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   540篇
  免费   8篇
化学   262篇
晶体学   1篇
力学   30篇
数学   28篇
物理学   227篇
  2022年   5篇
  2021年   13篇
  2020年   7篇
  2019年   5篇
  2018年   8篇
  2017年   11篇
  2016年   11篇
  2015年   7篇
  2014年   26篇
  2013年   17篇
  2012年   53篇
  2011年   38篇
  2010年   23篇
  2009年   16篇
  2008年   43篇
  2007年   28篇
  2006年   26篇
  2005年   30篇
  2004年   17篇
  2003年   11篇
  2002年   17篇
  2001年   11篇
  2000年   4篇
  1999年   6篇
  1998年   5篇
  1997年   2篇
  1996年   12篇
  1995年   14篇
  1994年   5篇
  1993年   4篇
  1992年   2篇
  1991年   2篇
  1987年   2篇
  1986年   5篇
  1985年   10篇
  1984年   11篇
  1983年   7篇
  1982年   6篇
  1981年   4篇
  1975年   3篇
  1972年   1篇
  1971年   2篇
  1968年   1篇
  1956年   2篇
  1955年   2篇
  1954年   1篇
  1938年   1篇
  1936年   1篇
  1935年   1篇
  1934年   1篇
排序方式: 共有548条查询结果,搜索用时 15 毫秒
81.
A fairly general sufficient condition for compatibility of the left Cauchy–Green deformation field in three dimensions has been derived. A related necessary condition is also indicated. The kinematical problem is phrased as a suitable problem in Riemannian geometry, whence the method of solution emerges naturally. The main result of the paper is general in scope and provides conditions for the existence of solutions to certain types of overdetermined systems of first-order, quasilinear partial differential equations with algebraic constraints. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
82.
Optical coherence tomography (OCT) images coupled with many learning techniques have been developed to diagnose retinal disorders. This work aims to develop a novel framework for extracting deep features from 18 pre-trained convolutional neural networks (CNN) and to attain high performance using OCT images. In this work, we have developed a new framework for automated detection of retinal disorders using transfer learning. This model consists of three phases: deep fused and multilevel feature extraction, using 18 pre-trained networks and tent maximal pooling, feature selection with ReliefF, and classification using the optimized classifier. The novelty of this proposed framework is the feature generation using widely used CNNs and to select the most suitable features for classification. The extracted features using our proposed intelligent feature extractor are fed to iterative ReliefF (IRF) to automatically select the best feature vector. The quadratic support vector machine (QSVM) is utilized as a classifier in this work. We have developed our model using two public OCT image datasets, and they are named database 1 (DB1) and database 2 (DB2). The proposed framework can attain 97.40% and 100% classification accuracies using the two OCT datasets, DB1 and DB2, respectively. These results illustrate the success of our model.  相似文献   
83.
The kinetics of base hydrolysis of some (aminomonocarboxylato)(tetraethylenepentamine)cobalt(III) complexes, [(tetren)CoO2CR]2+ (R= NH2CH2, pyridine‐2 ,  NH2CH2CH2,  NH2CH(CH3) (αβS isomer); R= NH2CH(CH3) (αβR isomer)), have been investigated in methanol–water media (0–80 vol % MeOH) at 15.0≤t°C≤40.0 (0.02 mol dm−3 NaOH). The second‐order rate constant at zero ionic strength, k2°, increases nonlinearly with XMeOH. The transfer free energy of the initial state and the transition state of the amido conjugate base ([ΔtG (i)](s←w)) for the glycinato‐ and pyridine‐2–carboxylato complexes have been calculated using the solubility data of their picrate salts, pK NH date of their N‐protonated forms, and the k2° values in mixed solvent media. The kinetic solvent effects have been interpreted in terms of preferential solvation of the initial state, transition state, and the solvent structure. The activation enthalpies and entropies varied nonlinearly with XMeOH displaying extrema, which is attributable to the solvent structural effects on these thermodynamic parameters. It is also evident that the mutation process, αβR→αβS isomer for the α‐alaninato complex, where this isomerisation refers to the arrangement of the tetren skeleton around the planar secondary NH is sensitive to the nature of the cosolvent molecules and solvent structure. The mutation process is generally more favorable for the five coordinate amido conjugate bases than the initial state. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 55–64, 1999  相似文献   
84.
Synthetic dyes have become an integral part of many industries such as textiles, tannin and even food and pharmaceuticals. Industrial dye effluents from various dye utilizing industries are considered harmful to the environment and human health due to their intense color, toxicity and carcinogenic nature. To mitigate environmental and public health related issues, different techniques of dye remediation have been widely investigated. However, efficient and cost-effective methods of dye removal have not been fully established yet. This paper highlights and presents a review of recent literature on the utilization of the most widely available biopolymers, specifically, cellulose, chitin and chitosan-based products for dye removal. The focus has been limited to the three most widely explored technologies: adsorption, advanced oxidation processes and membrane filtration. Due to their high efficiency in dye removal coupled with environmental benignity, scalability, low cost and non-toxicity, biopolymer-based dye removal technologies have the potential to become sustainable alternatives for the remediation of industrial dye effluents as well as contaminated water bodies.  相似文献   
85.
Synthesis of substituted phenanthridinones and dibenzoazepinones has been realized from 2-halo-benzamides in the presence of potassium tert-butoxide and a catalytic amount of 1,10-phenanthroline or AIBN. This new carbon-carbon bond forming reaction gives direct access to various biaryl lactams containing six- and seven-membered rings chemoselectively. Carbon-carbon coupling seems to proceed by the generation of a radical in the amide ring which leads to C-H arylation of aniline.  相似文献   
86.
A measurement of the production cross section of top quark pairs (tt¯) in proton–proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35pb?1, a tt¯ production cross section σtt¯=177±20(stat.)±14(syst.)±7(lum.)pb is measured for an assumed top quark mass of mt=172.5GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions.  相似文献   
87.
Bismuth ferrite is doped with a dilute concentration of cobalt, BiFe1XCoXO3BiFe1XCoXO3; X=0, 0.01, 0.02 is prepared by sol-gel auto combustion technique. X-ray diffraction data refined via Reitveld method shows single phase and shrinkage in cell volume for Co doped BiFeO3. Various magnetic ground states viz. superparamagnetic, glassy antiferromagnetic and glassy ferrimagnetic behavior is observed for X=0, 0.01, 0.02, respectively. A first-order magnetic transition is observed in the Arrott plot data of cobalt doped BiFeO3. Possibility of thermally induced magnetic transition is also seen in the magnetization data of cobalt doped BiFeO3. A model based on the existing spinoidal cyclic arrangement of spins is proposed to explain the observed data. Finally, a very dilute concentration of Co+3Co+3 in BiFeO3 is found sufficient to tailor the magnetic properties.  相似文献   
88.
The high dose rate electron beams are increasingly being used for radiation processing of various products worldwide. A comprehensive dosimetric evaluation of an in-house developed 10 MeV industrial electron beam irradiator was carried out in static as well as in dynamic mode of irradiations. Radiochromic B3 film and graphite calorimeter were used for dosimetric measurements. The dose rate from the electron beam was also calculated using the empirical relation prescribed in the ASTM report E2232-02. The measured electron beam profile indicates the dose rate variation within 8% in the irradiated product boxes. The most probable energy determined from the depth dose distribution in PMMA, Al and water was found in agreement with the intended energy of the electron beam. Measured dose rate using radiochromic film and graphite calorimeter were found in good agreement with each other and also found comparable with the theoretically estimated dose rates. Experimentally measured dose rates were considered for the trial irradiation of medical and industrial products. Dosimetric data obtained through this study confirms the suitability of the irradiator for routine radiation processing of various products.  相似文献   
89.
A search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9 fb(-1) collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of √s=7 TeV. In the diphoton mass range 110-150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110-150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113-115 GeV and 134.5-136 GeV.  相似文献   
90.
The results of a search for pair production of the scalar partners of bottom quarks in 2.05 fb(-1) of pp collisions at sqrt[s]=7 TeV using the ATLAS experiment are reported. Scalar bottom quarks are searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a bottom quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom quark decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the b(1) - χ(1)(0) mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded.  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