全文获取类型
收费全文 | 601篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 462篇 |
晶体学 | 10篇 |
力学 | 14篇 |
数学 | 39篇 |
物理学 | 88篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 14篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 18篇 |
2012年 | 35篇 |
2011年 | 35篇 |
2010年 | 28篇 |
2009年 | 24篇 |
2008年 | 32篇 |
2007年 | 38篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 36篇 |
2003年 | 32篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1986年 | 7篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 3篇 |
排序方式: 共有613条查询结果,搜索用时 15 毫秒
591.
592.
Tanaka Manabu Terasaki Hidenori Ushio Masao Lowke John J. 《Plasma Chemistry and Plasma Processing》2003,23(3):585-606
Numerical modeling of free burning arcs and their electrodes is useful for clarifying the heat transfer phenomena in the welding process and to elucidate those effects which determine the weld penetration. This paper presents predictions for a stationary welding process by the free-burning argon arc. The whole region of the welding process, namely, tungsten cathode, arc plasma and stainless steel anode is treated in a unified numerical model to take into account the close interaction between the arc plasma and the molten anode. The time dependent development of two-dimensional distributions of temperature and velocity, in the whole region of the welding process, are predicted at a current of 150 A. The weld penetration geometry as a function of time is thus predicted. It is shown also that different surface tension properties can change the direction of re-circulatory flow in the molten anode and dramatically vary the weld penetration geometry. 相似文献
593.
Daiki Kamakura Hidenori Todoroki Daisuke Urabe Koichi Hagiwara Masayuki Inoue 《Angewandte Chemie (International ed. in English)》2020,59(1):479-486
Talatisamine ( 1 ) is a member of the C19‐diterpenoid alkaloid family, and exhibits K+ channel inhibitory and antiarrhythmic activities. The formidable synthetic challenge that 1 presents is due to its highly oxidized and intricately fused hexacyclic 6/7/5/6/6/5‐membered‐ring structure (ABCDEF‐ring) with 12 contiguous stereocenters. Here we report an efficient synthetic route to 1 by the assembly of two structurally simple fragments, chiral 6/6‐membered AE‐ring 7 and aromatic 6‐membered D‐ring 6 . AE‐ring 7 was constructed from 2‐cyclohexenone ( 8 ) through fusing an N‐ethylpiperidine ring by a double Mannich reaction. After coupling 6 with 7 , an oxidative dearomatization/Diels–Alder reaction sequence generated fused pentacycle 4 b . The newly formed 6/6‐membered ring system was then stereospecifically reorganized into the 7/5‐membered BC‐ring of 3 via a Wagner–Meerwein rearrangement. Finally, Hg(OAc)2 induced an oxidative aza‐Prins cyclization of 2 , thereby forging the remaining 5‐membered F‐ring. The total synthesis of 1 was thus accomplished by optimizing and orchestrating 33 transformations from 8 . 相似文献
594.
Youngju Kim Hidenori Watanabe Bieong-Kil Kim Young-Bae Seu 《Tetrahedron: Asymmetry》2011,22(16-17):1658-1661
In order to develop new methyl substituted chiral building blocks which are useful for the synthesis of methyl branched natural products, the enantioselective bioreduction of an exo-methylene to a methyl group was investigated. 4-Acetoxy-2-methylene-1-butanol 3 was prepared from itaconic acid over four steps and converted to the chiral alcohol (R)-4-acetoxy-2-methyl-1-butanol 4, by growing cells of Pseudomonas putida. The bioconversion achieved a high enantioselectivity (92% ee) and a high chemical yield (65%) within a relatively short reaction time (18–20 h). 相似文献
595.
By introducing azobenzenes into RNA using d-threoninol as a scaffold, a photoresponsive RNA was constructed for efficiently photoswitching the formation and dissociation of RNA/RNA duplexes. The difference in melting temperature (T(m)) between the trans and cis forms was so large that efficient photoregulation of RNA hybridization became possible, irrespective of the sequence adjacent to the introduced azobenzene. Compared to the corresponding photoresponsive DNA, the photoregulatory efficiency of azobenzene-modified RNA was even higher due to the drastic destabilization by cis-azobenzene. Structural analysis by NMR and molecular modeling indicated that the planar trans-azobenzene could not stabilize the RNA/RNA duplex with a rigid A-form structure by base pair stacking. However, the large steric hindrance caused by nonplanar cis-azobenzene was quite effective at distorting and destabilizing the duplex structure. We also discuss the effect of methylation of azobenzene at the ortho positions on photoregulation of RNA/RNA duplex formation. This newly constructed photoresponsive RNA has promising applications such as photoswitching of RNA functions. 相似文献
596.
597.
Axially chiral dicarboxylic acid-catalyzed highly enantioselective imino aza-enamine reaction was elaborated into a surrogate of the asymmetric Strecker reaction building on the fact that the N,N-dialkylhydrazone moiety can be easily converted to the cyanide moiety by treatment with peracid. 相似文献
598.
Nishida H Mukaihira T Saitoh F Harada K Fukui M Matsusue T Okamoto A Hosaka Y Matsumoto M Shiromizu I Ohnishi S Mochizuki H 《Chemical & pharmaceutical bulletin》2004,52(4):406-412
In the course of development of factor Xa (FXa) inhibitor in an investigation involving the synthesis of 1-arylsulfonyl-3-piperazinone derivatives, we found new compounds containing a unique spiro skeleton. Among such compounds, (-)-7-[(6-chloro-2-naphthalenyl)sulfonyl]tetrahydro-8a-(methoxymethyl)-1'-(4-pyridinyl)-spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4'-piperidin]-5-one (28, M55529) had activity more favorable than those of previously reported compounds. The inhibitory activity of M55529 for FXa is IC(50)=2 nM, with high selectivity for FXa over thrombin and trypsin. 相似文献
599.
600.
One-pot synthetic protocols of novel azido functionalized silane coupling agents from corresponding terminal mesylated or tosylated 1-olefins were developed. Azido groups were successfully converted to the corresponding 1,2,3-triazol ring by the copper-catalyzed azido alkyne coupling (CuAAC) reaction without alkoxysilane decomposition. The CuAAC product was readily grafted onto the silica surface in good yield.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献