全文获取类型
收费全文 | 1542篇 |
免费 | 80篇 |
国内免费 | 76篇 |
专业分类
化学 | 1642篇 |
晶体学 | 3篇 |
力学 | 1篇 |
综合类 | 6篇 |
物理学 | 46篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 19篇 |
2020年 | 22篇 |
2019年 | 19篇 |
2018年 | 32篇 |
2017年 | 32篇 |
2016年 | 37篇 |
2015年 | 37篇 |
2014年 | 56篇 |
2013年 | 145篇 |
2012年 | 76篇 |
2011年 | 70篇 |
2010年 | 79篇 |
2009年 | 59篇 |
2008年 | 85篇 |
2007年 | 84篇 |
2006年 | 89篇 |
2005年 | 89篇 |
2004年 | 74篇 |
2003年 | 69篇 |
2002年 | 108篇 |
2001年 | 49篇 |
2000年 | 26篇 |
1999年 | 37篇 |
1998年 | 32篇 |
1997年 | 29篇 |
1996年 | 40篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 22篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有1698条查询结果,搜索用时 15 毫秒
991.
Adeem Mahmood 《Tetrahedron》2017,73(16):2173-2190
From what began as a casual discovery of the ketene-Claisen rearrangement (the Malherbe-Bellu? rearrangement) over 3 decades ago has flourished a reaction of substantial significance. The noticeable qualities of the ketene-Claisen rearrangement is accomplished in terms of experimental simplicity, forming new CC bonds, high levels of chemo- and stereocontrol, ring enlargements and constructing new stereocenters. This survey of the ketene-Claisen rearrangement with some applications in organic synthesis will not only recapitulate the prospective of this reaction so far but also illustrate the achievable future significant prospective. 相似文献
992.
Preparation and evaluation of novel chiral stationary phases based on quinine derivatives comprising crown ether moieties
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dongqiang Wang Jianchao Zhao Haixia Wu Haibo Wu Jianfeng Cai Yanxiong Ke Xinmiao Liang 《Journal of separation science》2015,38(2):205-210
The C9‐position of quinine was modified by meta‐ or para‐substituted benzo‐18‐crown‐6, and immobilized on 3‐mercaptopropyl‐modified silica gel through the radical thiol‐ene addition reaction. These two chiral stationary phases were evaluated by chiral acids, amino acids, and chiral primary amines. The crown ether moiety on the quinine anion exchanger provided a ligand‐exchange site for primary amino groups, which played an important role in the retention and enantioselectivity for chiral compounds containing primary amine groups. These two stationary phases showed good selectivity for some amino acids. The complex interaction between crown ether and protonated primary amino group was investigated by the addition of inorganic salts such as LiCl, NH4Cl, NaCl, and KCl to the mobile phase. The resolution results showed that the simultaneous interactions between two function moieties (quinine and crown ether) and amino acids were important for the chiral separation. 相似文献
993.
Unique Curing Properties through Living Polymerization in Crosslinking Materials: Polyurethane Photopolymers from Vinyl Ether Building Blocks
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)
Stefan Kirschbaum Prof. Dr. Katharina Landfester Dr. Andreas Taden 《Angewandte Chemie (International ed. in English)》2015,54(19):5789-5792
Photopolymers with unique curing capabilities were produced by combining living cationic polymerization with network formation and restricted polymer motion. A vinyl ether diol was synthesized as a functional building block and reacted with isophorone diisocyanate to form a highly functionalized vinyl ether polyurethane as a model system with high crosslinking ability. When using a cationic photoinitiator, fast polymerization is observed upon short UV irradiation. Curing proceeds in the absence of light and under ambient conditions without oxygen inhibition. Cationic active sites become trapped dormant species upon network‐induced vitrification and surprisingly remain living for several days. The polymerization can be reactivated by additional UV irradiation and/or raised temperature. The curing behavior was studied in detail by using UV and FT‐NIR coupled rheology and photo‐DSC to simultaneously study spectroscopic and mechanical information, as well as thermal effects. 相似文献
994.
Diaryl ethers have been prepared by a mild and efficient SNAr reaction by coupling of various phenols including that having a electron-withdrawing group with activated fluoroarenes using sonication in good to excellent yields at very low temperature (58 °C) under catalyst-free. 相似文献
995.
996.
997.
The (19)F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin-spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules. 相似文献
998.
Sarjit Kaur J. V. Crivello Nina Pascuzzi 《Journal of polymer science. Part A, Polymer chemistry》1999,37(2):199-209
Several 1‐butenyl and 1‐pentenyl ether monomers were prepared by the ruthenium catalyzed multistage double bond isomerization of the corresponding 3‐butenyl and 4‐pentenyl ethers and characterized. Employing tris(triphenylphosphine)ruthenium(II) dichloride as a catalyst, the isomerization of octyl 4‐pentenyl ether to octyl 1‐pentenyl ether in 60% yield could be achieved in 110 min at 200–205°C. Under similar conditions, 3‐butenyl octyl ether was isomerized to 1‐butenyl octyl ether in greater than 99% yield. The reactivities of both types of monomers in photoinitiated cationic polymerization were determined using real‐time infrared spectroscopy and the monomers were found to polymerize at very nearly the same rate in the presence of a diaryliodonium salt photoinitiator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 199–209, 1999 相似文献
999.
Katleen Verleysen Jos Vandijck Mark Schelfaut Pat Sandra 《Journal of separation science》1998,21(6):323-331
An overview is presented of the applicability of the crown ether 18-crown-6-tetracarboxylic acid (18C6H4) as buffer additive in capillary electrophoresis (CE) for the separation of enantiomers. The chiral selector 18C6H4 is particularly useful for the separation of racemates having a primary amino function. Unfortunately, the crown ether is no longer commercially available. The synthesis and spectroscopic characterization are therefore described in detail. Moreover, a method is presented for the regeneration of the crown ether after CE application. Some new enantiomeric separations of amino acids i.e. NORLEU, ARG, GLU, m-TYR, and o-TYR are listed and the influence of the pH and temperature of the separation buffer is discussed. An intermediate in the synthetic pathway, namely 18-crown-6-tetracarboxamide, did not exhibit any enantioselectivity in CE. 相似文献
1000.
Yingdong Wu Lu Bai Junping Zheng 《Journal of polymer science. Part A, Polymer chemistry》2024,62(5):870-879
In recent years, as an emerging dynamic bonding, silyl ether linkages have been concerned and applied. However, the reprocessability of vitrimers based on it is far from satisfactory because of the inactive dynamic exchange reaction. At the same time, the mechanical properties of polysiloxane elastomers are poor because of the high flexibility of polysiloxane molecular chains and weak intermolecular forces. Herein, we have successfully synthesized a PDMS elastomer incorporating Zn(II)-amine coordination bonds as sacrificial units, which are crosslinked through dynamic silyl ether linkages. Importantly, the presence of Zn ions promotes the exchange between the silyl ether linkages and hydroxyl groups. The elastomers exhibited excellent mechanical properties (35 times improvement in toughness) and outstanding reprocessability. The mechanical property recovery of the PDMS elastomers reached approximately 90% after four reprocessing cycles. Meanwhile, small-molecule simulation experiments were conducted to verify the significant catalytic effect of Zn (II) ions as Lewis acid catalysts on the exchange reaction of silyl ether linkages and hydroxyl groups. In a word, this work provides a facile strategy to simultaneously enhance the mechanical properties and reprocessing performance of silyl ether-linked polysiloxane elastomers. 相似文献