全文获取类型
收费全文 | 1823篇 |
免费 | 87篇 |
国内免费 | 29篇 |
专业分类
化学 | 1447篇 |
晶体学 | 20篇 |
力学 | 23篇 |
数学 | 85篇 |
物理学 | 364篇 |
出版年
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 25篇 |
2019年 | 30篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 43篇 |
2015年 | 33篇 |
2014年 | 45篇 |
2013年 | 71篇 |
2012年 | 107篇 |
2011年 | 149篇 |
2010年 | 64篇 |
2009年 | 61篇 |
2008年 | 155篇 |
2007年 | 111篇 |
2006年 | 123篇 |
2005年 | 122篇 |
2004年 | 124篇 |
2003年 | 103篇 |
2002年 | 105篇 |
2001年 | 39篇 |
2000年 | 35篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 17篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 4篇 |
1972年 | 5篇 |
排序方式: 共有1939条查询结果,搜索用时 26 毫秒
991.
Ken-ichi Itoh Kaoru Nakamura Tadashi Aoyama Tsuyoshi Kakimoto Masahiko Murakami Toshio Takido 《Tetrahedron letters》2014
Asymmetric reduction of ketone by a microalga, Synechocystis sp. PCC 6803, smoothly afforded to the corresponding (S)-alcohol in excellent enantiomeric excess by the aid of illumination of orange and red LED lights which are more effective than other LEDs such as blue and green lights. The condition under minimum energy flux (1.0 W/m2) of orange-red LEDs is enough for the reduction of ketone, and it seems that orange-red light rather effectively forwarded the regeneration of coenzyme. 相似文献
992.
Tsutomu Kimura Junichiro Nishida Gaku Kashiwamura Gen Kobayashi Tsuyoshi Satoh 《Tetrahedron letters》2014
A novel method for the synthesis of cyclopropane-fused α-chloro-γ-lactones was developed utilizing the nucleophilicity of cyclopropylmagnesium carbenoids. Cyclopropylmagnesium carbenoids were generated from i-PrMgCl and 1-chlorocyclopropyl p-tolyl sulfoxides with a [(phenoxycarbonyl)oxy]methyl group at the 2-position of the cyclopropane ring. The resulting cyclopropylmagnesium carbenoids reacted with an intramolecular carbonate unit to give 1-chloro-3-oxabicyclo[3.1.0]hexan-2-ones in moderate to good yields. The asymmetric synthesis of 1-chloro-3-oxabicyclo[3.1.0]hexan-2-one was achieved using optically active dichloromethyl p-tolyl sulfoxide as a starting material. 相似文献
993.
Masaki Shimoi Ilia Kevlishvili Takashi Watanabe Prof. Dr. Katsuhiro Maeda Dr. Steven J. Geib Prof. Dr. Dennis P. Curran Prof. Dr. Peng Liu Dr. Tsuyoshi Taniguchi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(2):913-919
An N-heterocyclic-carbene-ligated 3-benzoborepin with a bridged structure has been synthesized by double radical trans-hydroboration of benzo[3,4]cycloundec-3-ene-1,5-diyne with an N-heterocyclic carbene borane. The thermal reaction of the NHC-ligated borepin at 150 °C gives an isolable NHC-boranorcaradiene. Experiments and density functional theory calculations support a mechanism whereby the borepin initially rearranges to a boranorcaradiene by a thermal 6π-electrocyclic reaction. This is followed by 1,5-boron shift to give a rearranged boranorcaradiene. This shift occurs with stereoinversion at boron through a transition state with open-shell diradical character. This is the first example of the isolation of a boranorcaradiene from a thermal reaction of a borepin. 相似文献
994.
Masanobu Mori Toshinobu Suzuki Tsuyoshi Sugita Daisuke Nagai Kazuo Hirayama Makoto Onozato Hideyuki Itabashi 《Analytica chimica acta》2014
This study aimed to evaluate the heavy metal adsorptivity of calcium-alginate-modified diethylenetriamine-silica gel (CaAD) and incorporate this biosorbent into a flow analytical system for heavy metal ions using flame atomic absorption spectrometry (FAAS). The biosorbent was synthesized by electrostatically coating calcium alginate onto diethylenetriamine (dien)-silica gel. Copper ion adsorption tests by a batch method showed that CaAD exhibited a higher adsorption rate compared with other biosorbents despite its low maximum adsorption capacity. Next, CaAD was packed into a 1 mL microcolumn, which was connected to a flow analytical system equipped with an FAAS instrument. The flow system quantitatively adsorbed heavy metals and enriched their concentrations. This quantitative adsorption was achieved for pH 3–4 solutions containing 1.0 × 10−6 M of heavy metal ions at a flow rate of 5.0 mL min−1. Furthermore, the metal ions were successfully desorbed from CaAD at low nitric acid concentrations (0.05–0.15 M) than from the polyaminecarboxylic acid chelating resin (Chelex 100). Therefore, CaAD may be considered as a biosorbent that quickly adsorbs and easily desorbs analyte metal ions. In addition, the flow system enhanced the concentrations of heavy metals such as Cu2+, Zn2+, and Pb2+ by 50-fold. This new enrichment system successfully performed the separation and determination of Cu2+ (5.0 × 10−8 M) and Zn2+ (5.7 × 10−8 M) in a river water sample and Pb2+ (3.8 × 10−9 M) in a ground water sample. 相似文献
995.
In this study, a new synthetic approach to 4,5-branched Kdo trisaccharides based on the common acceptor Kdo(α2-4)Kdo was developed. The synthesis of three types of 4,5-branched trisaccharides, Hep(α1-5)[Kdo(α2-4)]Kdo, Man(α1-5)[Kdo(α2-4)]Kdo, and GalNAc(α1-5)[Kdo(α2-4)]Kdo, was achieved in good yield and high α-selectivity. 相似文献
996.
Tomoaki Nishida Dr. Aiko Fukazawa Eriko Yamaguchi Hiroya Oshima Prof. Dr. Shigehiro Yamaguchi Prof. Dr. Motomu Kanai Prof. Dr. Yoichiro Kuninobu 《化学:亚洲杂志》2014,9(4):1026-1030
Pyridine N‐oxide–BF2CF3 and –BF2C2F5 complexes and their derivatives were synthesized. Most of the complexes show fluorescence both in solution and in the solid state. By expanding the π‐conjugated skeleton, the color of the fluorescence could be changed dramatically. A fluorophore with a high solvent dependency could also be produced. Since such compounds can be synthesized on a gram scale in high yield, and are stable to oxygen, water, and heat, the complexes hold great potential as organic functional materials. 相似文献
997.
Acid–Base‐Responsive Intense Charge‐Transfer Emission in Donor–Acceptor‐Conjugated Fluorophores 下载免费PDF全文
Herein we report on the synthesis and acid‐responsive emission properties of donor–acceptor (D–A) molecules that contain a thienothiophene unit. 2‐Arylthieno[3,2‐b]thiophenes were conjugated with an N‐methylbenzimidazole unit to form acid‐responsive D–A‐type fluorophores. The D–A‐conjugated fluorophores showed intense intramolecular charge‐transfer (ICT) emission in response to acid. The effect of the substitution on their photophysical properties as well as their solvent‐dependence indicated non‐twisting ICT emission in protonated D–A molecules. The quinoidal character of 2‐arylthienothiophene as a donor part is discussed, as it is assumed that it contributes to suppression of the molecular twisting in the excited state, therefore decreasing the nonradiative rate constant, thereby resulting in the intense ICT emission. Acid–base‐sensitive triple‐color emission was also achieved by the introduction of a base‐responsive phenol group in the donor part. 相似文献
998.
Fluoro-dediazoniation of aromatic diazonium ions, produced by the diazotization of the corresponding aromatic amines with NaNO2 in anhydrous hydrogen fluorides (AHF) - organic base solutions, was accelerated photochemically to afford Ar-F efficiently in AHF - organic base solutions in situ. 相似文献
999.
Yuko Murakoshi Dr. Tsuyoshi Takahashi Prof. Dr. Hisakazu Mihara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(14):4525-4531
Aggregation of amyloid β‐peptide (Aβ) is closely related to the pathogenesis of Alzheimer’s disease (AD). Although much effort has been devoted to the construction of molecules that inhibit the aggregation of Aβ1‐42, high doses are needed for the inhibition of Aβ aggregation in many cases. Previously, we reported that designed green fluorescent protein (GFP) analogues that gives pseudo‐Aβ β‐sheet structures can work as an aggregation inhibitor against Aβ. To further test this design strategy, we constructed protein analogues that mimic Aβ β‐sheet structures of amyloids by using insulin‐like growth factor 2 receptor domain 11 (IGF2R‐d11) as a scaffold. A designed protein, named IG11KK, which has a parallel configuration of Aβ‐like β sheets, can bind more preferentially to oligomeric Aβ1‐42 than the monomer. Moreover, IG11KK suppressed the aggregation of Aβ1‐42 efficiently, even though lower concentrations of IG11KK than Aβ were used. The aggregation kinetics of Aβ in the presence of the designed proteins revealed that IG11KK can work as an inhibitor not only for the early to middle stages, but also in the latter stage of Aβ aggregation owing to its favorable binding to oligomeric structures of Aβ. The design strategy using β‐barrel proteins such as IGF2R‐d11 and GFP is useful in generating excellent inhibitors of protein misfolding and amyloid formation. 相似文献
1000.
Minoru Nagata Tsuyoshi Kiyotsukuri Taizou Hasegawa Naoto Tsutsumi Wataru Sakai 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):965-973
Abstract Network copolyesters were made from adipic acid and ethylene glycol with 10–40 mol% trimesic acid (Y). Prepolymers prepared by melt polycondensation were cast from dimethylformamide solution and postpolymerized at 260°C for various times to form a network. The degree of reaction (D R), estimated from the infrared absorbance of hydroxyl and methylene groups, increased with increasing postpolymerization time and leveled out at about 90% after 4–6 hours. Heat distortion temperatures (T h) measured by thermomechanical analysis increased greatly from ?83 to 48°C upon the incorporation of Y. Wide-angle x-ray diffraction patterns showed that the copolymer films are amorphous. Density, tensile strength, and Young's modulus decreased for the copolymers with 10–30 mol% Y, whereas they increased drastically for the copolymer with 40 mol% Y. The enzymatic degradation was estimated by the weight loss of the copolymer films in buffer solutions with a lipase at 37°C. The weight loss decreased remarkably with increasing Y and showed no weight loss for the copolymer with 40 mol% Y. On the other hand, the weight loss by alkali hydrolysis increased for the copolymers with 10 and 20 mol% Y, implying a difference in the degradation mechanism between enzymatic degradation and alkali hydrolysis. 相似文献