全文获取类型
收费全文 | 357篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 288篇 |
晶体学 | 4篇 |
力学 | 12篇 |
数学 | 35篇 |
物理学 | 39篇 |
出版年
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 40篇 |
2012年 | 27篇 |
2011年 | 25篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 17篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 12篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有378条查询结果,搜索用时 15 毫秒
91.
N. Bel Haj Mohamed M. Haouari Z. Zaaboub F. Hassen H. Maaref H. Ben Ouada 《Journal of Physics and Chemistry of Solids》2014
Cadmium sulfide (CdS) nanoparticles were synthesized by a novel wet chemical route with various organic thiol stabilizers. Systematic experimental studies, including X-ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), photoluminescence (PL) spectroscopy, and time-resolved photoluminescence (TRPL), have evidenced that the stability, crystallinity, and optical properties of the CdS nanoparticles are affected by the organic groups which generate significant effects in surface reconstruction. Particle size was evaluated from UV–vis spectroscopy using the effective mass approximation (EMA) method and from XRD patterns based on Scherrer?s formula. The S–H vibrations are not detectable in the infrared (IR) spectra of any of the bound ligands, which are expected for thiols covalently bound to the surface of nanoparticles. PL studies reveal that the emission from the nanostructures is not much influenced by the surface states, indicating a good passivation of the particle?s surface. The time-resolved measurements reveal a biexponential decay behavior. The fast decay component is attributed to the recombination of core states, while the slow decay component of PL is associated with the charge-carrier recombination process with the involvement of surface states. 相似文献
92.
H. A. Ashry Maha H. El-Kady N. E. Amin H. M. Roushdy 《Isotopes in environmental and health studies》2013,49(7):328-331
The objective of the present work is to investigate any possible role which could have been played by the long-term treatment with antimony as an antibilharzial drug, and the development of urinary bladder carcinoma in patients suffering bilharzial complications. The present work has been planned to investigate the concentration levels of copper, zinc and antimony in urinary bladder tissues sampled from normal, bilharzial and bladder cancer patients subjected to surgical intervention. Both atomic absorption spectrophotometry and neutron activation analysis have been utilized for elemental estimations. The data obtained showed significant increase in the concentration levels of the three investigated metals in bladder cancer tumours as compared with their control levels under either normal or cancer-free bilharzial complications. The results have been statistically evaluated and discussed in view of the relevant literature. It has been concluded that the contributing role of the antibilharzial antimonial treatment in development of urinary bladder cancer cases cannot be overlooked and awaits further investigation. 相似文献
93.
Maha Abdallah Alnuwaiser M. Faisal Javed M. Ijaz Khan M. Waqar Ahmed Ahmed M. Galal 《印度化学会志》2022,99(7):100538
The current study investigates the potential of well-known artificial neural network (ANN), Support vector regression (SVR), multilinear and multi-nonlinear regression techniques to predict total dissolve solids (TSO) and electrical conductivity (ECO), which are essential water quality indicators. To develop the anticipated models, seven effective parameters: Ca2+ Mg2+ Na+ Cl- SO42- HCO3- and pH were used as input variables. The external validation criteria were employed to address the modeling overfitting. The outcome of the study demonstrated a strong association between experimental and models predicted data. The coefficient of determination was 0.97, 0.96, 0.92, and 0.94 for SVR, ANN, MLR, and MNLR models, respectively. The lowest error value of 5.37 and 7.92 was attained by SVR model for training and testing data, respectively. Performance of the proposed techniques showed relative dominance of SVR compared to ANN, MLR and MNLR. Sensitivity analysis demonstrated that the HCO3- is the most sensitive parameter for both TSO and ECO followed by Cl- and SO42-. The models assessment on external criteria ensured generalized results. Conclusively, the outcome of the present research indicated that formulation of machine learning models for prediction of water quality parameters are cost effective and helpful in river water quality assessment, management and policy making. 相似文献
94.
Majdi Abid Hassen Trabelsi Mohamed Taktak Jérôme Antoni Jean Michel Ville Tahar Fakhfakh Mohamed Haddar 《Applied Acoustics》2012,73(10):1022-1028
The current techniques for monitoring and diagnostics of rotating machines to their conditional predictive maintenance mainly are based on vibration monitoring. In this research, experimental and theoretical methods to predict the tonal noise of a faulty fan are developed and validated. These methods can be used on identifying defects of an axial fan based on an acoustic monitoring in situations where it is necessary to operate remotely due to the inaccessibility of the areas of event defects. 相似文献
95.
96.
Nonlinear Dynamics - We present a systematic approach to deal with the modelling and analysis of the cracked rotating shafts behaviour. We begin by revisiting the problem of modelling the breathing... 相似文献
97.
98.
Maha Benzarti-GhédiraHaikel Hrichi Nejmeddine JaballahRafik Ben Chaâbane Mustapha MajdoubHafedh Ben Ouada 《Physica B: Condensed Matter》2012,407(7):1051-1054
The opto-electronic properties of native poly(p-phenylene vinylene) (PPV) were tuned by the confinement of the π-conjugation and the incorporation of a sulphur group as a spacer in order to obtain a blue-green emitting polymer (PPVS). The energy band gap of the PPVS thin film has been measured by UV-vis absorption spectroscopy and evaluated to 2.87 eV. Current-voltage characteristics and impedance spectroscopy measurements performed on sandwich structures [ITO/PPVS/Al] are used to elucidate the conduction mechanisms. The static electrical characterisations showed a space charge limited conduction (SCLC) and a conductivity with low power frequency behaviour characteristic of a hopping transport in disordered materials. The impedance spectra can be discussed in terms of an equivalent circuit model designed as a parallel resistor RP and capacitor CP network in series with a resistor RS. We extract numerical values of these parameters by fitting experimental data. Their evolution with bias voltages has shown that the SCLC mechanism is characterised by an exponential trap distribution. 相似文献
99.
100.
A simple and efficient one-pot, three-component synthesis of new trisubstituted ureas containing diastereotopic protons is achieved via the reaction of aromatic aldehydes, aromatic ketones, and dimethyl cyanamide using a TCS/ZnCl2 reagent mixture at room temperature. 相似文献