全文获取类型
收费全文 | 1208篇 |
免费 | 31篇 |
国内免费 | 8篇 |
专业分类
化学 | 887篇 |
晶体学 | 3篇 |
力学 | 26篇 |
数学 | 177篇 |
物理学 | 154篇 |
出版年
2023年 | 8篇 |
2022年 | 12篇 |
2021年 | 20篇 |
2020年 | 23篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 40篇 |
2015年 | 40篇 |
2014年 | 27篇 |
2013年 | 58篇 |
2012年 | 88篇 |
2011年 | 87篇 |
2010年 | 60篇 |
2009年 | 56篇 |
2008年 | 79篇 |
2007年 | 77篇 |
2006年 | 79篇 |
2005年 | 67篇 |
2004年 | 69篇 |
2003年 | 50篇 |
2002年 | 42篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 18篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有1247条查询结果,搜索用时 468 毫秒
61.
62.
63.
The lipase catalyzed resolution of trans-3,4-tetrahydrofuran and pyrrolidine bromohydrins by acylation or hydrolysis of their acylated derivatives has been studied. For both heterocycles, the best enantioselectivity was obtained using Candida antarctica lipase B as the catalyst in the hydrolytic processes. The enantiomerically pure bromohydrins are useful intermediates for the preparation of 3,4-fuctionalized cis-heterocycles. 相似文献
64.
Srigokul Upadhyayula Vicente Nu?ez Eli M. Espinoza Jillian M. Larsen Duoduo Bao Dewen Shi Jenny T. Mac Bahman Anvari Valentine I. Vullev 《Chemical science》2015,6(4):2237-2251
Cyanine dyes are broadly used for fluorescence imaging and other photonic applications. 3,3′-Diethylthiacyanine (THIA) is a cyanine dye composed of two identical aromatic heterocyclic moieties linked with a single methine, –CH. The torsional degrees of freedom around the methine bonds provide routes for non-radiative decay, responsible for the inherently low fluorescence quantum yields. Using transient absorption spectroscopy, we determined that upon photoexcitation, the excited state relaxes along two parallel pathways producing three excited-state transients that undergo internal conversion to the ground state. The media viscosity impedes the molecular modes of ring rotation and preferentially affects one of the pathways of non-radiative decay, exerting a dominant effect on the emission properties of THIA. Concurrently, the polarity affects the energy of the transients involved in the decay pathways and further modulates the kinetics of non-radiative deactivation. 相似文献
65.
66.
NMR line‐fitting quantification of polysaccharide N‐acylurea‐based modification in glycoconjugates of Salmonella Typhi Vi polysaccharide
下载免费PDF全文
![点击此处可从《Magnetic resonance in chemistry : MRC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Raine Garrido Jean Pierre Soubal Leonid Torres Ubel Ramírez Vicente Vérez 《Magnetic resonance in chemistry : MRC》2017,55(8):720-723
The polysaccharides modification via carbodiimide reaction is one of the most applied methods for obtaining conjugated vaccines against Salmonella enterica. However, N‐acylurea carbodiimide adduct generated in the process is a critical impurity in carbohydrate‐based vaccines. A quantitative NMR method was developed for assessing the N‐acylurea carbodiimide adduct impurity. The procedure was based on line‐fitting facilities for processing the NMR signals on complex spectra. The method showed good linearity, accuracy and precision under inter‐operator variation (relative standard deviation <5%). Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
67.
68.
Elena O. Alonso Maria E. R. Marcondes Vicente G. Toscano 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4)
Abstract As part of our continuing interest in the mechanistic photochemistry of phosphonium salts (Toscano et al., Chez. Commun., 567 (1973); J. Phys. Chem., 83(9), 1213 (1979)) we have investigated the photodecomposition (313 nm irradiation) of (1-naphthyl-methyl) triphenylphosphonium (I) chloride and tetrafluoroborate in deaerated isopropanol: 相似文献
69.
Brenno Santos Leite Melissa Tatiana Andreuccetti Sibele Augusta Ferreira Leite José Vicente Hallak d’Angelo 《Journal of Thermal Analysis and Calorimetry》2013,112(3):1539-1544
As a consequence of the continuous increase in the production rate of pulp and paper mills around the world, a great quantity of black liquor, a by-product of the wood digestion process, is produced. This by-product has a great potential as biomass, but needs to be concentrated to higher solids content to be burned as fuel in a recovery boiler. This is necessary to make the pulping process economically feasible, incinerating black liquor to produce high pressure steam, recycling inorganic chemicals to the process. The greater the solids content in black liquor, the better the combustion process in the boiler. Nevertheless, concentration of solids in black liquor above 75 mass/%, causes scaling formation on the heat transfer surfaces of evaporators and concentrators, due to the precipitation of sodium salts, reducing the overall efficiency of this equipment. The aim of this work is to evaluate the use of thermal analyses techniques, TG and DSC, as alternative methods to estimate solids content in eucalyptus black liquor samples since this information is essential to understand scaling formation process, allowing actions to reduce this industrial problem. Traditional techniques applied to determine solids content use gravimetric methods, which are simple, fine, but take a lot of time to be executed. Thermal analyses have proved to be very accurate and have the advantage to be faster than the traditional techniques. On the other hand, the cost-benefit relationship of the traditional technique is much greater and the final decision which one should be used depends on the conditions available. 相似文献
70.
M. H. T. Taddei R. Vicente J. T. Marumo S. K. Sakata L. A. A. Terremoto 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(2):951-957
Ion-exchange resins and activated charcoal beds are employed for purification of the cooling water that is pumped through the core of pool type nuclear research reactors. Once expended, these media are replaced and become radioactive wastes that contain low concentrations of long-lived fission and activation products, uranium isotopes and transuranium elements. Determination of the radioactive inventory is of paramount importance in the management of such radioactive wastes, which, besides high-energy photon emitters that can be identified and quantified directly by gamma-ray spectrometry, also contain pure alpha, pure beta and low-energy photon emitters whose quantitative determination require radiochemical separation. These later are collectively known as difficult to measure (DTM) radionuclides. A characterization program embracing the DTM radionuclides is currently in progress for spent ion-exchange resins and activated charcoal beds that were definitively withdrawn from the water cleanup system of the IEA-R1 nuclear research reactor. Radiochemical methods used in the characterization program include separations with specific anionic resins, chromatographic extractions and co-precipitation, which enabled the measurement of the activity concentrations of 90Sr, 234U, 235U, 238U, 238Pu, 239+240Pu, 241Pu, 241Am and 244Cm. An enhanced retention of uranium and transuranium elements was observed in the activated charcoal compared to the ion-exchange resins as a result of the tendency of actinides to undergo hydrolysis in aqueous solutions. 相似文献