全文获取类型
收费全文 | 844篇 |
免费 | 23篇 |
国内免费 | 4篇 |
专业分类
化学 | 716篇 |
晶体学 | 7篇 |
力学 | 1篇 |
数学 | 60篇 |
物理学 | 87篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 86篇 |
2021年 | 95篇 |
2020年 | 35篇 |
2019年 | 27篇 |
2018年 | 28篇 |
2017年 | 29篇 |
2016年 | 36篇 |
2015年 | 30篇 |
2014年 | 36篇 |
2013年 | 61篇 |
2012年 | 43篇 |
2011年 | 63篇 |
2010年 | 25篇 |
2009年 | 39篇 |
2008年 | 46篇 |
2007年 | 38篇 |
2006年 | 30篇 |
2005年 | 27篇 |
2004年 | 20篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有871条查询结果,搜索用时 15 毫秒
111.
Aleksandra Holownia Chieh‐Hung Tien Diego B. Diaz Reed T. Larson Andrei K. Yudin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(42):15292-15297
The synthesis and applications of carboxy‐MIDA‐boronate, a novel C1 building block, are described. This molecule is accessible via a ruthenium tetraoxide‐mediated cleavage of commercially available ethynyl‐MIDA‐boronate. In the course of this study, carboxy‐MIDA‐boronate was found to possess ambident reactivity towards nucleophiles. Carboxylic acid derivatization produces a broad range of previously unknown carbamoyl‐, oxycarbo‐ and thiocarboboronates. Carboxy‐MIDA‐boronate and its derivatives undergo condensations to access borylated heterocycles with boron at positions that are difficult to access using alternate methods. The resulting heterocycles participate in the Suzuki–Miyaura cross‐coupling reaction, enabling entry into diverse bis(heteroaryl) motifs. The carbon monoxide‐releasing capacity of carboxy‐MIDA‐boronate was also examined and applied in palladium‐catalyzed carbonylation. 相似文献
112.
Divergently activated double bonds in electron poor 4-oxo-butenoates and (2E,4E)-6-oxo-2,4-dienoates underwent stereoselective and regioselective addition of mercaptans catalyzed by simple Cinchona alkaloids. Application of quinine and quinidine afforded both enantiomers of the 1,4-adducts with respect to the ketone carbonyl group in ees of up to 80%. Single recrystallization of some adducts resulted in further enrichment of up to 99%ee. 相似文献
113.
114.
Maria Hägg Olofsson Aleksandra Mandic Havelka Slavica Brnjic Maria C Shoshan Stig Linder 《BMC chemical biology》2008,8(1):2
Background
Intracellular free calcium ([Ca2+]i) is a key element in apoptotic signaling and a number of calcium-dependent apoptosis pathways have been described. We here used a chemical biology strategy to elucidate the relative importance of such different pathways. 相似文献115.
A single or a limited number of UVR exposures is recognized to suppress cell-mediated immunity in human subjects. The complex pathway leading from the absorption of photons by chromophores in the skin to the generation of T regulatory cells has been, at least partially, elucidated. However, the effect of repeated UV exposures on immune responses and associated mediators is not well studied, particularly to assess whether they lead, first, to the development of photoprotection so that these immune changes are reduced or no longer occur, and, secondly, to the development of photoprotection against the normal downregulation of immunity induced by a high UV dose. For almost all the parameters evaluated in this review--epidermal DNA damage/erythema, urocanic acid, Langerhans and dendritic cells, natural killer cells, macrophages, mast cells, contact and delayed hypersensitivity responses--none, aside from epidermal DNA damage/erythema and macrophage phagocytic activity, show convincing evidence of photoadaptation or, where appropriate, photoprotection. It is concluded that repeatedly irradiating individuals with UVR is likely to continue to result in downregulation of immunity. 相似文献
116.
Stubbs KA Scaffidi A Debowski AW Mark BL Stick RV Vocadlo DJ 《Journal of the American Chemical Society》2008,130(1):327-335
The NagZ class of retaining exo-glucosaminidases play a critical role in peptidoglycan recycling in Gram-negative bacteria and the induction of resistance to beta-lactams. Here we describe the concise synthesis of 2-azidoacetyl-2-deoxy-5-fluoro-beta-d-glucopyranosyl fluoride as an activity-based proteomics probe for profiling these exo-glycosidases. This active-site directed reagent covalently inactivates this class of retaining N-acetylglucosaminidases with exquisite selectivity by stabilizing the glycosyl-enzyme intermediate. Inactivated Vibrio cholerae NagZ can be elaborated with biotin or a FLAG-peptide epitope using the Staudinger ligation or the Sharpless-Meldal click reaction and detected at nanogram levels. This ABPP enabled the profiling of the Pseudomonas aeruginosa proteome and identification at endogenous levels of a tagged protein with properties consistent with those of PA3005. Cloning of the gene encoding this hypothetical protein and biochemical characterization enabled unambiguous assignment of this hypothetical protein as a NagZ. The identification and cloning of this NagZ may facilitate the development of strategies to circumvent resistance to beta-lactams in this human pathogen. As well, this general strategy, involving such 5-fluoro inactivators, may prove to be of general use for profiling proteomes and identifying glycoside hydrolases of medical importance or having desirable properties for biotechnology. 相似文献
117.
Electrochemical behavior and antioxidant and prooxidant activity of natural phenolics 总被引:1,自引:0,他引:1
We have investigated the electrochemical oxidation of a number natural phenolics (salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, protocatechuic acid, o-coumaric acid, m-coumaric acid, p-coumaric acid, caffeic acid, quercetin and rutin) using cyclic voltammetry. The antioxidant properties of these compounds were also studied. A structural analysis of the tested phenolics suggests that multiple OH substitution and conjugation are important determinants of the free radical scavenging activity and electrochemical behavior. Compounds with low oxidation potentials (Epa lower than 0.45) showed antioxidant activity, whereas compounds with high Epa values (>0.45) act as prooxidants. 相似文献
118.
Humphreys AS Filipovska A Berners-Price SJ Koutsantonis GA Skelton BW White AH 《Dalton transactions (Cambridge, England : 2003)》2007,(43):4943-4950
The novel water soluble bidentate phosphine ligand 1,3-bis(di-2-pyridylphosphino)propane (d2pypp) has been synthesized by a convenient route involving treatment of 2-pyridyllithium with Cl(2)P(CH(2))(3)PCl(2) and isolation in crystalline form as the hydrochloride salt. The synthesis of the precursor Cl(2)P(CH(2))(3)PCl(2) has been optimized by the use of triphosgene as the chlorinating agent. The 2 : 1 and 1 : 2 AuCl : d2pypp adducts have been synthesized and characterized by NMR spectroscopy and single crystal X-ray studies, and shown to be of the form (AuCl)(2)(mu-d2pypp-P,P') and [Au(d2pypp-P,P')(2)]Cl(.3.75H(2)O), respectively. The latter is more lipophilic than analogous 1 : 2 adducts of gold(I) chloride with the diphosphine ligands 1,2-bis(di-n-pyridylphosphino)ethane (dnpype) for n = 2, 3 and 4, based on measurement of the n-octanol-water partition coefficient (log P = -0.46). A single crystal structure determination of the 1 : 2 Au(I) complex of the 3-pyridyl ethane ligand shows it to be of the form [Au(d3pype-P,P')(2)]Cl.5H(2)O. The in vitro cytotoxic activity of [Au(d2pypp)(2)]Cl was assessed in human normal and cancer breast cells and selective toxicity to the cancer cells found. The significance of these results to the antitumour properties of chelated 1 : 2 Au(I) diphosphine complexes is discussed. 相似文献
119.
Djurdjević P Joksović L Jelić R Djurdjević A Stankov MJ 《Chemical & pharmaceutical bulletin》2007,55(12):1689-1699
Complex formation between aluminum(III) ion and fluoroquinolone antibacterials-either moxifloxacin (4th generation antibiotic) or fleroxacin (2nd generation antibiotic) were studied in aqueous solutions without and in the presence of sodium dodecylsulfate (SDS). The investigations were performed by glass electrode potentiometric (ionic medium: 0.1 mol/dm(3) LiCl, 298 K), UV spectrophotometric, multinuclear (1H and 13C) magnetic resonance and ESI-MS measurements. The experimental data were consistent with the formation of Al(HL)L2+, Al(HL)3+ AlL2+, Al(OH)L+ and Al(OH)2L complexes in the pH interval ca. 3-8 and up to 5 : 1 ligand to metal mole ratio with range of Al3+ concentrations between ca. 0.025 to 1.0 mmol/dm3. The binary complex, AlL2+ is fairly stable (log beta(1,0,1) ca. 11.0) and its stability increases in the presence of SDS. At higher concentration ratios of ligands to aluminum, up to 5 : 1, the complex Al(HL)L2+ is formed with rather high overall stability constant (log beta(1,1,2) ca. 24.0). The ESI-MS data generally, confirmed the derived model, and the formation of the complex with ligand to metal ratio 2 : 1. NMR measurements indicate that both ligands utilize 4-carbonyl and carboxyl oxygens as donor atoms. The presence of surface active substance, SDS, favors the formation of the complex in which the ligand is protonated, i.e. Al(HL) and its maximum formation is shifted toward milder acidic region (pH ca. 4). The aluminum-quinolone complexes may affect the bio-distribution of both, quinolone and/or aluminum ion upon concomitant ingestion of aluminum-based antacids or phosphate binders and fluoroquinolones. 相似文献
120.
A density functional theory based on Wertheim's first order perturbation theory is developed for inhomogeneous complex fluids. The theory is derived along similar lines as interfacial statistical associating fluid theory [S. Tripathi and W. G. Chapman, J. Chem. Phys. 122, 094506 (2005)]. However, the derivation is more general and applies broadly to a range of systems, retaining the simplicity of a segment density based theory. Furthermore, the theory gives the exact density profile for ideal chains in an external field. The general avail of the theory has been demonstrated by applying the theory to lipids near surfaces, lipid bilayers, and copolymer thin films. The theoretical results show excellent agreement with the results from molecular simulations. 相似文献