全文获取类型
收费全文 | 1135篇 |
免费 | 63篇 |
国内免费 | 1篇 |
专业分类
化学 | 855篇 |
晶体学 | 12篇 |
力学 | 36篇 |
数学 | 78篇 |
物理学 | 218篇 |
出版年
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 34篇 |
2019年 | 25篇 |
2018年 | 29篇 |
2017年 | 29篇 |
2016年 | 57篇 |
2015年 | 42篇 |
2014年 | 55篇 |
2013年 | 85篇 |
2012年 | 100篇 |
2011年 | 75篇 |
2010年 | 44篇 |
2009年 | 44篇 |
2008年 | 89篇 |
2007年 | 50篇 |
2006年 | 47篇 |
2005年 | 44篇 |
2004年 | 39篇 |
2003年 | 28篇 |
2002年 | 34篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1994年 | 3篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1969年 | 6篇 |
1968年 | 6篇 |
1964年 | 4篇 |
1963年 | 6篇 |
1962年 | 6篇 |
1961年 | 12篇 |
1958年 | 7篇 |
1957年 | 3篇 |
1955年 | 5篇 |
排序方式: 共有1199条查询结果,搜索用时 31 毫秒
991.
Arumugam Vijaya Anand Balasubramanian Balamuralikrishnan Mohandass Kaviya Kathirvel Bharathi Aluru Parithathvi Meyyazhagan Arun Nachiappan Senthilkumar Shanmugam Velayuthaprabhu Muthukrishnan Saradhadevi Naif Abdullah Al-Dhabi Mariadhas Valan Arasu Mohammad Iqbal Yatoo Ruchi Tiwari Kuldeep Dhama 《Molecules (Basel, Switzerland)》2021,26(6)
The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome corona virus-2 (SARS-CoV-2), is the most important health issue, internationally. With no specific and effective antiviral therapy for COVID-19, new or repurposed antiviral are urgently needed. Phytochemicals pose a ray of hope for human health during this pandemic, and a great deal of research is concentrated on it. Phytochemicals have been used as antiviral agents against several viruses since they could inhibit several viruses via different mechanisms of direct inhibition either at the viral entry point or the replication stages and via immunomodulation potentials. Recent evidence also suggests that some plants and its components have shown promising antiviral properties against SARS-CoV-2. This review summarizes certain phytochemical agents along with their mode of actions and potential antiviral activities against important viral pathogens. A special focus has been given on medicinal plants and their extracts as well as herbs which have shown promising results to combat SARS-CoV-2 infection and can be useful in treating patients with COVID-19 as alternatives for treatment under phytotherapy approaches during this devastating pandemic situation. 相似文献
992.
Siva Sankar Murthy Bandaru Shatrughn Bhilare Carola Schulzke Anant R. Kapdi 《Chemical record (New York, N.Y.)》2021,21(1):188-203
Phosphines have, in combination with transition metals, played a pivotal role in the rapid development of efficient catalytic processes. Caged phosphines constitute a class of three‐dimensional scaffolds providing unique control over steric and electronic properties. The versatility of the caged phosphine ligands has been demonstrated elegantly by the groups of Verkade, Gonzalvi as well as Stradiotto. Our research group has also been working extensively for the past several years in the development of 1,3,5‐triaza‐7‐phosphaadamantane‐based caged ligands and in this personal note we have summarized these applications pertaining to the modification of biologically useful nucleosides and heteroarenes. 相似文献
993.
Surabhi Shrivastava Arun Kumar Nishith Verma Bor-Yann Chen Chang-Tang Chang 《Electroanalysis》2021,33(4):916-924
Aqueous glyphosate (GLYP) was voltammetrically detected using a Cu-(poly)pyrrole composite electrochemically deposited on activated carbon fiber for the first time in a single-step method. Differential pulse voltammetry indicated good linearity (R2 = 0.9902) in the response over 0.02–12 mg L−1 range, with a low limit of detection (0.01 mg L−1). The sensor exhibited reproducibility for soil and fruit samples (RSD values = 2.41 and 3.87%, respectively). The response showed repeatability over 100 consecutive measurements. The response was also unaffected by the interfering substances containing the same functional groups as in GLYP and its metabolite. The method described in this study is facile. 相似文献
994.
Stereoselective Total Synthesis of Iso‐Cladospolide B and the 12 Membered‐Macrolactone (6S,12R)‐6‐Hydroxy‐12‐methyloxacyclododecane‐2,5‐dione 下载免费PDF全文
Pendyala Venkata Arun Kumar Venkata Satyanarayana Mallula Palakodety Radha Krishna 《Helvetica chimica acta》2015,98(8):1115-1126
Total syntheses of iso‐cladospolide B ( 1 ) and the 12‐membered macrolactone (6S,12R)‐6‐hydroxy‐12‐methyloxacyclododecane‐2,5‐dione ( 2 ), a non‐natural product, were achieved from a common intermediate starting from commercially available 1,9‐nonane diol. 相似文献
995.
Yu-Lou Qiu Qing-Hua He Yang Xu Arun K. Bhunia Zhui Tu Bo Chen Yuan-Yuan Liu 《Analytica chimica acta》2015
In this study, using mycotoxin deoxynivalenol (DON) as a model hapten, we developed a nanobody-based environmental friendly immunoassay for sensitive detection of DON. Two nanobodies (N-28 and N-31) which bind to anti-DON monoclonal antibody (MAb) were isolated from a naive phage display library. These nanobodies are clonable, thermally stable and mycotoxin-free products and can be served as coating antigen mimetics in heterologous immunoassay. The half inhibition concentration (IC50) of the immunoassay developed with N-28 and N-31 was 8.77 ± 0.41 ng mL−1 and 19.97 ± 0.84 ng mL−1, respectively, which were 18- and 8-fold more sensitive than the conventional coating antigen (DON-BSA) based immunoassay. In order to better understand the molecular mechanism of antigen mimicry by nanobody, the 3D structure of “nanobody (N-28) - anti-DON MAb” complex was presented and verified by molecular modeling and alanine-scanning mutagenesis. The results showed that hydrogen bond and hydrophobic interaction formed between Thr 102 – Ser 106 of N-28 and CDR H3 residues of anti-DON antibody may contribute to their binding. This novel concept of enhancing sensitivity of immunoassay for DON based on nanobody may provide potential applications in a general method for immunoassay of various food chemical contaminants. 相似文献
996.
Neetu Ishwar Chandra Maurya Arun Kumar Gupta Pankaj Srivastava Lal Bahadur 《Journal of Solid State Electrochemistry》2017,21(5):1229-1241
In this work, we have prepared Al-doped TiO2 nanoparticles via a hydrothermal method and used it for making photoanode in dye-sensitized solar cell (DSSC). Material characterizations were done using XRD, AFM, SEM, TEM and EDAX. XPS results reveal that Al is introduced successfully into the structure of TiO2 creating new impurity energy levels in the forbidden gap. This resulted in tuning of the conduction band of TiO2 and reduced charge recombination which led to better current conversion efficiency of DSSC. Greater dye loading and enhanced surface area was obtained for Al-doped TiO2 compared to un-doped TiO2. I-V analysis, EIS and Bode plots are employed to evaluate photovoltaic performance. The short-circuit current density (J sc) and efficiency (η) of cell employing Al-doped TiO2 photoanode were extensively enhanced compared to the cell using un-doped TiO2. The optical band gap (E g) for Al-doped and un-doped TiO2 was obtained as 2.8 and 3.2 eV, respectively. J sc and η were 13.39 mAcm?2 and 4.27%, respectively, under illumination of 100 mWcm?2 light intensity when thin films of 1% Al-doped TiO2 was employed as photoanode in DSSC using N719 as the sensitizer dye. With the use of un-doped TiO2 as photoanode under similar conditions, J sc 5.12 mAcm?2 and η 1.06% only could be obtained. The maximum IPCE% obtained with Al-doped TiO2 and un-doped TiO2 was 67 and 38% respectively at the characteristic wavelength of dye (λ max = 540 nm). The EIS analyses revealed resistive and capacitive elements that provided an insight into various interfacial processes in terms of the charge transport. It was observed that Al-doping reduced the interfacial resistance leading to better charge transport which has improved both photocurrent density and conversion efficiency. Higher electron mobility and fast diffusion resulting in greater charge collection efficiency was obtained for Al-doped TiO2 compared to the un-doped TiO2. Using the Mott–Schottky plot, the donor density was calculated for un-doped and Al-doped TiO2. The work demonstrated that the Al-doped TiO2 is potential photoanode material for low-cost and high-efficiency DSSC. 相似文献
997.
Chen-I Wang Wei-Cheng Wu Arun Prakash Periasamy Huan-Tsung Chang 《Analytical and bioanalytical chemistry》2014,406(27):6917-6923
In this study, highly hydrophilic and photoluminescent sheets of reduced graphene oxide decorated with carbon dots (C-dots@RGO), methylene blue (MB), and a probe DNA have been used for the detection of DNA. The photoluminescence of C-dots@RGO is quenched by MB, which is restored in the presence of a target DNA. The combination of the C-dots@RGO, MB, and a DNA probe is selective for perfectly matched DNA over mismatched DNA, mainly because relative to single-stranded DNA, double-stranded DNA intercalates more strongly with MB, but interacts more weakly with RGO. In the presence of a target DNA, MB intercalates with the as-formed double-stranded DNA and is released from the surface of C-dots@RGO, leading to “turn-on” photoluminescence. The practicality of this assay has been validated by the determination of tumor suppressor gene BRCA1, with linearity over the concentration range from 25 to 250 nM and a limit of detection (LOD, at a signal-to-noise ratio of 3) of 14.6 nM. The C-dots@RGO probe provides higher specificity towards target DNA than towards common salts, carbohydrates, amino acids, and proteins found in real samples. Having the advantages of simplicity, cost-effectiveness, selectivity, and sensitivity, the DNA-P/C-dots@RGO–MB probe on microwells has been successfully employed for the detection of DNA, suggesting its potential for multiple analyses of DNA targets when various DNA probes are employed. 相似文献
998.
Dr. Melanie Rauschenberg Dr. Sateesh Bandaru Dr. Mark P. Waller Prof. Dr. Bart Jan Ravoo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(10):2770-2782
A broad spectrum of physiological processes is mediated by highly specific noncovalent interactions of carbohydrates and proteins. In a recent communication we identified several cyclic hexapeptides in a dynamic combinatorial library that interact selectively with carbohydrates with high binding constants in water. Herein, we report a detailed investigation of the noncovalent interaction of two cyclic hexapeptides (Cys‐His‐Cys (which we call HisHis) and Cys‐Tyr‐Cys (which we call TyrTyr)) with a selection of monosaccharides and disaccharides in aqueous solution. The parallel and antiparallel isomers of HisHis or TyrTyr were synthesized separately, and their interaction with monosaccharides and disaccharides in aqueous solution was studied by isothermal titration calorimetry, NMR spectroscopic titrations, and circular dichroism spectroscopy. From these measurements, we identified particularly stable complexes (Ka>1000 M ?1) of the parallel isomer of HisHis with N‐acetylneuraminic acid and with methyl‐α‐D ‐galactopyranoside as well as of both isomers of TyrTyr with trehalose. To gain further insight into the structure of the peptide–carbohydrate complexes, structure prediction was performed using quantum chemical methods. The calculations confirm the selectivity observed in the experiments and indicate the formation of multiple intermolecular hydrogen bonds in the most stable complexes. 相似文献
999.
Mn Oxide‐Silver Composite Nanowires for Improved Thermal Stability,SERS and Electrical Conductivity 下载免费PDF全文
Mukul Pradhan Arun Kumar Sinha Prof. Tarasankar Pal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(29):9111-9119
Redox transformation reaction between aqueous AgNO3 and Mn(CH3COO)2 at low temperature (~80 °C) has been adopted for industrial‐scale production of uniform Ag–MnOOH composite nanowires for the first time. Varying amounts of incorporated Ag in the composite retain the 1D morphology of the composite. Nanowires upon annealing evolve Ag–MnO2 nanocomposites, once again with the retention of the parental morphology. Just 4 % of silver incorporation in the composite demonstrates metal‐like conducting performance from the corresponding semiconducting material. Transition of MnO2 to Mn2O3 to Mn3O4 takes place upon heat treatment in relation to successive increase in Ag concentrations in the nanowires. The composites offer resistance to the observed oxide transformation. This is evidenced from the progressive increase in transition temperature. In situ Raman, ex situ thermal and XRD analysis corroborate the fact. The composite with 12 % Ag offers resistance to the transformation of MnO2, which is also verified from laser heating. Importantly, Ag nanoparticle incorporation is proved to offer a thermally stable and better surface enhanced Raman scattering (SERS) platform than the individual components. Both the Ag–MnOOH and Ag–MnO2 nanocomposites with 8 atomic % Ag show the best SERS enhancement (enhancement factor ~1010). The observed enhancement relates to charge transfer as well as electromagnetic effects. 相似文献
1000.
Mameda Naresh Peraka SwamyMacharla Arun Kumar Marri Mahender ReddyKodumuri Srujana Nama Narender 《Tetrahedron letters》2014
A mild and efficient protocol for the preparation of bromoformates as well as bromoacetates from olefins using NH4Br and oxone® in nucleophile sources (DMF or DMA) without employing catalyst at room temperature is described. This method is facile, environmentally friendly and cost effective. A variety of terminal, internal and cyclic alkenes reacted smoothly to give the corresponding bromoformate and acetate products in good to excellent yields. Moreover, 1,2-disubstituted olefins provided moderate to excellent diastereoselectivity. 相似文献