全文获取类型
收费全文 | 658篇 |
免费 | 54篇 |
国内免费 | 8篇 |
专业分类
化学 | 448篇 |
晶体学 | 3篇 |
力学 | 71篇 |
数学 | 69篇 |
物理学 | 129篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 33篇 |
2020年 | 38篇 |
2019年 | 30篇 |
2018年 | 62篇 |
2017年 | 27篇 |
2016年 | 43篇 |
2015年 | 33篇 |
2014年 | 43篇 |
2013年 | 86篇 |
2012年 | 57篇 |
2011年 | 61篇 |
2010年 | 28篇 |
2009年 | 27篇 |
2008年 | 15篇 |
2007年 | 17篇 |
2006年 | 13篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 9篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有720条查询结果,搜索用时 15 毫秒
711.
712.
Ali A. Mohammadi Hamed Rohi Ali Abolhasani Soorki 《Journal of heterocyclic chemistry》2013,50(5):1129-1133
An efficient synthesis of novel 2‐aryl‐3‐(phenylamino)‐2,3‐dihydroquinazolin‐4(1H)‐one derivatives using KAl(SO4)2.12H2O (Alum) as a catalyst from an aldehyde and 2‐amino‐N‐phenylbenzohydrazine in ethanol is described. All synthesized derivatives were screened for anti‐bacterial activity. Some compounds exhibited promising anti‐bacterial activity with reference to standard antibiotics. 相似文献
713.
In this article, the main target was to study the antitumor and antimicrobial efficacy of new heterocycles conjugated with biphenyl moiety in-vitro. This was implemented by utilizing N'-(1-([1,1'-biphenyl]-4-yl)ethylidene)-2-cyanoacetohydrazide 3 as a material for the synthesis of various heterocyclic compounds. Among of them, some compounds were selected and assayed against two antitumor cell lines as (HepG2) and (HCT-116). Conspicuously, the achieved results showed that compounds 6, 13, and 23 possess significant potency against both cancer cell lines. Particularly, compound 13 exhibited a remarkable efficacy, similar to the standard anticancer drug (doxorubicin), against both cancer cell lines. Noteworthy, compound 13 may serve as a potential anticancer therapeutic drug in the future. On the other hand, In-vitro antifungal and antibacterial activities of selected compounds were assayed and the results indicated that the compound 6 exhibited significant potency against Candida albicans, while compounds 6 and 8 displayed spectacular results for the antibacterial study. 相似文献
714.
A simple, rapid, and sensitive method based on dispersive liquid–liquid microextraction combined with HPLC‐UV detection applied for the quantification of chlordiazepoxide in some real samples. The effect of different extraction conditions on the extraction efficiency of the chlordiazepoxide drug was investigated and optimized using central composite design as a conventional efficient tool. Optimum extraction condition values of variables were set as 210 μL chloroform, 1.8 mL methanol, 1.0 min extraction time, 5.0 min centrifugation at 5000 rpm min?1, neutral pH, 7.0% w/v NaCl. The separation was reached in less than 8.0 min using a C18 column using isocratic binary mobile phase (acetonitrile/water (60:40, v/v)) with flow rate of 1.0 mL min?1. The linear response (r2 > 0.998) was achieved in the range of 0.005–10 μg mL?1 with detection limit 0.0005 μg mL?1. The applicability of this method for simultaneous extraction and determination of chlordiazepoxide in four different matrices (water, urine, plasma, and chlordiazepoxide tablet) were investigated using standard addition method. Average recoveries at two spiking levels were over the range of 91.3–102.5% with RSD < 5.0% (n = 3). The obtained results show that dispersive liquid–liquid microextraction combined with HPLC‐UV is a fast and simple method for the determination of chlordiazepoxide in real samples. 相似文献
715.
In this article a new coated platinum Cu2+ ion selective electrode based on 2-((2-(2-(2-(2-hydroxy-5-methoxybenzylideneamino)phenyl)disufanyl)phenylimino) methyl)-4-methoxyphenol Schiff base (L1) as a new ionophore is described. This sensor has a wide linear range of concentration (1.2 × 10−7-1.0 × 10−1 mol L−1) and a low detection limit of 9.8 × 10−8 mol L−1of Cu(NO3)2. It has a Nernstian response with slope of 29.54 ± 1.62 mV decade−1 and it is applicable in the pH range of 4.0-6.0 without any divergence in potentioal. The coated electrode has a short response time of approximately 9 s and is stable at least for 3.5 months. The electrode shows a good selectivity for Cu2+ ion toward a wide variety of metal ions. The proposed sensor was successfully applied for the determination of Cu2+ ion in different real and environmental samples and as indicator electrode for potentiometric titration of Cu2+ ion with EDTA. 相似文献
716.
Mehrorang Ghaedi Morteza Montazerozohori Farzaneh Marahel Mehdi Nejati Biareh Mostafa Soylak 《中国化学》2011,29(10):2141-2147
Preconcentration/separation of Co(II), Fe(III), Pb(II), Cr(III), Cu(II) and Cd(II) ions using bis(5‐bromo‐2‐hydroxy‐benzaldehyde)‐2‐methyl‐1,5‐pentane diimine (BBHBPDI) on SDS coated alumina has been reported. The influences of the analytical parameters including pH, ligand and SDS amount, type and concentration of eluent and sample volume on metal ions recoveries were investigated. At optimum values of all variables the relative standard deviation are between 2.5–2.7 and preconcentration factor was 375, while recoveries for all understudy metal ions are higher than 95%, determination limits are between 1.5–2.7. The method has been successfully applied to determination of Co(II), Fe(III), Pb(II), Cr(III), Cu(II) and Cd(II) ions content in some real samples. 相似文献
717.
Mahmoud R. Mahmoud Wael S.I. Abou‐Elmagd Hamed A. Derbala Mohamed H. Hekal 《中国化学》2011,29(7):1446-1450
Dimethyl homophthalate condensed with isatin to give the unexpected five membered lactone 3 rather than the half ester 1 and the δ‐lactone 2 . Treatment of compound 3 with excess hydrazine hydrate afforded phthalazinone carbohydrazide 4 which represents a novel method for the synthesis of phthalazinone derivatives. The carbohydrazide 4 upon treatment with carbon disulphide afforded 1,3,4‐oxadiazole derivative 5 , which reacted with ethylchloroacetate to give the S‐alkylated product 6 . The structure of compound 3 compared with 2 was discussed using hyperchem professional (7) AM1 calculations, X‐ray single crystal structure and complete spectral data. 相似文献
718.
The nonlinear dynamical characteristics of a doubly curved shallow microshell are investigated thoroughly. A consistent nonlinear model for the microshell is developed on the basis of the modified couple stress theory (MCST) in an orthogonal curvilinear coordinate system. In particular, based on Donnell’s nonlinear theory, the expressions for the strain and the symmetric rotation gradient tensors are obtained in the framework of MCST, which are then used to derive the potential energy of the microshell. The analytical geometrically nonlinear equations of motion of the doubly microshell are obtained for in-plane displacements as well as the out-of-plane one. These equations of partial differential type are reduced to a large set of ordinary differential equations making use of a two-dimensional Galerkin scheme. Extensive numerical simulations are conducted to obtain the nonlinear resonant response of the system for various principal radii of curvature and to examine the effect of modal interactions and the length-scale parameter. 相似文献
719.
The effect of different doses of γ‐rays on the behavior of the critical current density, Jc in an YBa2Cu3O7 polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a 60Co γ‐ray source at a dose rate of 0.5 MR/h. Jc was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of Jc above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non‐monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by γ‐rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
720.
In this work, CuO/n-Si and AuNPs-decorated CuO/n-Si heterojunction photodetectors were fabricated by deposition of CuO nanoplatelets and Au nanoparticles NPs decorated CuO nanoplatelets on silicon substrates by laser ablation in methanol. Atomic force microscope AFM, scanning electron microscope SEM and transmission electron microscope TEM were used to study the structural and surface morphology of CuO and AuNPs–CuO. The electrical properties showed that the CuO/Si and AuNPs decorated-CuO/Si showed rectifying behavior. The maximum values of quantum efficiency were about 41 and 78% at 700 nm for CuO/Si and AuNPs–CuO/Si photodetectors, respectively. The I–V characteristics of the photodetectors were measured under UV light. 相似文献