全文获取类型
收费全文 | 4941篇 |
免费 | 181篇 |
国内免费 | 34篇 |
专业分类
化学 | 3455篇 |
晶体学 | 48篇 |
力学 | 80篇 |
数学 | 654篇 |
物理学 | 919篇 |
出版年
2023年 | 29篇 |
2022年 | 102篇 |
2021年 | 111篇 |
2020年 | 110篇 |
2019年 | 109篇 |
2018年 | 102篇 |
2017年 | 67篇 |
2016年 | 179篇 |
2015年 | 138篇 |
2014年 | 165篇 |
2013年 | 273篇 |
2012年 | 338篇 |
2011年 | 411篇 |
2010年 | 206篇 |
2009年 | 177篇 |
2008年 | 290篇 |
2007年 | 273篇 |
2006年 | 277篇 |
2005年 | 244篇 |
2004年 | 187篇 |
2003年 | 168篇 |
2002年 | 150篇 |
2001年 | 61篇 |
2000年 | 68篇 |
1999年 | 44篇 |
1998年 | 31篇 |
1997年 | 43篇 |
1996年 | 67篇 |
1995年 | 57篇 |
1994年 | 28篇 |
1993年 | 38篇 |
1992年 | 42篇 |
1991年 | 34篇 |
1990年 | 28篇 |
1989年 | 24篇 |
1988年 | 27篇 |
1987年 | 17篇 |
1986年 | 21篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 23篇 |
1982年 | 36篇 |
1981年 | 30篇 |
1980年 | 30篇 |
1979年 | 26篇 |
1978年 | 26篇 |
1977年 | 16篇 |
1975年 | 17篇 |
1974年 | 15篇 |
1973年 | 17篇 |
排序方式: 共有5156条查询结果,搜索用时 32 毫秒
121.
Adam S. Paziak Lech Celewicz Krzysztof Ciszewski Krzysztof Golankiewicz 《Journal of mass spectrometry : JMS》1993,28(5):643-646
The electron impact mass spectra of 6-methyltetrazolo[1,5-c]pyrimidin-5(6H)-one, its 7- and 8-methyl derivatives, three 8-halo derivatives and two related nucleosides are reported. On the basis of the high-resolution data and detected metastable ions, the fragmentation routes of their molecular ions are proposed. Coexistence of the tautomeric forms of the title compounds of cyclic (tetrazole) or linear (azide) structure can be suggested owing to the fragmentation pathways identified for the bases. Decomposition of the related nucleosides lies in the breaking of nucleoside bonds to produce the appropriate base and sugar fragments. 相似文献
122.
A series of trialkylsilyl esters were deprotected or transesterificated into their corresponding carboxylic acids or methyl esters under a catalytic amount of CBr4 in alcohol reaction system. This method enables to desilylate secondary sp3-carbon, sp2-carbon, sp-carbon and aryl tethered trialkylsilyl esters to carboxylic acids, whereas primary sp3-carbon tethered trialkylsilyl esters were further converted into their methyl esters under CBr4/MeOH reaction conditions. The highly chemoselective deprotections can be modulated and achieved by the introduced protecting trialkylsilyl groups and the used alcohols such as MeOH and EtOH under this photochemically-induced reaction conditions. 相似文献
123.
Adam D. Martin Jonathan P. Wojciechowski Eric Y. Du Aditya Rawal Holly Stefen Carol G. Au Liming Hou Charles G. Cranfield Thomas Fath Lars M. Ittner Pall Thordarson 《Chemical science》2020,11(5):1375
Peptide-based nanofibres are a versatile class of tunable materials with applications in optoelectronics, sensing and tissue engineering. However, the understanding of the nanofibre surface at the molecular level is limited. Here, a series of homologous dilysine–diphenylalnine tetrapeptides were synthesised and shown to self-assemble into water-soluble nanofibres. Despite the peptide nanofibres displaying similar morphologies, as evaluated through atomic force microscopy and neutron scattering, significant differences were observed in their ability to support sensitive primary neurons. Contact angle and labelling experiments revealed that differential presentation of lysine moieties at the fibre surface did not affect neuronal viability; however the mobility of phenylalanine residues at the nanofibre surface, elucidated through solid- and gel-state NMR studies and confirmed through tethered bilayer lipid membrane experiments, was found to be the determining factor in governing the suitability of a given peptide as a scaffold for primary neurons. This work offers new insights into characterising and controlling the nanofibre surface at the molecular level.The mobility of hydrophobic moieties at a peptide nanofibre surface determines its suitability as a scaffold for sensitive primary cells. 相似文献
124.
Mariusz?T.?Galkowski Pawel?J.?KuleszaEmail author Krzysztof?Miecznikowski Malgorzata?Chojak Henryk?Bala 《Journal of Solid State Electrochemistry》2004,8(6):430-434
We propose a novel composite organic-inorganic coating in the form of a redox polymer film for protection of stainless steel against general corrosion in strong acid medium (2 M H2SO4). We utilize an anion exchange polymer, protonated poly(4-vinylpyridine), into which hexacyanoferrate anions have been introduced. Owing to the presence of Fe(CN)63–/4– at the interface formed by the film and the steel, a sparingly soluble metal hexacyanoferrate (mostly Prussian blue, PB) is formed as an overcoating on the steels surface, presumably on the passive (metal oxide) layer. The redox polymer film on the steel seems to act as a composite three-dimensional bilayer-type coating in which hexacyanoferrate(III,II) anions (that are capable of effective charge storage) exist in the outer portions of the film, whereas the inner PB layer improves the systems overall adherence and stability. By analogy to a conducting polymer (e.g. polyaniline, polypyrrole), introduction of the redox polymer composite film leads to stabilization of the steel substrates potential within the passive range.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003) 相似文献
125.
Poon T Turro NJ Chapman J Lakshminarasimhan P Lei X Jockusch S Franz R Washington I Adam W Bosio SG 《Organic letters》2003,5(26):4951-4953
Oxazolidinone-substituted enecarbamates represent a mechanistically rich system for the study of stereoelectronic, steric, and conformational effects on stereoselectivity and mode selectivity in (1)O(2) [2 + 2] and ene reactions. Photooxygenation of these enecarbamates with (1)O(2) leads to diastereomerically pure dioxetanes that decompose to yield an oxazolidinone carbaldehyde and one of the two enantiomers of methyldesoxybenzoin in enantiomeric excess. Stereoselectivity originates at the allylic stereocenter, a result supported by quenching studies, computational analysis, and deuterium solvent isotope effects. [reaction: see text] 相似文献
126.
Akita M Miyaji T Muroga N Mock-Knoblauch C Adam W Hikichi S Moro-oka Y 《Inorganic chemistry》2000,39(10):2096-2102
Mono- and dinuclear hydroxopalladium complexes (kappa 2-TpiPr2,X)(py)Pd-OH (1; X = H, Br) and (mu-OH)2[Pd(kappa 2-TpiPr2)(H2O)]2 (2) are prepared by base hydrolysis of the corresponding chloride complexes (kappa 2-TpiPr2,X)(py)Pd-Cl (3) and (mu-Cl)2[Pd(kappa 3-TpiPr2)]2 (4), respectively. Functionalization of the OH part in 1 is effected via dehydrative condensation with protic substrates (H-A) to give a series of substituted products, (kappa 2-TpiPr)(py)Pd-A (5), and treatment of the dinuclear complex 2 with excess acetic acid affords the mononuclear diacetato complex 6, (kappa 2-TpiPr2-H)Pd(OAc)2(HOAc). Complexes 1-4 and 6 have been characterized crystallographically, and it is revealed that complexes 2 and 6 involve cyclic hydrogen-bonding interaction among the nitrogen atom of the pendent noncoordinated pyrazolyl group, the hydrogen atom in the protic part of the ligand (OH, AcOH), and, in the case of 2, an external water molecule. 相似文献
127.
Adam Bechler 《Annals of Physics》1977,108(1):49-68
Perturbation method based on the group theory is developed for the radial solution of the Schrödinger equation with screened Coulomb potential. It may be treated as an alternative to the analytic perturbation theory proposed recently by McEnnan, Kissel, and Pratt (Phys. Rev. A, 2 (1976), 532) and is based on the expansion of the potential of the following form . Corrections to the point-Coulomb energy levels are given as series in λ and also the screened Coulomb eigenstates are given in the form of expansions in powers of λ. The method is applied also to the continuous spectrum and similar expansions are found. The problem of the normalization of both discrete and continuous spectrum eigenstates is discussed and we find some differences in the case of the scattering states. Origin of this discrepancy is explained. 相似文献
128.
Biosensors designed for environmental and food quality control based on screen-printed graphite electrodes with different configurations 总被引:3,自引:0,他引:3
Avramescu A Andreescu S Noguer T Bala C Andreescu D Marty JL 《Analytical and bioanalytical chemistry》2002,374(1):25-32
Graphite electrodes fabricated by screen-printing have been used as amperometric detectors in biosensors based on NAD(+)-dependent dehydrogenases, tyrosinase, or genetically modified acetylcholinesterases. The mono-enzyme sensors have been optimized as disposable or reusable devices for detection of a variety of substrates important in the food industry ( D-lactic acid, L-lactic acid, acetaldehyde) or in environmental pollution control (phenols and dithiocarbamate, carbamate and organophosphorus pesticides). The sensors were prepared in four configurations differing in enzyme confinement, enzyme immobilization and location of the immobilization agent in the biosensor assembly. Tests on real samples have been performed with the biosensors; D-lactic acid and acetaldehyde have been detected in wine and phenols in air. 相似文献
129.
Delphine Batt-Coutrot David M. Haddleton Adam P. Jarvis Ray L. Kelly 《European Polymer Journal》2003,39(12):2243-2252
Polymerisation of vinyl acetate by conventional free radical polymerisation using a diazo initiator followed by copper mediated living radical polymerisation with a range of monomers was studied. This method led to the synthesis of triblock copolymers. We have thus successfully prepared several new ABA triblock copolymers where B is poly(vinyl acetate) and A is (dimethylamino)ethyl methacrylate (DMAEMA), (polyethylene glycol) methyl ether methacrylate (MeO(PEG)MA) or solketal methacrylate (SMA). The sequential conventional/living radical polymerisation approach provided an efficient route to synthesis of new block copolymers. The properties of these amphiphilic polymers have been subsequently investigated by 1H NMR, fluorescence spectroscopy, tensiometry and dynamic light scattering to investigate their behaviour as potential surfactants. 相似文献
130.
Zi-Shu Yang Yuhang Yao Adam C. Sedgwick Cuicui Li Ye Xia Yan Wang Lei Kang Hongmei Su Bing-Wu Wang Song Gao Jonathan L. Sessler Jun-Long Zhang 《Chemical science》2020,11(31):8204
We report here porphodilactol derivatives and their corresponding metal complexes. These systems show promise as “all-in-one” phototheranostics and are predicated on a design strategy that involves controlling the relationship between intersystem crossing (ISC) and photothermal conversion efficiency following photoexcitation. The requisite balance was achieved by tuning the aromaticity of these porphyrinoid derivatives and forming complexes with one of two lanthanide cations, namely Gd3+ and Lu3+. The net result led to a metalloporphodilactol system, Gd-trans-2, with seemingly optimal ISC efficiency, photothermal conversion efficiency and fluorescence properties, as well as good chemical stability. Encapsulation of Gd-trans-2 within mesoporous silica nanoparticles (MSN) allowed its evaluation for tumour diagnosis and therapy. It was found to be effective as an “all-in-one” phototheranostic that allowed for NIR fluorescence/photoacoustic dual-modal imaging while providing an excellent combined PTT/PDT therapeutic efficacy in vitro and in vivo in 4T1-tumour-bearing mice.We report here porphodilactol derivatives and their corresponding metal complexes as “all-in-one” phototheranostics by controlling the relationship between intersystem crossing (ISC) and photothermal conversion efficiency following photoexcitation. 相似文献