全文获取类型
收费全文 | 457篇 |
免费 | 25篇 |
国内免费 | 11篇 |
专业分类
化学 | 336篇 |
晶体学 | 6篇 |
力学 | 12篇 |
数学 | 15篇 |
物理学 | 124篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 33篇 |
2020年 | 27篇 |
2019年 | 15篇 |
2018年 | 21篇 |
2017年 | 20篇 |
2016年 | 35篇 |
2015年 | 20篇 |
2014年 | 12篇 |
2013年 | 43篇 |
2012年 | 39篇 |
2011年 | 31篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 16篇 |
2007年 | 17篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 6篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 5篇 |
1968年 | 7篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有493条查询结果,搜索用时 15 毫秒
71.
Habib Aqsa Iqbal Muhammad Adnan Bhatti Haq Nawaz Shahid Muhammad 《Transition Metal Chemistry》2019,44(5):431-443
Transition Metal Chemistry - A series of bidendate 5,6-dimethyl benzimidazolium-based N-heterocyclic carbene (NHC) proligands and their silver complexes were synthesized. The synthetic approaches... 相似文献
72.
Hamid Latif M. Shahid Rafique R.S. Rawat Shahzad Naseem 《Applied Surface Science》2008,254(22):7505-7511
In the paper an attempt has been made to use the laser-induced plasma as an X-ray source for the growth of nanostructures on the surface of gold. For this purpose, an Nd:YAG laser operated at second harmonics (λ = 532 nm, E = 400 mJ) is used to produce plasma from analytical grade 5N pure Al, Cu and W targets. An analytical grade (5N pure) gold substrate was irradiated by X-rays generated from Al, Cu and W plasma under the vacuum ∼10−4 Torr. The surface was analyzed by two techniques, XRD and AFM. The aberrations in the XRD peaks show that there are significant structural changes in the exposed gold, in terms of decreased reflection intensities, increased dislocation line density, changes in the d-spacing and disturbance in the periodicity of the planes. AFM used to explore the topography of the irradiated gold reveals that regardless of the source, nm sized hillocks have been produced on the gold surface. The roughness of the surface has increased due to the growth of these hillocks. 相似文献
73.
Total fragmentation cross section for the reaction 158A Pb ions + Cu target is measured using the most sensitive track detector CR-39. Measured values are compared with calculations. Exposures of target-detector stack with 158A P5 projectiles are made at CERN-SPS beam facility. Results of calibration of CR-39 detector in a charge region (63 ≤ Z ≤ 83) are also reported, which can be used for high energy particle identification using CR-39 and in determination of partial charge changing cross sections. The charge resolution δz achieved by this technique is about 0.2e. A systematic dependence of total fragmentation cross section on target properties is revealed and the corresponding results are presented. 相似文献
74.
75.
Abid Nazir Gill Areeba Iftikhar Ayoub Rashid Muhammad Amin Rana Rashad Mahmood Khan Hafiz M. Rafique Seemal Jelani Ahmad Adnan 《Journal of the Iranian Chemical Society》2018,15(9):1939-1945
The present study reports the green synthesis of starch–maleate (SM) at ambient temperature in solvent-free system using Rhizopus arrhizus lipase as a biocatalyst and maleic acid (MA) as an esterification agent. The synthetic scheme was found to be efficient, economical, and ecofriendly. The newly synthesized SM samples were characterized using Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopic techniques. The degree of substitution (DS) was found in the range of 0.53–0.62. Moreover, DS was found to be temperature and time-dependent. X-ray diffraction (XRD) exhibited that maleation did not change the crystalline nature of native starch. Scanning electron microscopy (SEM) revealed that size of SM granules was in the range of 4–18 µm. The activation energy (Ea) of SM formation was calculated to be 42.94 kcal mol?1 which clearly indicated the effective and rapid interaction of functional groups. Hence, the solvent-free solid-state synthetic methodology proved to be excellent for the synthesis of novel biomaterials with appreciable high DS for drug delivery and sorption of heavy metal ions from water. 相似文献
76.
Luana Bettanin Sumbal Saba Carlos V. Doerner Marcelo S. Franco Marcelo Godoi Jamal Rafique Antonio L. Braga 《Tetrahedron》2018,74(29):3971-3980
Herein, we described the NH4I-catalyzed CH bond chalcogenation of N-heteroaryls in the presence of a minimum amount of DMSO/H2O/acetic acid as additives (2.5/2.5/1?M equiv., respectively), under metal-free conditions. Under optimized conditions, a wide variety of sulfenyl/selenyl imidazo[1,2-α]pyridines were prepared in very good yields. Moreover, the present approach was also highly efficient for the chalcogenation of different 5-membered N-heteroaryls, e.g., indole, imidazothiazole, indazole and imidazopyrimidine derivatives. 相似文献
77.
Nasima Arshad Pervaiz Ali Channar Aamer Saeed Shahid Iqbal Farooqi Aneela Javeed Fayaz Ali Larik Waqar Ahmad Abbasi Ulrich Flörke 《Journal of Saudi Chemical Society》2018,22(8)
Compound 3 {(E)-1-(2-fluorobenzylidene)thiosemicarbazide} – a new Schiff base of thiosemicarbazide has been synthesized, characterized and reported for crystal structure. Planer side chain in the crystal structure was observed co-planer with aromatic ring plane and molecules were connected into centrosymmetric dimmers via intermolecular hydrogen bonding. DFT geometry optimization and the relevant quantum parameters indicated unstable and reactive nature of compound 3. Experimental and theoretical findings for DNA binding by UV–visible, cyclic voltammetry and molecular docking studies showed consistency in kinetic (Kb) and thermodynamic (ΔG) parameters and that compound 3 significantly interacted with DNA via intercalation. Viscometric analysis further comprehended intercalation as possible binding mode of the compound with DNA and non-denaturing of DNA in the presence of 10% aqueous DMSO. Docked parameters further assured the drug like characteristics of the investigated compound as fit in Lipinski’s criteria. Dose dependant cytotoxic activity of compound 3 against human Huh-7 cell line indicated its anti-cancer potential at 100?µg/ml concentration. 相似文献
78.
Shahzeb Ahmad Shazia Bashir Mahreen Akram Rizwan Amir Muhammad Shahid Rafique Wolfgang Husinsky Mubashir Javed 《Surface and interface analysis : SIA》2023,55(2):113-126
The present paper reports the investigation of surface morphology, elemental composition, phase changes and field emission properties of Si ion irradiated nickel (Ni) and titanium (Ti). The Ni and Ti targets have been irradiated with 500 keV Si ions generated by Pelletron accelerator at various fluences ranging from 6.9 × 1013 to 77.1 × 1013 ions/cm2. Stopping range of ions in matter analysis revealed higher values of electronic stopping and sputtering yield for Ni as compared with Ti. For both irradiated metals, electronic energy loss dominant over the nuclear stopping. The growth of induced surface structures have been analysed by using field emission scanning electron microscopy (FESEM) analysis. In case of Ni, as the ion fluence increases from 6.9 × 1013 to 65.8 × 1013 ions/cm2, the formation of spherical particulates, agglomers and sputtering is observed. Although in the case of Ti, with the increase of Si ion fluence from 11.6 × 1013 to 77.1 × 1013 ions/cm2, the formation of irregular-shaped particulates along with crater and sputtered channels is observed. X-ray diffraction (XRD) analysis shows that no new phase is identified. However, a significant increase in peak intensity is observed with increasing ion fluence. The variation in crystallite size and dislocation line density is also observed as a function of Si ion fluence. Fourier transform infrared spectroscopy analysis shows that no bands are formed after the Si ion irradiation. Field emission properties of ion-structured Ni and Ti are well correlated with the growth of surface structures observed by SEM and dislocation line density evaluated by XRD analysis. 相似文献
79.
Fansheng Ning Heng Zhu Huijiao Yan Jiguo Liu Shahid Aziz Hidayat Hussain Xiangyun Song Lei Xie Zhaoqing Meng Guiyun Cao Daijie Wang 《Journal of separation science》2023,46(16):2300053
In this work, the preparative separation of quinolyridine alkaloids from seeds of T. lanceolata by conventional and pH-zone-refining counter-current chromatography. Traditional counter-current chromatography separation was performed by a flow-rate changing strategy with a solvent system of ethyl acetate-n-butanol-water (1:9:10, v/v) and 200 mg sample loading. Meanwhile, the pH-zone-refining mode was adopted for separating 2.0 g crude alkaloid extracts with the chloroform-methanol-water (4:3:3, v/v) solvent system using the stationary and mobile phases of 40 mM hydrochloric acid and 10 mM triethylamine. Finally, six compounds, including N-formylcytisine (two conformers) ( 1 ), N-acetycytisine (two conformers) ( 2 ), (-)-cytisine ( 3 ), 13-β-hydroxylthermopsine ( 4 ), N-methylcytisine ( 5 ), and thermopsine ( 6 ) were successfully obtained in the two counter-current chromatography modes with the purities over 96.5%. Moreover, we adopted nuclear magnetic resonance and mass spectrometry for structural characterization. Based on the obtained findings, the pH-zone-refining mode was the efficient method to separate quinolyridine alkaloids relative to the traditional mode. 相似文献
80.
Regioselective,Solvent‐ and Metal‐Free Chalcogenation of Imidazo[1,2‐a]pyridines by Employing I2/DMSO as the Catalytic Oxidation System
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jamal Rafique Dr. Sumbal Saba Dr. Alisson R. Rosário Prof. Dr. Antonio L. Braga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11854-11862
Highly efficient molecular‐iodine‐catalyzed chalcogenations (S and Se) of imidazo[1,2‐a]pyridines were achieved by using diorganoyl dichalcogenides under solvent‐free conditions. This approach afforded the desired products that had been chalcogenated regioselectively at the C3 position in up to 96 % yield by using DMSO as an oxidant, in the absence of a metal catalyst, and under an inert atmosphere. This mild, green approach allowed the preparation of different types of chalcogenated imidazo[1,2‐a]pyridines with structural diversity. Furthermore, the current protocol was also extended to other N‐heterocyclic cores. 相似文献