全文获取类型
收费全文 | 1310篇 |
免费 | 25篇 |
国内免费 | 7篇 |
专业分类
化学 | 1062篇 |
晶体学 | 4篇 |
力学 | 17篇 |
数学 | 108篇 |
物理学 | 151篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 19篇 |
2014年 | 28篇 |
2013年 | 67篇 |
2012年 | 74篇 |
2011年 | 108篇 |
2010年 | 45篇 |
2009年 | 65篇 |
2008年 | 62篇 |
2007年 | 74篇 |
2006年 | 87篇 |
2005年 | 66篇 |
2004年 | 66篇 |
2003年 | 54篇 |
2002年 | 63篇 |
2001年 | 13篇 |
2000年 | 21篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 17篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 7篇 |
1986年 | 6篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1979年 | 22篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1971年 | 6篇 |
1968年 | 5篇 |
排序方式: 共有1342条查询结果,搜索用时 15 毫秒
991.
Nobuhito Imanaka Toshiyuki Masui Young Woon Kim 《Journal of solid state chemistry》2004,177(10):3839-3842
Single crystals of Tb16O30 (TbO1.875) were successfully grown for the first time by DC electrolysis of the Tb3+ ion conducting Tb2(MoO4)3 solid electrolyte at 11 V, 900 °C. The Tb16O30 phase is the intermediate phase of fluorite-related rare earth oxides and it is extremely difficult to grow in a single crystal form, because this intermediate phase is usually obtained as one of the mixture of the fluorite related TbOx phases. Because there are many non-stoichiometric phases in the terbium oxide system, it is impossible to grow a specific intermediate phase in a single crystal form by the conventional methods via melt. Although single crystals of TbOx have been recently obtained by anodic electrocrystallization from alkaline hydroxide melts containing TbCl3, the composition has been confirmed to be TbOx with 1.75<x<1.82. On the contrary, the presently developed DC electrolysis method can be simply applicable at moderate temperatures around 900 °C to artificially grow an intermediate phase of Tb16O30 (x=1.875) in a single crystal form, which was evidenced by the electron diffraction patterns for each particle. 相似文献
992.
The properties of cis- and trans-bis(crown ether)s containing benzo-15-crown-5 or benzo-18-crown-6 units as complexants and extractants for alkali metal picrates have been studied. The optical spectra suggest that the cis-bis(crown ether)s can form intramolecular 2:1 crown ether unit/cation complexes with particular metal cations easily, while the trans-bis(crown ether)s can form only 1:1 crown ether unit/cation complexes because of the unfavourable trans configuration for the formation of the 2:1 complexes. It was found that the cis isomer possesses much higher extractive power than the trans isomer for the metal cations, which also reflects their complexing properties. The extraction equilibrium constants and thermodynamic quantities have been also evaluated, and the effect of the stereochemical structure of the bis(crown ether) on the complexing and extractive properties is discussed. 相似文献
993.
DMSO or DMF as a solvent strongly accelerated the thiocarboxylation of amines and alcohols with carbon monoxide and sulfur. Under mild conditions (1 atm, 20 °C), this thiocarboxylation of amines assisted by DMSO with carbon monoxide and sulfur has been developed into a practical and convenient synthetic method for S-alkyl thiocarbamates in good to excellent yields, including EPTC, thiobencarb, orbencarb, and molinate (herbicides). DMF also showed the similar solvent effect. NMP slightly decreased the effect for the thiocarboxylation of amines, and the yield of S-alkyl thiocarbamate was lowered in DMAc. Surprisingly, no formation of S-alkyl thiocarbamate was observed at the use of the other solvents, such as THF, hexane, toluene, AcOEt, MeCN, MeOH, and H2O. The present solvent-assisted thiocarboxylation with carbon monoxide and sulfur could be also applied to a new synthesis of S-alkyl O-alkyl carbonothioates from alcohols under mild conditions (1 atm, 20 °C) in DMF using DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). 相似文献
994.
Toshiyuki Gotoh 《Journal of statistical physics》1990,59(1-2):371-402
The Langevin equations for a particle of an arbitrary shape and the correlation functions for the fluctuating forces, torques, or force-torque acting on the particle in a rotating flow are derived from the semimicroscopic level of coarse graining by using fluctuating hydrodynamics. In order to obtain the solution of the Navier-Stokes Langevin equation valid over the entire flow region, use is made of the method of matched asymptotic expansions in (
f
a2/v)1/2 1. The cases of slow and rapid rotation are analyzed. It is shown that the fluctuation-dissipation theorems hold up to the order of (
f
a2/v)1/2 in both slow and rapid rotation, and that the diffusivity tensor depends on the angular velocity of the fluid and becomes anisotropic. 相似文献
995.
Total syntheses of SB-203207 (1) and sphingofungin E (2) were accomplished by utilizing an asymmetric desymmetrization strategy to introduce multiple stereogenic centers into meso starting compounds in a single step. Thus, rhodium carbenoid-mediated CH insertion into 3 provided the bicyclo[3.3.0]framework 4 for 1, while organocatalyst-mediated bromolactonization of 5 afforded 6 for the synthesis of 2. Similarly, we utilized desymmetric rhodium nitrenoid-mediated aziridination reaction of 5 to obtain a key intermediate required for a total synthesis of pactamycin (29), a complex aminocyclopentitol antibiotic featuring six contiguous stereogenic centers. 相似文献
996.
Asaki Uehara Narumi Takahashi Mei Moriyama Takako Hirano Wataru Hakamata Toshiyuki Nishio 《Applied biochemistry and biotechnology》2018,184(2):673-684
Bacterial strain NYT501, which we previously isolated from soil, was identified as Stenotrophomonas maltophilia, and it was confirmed that this strain produces an intracellular β-N-acetylhexosaminidase exhibiting transglycosylation activity. Several properties of this enzyme were characterized using a partially purified enzyme preparation. Using N,N′-diacetylchitobiose (GlcNAc)2 and N,N′,N″-triacetylchitotriose (GlcNAc)3 as substrates and dried cells of this bacterium as a whole-cell catalyst, chitin oligosaccharides of higher degrees of polymerization were synthesized. (GlcNAc)3 was generated from (GlcNAc)2 as the major transglycosylation product, and a certain amount of purified sample of the trisaccharide was obtained. By contrast, in the case of the reaction using (GlcNAc)3 as a substrate, the yield of higher-degree polymerization oligosaccharides was comparatively low. 相似文献
997.
Liming Shao Toshiyuki Seki Hiroyuki Kawano Masahiko Saburi 《Tetrahedron letters》1991,32(52):7699-7702
Hydrogenation of methyl 3,5-dioxohexanoate 3 using Ru2Cl4((R) or (S)-binap)2(NEt3) as the catalyst gave dominantly anti 3,5-dihydroxyester 9, which was then converted into unsaturated lactone 4. The pathway of the hydrogenation reaction was also investigated. 相似文献
998.
Capillary electrochromatographic separation of amino acid enantiomers with molecularly imprinted polymers as chiral recognition agents 总被引:3,自引:0,他引:3
J.-M. Lin Tatsuro Nakagama Xing-Zheng Wu Katsumi Uchiyama Toshiyuki Hobo 《Analytical and bioanalytical chemistry》1997,357(1):130-132
The use of molecularly imprinted polymers polymerized in a capillary for the separation of amino acid enantiomers by electrochromatography
is described. The substrate-selective polymers were prepared by using l-phenylalanine anilide as print molecule and methacrylic acid as the functional monomer. The treatment of the inside surface
of the capillary, the composition of the polymer and the electrochromatographic running conditions were investigated. This
preliminary report demonstrated a novel and simple method for capillary electrochromatographic separations of amino acid enantiomers
using molecularly imprinted polymers.
Received: 9 April 1996 / Revised: 8 August 1996 / Accepted: 8 August 1996 相似文献
999.
Kuwada T Fukui M Hata T Choshi T Nobuhiro J Ono Y Hibino S 《Chemical & pharmaceutical bulletin》2003,51(1):20-23
The specific optical rotations of (R)-oxopropaline D calculated by two ab initio MO methods were +52+/-31 degrees and +61+/-29 degrees, respectively, and (+)-oxopropaline D (3) was presumed to have an R-configuration. On the basis of this theoretical result, the reaction of 1-litio-beta-carboline with (R)-glyceraldehyde acetonide followed by oxidation with MnO(2) gave (R)-oxopropaline D acetonide (4a), which was consistent with the previously synthesized (+)-oxopropaline D acetonide (4) in all respects. From the results of theoretical calculations and the experimental synthesis, we determined that natural (+)-oxopropaline D (3) has an R-configuration. 相似文献
1000.
The chlorinative ene-type reaction of isoprenoids ( → ) has been performed by electrolysis in CH2Cl2-H2O-NaCl system. The reaction provides useful allylic chlorides for terpene synthesis in high yields and is affected strikingly by the nature of halide ions and solvents. dl-Theaspirane was prepared from α-dihydroionol the electrolysis. 相似文献