全文获取类型
收费全文 | 1226篇 |
免费 | 57篇 |
国内免费 | 8篇 |
专业分类
化学 | 791篇 |
晶体学 | 33篇 |
力学 | 58篇 |
综合类 | 2篇 |
数学 | 168篇 |
物理学 | 239篇 |
出版年
2023年 | 7篇 |
2022年 | 21篇 |
2021年 | 46篇 |
2020年 | 37篇 |
2019年 | 33篇 |
2018年 | 42篇 |
2017年 | 28篇 |
2016年 | 61篇 |
2015年 | 42篇 |
2014年 | 65篇 |
2013年 | 115篇 |
2012年 | 88篇 |
2011年 | 106篇 |
2010年 | 70篇 |
2009年 | 60篇 |
2008年 | 54篇 |
2007年 | 72篇 |
2006年 | 53篇 |
2005年 | 50篇 |
2004年 | 29篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 10篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 16篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1964年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有1291条查询结果,搜索用时 31 毫秒
951.
Hasan?Karab?y?kEmail author Muhittin?Aygün Necdet?Co?kun Canan?Kazak 《Journal of chemical crystallography》2005,35(8):577-582
Molecular and crystal structure of 2-methyl-3-(2-nitro-phenyl)-4-phenyl-[1,2,4]oxadiazolidin-5-one, C15H13N3O4, have been determined by single crystal X-ray diffraction study. The title compound is monoclinic, with a = 10.0313(8) Å, b = 9.0372(5) Å, c = 15.5964(14) Å, β = 96.926(7)∘, Z = 4, Dx = 1.42 g/cm3, μ (Mo-Kα) = 0.105 mm−1, and space group is P 21/c. The structure was solved by direct methods and refined to a final R = 0.036 for 1894 reflections with I > 4σ (I). The crystal structure is stabilized by C–H⋅sO type inter-molecular, C–H⋅sN and C–H⋅sO type intra-molecular, π–π stacking and edge to face (C–H⋅s π-ring) interactions. To enlighten conformational flexibility of the title molecule, selected two torsion angles are varied from −180∘ to +180∘ in every 10∘ separetely and then molecular energy profile is calculated and construed. 相似文献
952.
Mohammad R. Hasan Michael B. Hursthouse Shariff E. Kabir K.M. Abdul Malik Edward Rosenberg Tasneem A. Siddiquee 《Journal of chemical crystallography》1999,29(5):597-602
The reaction of [Ru3(CO)10(-dppm)] 1 with PPhCl2 in refluxing CHCl3 results in the isolation of [(-H)Ru3(CO)8(-Cl)(-dppm)] 3 in 10% yield. Compound 3, which has been structurally characterized by crystallographic methods, is also formed from the reaction of 1 with H2 in refluxing CCl4. The compound crystallizes in the monoclinic space group P21/c with a = 16.814(2), b = 18.7590(12), c = 11.486(2) Å, = 97.745(11)°, V = 3589.8(8) Å3, and Z = 4. The hydride and chloride ligands bridge the same edge of the triruthenium cluster as the dppm ligand. 相似文献
953.
954.
Topological design of centralized computer communication networks is a complex problem that is generally solved in two phases. The first phase of the design process involves dividing network nodes (terminals or clusters of terminals) into groups, and selecting a concentrator location for each group so that all the nodes in a group are assigned to the same concentrator. The next phase determines topology of links that connect network nodes to concentrators and concentrators to each other and to the central computer. The design problem studied in this paper contains some aspects of both phases. In this problem locations of concentrators, assignments of user nodes to concentrators and the topology of the links connecting concentrators to the central computer are jointly determined. The proposed design method is built around the well known sweep heuristic which is used to partition the node space into sectors. Each of these sectors contain a backbone path connecting concentrators to the central computer. 相似文献
955.
Armstrong TA Bettoni D Bharadwaj V Biino C Borreani G Broemmelsiek D Buzzo A Calabrese R Ceccucci A Cester R Church MD Dalpiaz P Dalpiaz PF Dibenedetto R Dimitroyannis D Fabbri MG Fast JE Gianoli A Ginsburg CM Gollwitzer KE Hahn AA Hasan MA Hsueh SY Lewis RA Luppi E Macrí M Majewska A Mandelkern MA Marchetto F Marinelli M Marques JL Marsh W Martini M Masuzawa M Menichetti E Migliori A Mussa R Palestini S Pallavicini M Pastrone N Patrignani C Peoples J Pesando L Petrucci F Pia MG Pordes S 《Physical review letters》1993,70(9):1212-1215
956.
957.
Mohammad K. Rofouei Hamid Khoshsafar Hasan Bagheri Roozbeh J. Kalbasi 《International journal of environmental analytical chemistry》2018,98(2):156-170
In this study, a new strategy for the preparation of a modified glassy carbon electrode (GCE) based on a novel nano-sensing layer for the electrocatalytic oxidation of hydrazine was suggested. The suggested nano-sensing layer was prepared with the immobilisation of silver nanoparticles (AgNPs) on ordered mesoporous carbon. The morphology and properties of the prepared nanocomposite on the surface of GCE were characterised by scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, X-ray powder diffraction and electrochemical impedance spectroscopy. The electrochemical response characteristics of the modified electrode towards the target analyte were investigated by cyclic voltammetry. Under optimal experimental conditions, the suggested modified GCE showed excellent catalytic activity towards the electro-oxidation of hydrazine (pH = 7.5) with a significant increase in anodic peak currents in comparison with the unmodified GCE. By differential pulse voltammetry and amperometric methods, the suggested sensor demonstrated wide dynamic concentration ranges of 0.08–33.8 µM and 0.01–128 µM with the detection limit (S/N = 3) of 0.027 and 0.003 µM for hydrazine, respectively. The suggested hydrazine sensor was successfully applied for the highly sensitive determination of hydrazine in different real samples with satisfactory results. 相似文献
958.
N. C. Roy M. M. Hasan M. R. Talukder M. D. Hossain A. N. Chowdhury 《Plasma Chemistry and Plasma Processing》2018,38(1):13-28
Medium pressure (~ 10 torr) low frequency (3–5 kHz) glow discharge (LFGD) plasmas were applied to treat wheat (Triticum aestivum) seeds to investigate the effects on water absorption, seed germination rate, seedling growth and yield. The LFGD plasmas were produced with air and air/O 2. Optical emission spectroscopic diagnostic methods were revealed that the \({\text{N}}_{2} \left( {{\text{C}}^{3}\Pi _{\text{u}} - {\text{B}}^{3}\Pi _{\text{g}} } \right)\), \({\text{N}}_{2}^{ + } \left( {{\text{B}}^{2}\Sigma _{\text{u}}^{ + } - {\text{X}}^{2}\Sigma _{\text{g}}^{ + } } \right)\) and \({\text{N}}_{2} \left( {{\text{B}}^{3}\Pi _{\text{g}} - {\text{A}}^{3}\Sigma _{\text{u}}^{ + } } \right)\) produced with air, and O species were produced along with nitrogen species with air/O 2 plasmas, respectively. The SEM images were revealed that the surface architectures and functionalities of the seeds were modified due to plasma treatments. Water absorption was found to increase with treatment time. 6 min treatment was provided 95–100% seed germination. The plants grown from treated seeds for 3 and 9 min duration by air/O 2 plasma were showed the highest growth activity and dry matter accumulation. Total chlorophyll contents of the leaves, longest spikes and number of spikes/spikelet were also increased. The wheat yield was increased ~ 20% over control by 6 min treatment with air/O 2 plasma. Overall results revealed that LFGD plasmas can significantly change seed surface architecture, water absorption, germination rate, seedling growth and yield of wheat. 相似文献
959.
Hasan Karabıyık Gülsiye Öztürk Ürüt Resul Sevinçek 《Journal of Saudi Chemical Society》2018,22(5):519-526
Molecular structures of two unsaturated oxazolone derivatives involving furan rings, which are decorated with p-tolyl (FurM) and 4-nitro phenyl (FurN), were investigated by X-ray crystallography and quantum chemical calculations. Their ground and excited states were examined by DFT and TD-DFT computations with the aid of topological electron density studies, NBO and Charge Decomposition Analysis. Both compounds have push-pull (D–π–A) framework using oxazolone ring as π-linker. Depending on the transitions from the ground to excited states, intramolecular charge transfer (ICT) in both compounds results in aromatization of oxazolones. Push-pull ability of FurN has more pronounced than that of FurM. The use of furan instead of almost fully aromatic benzenoid ring reduces HOMO?LUMO band gap due to relatively low aromaticity level of furan. Introduction of nitro substituent leads to a further reduction in HOMO?LUMO gap. In addition, electronic redistribution in the excited state results in aromatization of oxazolone moieties without elongation of carbonyl bonds. 相似文献
960.
Gülin Renda Büşra Korkmaz Merve Kılıç Mine Kadıoğlu Duman Hasan Kırmızıbekmez 《Natural product research》2018,32(16):1902-1910
The present study was undertaken to evaluate the in vivo analgesic activities of the extracts prepared from the aerial parts and roots of Scrophularia kotscyhana and to isolate the bioactive metabolites from the most active extract. Analgesic activities of all extracts and subextracts at the doses of 5, 10 and 30 mg/kg (i.p.) were examined using hot plate test in mice. Among the tested extracts, MeOH extract prepared from the aerial parts and the n-butanol subextract prepared thereof displayed the best analgesic activity at all doses. Phytochemical studies on n-butanol subextract led to the isolation of two new iridoid glycosides as an inseparable mixture, 8-O-acetyl-4′-O-(E)-(p-coumaroyl)-harpagide (1) and 8-O-acetyl-4′-O-(Z)-(p-coumaroyl)-harpagide (2) along with five known secondary metabolites, β-sitosterol 3-O-β-glucopyranoside (3), apigenin 7-O-β-glucopyranoside (4), apigenin 7-O-rutinoside (5), luteolin 7-O-β-glucopyranoside (6) and luteolin 7-O-rutinoside (7). The iridoid mixture (1 and 2), 3 and 4 elicited significant inhibition of pain at 5 mg/kg dose. 相似文献