全文获取类型
收费全文 | 478篇 |
免费 | 28篇 |
专业分类
化学 | 315篇 |
晶体学 | 1篇 |
力学 | 21篇 |
数学 | 66篇 |
物理学 | 103篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 21篇 |
2019年 | 7篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 19篇 |
2015年 | 27篇 |
2014年 | 27篇 |
2013年 | 27篇 |
2012年 | 49篇 |
2011年 | 52篇 |
2010年 | 26篇 |
2009年 | 18篇 |
2008年 | 28篇 |
2007年 | 29篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 14篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有506条查询结果,搜索用时 15 毫秒
101.
Influence of the particle size of the MgCl2 support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An Philippaerts Richard Ensinck Nicolas Baulu Astrid Cordier Kersten Woike Romain Berthoud Gert De Cremer John R. Severn 《Journal of polymer science. Part A, Polymer chemistry》2017,55(16):2679-2690
A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl2 support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 µm, leads to a pronounced impact on the activity in ultra‐high molecular weight polyethylene (UHMWPE) polymerization, while the Mw capabilities are only affected to a limited extend. In addition, it is observed that both the Mws as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the Mw and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2679–2690 相似文献
102.
Cassandre Piriou Lucas Viers Romain Lucas Fabien Bouzat Hatim Laadoua Yves Champavier Sylvie Foucaud Cristina Coelho Florence Babonneau 《应用有机金属化学》2018,32(9)
A hyperbranched polymer, a precursor of silicon carbide (SiC), was successfully synthesized using a hydrosilylation reaction with Karstedt's catalyst. This reaction was optimized with the use of a rheometer coupled with an infrared spectrometer. The polymeric precursor was characterized using NMR and Fourier transform infrared spectroscopies, and dynamic rheology. The polymerization reaction was followed in situ by combined rheological and infrared measurements, indicating a gel‐like behaviour for alkene conversions higher than 0.55. Overall second‐order kinetics was determined for the hydrosilylation reaction. Pyrolysis at 1400 °C led to porous materials with β‐SiC and free carbon. 相似文献
103.
Using CrCl2 in THF at room temperature, trichloromethyl carbinols and trichloromethylalkanes are readily transformed to the highly reactive α-chlorocarbenes, carbynes and α-chloro-α-chromium(III) vinylidene carbenoids. A mechanistic study is carried out to determine the nature of the intermediates. 相似文献
104.
A small library of squamocin analogues has been prepared and screened biologically (cytotoxicity, inhibition of mitochondrial complex I and complex III). To centre diversity on a crucial part of the molecule (i.e., the α,β-unsaturated lactone), an original and reliable lactone opening reaction has been discovered and exploited among other efficient reactions. 相似文献
105.
Dr. Victor Zdorichenko Romain Paumier Thomas Whitmarsh-Everiss Dr. Mark Roe Prof. Brian Cox 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(5):1286-1292
Chagas disease also know as American Trypanosomiasis (AT) is a tropical parasitic disease endemic in South America, is caused by Trypanosoma cruzi, which is transmitted by the blood-sucking insect vectors called triatomine bugs. Quinoline alkaloids from the root extract of Waltheria indica are known to possess antitrypanosomal activity. Waltherione F, one of those alkaloids, was synthesised in 5 steps in 11 % overall yield. We report here the first X-ray crystallographic confirmation of the structure of Waltherione F 3 . A key step in the sequence utilised the Conrad–Limpach synthesis for the formation of the quinolin-4(1H)-one ring system. Our synthetic strategy was designed to enable the modification of the 2- and 3-positions of the scaffold, allowing the generation of a diverse library of analogues to support our on-going medicinal chemistry program that is looking for new agents to tackle this devastating disease. 相似文献
106.
Dr. Jørn Eivind Tungen Dr. Lisa Gerstmann Prof. Dr. Anders Vik Roberta De Matteis Dr. Romain Alexandre Colas Prof. Dr. Jesmond Dalli Prof. Dr. Nan Chiang Prof. Dr. Charles Nicholas Serhan Prof. Dr. Markus Kalesse Prof. Dr. Trond Vidar Hansen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(6):1476-1480
New drugs that can resolve inflammation without immunosuppressive effects are at the medicinal chemistry frontier. Pro-resolving endogenously formed small molecules, that is, the resolvins, are excellent candidates displaying such bioactions. The first total synthesis of the specialized pro-resolving mediator RvD1n−3 DPA has been achieved using the underutilized sp3–sp3 Negishi cross coupling reaction and an alkyne hydrosilylation–protodesilylation protocol. Biological evaluations revealed that this novel mediator displays low nanomolar pro-resolving properties and potently activates the human DRV1/GPR32 receptor. As such, this endogenous natural product is a lead compound for the development of novel immunoresolvents. 相似文献
107.
Allocating the right person to a task or job is a key issue for improving quality and performance of achievements, usually addressed using the concept of “competences”. Nevertheless, providing an accurate assessment of the competences of an individual may be in practice a difficult task. We suggest in this paper to model the uncertainty on the competences possessed by a person using a possibility distribution, and the imprecision on the competences required for a task using a fuzzy constraint, taking into account the possible interactions between competences using a Choquet integral. As a difference with comparable approaches, we then suggest to perform the allocation of persons to jobs using a robust optimisation approach, allowing to minimise the risk taken by the decision maker. We first apply this framework to the problem of selecting a candidate within n for a job, then extend the method to the problem of selecting c candidates for j jobs (c ? j) using the leximin criterion. 相似文献
108.
Dr. David P. Tilly Dr. William Cullen Heng Zhong Romain Jamagne Dr. Inigo Vitórica-Yrezábal Prof. Dr. Simon J. Webb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(9):e202104293
To investigate how remotely induced changes in ligand folding might affect catalysis by organometallic complexes, dynamic α-amino-iso-butyric acid (Aib) peptide foldamers bearing rhodium(I) N-heterocyclic carbene (NHC) complexes have been synthesized and studied. X-ray crystallography of a foldamer with an N-terminal azide and a C-terminal Rh(NHC)(Cl)(diene) complex showed a racemate with a chiral axis in the Rh(NHC) complex and a distorted 310 helical body. Replacing the azide with either one or two chiral L-α-methylvaline (L-αMeVal) residues gave diastereoisomeric foldamers that each possessed point, helical and axial chirality. NMR spectroscopy revealed an unequal ratio of diastereoisomers for some foldamers, indicating that the chiral conformational preference of the N-terminal residue(s) was relayed down the 1 nm helical body to the axially chiral Rh(NHC) complex. Although the remote chiral residue(s) did not affect the stereoselectivity of hydrosilylation reactions catalysed by these foldamers, these studies suggest a potential pathway towards remote conformational control of organometallic catalysts. 相似文献
109.
Blanc R Héran V Rahmani R Commeiras L Parrain JL 《Organic & biomolecular chemistry》2010,8(24):5490-5494
An efficient synthesis of deoxy-lambertellols was reported through a highly chemo- and diastereoselective intermolecular Diels-Alder cycloaddition between trans-1,2-disiloxybenzocyclobutenes and 2-methylprotoanemonine. Such transformation with δ-substituted γ-alkylidenebutenolides, to prepare new analogues of these tricyclic spirolactones, which would be very difficult to prepare by other ways, was also studied. 相似文献
110.
Daniel Chappard Bernard Guillaume Romain Mallet Florence Pascaretti-Grizon Michel F. Baslé Hélène Libouban 《Micron (Oxford, England : 1993)》2010,41(4):321-326
Sinus lift elevation is an interesting method to restore bone mass at the maxilla in edentulated patients. We have investigated the histological effects of beta tricalcium phosphate (β-TCP) combined with autograft bone for sinus lift elevation. A series of 14 patients who were candidate for dental implantation were grafted with β-TCP granules and morcellized autograft bone harvested at the chin. β-TCP was characterized by scanning electron microscopy and optical profilometry. Before implant placement, a small bone biopsy (2 mm in diameter) was done. The amount of residual material and newly formed bone were determined by microcomputed tomography. Histological analysis was done on undecalcified sections stained by Goldner's trichrome and osteoclast identification (TRAcP). β-TCP served as a template for bone apposition by osteoblasts onto the granules’ surface. The material was simultaneously resorbed by TRAcP positive osteoclasts and macrophages. Fragments of the material remained buried in bone trabeculae as long as 12 months post-graft but the formed bone onto the granules surface had a lamellar texture. β-TCP combined with autograft bone appears a suitable biomaterial for sinus lift augmentation before the placement of bone implants. The material favors the apposition of lamellar bone by osteoblasts and is simultaneous resorbed by two types of cells. 相似文献