全文获取类型
收费全文 | 1401篇 |
免费 | 53篇 |
国内免费 | 2篇 |
专业分类
化学 | 1201篇 |
晶体学 | 11篇 |
力学 | 3篇 |
数学 | 100篇 |
物理学 | 141篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 127篇 |
2021年 | 116篇 |
2020年 | 39篇 |
2019年 | 34篇 |
2018年 | 31篇 |
2017年 | 32篇 |
2016年 | 67篇 |
2015年 | 44篇 |
2014年 | 64篇 |
2013年 | 112篇 |
2012年 | 122篇 |
2011年 | 109篇 |
2010年 | 83篇 |
2009年 | 59篇 |
2008年 | 75篇 |
2007年 | 58篇 |
2006年 | 72篇 |
2005年 | 65篇 |
2004年 | 30篇 |
2003年 | 32篇 |
2002年 | 20篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1456条查询结果,搜索用时 0 毫秒
121.
Denise T. B. De Salvi Hernane S. Barud Agnieszka Pawlicka Ritamara I. Mattos Ellen Raphael Younés Messaddeq Sidney J. L. Ribeiro 《Cellulose (London, England)》2014,21(3):1975-1985
New bacterial cellulose (BC)–triethanolamine (TEA) ion-conducting membranes have been prepared and characterized. The samples were obtained by soaking BC membranes in triethanolamine aqueous solutions and drying. The scanning electron microscopy pictures revealed that the incorporation of TEA in BC membranes covers the cellulose microfibrils. Raman spectra exhibited BC and TEA characteristic group frequencies and thermal analysis evidenced an influence of TEA content on the sample thermal stability. The ion-conductivity as a function of the temperature showed an Arrhenius behavior increasing from 1.8 × 10?5 S/cm at room temperature to 7.0 × 10?4 S/cm at 80 °C for the BC–TEA 1 M sample. 相似文献
122.
Gyroscope‐Like Molecules Consisting of PdX2/PtX2 Rotators within Three‐Spoke Dibridgehead Diphosphine Stators: Syntheses,Substitution Reactions,Structures, and Dynamic Properties 下载免费PDF全文
Dr. Agnieszka J. Nawara‐Hultzsch Dr. Michael Stollenz Dr. Michał Barbasiewicz Dr. Sławomir Szafert Dr. Tadeusz Lis Dr. Frank Hampel Dr. Nattamai Bhuvanesh Prof. Dr. John A. Gladysz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4617-4637
Threefold intramolecular ring‐closing metatheses of trans‐[MCl2(P{(CH2)mCH?CH2}3)2] are effected with Grubbs’ catalyst. Following hydrogenation catalyzed by [RhCl(PPh3)3], the title complexes trans‐[MCl2(P((CH2)n)3P )] (n=2m+2; M/n=Pt/14, 4 c ; Pt/16, 4 d ; Pt/18, 4 e ; Pd/14, 5 c ; Pd/18, 5 e ) and sometimes isomers partly derived from intraligand metathesis, trans‐[MCl2{P(CH2)n(CH2)n}P (CH2)n)] ( 4′c–e , 5′e ), are isolated. These react with LiBr, NaI, and KCN to give the corresponding MBr2, MI2, and M(CN)2 species (58–99 %). 13C NMR data show that the MX2 moieties rapidly rotate within the diphosphine cage on the NMR timescale, even at ?120 °C. The reaction of 4 c and KSCN gives separable Pt(NCS)2 and Pt(NCS)(SCN) adducts ( 13 c , 28 %; 14 c , 20 %), and those of 4 c , e and Ph2Zn give PtPh2 species ( 15 c , 61 %; 15 e , 90 %). 13C NMR spectra of 13 c – 15 c show two sets of CH2 signals (ca. 2:1 intensity ratios), indicating that MX2 rotation is no longer rapid. Reactions of 4 c or 4′c and excess NaC?CH afford the free diphosphines P{(CH2)14}3P (91 %) and (CH2)14P (CH2)14P(C H2)14 (90 %). The latter has been crystallographically characterized as a bis(BH3) adduct. The crystal structures of eight complexes with P(CH2)14P linkages (PtCl2, PtBr2, PtI2, Pt(NCS)2, PtPh2, PdCl2, PdBr2, PdI2) and 15 e have been determined, and intramolecular distances analyzed with respect to MX2 rotation. The conformations of the (CH2)14 moieties and features of the crystal lattices are also discussed. 相似文献
123.
Agnieszka Wojciechowska Andrzej Kochel Wiktor Zierkiewicz 《Journal of Coordination Chemistry》2016,69(5):886-900
We synthesized a l-arginine containing Zn2+ complex and oxalate ions. {[Zn2(l-Arg)2(ox)2]·8H2O}n (1) (l-Arg =l-arginine, ox = oxalate) crystallize in the monoclinic space group P21 with a = 8.979(2), b = 9.840(2) (Å), c = 18.509(3) (Å), β = 95.58(3) (Å), V = 1627.6(6) Å3, and Z = 2. The zinc centers are six-coordinate via one l-arginine zwitterion and two bridging oxalates. The binuclear [Zn2(l-Arg)2(ox)2] units are linked via oxalate and form 1-D “stair-like” linear chains. The complex was characterized using FT-IR, FT-Raman, UV–vis spectroscopy, and thermal analysis techniques, as well as DFT methods. Electronic bands above 31,000 cm?1 originate in 1,3Au (n→π*) transitions within oxalate ions. Theoretical studies were performed for the model compound {[Zn(l-Arg)(Hox)2]·4H2O} using the fragment of the crystallographic structure of 1. The interaction energy (ΔE) values for l-arginine and two oxalate ions are comparable at -145 kcal mol?1. Natural bond orbital (NBO) analysis of the electronic structure and bonding is also discussed. 相似文献
124.
Karolina Kula Agnieszka Kcka-Zych Agnieszka apczuk-Krygier Zbigniew Wzorek Anna K. Nowak Radomir Jasiski 《Molecules (Basel, Switzerland)》2021,26(5)
The present paper is a continuation of comprehensive study regarding to synthesis and properties of pyrazoles and their derivatives. In its framework an experimental and theoretical studies of thermal decomposition of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline were performed. It was found, that the decompositions of the mentioned pyrazoline system in the solution and at the melted state proceed via completely different molecular mechanisms. These mechanisms have been explained in the framework of the Molecular Electron Density Theory (MEDT) with the computational level of B3LYP/6-31G(d). A Bonding Evolution Theory (BET) examination of dehydrochlorination of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline permits elucidation of the molecular mechanism. It was found, that on the contrary for most known HCl extrusion processes in solution, this reaction is realised via single-step mechanism. 相似文献
125.
Agnieszka Bajorek Marcin Ciepluch Jerzy Pczkowski 《Journal of polymer science. Part A, Polymer chemistry》2002,40(20):3481-3488
The series of 9‐acridyl derivatives of aromatic amines have been investigated as fluorescent probes for monitoring the progress of free‐radical polymerization. This study on the changes in the fluorescence intensity and spectroscopic shift of specific compounds was carried out during thermally initiated polymerization of methyl methacrylate and photoinitiated polymerization of 2‐ethyl‐2‐(hydroxymethyl)‐1,3‐propanediol triacrylate‐1‐methyl‐2‐pyrrolidonone mixture. The purpose of this investigation was to find a relationship between the changes in the shape and intensity of fluorescent probes and the degree of monomer conversion into a polymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3481–3488, 2002 相似文献
126.
Jolanta Obniska Krzysztof Kaminski Agnieszka Dzierzawska-Majewska 《Journal of fluorine chemistry》2006,127(3):417-425
A series of N-phenyl- and N-benzyl-2-azaspiro[4.4]nonane- and [4.5]decane-1,3-diones containing a fluoro or trifluoromethyl substituents at the aryl ring was synthesized and tested for their anticonvulsant activity in the maximal electroshock (MES) and subcutaneous metrazole (sc.Met) tests. Among them, the most active were N-benzyl derivatives with fluoro and trifluoromethyl substituents especially at position-2 of the aryl moiety. The introduction of the phenyl ring at the imide nitrogen atom resulted in less active compounds. The results obtained showed that incorporation of fluoro or trifluoromethyl substituents increased the anticonvulsant activity in comparison to respective chloro, methoxy or methyl analogues. Crystallographically obtained conformation for one active and two inactive derivatives with trifluoromethyl substituents at position-2 or -3 of phenyl ring were initially used for molecular electrostatic potentials (MEP) calculation. The MEP distribution at carbonyl oxygen atoms was different for active and inactive molecules. 相似文献
127.
Kaczor A Gómez-Zavaglia A Cardoso AL Pinho e Melo TM Fausto R 《The journal of physical chemistry. A》2006,110(37):10742-10749
The aliphatic 2H-azirine, methyl 3-methyl-2H-azirine-2-carboxylate (MMAC), has been synthesized and its monomeric form investigated by IR spectroscopy in an argon matrix, at 10 K, as well as theoretically (DFT/B3LYP/6-311++G(d,p)). Two low-energy conformers of MMAC (Ct and Cc) were found in the matrix, both exhibiting the cis conformation around the C-O bond but differing in the arrangement around the C-C(alpha) bond. The two conformers were photoreactive upon in situ broadband UV excitation (lambda > 235 nm), yielding nitrile ylide (P1) and ketene imine (P2) type products, which resulted from cleavage of the C-C or C-N bond, respectively. The kinetics of the reactions leading to the formation of P1 and P2 are of first order, with the processes being favored when the reactant is in the Cc conformation. Very interestingly, the C-N bond photocleavage, which is unusual for aliphatic 2H-azirines, was found to be preferred over the generally favored in 2H-azirines C-C bond breakage. This behavior is attributed to the presence in the molecule of the electron-withdrawing methoxycarbonyl substituent, which accelerates the intersystem crossing toward the T(1) triplet state and, in this way, favors the C-N bond cleavage. In addition to the primary photoprocesses leading to formation of P1 and P2, secondary photoprocesses leading to the decarboxylation and decarbonylation of P2 have been also observed. 相似文献
128.
Marta Klimek-Szczykutowicz Micha Dziurka Ivica Blaevi Azra ulovi Sebastian Granica Izabela Korona-Glowniak Halina Ekiert Agnieszka Szopa 《Molecules (Basel, Switzerland)》2020,25(22)
The main compounds in both extracts were gluconasturtiin, 4-methoxyglucobrassicin and rutoside, the amounts of which were, respectively, determined as 182.93, 58.86 and 23.24 mg/100 g dry weight (DW) in biomass extracts and 640.94, 23.47 and 7.20 mg/100 g DW in plant herb extracts. The antioxidant potential of all the studied extracts evaluated using CUPRAC (CUPric Reducing Antioxidant Activity), FRAP (Ferric Reducing Ability of Plasma), and DPPH (1,1-diphenyl-2-picrylhydrazyl) assays was comparable. The anti-inflammatory activity of the extracts was tested based on the inhibition of 15-lipoxygenase, cyclooxygenase-1, cyclooxygenase-2 (COX-2), and phospholipase A2. The results demonstrate significantly higher inhibition of COX-2 for in vitro cultured biomass compared with the herb extracts (75.4 and 41.1%, respectively). Moreover, all the studied extracts showed almost similar antibacterial and antifungal potential. Based on these findings, and due to the fact that the growth of in vitro microshoots is independent of environmental conditions and unaffected by environmental pollution, we propose that biomass that can be rapidly grown in RITA® bioreactors can serve as an alternative source of bioactive compounds with valuable biological properties. 相似文献
129.
Ignacio García Agnieszka Tercjak Nikolaos E. Zafeiropoulos Manfred Stamm Iaki Mondragon 《Macromolecular rapid communications》2007,28(24):2361-2365
Magnetic nanomaterials have been studied in order to generate novel nanocomposites that display both the magnetic properties of the nanoparticles and the ability to self‐assemble of the amorphous block copolymer matrix. Towards this goal, iron oxide magnetic nanoparticles have been modified with PS brushes by ATRP in order to improve both the dispersion and the affinity of the nanoparticles with one of the blocks of a polystyrene‐block‐polybutadiene‐block‐polystyrene block copolymer. This method of preparation of nanocomposites opens new strategies for the generation of magnetic nanomaterials. The samples are characterized using DSC and atomic and magnetic force microscopies.
130.
Agnieszka Kaamajska 《Mathematical Methods in the Applied Sciences》2006,29(11):1307-1325
The weak limits of sequences {f(uν)}ν∈? where uν's are vector‐valued µ‐measurable functions defined on a compact set Ω and f is (possibly) discontinuous are investigated. As shown by the author (J. Conv. Anal. (to appear)), they are described in terms of integral formulae involving parametrized measures independent of f, similarly as in the classical theorem by Young and its generalization due to DiPerna and Majda. In the present paper we describe the supports of the involved parametrized measures. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献