全文获取类型
收费全文 | 207篇 |
免费 | 11篇 |
专业分类
化学 | 186篇 |
晶体学 | 1篇 |
数学 | 7篇 |
物理学 | 24篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2012年 | 15篇 |
2011年 | 17篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 9篇 |
2005年 | 19篇 |
2004年 | 14篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
排序方式: 共有218条查询结果,搜索用时 15 毫秒
101.
Yamazaki S Morikawa S Iwata Y Yamamoto M Kuramoto K 《Organic & biomolecular chemistry》2004,2(21):3134-3138
A novel cyclization reaction of ethenetricarboxylate derivative aromatic compounds in the presence of various Lewis acids gave benzo-annulated cyclic compounds such as oxindole and benzofuran derivatives via Friedel-Crafts intramolecular Michael addition in high yields. For example, the reaction of diethyl 2-[(N-methyl-N-phenylcarbamoyl)methylene]malonate (1a) in the presence of ZnCl2 at room temperature gave diethyl 2-(1-methyl-2-oxoindolin-3-yl)malonate (2a) in 98% yield. The reactions also proceeded with a catalytic amount of a Lewis acid such as AlCl3, ZnCl2, ZnBr2, Sc(OTf)3, or InBr3. 相似文献
102.
Sakamoto R Murata M Kume S Sampei H Sugimoto M Nishihara H 《Chemical communications (Cambridge, England)》2005,(9):1215-1217
A new platinum complex with both an azo-bound dithiolato ligand and an azobenzene-bound bipyridine ligand exhibits tristability reversibly controllable using different energy lights. 相似文献
103.
Hydrogen dynamics in one-dimensional hydrogen bonded organic antiferroelectric, co-crystal of 5,5’-dimethyl-2,2’-bipyridine (55DMBP) and chloranilic acid (H2ca), was investigated by use of 2H high resolution solid-state NMR. The two types of hydrogen bonds O-H …N and N+-H …O? in the antiferroelectric phase were clearly observed as the splitting of the side band of the 2H MAS NMR spectra of the acid-proton deuterated compound 55DMBP-D 2ca. The temperature dependence of the spin-lattice relaxation time was measured of the N+-H and O-H deuterons, respectively. It was suggested that the motion of the O-H deuteron is already in the antiferroelectric phase in the fast-motion regime in the NMR time scale, while that of the N+-H deuteron is a slow motion. In the high-temperature paraelectric phase, the both deuterons become equivalent and the fast motion of the deuterons in the NMR time scale is taking place with the activation energy of 7.9 kJ mol?1. 相似文献
104.
A nitrogen-directed regioselective homocoupling reaction of aromatic compounds has been found to be catalyzed by a ruthenium complex in the presence of methallyl acetate as a hydrogen scavenger. 相似文献
105.
The efficient selective synthesis of secondary and tertiary amines has been achieved by means of Cp*Ir-catalyzed multialkylation of ammonium salts with alcohols without solvent: the reactions of ammonium acetate with alcohols gave tertiary amines exclusively, while those of ammonium tetrafluoroborate afforded secondary amines selectively. Using this method, secondary 5- and 6-membered cyclic amines were synthesized from ammonium tetrafluoroborate and diols in one pot. 相似文献
106.
Yui H Minamikawa H Danev R Nagayama K Kamiya S Shimizu T 《Langmuir : the ACS journal of surfaces and colloids》2008,24(3):709-713
Phase-contrast transmission electron microscopy (PC-TEM) and quick freezing method have been combined to study the initial growing process of a self-assembled lipid nanotube in water. The PC-TEM enabled us to detect thin lamellar edge structure and the very fast growth of the newborn edge to a thin tube with high contrast. The thin tube acts as a core structure for further growth into thick complete lipid nanotube. The initially formed nanotube structure is denoted as a "core tube". The core tube has uniform wall structure that consists of five lamellar layers and the inner and outer diameters of the core tube are 130 and 180 nm, respectively. The evaluated lamellar spacing of 4.6 nm is well compatible with that measured by X-ray diffraction. We also discussed the molecular packing of the nanotube from the pitch angle determined by the PC-TEM images, X-ray diffraction pattern in wide-angle region, and IR spectroscopy. The subcell structure of the nanotube is assigned to an orthorhombic type. The twisting angle between the neighboring lipid molecules is determined as ca. 0.26 degrees for the first time; it is a crucial parameter for the formation of a lipid nanotube in chiral packing but has not been elucidated before. 相似文献
107.
Dubs C Hamashima Y Sasamoto N Seidel TM Suzuki S Hashizume D Sodeoka M 《The Journal of organic chemistry》2008,73(15):5859-5871
Detailed mechanistic studies on our recently reported asymmetric addition reactions of malonates to dihydroisoquinolines (DHIQs) catalyzed by chiral Pd(II) complexes were carried out. It was found that an N,O-acetal was generated in situ by the reaction of DHIQ with (Boc)2O, and cooperative action of the Pd(II) complex as an acid-base catalyst allowed the formation of a chiral Pd enolate and a reactive iminium ion via alpha-fragmentation. The iminium ion was also accessible via oxidation with DDQ as an oxidant, and a catalytic asymmetric oxidative Mannich-type reaction was achieved with tetrahydroisoquinolines (THIQs) as starting materials. This oxidation protocol was applicable to N-acryloyl-protected THIQs, allowing the efficient synthesis of optically active tetrahydrobenzo[a]quinolizidine derivatives via intramolecular Michael reaction. 相似文献
108.
Kawaguchi S Nagata S Nomoto A Sonoda M Ogawa A 《The Journal of organic chemistry》2008,73(20):7928-7933
A novel transition-metal-catalyzed hydrophosphination of terminal alkynes using a diphosphine-hydrosilane binary system takes place regioselectively to provide vinylic phosphines, which undergo air oxidation during workup, affording the corresponding vinylphosphine oxides in good yields. In this hydrophosphination, hydrosilanes act as a useful hydrogen source, and furthermore, small amounts of oxygen is required to accomplish the reaction efficiently. 相似文献
109.
Nakagawa S Suzuki R Yamazaki R Kusuhara Y Mitsumoto S Kobayashi H Shimoeda S Ohta S Yamato S 《Chemical & pharmaceutical bulletin》2008,56(3):328-331
A simple column-switching high performance liquid chromatographic (HPLC) method that does not require any complicated pretreatment has been developed to determine voriconazole in human plasma samples. An internal standard (IS) and borate buffer (pH 9.0) were added to plasma samples, which were then injected directly into the column-switching HPLC system using MAYI-ODS as a pre-column. The calibration curve for voriconazole showed good linearity in the range of 0.2-10 mug/ml in human plasma. The mean RSD (%) value of intra-day (n=6) and inter-day (n=5) precision were less than 5.4% and 8.2%, respectively. This system could make more than three hundred successive, accurate measurements when a washing step with ammonium acetate solution was added. This method was successfully applied to measure the therapeutic voriconazole level in patients' plasma, and was used in a study of voriconazole pharmacokinetics after oral administration. 相似文献
110.
The peculiar features of instability of Dzhanelidze's model, which is composed of a massless flexible bar and a concentrated mass at the tip and is subjected to a tangential follower force at the tip, are considered. By discussing the eigenvalue curves of Pflüger's model, which has distributed mass in addition to the case of Dzhanelidze's model, and of the corresponding discrete model, it is shown that the critical value, which one must use the dynamic method to obtain, can be identical with the classical Euler value obtainable by the static method only as a result of ignoring a crucial mass. The mathematical meaning of the infinitely large critical frequency is pertinently interpreted. 相似文献