全文获取类型
收费全文 | 1254篇 |
免费 | 55篇 |
国内免费 | 21篇 |
专业分类
化学 | 964篇 |
晶体学 | 20篇 |
力学 | 28篇 |
综合类 | 1篇 |
数学 | 97篇 |
物理学 | 220篇 |
出版年
2024年 | 6篇 |
2023年 | 12篇 |
2022年 | 92篇 |
2021年 | 112篇 |
2020年 | 46篇 |
2019年 | 48篇 |
2018年 | 67篇 |
2017年 | 38篇 |
2016年 | 77篇 |
2015年 | 60篇 |
2014年 | 68篇 |
2013年 | 98篇 |
2012年 | 119篇 |
2011年 | 115篇 |
2010年 | 67篇 |
2009年 | 51篇 |
2008年 | 35篇 |
2007年 | 37篇 |
2006年 | 27篇 |
2005年 | 21篇 |
2004年 | 10篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1936年 | 1篇 |
1935年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有1330条查询结果,搜索用时 15 毫秒
111.
Coir fiber from coconut husk is an important agricultural waste in Malaysia. Acoustic absorption coefficient of the fiber as a porous material is studied in this paper. Two types of fiber are investigated, fresh from wet market and industrial prepared mixed with binder. Moreover two analytical models, namely; Delany–Bazley and Biot–Allard are used for analysis. Experimental measurements in impedance tube are conducted to validate the analytical outcomes. Results show that fresh coir fiber has an average absorption coefficient of 0.8 at f > 1360 Hz and 20 mm thickness. Increasing the thickness is improved the sound absorption in lower frequencies, having the same average at f > 578 Hz and 45 mm thickness. Delany–Bazley technique can be used for both types of fiber while Biot–Allard method is compensated for the industrial prepared fiber considering the binder additive. This form generally shows poor acoustical absorption in low frequencies. Inevitably, fiber has to be mixed with additives in commercial use to enhance its characteristics such as stiffness, unti-fungus and flammability. Hence other approaches such as adding air gap or perforated plate should be used to improve the acoustical properties of industrial treated coir fiber. 相似文献
112.
M.A. Abid H. Abu HassanZ. Hassan S.S. NgS.K. Mohd. Bakhori N.H. Abd. Raof 《Physica B: Condensed Matter》2011,406(8):1379-1384
Raman and Fourier transform infrared (FTIR) spectroscopies have been utilized to measure long-wavelength optical lattice vibrations of high-quality quaternary AlxInyGa1−x−yN thin films at room temperature. The AlxInyGa1−x−yN films were grown on c-plane (0 0 0 1) sapphire substrates with AlN as buffer layers using plasma assisted molecular beam epitaxy (PA-MBE) technique with aluminum (Al) mole fraction x ranging from 0.0 to 0.2 and constant indium (In) mole fraction y=0.1. Pseudo unit cell (PUC) model was applied to investigate the phonons frequency, mode number, static dielectric constant, and high frequency dielectric constant of the AlxInyGa1−x−yN mixed crystals. The theoretical results were compared with the experimental results obtained from the quaternary samples by using Raman and FTIR spectroscopies. The experimental results indicated that the AlxInyGa1−x−yN alloy had two-mode behavior, which includes A1(LO), E1(TO), and E2(H). Thus, these results are in agreement with the theoretical results of PUC model, which also revealed a two-mode behavior for the quaternary nitride. We also obtained new values of E1(TO) and E2(H) for the quaternary nitride samples that have not yet been reported in the literature. 相似文献
113.
Li-ion rechargeable batteries based on polymer electrolytes are of great interest for solid state electrochemical devices
nowadays. Many studies have been carried out to improve the ionic conductivity of polymer electrolytes, which include polymer
blending, incorporating plasticizers and filler additives in the electrolyte systems. This paper describes the effects of
incorporating nano-sized MnO2 filler on the ionic conductivity enhancement of a plasticized polymer blend PMMA–PEO–LiClO4–EC electrolyte system. The maximum conductivity achieved is within the range of 10−3 S cm−1 by optimizing the composition of the polymers, salts, plasticizer, and filler. The temperature dependence of the polymer
conductivity obeys the VTF relationship. DSC and XRD studies are carried out to clarify the complex formation between the
polymers, salts, and plasticizer. 相似文献
114.
A brief review of the experimental situation concerning the electrically charged charmoniumlike meson candidates, Z-, is presented. 相似文献
115.
Mohamad Kamarol Mohd Jamil Shinya Ohtsuka Masayuki Hikita Hitoshi Saitoh Masayuki Sakaki 《Journal of Electrostatics》2011,69(6):611-617
This paper presents the decomposition by-products of trifluro-iodo-methane and their relative proportions in the gas phase under the occurrence of partial discharge. The experiment was performed in the presence of water vapor from 250 to 400 ppm under a non-uniform electric field configuration. The experimental results reveal that the by-products of C2F6, C2F4, C2F5I with the amount of 1300, 200, and 55 (CH3I) ppm, respectively, were produced for a cumulative charge of 161 mC. Other by-products, such as C3F8, CHF3, C3F6 CH3I were obtained at less than 30 ppm C2F6 was the dominant gas by-product of trifluro-iodo-methane suffering partial discharge. 相似文献
116.
Ahmed Alsaedi Mohammed S. Alhothuali Bashir Ahmad Sebti Kerbal Mokhtar Kirane 《Mathematical Methods in the Applied Sciences》2014,37(13):2009-2016
Sobolev type nonlinear equations with time fractional derivatives are considered. Using the test function method, limiting exponents for nonexistence of solutions are found. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
117.
Ahmed Ait Mokhtar 《Comptes Rendus Mathematique》2010,348(1-2):1-4
In this Note, we show essentially two results which complete the article by Ait Mokhtar et al., 2008. The first one, having defined the maps purement semi-affines, consists in looking the writing clarify of the compound of these maps. The second result, having defined the tressage, consists in showing that the compound of two tressages is also a tressage. 相似文献
118.
Hyder H. Balla Shahrir Abdullah Wan Mohd Faizal WanMahmood M. Abdul Razzaq Rozli Zulkifli Kamaruzaman Sopian 《Research on Chemical Intermediates》2013,39(6):2801-2815
A metallic nanofluid is a suspension of metallic nanoparticles in a base fluid. Multi-metallic nanoparticles are a combination of two or more types of metallic particles. Such multi-metallic nanoparticles were suspended in water using an ultrasonic vibrator for different total volume fractions and different ratios of metallic/metallic nanoparticles. A transient hot wire setup was built to measure the thermal conductivity of the nanofluid at different temperatures. The experimental results were in good agreement with the results in the literature. Then, the experimental results were used as input data for an adaptive neural fuzzy inference system (ANFIS) to predict the thermal conductivity of the multi-metallic nanofluid. The maximum deviation between the ANFIS results and experimental measurements was 1 %. The predicted results and the experimental data were compared with other models. The ANFIS model was found to have good ability to predict the thermal conductivity of the multi-metallic nanofluid over the range of the experimental results. 相似文献
119.
Alaa Eldin Mokhtar Abdel-Hady Rabie S. Farag Ahmad S. Abu-Khadra 《Transition Metal Chemistry》2010,35(5):571-576
The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H2O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H2O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed. 相似文献
120.
Dan He Zhigang Xue Mohd Yusuf Khan Seok Kyun Noh Won Seok Lyoo 《Journal of polymer science. Part A, Polymer chemistry》2010,48(1):144-151
Styrene polymerization via generation of activators by monomer addition (GAMA) for atom transfer radical polymerization (ATRP) has been examined extensively with bulk FeX3 and FeX2 at 110 °C in conjunction with various phosphorus‐bearing ligands. It was found that GAMA possesses advantages over normal ATRP. Most importantly, narrower polydispersity index (PDI) values were observed from the styrene polymerizations with Fe(III) over those with Fe(II). Every instance of 2‐(diphenylphosphino)‐N,N′‐dimethyl‐[1,1′‐biphenyl]‐2‐amine and 2‐(diphenylphosphino) pyridine with the Fe(III) system were controlled excellently without addition of any radical initiator or reducing agent additives. Initiator type was found to exert a significant factor to influence on the controllability of polymerization. The initiation of 1‐phenylethyl chloride and methyl‐2‐chloropropionate gave rise to formation of polymers with narrow PDI (1.05–1.20), whereas those from 1‐phenylethyl bromide increased to 1.35. The GAMA of bulk styrene exhibited the best performance in terms of both rate and controllability compared with toluene and anisole. Both formation of block copolymer from the macroinitiator and efficient perturbation of polymerization with 2,2,6,6‐tetramethylpiperidine 1‐oxyl provided firm evidence to support the living and radical characteristics for the GAMA of styrene. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 144–151, 2010 相似文献