全文获取类型
收费全文 | 1695篇 |
免费 | 90篇 |
国内免费 | 12篇 |
专业分类
化学 | 1366篇 |
晶体学 | 14篇 |
力学 | 18篇 |
数学 | 86篇 |
物理学 | 313篇 |
出版年
2023年 | 12篇 |
2022年 | 15篇 |
2021年 | 16篇 |
2020年 | 22篇 |
2019年 | 30篇 |
2018年 | 21篇 |
2017年 | 12篇 |
2016年 | 56篇 |
2015年 | 37篇 |
2014年 | 63篇 |
2013年 | 90篇 |
2012年 | 119篇 |
2011年 | 122篇 |
2010年 | 41篇 |
2009年 | 64篇 |
2008年 | 120篇 |
2007年 | 110篇 |
2006年 | 131篇 |
2005年 | 121篇 |
2004年 | 88篇 |
2003年 | 79篇 |
2002年 | 72篇 |
2001年 | 26篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1986年 | 6篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1973年 | 8篇 |
1970年 | 5篇 |
排序方式: 共有1797条查询结果,搜索用时 62 毫秒
71.
Observation of bubble layer formed on hydrogen and oxygen gas-evolving electrode in a magnetic field
Hisayoshi Matsushima Takami Iida Yasuhiro Fukunaka 《Journal of Solid State Electrochemistry》2012,16(2):617-623
The evolution of hydrogen and oxygen gasses in a 0.36-M KOH electrolyte was observed in a magnetic field, and the void fraction
was calculated by a hydrodynamic model. Both gasses evolving on a platinum working electrode formed a bubble layer which increased
the ohmic resistance. In addition to natural convection, magnetohydrodynamic (MHD) convection in a magnetic field improved
the electrolytic conductivity by supplying a fresh solution (pumping effect) and removing gas bubbles. The MHD convection
reduced the void fraction of hydrogen gas more than that of oxygen, which can be explained by the poor wettability of the
oxygen evolving electrode. 相似文献
72.
Yasuhiro Matoba Hiroshi Inoue Jun-Ichi Akagi Takuji Okabayashi Yasutaka Ishii Masaya Ogawa 《合成通讯》2013,43(9):865-873
Applicatims a Mo- and W-based heteropoly acids (HPA) as a catalyst in the oxidation of olefins have extensively been investigated1. However, a patent work is only attempted concerning the evoxidatim of olefins with H202 by HPA2) since the oxirane ring is cleaved because of a strong acidity of HPA itself. Herein, an effective epoxidatim of some allylic alcohols with H202 by a new Mo-species (MPCP), which was prepared from 12-molybdatophosphoric acid (H3PMo12040) and cetylpyridinium chloride (C5H5N (CH2), 15CH3- C1-) under two-phase conditions using chloroform as an organic solvent, is described. 相似文献
73.
Frantisek Mikes Hongxiang Teng Yasuhiro Koike Yoshiyuki Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2012,50(22):4717-4720
Copolymerizations of hexafluoroisobutylene (HFIB) with vinyl pentafluorobenzoate (VPFB) and vinyl trifluoroacetate (VTFA) were carried out in bulk using perfluorodibenzoyl peroxide as the radical initiator. The copolymers obtained were characterized by proton and fluorine NMR spectroscopy. The monomer reactivity ratios in the polymerization of HFIB with VPFB were r1 (HFIB) = 0, r2 (VPFB) = 0.373, and r1r2 = 0. The results indicated that these copolymers have alternating structures. Similarly, the copolymers of HFIB and VTFA also showed alternating structures. The films of HFIB‐co‐VPFB were prepared by casting THF solution of polymers. Films obtained were flexible and transparent. The refractive indices of copolymers were 1.4549, 1.4490, and 1.4438 at 532, 633, and 839 nm, respectively. The average Tgs of HFIB‐co‐VTFA and HFIB‐co‐VPFB were 52 and 71 °C, respectively. From these results, the Tg of the hypothetical HFIB homopolymer is postulated to be in between 70 and 90 °C, which may be useful in the assessment of Tgs of HFIB copolymers with other vinyl monomers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
74.
75.
General acid‐catalyzed reaction can be enhanced by the addition of base. Self‐catalyzed esterification of benzoic acid and octan‐1‐ol was enhanced by the addition of certain base such as imidazole. The rate of the esterification was accelerated as the concentration of imidazole increased. Trans‐esterification of 4‐nitrophenyl acetate was promoted in chloroform by the mixture of benzoic acid and imidazole, but not by benzoic acid or imidazole alone. 相似文献
76.
Yoshino Katsurayama Prof. Yasuhiro Ikabata Prof. Hajime Maeda Prof. Masahito Segi Prof. Hiromi Nakai Prof. Taniyuki Furuyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(2):e202103223
The high penetration of near-infrared (NIR) light makes it effective for use in selective reactions under light-shielded conditions, such as in sealed reactors and deep tissues. Herein, we report the development of phthalocyanine catalysts directly activated by NIR light to transform small organic molecules. The desired photocatalytic properties were achieved in the phthalocyanines by introducing the appropriate peripheral substituents and central metal. These phthalocyanine photocatalysts promote cross-dehydrogenative-coupling (CDC) under irradiation with 810 nm NIR light. The choice of solvent is important, and a mixture of a reaction-accelerating (pyridine) and -decelerating (methanol) solvents was particularly effective. Moreover, we demonstrate photoreactions under visible-light-shielded conditions through the transmission of NIR light. A combined experimental and computational mechanistic analysis revealed that this NIR reaction does not involve a photoredox-type mechanism with electron transfer, but instead a singlet-oxygen-mediated mechanism with energy transfer. 相似文献
77.
78.
Acta Mathematicae Applicatae Sinica, English Series - In this paper, we investigate a delayed HIV infection model that considers the homeostatic proliferation of CD4+ T cells. The existence and... 相似文献
79.
Genki Namba Yuki Mimura Prof. Yoshitane Imai Dr. Ryo Inoue Prof. Yasuhiro Morisaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14871-14877
Optically active X-shaped molecules based on the planar chiral [2.2]paracyclophane building block were prepared, in which di(methoxy)terphenyl units were stacked on the central benzene rings. At 25 °C, anisolyl rings freely rotate in solution, while in the crystal form, they are fixed by intramolecular CH–π interactions, thereby leading to the expression of the axial chirality, i.e., propeller chirality was exhibited by the planar chiral [2.2]paracyclophane moiety. The X-shaped molecule exhibited good circularly polarized luminescence (CPL) profiles with moderate ΦPL and a large glum value in the order of 10−3 at 25 °C, in solution. In contrast, at −120 °C, dual CPL emission with opposite signs was observed. According to the theoretical studies, the rotary motion of the anisolyl units is suppressed in the excited states, and so emission from two isomers could be observed. These results demonstrate that the axial chirality was controlled by the planar chirality, leading ultimately to propeller chirality. 相似文献
80.
Yasuhiro Igarashi Daisuke Asano Kazuo Furihata Naoya Oku Satoshi Miyanaga Hiroaki Sakurai Ikuo Saiki 《Tetrahedron letters》2012,53(6):654-656
During the course of screening natural products for the inhibitors of tumor cell invasion, pterocidin, a linear polyketide with a δ-lactone terminus, was rediscovered from a Streptomyces strain of a marine sediment-origin. A series of J-based configuration analyses and NOESY analysis, coupled with chemical derivatization and chiral anisotropy analysis, established the absolute stereochemistry of five asymmetric centers in this compound. 相似文献