全文获取类型
收费全文 | 776篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
化学 | 634篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 62篇 |
物理学 | 100篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 49篇 |
2021年 | 48篇 |
2020年 | 27篇 |
2019年 | 35篇 |
2018年 | 20篇 |
2017年 | 18篇 |
2016年 | 27篇 |
2015年 | 34篇 |
2014年 | 43篇 |
2013年 | 61篇 |
2012年 | 63篇 |
2011年 | 76篇 |
2010年 | 37篇 |
2009年 | 29篇 |
2008年 | 42篇 |
2007年 | 48篇 |
2006年 | 35篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1976年 | 1篇 |
1969年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有808条查询结果,搜索用时 15 毫秒
51.
Aysun apc Mlanie M. Lorion Hui Wang Nina Simon Maria Leidenberger Mariana C. BorgesSilva Diogo R. M. Moreira Yongping Zhu Yuqing Meng Jia Yun Chen Yew Mun Lee Oliver Friedrich Barbara Kappes Jigang Wang Lutz Ackermann Svetlana B. Tsogoeva 《Angewandte Chemie (International ed. in English)》2019,58(37):13161-13161
52.
Different physical chemical methods were used to study the thermochemical processes in a system involving a natural phosphate and complex acid salts of ammonium sulphate. The products of decomposition of the double ammonium salt and the products of their interactions with the phosphate were identified. The formation of ammonium and calcium polyphosphates and the disproportionation of P3O 10 5? and P2O 7 4? to PO 4 3? and PO 3 ? were found to depend on the circumstances of the thermal interactions. 相似文献
53.
Danielly S. Campos-Ferreira Gustavo A. Nascimento Elaine V.M. Souza Maria A. Souto-Maior Mariana S. Arruda Deborah M.L. Zanforlin Marek H.F. Ekert Danyelly Bruneska José L. Lima-Filho 《Analytica chimica acta》2013
An electrochemical DNA biosensor for human papillomavirus (HPV) 16 detection has been developed. For this proposed biosensor, l-cysteine was first electrodeposited on the gold electrode surface to form l-cysteine film (CYSFILM). Subsequently, HPV16-specific probe was immobilized on the electrode surface with CYSFILM. Electrochemistry measurement was studied by differential pulse voltammetry method (DPV). The measurement was based on the reduction signals of methylene blue (MB) before and after hybridization either between probe and synthetic target or extracted DNA from clinical samples. The effect of probe concentration was analyzed and the best results were seen at 1000 nM. The hybridization detection presented high sensitivity and broad linear response to the synthetic-target concentration comprised between 18.75 nM and 250 nM as well as to a detection limit of 18.13 nM. The performance of this biosensor was also investigated by checking probe-modified electrode hybridization with extracted DNA from samples. The results showed that the biosensor was successfully developed and exhibited high sensitivity and satisfactory selectivity to HPV16. These results allow for the possibility of developing a new portable detection system for HPVs and for providing help in making an effective diagnosis in the early stages of infection. 相似文献
54.
Natural-based plasticizers and biopolymer films: A review 总被引:2,自引:0,他引:2
Melissa Gurgel Adeodato Vieira Mariana Altenhofen da Silva Lucielen Oliveira dos Santos Marisa Masumi Beppu 《European Polymer Journal》2011,(3):254-263
In recent years, much attention has been focused on research to replace petroleum-based commodity plastics, in a cost-effective manner, with biodegradable materials offering competitive mechanical properties. Biopolymers have been considered as the most promising materials for this purpose. However, they generally present poor mechanical properties regarding processability and end-use application, since the fragility and brittleness exhibited during thermoformation can limit their potential for application. In order to overcome this problem, plasticizers are added to provide the necessary workability to biopolymers. This class of products became more visible when biodegradable additives and plasticizers also became the focus of material scientists. The use of natural and/or biodegradable plasticizers, with low toxicity and good compatibility with several plastics, resins, rubber and elastomers in substitution of conventional plasticizers, such as phthalates and other synthetic conventional plasticizers attracted the market along with the increasing worldwide trend towards use of biopolymers. Here we discuss the main results and developments in natural plasticizer/synthetic and biopolymer-based films during the last decades. 相似文献
55.
Mariana P. Serrano Claudio D. Borsarelli Andrés H. Thomas 《Photochemistry and photobiology》2013,89(6):1456-1462
Biopterin (Bip) and its photoproducts 6‐formylpterin (Fop) and 6‐carboxypterin (Cap) accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder where the protection against UV radiation fails because of the lack of melanin. These compounds absorb in the UV‐A inducing a potential photosensitizing action that can cause damage to DNA and other biomolecules. In this work, we have investigated the capability of these pterin derivatives (Pt) to act as photosensitizers under UV‐A irradiation for the degradation of 2′‐deoxyadenosine 5′‐monophosphate (5′‐dAMP) in aqueous solutions, as model DNA target. Steady‐state and time‐resolved experiments were performed and the effect of pH was evaluated. The results showed that photosensitized degradation of 5′‐dAMP was only observed under acidic conditions, and a mechanistic analysis revealed the participation of the triplet excited state of the pterin derivatives (3Pt*) by electron transfer yielding the corresponding pair of radical ions (Pt?? and 5′‐dAMP?+), with successive photosensitizer recovery by electron transfer from Pt?? to O2. Finally, 5′‐dAMP?+ participates in subsequent reactions to yield degradation products. 相似文献
56.
Topchieva IN Tonelli AE Panova IG Matuchina EV Kalashnikov FA Gerasimov VI Rusa CC Rusa M Hunt MA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(21):9036-9043
Wide-angle X-ray scattering observations of alpha-cyclodextrin (CD)-poly(ethylene glycol) (PEG) inclusion complexes (ICs) have shown for the first time that two crystalline columnar modifications (forms I and II) are produced in the process of their formation. This was made possible by precise azimuthal X-ray diffraction scanning of oriented IC samples. Form I is characterized by CDs threaded onto PEG chains and arranged along channels in the order head-to-head/tail-to-tail, while form II is formed by unbound CDs also arranged into columns in a head-to-tail and also possibly a head-to-head/tail-to-tail manner, probably as a result of template crystallization on the form I IC crystals. It was shown that similar structural peculiarities are inherent for channel structures based on ICs obtained with PEG with a wide range of molecular weights (MWs). The characteristic feature of ICs based on PEG, especially with MW > 8000, is the presence of unbound polymer in the composition of the complex. The amount of unbound PEG was shown to rise with increasing MW of PEG, resulting in greater imperfections in the IC crystalline structure. The polyblock structure of ICs based on alpha-CD and PEG was therefore proposed. 相似文献
57.
58.
This study investigated the organic and inorganic constituents of healthy leaves and Candidatus Liberibacter asiaticus (CLas)-inoculated leaves of citrus plants. The bacteria CLas are one of the causal agents of citrus greening (or Huanglongbing) and its effect on citrus leaves was investigated using laser-induced breakdown spectroscopy (LIBS) combined with chemometrics. The information obtained from the LIBS spectra profiles with chemometrics analysis was promising for the construction of predictive models to identify healthy and infected plants. The major, macro- and microconstituents were relevant for differentiation of the sample conditions. The models were then applied to different inoculation times (from 1 to 8 months). The models were effective in the classification of 82-97% of the diseased samples with a 95% significance level. The novelty of this method was in the fingerprinting of healthy and diseased plants based on their organic and inorganic contents. 相似文献
59.
Juliana Ivanova Ivayla N. Pantcheva Mariana Mitewa Svetlana Simova Heike Mayer-Figge William S. Sheldrick 《Central European Journal of Chemistry》2010,8(4):852-860
The single crystal X-ray structures and the spectroscopic properties of complexes of monensic acid (C36H62O11·H2O) with toxic metal ions of Cd(II) and Hg(II) are discussed. The cadmium(II) complex (1) is of composition [Cd(C36H61O11)2(H2O)2] and crystallizes in the monoclinic system (space group P2(1), Z = 2) with a = 12.4090(8), b = 24.7688(16), c = 14.4358(11) Å, β = 91.979(7)°. Two ligand monoanions are bound in a bidentate coordination mode to Cd(II) via the carboxylate and the primary hydroxyl oxygens occupying the equatorial plane of the complex. The axial positions of the inner coordination sphere of Cd(II) are filled by two water molecules additionally engaged in intramolecular hydrogen bonds. The Hg(II) complex (2), [Hg(C36H60O11)(H2O)], crystallizes in the orthorhombic system (space group P2(1)2(1)2(1), Z = 4) with a = 12.7316(2), b = 16.4379(3), c = 18.7184(4) Å. The monensic acid reacts with Hg(II) in a tetradentate coordination manner via both oxygen atoms of the carboxylate function and oxygens of two hydroxyl groups. The twofold negative charge of the ligand is achieved by deprotonation of carboxylic and secondary hydroxyl groups located at the opposite ends of the molecule. Hg(II) is surrounded by five oxygen atoms in a distorted square pyramidal molecular geometry.
相似文献