全文获取类型
收费全文 | 659篇 |
免费 | 84篇 |
国内免费 | 127篇 |
专业分类
化学 | 763篇 |
晶体学 | 8篇 |
力学 | 14篇 |
综合类 | 4篇 |
物理学 | 81篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 27篇 |
2021年 | 37篇 |
2020年 | 47篇 |
2019年 | 48篇 |
2018年 | 34篇 |
2017年 | 52篇 |
2016年 | 41篇 |
2015年 | 28篇 |
2014年 | 51篇 |
2013年 | 70篇 |
2012年 | 36篇 |
2011年 | 35篇 |
2010年 | 20篇 |
2009年 | 36篇 |
2008年 | 30篇 |
2007年 | 26篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 30篇 |
2003年 | 26篇 |
2002年 | 12篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 2篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有870条查询结果,搜索用时 46 毫秒
231.
232.
Palladium catalysis was used in Stille-type carbonylative cross-couplings employing Mo(CO)6 as the carbon monoxide source. Robust and convenient transformations were carried out in closed vessels at 100 °C, providing a set of diaryl ketones in good yields. Aryl triflates and bromides were used as coupling partners with aryl stannanes. Inclusion of the Mo(CO)6 destabilizing agent DBU made this protocol operationally simple and suppressed side-product formation. 相似文献
233.
Preparation and functionalization of linear and reductively degradable highly branched cyanoacrylate‐based polymers
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)
Houliang Tang Nicolay V. Tsarevsky 《Journal of polymer science. Part A, Polymer chemistry》2016,54(23):3683-3693
Ethyl cyanoacrylate (ECA) was polymerized radically in the presence of small amounts of trifluoroacetic acid as effective inhibitor of incidental anionic polymerization. Methyl methacrylate and other functional vinyl monomers (e.g., 2‐chloroethyl and 2‐bromoethyl methacrylate) were copolymerized with ECA, yielding linear ECA‐rich copolymers, which could readily undergo further modifications, for instance nucleophilic substitution with azide. In the presence of a disulfide‐containing dimethacrylate crosslinker and a chain transfer agent (CBr4) during the free radical copolymerizations of ECA with methacrylates, highly branched ECA‐based polymers containing disulfide groups at the branching points were obtained prior to gelation. The polymers degraded upon addition of reducing agents. The prepared polymers, which contained peripheral (chain end) alkyl bromide groups as well as pendant alkyl chloride or bromide groups were then reacted with sodium azide, affording azide‐containing polymers that were reacted with functional alkynes under copper‐catalyzed “click” chemistry conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3683–3693 相似文献
234.
Two series of ordered mesoporous organosilica (OMO) SBA-15 materials with surface and bridging groups were fabricated by varying
the organic precursor addition at different synthesis stages. The consequence of the delayed introduction of organic precursor
on the structural and adsorption properties of the resulting OMOs was investigated. The OMOs studied were synthesized via
co-condensation of tetraethyl orthosilicate (TEOS) and ureidopropyltrimethoxysilane (UPS) as well as TEOS and bis(triethoxysilylpropyl)
disulfide (BTDS) in the presence of poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) triblock copolymer Pluronic
P123 (EO20PO70EO20). The aforementioned OMOs were characterized by nitrogen adsorption-desorption isotherms at −196 °C and powder X-ray diffraction
(XRD). Nitrogen adsorption isotherms were used to estimate the pore volume, mesopore diameter and the BET specific surface
area, whereas the XRD data provided information about structural ordering and unit cell of the samples studied.
Ryan Felix, undergraduate student from Oberlin College (Oberlin, OH, USA) participating in the NSF-REU program during Summer
2006. 相似文献
235.
Donald F. Mullica Mary Lynn Trawick Paul W. N. Wu Eric L. Sappenfield 《Journal of chemical crystallography》1998,28(10):761-765
Di-(2,4-imidazolidinedione-5-ethyl)disulfide or homocystine hydantoin, C10H14N4O4S2 (I), crystallizes in the non-centrosymmetric space group P21 (No. 4) with two molecules in the unit cell with a = 7.132(1), b = 9.282(2), c = 10.770(2) Å and = 105.68(1)°. The two imidazolidinedione rings are planar with a dihedral angle of 46.9°. The rings are joined by a diethyl disulfide bridge at chiral centers on the rings. The C-S-S-C torsion angle is –80°(–sc). The absolute stereochemistry of the chiral centers was determined to be (5S, 5S), = + 0.92 (11). Important bond distances include: S-S = 2.022(4); S-C (mean) = 1.809(8); and C=O (mean) = 1.224(7) Å. The compound is stabilized by a network of intermolecular carbonyl-to-amine hydrogen bonding and van der Waals cohesive forces. 相似文献
236.
This paper describes the development of oligonucleotide-functionalized nanoparticles. We used disulfide-coupling chemistry for the immobilization of oligonucleotides onto silica nanoparticles and subsequently demonstrated the properties of the resulting DNA nanoparticles. Factors influencing the immobilization and hybridization processes were examined and optimized. The oligonucleotide-modified silica nanoparticles provide an efficient substrate for hybridization and can be used in the development of DNA biosensors and biochips. 相似文献
237.
During the preparation of AsBr4(+)[Al(OR)4]-, the novel carbocation CS2Br3+ was synthesized by reaction of AsBr3, Br2, CS2, and Ag[Al(OR)4] (R=C(CF3)3). CS2Br3(+)[Al(OR)4]- was characterized by its crystal structure, NMR and IR spectroscopy, and quantum chemical calculations (including COSMO solvation enthalpies). Additional experiments as well as the computed thermodynamics indicated two likely reaction pathways: Ag(+) +2Br2 +CS2-->CS2Br3(+) +AgBr and the direct 4e- oxidation reaction AsBr4(+) +CS2-->CS2Br3(+) + 1/6As6Br6. Both reactions were observed experimentally and were calculated to be exergonic in solution by -226 and -56 kJ mol(-1) respectively. As a result of charge delocalization the C-S and C-Br distances in the cation are shortened by 0.06 to 0.08 A; the S--Br distances are also slightly shortened indicating a delocalization of the charge also to the bromine atoms in the (S--Br moieties. Based on an analysis of the cation-anion contacts as well as quantum chemical MP2 calculations, a delocalization model as a planar 10 pi electron system is discussed and the pi molecular orbitals are given. It will be shown that the electronic situation of CS2Br3+ is very close to that in CBr3+, that is, the properties of SBr moieties and Br atoms as pi donors towards a formal C+ center are comparable. 相似文献
238.
The reaction of triethoxy(3-aminopropyl)silane with carbon disulfide andortho-chloroethyl formate in absolute ethanol gave triethoxy(3-isothiocyanatopropyl)silane for the first time. The presence of SCN and (C2H5O)3Si groups in this compound enabled us to use it for the preparation of adsorbents and polymer coatings with biocidal activity.Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2681–2682, November, 1992. 相似文献
239.
Reduction and oxidation peak potentials of poly[dithio-2,5-(1,3,4-thiadiazole)] were observed in hot γ-butyrolactam (90°C) at −0.1 and 0.1 V vs. Ag respectively. To clarify the redox reaction of the polymer (oligomer), bis(2-methyl-1,3,4-thiadiazoyl)-5,5′-disulfane was synthesized as a model compound and its redox reaction examined by experiment and molecular orbital calculation. Reduction and oxidation peak potentials of this model were observed at −0.65 and 0.2 V respectively, potentials corresponding to the cleavage and formation reactions of the disulfide bond. The bond cleavage reaction was also suggested by molecular orbital calculations. From a comparison of the shape and response of the cyclic voltammogram between the monomeric and polymeric disulfides, it became clear that reduction and oxidation of the polymer meant the cleavage and formation reactions of the disulfide bond respectively, and that the redox reaction is quasi-reversible. 相似文献
240.
Jordan M. Fletcher 《Tetrahedron letters》2004,45(38):6999-7001
We describe a novel acetamidomethyl to S-pyridinyl exchange that is used for the synthesis of a multi-disulfide-linked and constrained heterodimeric bicyclic peptide mimetic of brain-derived neurotrophic factor (BDNF). This simple and effective method should be readily transferable to the synthesis of similar disulfide-linked heterodimeric peptides, as well as being of general utility for the synthesis of peptides bearing multiple cystine frameworks. 相似文献