全文获取类型
收费全文 | 348篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 291篇 |
晶体学 | 2篇 |
力学 | 3篇 |
数学 | 17篇 |
物理学 | 49篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 17篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 2篇 |
2014年 | 13篇 |
2013年 | 18篇 |
2012年 | 20篇 |
2011年 | 22篇 |
2010年 | 13篇 |
2009年 | 9篇 |
2008年 | 27篇 |
2007年 | 25篇 |
2006年 | 14篇 |
2005年 | 27篇 |
2004年 | 19篇 |
2003年 | 7篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1966年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有362条查询结果,搜索用时 234 毫秒
51.
Heterogeneous strong base catalysis for the intramolecular Tishchenko reaction of aromatic 1,2-dicarbaldehydes to the corresponding phthalides in supercritical CO2CscCO2 has been realized with mesoporous alumina containing SO4(2-) ions in the alumina framework (mesoAl2O3/SO4(2-)). Infrared spectroscopy of pyrrole adsorbed on the alumina and strong poisoning by a weak Br?nsted acid of methanol revealed that the SO4(2-) ions in the framework slightly suppressed the average strength of base sites (O2-) on mesoAl2O3/SO4(2-), but there exists a small number of strong base sites that promote the Tishchenko reaction in scCO2. Although the intramolecular Tishchenko reaction of phthalaldehyde to phthalide in scCO2 was somewhat slower than those in organic solvents such as tetrahydrofuran (THF) and benzene, the addition of a small amount of THF as a cosolvent remarkably increased the reaction rate; the reaction in the scCO2-THF system proceeded 1.5-fold faster than those in pure benzene and THF solvents. 相似文献
52.
Susumu Onaka 《哲学杂志》2013,93(18):2264-2271
Onaka has shown (2010) that the Hencky equivalent strain is the appropriate quantity to represent the degree of severe plastic deformation based on simple-shear deformation. In a recent paper, Shrivastava et al. have criticized (2011) the Onaka paper and stated that the Hencky formulation does not apply to large simple-shear deformation. In this response, it is shown that this claim of Shrivastava et al. is not consistent with recent accepted knowledge on the Hencky strain. 相似文献
53.
Kazuto Takaishi Bikash Dev Nath Yuya Yamada Hiroyasu Kosugi Tadashi Ema 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(29):10089-10093
Unique self‐assembled macrocyclic multinuclear ZnII and NiII complexes with binaphthyl‐bipyridyl ligands (L) were synthesized. X‐ray analysis revealed that these complexes consisted of an outer ring (Zn3L3 or Ni3L3) and an inner core (Zn2 or Ni). In the ZnII complex, the inner Zn2 part rotated rapidly inside the outer ring in solution on an NMR timescale. These complexes exhibited dual catalytic activities for CO2 fixations: synthesis of cyclic carbonates from epoxides and CO2 and temperature‐switched N‐formylation/N‐methylation of amines with CO2 and hydrosilane. 相似文献
54.
Ryosuke Sugiyama Takahiro Nakatani Shinichi Nishimura Kei Takenaka Taro Ozaki Shumpei Asamizu Hiroyasu Onaka Hideaki Kakeya 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(38):13620-13625
Organisms often produce secondary metabolites as a mixture of biosynthetically related congeners. However, why are metabolites with minor chemical variations produced simultaneously? 5‐Alkyl‐1,2,3,4‐tetrahydroquinolines (5aTHQs) are small, lipophilic metabolites produced by Streptomyces nigrescens HEK616 when cultured with Tsukamurella pulmonis TP‐B0596. A mixture of 5aTHQs forms aggregates that show enhanced membrane affinity and biological activity. The ability to form aggregates and membrane‐binding activity is regulated by the length of the alkyl chains. Aggregates with long alkyl chains were too stable to fuse with lipid membranes. However, if inactive 5aTHQ congener was mixed with active congener, the mixture showed increased membrane affinity, enabling cellular entry and biological activity. Therefore, it is shown that sloppiness in a biosynthetic pathway, by which minor structural variations can be produced, is functionally rational, as the metabolites show synergistic action. 相似文献
55.
Susumu Onaka 《哲学杂志》2020,100(13):1703-1715
56.
57.
Masaki Matsui Yuya Tsuzuki Yasuhiro Kubota Kazumasa Funabiki Toshiyasu Inuzuka Kazuhiro Manseki Shinji Higashijima Hidetoshi Miura Hiroyasu Sato Tsukasa Yoshida 《Tetrahedron》2018,74(40):5867-5878
(2R,3aR,8bR)- and (2S,3aS,8bS)-2-Methyl indoline dye tetrabutylammonium carboxylates exhibited the highest conversion efficiency among four regio and stereo isomers. These indoline dyes also showed higher conversion efficiency than DN350. 相似文献
58.
Dr. Pengfei Wu Prof. Dr. Adriana Pietropaolo Dr. Mariagrazia Fortino Dr. Masayoshi Bando Prof. Dr. Katsuhiro Maeda Dr. Tatsuya Nishimura Shuhei Shimoda Dr. Hiroyasu Sato Prof. Dr. Naofumi Naga Prof. Dr. Tamaki Nakano 《Angewandte Chemie (International ed. in English)》2023,62(29):e202305747
Optically active, hyperbranched, poly(fluorene-2,4,7-triylethene-1,2-diyl) [poly(fluorenevinylene)] derivatives bearing a neomenthyl group and a pentyl group at the 9-position of the fluorene backbone at various ratios acted as a chirality donor (host polymers) efficiently included naphthalene, anthracene, pyrene, 9-phenylanthracene, and 9,10-diphenyanthracene as a chirality acceptor (guest molecules) in their interior space in film as well as in solution, with the guest molecules exhibiting intense circular dichroism through chirality transfer with chirality amplification. The efficiency of the chirality transfer was much higher with higher-molar-mass polymers than lower-molar-mass ones as well as with hyperbranched polymers compared to the analogous linear ones. The hyperbranched polymers include the small molecules in their complex structure without any specific interactions at various stoichiometries. The included molecules may have ordered intermolecular arrangement that may be somewhat similar to those of liquid crystals. Naphthalene, anthracene, and pyrene included in the polymer exhibited efficient circularly polarized luminescence, where the chirality was remarkably amplified in excited states, and anthracene exhibited especially high anisotropies in the emission on the order of 10−2. 相似文献
59.
Wang Y Hirao H Chen H Onaka H Nagano S Shaik S 《Journal of the American Chemical Society》2008,130(23):7170-7171
QM/MM calculations support experiment and show that StaP is a P450 that functions like a peroxidase: its active species is the one-electron-reduced Cpd II species with a radical on CPA, by analogy to cytochrome c peroxidase (CcP), and its reaction with the substrate proceeds by overall proton-coupled electron transfer (PCET), in analogy to the corresponding mechanism in horseradish peroxidase (HRP). The electron transfer is enabled by His250, the presence of carboxylate groups in CPA, and by the H-bonding network that tunes the energetic of the process. Theory supports experiment but reveals some novel aspects of this unusual P450. 相似文献
60.
Li WS Yamamoto Y Fukushima T Saeki A Seki S Tagawa S Masunaga H Sasaki S Takata M Aida T 《Journal of the American Chemical Society》2008,130(28):8886-8887
For tailoring solution-processable optoelectronic thin films, a rational strategy with amphiphilic molecular design is proposed. A donor-acceptor dyad consisting of an oligothiophene and C60, when modified with a hydrophilic wedge on one side and a paraffinic wedge on the other (1Amphi), forms over a wide temperature range a photoconducting smectic A liquid crystal having bicontinuous arrays of densely packed donor and acceptor units. In contrast, when modified with only paraffinic wedges (1Lipo), the dyad forms a smectic A liquid crystalline mesophase, which however is poorly conductive. As indicated by an absorption spectral feature along with a synchrotron radiation small-angle X-ray scattering profile, 1Lipo in the lamellar structure does not adopt a uniform head/tail orientation. Such defective donor and acceptor arrays likely contain a large number of trapping sites, leading to short-lived charge carriers, as observed by a flash photolysis time-resolved microwave conductivity study. 相似文献