全文获取类型
收费全文 | 605篇 |
免费 | 82篇 |
国内免费 | 46篇 |
专业分类
化学 | 208篇 |
晶体学 | 7篇 |
力学 | 12篇 |
综合类 | 53篇 |
数学 | 308篇 |
物理学 | 145篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 41篇 |
2021年 | 52篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 15篇 |
2017年 | 24篇 |
2016年 | 30篇 |
2015年 | 19篇 |
2014年 | 24篇 |
2013年 | 46篇 |
2012年 | 34篇 |
2011年 | 30篇 |
2010年 | 28篇 |
2009年 | 25篇 |
2008年 | 17篇 |
2007年 | 35篇 |
2006年 | 21篇 |
2005年 | 34篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有733条查询结果,搜索用时 15 毫秒
41.
Karunanithi Masilan Neethirajan Neethiselvan Robinson Jeya Shakila Arjunan Karthy Ulaganathan Arisekar Nagarajan Muralidharan Thangaraji Ravikumar Balasubramanian Sivaraman Chellapa Kalidas Lakshmanan Ranjith Dhanasekaran Linga prabhu 《印度化学会志》2022,99(3):100376
The study dealt with evolving an artificial fish bait by incorporating bioattractant concentrates derived from seafood processing wastes by enzymatic hydrolysis namely fish waste concentrate (FWC), squid waste concentrate (SWC), and shrimp processing concentrate (SPWC). They were characterized based on amino acid content and presence of different functional groups using FTIR. Among them, SWC was found to have the highest amino acid content of 60.85mg/100 mg followed by FWC (42.21mg/100 mg) and SPWC (24.82mg/100 mg). The developed artificial fish baits were subjected to protein leaching, solubility in seawater besides testing for acceptability by the red snapper. The study revealed that the bait incorporated with SWC at 3% level was found be the most ideal, with the protein leaching rate of 24.82 mg/g/h, solubility rate of 36.6 mg/g/h and the attractability score of 29/30. The amino acid leaching rate was 3.11 mg/h/100 mg and it was found to contain five amino acids such as glycine, proline, glutamic acid, alanine and serine. The study revealed that the hydrolyzed squid waste concentrate can be incorporated at 3% (w/w) with fish gelatin based biomatrix during gelation to prepare artificial bait. 相似文献
42.
二氧化碳浓度持续升高导致的温室效应已在全球范围内引发极端天气、冰川融化等一系列生态环境问题。为降低二氧化碳含量,改善气候变暖带来的恶劣影响,研发高效、绿色、安全的二氧化碳处理技术,促进碳资源循环可持续发展刻不容缓。熔盐离子液体作为一种良好的电化学转化介质,为二氧化碳还原提供了一条极具应用前景的技术路线。综述了国内外近几年高温熔盐中二氧化碳的捕获与电化学还原的研究,简述了熔盐电沉积碳的电化学机理和热力学机制,对不同形貌高附加值碳材料:无定形碳、碳球和碳纳米管的制备进行了总结,最后对未来发展方向做出展望。 相似文献
43.
在温和条件下,发展了一种以丁二醇-乙二胺体系新颖、高效地固定CO2的方法。在此方法中,CO2被快速激活并转化为一种固态的CO2储集材料(CO2SM),通过XPS、XRD、FTIR和13C NMR等技术表征证实为烷基碳酸胺。基于TGA结果,CO2SM的水溶液可以与Ca(OH)2和Ba(OH)2反应制备CaCO3和BaCO3微粒,还可用于循环吸收和解吸CO2的过程。此外,丁二醇-乙二胺水溶液在20 ℃下吸收CO2并在98.6 ℃下解吸CO2,没有明显的溶液损失。因此,丁二醇-乙二胺体系提供了一种绿色、高效、低成本的二氧化碳捕集利用方法。 相似文献
44.
Adamantini Kyriacou Costas Balis Milton A. Typas 《Applied biochemistry and biotechnology》1997,66(3):281-289
An acetylene utilizingGordona (Rhodococcus) bronchialis strain, screened for the production of fine chemicals, was found to be capable of producing small amounts of lysine. Attempts
to produce amino-acid analogresistant and/or sensitive mutants and auxotrophs of this strain with increased lysine production
were made following UV-irradiation orN-methyl-N’-nitro-N-nitrosoguanidine (MNNG) treatment. The bacterium exhibited surprisingly high resistance levels to the aforementioned mutagens
which is attributed to highly effective inborn-repair systems. Natural resistance to high levels ofS-(2-aminoethyl)-l-cysteine (AEC) (2%) was observed, in contrast withd, l-aspartic acid hydroxamate (AAH),l-lysine hydroxamate (LHX) and β-fluoropyruvate (FP). A variety of amino-acid analog-resistant (AAHr, LHXr) or analog-sensitive (FPs) mutants were produced following UV-irradiation or MNNG treatment. Similarly, a large number of auxotrophs (68) of different
types were also obtained. From these, one FPs mono-auxotroph and two poly-auxotrophs (with at least one requirement for the aspartic acid family) showed an increased lysine
production (~1.8 g/L) comparable (4 g/L) to that found in other bacteria capable of utilizing long-chain hydrocarbons(1). 相似文献
45.
Desulfurized gypsum (DG) as a soil modifier imparts it with bulk solid sulfite. The Fe(III)–sulfite process in the liquid phase has shown great potential for the rapid removal of As(III), but the performance and mechanism of this process using DG as a sulfite source in aqueous solution remains unclear. In this work, employing solid CaSO3 as a source of SO32−, we have studied the effects of different conditions (e.g., pH, Fe dosage, sulfite dosage) on As(III) oxidation in the Fe(III)–CaSO3 system. The results show that 72.1% of As(III) was removed from solution by centrifugal treatment for 60 min at near-neutral pH. Quenching experiments have indicated that oxidation efficiencies of As(III) are due at 67.5% to HO•, 17.5% to SO5•− and 15% to SO4•−. This finding may have promising implications in developing a new cost-effective technology for the treatment of arsenic-containing water using DG. 相似文献
46.
随着全球人为温室气体排放量(主要是甲烷和二氧化碳)的增加,全球变暖的趋势逐渐增加,因此,迫切需要通过各种技术来捕获和利用这些温室气体.甲烷干气重整反应(DRM)可以有效地将甲烷和二氧化碳这两种资源丰富、价格低廉的温室气体转化为高附加值化学品,减少它们向大气排放.尽管DRM工艺的应用具有许多优势,但是反应期间碳沉积和活性组分的烧结是阻碍其工业应用的两个主要原因.这些碳沉积物可能覆盖活性中心或阻塞催化剂的孔道,从而导致催化剂活性降低.镍基催化剂因其价格低廉、初始活性高和资源丰富而得到广泛的应用.但应用于DRM反应的Ni基催化剂在反应中容易烧结和积碳,导致催化剂迅速失活.为解决上述问题,本文从三功能策略角度出发,即SiO2壳层的限域作用和Ni-Ce之间的协同作用以及CeO2的消除积碳作用,采用原位一锅法设计合成了一种限域型Ni-CeO2核壳结构催化剂(Ni-CeO2@SiO2).通过X射线衍射、透射电子显微镜、能量色散X射线光谱、N2吸附/脱附、氢气程序升温还原和脱附、氧气程序升温脱附、拉曼光谱、热重分析和原位漫反射红外傅里叶变换光谱测试对催化剂进行了系统的表征,来揭示催化剂的理化性质和反应机理.催化剂应用于甲烷干气重整反应结果表明,在温度区间为550~800℃时,与传统浸渍法合成的催化剂相比,Ni-CeO2@SiO2催化剂具有更高的活性.高温800℃下的稳定性测试结果显示,传统浸渍法合成的催化剂在反应20 h后就出现了大量的积碳且活性下降明显;而Ni-CeO2@SiO2催化剂在800℃下反应100 h后未检测到积碳,并且催化剂中的Ni纳米颗粒的平均粒径从5.01 nm仅增长到5.77 nm,表现出很好的高温抗积碳和耐烧结性能.值得注意的是,Ni-CeO2@SiO2催化剂在低温600℃(形成碳沉积的最可能温度区域)下反应20h后也未检测到积碳的形成,表现出催化剂良好的低温稳定性和抗积碳性能.这可能归因于对Ni-CeO2@SiO2催化剂的三功能作用,即多孔二氧化硅壳层的限域作用、Ni与CeO2之间强的金属-金属氧化物相互作用以及具有丰富活性氧物种CeO2的消除积碳的作用.通过原位漫反射红外傅里叶变换光谱测试来探究反应机理.结果 表明,DRM反应在Ni-CeO2@SiO2催化剂上遵循L-H机理,添加CeO2可以消除碳沉积并促进CO2活化.该三功能策略为设计其他应用于DRM的高性能催化剂提供了指导,有望加快该工艺的工业化. 相似文献
47.
Neven Voa Josip Leto Tomislav Karaija Nikola Bilandija Anamarija Peter Hrvoje Kutnjak Jona uri Milan Poljak 《Molecules (Basel, Switzerland)》2021,26(14)
The application of municipal sewage sludge as fertilizer in the production of non-food energy crops is an environmentally and economically sustainable approach to sewage sludge management. In addition, the application of municipal sewage sludge to energy crops such as Miscanthus x giganteus is an alternative form of recycling nutrients and organic material from waste. Municipal sewage sludge is a potential source of heavy metals in the soil, some of which can be removed by growing energy crops that are also remediation agents. Therefore, the objective of the research was to investigate the effect of municipal sewage sludge applied at three different rates of 1.66, 3.22 and 6.44 t/ha on the production of Miscanthus. Based on the analyses conducted on the biomass of Miscanthus fertilized with sludge from the wastewater treatment plant in three fertilization treatments, it can be concluded that the biomass of Miscanthus is a good feedstock for the process of direct combustion. Moreover, the application of the largest amount of municipal sewage sludge during cultivation had no negative effect on the properties of Miscanthus biomass. Moreover, the cellulose and hemicellulose content of Miscanthus is ideal for the production of second-generation liquid biofuels. Fertilizer treatments had no effect on the content of cellulose and lignin, while a significant statistical difference was found for hemicellulose. 相似文献
48.
Maria Fernanda Taviano Emilia Cav Vivienne Spadaro Francesco Maria Raimondo Vincenzo Musolino Francesco Cacciola Yassine Oulad El Majdoub Luigi Mondello Concetta Condurso Fabrizio Cincotta Antonella Verzera Natalizia Miceli 《Molecules (Basel, Switzerland)》2021,26(14)
In a project designed to investigate the specific and infraspecific taxa of Matthiola endemic to Sicily (Italy) as new potential sources of bioactive compounds in this work, the infraspecific taxa of Matthiola fruticulosa were studied, namely, subsp. fruticulosa and subsp. coronopifolia. HPLC–PDA/ESI–MS and SPME–GC/MS analyses of hydroalcoholic extracts obtained from the aerial parts of the two subspecies led to the detection of 51 phenolics and 61 volatile components, highlighting a quite different qualitative–quantitative profile. The antioxidant properties of the extracts were explored through in vitro methods: 1,1-diphenyl-2-picrylhydrazyl (DPPH), reducing power and Fe2+ chelating activity assays. The results of the antioxidant tests showed that the extracts possess a different antioxidant ability: particularly, the extract of M. fruticulosa subsp. fruticulosa exhibited higher radical scavenging activity than that of subsp. coronopifolia (IC50 = 1.25 ± 0.02 mg/mL and 2.86 ± 0.05 mg/mL), which in turn displayed better chelating properties (IC50 = 1.49 ± 0.01 mg/mL and 0.63 ± 0.01 mg/mL). Lastly, Artemia salina lethality bioassay was performed for toxicity assessment. The results of the bioassay showed lack of toxicity against brine shrimp larvae for both extracts. The data presented indicate the infraspecific taxa of M. fruticulosa as new and safe sources of antioxidant compounds. 相似文献
49.
50.
与贵金属铂基电化学氧还原反应(ORR)催化剂相比,廉价的非贵金属催化剂引起了广泛的关注。本文以壳聚糖作为一种富含氮和碳元素的生物质资源,利用碳浴法成功制备了氮掺杂碳原位负载铜纳米颗粒(Cu/N-C)催化剂。纯壳聚糖碳化得到的样品N-C的比表面积为67.5 m2·g-1、平均孔径0.14 nm、平均孔体积8.00 m2·g-1,与之相比,Cu/N-C比表面积可达607.3 m2·g-1、平均孔径为2.5 nm、平均孔体积为0.40 cm3·g-1。通过密度泛函理论(DFT)进行计算表明,Cu(111)/N-C的自由能值低于N-C,更有利于氧还原催化进行。在0.1 mol·L-1 KOH的介质中,Cu/N-C不仅表现出优异的起始和半波电势(分别为0.96 V和0.84 V),而且还表现出了优异的抗甲醇性能和稳定性,并且Cu元素掺杂量达到1.67wt.%。 相似文献