全文获取类型
收费全文 | 224篇 |
免费 | 27篇 |
国内免费 | 9篇 |
专业分类
化学 | 161篇 |
力学 | 2篇 |
综合类 | 2篇 |
数学 | 56篇 |
物理学 | 39篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 18篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 14篇 |
2011年 | 16篇 |
2010年 | 14篇 |
2009年 | 18篇 |
2008年 | 5篇 |
2007年 | 10篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 20篇 |
2003年 | 6篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有260条查询结果,搜索用时 343 毫秒
251.
S. Roy Choudhury 《Nonlinear Analysis: Theory, Methods & Applications》1997,30(8):5491-5498
The canonical equations for evolution of the amplitude order parameters order parameters describing the nonlinear development and persistence of two-dimensional three-mode spatial patterns generated by Turing instability in dissipative systems are considered. The stability conditions for persistent hexagonal patterns are generalized, and the conditions under which patterns are either disrupted, exhibit bounded quasiperiodic or chaotic behavior, or decay under nonlinear evolution are derived. These conditions are applied to the specific three-mode amplitude evolution equations derived for the Schnakenberg model and a delay predator system in Chapter 3. Numerical results are presented for the persistence, disruption and decay of patterns in these systems, including fairly detailed comparisons with simulations results for the Snackenberg model. 相似文献
252.
In this research, a two-stage batch production–inventory system is introduced. In this system, the production may be disrupted, for a given period of time, either at one or both stages. In this paper, firstly, a mathematical model has been developed to suggest a recovery plan for a single occurrence of disruption at either stage. Secondly, multiple disruptions have been considered, for which a new disruption may or may not affect the recovery plan of earlier disruptions. We propose a new approach that deals with a series of disruptions over a period of time, which can be implemented for disruption recovery on a real time basis. In this approach, the model formulated for single disruption has been integrated to generate initial solutions for individual disruptions and the solutions have been revised for multiple dependent disruptions with changed parameters. With the proposed approach, an optimal recovery plan can be obtained in real time, whenever the production system experiences either a sudden disruption or a series of disruptions, at different points in time. Some numerical examples and a real-world case study are presented to explain the benefits of our proposed approach. 相似文献
253.
254.
Angela Bonfà Francesco Busetti Anna Collarin 《International journal of environmental analytical chemistry》2013,93(10):717-727
A new analytical method was developed for the simultaneous determination of estrogenic compounds of natural (estradiol, estriol, estrone) and synthetic origin, both steroidal (ethinylestradiol, mestranol) and non-steroidal (benzophenone, bisphenol-A, diethylstilbestrol, octylphenol, nonylphenol, nonylphenol monoethoxylate carboxylate), in environmental aqueous samples by high-performance liquid chromatography coupled with ion trap-mass spectrometry via electrospray interface (HPLC-ESI-IT-MS). Quantitative MS detection was performed in the negative mode for all compounds except mestranol and benzophenone, which were detected under positive ion conditions. Very low method detection limits (MDLs), between 0.1 and 2.6?ng/L, were achieved in coastal lagoon water samples, while the developed solid-phase-extraction (SPE) procedure permitted simultaneous recovery of all analytes from spiked water samples with yields >70% (7–11 RSD%), except estriol and benzophenone, which were recovered with 60% (9 RSD%) and 50% (11 RSD%) yields, respectively. The proposed method was applied to the analysis of Venice (Italy) lagoon waters, where average concentrations of selected compounds in the 2.8–33?ng/L concentration range were found. 相似文献
255.
Julio César Benítez‐Villalba Alberto Zafra‐Gómez Noemí Dorival‐García Francisco Javier Camino‐Sánchez Samuel Cantarero José Luis Vílchez 《Journal of separation science》2013,36(16):2635-2645
The efficiency of two extraction techniques—ultrasound‐assisted extraction and pressurized liquid extraction—are compared and evaluated in the determination of parabens in compost samples. The extraction parameters for each technique were accurately optimized. The selected compounds were detected and quantified using ultra‐performance LC MS/MS, operating in negative ESI and in SRM mode. The analytes were separated in less than 5 min. Ethylparaben (ring‐13C6 labeled) was used as an internal standard. Two selective, sensitive, and accurate analytical methods were developed and validated. The LODs of the methods ranged from 3 to 7 ng/g and the LOQs from 10 to 23 ng/g, while inter‐ and intraday variability was under 6% in all cases. The methods were validated separately by using matrix‐matched calibration and recovery assays with spiked samples. Recovery rates ranged from 94.0 to 105.0%. Compost samples were taken from different composting plants. Although the statistical comparison demonstrated no statistically significant differences between the two extraction techniques, the method based on pressurized liquid extraction was more sensitive than the ultrasound extraction based method. 相似文献
256.
Microalgae are a promising feedstock for the production of biofuels, nutraceuticals, pharmaceuticals and cosmetics, due to their superior capability of converting solar energy and CO2 into lipids, proteins, and other valuable bioactive compounds. To facilitate the release of these important biomolecules from microalgae, effective cell disruption is usually necessary, where the use of ultrasound has gained tremendous interests as an alternative to traditional methods. This review not only summarizes the mechanisms of and operation parameters affecting cell disruption, but also takes an insight into measuring techniques, synergistic integration with other disruption methods, and challenges of ultrasonication for microalgal biorefining. Optimal conditions including ultrasonic frequency, intensity, and duration, and liquid viscosity and sonochemical reactor are the key factors for maximizing the disruption and extraction efficiency. A combination of ultrasound with other disruption methods such as ozonation, microwave, homogenization, enzymatic lysis, and solvents facilitates cell disruption and release of target compounds, thus provides powerful solutions to commercial scale-up of ultrasound extraction for microalgal biorefining. It is concluded that ultrasonication is a sustainable “green” process, but more research and work are needed to upscale this process without sacrificing performance or consuming more energy. 相似文献
257.
Christian Ptrier Ricardo Torres-Palma Evelyne Combet Georgios Sarantakos Stphane Baup Csar Pulgarin 《Ultrasonics sonochemistry》2010,17(1):111-115
Sonochemical elimination of organic pollutants can take place through two degradation pathways. Molecules with relatively large Henry’s law constants will be incinerated inside the cavitation bubble, while nonvolatile molecules with low Henry’s law constants will be oxidised by the OH ejected from the bubble of cavitation. Taking bisphenol-A as a model pollutant, this study points out an alternate degradation route, mediated by bicarbonate ions, which is significant for the elimination of micro-pollutants at concentrations present in natural waters. In this process, OH radicals react with bicarbonate ions to produce the carbonate radical, which, unlike the OH radical, can migrate towards the bulk of the solution and therefore induce the degradation of the micro-pollutants present in the bulk solution. As a consequence, initial degradation rate is increased by a factor 3.2 at low concentration of bisphenol-A (0.022 μmol l−1) in presence of bicarbonate in water. 相似文献
258.
Microalgae have evolved into a promising sustainable source of a wide range of compounds, including protein, carbohydrates, biomass, vitamins, animal feed, and cosmetic products. The process of extraction of intracellular composites in the microalgae industry is largely determined by the microalgal species, cultivation methods, cell wall disruption techniques, and extraction strategies. Various techniques have been applied to disrupt the cell wall and recover the intracellular molecules from microalgae, including non-mechanical, mechanical, and combined methods. A comprehensive understanding of the cell disruption processes in each method is essential to improve the efficiency of current technologies and further development of new methods in this field. In this review, an overview of microalgal cell disruption techniques and an analysis of their performance and challenges are provided. A number of studies on cell disruption and microalgae extraction are examined in order to highlight the key challenges facing the field of microalgae and their future prospects. In addition, the amount of product recovery for each species of microalgae and the important parameters for each technique are discussed. Finally, pulsed electric field (PEF)-assisted treatments, which are becoming an attractive option due to their simplicity and effectiveness in extracting microalgae compounds, are discussed in detail. 相似文献
259.
《Arabian Journal of Chemistry》2023,16(6):104723
Imidacloprid and sulfoxaflor have potential damage to nontarget aquatic organisms. However, limited information has been provided on their underlying toxicity effects on Rana nigromaculata tadpoles. Thus, the acute toxicity and chronic effects of imidacloprid and sulfoxaflor on R. nigromaculata tadpoles were studied. Acute toxicity indicted that 96 h for LC50 values of imidacloprid and sulfoxaflor were 173.55 and 427.37 mg/L, respectively. In this research, we explored antioxidant enzymes, some biological indexes, hormone levels and expression of relative tadpole genes involved in thyroid hormone-dependent metaplastic development after exposure for 28 days under 1/10 and 1/100 LC50. Results showed an increase in the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) in the tadpoles, and a low bioconcentration level with a bioconcentration factor (BCFs) < 1. The impact on the development of tadpoles was induced by the breakdown of hormonal levels engaged in metamorphosis. According to the real-time PCR results, imidacloprid and sulfoxaflor delayed amphibian metamorphosis by modifying mRNA expression, indicating that imidacloprid and sulfoxaflor may have an endocrine-disrupting effect on R. nigromaculata tadpoles. These findings were indicative of the toxicity of imidacloprid and sulfoxaflor to R. nigromaculata tadpoles. 相似文献
260.