全文获取类型
收费全文 | 791篇 |
免费 | 34篇 |
国内免费 | 5篇 |
专业分类
化学 | 730篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 54篇 |
物理学 | 43篇 |
出版年
2023年 | 4篇 |
2022年 | 26篇 |
2021年 | 32篇 |
2020年 | 23篇 |
2019年 | 26篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 26篇 |
2015年 | 38篇 |
2014年 | 25篇 |
2013年 | 49篇 |
2012年 | 62篇 |
2011年 | 71篇 |
2010年 | 51篇 |
2009年 | 36篇 |
2008年 | 56篇 |
2007年 | 60篇 |
2006年 | 45篇 |
2005年 | 53篇 |
2004年 | 33篇 |
2003年 | 31篇 |
2002年 | 20篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有830条查询结果,搜索用时 0 毫秒
121.
Carolina Fernandez-Gonzalez Antonio Dominguez-Ramos Raquel Ibañez Angel Irabien 《Separation & Purification Reviews》2016,45(4):275-287
Several industrial processes, such as desalination or neutralization, generate brines defined as concentrated solutions of salts in water, usually NaCl, typically discharged in the vicinities of the desalination plant or factory. To reduce the environmental impact and promote the valorization of the wasted resources, alternatives must be sought. Among sustainable alternatives for the recovery of brines, the possibility of using Electrodialysis with Bipolar Membranes (EDBM) is of interest, because it allows recovering brines as useful acids and bases. This review focuses on the discussion of the technical aspects of the EDBM as a means to treat streams rich in NaCl from reverse osmosis desalination and industrial processes in order to complete the direct delivery of chemicals for self-supply. The main environmental issues associated with desalination brine disposal are presented. The state-of-the-art of valorization of brines by EDBM to acids and bases is completed. This work concludes with an in-depth discussion of the technical, techno-economic and economic barriers that prevent the widespread use of EDBM technology. 相似文献
122.
Muñiz-Valencia R Gonzalo-Lumbreras R Santos-Montes A Izquierdo-Hornillos R 《Journal of separation science》2007,30(17):2950-2957
A LC method for corticosteroids (CC) determination in poultry feed using a Chromolith column and UV detection has been developed and validated. The method development involved the optimization of different hydro-organic mobile phases using methanol or ACN as organic modifiers, flow rate, and temperature. The optimum separation was achieved at 40 degrees C using ACN/water (21:79 v/v) as mobile phase and 3 mL/min flow rate, allowing the separation to baseline of four out of seven CC in about 10 min. Prior to LC, a sample preparation procedure previously assayed for anabolics was used. It includes a leaching process, saponification of the esters from fatty acids, and SPE. Method validation was carried out according to the EU criteria established for quantitative screening methods. The extraction efficiencies, decision limits (CCalpha), and detection capabilities (CCbeta) for these compounds were in the ranges of 86-92%, 27-36 microg/kg, and 33-43 microg/kg, respectively. The repeatability and the within-laboratory reproducibility at 1, 1.5, and 2 CCbeta concentration levels were smaller than 9.0, 5.0, and 4.2% and 9.4, 6.4, and 4.9%, respectively. The CV values of the robustness test were less than 3.8% and the accuracy was in the range of 98-103%. The proposed method was applied to other feed with satisfactory results. 相似文献
123.
Ito FM Petroni JM de Lima DP Beatriz A Marques MR de Moraes MO Costa-Lotufo LV Montenegro RC Magalhães HI Pessoa Cdo O 《Molecules (Basel, Switzerland)》2007,12(2):271-282
Part of our research program concentrates on the discovery of new bioactive compounds prepared either by total synthesis or molecular transformation of compounds with bioactivity profiles. In this work we have focused our interest on chemical transformations of the Diels-Alder adduct tricyclo[6.2.1.0(2,7)]undeca-4,9-dien-3,6-dione in order to obtain cage-like compounds and derivatives, followed by an evaluation of their biological activity. 相似文献
124.
The fine-tuning of the enzymatic hydrolysis of proteins may provide a pool of peptides with predefined molar mass distributions. However, the complex mixture of molecules (peptides and amino acids) that results after the proteolysis of cheese whey turns unfeasible the assessment of individual species. In this work, a hybrid kinetic model for the proteolysis of whey by alcalase, multipoint-immobilized on agarose, is presented, which takes into account the influence of pH (8.0-10.4) and temperature (40-55 degrees C) on the activity of the enzyme. Five ranges of peptides' molar mass have their reaction rates predicted by neural networks (NNs). The output of NNs trained for constant pH and temperatures was interpolated, instead of including these variables in the input vector of a larger NN. Thus, the model complexity was reduced. Coupled to differential mass balances, this hybrid model can be employed for the online inference of peptides' molar mass distributions. Experimental kinetic assays were carried out using a pH-stat, in a laboratory-scale (0.03 L) batch reactor. The neural-kinetic model was integrated to a supervisory system of a bench-scale continually stirred tank reactor (0.5 L), providing accurate predictions during validation tests. 相似文献
125.
126.
Ali I. M. Ibrahim Balqis Ikhmais Elisabet Batlle Waed K. AbuHarb Vibhu Jha Khaled T. Jaradat Rafael Jimnez Raquel Pequerul Xavier Pars Jaume Farrs Klaus Pors 《Molecules (Basel, Switzerland)》2021,26(19)
Aldehyde dehydrogenase 1A3 (ALDH1A3) has recently gained attention from researchers in the cancer field. Several studies have reported ALDH1A3 overexpression in different cancer types, which has been found to correlate with poor treatment recovery. Therefore, finding selective inhibitors against ALDH1A3 could result in new treatment options for cancer treatment. In this study, ALDH1A3-selective candidates were designed based on the physiological substrate resemblance, synthesized and investigated for ALDH1A1, ALDH1A3 and ALDH3A1 selectivity and cytotoxicity using ALDH-positive A549 and ALDH-negative H1299 cells. Two compounds (ABMM-15 and ABMM-16), with a benzyloxybenzaldehyde scaffold, were found to be the most potent and selective inhibitors for ALDH1A3, with IC50 values of 0.23 and 1.29 µM, respectively. The results also show no significant cytotoxicity for ABMM-15 and ABMM-16 on either cell line. However, a few other candidates (ABMM-6, ABMM-24, ABMM-32) showed considerable cytotoxicity on H1299 cells, when compared to A549 cells, with IC50 values of 14.0, 13.7 and 13.0 µM, respectively. The computational study supported the experimental results and suggested a good binding for ABMM-15 and ABMM-16 to the ALDH1A3 isoform. From the obtained results, it can be concluded that benzyloxybenzaldehyde might be considered a promising scaffold for further drug discovery aimed at exploiting ALDH1A3 for therapeutic intervention. 相似文献
127.
Francisca T. S. M. Ferreira Raquel B. R. Mesquita Antnio O. S. S. Rangel 《Molecules (Basel, Switzerland)》2021,26(21)
In this work, the design of a microfluidic paper-based analytical device (μPAD) for the quantification of nitrate in urine samples was described. Nitrate monitoring is highly relevant due to its association to some diseases and health conditions. The nitrate determination was achieved by combining the selectivity of the nitrate reductase enzymatic reaction with the colorimetric detection of nitrite by the well-known Griess reagent. For the optimization of the nitrate determination μPAD, several variables associated with the design and construction of the device were studied. Furthermore, the interference of the urine matrix was evaluated, and stability studies were performed, under different conditions. The developed μPAD enabled us to obtain a limit of detection of 0.04 mM, a limit of quantification of 0.14 mM and a dynamic concentration range of 0.14–1.0 mM. The designed μPAD proved to be stable for 24 h when stored at room temperature in air or vacuum atmosphere, and 60 days when stored in vacuum at −20 °C. The accuracy of the nitrate μPAD measurements was confirmed by analyzing four certified samples (prepared in synthetic urine) and performing recovery studies using urine samples. 相似文献
128.
129.
Yesenia Mendoza García Ana Luiza Coeli Cruz Ramos Afonso Henrique de Oliveira Júnior Ana Cardoso Clemente Filha Ferreira de Paula Angelita Cristine de Melo Moacir Alves Andrino Mauro Ramalho Silva Rodinei Augusti Raquel Linhares Bello de Araújo Eurico Eduardo Pinto de Lemos Júlio Onsio Ferreira Melo 《Molecules (Basel, Switzerland)》2021,26(23)
Myrciaria floribunda, also known as rumberry, is a tree native to the Brazilian Atlantic Forest, where its fruits have the potential for commercial use. This study evaluates the antioxidant potential, determines the phytochemical profile, and chemically characterizes the rumberry fruit. Accessions were sampled from the Rumberry Active Germplasm Bank of the Federal University of Alagoas, Brazil. Physical characteristics, chemical characteristics, and phenolic compound content were analyzed. Chemical profile characterization was carried out using PSMS. Accessions had an average weight of 0.86 g. Accession AC137 presented a higher pulp yield (1.12 g). AC132 and AC156 had larger fruits, AC137 showed greater firmness (5.93 N), and AC160 had a higher and total phenolic content ratio (279.01 ± 11.11). Orange-colored accessions scored higher in evaluated parameters, except for AC160 for phenolic content. Thirty-two compounds were identified on positive ionization mode and 42 compounds on negative ionization mode using PSMS. Flavonoids, followed by the derivatives of benzoic acid, sugars, and phenylpropanoids, were the most prominent. Myricitrin, quercitrin, and catechin stand out as flavonoids that have been reported in previous studies with antioxidant and antimicrobial properties, in addition to health and therapeutical benefits, demonstrating the potential of the rumberry fruit. 相似文献
130.