全文获取类型
收费全文 | 369篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
化学 | 273篇 |
晶体学 | 2篇 |
力学 | 8篇 |
数学 | 11篇 |
物理学 | 95篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 28篇 |
2012年 | 29篇 |
2011年 | 28篇 |
2010年 | 14篇 |
2009年 | 14篇 |
2008年 | 16篇 |
2007年 | 24篇 |
2006年 | 26篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 12篇 |
2002年 | 13篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有389条查询结果,搜索用时 15 毫秒
81.
82.
Tatsuya Morozumi Takashi Kimura Tomomi Ujiie Hiroaki Yonemura Taku Matsuo Hiroshi Nakamura 《Journal of inclusion phenomena and macrocyclic chemistry》2004,50(1-2):105-110
The complexation behavior of a series of electron donor–accepter (D–A) covalently linked compounds with cyclodextrins (CyDs) has been reviewed. The structure of these complexes showed rotaxane type conformations, which were investigated by means of 1 H NMR spectrometry. The complex formations induced a fixation of a conformation of guest D–A molecules, and D–A distances were enlarged. Thus, accurate photo-induced charge transfer behaviors can be discussed. 相似文献
83.
Matsukawa T Hasegawa H Shinohara Y Kobayashi J Shinohara A Chiba M Ichida K Yokoyama K 《Chemical & pharmaceutical bulletin》2010,58(12):1658-1660
The synthesis of D- and L-selenomethionine labeled with ?2Se and three deuteriums at Se-methyl group (D- and L-[2H?, ?2Se]selenomethionine) was described. D- And L-[2H?, ?2Se]selenomethionine were prepared by condensation of (R)- and (S)-2-amino-4-bromobutylic acid with lithium [2H?, ?2Se]methaneselenolate, which was prepared from metal (82)Se and [2H?]methyl iodide. The optical purities of D- and L-[2H?, ?2Se]selenomethionine were determined by HPLC with a chiral stationary phase column and were found more than 99% ee. The chemical ionization mass spectra showed that the molecular related ion for N-isobutyloxycarbonyl ethyl ester derivatives of [2H?, ?2Se]selenomethionine did not overlap with the m/z values known from that of non-labeled selenomethionine. 相似文献
84.
Taku Shibue Toshihiro Hirai Dr. Iwao Okamoto Dr. Nobuyoshi Morita Dr. Hyuma Masu Prof. Dr. Isao Azumaya Prof. Dr. Osamu Tamura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(38):11678-11688
The total syntheses of tetrapeptides tubulysins D ( 1 b ), U ( 1 c ), and V ( 1 d ), which are potent tubulin polymerization inhibitors, are described. The synthesis of Tuv ( 2 ), an unusual amino acid constituent of tubulysins, includes an 1,3‐dipolar cycloaddition reaction of chiral nitrone D ‐ 6 derived from D ‐gulose with N‐acryloyl camphor sultam (?)‐ 9 employing the double asymmetric induction, whereas the synthesis of Tup ( 20 ), another unusual amino acid, involves a stereoselective Evans aldol reaction of (Z)‐boron enolate generated from (S)‐4‐isopropyl‐3‐propionyl‐2‐oxazolidinone with N‐protected phenylalaninal and a subsequent Barton deoxygenation protocol. We accomplished the total syntheses of tubulysins U ( 1 c ) and V ( 1 d ) by using these methodologies, in which the isoxazolidine ring was used as the effective protective group for γ‐amido alcohol functionality. Furthermore, to understand the structure‐activity relationship of tubulysins, we synthesized tubulysin D ( 1 b ) and cyclo‐tubulysin D ( 1 e ) from 2 ‐Me and 20 , and ent‐tubulysin D (ent‐ 1 d ) from ent‐ 2 ‐Me and ent‐ 20 , respectively. The preliminary results regarding their biological activities are also reported. 相似文献
85.
Kaoru Wada Taku Chiba Yutaka Takei Hideko Ishihara Hidetoshi Hayashi Kikuo Onozaki 《Journal of carbohydrate chemistry》2013,32(7):941-965
Abstract Recombinant cytokines generated by bacteria, especially E. coli, are nonglycosylated. To investigate the effects of carbohydrates on their activities, we attempted to develop new cytokines by introduction of carbohydrates. As a model we synthesized neoglycoproteins in which potential immunoregulatory carbohydrates were coupled to bovine serum albumin(BSA). Mannose dimers with C9 spacer, Manα1-6Man, which is reported to be immunosuppressive, and a reference substance Manα1-4Man were synthesized as follows. Benzylidenation of 8-(methoxycarbonyl)octyl α-D-mannopyranoside (10), followed by acetylation and cleavage of the benzylidene acetal, gave a glycosyl acceptor (13) with a free hydroxyl group in the C-4 position. Glycosylation of 13 with acetobromomannose (8), followed by debenzylation, deacetylation, and hydrazidation, gave 8-(hydrazinocarbonyl)octyl 4-O-α-D-mannopyranosyl-α-D-mannopyranoside (1). Total yield of 1 from 10 was 25.1%. Tritylation of 10, followed by acetylation and detritylation, gave a glycosyl acceptor (18) with a free hydroxyl group in the C-6 position. Analogous condensation of 18 with 8, followed by deacetylation and hydrazidation, gave 8-(hydrazinocarbonyl)octyl 6-O-α-D-mannopyranosyl-α-D-mannopyranoside (2). Total yield of 2 from 10 was 22.9%. These mannose dimers were coupled to BSA by the acyl azide method. Using the antibodies against the mannose dimers, an enzyme linked immunosorbent assay (ELISA) was established to measure the small amount of mannose dimers coupled to proteins. These two neoglycoproteins appeared to inhibit the antigen-specific human T cell proliferation over 100 fold more efficiently than free mannose dimers. 相似文献
86.
Systematic Control of the Excited‐State Dynamics and Carrier‐Transport Properties of Functionalized Benzo[ghi]perylene and Coronene Derivatives 下载免费PDF全文
Sunao Hirayama Dr. Hayato Sakai Prof. Yasuyuki Araki Minako Tanaka Masaki Imakawa Prof. Takehiko Wada Prof. Taishi Takenobu Prof. Taku Hasobe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(29):9081-9093
A series of benzo[ghi]perylene (Bp) and coronene (Cor) derivatives substituted with electron‐withdrawing methoxycarbonyl (COOMe) or electron‐donating methoxyl (MeO) groups was synthesized. The electrochemical, spectroscopic, and photophysical properties of these compounds were investigated by cyclic voltammetry, steady‐state and time‐resolved spectroscopy, and quantum‐yield measurements. Introduction of suitable substituents onto the aromatic rings enabled control of electrochemical and spectroscopic behavior. Examination of excited‐state dynamics revealed that fluorescence quantum yields increased with increasing number of COOMe groups in both Bp and Cor derivatives, consistent with the findings of DFT calculations. Single‐crystal analysis allowed the performance of field‐effect transistors containing single crystals of the derivatives to be rationalized. 相似文献
87.
Formation of Anatase Nanocrystals in Sol-Gel Derived TiO2-SiO2 Thin Films with Hot Water Treatment 总被引:8,自引:0,他引:8
Yoshinori Kotani Atsunori Matsuda Masahiro Tatsumisago Tsutomu Minami Taku Umezawa Toshihiro Kogure 《Journal of Sol-Gel Science and Technology》2000,19(1-3):585-588
We have successfully prepared transparent and porous anatase nanocrystals-dispersed films by treating the sol-gel derived TiO2-SiO2 films containing poly(ethylene glycol), PEG, with hot water. This process was done at temperatures lower than 100°C under atmospheric pressure, and thus anatase nanocrystals-dispersed films can be formed on various kinds of substrates including organic polymers with poor heat resistance. The changes in structure and composition of the TiO2-SiO2 gel films with hot water treatment were related to the formation process of anatase nanocrystals in the TiO2-SiO2 gel films with hot water treatment. The formation of anatase nanocrystals was found to proceed to hydrolysis of Si–O–Ti bonds and dissolution of SiO2 component. In addition, porous film structure formed by leaching of PEG with hot water treatment led to homogenous dispersion of anatase nonocrystals in the films. 相似文献
88.
Treatment of fluoroalkylated alkynes with various aryl halides and arylboronic acids in the presence of Pd(0) in DMF/H2O at 100 °C for 2 h led to the smooth three-component coupling reaction, the corresponding tetrasubstituted alkenes being obtained in high yields stereoselectively. 相似文献
89.
Catalytic conversion of cellulose into 5-hydroxymethylfurfural in high yields via a two-step process
Xinhua Qi Masaru Watanabe Taku M. Aida Richard L. SmithJr. 《Cellulose (London, England)》2011,18(5):1327-1333
As a key renewable chemical for plastics and fine chemicals, the preparation of 5-hydroxymethylfurfural (5-HMF) from biomass
is an important research topic. Cellulose, although abundant in nature, is difficult to convert to 5-HMF in good yields due
to its recalcitrant and heterogeneous nature. In this work, we show an efficient two-step process for converting microcrystalline
cellulose into 5-HMF with ionic liquids under mild conditions. In the first step, high glucose yields of above 80% could be
obtained from the cellulose hydrolysis by a strong acidic cation exchange resin in 1-ethyl-3-methyl imidazolium chloride ([EMIM][Cl])
with gradual addition of water. In the second step, the resin was separated from the reaction mixture and CrCl3 was added which lead to a 5-HMF yield of 73% based on cellulose substrate. The strategy can allow practical conversion of
biomass into bio-derived products. 相似文献
90.