全文获取类型
收费全文 | 1316篇 |
免费 | 21篇 |
国内免费 | 3篇 |
专业分类
化学 | 1107篇 |
晶体学 | 13篇 |
力学 | 20篇 |
数学 | 59篇 |
物理学 | 141篇 |
出版年
2021年 | 7篇 |
2020年 | 14篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2016年 | 22篇 |
2015年 | 15篇 |
2014年 | 21篇 |
2013年 | 64篇 |
2012年 | 37篇 |
2011年 | 58篇 |
2010年 | 39篇 |
2009年 | 31篇 |
2008年 | 66篇 |
2007年 | 70篇 |
2006年 | 63篇 |
2005年 | 73篇 |
2004年 | 68篇 |
2003年 | 70篇 |
2002年 | 89篇 |
2001年 | 21篇 |
2000年 | 20篇 |
1999年 | 12篇 |
1998年 | 17篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 12篇 |
1994年 | 19篇 |
1993年 | 26篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1985年 | 29篇 |
1984年 | 30篇 |
1983年 | 13篇 |
1982年 | 27篇 |
1981年 | 32篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有1340条查询结果,搜索用时 15 毫秒
51.
An azaanalog of adamantene, 2-azaadamant-1-ene () and 4-azaprotoadamant-3-ene () were generated in the nonstatistical ratio via photolysis of 3-azidonoradamantane (). The highly strained and could not be isolable but were trapped by MeOH. Acidolysis of was also reported, and discussed in comparison with the photolysis. 相似文献
52.
SERS from crystal violet (CV) on a Ag electrode was investigated under preresonance and resonance conditions. The excitation profile of the chemisorbed species is like that of dissolved molecules but intensities are ≈ 1000 times larger. The Raman enhancement is ≈ 108 and exhibits a specific potential dependence even in the absence of adsorption-desorption process. At potentials where reduction of CV occurs leuco crystal violet was detected. 相似文献
53.
Mikio Hori Tadashi Kataoka Hiroshi Shimizu Eiji Imai Yukiharu Matsumoto Iwao Miura 《Tetrahedron letters》1981,22(13):1259-1262
The novel ring transformation reactions were found in the reactions of 1,3,7,9-tetra-alkyl-8,9-dihydroxanthines and acetylenic compounds. The reaction of the dihydroxanthine with DMAD gave a propellane type compound and with methyl propiolate afforded the similar type compound and a pyrimido[4,5-b]diazepine derivative. The mechanism of these reactions was also discussed. 相似文献
54.
Tadashi Okuyama 《Tetrahedron letters》1982,23(26):2665-2666
1,2-Ethanedithiol and 1,3-propanedithiol were treated with perchloric acid in acetic anhydride to give 2-methyl-1,3-dithiolan-2-yl and 2-methyl-1,3-dithian-2-yl perchlorates, respectively, which were converted to ketene dithioacetals by deprotonation with tertiary amines. 相似文献
55.
Eigoro Murayama Masahiro Uematsu Hiroyuki Nishio Tadashi Sato 《Tetrahedron letters》1984,25(3):313-316
Internal reaction of secondary alkyltin(IV) compounds having thionium ion gave internal trans olefins with high yield and regio- and stereoselectivity via 1,5- or 1,6-transfer of a hydride β to the trialkylstannyl group. 相似文献
56.
Large-scale separation of metallic and semiconducting single-walled carbon nanotubes 总被引:6,自引:0,他引:6
Maeda Y Kimura S Kanda M Hirashima Y Hasegawa T Wakahara T Lian Y Nakahodo T Tsuchiya T Akasaka T Lu J Zhang X Gao Z Yu Y Nagase S Kazaoui S Minami N Shimizu T Tokumoto H Saito R 《Journal of the American Chemical Society》2005,127(29):10287-10290
In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way. 相似文献
57.
Hiroyuki Hayakawa Hiromichi Tanaka Keiko Sasaki Kazuhiro Haraguchi Takafumi Saitoh Fumi Takai Tadashi Miyasaka 《Journal of heterocyclic chemistry》1989,26(1):189-192
Several 8-substituted cordycepins were prepared via LDA lithiation of 2′,5′-bis-O-(t-butyldimethylsilyl)-cordycepin and successive reactions of its C-8 lithiated species with various types of electrophiles. Wittig reaction of the 8-formyl derivative was also examined. 相似文献
58.
2,3-Dideoxy-3-fluoro-α-d-ribose 1-phosphate 2 was stereoselectively synthesized and converted to 2′,3′-dideoxy-3-fluoro-β-d-guanosine 1 by enzymatic reaction using purine nucleoside phosphorylase. This chemo-enzymatic strategy was first applied to the synthesis of 1. 相似文献
59.
Toshio Takido Sachiko Tamura Kenji Sato Haruo Kamijo Toshikatsu Nakazawa Manabu Seno Tadashi Hata 《Journal of heterocyclic chemistry》1998,35(2):437-443
The synthesis of hexahydrooxoepithiopyridinedicarboxyimide (5: X2 = N-Ph) by the reaction of thioamides 1 with N-substituted maleimide ( 2a ) was examined. The reaction of primary thioamides, such as thiobenzamide and p-toluthioamide with N-phenylmaleimide gives compounds 5 together with corresponding 4-hydroxy-1,3-thiazoles 4 . However, a similar reaction of secondary thioamides, such as N-methylthioacetamide, thiobenzanilide, with N-phenylmaleimide did not provide compounds 5 without addition of acid. The reaction pathway and the configuration of 5 were also investigated. 相似文献
60.
In the present paper, a study was undertaken of molecular transport in ploy(dimethylsiloxane) microchannels that were fabricated by ultraviolet (UV)-photolithography and synchrotron radiation (SR)-lithography characterized and compared for microchip capillary electrophoresis by evaluating in-channel molecular dispersion. A fluorescent tag, sulforhodamine B was used as the probing molecule. It was found that microchannels made by SR-lithography fabrication were superior to those made by UV-photolithography fabrication in terms of molecular transport performance. A deep insight into surface conditions characterized by scanning electron microscopy suggested it was related to the difference in surface roughness. Chromatographic retention in electropherograms further supported such a conclusion, which depended on the phase ratio of the channel surface. The results revealed for PDMS microchannels in this work were in good agreement with the phenomenon found for glass microchannels in the literature. 相似文献