全文获取类型
收费全文 | 306篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 194篇 |
晶体学 | 11篇 |
力学 | 4篇 |
数学 | 19篇 |
物理学 | 55篇 |
无线电 | 47篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 18篇 |
2021年 | 13篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 23篇 |
2016年 | 20篇 |
2015年 | 12篇 |
2014年 | 16篇 |
2013年 | 32篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 8篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 9篇 |
2004年 | 11篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有330条查询结果,搜索用时 19 毫秒
251.
Cyclopropyl carbinols 1a-e react with H2O2 in the presence of concd H2SO4 at 0-5 °C to furnish the corresponding hydroperoxides 2a-e in 45-82% yields. This efficient trapping of cyclopropylmethyl cations by the hydroperoxy group has been exploited to prepare compounds 14-23, a new series of cyclopropyl substituted β-peroxy-lactones. 相似文献
252.
Desulfurization is a technology commonly used by refineries to mitigate the environmental burden caused by toxic gas emissions from hydrocarbon fuels. Expanding global population will increase liquid fuel demand by 20% between 2018 and 2050, with a total consumption of 240 quadrillion British thermal units (Btu) in 2050. Conventional catalytic Hydrodesulfurization (HDS) accounts for high cost and severe operating conditions (high temperature, pressure, catalyst poisoning and H2S safety). While studies have shown that adsorptive desulfurization (ADS) is highly effective in the removal of organic sulfur, limitations in the regeneration of adsorbent and selection of adsorbent with suitable structure to remove organic sulfur compounds exist. On the other hand, Prosopis juliflora, the world's most threatening invasive weed causes multifaceted environmental problems. The present study offers a novel solution that addresses both these issues contributing to climate change. Desulfurization of sour crude oil sample is performed using chemical-free, non-activated charcoal obtained from invasive weed species as adsorbent. XRD analysis showed amorphous structure and FTIR analysis confirmed the presence of CC bending functional group of the adsorbent. Adsorption-desorption isotherm showed presence of mesopores with pore diameter of 2.718 ?nm. Kinetic study findings reported 46% removal of total sulfur. GCMS findings showed efficient removal of some organic sulfur, including 100% removal of dibenzothiophene 4-methyl -. The equilibrium data is best represented by Freundlich isotherm. ICP-OES tests indicate the removal of toxic elements as well. The cost of the adsorbent is USD 0.12628 per kg, the lowest among all the adsorbents known thus far. The present study describes a novel, ultra-low cost, efficient, eco-friendly, desulfurization process that implements a chemical-free, non-activated adsorbent, achieves synergy, and offers multi-dimensional benefits to the environmental development. To our knowledge, this is the first study to characterize desulfurization of sour crude oil using an invasive weed. 相似文献
253.
New sphingolipids, 1,3,5-trihydroxy-2-hexadecanoylamino-(6E,9E)-heptacosdiene (1). 1,3,5-trihydroxy-2-hexadecanoylamino-(6E,9E)-heptacosdiene-1-O-glucopyranoside (2). 1,3-dihydroxy-2-hexanoylamino-(4E)-heptadecene (3). have been isolated from Conyza canadensis, along with five known compounds, p-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 3,5-dimethoxybenzoic acid, 3beta-hydroxyolean-12-en-28-oic acid, and 3beta-erythrodiol, isolated for the first time from this species. Their structures were determined by spectroscopic methods ((1)H- and (13)C-NMR, IR and MS) and two dimensional (2D)-NMR experiments. 相似文献
254.
J.S. Yadav P. Purushothama Rao D. Sreenu R. Srinivasa Rao V. Naveen Kumar K. Nagaiah A.R. Prasad 《Tetrahedron letters》2005,46(42):7249-7253
o-Aminoaryl ketones undergo smooth condensation with α-methylene ketones in the presence of sulfamic acid (NH2SO3H) (SA) under mild reaction conditions to afford the corresponding polysubstituted quinolines in excellent yields. The catalyst can be recovered by simple filtration and can be recycled in subsequent reactions. The method is simple, cost-effective and environmentally benign. 相似文献
255.
Rathee Geetanjali Jaglan Naveen Saini Hemraj Gupta Samir Dev Kanaujia Binod Kumar 《Wireless Personal Communications》2019,104(4):1553-1571
Wireless Personal Communications - In this paper, we have proposed a secure handoff procedure by generating and assessing the tickets for each mesh client which are divided among various zones of... 相似文献
256.
Dealloyed AuNi Dendrite Anchored on a Functionalized Conducting Polymer for Improved Catalytic Oxygen Reduction and Hydrogen Peroxide Sensing in Living Cells
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Malenahalli Halappa Naveen Nanjanagudu Ganesh Gurudatt Hui‐Bog Noh Yoon‐Bo Shim 《Advanced functional materials》2016,26(10):1590-1601
Dealloyed‐AuNi dendrite anchored on carboxylic acid groups of a conducting polymer is prepared and demonstrated for the catalysis of the oxygen reduction reaction (ORR) and detection of hydrogen peroxide (H2O2) released from living cells. The dendrite formation is initiated on a poly(benzoic acid‐2,2′:5′,2′′‐terthiophene) (pTBA) layer, where the polymer layer acts as a stable substrate to improve the long‐term stability and catalytic activity of the alloy electrode. A co‐deposition of Au and Ni is performed to produce a Ni‐rich Au surface at first; subsequent removal of the surface Ni atoms through electrochemical dealloying enhances the performance of the catalyst because of an increase in the electrochemically active area by 12 times. The hydrodynamic voltammetry of dealloyed‐AuNi@pTBA shows a half‐wave potential at –0.08 V, which is a large shift towards more positive potential when compared to those on AuNi@pTBA (?0.14 V) and commercial Pt/C (–0.12 V) electrodes. The proposed catalytic electrode achieved a superior analytical performance for the detection of trace H2O2 (at –0.15 V) released from cancer and normal cells with a very low detection limit (ca. 5 nM). In addition, the in vitro studies suggest no significant cytotoxicity effect for the dealloyed sample and the viability of the cells are more than 85% even after 48 h of incubation. 相似文献
257.
A Post‐Synthetically Modified MOF for Selective and Sensitive Aqueous‐Phase Detection of Highly Toxic Cyanide Ions
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)
Avishek Karmakar Naveen Kumar Partha Samanta Aamod V. Desai Dr. Sujit K. Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):864-868
Selective and sensitive detection of toxic cyanide (CN?) by a post‐synthetically altered metal–organic framework (MOF) has been achieved. A post‐synthetic modification was employed in the MOF to incorporate the specific recognition site with the CN? ion over all other anions, such as Cl?, Br?, and SCN?. The aqueous‐phase sensing and very low detection limit, the essential prerequisites for an effective sensory material, have been fulfilled by the MOF. Moreover, the present detection level meets the standard set by the World Health Organization (WHO) for the permissible limit of cyanide concentration in drinking water. The utilization of MOF‐based materials as the fluorometric probes for selective and sensitive detection of CN? ions has not been explored till now. 相似文献
258.
A thin film of dilute Fe (0.008)-doped Sb0.95Se0.05 alloy was grown on silicon substrate using the thermal evaporation technique. This film was irradiated with swift heavy ions (SHIs) Ag+15 having 200?MeV energy at ion fluences of 1?×?1012 and 5?×?1012 ions per cm2, respectively. The thickness of the thin film was ~500?nm. We study the effect of irradiation on structural, electrical, surface morphology and magnetic properties of this film using grazing angle XRD (GAXRD), DC resistivity, atomic force microscopy (AFM) and magnetic force microscopy (MFM), respectively. GAXRD suggests that no significant change is observed in this system due to SHI irradiation. The average crystallite size increases with fluence, whereas the AFM image shows the rms roughness decreases due to irradiation with respect to the un-irradiated thin film. The MFM image shows that the magnetic interaction in irradiated film decreases due to the irradiation effect. Although the un-irradiated sample shows metal to semiconducting transition, but after irradiation with fluence of 5?×?1012 ions per cm2, the sharpness of the metal to semiconducting phase transition is observed to increase dramatically at ~300?K. This characteristic of the thin film makes it a promising candidate for an electrical switching device after irradiation. 相似文献
259.
Bhuvan Kulkarni Sharada Thimmappaiah Harisha Padigar Suchetan Parameshwar Adimule Naveen Shivalingegowda Lokanath Krishnappagowda Neratur Manjunatha Kumsi 《Research on Chemical Intermediates》2016,42(10):7375-7396
Two derivatives of N-Boc piperazine, an ester derivative, i.e., tert-butyl 4-(2-ethoxy-2-oxoethyl)-piperazine-1-carboxylate (1), and, a hydrazide derivative tert-butyl 4-(2-hydrazino-2-oxoethyl)piperazine-1-carboxylate (2) were synthesized and were characterized by FT-IR, 1H & 13C NMR and LCMS spectroscopic studies. The structures of both 1 and 2 were further confirmed by single crystal X-ray diffraction analysis. The molecule of 1 is linear in shape with the ethyl acetate moiety adopting fully extended conformation, while the molecule of 2 is L-shaped with the molecule being twisted at the C10 atom. The crystal structure of 1 adopts a two-dimensional zig-zag architecture featuring C–H…O intermolecular interactions, while that of 2 features strong N–H…O hydrogen bonds and intermolecular interactions of the type N–H…N and C–H…N, resulting in a two-dimensional structure. Furthermore, a detailed analysis of the intermolecular interactions and crystal packing of 1 and 2 via Hirshfeld surface analysis and fingerprint plots was performed. The antibacterial and antifungal activities of both the compounds have been studied against several microorganisms, and were found to be moderately active. 相似文献
260.
Dr. Qiang Wen Dr. Maria Chiara di Gregorio Dr. Linda J. W. Shimon Dr. Iddo Pinkas Dr. Naveen Malik Dr. Anna Kossoy Dr. Eugeny V. Alexandrov Prof. Davide M. Proserpio Dr. Michal Lahav Prof. Milko E. van der Boom 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(54):e202201108
Formation of highly interpenetrated frameworks is demonstrated. An interesting observation is the presence of very large adamantane-shaped cages in a single network, making these crystals new entries in the collection of diamondoid-type metal–organic frameworks (MOFs). The frameworks were constructed by assembling tetrahedral pyridine ligands and copper dichloride. Currently, the networks’ degree of interpenetration is among the highest reported and increases when the size of the ligand is increased. Highly interpenetrated frameworks typically have low surface contact areas. In contrast, in our systems, the voids take up to 63 % of the unit cell volume. The MOFs have chiral features but are formed from achiral components. The chirality is manifested by the coordination chemistry around the metal center, the structure of the helicoidal channels, and the motifs of the individual networks. Channels of both handednesses are present within the unit cells. This phenomenon shapes the walls of the channels, which are composed of 10, 16, or 32 chains correlated with the degree of interpenetration 10-, 16-, and 32-fold, respectively. By changing the distance between the center of the ligand and the coordination moieties, we succeeded in tuning the diameter of the channels. Relatively large channels were formed, having diameters up to 31.0 Å×14.8 Å. 相似文献