全文获取类型
收费全文 | 3276篇 |
免费 | 140篇 |
国内免费 | 10篇 |
专业分类
化学 | 2594篇 |
晶体学 | 8篇 |
力学 | 61篇 |
数学 | 435篇 |
物理学 | 328篇 |
出版年
2023年 | 25篇 |
2022年 | 86篇 |
2021年 | 129篇 |
2020年 | 86篇 |
2019年 | 93篇 |
2018年 | 65篇 |
2017年 | 29篇 |
2016年 | 118篇 |
2015年 | 106篇 |
2014年 | 136篇 |
2013年 | 224篇 |
2012年 | 238篇 |
2011年 | 279篇 |
2010年 | 168篇 |
2009年 | 168篇 |
2008年 | 247篇 |
2007年 | 193篇 |
2006年 | 180篇 |
2005年 | 181篇 |
2004年 | 141篇 |
2003年 | 118篇 |
2002年 | 108篇 |
2001年 | 32篇 |
2000年 | 31篇 |
1999年 | 19篇 |
1998年 | 19篇 |
1997年 | 26篇 |
1996年 | 22篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有3426条查询结果,搜索用时 15 毫秒
101.
A model-based sensitivity analysis was performed in order to evaluate the importance of the individual operating parameters of a three-phase fluidised-bed biological reactor used for removing mercury ions from wastewater. The parameters analysed involve the immobilised biomass load (bacteria P. putida) on alginate beads, particle size, inlet flow-rate, mercury ion loads in the fed wastewater, and the solid fraction in the reactor. Predictions were generated by using pseudo-first-order, Michaelis-Menten, or pseudo-Haldane kinetic models. The results highlight the major influence of the biomass/solid load and of the liquid residence time on the reactor efficiency. Also, the resultant significant differences in the model predictions underline the importance of using a more accurate kinetic model for process design and control purposes. 相似文献
102.
E. Manuela Garrido Josél Costa Lima Cristina M. Delerue-matos Ana Maria Oliveira Brett 《International journal of environmental analytical chemistry》2013,93(1-2):149-157
Abstract Cyclic, differential pulse and square wave voltammetry were applied to develop an electroanalytical procedure for the determination of a group of herbicides used to treat rice crops: molinate, bensul-ruron-methyl, mefenacet and thiobencarb. The oxidation mechanism causes adsorption problems and consequent poisoning of the electrode surface by the products of the electrochemical reaction. Parameters such as pH, frequency and electrochemical electrode surface treatment were optimized. The analytical methodology developed using square wave voltammetry was applied to the determination of molinate and bensulfuron-methyl in simple or mixed commercial products. 相似文献
103.
Tilde De Caro Cristina Riccucci Erica I. Parisi Federica Faraldi D. Caschera 《Applied Physics A: Materials Science & Processing》2013,113(4):945-957
Different pyrometallurgical materials such as slags, refractory materials and thermally treated lead ores likely related to smelting and extractive processes and chronologically related to Punic and Roman periods (IV–III BC) have been found at Bocche di Sciria and Conca e Mosu in the Montevecchio mine basin (south western Sardinia, Italy), where archaeological findings and classical authors locate extractive metallurgy activities since pre-Roman times. By means of the combined use of X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS), selected-area X-ray photoelectron spectroscopy (XPS) and optical microscopy (OM), micro-chemical and micro-structural investigations have been carried out in order to identify the nature of the pyrometallurgical materials, to decipher the processes carried out there and their technological steps and to determine the technological level of competence reached by the ancient metallurgists. The results confirm that the findings can be associated with smelting and extractive processes carried out close to the metal ore deposits first for the argentiferous lead production and, then, for the silver recovery via a cupellation process. Finally, the results disclose the high level of technological competence of the ancient metallurgists able to carry out complex high-temperature processes to treat the argentiferous lead ores and to recover low amounts of silver via high-temperature lead-selective oxidation. 相似文献
104.
Cristina Trujillo Goar Sánchez-Sanz Ibon Alkorta José Elguero 《Structural chemistry》2013,24(4):1145-1151
Theoretical calculations at the B3LYP/6-311++G(d,p) level have been carried out on the reaction path connecting a dipeptide to an imidazolinone as a model for the formation of GFP. In addition, we have studied the hydration effects on the processes, adding a water molecule to assist the cyclization. The solvent effects have been taken into account by introducing the monohydrated molecules into a solvent cavity with a polarized continuum model. Significant reductions of the energy barriers for the reaction path can be observed within the water-assisted processes. The solvent effects account for a barrier lowering of 4–5 kJ mol?1. 相似文献
105.
Sandra J. Atkinson Heather E. Robertson Margit Hölbling Wolf-Walther du Mont Cristina Mitrofan Karl Hassler Sarah L. Masters 《Structural chemistry》2013,24(3):851-857
The gas-phase molecular structures of a series of halogen-substituted disilanes [X3SiSiMe3 (X = H, F, Cl and Br)], 1,1,1-trimethyldisilane (H3SiSiMe3), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F3SiSiMe3), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl3SiSiMe3) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br3SiSiMe3), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C 3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X3SiSiXMe2 (X = F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes. 相似文献
106.
Dr. David Martínez-López Eduardo Santamaría-Aranda Dr. Marco Marazzi Dr. Cristina García-Iriepa Dr. Diego Sampedro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(13):4420-4429
Donor–acceptor Stenhouse adducts (DASAs) are playing an outstanding role as innovative and versatile photoswitches. Until now, all the efforts have been spent on modifying the donor and acceptor moieties to modulate the absorption energy and improve the cyclization and reversion kinetics. However, there is a strong dependence on specific structural modifications and a lack of predictive behavior, mostly owing to the complex photoswitching mechanism. Here, by means of a combined experimental and theoretical study, the effect of chemical modification of the π-bridge linking the donor and acceptor moieties is systematically explored, revealing the significant impact on the absorption, photocyclization, and relative stability of the open form. In particular, a position along the π-bridge is found to be the most suited to redshift the absorption while preserving the cyclization. However, thermal back-reaction to the initial isomer is blocked. These effects are explained in terms of an increased acceptor capability offered by the π-bridge substituent that can be modulated. This strategy opens the path toward derivatives with infra-red absorption and a potential anchoring point for further functionalization. 相似文献
107.
108.
109.
110.
Angela Somavilla Higioka Renata Cristina Messores Rudolf-Oliveira Flavia Martinello Maria Luiza Bazzo 《Accreditation and quality assurance》2016,21(2):143-149
Point-of-care (POC) testing of glucose (glucometers) represents a convenient alternative to monitor glycemia since the measurement procedure is performed without delay after sampling of the capillary blood, thereby avoiding the metabolism by the blood cells of glucose present in plasma. Likely because of sample instability, there is no proficiency test provider in Brazil for this type of POC sample. In this context, this study aimed to evaluate the analytical performance of glucometers used in a tertiary care hospital. The glucometers used were the Accu-Chek Performa® model from Roche Diagnostics, which use the principle of amperometry. The reference method was the reaction with modified hexokinase/glucose-6-phosphate in a Dimension® device. The stability evaluation of the control samples showed that it can be performed up to 90 min after the collection of whole blood samples. In the two rounds performed, only one result of the 17 glucometers evaluated was out of the threshold of two standard deviation. Thus, this method for control of glucometers met the expectations and enabled comparing the glucometers in a hospital. Given the current quality guidelines, daily internal quality control of glucometers is recommended, besides at least two annual comparisons between the results of the glucometers and the reference method and one EQA every 3 months. 相似文献