)b(α,Xt) and diffusion coefficient ?σ(β,Xt)?σ(β,Xt). The diffusion sample path is discretely observed at times tk=kΔtk=kΔ for k=1…nk=1n on a fixed interval [0,T][0,T]. We study minimum contrast estimators derived from the Gaussian process approximating XX for small ??. We obtain consistent and asymptotically normal estimators of αα for fixed ΔΔ and ?→0?0 and of (α,β)(α,β) for Δ→0Δ0 and ?→0?0 without any condition linking ?? and ΔΔ. We compare the estimators obtained with various methods and for various magnitudes of ΔΔ and ?? based on simulation studies. Finally, we investigate the interest of using such methods in an epidemiological framework.  相似文献   
35.
This work reports the first structure–properties relationship study of ortho [2,1‐c]‐, meta [1,2‐a]‐, and para [1,2‐b]dihydroindenofluorenes, highlighting the influence of bridge rigidification on the electronic properties. This study has made it possible to devise an extended π‐conjugated molecule with both a high triplet state energy level and excellent thermal and morphological stability. As a proof of concept, dihydroindenofluorenes were used as the host in sky‐blue phosphorescent organic light‐emitting diodes (PhOLEDs) w ith high performance.  相似文献   
36.
This paper describes the synthesis of triptycene‐based building blocks that are able to interact through hydrogen bonds to form one‐dimensional self‐assembled motifs on surfaces. We designed 9,10‐diethynyltriptycene derivatives functionalized at the ethynyl end groups by a variety of hydrogen‐bonding groups for homomolecular recognition and complementary building blocks for heteromolecular recognition. We also present the synthesis of bis‐ and trisethynyltriptycenes with terminal alkyne functional groups available for on‐surface azide–alkyne cycloaddition reaction to expand the potential of the triptycene building block.  相似文献   
37.
Understanding bacterial adhesion on a surface is a crucial step to design new materials with improved properties or to control biofilm formation and eradication. Sum Frequency Generation (SFG) vibrational spectroscopy has been employed to study in situ the conformational response of a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film to the adhesion of hydrophilic and hydrophobic ovococcoid model bacteria. The present work highlights vibrational SFG spectroscopy as a powerful and unique non-invasive biophysical technique to probe and control bacteria interaction with ordered surfaces. Indeed, the SFG vibrational spectral changes reveal different ODT SAM conformations in air and upon exposure to aqueous solution or bacterial adhesion. Furthermore, this effect depends on the bacterial cell surface properties. The SFG spectral modeling demonstrates that hydrophobic bacteria flatten the ODT SAM alkyl chain terminal part, whereas the hydrophilic ones raise this ODT SAM terminal part. Microorganism-induced alteration of grafted chains can thus affect the desired interfacial functionality, a result that should be considered for the design of new reactive materials.  相似文献   
38.
Several methods for the separation of vitamins on HPLC columns were already validated in the last 20 years. However, most of the techniques focus on separating either fat- or water-soluble vitamins and only few methods are intended to separate lipophilic and hydrophilic vitamins simultaneously. A mixed-mode reversed-phase weak anion exchange (RP-WAX) stationary phase was developed in our laboratory in order to address such mixture of analytes with different chemical characteristics, which are difficult to separate on standard columns. The high versatility in usage of the RP-WAX chromatographic material allowed a baseline separation of ten vitamins within a single run, seven water-soluble and three fat-soluble, using three different chromatographic modes: some positively charged vitamins are eluted in ion exclusion and ion repulsion modes whereas the negatively charged molecules are eluted in the ion exchange mechanism. The non-charged molecules are eluted in a classical reversed-phase mode, regarding their polarities. The method was validated for the vitamin analysis in tablets, evaluating selectivity, robustness, linearity, accuracy, and precision. The validated method was finally employed for the analysis of the vitamin content of some commercially available supplement tablets.  相似文献   
39.
{Mo(132)} Keplerate anion reacts with tellurites to give a soluble precursor to produce in hydrothermal conditions single-phase M1 MoVTeO light-alkanes oxidation catalyst. Characterization of this Te-containing intermediate by single-crystal X-ray diffraction, (125)Te NMR, UV-visible and redox titration reveals a molybdotellurite anion as a crown-capped Keggin derivative.  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