全文获取类型
收费全文 | 752篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
化学 | 498篇 |
晶体学 | 6篇 |
力学 | 36篇 |
数学 | 62篇 |
物理学 | 192篇 |
出版年
2024年 | 6篇 |
2023年 | 3篇 |
2022年 | 32篇 |
2021年 | 30篇 |
2020年 | 23篇 |
2019年 | 15篇 |
2018年 | 26篇 |
2017年 | 22篇 |
2016年 | 39篇 |
2015年 | 42篇 |
2014年 | 35篇 |
2013年 | 55篇 |
2012年 | 49篇 |
2011年 | 52篇 |
2010年 | 34篇 |
2009年 | 34篇 |
2008年 | 30篇 |
2007年 | 28篇 |
2006年 | 19篇 |
2005年 | 17篇 |
2004年 | 15篇 |
2003年 | 22篇 |
2002年 | 12篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有794条查询结果,搜索用时 15 毫秒
71.
Tin dioxide (SnO2) nanoparticles having 3 nm size were synthesized by irradiating pure tin metal using high power Nd:YAG laser in deionized water. Formation of nano-SnO2 crystallites was confirmed by X-ray diffraction (XRD) and AFM study. UV-vis absorption spectral studies showed a peak at 240 nm. FTIR spectrum showed a band in the range of 400-700 cm−1 which was assigned to Sn-O antisymmetric vibrations. Photoluminescence spectrum of synthesized SnO2 nanoparticles showed peak corresponding to 3.175, 2.901 and 2.613 eV respectively. 相似文献
72.
Y Nakai A el-Said Aboutaleb K Yamamoto S I Saleh M O Ahmed 《Chemical & pharmaceutical bulletin》1990,38(3):728-732
Inclusion complexes of clobazam with alpha-, beta-, gamma-cyclodextrins (CyDs) and heptakis(2.6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD) in aqueous solution and in the solid phase were studied by the solubility method, infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and X-ray diffractometry. In addition, inclusion complex of clobazam with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin and the solid dispersion of clobazam with methyl cellulose (MC) in a ground mixture were investigated by IR, DSC and X-ray diffractometry. It was observed that DM-beta-CyD had the highest stability constant among the four CyDs in solution. Thermal and X-ray diffraction analyses showed that clobazam molecules existed in a molecularly dispersed state in the ground mixture of CyDs. Infrared spectra showed lower frequency shifts in the case of the ground mixtures of clobazam with natural CyDs, which can be attributed to the formation of hydrogen bonds between the two carbonyl groups of clobazam and hydroxyl groups of natural CyDs. In contrast, higher frequency shifts were observed in the case of the ground mixtures of clobazam with methylated CyDs and MC and these were considered to be due to the monomolecular dispersion of clobazam in a hydrophobic environment. The mode of interaction of clobazam with DM-beta-CyD was different from that with natural CyDs in the ground mixtures. Furthermore, the crystalline inclusion complex of clobazam with DM-beta-CyD was obtained by heating of the coprecipitate in vacuo at 120 degrees C for 1 h. 相似文献
73.
74.
Innus Mohammad JiYoung Mun Amber Onorato Martha D. Morton Abdullah I. Saleh Michael B. Smith 《Tetrahedron letters》2017,58(44):4162-4165
When compared to a long-straight chain terminal alkyne, a long chain terminal alkyne with a distal isopropyl unit (isobranched) isomerizes about two times faster when treated with strong base under identical conditions, and appears to follow pseudo first order kinetics. In both cases, equilibration to a 95–97:5–3 mixture of terminal:internal alkyne accompanies isomerization. The difference in rate may be due to an unusual folding of both long-chain alkynes, bringing the distal substituent close to the carbon-carbon-triple bond moiety. The distal isopropyl moiety may provide unanticipated steric hindrance that disrupts such folding, making the propargylic proton more available for reaction with base. 相似文献
75.
Three sorbent materials (A18C6-MS, DA18C6-MS and AB18C6-MS) based on the crown ether ligands, 1-aza-18-crown-6, 1,4,10,13-tetraoxa-7,16-diazacyclo octadecane and 4′-aminobenzo-18-crown-6, respectively, were prepared by the chemical immobilization of the ligand onto mesoporous silica support. The sorbents were characterized by FT-IR, scanning electron microscopy-energy dispersive X-ray microanalysis, elemental analysis and nitrogen adsorption-desorption test. The applicability of the sorbents for the extraction of biogenic amines by the batch sorption method was extensively studied and evaluated as a function of pH, biogenic amines concentration, contact time and reusability. Under the optimized conditions, all the sorbents exhibited highest selectivity toward spermidine (SPD) compared to other biogenic amines (tryptamine, putrescine, histamine and tyramine). Among the sorbents, AB18C6-MS offer the highest capacity and best selectivity towards SPD in the presence of other biogenic amines. The AB18C6-MS sorbent can be repeatedly used three times as there was no significant degradation in the extraction of the biogenic amines (%E > 85). The optimized procedure was successfully applied for the separation of SPD in food samples prior to the reversed-phase high performance liquid chromatography separation. 相似文献
76.
Saleh Ahmed Mohamed Ehab A. Drees Mohamed O. El-Badry Afaf S. Fahmy 《Applied biochemistry and biotechnology》2010,160(7):2054-2065
α-Amylase activity was screened in the peel, as waste fruit, of 13 species and cultivars of Egyptian citrus. The species Citrus sinensis cv. Abosora had the highest activity. α-Amylase AI from Abosora peel was purified to homogeneity using anion and cation-exchange,
and gel filtration chromatographies. Molecular weight of α-amylase AI was found to be 42 kDa. The hydrolysis properties of
α-amylase AI toward different substrates indicated that corn starch is the best substrate. The α-amylase had the highest activity
toward glycogen compared with amylopectin and dextrin. Potato starch had low affinity toward α-amylase AI but it did not hydrolyze
β-cyclodextrin and dextran. Apparent Km for α-amylase AI was 5 mg (0.5%) starch/ml. α-Amylase AI showed optimum activity at
pH 5.6 and 40 °C. The enzyme was thermally stable up to 40 °C and inactivated at 70 °C. The effect of mono and divalent metal
ions were tested for the α-amylase AI. Ba2+ was found to have activating effect, where as Li+ had negligible effect on activity. The other metals caused inhibition effect. Activity of the α-amylase AI was increased
one and half in the presence of 4 mM Ca2+ and was found to be partially inactivated at 10 mM Ca2+. The reduction of starch viscosity indicated that the enzyme is endoamylase. The results suggested that, in addition to citrus
peel is a rich source of pectins and flavanoids, α-amylase AI from orange peel could be involved in the development and ripening
of citrus fruit and may be used for juice processing. 相似文献
77.
Sayed M. Saleh Rainer Müller Heike S. Mader Axel Duerkop Otto S. Wolfbeis 《Analytical and bioanalytical chemistry》2010,398(4):1615-1623
Fluorescent silica nanoparticles (SiNPs) were prepared by covalent attachment of fluorophores to the amino-modified surface
of SiNPs with a typical diameter of 15 nm. The SiNPs are intended for use in novel kinds of fluorescence resonance energy
transfer (FRET)-based affinity assays at the interface between nanoparticle and sample solution. Various labels were employed
to obtain a complete set of colored SiNPs, with excitation maxima ranging from 337 to 659 nm and emission maxima ranging from
436 nm to the near infrared (710 nm). The nanoparticles were characterized in terms of size and composition using transmission
electron microscopy, thermogravimetry, elemental analysis, and dynamic light scattering. The surface of the fluorescent SiNPs
was biotinylated, and binding of labeled avidin to the surface was studied via FRET in two model cases. In the first, FRET
occurs from the biotinylated fluorescent SiNP (the donor) to the labeled avidin (the acceptor). In the second, FRET occurs
in the other direction. Aside from its use in the biotin–avidin system, such SiNPs also are believed to be generally useful
fluorescent markers in various kinds of FRET assays, not the least because the fluorophore is located on the surface of the
SiNPs (and thus always much closer to the second fluorophore) rather than being doped deep in its interior. 相似文献
78.
M. Faraji Y. Yamini E. Tahmasebi A. Saleh F. Nourmohammadian 《Journal of the Iranian Chemical Society》2010,7(2):S130-S144
The utilization of modified magnetite nanoparticles (Fe3O4 NPs) with a cationic surfactant (cetyltrimethylammonium bromide (CTAB)) as an efficient adsorbent was successfully carried out to remove reactive black 5 (RBBA), reactive red 198 (RRR) and reactive blue 21 (RTB) dyes from aqueous solutions. First, a reactor was designed to be simple, repeatable and efficient in its synthesis of Fe3O4 NPs via co-precipitation method. Then, an orthogonal array design (OAD), four factor-four level (44) matrix was applied to assign affecting factors on removing of the dyes from aqueous solutions. The obtained results from ANOVA showed that the amount of CTAB and NaCl% significantly affect the adsorption of RBBA, RRR and RTB dyes. The sorption kinetics of the dyes were best described by a second-order kinetic model, suggesting chemisorptions mechanism. Also, dye adsorption equilibrium state data were fitted well to the Langmuir isotherm rather than Freundlich isotherm. Also, the maximum monolayer capacity, qmax, obtained from the Langmuir was 312.5, 163.9 and 556.2 mg g-1 for RBBA, RRR and RTB, respectively. The obtained results in the present study indicated that the CTAB-coated Fe3O4 NPs can be an efficient adsorbent material for removal of reactive dyes form aqueous solutions. 相似文献
79.
Ahmed F. Saleh Mazin M. Elias Nada F. Tawfiq 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(1):187-193
Precise determination of uranium concentration in human urine is quite important in assessment of occupational and public exposure to uranium. In the present work, a pulsed dye nitrogen laser-induced kinetic phosphorescence analysis (KPA) was used to determine uranium in urine of Iraqi phosphate mine and fertilizer plant workers and in the population living near the mining region. A total of 92 urine samples were collected from workers of the Akashat phosphate mine, the Al-Qaim fertilizer complex, and the Akashat residential region. Uranium concentration in urine of all samples ranged between 0.49 to 5.26 μg L?1 with a total average of 1.47 ± 0.01 μg L?1. For comparison, all samples were also analyzed using a completely different technique; the nuclear fission track analysis using CR-39 SSNTD. Both techniques were capable of such measurements, although not with an equal degree of uncertainty. KPA technique is found to be more suitable for analysis of urine samples having high concentrations of uranium. 相似文献
80.
Alqasoumi Saleh I. Alam Prawez Al-Rehaily Adnan J. Shakeel Faiyaz Abdel-Kader Maged S. 《平面色谱法杂志一现代薄层色谱法》2011,24(1):48-52
JPC – Journal of Planar Chromatography – Modern TLC - A densitometric high-performance thin-layer chromatographic (HPTLC) method for analysis of hydroquinone has been developed and... 相似文献