全文获取类型
收费全文 | 2506篇 |
免费 | 97篇 |
国内免费 | 23篇 |
专业分类
化学 | 1662篇 |
晶体学 | 25篇 |
力学 | 109篇 |
综合类 | 1篇 |
数学 | 257篇 |
物理学 | 316篇 |
无线电 | 256篇 |
出版年
2024年 | 6篇 |
2023年 | 18篇 |
2022年 | 154篇 |
2021年 | 115篇 |
2020年 | 69篇 |
2019年 | 75篇 |
2018年 | 75篇 |
2017年 | 63篇 |
2016年 | 118篇 |
2015年 | 76篇 |
2014年 | 91篇 |
2013年 | 217篇 |
2012年 | 155篇 |
2011年 | 161篇 |
2010年 | 95篇 |
2009年 | 79篇 |
2008年 | 87篇 |
2007年 | 97篇 |
2006年 | 81篇 |
2005年 | 61篇 |
2004年 | 57篇 |
2003年 | 65篇 |
2002年 | 67篇 |
2001年 | 43篇 |
2000年 | 51篇 |
1999年 | 24篇 |
1998年 | 25篇 |
1997年 | 19篇 |
1996年 | 27篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 23篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 21篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1975年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有2626条查询结果,搜索用时 31 毫秒
71.
Ibrahim A. Darwish Abdul-Rahman M. Al-Obaid Hamoud A. Al-Malaq 《Mikrochimica acta》2010,170(1-2):67-74
This study describes the development and validation of a highly sensitive and specific enzyme immunoassay (EIA) for therapeutic monitoring and pharmacokinetic studies of atorvastatin (ATR). The assay employs a polyclonal antibody that recognizes ATR with high specificity and affinity, and ATR conjugated to bovine serum albumin (ATR-BSA) immobilized onto microwell plates as a solid phase. The assay involved a competitive binding reaction between ATR and the immobilized ATR-BSA for the binding sites on a limiting amount of the anti-ATR antibody. The bound anti-ATR antibody was quantified with horseradish peroxidase-labeled anti-immunoglobulin secondary antibody and 3,3′,5,5′-tetramethylbenzidine as a substrate for the peroxidase enzyme. The concentration of ATR in the sample was quantified by its ability to inhibit the binding of the anti-ATR antibody to the immobilized ATR-BSA and subsequent color development in the assay wells. The conditions for the EIA were investigated and optimized for the determination of ATR in plasma samples. The limit of detection was 0.04 ng mL?1 and the effective working range at relative standard deviations (RSD) of ≤5% was 0.1–10 ng mL?1. Mean analytical recovery of ATR from spiked plasma was 99.3?±?2.8%. The precision of the assay was satisfactory; RSD were 2.7–4.6 and 3.3–5.7% for intra- and inter-assay precision, respectively. The reliability of the EIA was confirmed by HPLC. The EIA is convenient, and one can analyze ~ 200 samples per working day, facilitating the processing of large-number of samples of ATR. 相似文献
72.
Ibrahim MS 《Fresenius' Journal of Analytical Chemistry》2000,367(2):189-194
The electrochemical behavior of lumazine (LMZ), an important antibacterial agent, has been studied at the hanging mercury drop electrode (HMDE). The nature of the process taking place at the HMDE was clarified. Its adsorption behavior at HMDE has been studied by using a.c and cyclic voltammetry (CV). Both the molecule and its reduced product appeared to be adsorbed at the surface of the electrode. Controlled adsorptive accumulation of LMZ on the HMDE provides the basis for the direct stripping measurement of that compound in the subnanomolar concentration level. Experimental and instrumental parameters for the quantitative determination were optimized. Phase-selective a.c voltammetry provided the best signal and gave a detection limit of 0.15 microg L(-1) (9.0 x 10(-10) mol/L) LMZ in aqueous solution. Molecules or ions which may interfere were studied. 相似文献
73.
The kinetics of H2O2 decomposition have been investigated using ZrO2 supported with transition metal ions including CuII, AgI, HgII, CoII, MnII, NiII and FeIII. At pH = 6.8, the reaction rate exhibits a first order dependence on the initial H2O2 concentration at low concentrations. The order of activity of the different catalysts is strongly dependent on the [H2O2]0 used. The reaction proceed via the formation of the peroxo-intermediate which has an inhibiting effect on the reaction rate. The rate increases with increasing pH, and attains a limiting rate at higher pH's. A reaction mechanism is proposed involving liberation of HO2 radicals from the peroxo-intermediate as the rate-determining step. 相似文献
74.
Organoiron thio- and seleno-terephthaloyl chloride complexes CpFe(CO)2ECO(C6H4)COCl (E = S and Se) react with NaOH and NaNH2 to give quantitative yields of the acid Cp(CO)2ECO(C6H4)CO2H and the amide CpFe(CO)2ECO(C6H4)CONH2 respectively. These amide and acid derivatives react with the terephthaloyl chloride complexes to give a new series of imide-bridged
[CpFe(CO)2ECO(C6H4)CO]2NH and anhydride-bridged [CpFe(CO)2ECO(C6H4)CO]2O organoiron dinuclear homo and hetero dichalcogeno terephthalate complexes. The complexes were characterized by elemental
analysis, i.r. and 1H-n.m.r. spectra.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
75.
Emad A. Jaffar Al-Mulla Nor Azowa Bt Ibrahim Kamyar Shameli Mansor Bin Ahmad Wan Md. Zin Wan Yunus 《Research on Chemical Intermediates》2013,39(3):1313-1321
In this study, fatty amides (FAs) synthesized from palm olein were used to extract and separate Mo(VI) from acidic media. Effects of various parameters upon the separation of Mo(VI) from Co(II), Ni(II), Al(III) and Mn(II), including extractant concentration, metal ion concentration, contact time, diluent, and acidity, were investigated. It was found that Mo(VI) was successfully separated from the above commonly associated metal ions by stripping from the loaded organic phase. Different acidic and alkaline solutions were used. Ammonium hydroxide solution was an optimal. Extraction of Mo(VI) into the organic phase involved the formation of 1:3 complexes. This work presents the development of a low-cost and environmentally friendly extractant to recycle and recover molybdenum. 相似文献
76.
I. A. Alnour H. Wagiran N. Ibrahim S. Hamzah B. S. Wee M. S. Elias J. A. Karim 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(3):1231-1237
In standardization NAA, it is necessary to characterize the neutron spectrum parameters such as epithermal neutron flux shape factor (α), thermal to epithermal neutron flux ratio (f), thermal neutron flux (φ th) and epithermal neutron flux (φ epi) in the irradiation facility to determine the concentration of an element in the sample using absolute and k 0 standardization methods. The α and f were determined using Cd-ratio multi monitor method using experimental data obtained in PUSPATI TRIGA Mark II research reactor at four irradiation positions (10, 20, 30 and 40) of the rotary rack. The calculated values of α and f ranged from 0.006 to 0.0281 and 18.56 to 19.12 respectively. The average values of φ th and φ epi were found as 2.33 × 1012 and 1.23 × 1011 n cm?2 s?1 respectively. Moreover, a comparison of the neutron flux parameters in the present study shows an acceptable level of consistency with those of previous studies. 相似文献
77.
Sazlinda Kamaruzaman Peter C. Hauser Mohd Marsin Sanagi Wan Aini Wan Ibrahim Salasiah Endud Hong Heng See 《Analytica chimica acta》2013
A simple adsorption/desorption procedure using a mixed matrix membrane (MMM) as extraction medium is demonstrated as a new miniaturized sample pretreatment and preconcentration technique. Reversed-phase particles namely polymeric bonded octadecyl (C18) was incorporated through dispersion in a cellulose triacetate (CTA) polymer matrix to form a C18-MMM. Non-steroidal anti-inflammatory drugs (NSAIDs) namely diclofenac, mefenamic acid and ibuprofen present in the environmental water samples were selected as targeted model analytes. The extraction setup is simple by dipping a small piece of C18-MMM (7 mm × 7 mm) in a stirred 10 mL sample solution for analyte adsorption process. The entrapped analyte within the membrane was then desorbed into 100 μL of methanol by ultrasonication prior to high performance liquid chromatography (HPLC) analysis. Each membrane was discarded after single use to avoid any analyte carry-over effect. Several important parameters, such as effect of sample pH, salting-out effect, sample volume, extraction time, desorption solvent and desorption time were comprehensively optimized. The C18-MMM demonstrated high affinity for NSAIDs spiked in tap and river water with relative recoveries ranging from 92 to 100% and good reproducibility with relative standard deviations between 1.1 and 5.5% (n = 9). The overall results obtained were found comparable against conventional solid phase extraction (SPE) using cartridge packed with identical C18 adsorbent. 相似文献
78.
Moamen S. Refat Gehad G. Mohamed Mohamed Y. S. Ibrahim Hamada M. A. Killa Hammad Fetooh 《Russian Journal of General Chemistry》2013,83(12):2479-2487
Solid complexes have been prepared and characterized by IR, UV-Vis, elemental analysis, and 1H NMR. Indomethacin forms complexes with Cd(II), Ce(III), and Th(IV) ions in molar ratios (ligand: metal) (2: 1), (3: 1), and (4: 1), respectively. The IR spectra of the complexes suggest that the Indomethacin behaves as a monobasic monodentate ligand coordinated to the metal ions via the deprotonated carboxylate group. Prepared complexes exhibit higher antimicrobial activity against several microorganisms, compared to free ligand. 相似文献
79.
1-(2-pyridylazo) 2-naphtol (PAN) impregnated Ambersorb 563 resin was used as solid phase extractor of copper, nickel, cadmium, lead, chromium and cobalt ions in aqueous solutions prior to their atomic absorption spectrometric determinations. The parameters including pH, sample volume, matrix effects were also investigated. The relative standard deviation (R.S.D.) of the combined method of sample treatment, preconcentration and determination with atomic absorption spectrometry is generally lower than 10%. The limit of detection was between 0.21 and 1.4 μg l−1. The results were used for preconcentration of analyte ions from natural water samples. The method was also applied to a stream sediment standard reference material (GBW7309) for the determination of Cu, Ni, Cd, Pb, Cr and Co. 相似文献
80.
Ibrahim O. Mohamed 《Applied biochemistry and biotechnology》2013,171(3):655-666
Cocoa butter equivalent (CBE) was prepared by enzymatic acidolysis reaction of substrate consisting of refined palm mid fraction oil and palmitic–stearic fatty acid mixture. The reactions were performed in a batch reactor at a temperature of 60 °C in an orbital shaker operated at 160 RPM. Different mass ratios of substrates were explored, and the composition of the five major triacylglycerols (TAGs) of the structured lipids was identified and quantified using cocoa butter certified reference material IRMM-801. The reaction resulted in production of cocoa butter equivalent with the TAGs' composition (1,3-dipalmitoyl-2-oleoyl-glycerol 30.7 %, 1-palmitoyl-2-oleoyl-3-stearoyl-rac-glycerol 40.1%, 1-palmitoy-2,3- dioleoyl glycerol 9.0 %, 1,3-distearoyl-2-oleoyl-glycerol 14.5 %, and 1-stearoyl-2,3-dioleoyl glycerol 5.7 %) and with onset melting temperature of 31.6 °C and peak temperature of 40.4 °C which are close to those of cocoa butter. The proposed kinetics model for the acidolysis reaction presented the experimental data very well. The results of this research showed that palm mid fraction oil TAGs could be restructured to produce value added product such as CBE. 相似文献