全文获取类型
收费全文 | 630篇 |
免费 | 23篇 |
国内免费 | 6篇 |
专业分类
化学 | 376篇 |
晶体学 | 21篇 |
力学 | 35篇 |
数学 | 102篇 |
物理学 | 125篇 |
出版年
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 22篇 |
2020年 | 25篇 |
2019年 | 16篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 22篇 |
2015年 | 16篇 |
2014年 | 23篇 |
2013年 | 61篇 |
2012年 | 24篇 |
2011年 | 34篇 |
2010年 | 31篇 |
2009年 | 20篇 |
2008年 | 37篇 |
2007年 | 25篇 |
2006年 | 26篇 |
2005年 | 22篇 |
2004年 | 29篇 |
2003年 | 19篇 |
2002年 | 22篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1966年 | 2篇 |
1964年 | 2篇 |
1956年 | 2篇 |
排序方式: 共有659条查询结果,搜索用时 15 毫秒
641.
Djillali Imessaoudene Salah Hanini Abdelkader Bouzidi 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(2):893-902
A set of experiments was carried out to evaluate the strontium uptake potential of spent coffee grounds (SCG) by batch tests in aqueous medium. Adsorption of Sr2+ as a function of contact time and adsorbent dose, pH, particles size, agitation speed, temperature and co-ions presence was investigated. Obtained results revealed that the maximum adsorption took place at pH range of 5–8 and temperature values between 283 and 333 K. Particles size effect was not very significant and agitation speed influenced on the equilibrium time. Competitive adsorption experiments allowed us to classify the negative effect on the Sr2+ uptake according to this order Al3+ ? Co2+ > Mg2+ > Ca2+ ? Na+ > K+ > Cs+. Kinetic study indicated that the Sr2+ uptake was fast and it was well fitted by the pseudo second order reaction model. Adsorption isotherm was well interpreted by Langmuir model. The maximum adsorption capacity was found to be 69.01 mg g?1 at pH 7, 293 K, particles sizes = 200–400 μm and agitation speed 250 rpm. The thermodynamic study revealed that the process was spontaneous (ΔG 0 < 0), exothermic (ΔH 0 < 0) with a raised affinity for Sr2+ (ΔG 0 < 0, ΔS 0 > 0) and occurred by physical adsorption (E a = 8.37 kJ mol?1). FTIR analysis showed carboxylic acid and amino group presence on SCG surface playing a vital role in Sr2+ biosorption. 相似文献
642.
Nabila Aliouane Jean-Jacques Hélesbeux Tahar Douadi Mustayeen A. Khan Gilles Bouet Salah Chafaa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):354-364
Abstract New di-, tri-, and tetraphosphonic acids were synthesized starting from four o-hydroxymethyl phenol derivatives and obtained in three steps in good overall yield. The phosphonic acids were isolated and purified using semi-preparative C18 HPLC column. The new compounds were characterized using different spectroscopic methods (1H, 13C, and 31P NMR; ESI MS; and MSn, IR). GRAPHICAL ABSTRACT 相似文献
643.
644.
Eisa E. Hekal Salah A. Abo-El-Enein S. A. El-Korashy G. M. Megahed T. M. El-Sayed 《Journal of Thermal Analysis and Calorimetry》2013,114(2):613-619
Electric arc furnace dust (EAFD) is termed as a hazardous waste due to its contamination with heavy metals. Inertization of such very fine dust can be occurred via stabilization and solidification process within the hydrated Portland cement matrix. In this paper, the effect of the addition of various ratios of EAFD on the properties of the hardened Portland cement paste was investigated. Compressive strength, chemically combine water and free lime contents were determined. In addition, phase composition using XRD; DTA analysis; as well as microstructure of the formed hydrates for some selected samples were investigated using SEM. The obtained results showed that the paste containing 1/mass% EAFD give the highest compressive strength values at most hydration ages, specially the later ages, compared to the neat Portland cement blank paste. Whileas, the pastes containing 3 and 5/mass% EAFD showed lower values of compressive strength compared to those of the blank paste. 相似文献
645.
A new series of dinuclear phosphinato-bridged manganese(II) complexes [Mn(μ-bmp)(bpy)(NO3)]2 (1), [Mn(μ-bmp)(phen)(NO3)]2·4CH2Cl2 (2) and [Mn2(μ-bmp)2(5-dmbpy)2(NO3)]2 (3) where Hbmp is bis(4-methoxyphenyl)phosphinic acid, bpy = 2,2′-bipyridyl, phen = 1,10-phenanthroline and 5-dmbpy = 5,5′-dimethyl-2,2′-dipyridyl, have been synthesized and structurally characterized by X-ray crystallography. In this series, the structures consist in bis(4-methoxyphenyl)phosphinato anions (bmp) bridging the two Mn(II) centers in a syn-syn coordination mode. The coordination geometry around the Mn(II) ions in 1-3 is six-coordinate with distorted octahedral environment. The magnetic behavior of these complexes is reported. The complexes show weak antiferromagnetic coupling with |J| in the range 0.1-0.6 cm−1. The magnetic properties are discussed in relation to the structural data. 相似文献
646.
In this paper, the problem of outer synchronization between two complex networks with the same topological structure and time-varying coupling delay is investigated. In particular, we introduce a new type of outer synchronization behavior, i.e., mixed outer synchronization (MOS), in which different state variables of the corresponding nodes can evolve into complete synchronization, antisynchronization, and even amplitude death simultaneously for an appropriate choice of the scaling matrix. A novel nonfragile linear state feedback controller is designed to realize the MOS between two networks and proved analytically by using Lyapunov-Krasovskii stability theory. Finally, numerical simulations are provided to demonstrate the feasibility and efficacy of our proposed control approach. 相似文献
647.
Bidhan Pandit Emad S.Goda Mahmoud H.Abu Elella Aafaq ur Rehman Sang Eun Hong Sachin R.Rondiya Pranay Barkataki Shoyebmohamad F.Shaikh Abdullah M.Al-Enizi Salah MEl-Bahy Kuk Ro Yoon 《Journal of Energy Chemistry》2022,(2):116-126
An eco-friendly, new, and controllable approach for the preparation of manganese oxide(a-MnO2) nanorods has been introduced using hydrothermal reaction for supercapacitor application. The in-depth crystal structure analysis of α-MnO2 is analyzed by X-ray Rietveld refinement by using Full Prof program with the help of pseudo-Voigt profile function. The developed a-MnO2 electrode attains a remarkable capacitance of 577.7 F/g recorded at a current density value of 1... 相似文献
648.
Fathi Hamdi Senda Agrebi Mohamed Salah Idrissi Kambale Mondo Zeineb Labiadh Amsini Sadiki Mouldi Chrigui 《Entropy (Basel, Switzerland)》2022,24(5)
The behaviors of spray, in Reactivity Controlled Combustion Ignition (RCCI) dual fuel engine and subsequent emissions formation, are numerically addressed. Five spray cone angles ranging between 5° and 25° with an advanced injection timing of 22° Before Top Dead Center (BTDC) are considered. The objective of this paper is twofold: (a) to enhance engine behaviors in terms of performances and consequent emissions by adjusting spray cone angle and (b) to outcome the exergy efficiency for each case. The simulations are conducted using the Ansys-forte tool. The turbulence model is the Renormalization Group (RNG) K-epsilon, which is selected for its effectiveness in strongly sheared flows. The spray breakup is governed by the hybrid model Kelvin–Helmholtz and Rayleigh–Taylor spray models. A surrogate of n-heptane, which contains 425 species and 3128 reactions, is used for diesel combustion modeling. The obtained results for methane/diesel engine combustion, under low load operating conditions, include the distribution of heat transfer flux, pressure, temperature, Heat Release Rate (HRR), and Sauter Mean Diameter (SMD). An exergy balance analysis is conducted to quantify the engine performances. Output emissions at the outlet of the combustion chamber are also monitored in this work. Investigations show a pressure decrease for a cone angle θ = 5° of roughly 8%, compared to experimental measurement (θ = 10°). A broader cone angle produces a higher mass of NOx. The optimum spray cone angle, in terms of exergy efficiency, performance, and consequent emissions is found to lie at 15° ≤ θ ≤ 20°. 相似文献
649.
Essam Mohamed Sharshira Ahmed A. Ataalla Mohamed Hagar Mohammed Salah Mariusz Jaremko Nader Shehata 《Molecules (Basel, Switzerland)》2022,27(17)
A series of novolac phenolic polymeric networks (NPPN) were prepared via an acid-catalyzed polycondensation reaction of formaldehyde with chalcones possessing a p-phenolic OH group. When p-hydroxybenzaldehyde was treated with formaldehyde under the same conditions, a phenolic polymer (PP) was obtained. The resulting polymers were isolated in excellent yields (83–98%). Isolated polymers (NPPN, PP) were characterized using FTIR, TGA, and XRD. The results obtained from the TGA revealed that all prepared phenolic polymers have high thermal stability at high temperatures and can act as thermosetting materials. XRD data analysis showed a high degree of amorphousness for all polymers (78.8–89.2%). The electrical conductivities and resistivities of all chalcone-based phenolic networks (NPPN) and p-hydroxybenzaldehyde polymer (PP) were also determined. The physical characteristics obtained from the I-V curve showed that the conductivity of phenolic polymers has a wide range from ultimately negligible values of 0.09 µS/cm up to 2.97 μS/cm. The degree of polarization of the conjugated system’s carbonyl group was attributed to high, low, or even no conductivity for all phenolic polymers since the electronic effects (inductive and mesomeric) could impact the polarization of the carbonyl group and, consequently, change the degree of the charge separation to show varied conductivity values. 相似文献
650.