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   1141篇
  免费   56篇
  国内免费   3篇
化学   769篇
晶体学   32篇
力学   44篇
数学   105篇
物理学   250篇
  2023年   12篇
  2022年   18篇
  2021年   25篇
  2020年   34篇
  2019年   29篇
  2018年   26篇
  2017年   26篇
  2016年   54篇
  2015年   33篇
  2014年   60篇
  2013年   80篇
  2012年   83篇
  2011年   102篇
  2010年   46篇
  2009年   44篇
  2008年   81篇
  2007年   58篇
  2006年   56篇
  2005年   29篇
  2004年   45篇
  2003年   33篇
  2002年   16篇
  2001年   11篇
  2000年   6篇
  1999年   4篇
  1998年   6篇
  1997年   11篇
  1996年   9篇
  1995年   8篇
  1994年   11篇
  1993年   8篇
  1992年   12篇
  1991年   6篇
  1990年   6篇
  1989年   9篇
  1988年   8篇
  1987年   9篇
  1986年   4篇
  1985年   7篇
  1984年   10篇
  1983年   4篇
  1982年   12篇
  1981年   7篇
  1980年   10篇
  1978年   3篇
  1976年   4篇
  1975年   3篇
  1974年   3篇
  1973年   3篇
  1972年   3篇
排序方式: 共有1200条查询结果,搜索用时 203 毫秒
1.
Quantum correlations provide dramatic advantage over the corresponding classical resources in several communication tasks. However, a broad class of probabilistic theories exists that attributes greater success than quantum theory in many of these tasks by allowing supra-quantum correlations in “space-like” and/or “time-like” paradigms. In this letter, a communication task involving three spatially separated parties is proposed where one party (verifier) aims to verify whether the bit strings possessed by the other two parties (terminals) are equal or not. This task is called authentication with limited communication, the restrictions on communication being: i) the terminals cannot communicate with each other, but (ii) each of them can communicate with the verifier through single use of channels with limited capacity. Manifestly, classical resources are not sufficient for perfect success of this task. Moreover, it is also not possible to perform this task with certainty in several nonclassical theories although they might possess stronger “space-like” and/or “time-like” correlations. Surprisingly, quantum resources can achieve the perfect winning strategy. The proposed task thus stands apart from all previously known communication tasks as it exhibits quantum advantage over other nonclassical strategies.  相似文献   
2.
Molecular Diversity - The antifungals that are in current clinical practice have a high occurrence of a side effect and multidrug resistance (MDR). Researchers across the globe are trying to...  相似文献   
3.
For a Dirichlet character modulo an integer \(q\ge 3\), we use a highly simple elementary method to give an asymptotic formula for \(\sum _{\chi \ne \chi _0 ({\bmod q})} {|L(1, \chi )|^{4}} ,\) where \(\chi _0 ({\bmod \, q})\) is the principal character. This result seems to be new.  相似文献   
4.
Respiratory complex I is a key enzyme in the electron transport chains of mitochondria and bacteria. It transfers two electrons to quinone and couples this redox reaction to proton pumping to electrically charge the membrane it is embedded in. The charge and pH gradient across the membrane drives the synthesis of ATP. The redox reaction and proton pumping in complex I are separated in space and time, which raises the question of how the two reactions are coupled so efficiently. Here, we focus on the unique ~35 Å long tunnel of complex I, which houses the binding site of quinone reduction. We discuss the redox and protonation reactions that occur in this tunnel and how they influence the dynamics of protein and substrate. On the basis of recent structural data and results from molecular simulations, we review how quinone reduction and dynamics may be coupled to proton pumping in complex I.  相似文献   
5.
The pyrolysis of propane plays an important role in determining the combustion properties of natural gas mixtures and offers insight into the cracking patterns of larger fuels. This work investigates propane pyrolysis behind reflected shock waves with a multiwavelength laser-absorption speciation technique. Nine laser wavelengths, sensitive to key pyrolysis species, were used to measure absorbance time histories during the decomposition of 2% propane in argon between 1022 and 1467 K, 3.7-4.3 atm. Absorbance models were developed at each diagnostic wavelength to interrogate common initial conditions, and time histories of all major species are reported at 1250, 1290, 1330, 1370, and 1410 K. Nearly complete carbon recovery observed at lower temperatures enabled the inference of hydrogen formation from atomic conservation, while decaying carbon recovery at high temperatures suggests the formation of allene and 1-butene. The results show systematically faster pyrolysis than predicted by kinetic modeling and motivate further study into the kinetics of propane pyrolysis.  相似文献   
6.
To circumvent costly fluorescent labeling, five nonconventional, multifunctional, intrinsically fluorescent aliphatic terpolymers ( 1 – 5 ) have been synthesized by C−C/C−N-coupled, solution polymerization of two non-emissive monomers with protrusions of fluorophore monomers generated in situ. These scalable terpolymers were suitable for sensing and high-performance exclusion of CuII, logic function, and bioimaging. The structures of the terpolymers, in situ attachment of fluorescent monomers, aggregation-induced enhanced emission, bioimaging ability, and super adsorption were investigated by 1H and 13C NMR, EPR, FTIR, X-ray photoelectron, UV/Vis, and atomic absorption spectroscopy, thermogravimetric analysis, high-resolution transmission electron microscopy, dynamic light scattering, solid-state fluorescence, fluorescence imaging, and fluorescence lifetime measurements, as well as by isotherm, kinetics, and thermodynamic studies. The geometries and electronic structures of the fluorophores and the absorption and emission properties of the terpolymers were examined by DFT, time-dependent DFT, and natural transition orbital analyses. For 1 , 2 , and 5 , the limits of detection were determined to be 1.03×10−7, 1.65×10−7, and 1.77×10−7 m , respectively, and the maximum adsorption capacities are 1575.21, 1433.70, and 1472.21 mg g−1, respectively.  相似文献   
7.
Organic phosphors have been widely explored with an understanding that crystalline molecular ordering is a requisite for enhanced intersystem crossing. In this context, we explored the room‐temperature phosphorescence features of a solvent‐free organic liquid phosphor in air. While alkyl chain substitution varied the physical states of the bromonaphthalimides, the phosphorescence remained unaltered for the solvent‐free liquid in air. As the first report, a solvent‐free liquid of a long swallow‐tailed bromonaphthalimide exhibits room‐temperature phosphorescence in air. Doping of the phosphor with carbonyl guests resulted in enhanced phosphorescence, and hence a large‐area paintable phosphorescent liquid composite with improved lifetime and quantum yield was developed.  相似文献   
8.
A metal-free and greener approach for the one-pot direct iodination and dehydrogenation of dihydrobenzo[a]carbazoles has been developed using periodic acid in polyethylene glycol-400 (PEG-400) under mild condition. This method has been proven to be tolerate to a broad range of functional groups, with good to excellent yields include metal-free inexpensive catalyst, easy work-up, benign reaction condition and high regioselectivity. The solvent has been successfully recycled up to 5 times without any loss of activity in an aqueous medium.  相似文献   
9.
Two vanadium (IV) complexes [VIVO(Haeae-sal)(MeOH)]+ ( 1 ) and [VIVO(Haeae-hyap)(MeOH)]+ ( 2 ) were prepared by reacting [VO(acac)2] with ligands [H2aeae-sal] ( I ) and [H2aeae-hyap] ( II ) respectively. Condensation of 2-(2-aminoethylamino)ethanol with salicylaldehyde and 2-hydroxyacetophenone produces the ligands ( I ) and ( II ) respectively. Both vanadium complexes 1 and 2 are sensitive towards aerial oxygen in solution and rapidly convert into vanadium(V) dioxido species. Vanadium(V) dioxido species crystalizes as the dimeric form in the solid-state. Single-crystal XRD analysis suggests octahedral geometry around each vanadium center in the solid-state. To access the benefits of heterogeneous catalysis, vanadium(V) dioxido complexes were anchored into the polymeric chain of chloromethylated polystyrene. All the synthesized neat and supported vanadium complexes have been studied by a number of techniques to confirm their structural and functional properties. Bromoperoxidase activity of the synthesized vanadium(V) dioxido complexes 3 and 4 was examined by carrying out oxidative bromination of salicylaldehyde and oxidation of thioanisole. In the presence of hydrogen peroxide, 3 shows 94.4% conversion ( TOF value of 2.739 × 102 h−1) and 4 exhibits 79.0% conversion (TOF value of 2.403 × 102 h−1) for the oxidative bromination of salicylaldehyde where 5-bromosalicylaldehyde appears as the major product. Catalysts 3 and 4 also efficiently catalyze the oxidation of thioanisole in the presence of hydrogen peroxide where sulfoxide is observed as the major product. Covalent attachment of neat catalysts 3 and 4 into the polymer chain enhances substrate conversion (%) and their catalytic efficiency increases many folds, both in the oxidative bromination and oxidation of thioether. Polymer supported catalysts 5 displayed 98.8% conversion with a TOF value of 1.127 × 104 h−1 whereas catalyst 6 showed 95.7% conversion with a TOF value of 4.675 × 103 h−1 for the oxidative bromination of salicylaldehyde. These TOF values are the highest among the supported vanadium catalysts available in the literature for the oxidative bromination of salicylaldehyde.  相似文献   
10.
JPC – Journal of Planar Chromatography – Modern TLC - The Inula genus has been used for the cure of pulmonary, heart diseases and also acts as a rejuvenator, immunomodulator in...  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