全文获取类型
收费全文 | 777篇 |
免费 | 37篇 |
国内免费 | 7篇 |
专业分类
化学 | 549篇 |
晶体学 | 6篇 |
力学 | 25篇 |
数学 | 29篇 |
物理学 | 112篇 |
无线电 | 100篇 |
出版年
2023年 | 8篇 |
2022年 | 18篇 |
2021年 | 25篇 |
2020年 | 26篇 |
2019年 | 24篇 |
2018年 | 41篇 |
2017年 | 13篇 |
2016年 | 27篇 |
2015年 | 25篇 |
2014年 | 35篇 |
2013年 | 51篇 |
2012年 | 81篇 |
2011年 | 57篇 |
2010年 | 39篇 |
2009年 | 34篇 |
2008年 | 45篇 |
2007年 | 41篇 |
2006年 | 31篇 |
2005年 | 35篇 |
2004年 | 26篇 |
2003年 | 20篇 |
2002年 | 12篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有821条查询结果,搜索用时 343 毫秒
41.
Akkaraboyina Lakshmi Lavanya K. Gowri Bala Kumari K. R. S. Prasad Pradeep Kumar Brahman 《Electroanalysis》2021,33(4):1096-1106
The development and fabrication of a simple, portable, and sensitive detection tool to precisely monitor nitrite level is of growing importance in electrochemistry research, given the strong interest in the protection of drinking water quality, treatment of wastewater, food production, and control of remediation processes. This work describes the fabrication of a simple, cost-effective, pen-type electrochemical sensor based on bimetallic gold and tungsten nanoparticles electrochemically decorated on graphene-chitosan modified pencil graphite electrode (PGE) for the trace detection of nitrite in real samples. The prepared nanocomposite was characterized using XRD, SEM, and EDS. The electrochemical behavior of the sensor was evaluated by cyclic voltammetry (CV) and impedance electrochemical spectroscopy (EIS). Results revealed that the proposed sensor displayed excellent electrocatalytic activity towards electro-oxidation of nitrite with an irreversible redox reaction. The AuNPs-WNPs@Gr-Chi/PGE sensor exhibited excellent analytical performance with a wide linear range from 10 to 250 μM towards nitrite. The LOD and LOQ were calculated to be 0.12 μM and 0.44 μM, respectively. The designed electrochemical sensor was successfully applied for the detection of nitrite in water, milk, and natural fruit juice samples. 相似文献
42.
Sunil V. Gaikwad Milind V. Gaikwad Pradeep D. Lokhande 《Journal of heterocyclic chemistry》2021,58(7):1408-1414
We have developed a simple method for the chemoselective aromatization of tetrahydro-β-carboline with selective nondeallylation O-allyl groups in the presence of iodine (100 mol %) in dimethyl sulfoxide/H2O2. A convergent approach toward the oxidative aromatization with selective deallylation (deprotection) of O-allyl-tetrahydro-β-carboline using iodine in dimethyl sulfoxide/HCl has been described. The present protocol contains cheap catalyst, easy work up, normal reaction conditions, and high selectivity. 相似文献
43.
Jena Sudipta Ray Asit Sahoo Ambika Kamila Pradeep Kumar Nayak Sanghamitra Panda Pratap Chandra 《Chemistry of Natural Compounds》2021,57(6):1147-1149
Chemistry of Natural Compounds - 相似文献
44.
Archana Chaudhary Nikita Sharma Meena Nagar Shaikh M. Mobin Pradeep Mathur Rakesh Bohra 《Journal of Sol-Gel Science and Technology》2014,70(3):464-472
Modification of [VO(OPri)3] with oximes in different molar ratios, yielded new class of vanadia precursors, [VO{OPri}3?n{L}n] {where, n = 1–3 and LH = C9H16C=NOH (1–3) and (CH3)2C=NOH (4–6)}.All the products are yellow in colour. (1) and (2) are liquid/viscous liquid, while others are solids. Molecular weight measurements of all these derivatives and the ESI-mass spectral studies of (1), (2), (3) and (5) indicate their monomeric nature. 1H and 13C{1H} NMR spectra suggest that the oximato moieties are monodentate in solution which was further confirmed by the 51V NMR signals, appeared in the region expected for tetra-coordinated oxo-vanadium atoms. On ageing, a disproportionation reaction occurs in (1) and some crystals appeared. Single crystal X-ray diffraction analyses of the crystals obtained from (1) as well as from (3) were found to be the same and indicate the presence of side-on {dihapto η 2-(N, O)} binding modes of the oximato ligands, leading to the formation of seven coordination environment around the vanadium atom. Thermogravimetric curve of (1) exhibits multi-step decomposition with the formation of V2O5 as the final product at ~850 °C. Sol–gel transformation of (3) yielded (a) VO2 sintered at 300 °C and (b) V2O5 at 600 °C. Similarly, sol–gel transformations of (1) and (2) yielded V2O5 (c) and (d) at 600 °C, respectively. Formation of monoclinic phase in (a) and orthorhombic phase in (b), (c) and (d) were confirmed by powder XRD patterns. 相似文献
45.
Márton Zwillinger Dr. Post Sai Reddy Dr. Barbara Wicher Dr. Pradeep K. Mandal Dr. Márton Csékei Dr. Lucile Fischer Dr. András Kotschy Prof. Dr. Ivan Huc 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(72):17366-17370
Helically folded aromatic oligoamide foldamers have a size and geometrical parameters very distinct from those of α-helices and are not obvious candidates for α-helix mimicry. Nevertheless, they offer multiple sites for attaching side chains. It was found that some arrays of side chains at the surface of an aromatic helix make it possible to mimic extended α-helical surfaces. Synthetic methods were developed to produce quinoline monomers suitably functionalized for solid phase synthesis. A dodecamer was prepared. Its crystal structure validated the initial design and showed helix bundling involving the α-helix-like interface. These results open up new uses of aromatic helices to recognize protein surfaces and to program helix bundling in water. 相似文献
46.
47.
Nehal Gupta Kshitij Verma Sarath Nalla Alok Kulshreshtha Rajiv Lall Sahdeo Prasad 《Molecules (Basel, Switzerland)》2020,25(22)
Free radicals, generally composed of reactive oxygen species (ROS) and reactive nitrogen species (RNS), are generated in the body by various endogenous and exogenous systems. The overproduction of free radicals is known to cause several chronic diseases including cancer. However, increased production of free radicals by chemotherapeutic drugs is also associated with apoptosis in cancer cells, indicating the dual nature of free radicals. Among various natural compounds, curcumin manifests as an antioxidant in normal cells that helps in the prevention of carcinogenesis. It also acts as a prooxidant in cancer cells and is associated with inducing apoptosis. Curcumin quenches free radicals, induces antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), and upregulates antioxidative protein markers–Nrf2 and HO-1 that lead to the suppression of cellular oxidative stress. In cancer cells, curcumin aggressively increases ROS that results in DNA damage and subsequently cancer cell death. It also sensitizes drug-resistant cancer cells and increases the anticancer effects of chemotherapeutic drugs. Thus, curcumin shows beneficial effects in prevention, treatment and chemosensitization of cancer cells. In this review, we will discuss the dual role of free radicals as well as the chemopreventive and chemotherapeutic effects of curcumin and its analogues against cancer. 相似文献
48.
A p‐Hydroxyphenacyl–Benzothiazole–Chlorambucil Conjugate as a Real‐Time‐Monitoring Drug‐Delivery System Assisted by Excited‐State Intramolecular Proton Transfer
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shrabani Barman Sourav K. Mukhopadhyay Sandipan Biswas Surajit Nandi Moumita Gangopadhyay Satyahari Dey Anakuthil Anoop N. D. Pradeep Singh 《Angewandte Chemie (International ed. in English)》2016,55(13):4194-4198
Among the well‐known phototriggers, the p‐hydroxyphenacyl (pHP) group has consistently enabled the very fast, efficient, and high‐conversion release of active molecules. Despite this unique behavior, the pHP group has been ignored as a delivery agent, particularly in the area of theranostics, because of two major limitations: Its excitation wavelength is below 400 nm, and it is nonfluorescent. We have overcome these limitations by incorporating a 2‐(2′‐hydroxyphenyl)benzothiazole (HBT) appendage capable of rapid excited‐state intramolecular proton transfer (ESIPT). The ESIPT effect also provided two unique advantages: It assisted the deprotonation of the pHP group for faster release, and it was accompanied by a distinct fluorescence color change upon photorelease. In vitro studies showed that the p‐hydroxyphenacyl–benzothiazole–chlorambucil conjugate presents excellent properties, such as real‐time monitoring, photoregulated drug delivery, and biocompatibility. 相似文献
49.
T. Pradeep B. Feng T. Ast J. S. Patrick R. G. Cooks S. J. Pachuta 《Journal of the American Society for Mass Spectrometry》1995,6(3):187-194
Reactive collisions of low energy (<100-eV) mass-selected ions are used to chemically modify fluorinated self-assembled monolayer surfaces comprised of alkanethiolate chains CF3(CF2)11(CH2)2S— bound to Au. Typical experiments were done by using 1-nA/cm2 beams and submonolayer doses of reactant ions. Characterization of the modified surface was achieved by in situ chemical sputtering (60-eV Xe+·) and by independent high mass resolution time-of-flight-secondary ionization mass spectrometry (TOF-SIMS) (15–25-keV, Ga+) experiments. Treatment with Si35C1 4 +· produced a surface from which Xe+ sputtering liberated CF2 35C1+ ions, which suggested Cl-for-F halogen exchange at the surface. Isotopic labeling studies that used Si35Cl2 37Cl 2 +· ; and experiments with bromine-containing and iodine-containing projectiles, confirmed this reaction. High mass resolution TOF-SIMS spectra, as well as high spatial resolution images, provided further evidence as to the existence of halogen-exchanged species at the bombarded surface. Analogous Cl-for-F halogen substitution was observed in a model gas-phase reaction. The ion-surface reaction is suggested to proceed through an intermediate fluoronium ion in which the projectile is bonded to the target molecule. The most significant conclusion of the study is that selective chemical modification of monolayer surfaces can be achieved by using reactive ion beams, which lead to new covalent bonds at the surface and in the scattered ions. 相似文献
50.
Pradeep R. Varadwaj Arpita Varadwaj Helder M. Marques Koichi Yamashita 《Molecules (Basel, Switzerland)》2022,27(5)
The phosphorus bond in chemical systems, which is an inter- or intramolecular noncovalent interaction, occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a covalently or coordinately bonded phosphorus atom in a molecular entity and a nucleophile in another, or the same, molecular entity. It is the second member of the family of pnictogen bonds, formed by the second member of the pnictogen family of the periodic table. In this overview, we provide the reader with a snapshot of the nature, and possible occurrences, of phosphorus-centered pnictogen bonding in illustrative chemical crystal systems drawn from the ICSD (Inorganic Crystal Structure Database) and CSD (Cambridge Structural Database) databases, some of which date back to the latter part of the last century. The illustrative systems discussed are expected to assist as a guide to researchers in rationalizing phosphorus-centered pnictogen bonding in the rational design of molecular complexes, crystals, and materials and their subsequent characterization. 相似文献