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   176篇
  免费   3篇
  国内免费   5篇
化学   114篇
晶体学   3篇
数学   10篇
物理学   57篇
  2023年   2篇
  2022年   14篇
  2021年   7篇
  2020年   6篇
  2019年   5篇
  2018年   5篇
  2017年   2篇
  2015年   1篇
  2014年   2篇
  2013年   18篇
  2012年   10篇
  2011年   7篇
  2010年   9篇
  2009年   14篇
  2008年   10篇
  2007年   9篇
  2006年   3篇
  2005年   3篇
  2004年   4篇
  2003年   5篇
  2002年   7篇
  2001年   3篇
  2000年   1篇
  1999年   1篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   6篇
  1992年   3篇
  1991年   2篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   2篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1975年   1篇
  1965年   1篇
排序方式: 共有184条查询结果,搜索用时 15 毫秒
171.
Considering the importance ofE 6 as the grand unification group in superstring theories, several breakdown patterns ofE 6 through maximal subgroups are studied. The Higgs which break the low energy group and give masses to the fermions are determined in each case. At each scale we consider minimal Higgs and apply extended survival hypothesis to determine the limits on the mass scales. The combination of intermediate mass scales that give rise to acceptable electroweak mixing angle and unification mass is determined. Proton decay rate is found to be acceptable in all cases except one.  相似文献   
172.
Summary Positron flux at high energies is evaluated within the framework of the simple leaky box model (SLBM) and a dynamical model of multiple production of pions in high-energy proton-proton collisions. It is seen that, if the proton spectrum is modified a bit in accordance with the primary electron spectrum as proposed by Mauger and Ormes, the theoretical estimations tally nicely with the experimental measurements of the positron flux. This work highlights, once again, the role and merit of the simple leaky box model for galactic propagation.
Riassunto Si valuta il flusso di positroni ad alta energia nell'ambito del modello semplice della scatola non isolata (SLBM) come modello dinamico di produzione di pioni nelle collisioni tra protoni ad alta energia. Si osserva che, se si modifica leggermente lo spettro protonico secondo lo spettro elettronico primario come proposto da Mauger e Ormes le stime teoriche risultano in buon accordo con le misure sperimentali del flusso positronico. Questo lavoro mette in luce, ancora una volta, il ruolo e il merito del modello semplice della scatola non isolata nella propagazione galattica.

Резюме В рамках модели SLBM и динамической модели множественного рождения пионов в протон-протонных соударениях при высоких энергиях оценивается поток позитронов при высоких энергиях. Если спектр протонов слегка изменяется по сравнению с первичным сректром электронов, как предполагалось Маугером и Ормесом, то теоретические оценки хорошо согласуются с экспериментальными измерениями потока позитронов. Зта работа еще раз подчеркивает роль и преимушества модели SLBM для развития галактики.
  相似文献   
173.
In this paper we use the beautiful formula of Faa di Bruno for the th derivative of composition of two functions to obtain the generalized Schwarz-Pick estimates. By means of those estimates we show that the hyperbolic derivative of an analytic self-map of the unit disk is Lipschitz with respect to the pseudohyperbolic metric.

  相似文献   

174.
175.
The moderate energy primary cosmic ray nucleon spectrum has been calculated from the direct measurements of Webber et al., Seo et al., and Menn et al. along with the other results surveyed by Swordy. Using these directly measured primary mass composition results all particle primary nucleon energy spectrum has been constructed using superposition model to estimate the energy spectra of muons from the decay of the cosmic ray non-prompt and prompt mesons in the atmosphere. The Z-factors have been estimated from the CERN LEBC-EHS on the Lorentz invariant cross section results on pp ±X and pp K±X inclusive reactions and FNAL data on ±p ±X reactions, and duly corrected for A--A collisions. Using these Z-factors the meson energy spectra in the atmosphere have been calculated. The sea level muon energy spectra at zenith angles 0°, 45°, 72°, and 75° have been derived from the decay of non-prompt mesons by adopting standard diffusion equation of hadronic cascades. The contribution of charmed mesons to muon spectrum has also been accounted by adapting the conventional procedure. The derived differential sea level muon energy spectra for energies 10 TeV have been found to follow the power law fits of the form N (E) const. E -. Our estimated muon energy spectra at zenith angles 75° have been found comparable with the global spectrograph muon flux results of MARS, DEIS, and MSU groups.  相似文献   
176.
Parkinson’s disease (PD) and Alzheimer’s disease (AD) are neurodegenerative disorders that have emerged as among the serious health problems of the 21st century. The medications currently available to treat AD and PD have limited efficacy and are associated with side effects. Natural products are one of the most vital and conservative sources of medicines for treating neurological problems. Karanjin is a furanoflavonoid, isolated mainly from Pongamia pinnata with several medicinal plants, and has been reported for numerous health benefits. However, the effect of karanjin on AD and PD has not yet been systematically investigated. To evaluate the neuroprotective effect of karanjin, extensive in silico studies starting with molecular docking against five putative targets for AD and four targets for PD were conducted. The findings were compared with three standard drugs using Auto Dock 4.1 and Molegro Virtual Docker software. Additionally, the physiochemical properties (Lipinski rule of five), drug-likeness and parameters including absorption, distribution, metabolism, elimination and toxicity (ADMET) profiles of karanjin were also studied. The molecular dynamics (MD) simulations were performed with two selective karanjin docking complexes to analyze the dynamic behaviors and binding free energy at 100 ns time scale. In addition, frontier molecular orbitals (FMOs) and density-functional theory (DFT) were also investigated from computational quantum mechanism perspectives using the Avogadro-ORCA 1.2.0 platform. Karanjin complies with all five of Lipinski’s drug-likeness rules with suitable ADMET profiles for therapeutic use. The docking scores (kcal/mol) showed comparatively higher potency against AD and PD associated targets than currently used standard drugs. Overall, the potential binding affinity from molecular docking, static thermodynamics feature from MD-simulation and other multiparametric drug-ability profiles suggest that karanjin could be considered as a suitable therapeutic lead for AD and PD treatment. Furthermore, the present results were strongly correlated with the earlier study on karanjin in an Alzheimer’s animal model. However, necessary in vivo studies, clinical trials, bioavailability, permeability and safe dose administration, etc. must be required to use karanjin as a potential drug against AD and PD treatment, where the in silico results are more helpful to accelerate the drug development.  相似文献   
177.
A new route was designed to achieve the synthesis of purine derivatives under phase‐transfer catalysis conditions using calix[n]arenes TACnA (n = 4, 6, and 8) as phase‐transfer catalyst for the first time in this particular type of synthesis. The compounds were synthesized in excellent yields (70%–80%) and the structures were established on the basis of consistent IR, 1H NMR, FAB‐Mass, and elemental analyses data. Their purity has been ascertained by chromatographic resolution using acetonitrile, methanol, and water (50:30:20, v/v) as eluenting system. Moreover, the kinetics of the reaction was studied and it was found to obey first‐order kinetics. Effect of various parameters, namely, temperature, amount of catalyst, stirring speed, and so on was also investigated. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 265–274, 2009  相似文献   
178.
179.
The negatively charged nitrogen-vacancy (NV(-)) center in diamond is considered to be one of the most promising solid state systems for quantum information applications. Excited states of the NV(-) center play a center role in the proposed applications. Using a combination of first-principles calculations and vibronic interaction model analysis, we establish the presence of a dynamic Jahn-Teller effect in the (3)E excited state. The calculated temperature-dependent dephasing rate for the zero phonon line as well as the splitting of the first two vibronic states are in good agreement with experiment.  相似文献   
180.
A novel series of alloxan-derived 1,4-disubstituted 1,2,3-triazoles was synthesized in excellent yields under catalytic conditions using a click reaction strategy through 1,3-dipolar cycloaddition. Their structures have been ascertained on the basis of spectroanalytical and elemental analysis data. Synthesis of hybrid compounds with varying substitutions in the triazole ring was achieved by reaction between alloxan-derived terminal alkyne and a pertinent azide derivative in the presence of clay-Cu(II) as the catalyst in methanolic medium. Also, comparative evaluation of various catalytic systems [viz., CuI, CuSO4, CuI-zeolite, K10Ti, and clay-Cu(II)] was investigated. Of these catalytic systems, clay-Cu(II) was observed to be the best. The catalyst was recyclable for several runs without showing significant loss in its activity. The good selectivity, cost-efficiency, short reaction time, milder reaction conditions, and simple workup procedure are the added salient features of this synthetic protocol.  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