全文获取类型
收费全文 | 292篇 |
免费 | 15篇 |
专业分类
化学 | 200篇 |
晶体学 | 5篇 |
力学 | 5篇 |
数学 | 33篇 |
物理学 | 64篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 16篇 |
2015年 | 8篇 |
2014年 | 4篇 |
2013年 | 20篇 |
2012年 | 23篇 |
2011年 | 19篇 |
2010年 | 19篇 |
2009年 | 20篇 |
2008年 | 20篇 |
2007年 | 18篇 |
2006年 | 9篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1974年 | 3篇 |
排序方式: 共有307条查询结果,搜索用时 15 毫秒
301.
Zahuiti Hernández-Monta?ez Margarita Juárez-Montiel Martha Velázquez-ávila Eliseo Cristiani-Urbina César Hernández-Rodríguez Lourdes Villa-Tanaca Griselda Chávez-Camarillo 《Applied biochemistry and biotechnology》2012,167(7):2117-2129
A yeast isolate able to produce high levels of extracellular ??-amylase was selected from a collection of 385 yeasts and identified as Wickerhamia sp. by the sequence of the D1/D2 domain of the 26?S rDNA gene. Part of the nucleotide sequence of the amy1-W gene was cloned, and a sequence of 191 amino acids deduced from this gene was analyzed. The peptide contains three characteristic well-conserved regions in the active sites of ??-amylases (EC 3.2.1.1). The enzyme was purified and in situ activity showed only one band with amylolytic activity. The molecular mass of the ??-amylase was estimated at 54?kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Enzymatic activity on soluble starch as substrate was optimal at pH 5?C6 and 50 °C. This thermostable enzyme was inhibited by EDTA?CNa2 and 1,10-phenanthroline; the activity of the dialyzed enzyme was reactivated with Ca2+ and Mg2+ cations, which indicates that the ??-amylase is a metalloenzyme. ??-Amylase production was induced by starch and maltose and repressed by glucose. The high yield and productivity found in this work makes this Wickerhamia sp. strain a promising candidate for the biotechnological production of ??-amylase. 相似文献
302.
Serigne Sarr Julien Pilm Gilles Montavon Jean-Yves Le Questel Nicolas Galland 《Molecules (Basel, Switzerland)》2021,26(15)
The nature of halogen-bond interactions was scrutinized from the perspective of astatine, potentially the strongest halogen-bond donor atom. In addition to its remarkable electronic properties (e.g., its higher aromaticity compared to benzene), C6At6 can be involved as a halogen-bond donor and acceptor. Two-component relativistic calculations and quantum chemical topology analyses were performed on C6At6 and its complexes as well as on their iodinated analogues for comparative purposes. The relativistic spin–orbit interaction was used as a tool to disclose the bonding patterns and the mechanisms that contribute to halogen-bond interactions. Despite the stronger polarizability of astatine, halogen bonds formed by C6At6 can be comparable or weaker than those of C6I6. This unexpected finding comes from the charge-shift bonding character of the C–At bonds. Because charge-shift bonding is connected to the Pauli repulsion between the bonding σ electrons and the σ lone-pair of astatine, it weakens the astatine electrophilicity at its σ-hole (reducing the charge transfer contribution to halogen bonding). These two antinomic characters, charge-shift bonding and halogen bonding, can result in weaker At-mediated interactions than their iodinated counterparts. 相似文献
303.
A. Barrera F. TzompantziR. Gómez 《Journal of photochemistry and photobiology. A, Chemistry》2012,227(1):45-50
The photocatalytic activity of 1.0 wt% PdO supported on Al2O3-Nd2O3 binary oxides prepared by the sol-gel method was studied in the photodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The photocatalysts were characterized by N2 physisorption, XRD and UV-vis spectroscopy. PdO supported on γ-Al2O3 photo-degrades the 2,4-D, however the addition of Nd2O3 to γ-Al2O3 notably improves the photocatalytic activity. As the concentration of Nd2O3 in the binary oxide increases from 2 to 10 wt%, the photodegradation of 2,4-D is highly enhanced. The catalytic test for PdO supported on pure Nd2O3 showed scarce photocatalytic activity. Total organic carbon (TOC) analysis showed that the 2,4-D has been completely destroyed on the PdO/Al2O3-Nd2O3 photocatalysts after 6 h under irradiation. 相似文献
304.
JF Barrera M Tebaldi D Amaya WD Furlan JA Monsoriu N Bolognini R Torroba 《Optics letters》2012,37(14):2895-2897
In this Letter, we present to the best of our knowledge a new all-optical technique for multiple-image encryption and multiplexing, based on fractal encrypting masks. The optical architecture is a joint transform correlator. The multiplexed encrypted data are stored in a photorefractive crystal. The fractal parameters of the key can be easily tuned to lead to a multiplexing operation without cross talk effects. Experimental results that support the potential of the method are presented. 相似文献
305.
N. Balucani O. Asvany Y. T. Lee R. I. Kaiser N. Galland M. T. Rayez Y. Hannachi 《Journal of computational chemistry》2001,22(13):1359-1365
A novel supersonic beam of ground‐state boron atoms [B(2P)] was employed to investigate the reaction of B(2P) with acetylene [C2H2(1Σg+)] at an average collision energy of 16.3±0.4 kJ mol?1 at the most fundamental microscopic level. The crossed molecular beam technique was used to record time of flight spectra at mass to charge ratios of 36 (11BC2H+), 35 (10BC2H+/11BC2+), and 34 (10BC2+) at different laboratory angles. Forward‐convolution fitting of the laboratory data showed that only a product with the gross formula BC2H was formed via a boron versus hydrogen exchange. By combining experimental results with electronic structure calculations, the conclusion was that the reaction proceeded via the initial addition of B(2P) to the two carbon atoms of acetylene, leading to the formation of a first intermediate, the borirene radical (c‐BC2H2). This intermediate underwent various isomerization processes on the BC2H2 potential energy surface before decomposing into the linear HBCC(X1Σ) isomer via a hydrogen atom elimination. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1359–1365, 2001 相似文献
306.
Grace W. Muna Emily Barrera Lucas Robinson Hiba Majeed Keon Jones Abigail Damschroder Andrew Vila 《Electroanalysis》2023,35(8):e202300019
This work reports on the electroanalytical performance of a glassy carbon electrode (GCE) modified with antimony and bismuth (Sb/Bi-GCE) in detecting heavy metal ions using lead and cadmium as model analytes. The electroanalytical performance of the Sb/Bi-GCE surface was compared to the bismuth modified glassy carbon electrode (Bi-GCE) as well as the antimony modified glassy carbon electrode (Sb-GCE). The Sb/Bi-GCE exhibited excellent figures of merit compared to Bi-GCE and Sb-GCE surfaces. For example, the limit of detection for lead was 0.01 ppb using Sb/Bi-GCE and 0.1 and 1 ppb on Bi-GCE and Sb-GCE, respectively. 相似文献
307.
Francisco J. Ariza-López Domingo Barrera Salah Eddargani María José Ibáñez Juan F. Reinoso 《Mathematical Methods in the Applied Sciences》2023,46(2):1687-1698
A nonstandard low-cost spline approximation method for approximating bivariate functions is constructed. It is applied for Digital Elevation approximation and then its accuracy in the downscaling process is studied. 相似文献