全文获取类型
收费全文 | 2651篇 |
免费 | 133篇 |
国内免费 | 15篇 |
专业分类
化学 | 1629篇 |
晶体学 | 16篇 |
力学 | 133篇 |
数学 | 553篇 |
物理学 | 468篇 |
出版年
2023年 | 24篇 |
2022年 | 37篇 |
2021年 | 78篇 |
2020年 | 74篇 |
2019年 | 55篇 |
2018年 | 48篇 |
2017年 | 49篇 |
2016年 | 120篇 |
2015年 | 113篇 |
2014年 | 110篇 |
2013年 | 173篇 |
2012年 | 203篇 |
2011年 | 199篇 |
2010年 | 98篇 |
2009年 | 111篇 |
2008年 | 176篇 |
2007年 | 144篇 |
2006年 | 126篇 |
2005年 | 110篇 |
2004年 | 104篇 |
2003年 | 92篇 |
2002年 | 69篇 |
2001年 | 34篇 |
2000年 | 32篇 |
1999年 | 22篇 |
1998年 | 20篇 |
1997年 | 26篇 |
1996年 | 18篇 |
1995年 | 13篇 |
1994年 | 20篇 |
1993年 | 18篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 17篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1969年 | 4篇 |
排序方式: 共有2799条查询结果,搜索用时 15 毫秒
111.
112.
113.
Constantin Mateescu Ecaterina Princz Gilles Bouet Mustayeen A. Khan 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):947-958
The complex formation equilibrium of ethylenediaminetetramethylenephosphonic acid (EDTMP, H8L) with iron (III) has been studied potentiometrically at 25°C and an ionic strength of 0.2 M (NaCl). The successive protonation constants of ligand EDTMP and the complex formation constants were determined with the PSEQUAD program. Keeping in view the biological studies, the speciation in the system Fe (III)—EDTMP was calculated and drawn with the HySS computer program, and pFe values are compared. 相似文献
114.
Rodica Cǎpriţǎ Adrian Cǎpriţǎ Ludovic Kurunczi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract The polyphosphates have the capacity of forming chelates with most of that metal cations[l]. Polyphosphatic complexes with trace- and macroelements art used as fodder additives for animals. In our experiments we studied the effect 01pyrophosphate (PP), tripolyphosphate (TPP) and hexametaphosphate (HMP), at different concentrations (0.909 mM, 1.8 I8 mM and 2.727 mM), on the enzymatic activity of carbonic anhydrase (CA), and the effect of polyphosphate chelates or the enzymatic activity of alkaline phosphatase (AP), both zincenzymes. The meta; ion, which can be dissociated in the presence of a chelating agent, is essential foi their catalytic activity 121. The presence of metal atoms as essential constituents of some enzymes, and the metal requirements of others for maximum activity, provide an obvious link between enzymatic reaction and coordination chemistry. 相似文献
115.
Sebastian Reimann Alina Bunescu Andranik Petrosyan Muhammad Sharif Silke Erfle Constantin Mamat Tariel V. Ghochikyan Ashot S. Saghyan Anke Spannenberg Alexander Villinger Peter Langer 《Helvetica chimica acta》2013,96(10):1955-1967
A variety of 6‐(trichloromethyl)salicylates (=2‐hydroxy‐6‐(trichloromethyl)benzoates) were prepared by TiCl4‐mediated cyclization of 1,3‐bis(trimethylsilyloxy)buta‐1,3‐dienes with 1,1,1‐trichloro‐4,4‐dimethoxybut‐3‐en‐2‐one. The employment of trimethylsilyl trifluoromethanesulfonate (Me3SiOTf) as Lewis acid resulted in the formation of trichloromethyl‐substituted cyclohexenones. The cyclizations proceeded with good‐to‐very‐good regioselectivities. 相似文献
116.
Adrian Adamski Andrzej Biadasz Krzysztof Domieracki Marek Andrzej Kojdecki Dominik Paukszta Dominika Uryzaj 《Liquid crystals》2013,40(4):456-462
Liquid-crystalline perylene-3,4,9,10-tetra-(n-hexylester) forms characteristic dendritic or flower-like structures at room temperature when it is deposited on a hydrophilic glass substrate using the zone-casting technique. It was found that such unique structures were not possible to be created simply by recrystallisation of this dye from a liquid-crystalline columnar phase. On the basis of the observations using a confocal microscope and the study of wide angle X-ray scattering (WAXS) as well as the analysis of the absorption and fluorescence spectra, some conclusions, concerning the molecular organisation in the dendritic structure, are drawn. Based on the research, one can assume that the dendrites are formed by columnar molecular aggregates with the column axes parallel to the substrate. Such an organisation of the molecules can be interesting from the point of view of organic electronics. 相似文献
117.
Viorel Cîrcu Doina Mănăilă-Maximean Constantin Roşu Monica Iliş Yann Molard Florea Dumitraşcu 《Liquid crystals》2013,40(2):123-132
A series of ortho-metallated Pd and Pt complexes containing an imine ligand carrying three alkoxy chains and N-benzoylthiourea derivatives as co-ligands were prepared and their liquid crystalline properties investigated. Their structures were assigned based on elemental analysis, IR and 1H NMR spectroscopy, whereas thermal properties were investigated by differential scanning calotimetry and polarising optical microscopy. All the compounds exhibit monotropic transitions involving nematic and smectic A phases, with the mesomorphic behaviour strongly related to the type of N-benzoylthiourea as well as the metal centre used. The thermally stimulated depolarisation current technique was employed to determine the conduction mechanism, phase transition temperature and the activation energies for one of the ortho-metallated Pd complexes. 相似文献
118.
Dr. Paul Smart Dr. Charles A. Mason Jason R. Loader Dr. Anthony J. H. M. Meijer Prof. Alastair J. Florence Dr. Kenneth Shankland Dr. Ashleigh J. Fletcher Dr. Stephen P. Thompson Dr. Michela Brunelli Dr. Adrian H. Hill Prof. Lee Brammer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(11):3552-3557
119.
Nataliya A. Samoylova Nikita M. Belov Victor A. Brotsman Dr. Ilya N. Ioffe Dr. Natalia S. Lukonina Dr. Vitaliy Yu. Markov Dr. Adrian Ruff Alexey V. Rybalchenko Paul Schuler Olesya O. Semivrazhskaya Prof. Dr. Bernd Speiser Prof. Dr. Sergey I. Troyanov Prof. Dr. Tatiana V. Magdesieva Dr. Alexey A. Goryunkov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17969-17979
Novel difluoromethylenated [70]fullerene derivatives, C70(CF2)n (n=1–3), were obtained by the reaction of C70 with sodium difluorochloroacetate. Two major products, isomeric C70(CF2) mono‐adducts with [6,6]‐open and [6,6]‐closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X‐ray analysis and high‐level spectroscopic techniques. The [6,6]‐open isomer of C70(CF2) constitutes the first homofullerene example of a non‐hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C70(CF2) isomers showed that it is substantially higher for the [6,6]‐open isomer (the 70‐electron π‐conjugated system is retained) than the [6,6]‐closed form, the latter being similar to the electron affinity of pristine C70. In situ ESR spectroelectrochemical investigation of the C70(CF2) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter‐conversion between the [6,6]‐closed and [6,6]‐open forms of a cage‐modified fullerene driven by an electrochemical one‐electron transfer. Thus, [6,6]‐closed C70(CF2) constitutes an interesting example of a redox‐switchable fullerene derivative. 相似文献
120.
Andreia Alves Agnieszka Kucharska Claudio Erratico Fuchao Xu Elly Den Hond Gudrun Koppen Guido Vanermen Adrian Covaci Stefan Voorspoels 《Analytical and bioanalytical chemistry》2014,406(17):4063-4088
Human biomonitoring (HBM) is a scientific technique that allows us to assess whether and to what extent environmental pollutants enter humans. We review here the current HBM efforts for organophosphate esters, emerging flame retardants, perfluoroalkyl substances, and phthalate esters. Use of some of these chemicals has already been banned or restricted; they are regularly detected in the environment, wildlife, and human matrices. Traditionally, blood and urine collection have been widely used as sampling methods. New non-invasive approaches (e.g., saliva, hair, nails) are emerging as valid alternatives since they offer advantages with respect to sampling, handling, and ethical aspects, while ensuring similar reliability and sensitivity. Nevertheless, the identification of biomarkers of exposure is often difficult because chemicals may be metabolized in the human body. For many of the above-mentioned compounds, the mechanisms of the favorable metabolization pathways have not been unraveled, but research on important metabolites that could be used as biomarkers of exposure is growing. This review summarizes the state of the art regarding human exposure to, (non-invasive) HBM of, and metabolism of major organophosphate esters, emerging flame retardants, perfluoroalkyl substances, and phthalate esters currently detected in the environment. Figure
Human biomonitoring of emerging contaminants-non-invasive versus invasive matrices 相似文献