全文获取类型
收费全文 | 1641篇 |
免费 | 83篇 |
国内免费 | 10篇 |
专业分类
化学 | 1242篇 |
晶体学 | 34篇 |
力学 | 44篇 |
数学 | 110篇 |
物理学 | 304篇 |
出版年
2024年 | 15篇 |
2023年 | 17篇 |
2022年 | 103篇 |
2021年 | 86篇 |
2020年 | 51篇 |
2019年 | 56篇 |
2018年 | 81篇 |
2017年 | 60篇 |
2016年 | 79篇 |
2015年 | 60篇 |
2014年 | 55篇 |
2013年 | 131篇 |
2012年 | 132篇 |
2011年 | 121篇 |
2010年 | 73篇 |
2009年 | 65篇 |
2008年 | 81篇 |
2007年 | 63篇 |
2006年 | 44篇 |
2005年 | 33篇 |
2004年 | 27篇 |
2003年 | 29篇 |
2002年 | 51篇 |
2001年 | 34篇 |
2000年 | 40篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1937年 | 2篇 |
排序方式: 共有1734条查询结果,搜索用时 15 毫秒
921.
Wan Aini Wan Ibrahim Aemi Syazwani Abdul Keyon Niki Prastomo Atsunori Matsuda 《Journal of Sol-Gel Science and Technology》2011,59(1):128-134
New inorganic–organic hybrid materials were synthesized by hydrolysis and condensation of cyanopropyltriethoxysilane (CNPrTEOS)
and polydimethylsiloxane (PDMS) in the presence of hydrochloric acid, HCl catalyst and methyl trimethylmethoxysilane as precursor
via sol–gel method and coated on glass encased stir bar for use in stir bar sorptive extraction (SBSE). The cyano part provides
polar moiety, which may improve the extraction of polar analytes. The physico-chemical properties and extraction ability of
PDMS-CNPrTEOS-derived hybrid coatings can be fine tuned via manipulation of solvents (tetrahydrofuran (THF)-based and dichloromethane
(DCM)-based) and PDMS-CNPrTEOS molar concentrations during the sol synthesis. Clear, homogeneous PDMS-CNPrTEOS-derived hybrid
sols were obtained using THF and DCM at optimized molar ratios. The optimized molar ratios of THF:CNPrTEOS and THF:PDMS were
5:1 and 25:1, respectively. The optimized molar ratios of DCM:CNPrTEOS and DCM:PDMS were 10:1 and 70:1, respectively. FTIR
spectrum showed that the intensity of the CN peak increased with increasing content of CNPrTEOS in the PDMS;CNPrTEOS-derived
hybrid. The Field Emission Scanning Electron micrographs of prepared coatings revealed smooth, homogenous surfaces and crack-free
coatings with film thickness of 200 nm to 2.5 μm attributing to different solvent types. All coatings prepared were thermally
stable at temperature higher than 200 °C. The DCM-based PDMS-CNPrTEOS-derived coating shows more advantages in terms of physical
characteristics and extraction ability compared to THF-based PDMS-CNPrTEOS-derived coatings due to higher cyano part content
and its thicker coating. The PDMS-CNPrTEOS-derived hybrid coatings can be used as extraction sorbent for analysis of non steroidal
anti-inflammatory drugs namely ketoprofen and diclofenac sodium in SBSE. 相似文献
922.
A parametric study of methane decomposition into carbon nanotubes over 8Co-2Mo/Al2O3 catalyst
下载免费PDF全文
![点击此处可从《天然气化学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The effects of reaction temperature, partial pressure of methane, catalyst weight and gas hourly space velocity (GHSV) on methane decomposition were reported. The decomposition reaction was performed in a vertical fixed-bed reactor over 8Co-2Mo/Al 2 O 3 catalyst. The experimental results show that these four process parameters studied had vital effects on carbon yield. As revealed by the electron microscopy and Raman spectroscopy analyses, the reaction temperature and GHSV governed the average diameter, the diameter distribution and the degree of graphitization of the synthesized carbon nanotubes (CNTs). Also, an evidence is presented to show that higher temperatures and higher GHSV favored the formation of better-graphitized CNTs with larger diameters. 相似文献
923.
A theoretical investigation has been carried out for electromagnetic waves scattering from a perfect electromagnetic conductor (PEMC) sphere which is placed in chiral media. The formulation of the problem is realized by expanding the incident as well as the scattered electromagnetic fields in terms of left circularly polarized (LCP) and right circularly polarized (RCP) waves. By applying the boundary conditions at the chiral-PEMC interface, eight simultaneous equations are generated, which yield the scattering coefficients associated with the Left and Right electromagnetic waves. The relative contribution of Co-polarized and Cross-polarized components of fields to the calculations of scattering cross-section is presented. The effect of admittance parameter and the effect of chirality parameter in cases of lossless, lossy permittivity and lossy permeability on Co and Cross components of scattering cross sections are observed. The results are also compared with available published literatures which are in good agreement. 相似文献
924.
Ravikumar Ramakrishnaiah Ghufran ur Rehman Santhosh Basavarajappa Abdulaziz Abdullah Al Khuraif B. H. Durgesh Abdul Samad Khan 《应用光谱学评论》2013,48(4):332-350
Abstract: Tooth enamel is the most mineralized tissue in the human body, and in this article the use of Raman spectroscopy for the analysis of tooth structure, a comparison with synthetic apatites, and use in dentistry are described. Spectral peaks that are related to dental hard and soft tissues are discussed, which provide crucial data in understanding the chemical structural properties of dentin and enamel. The Raman spectrum of dentin confirms the presence of crystalline phosphate-based minerals in dentin. Both dentin and enamel consist of two primary components: an inorganic or mineral phase that closely resembles hydroxyapatite and the Raman spectrum of dentin that confirms the presence of crystalline phosphate-based minerals in dentin. Hence, the mineral phase in dentin and enamel may be characterized essentially as nonstoichiometric substituted apatite. The presence of carbonate (A and B type) incorporated in the hydroxyapatite lattice is also confirmed by the presence of spectral bands. The organic phase, which is mainly composed of type I collagen, is confirmed by the spectral bands of amide I and amide II bands, tryptophan, and phenylalanine. Furthermore, these spectral bands associated with organic and inorganic parts of the enamel and dentin are useful in predicting early formation of carries formation. 相似文献
925.
Abstract: One of the emerging issues in herbal medicine is its authenticity. The substitution of highly valuable materials in herbal medicine with lower ones is common practice in the herbal medicine industry. This practice can cause serious effects or be harmful to human health; therefore, the authentication of herbal medicine using analytical techniques is necessary. Due to its capability as fingerprint technique, vibrational spectroscopy (infrared and Raman), especially in combination with several chemometrics techniques, is the method of choice for authentication purposes. This review highlights the use of mid-infrared, near-infrared, and Raman spectroscopy for authentication of herbal medicine, either in raw materials or in final products. 相似文献
926.
Jian Fuh Ong Ithnin Abdul Jalil Wan Ahmad Tajuddin Wan Abdullah 《International Journal of Theoretical Physics》2013,52(3):679-688
We study the $\overline{\nu}_{e}-e$ scattering from low to ultrahigh energy in the framework of Higgs Triplet Model (HTM). We add the contribution of charged Higgs boson exchange to the total cross section of the scattering. We obtain the upper bound $h_{ee}/M_{H^{\pm}}\lesssim2.8\times10^{-3}~\mbox{GeV}^{-1}$ in this process from low energy experiment. We show that by using the upper bound obtained, the charged Higgs contribution can give enhancements to the total cross section with respect to the SM prediction up to 5.16 % at E≤1014 eV and maximum at $s\approx M_{H^{\pm}}^{2}$ and would help to determine the feasibility experiments to discriminate between SM and HTM at current available facilities. 相似文献
927.
Md. Abdul Khan 《Few-Body Systems》2014,55(11):1125-1139
The energies of the low-lying bound S-states of some two-electron systems (treating them as three-body systems) like negatively charged hydrogen, neutral helium, positively charged-lithium, beryllium, carbon, oxygen, neon, argon and negatively charged muonium and exotic positronium ions have been calculated employing hyperspherical harmonics expansion method. The matrix elements of two-body interactions involve Raynal–Revai coefficients which are particularly essential for the numerical solution of three-body Schr?dinger equation when the two-body potentials are other from Coulomb or harmonic. The technique has been applied for to two-electron ions 1H? (Z = 1) to 40Ar16+ (Z = 18), negatively charged-muonium Mu? and exotic positronium ion Ps?(e + e ? e ?) considering purely Coulomb interaction. The available computer facility restricted reliable calculations up to 28 partial waves (i.e. K m = 28) and energies for higher K m have been obtained by applying an extrapolation scheme suggested by Schneider. 相似文献
928.
Niken Taufiqurrahmi Abdul Rahman Mohamed Subhash Bhatia 《Journal of nanoparticle research》2011,13(8):3177-3189
Nanocrystalline zeolites with crystal size smaller than 100 nm are potential replacement for conventional zeolite catalysts
due to their unique characteristics and advantages. In this study, the synthesis of nanocrystalline zeolite Y (FAU) and nanocrystalline
zeolite beta (BEA) under hydrothermal conditions is reported. The effect of crystal size on the physico-chemical characteristics
of the zeolite, Y (FAU), and beta (BEA) is reported. The properties of nanocrystalline zeolites Y and Beta with crystal size
around 50 nm are compared with the microcrystalline zeolite Y and microcrystalline zeolite beta, respectively. The performance
of the nanocrystalline zeolite as a catalyst was investigated in the cracking of used palm oil for the production of biofuel.
The nanocrystalline zeolite catalytic activity was compared with the activity of microcrystalline zeolite in order to study
the effect of crystal size on the catalytic activity. Both nanocrystalline zeolites gave better performance in terms of conversion
of used palm oil as well as selectivity for the formation of gasoline fraction. The increase in surface area and improved
accessibility of the reactant in nanocrystalline zeolites enhanced the cracking activity as well as the desired product selectivity. 相似文献
929.
This article presents the optical properties of Tb3+ in lead fluoroborate glasses of the type X PbF2·(89–X)B2O3·10 Al2O3·1Tb2O3 (where X=8, 12, 16, 20, 24, 28, 34 and 36). The standard Judd–Ofelt model was applied to the room temperature absorption intensities of Tb3+ (4 f8) to determine the phenomenological intensity parameters Ω2, Ω4 and Ω6. These parameters have been used to calculate radiative transition probabilities (Arad), lifetimes (τR) and branching ratios (βR) for the excited level 5D4. The predicted values of τR are compared with the measured values for 5D4 level for eight glass compositions (Glass (A–H)). Among the eight-terbium glasses Glass A with 8 mol% of PbF2 (as the optimum content) has revealed an intense green emission with maximum life time and higher quantum efficiency. The stimulated emission cross section σ(λP) is also evaluated for the 5D4→7FJ (J=6, 5, 4 and 3) transitions. 相似文献
930.
Bushra Nisar Syeda Laila Rubab Abdul Rauf Raza Sobia Tariq Ayesha Sultan Muhammad Nawaz Tahir 《Molecular diversity》2018,22(3):709-722
Novel and highly sensitive indole-based imines have been synthesized. Their synthesis has been compared employing a variety of protocols. Ultimately, a convenient, economical and high yielding set of conditions employing green chemistry have been designed for their synthesis. 相似文献