全文获取类型
收费全文 | 2327篇 |
免费 | 75篇 |
国内免费 | 114篇 |
专业分类
化学 | 2096篇 |
晶体学 | 3篇 |
力学 | 164篇 |
综合类 | 26篇 |
数学 | 127篇 |
物理学 | 100篇 |
出版年
2024年 | 2篇 |
2023年 | 26篇 |
2022年 | 39篇 |
2021年 | 37篇 |
2020年 | 41篇 |
2019年 | 42篇 |
2018年 | 44篇 |
2017年 | 67篇 |
2016年 | 66篇 |
2015年 | 62篇 |
2014年 | 68篇 |
2013年 | 103篇 |
2012年 | 126篇 |
2011年 | 152篇 |
2010年 | 133篇 |
2009年 | 116篇 |
2008年 | 84篇 |
2007年 | 92篇 |
2006年 | 121篇 |
2005年 | 112篇 |
2004年 | 87篇 |
2003年 | 71篇 |
2002年 | 58篇 |
2001年 | 56篇 |
2000年 | 73篇 |
1999年 | 51篇 |
1998年 | 52篇 |
1997年 | 51篇 |
1996年 | 47篇 |
1995年 | 55篇 |
1994年 | 39篇 |
1993年 | 22篇 |
1992年 | 30篇 |
1991年 | 18篇 |
1990年 | 22篇 |
1989年 | 25篇 |
1988年 | 36篇 |
1987年 | 18篇 |
1986年 | 19篇 |
1985年 | 27篇 |
1984年 | 33篇 |
1983年 | 21篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1975年 | 1篇 |
排序方式: 共有2516条查询结果,搜索用时 15 毫秒
991.
大气压液体电极放电在生物医疗、化学降解、环境保护等众多方面具有广泛的应用前景,引起了研究者的关注.本文利用直流电压激励棒-水电极装置,在6 mm气隙间产生了大气压辉光放电.研究发现,随着电流的增大,放电由锥状转变成柱状,且此过程中水面上放电环的直径先增大后减小.利用高速照相机对放电进行研究,发现锥状放电是由单个放电丝旋转形成的.通过测量放电的伏安特性,表明放电处于正常辉光机理.利用光谱学方法,研究了不同电流下的振动温度、转动温度和谱线强度比I_(391.4)/I_(337.1),发现它们均随电流的增加而增大.根据气体放电理论,分析和解释了放电丝的运动机理,并对水面上放电环直径随电流的变化关系进行了解释.这些结果对于大气压液体电极放电的理论研究和实际应用均具有一定参考价值. 相似文献
992.
Sorin Bucsa Alexandru Serban Mugur C. Balan Claudia Ionita Gabriel Nastase Catalina Dobre Alexandru Dobrovicescu 《Entropy (Basel, Switzerland)》2022,24(2)
This case study analyzes a cryogenic air separation unit (ASU) with a production of of gaseous oxygen with a concentration greater than 98.5%, operating in Romania on a steel plant platform. The goal of the paper is to provide an extensive model of exergetic analysis that could be used in an optimization procedure when decisional parameters are changed or structural design modifications are implemented. For each key part of the Air Separation Unit, an exergetic product and fuel were defined and, based on their definition, the coefficient of performance of each functional zone was calculated. The information about the magnitude of the exergetic losses offers solutions for their future recovery. The analysis of the exergy destructions suggests when it is worth making a larger investment. The exergetic analysis of the compression area of the ASU points out an exergy destruction and loss of 37% from the total plant’s electrical energy input. The exergy loss with the heat transferred to the cooling system of compressors can be recovered; for the exergy destruction portion, the challenge between investment and operating costs should be considered. The exergy destruction of the air separation columns found the High Pressure Column (HPC) to be more destructive than the Low Pressure Column. The share of the exergy destruction in the total plant’s electrical energy input is 8.3% for the HPC. The local COP of the HPC, calculated depending on the total exergy of the local product and fuel, is 62.66%. The calculus of the air separation column is performed with the ChemSep simulator. 相似文献
993.
994.
Batch and column biosorption experiments were carried on for lead uptake using ecofriendly biosorbents (raw and calcium chloride [CaCl2] or formaldehyde pretreated form of red marine algae Jania ruben [Linnaeus]). The best-fit (linear and nonlinear) isotherms, kinetics, and column adsorption models were identified using statistical analysis. Freundlich, Langmuir, Temkin, Redlich–Peterson, and Elovich adsorption isotherm models were tested. Highest adsorption capacity (774 mg/g) has been observed with Jania algae pretreated with formaldehyde. Pseudo-first- and second-order adsorption kinetics were applicable. The column capacity for lead removal with Jania pretreated with CaCl2 was found to be 1089.6 (mg/g) from the breakthrough curve area method. Thomas, Yoon-Nelson, Yan, and Clark column models were tested with regression analysis. Thomas model is the best column model with capacity qTh = 1092.4 mg/g. Overall, 98.5% regeneration of column was achieved, indicating the suitability of using algae materials in multioperational cycles. Adsorbed lead present in algae material was confirmed by thermal analysis. 相似文献
995.
Enantiomeric separation of indoxacarb on an amylose‐based chiral stationary phase and its application in study of indoxacarb degradation in water
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yuping Zhang Kankan Zhang Baoan Song Hurong Ling Zhining Li Meichuan Li Deyu Hu 《Biomedical chromatography : BMC》2014,28(10):1371-1377
Direct semipreparative enantioseparation of indoxacarb was performed on a semipreparative Chiralpak IA column using normal‐phase high‐performance liquid chromatography (HPLC) with n‐hexane–isopropanol–ethyl acetate (70:20:10) mixture as mobile phase. Degradation of indoxacarb (2.33S + 1R) and its two enantiopure isoforms in three aqueous buffer solutions and four water samples collected from natural water sources was then elucidated by HPLC analysis on Chiralpak IA column. Degradation of all three indoxacarbs complied with first‐order kinetics and demonstrated linearity with regression coefficients R2 > 0.88. Indoxacarb (2.33S + 1R) underwent enantioselective degradation in river water, rain water, and buffer solution of pH 7.0. Enantiopure S‐(+)‐indoxacarb and R‐(?)‐indoxacarb were both found to be configurationally stable in water. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
996.
以四乙氧基硅烷,N-氨乙基-3-氨丙基三乙氧基硅烷,3-甲基丙烯酰氧丙基三甲氧基硅烷作为前驱,4-乙烯基苯硼酸为单体,在毛细管中原位制备硼酸亲和杂化整体柱,该柱可在中性条件下选择性的富集顺式二羟基生物分子,实现了对蒲公英中活性成分咖啡酸及绿原酸的选择性富集。 相似文献
997.
998.
A system to use fluorometry for the search of protein crystallization buffers was developed. The screening of candidates was done with a use of short gel-filtration column (Sephacryl S-100 HR) linked to the fluorometer. Protein elution was monitored by intrinsic fluorescence or emission from its labels. This method was applied to actin and actin complexes. When nuclei were formed in actin solution, preceding the peak of actin, a new peak appeared on the elution curve. It was found that the fluorescence allows detection of even small amount of nuclei formed in the buffer. Using the screened buffers, crystal growths were attempted. The images of crystals were captured by fluorescence microscope. The monitoring of nuclei with this method will accelerate the screening of crystallization buffers. This system is applicable to the crystallization of other proteins and their complexes. 相似文献
999.
Summary This paper summarizes the work of Gottfried Kränzlin, who, in 1906–1908, was the first after Tswett to utilize chromatography for the investigation of plant pigments. 相似文献
1000.
Summary An on-line application of capillary SFC-FTIR for the analysis of five steroids has been demonstrated. Baseline resolution
is achieved for all the components of the mixture and IR spectra are obtained which match well with spectra of the neat materials.
Also, the injected minimum detectable quantity (IMDQ) of caffeine (approximately 2 ng) under similar chromatographic conditions
is demonstrated for this interface. Very low IMDQ's achieved using this flow cell interface will facilitate the use of this
technique for the analysis of biological fluids and other materials where very low detection limits are required. 相似文献