全文获取类型
收费全文 | 379篇 |
免费 | 17篇 |
国内免费 | 4篇 |
专业分类
化学 | 289篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 41篇 |
物理学 | 65篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 35篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 25篇 |
2008年 | 36篇 |
2007年 | 28篇 |
2006年 | 23篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
排序方式: 共有400条查询结果,搜索用时 15 毫秒
21.
The stereoselective reaction of 4-oxoazetidine-2-carbaldehydes and their corresponding imines with cyanide-based reagents give β-lactam α-aminonitriles, which are chameleonic building blocks for the controlled synthesis of a variety of new compounds including functionalized γ-lactams, succinimide derivatives, and diamino-lactams derivatives in optically pure form. 相似文献
22.
Alcaide B Almendros P Alonso JM Aly MF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(14):3415-3426
Imines derived from 4-oxoazetidine-2-carbaldehydes have been found to be versatile Diels-Alder reagents in that they exhibit two reactivity patterns. 2-Azetidinone-tethered imines undergo diastereoselective reaction with Danishefsky's diene in the presence of different Lewis acids. The effect of the amount of catalyst on the conversion rate as well as on the product ratio has been studied. Under standard reaction conditions, indium(III) chloride and zinc(II) iodide provided the best yields, and indium(III) triflate the highest diastereoselectivity in the Lewis acid promoted aza-Diels-Alder cycloaddition. Treatment of the aforementioned imines with cyclopentadiene, 2,3-dimethyl-1,3-butadiene or 3,4-dihydro-2 H-pyran led to cycloadducts arising from inverse electron-demand condensation involving the beta-lactam-tethered aryl imine as the heterodiene component. In addition, the first methodology for preparing indolizidines from beta-lactams has been developed. This process involves amide bond cleavage of the beta-lactam ring in the aza-Diels-Alder cycloadducts with concomitant cyclization. Full chirality transfer occurs when the reaction is performed with an enantiomerically pure substrate. 相似文献
23.
Phosphatidylcholine‐Coated Iron Oxide Nanomicelles for In Vivo Prolonged Circulation Time with an Antibiofouling Protein Corona 下载免费PDF全文
Hugo Groult Dr. Jesús Ruiz‐Cabello Ana Victoria Lechuga‐Vieco Dr. Jesús Mateo Dr. Marina Benito Izaskun Bilbao Dr. María Paz Martínez‐Alcázar Dr. Juan. Antonio Lopez Dr. Jesús Vázquez Dr. Fernando F. Herranz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16662-16671
We report the synthesis of micellar phosphatidylcholine‐coated superparamagnetic iron oxide nanoparticles as a new long circulation contrast agents for magnetic resonance imaging. Oleic acid‐coated Fe3O4 nanoparticles were first prepared through thermal degradation and then encapsulated into small clusters with a phosphatidylcholine coating to obtain hydrophilic nanomicelles. A thorough characterization confirmed the chemical nature of the coating and the excellent colloidal stability of these nanomicelles in aqueous media. Magnetization and relaxivity properties proved their suitability as magnetic resonance imaging (MRI) contrast agent and in vitro cell viability data showed low toxicity. Vascular lifetime and elimination kinetics in the liver were assessed by blood relaxometry and by in vivo MRI in rats and compared with “control” particles prepared with a polyethylene glycol derivative. These micellar particles had a lifetime in blood of more than 10 h, much longer than the control nanoparticles (≈2 h), which is remarkable considering that the coating molecule is a small biocompatible zwitterionic phospholipid. The protein corona was characterized after incubation with rat serum at different times by high‐throughput proteomics, showing a higher proportion of bound apolipoproteins and other dysopsonins for the phosphatidylcholine particles. The antibiofouling properties of this corona and its resistance to the adsorption of proteins corroborate the observed enhanced stability and prolonged systemic circulation. 相似文献
24.
Javier Benito Mónica García-Mardones Víctor Pérez-Gregorio Ignacio Gascón Carlos Lafuente 《Journal of solution chemistry》2014,43(4):696-710
In this work, thermophysical properties of n-ethylpyridinium bis(trifluoromethylsulfonyl)imide have been studied at atmospheric pressure in the temperature range 288.15–338.15 K. Density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, electrical conductivity and kinematic viscosity have been measured; from these data the isobaric expansibility, isentropic compressibility, molar refraction, entropy and enthalpy of surface formation per unit of surface area, and dynamic viscosity have been calculated. Moreover, we have characterized the thermal behavior of the compound. Results have been analyzed paying special attention to the structural and energetic factors. The magnitude and directionality of the cation–anion interactions have been studied using ab initio quantum calculations, which allow a better understanding of the physicochemical behavior of the ionic liquid. Finally, density values and radial distribution functions were also estimated ab initio from classical molecular dynamics simulations, providing acceptable density predictions. 相似文献
25.
Dr. David Benito‐Alifonso Shirley Tremel Bo Hou Harriet Lockyear Dr. Judith Mantell Prof. David J. Fermin Dr. Paul Verkade Dr. Monica Berry Dr. M. Carmen Galan 《Angewandte Chemie (International ed. in English)》2014,53(3):810-814
A series of glycan‐coated quantum dots were prepared to probe the effect of glycan presentation in intracellular localization in HeLa and SV40 epithelial cells. We show that glycan density mostly impacts on cell toxicity, whereas glycan type affects the cell uptake and intracellular localization. Moreover, we show that lactose can act as a “Trojan horse” on bi‐functionalized QDs to help intracellular delivery of other non‐internalizable glycan moieties and largely avoid the endosomal/lysosomal degradative pathway. 相似文献
26.
Cover Picture: A Versatile Approach to CF3‐Containing 2‐Pyrrolidones by Tandem Michael Addition–Cyclization: Exemplification in the Synthesis of Amidine Class BACE1 Inhibitors (Chem. Eur. J. 33/2015) 下载免费PDF全文
27.
Surface‐Functionalized Nanoparticles by Olefin Metathesis: A Chemoselective Approach for In Vivo Characterization of Atherosclerosis Plaque 下载免费PDF全文
Dr. Beatriz Salinas Dr. Jesús Ruiz‐Cabello Ana V. Lechuga‐Vieco Dr. Marina Benito Dr. Fernando Herranz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(29):10450-10456
The use of click chemistry reactions for the functionalization of nanoparticles is particularly useful to modify the surface in a well‐defined manner and to enhance the targeting properties, thus facilitating clinical translation. Here it is demonstrated that olefin metathesis can be used for the chemoselective functionalization of iron oxide nanoparticles with three different examples. This approach enables, in one step, the synthesis and functionalization of different water‐stable magnetite‐based particles from oleic acid‐coated counterparts. The surface of the nanoparticles was completely characterized showing how the metathesis approach introduces a large number of hydrophilic molecules on their coating layer. As an example of the possible applications of these new nanocomposites, a focus was taken on atherosclerosis plaques. It is also demonstrated how the in vitro properties of one of the probes, particularly its Ca2+‐binding properties, mediate their final in vivo use; that is, the selective accumulation in atherosclerotic plaques. This opens promising new applications to detect possible microcalcifications associated with plaque vulnerability. The accumulation of the new imaging tracers is demonstrated by in vivo magnetic resonance imaging of carotids and aorta in the ApoE?/? mouse model and the results were confirmed by histology. 相似文献
28.
Sayra L. Orozco Erick R. Bandala Camilo A. Arancibia-Bulnes Benito Serrano Raúl Surez-Parra Isaias Hernndez-Prez 《Journal of photochemistry and photobiology. A, Chemistry》2008,198(2-3):144-149
The effect of chloride, sulfate and nitrate anions on the color removal of water containing the azo-dye reactive blue 69 (RB69) in acidic solution, by using photo-assisted Fenton process with Fe(II)/H2O2 and Fe(III)/H2O2 systems was investigated. Experiments were conducted in a batch reactor irradiated during 5 h with a domestic 15 W lamp with emission in the visible spectra. Experimental results showed color disappearance in the first 5 min of reaction in the photo-assisted process for all of the different salts, greatly enhancing the reaction rate with respect to the corresponding systems under dark conditions. The exception of the general trend was the Fe2(SO4)3/H2O2/UV system, where the decolorization process is slower probably because the oxidative species generated by rupture of Fe(III)–peroxo complexes are less reactive. Total organic matter depletion and mineralization of the effluent were also tested during the experimental runs by means of total organic carbon (TOC) showing that, for most of the photo-assisted experiments high mineralization was reached after 3 h of reaction. 相似文献
29.
30.
The hybrid allenic β‐lactam moiety represents an excellent building block for carbo‐ and heterocyclization reactions, affording a large number of cyclic structures containing different sized skeletons in a single step. This strategy has been studied under thermal and radical‐induced conditions. More recently, the use of transition‐metal catalysis has been introduced as an alternative that relies on the activation of the allenic component. On the other hand, the intramolecular version has attracted much attention as a strategy for the synthesis of bi‐ and tricyclic compounds in a regio‐ and stereoselective manner. This overview focuses on the most recently developed cyclizations on 2‐azetidinone‐tethered allenes along with remarkable early works accounting for the mechanism, as well as for the regio‐ and diastereoselectivities of the cyclizations. DOI 10.1002/tcr.201100011 相似文献