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排序方式: 共有1687条查询结果,搜索用时 234 毫秒
101.
DongXiangLI WanGuoHOU ShuPingLI MingTuHAO GaoYongZHANG 《中国化学快报》2004,15(2):224-227
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations. 相似文献
102.
103.
In this study, activated carbon particles were magnetized by different amounts of maghemite in different temperatures using co-precipitation method and the resultant nanocomposite were modified with ethylenediaminetetraacetic acid (EDTA) to increase the permanganate contaminants adsorption capacity and to prevent degradation and oxidation of maghemite nanoparticles. Various properties of nanocomposite were investigated using different techniques including, vibrating sample magnetometer, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometer. Different kinetics, isotherms and thermodynamic models of adsorption process were investigated. Comparing data with kinetic models showed that the adsorption process complies with the pseudo-second-order kinetic model. The study of equilibrium isotherms data at different temperatures indicated that the adsorption process is more compatible with Langmuir model. Negative values of ΔG and positive values of ΔH revealed that adsorption process is spontaneous and endothermic. Response surface methodology was used to determine optimal parameters of an adsorbent dose of 1 g L−1, pH = 2 and initial permanganate concentration of 50 mg L−1, according to which, the maximum capacity of permanganate adsorption obtained under optimal conditions was 93.86 mg g−1. 相似文献
104.
基于氟钛配合物的原位水解以及硝酸镧电位滴定法建立了测定钛合金化铣腐蚀溶液中总氟化物浓度的新方法。在六次甲基四胺(HMTA)缓冲溶液中,氟钛配合物发生原位水解并释放出游离氟离子,以氟离子选择电极(F-ISE)为指示电极进行测定。对影响测定的各项参数(如p H值、HMTA溶液用量、钛离子浓度等)做了条件实验并予以优化。实验结果表明Ti(Ⅳ)浓度在0~20 g/L范围内对于氟离子测定无干扰,方法的相对标准偏差(RSDs,n=6)在0.27%~0.62%之间,加标回收率在99.5%~101.1%之间。此外,本文对氟钛配合物原位水解反应的机理也进行了探讨,溶液中氟钛配合物的主要存在形式为TiF_6~(2-),适宜的酸度是水解反应进行的必要条件,HMTA作为缓冲溶液为水解反应持续进行提供恒定的p H环境,La(NO_3)_3作为氟清除剂降低游离氟离子浓度促进水解反应的进行,伴随滴定过程氟钛配合物发生完全水解。 相似文献
105.
Novel Simultaneous Determination of Calcium and Magnesium Based on Flow Injection Gradient Titration
J. Kozak J. Paluch M. Kozak J. Kochana M. Wieczorek P. Kościelniak 《Analytical letters》2018,51(14):2157-2172
A novel approach based on flow injection gradient titration is proposed for the simultaneous spectrophotometric determination of Ca and Mg based on parameters of a single signal. Two reagents, calmagite and EDTA, are used to perform the determinations. Calmagite is introduced into a sample to form complexes with the analytes and the solutions are introduced into the holding coil of a sequential injection system in the sequence: carrier, air, sample, EDTA, and sample. In the system, EDTA replaces calmagite to form more stable complexes in turn with Ca and Mg. Next, the flow is reversed and the mixture is directed to the detector where the signal is measured at 680?nm. The signal consists of two parts: a short plateau (the signal for the sum of absorbance of complexes of Ca and Mg with calmagite) and a peak (the signal corresponding to titration of both complexes using EDTA). The absorbance values measured at the plateau and appropriately measured peak width were applied to determine analytes using two-component calibration. The method was verified for the determination of analytes in synthetic samples and in a certified reference material of surface water. Using the developed method, Mg and Ca were determined within the concentration ranges of 0.5–5.0 and 1.0–10.0?mg?L?1, with precision better than 2.2 and 4.2% (relative standard deviation) and accuracy of 7.0 and 6.8% (relative error). The detection limits were 0.1 and 0.3?mg?L?1 for Mg and Ca, respectively. The method was applied to analysis of mineral water samples. 相似文献
106.
以滴定管的教学为例,分析在实验仪器教学过程中,如何提高学生的学习效果,促进学生的思维能力发展。在实验仪器教学过程中,应该引入合适的教学情境,让学生结合自己的直接经验和科学发展过程,正确认识和使用实验仪器,实现思维能力的发展。 相似文献
107.
Carboxyl groups in pre-treated regenerated cellulose fibres 总被引:1,自引:1,他引:0
Lidija Fras Zemljič Zdenka Peršin Per Stenius Karin Stana Kleinschek 《Cellulose (London, England)》2008,15(5):681-690
The influence of peroxide bleaching and slack-mercerization on the amount of acidic groups in regenerated fibres (viscose,
modal and lyocell) were studied. Conductometric titration was used to determine the total content of acidic carboxylic groups.
Polyelectrolyte titration was used for surface and total charge determination, and to obtain information about the charge
distribution and accessibilities of charged groups. Changes in fibre crystallinity to pre-treatment processes were characterized
using iodine sorption (Schwertassek method) and correlated to treatments and the amount of carboxylic groups. For all three
types of fibres the amount of accessible carboxyl groups was lowered by an increase in the degree of crystallinity. Bleaching
with hydrogen peroxide causes some oxidative cellulose damage and, therefore, a larger amount of carboxyl groups (presumably
formed at the end of cellulose chains). Slack-mercerization did not significantly change the total amount of acidic groups
in the fibres, but their accessibility to cationic polyelectrolytes, in particular to polymers with high molecular weight
was substantially lowered.
Lidija Fras Zemljič, Zdenka Peršin, and Karin Stana Kleinschek are the members of the European Polysaccharide Network of Excellence
(EPNOE). 相似文献
108.
Lidija Fras Zemljič Per Stenius Janne Laine Karin Stana-Kleinschek 《Cellulose (London, England)》2008,15(2):315-321
Adsorption of carboxymethyl cellulose (CMC) as a method to introduce charged (ionizable) groups onto cellulose cotton fibre
surfaces was investigated. The method was based on application of a previously published method used for wood fibres. The
amount of adsorbed ionizable groups was determined indirectly by analysis of CMC in solution by the phenol–sulphuric acid
method and directly by conductometric titration of the fibres. Results from the two methods correlated well. The molecular
weight and purity of the CMC had an influence on its adsorption onto cotton; high molecular weight CMC was preferentially
adsorbed. The adsorbed charge correlated linearly with the amount of CMC adsorbed. The total charge of the cotton fibres could
be increased by more than 50% by adsorption of CMC. It is expected that this modification procedure can be used in a wide
spectrum of practical applications.
Lidija Fras Zemljič and Karin Stana-Kleinschek are the members of the European Polysaccharide Network of Excellence (EPNOE). 相似文献
109.
A versatile method for evaluation of equilibrium constants from automated spectrophotometric titrations is described. General algorithms were derived for normalized titration curves of reactions having various stoichiometric ratios. Normalization of data involve converting it from absorption versus time to product formed (0 to 1) versus equivalents of titrant added. Relevance of derived algorithms was assessed by the quality of their fit to real data. The demonstration system chosen for this investigation was the 1:3 complexation reaction of Fe(II) and 1,10-phenantroline (o-Phen). Titrations were performed at three distinct infusion rates under controlled pH of 5.0 and at 25.0 °C, with sets produced using both Fe(II) and o-Phen as the titrant. Direct fitting of titration curves yielded values for overall equilibrium constants. Furthermore, resulting curves revealed reproducible initial deviation, consistent with step-wise reaction, when titrating Fe(II) with o-Phen. No unusual deviations were evident anywhere in the titration curves when Fe(II) was the titrant. Overall, our approach facilitates adoption of automated titrimetry and data analysis methodologies for the determination of stoichiometries and equilibrium constants of many UV/Vis active reactions. 相似文献
110.
Up to now the content of the organic halides in sediments was measured as extractable organic halides compounds by different
methods including microcoulometric titration one. We describe a procedure for microcoulometric determination of total organic
halide pollutants by using a direct combustion of the sediments into the microcoulometric system furnace. An accelerated removal
of the inorganic chlorides by reaction with potassium nitrate using ultrasonic radiation was attained. The procedure was validated
for analysis of bottom sediments from natural and anthropogenic sources. The repeatability RSD = 8.5%, the expanded relative
uncertainty U (n = 7, P = 95%, k = 2) = 6.4%, the reproducibility RSD was within the range 10.0–7.3%, the average recovery R = 97.6% and method LOD = 11 mg kg−1 Cl.
Correspondence: Zara V. Aneva, Analytical Department, University “Prof. Dr. Assen Zlatarov”, Nr. 1 Prof. Yakimov street, 8010
Bourgas, Bulgaria 相似文献