全文获取类型
收费全文 | 1793篇 |
免费 | 166篇 |
国内免费 | 5篇 |
专业分类
化学 | 1478篇 |
晶体学 | 19篇 |
力学 | 14篇 |
数学 | 78篇 |
物理学 | 375篇 |
出版年
2023年 | 22篇 |
2022年 | 22篇 |
2021年 | 38篇 |
2020年 | 64篇 |
2019年 | 73篇 |
2018年 | 43篇 |
2017年 | 27篇 |
2016年 | 99篇 |
2015年 | 88篇 |
2014年 | 84篇 |
2013年 | 104篇 |
2012年 | 186篇 |
2011年 | 206篇 |
2010年 | 76篇 |
2009年 | 61篇 |
2008年 | 126篇 |
2007年 | 100篇 |
2006年 | 98篇 |
2005年 | 87篇 |
2004年 | 74篇 |
2003年 | 40篇 |
2002年 | 32篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有1964条查询结果,搜索用时 15 毫秒
981.
Yusuke Hirasawa Hiroko Arai Abdul Rahman Idha Kusumawati Noor Cholies Zaini Osamu Shirota Hiroshi Morita 《Tetrahedron》2013
Five new indole alkaloids, voacalgines A–E (1–5) consisting of a C-mavacurine type of skeleton with 2,3-dihydroxybenzoate moiety, a macroline-type of skeleton, or a macroline-type of skeleton with C6 unit, were isolated from the bark of Voacanga grandifolia. Their relative structures were determined by means of NMR data. Voacalgine A showed moderate cell growth inhibitory activities against HL-60 and HCT116 cells. 相似文献
982.
Yoshiaki Ueda Yusuke Tanigawa Prof. Chitoshi Kitamura Prof. Hiroshi Ikeda Yuichi Yoshimoto Mirai Tanaka Prof. Kazuhiko Mizuno Prof. Hiroyuki Kurata Prof. Takeshi Kawase 《化学:亚洲杂志》2013,8(2):392-399
A series of 17,17‐dialkyl‐3,14‐diaryltetrabenzofluorenes were efficiently prepared by using Suzuki–Miyaura cross‐coupling reactions of the corresponding 3,14‐dibromo derivatives. Studies of the unique fluorescence properties of these compounds showed that they display intense blue to yellow fluorescence with high quantum yields in the solution state and blue to orange fluorescence with moderate quantum yields in the solid state. In addition, the fluorescence wavelength of the bis(p‐nitrophenyl) derivative is remarkably solvent‐dependent in a manner that correlates with the solvent polarity parameter ET(30). The results of density function theory calculations suggest that the intramolecular charge‐transfer character of the HOMO–LUMO transition is responsible for the large solvent effect. Moreover, addition of water to a tetrahydrofuran (THF) solution of this compound leads to quenching of the yellow fluorescence owing to an increase in the solvent polarity. However, when the amount of water fraction exceeds 70 %, a new fluorescence band appears at the same orange‐red emission wavelength as that of the solid‐state fluorescence. This observation suggests the occurrence of a crystallization‐induced emission (CIE) phenomenon in highly aqueous THF. 相似文献
983.
984.
Sanae Izumi Yusuke Kobayashi Yoshiji Takemoto 《Angewandte Chemie (International ed. in English)》2020,59(33):14054-14059
The highly stereoselective synthesis of 1,1′‐disaccharides was achieved by using 1,2‐dihydroxyglycosyl acceptors and glycosyl donors in the presence of a tricyclic borinic acid catalyst. In this reaction, the complexation of the diols and the catalyst is crucial for the activation of glycosyl donors, as well as for the 1,2‐cis‐configuration of the products. The anomeric stereochemistry of the glycosyl donor depends on the employed glycosyl donor. Applications of the produced 1,1′‐disaccharides are also described. 相似文献
985.
Takumi Nakanishi Yuta Hori Shuqi Wu Hiroyasu Sato Atsushi Okazawa Norimichi Kojima Yusuke Horie Hajime Okajima Akira Sakamoto Yoshihito Shiota Kazunari Yoshizawa Osamu Sato 《Angewandte Chemie (International ed. in English)》2020,59(35):14781-14787
A proton–electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi‐step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric‐like arrangement. 相似文献
986.
Nobuto Yoshinari Natthaya Meundaeng Hiroyasu Tabe Yusuke Yamada Satoshi Yamashita Yasuhiro Nakazawa Takumi Konno 《Angewandte Chemie (International ed. in English)》2020,59(41):18048-18053
Postsynthetic installation of lanthanide cubanes into a metallosupramolecular framework via a single‐crystal‐to‐single‐crystal (SCSC) transformation is presented. Soaking single crystals of K6[Rh4Zn4O(l ‐cys)12] (K6[ 1 ]; l ‐H2cys=l ‐cysteine) in a water/ethanol solution containing Ln(OAc)3 (Ln3+=lanthanide ion) results in the exchange of K+ by Ln3+ with retention of the single crystallinity, producing Ln2[ 1 ] ( 2Ln ) and Ln0.33[Ln4(OH)4(OAc)3(H2O)7][ 1 ] ( 3Ln ) for early and late lanthanides, respectively. While the Ln3+ ions in 2Ln exist as disordered aqua species, those in 3Ln form ordered hydroxide‐bridged cubane clusters that connect [ 1 ]6? anions in a 3D metal‐organic framework through coordination bonds with carboxylate groups. This study shows the utility of an anionic metallosupramolecular framework with carboxylate groups for the creation of a series of metal cubanes that have great potential for various applications, such as magnetic materials and heterogeneous catalysts. 相似文献
987.
Yunzhu Wang Shinya Furukawa Song Song Qian He Hiroyuki Asakura Ning Yan 《Angewandte Chemie (International ed. in English)》2020,59(6):2289-2293
Chemical synthesis of amino acids directly from biomass feedstock is rare. Reported here is a one‐step protocol to convert crude glycerol, from the biodiesel industry, into 43 % alanine over a Ru1Ni7/MgO catalyst. The multifunctional catalytic system promotes glycerol conversion into lactic acid, and then into alanine. X‐ray absorption spectroscopy and scanning transmission electron microscopy revealed the existence of bimetallic RuNi species, whereas density‐functional theory calculations suggested Ni‐doped Ru substantially decreased the Ea of C?H bond dissociation of lactate alkoxide to form pyruvate, which is the rate‐determining step. The catalytic route established in this work creates new opportunities for glycerol utilization and enriches the substrate scope of renewable feedstock to access value‐added amino acids. 相似文献
988.
Banana-shaped molecules having two side wings attached to a bent core may exhibit liquid crystallinity. The most studied material is 8-OPIMB that comprises 1,3-dihydroxybenzene as a central core, a Schiff 's base moieties as the wing groups and octyloxy tail groups. To clarify the effect of chemical structure on the liquid crystallinity of such a molecule, we have prepared several banana-shaped molecules, with side wings and central cores different from those of 8-OPIMB and examined their liquid crystallinity, which is sensitive to change in chemical structure. Especially, changing the position of the carbonyl group of the ester function linking the central core to the wing and the position of the nitrogen atom in the Schiff 's base moiety caused a loss of liquid crystallinity. On the other hand, smectic liquid crystallinity was maintained for five new types of banana-shaped molecule with different central cores. Although all these smectic phases have liquid-like association of the molecules within the smectic layers, they showed unconventional smectic textures through the separation of spiral, fractal and germ textures from the isotropic melt. Moreover, a frustrated smectic phase and chiral smectic phases were found. Several possible smectic structures for those phases will be discussed. 相似文献
989.
Yusuke Koito Kazuhiko Yamada Shinji Ando 《Journal of inclusion phenomena and macrocyclic chemistry》2013,76(1-2):143-150
An inclusion complex (IC) composed of a hydrofluoroether (HFE) guest and a β-cyclodextrin (β-CD) host was newly prepared, and the crystalline structure and the thermal stability of the IC were examined using several analytical methods, including wide-angle X-ray diffraction (WAXD), solid-state NMR, thermogravimetric analysis (TGA), TG–mass spectrometry (TG–MS), and quantum chemical calculation. The WAXD patterns and elemental analysis identified that the IC of an HFE/β-CD form of a channel-type structure, in which one HFE molecule is included in a common cavity of two β-CD molecules. TGA and TG–MS analysis indicated that the HFE molecules included in β-CD are hardly evaporated or degraded up to the decomposition temperature of the β-CD host. Solid-state 13C NMR indicated that the β-CD ring structure was deformed by including an HFE molecule in it, and that the 19F NMR signals of the HFE guest were significantly shifted to higher frequencies by the inclusion due to the dielectric media effect in the cavity of β-CD. Moreover, the 19F NMR signals of HFE included in IC were further shifted after annealing at 150 °C, which reflected structural changes in HFE/β-CD IC caused at elevated temperatures. The WAXD patterns also confirmed that the packing structure along the crystalline b-direction of HFE/β-CDs, which penetrates the cavities of β-CDs, was compressed by annealing and transformed to a more stable structure. 相似文献
990.
The optical and electrical characteristics of heterojunction organic photovoltaic cells consisting of tin–phthalocyanine as a p-type semiconductor and fullerene as an n-type semiconductor were studied using multiple-layer structures incorporating two hetero-junctions. In order to prevent formation of a reverse heterojunction, an ultra-thin layer of Au clusters was set between dual heterojunctions. The power conversion efficiencies of the cells were evaluated and the efficiency of the cell with two incorporated heterojunctions was found to be 4.5 times greater than that of a single hetero-junction. By using surface plasmon polaritons, the power conversion efficiency of an Al/C⋐70/SnPc/Au cell was enhanced and increased by a factor of 3. 相似文献