全文获取类型
收费全文 | 1713篇 |
免费 | 35篇 |
国内免费 | 3篇 |
专业分类
化学 | 1282篇 |
晶体学 | 14篇 |
力学 | 23篇 |
数学 | 116篇 |
物理学 | 316篇 |
出版年
2022年 | 8篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 22篇 |
2018年 | 21篇 |
2017年 | 18篇 |
2016年 | 32篇 |
2015年 | 27篇 |
2014年 | 24篇 |
2013年 | 70篇 |
2012年 | 68篇 |
2011年 | 103篇 |
2010年 | 58篇 |
2009年 | 62篇 |
2008年 | 99篇 |
2007年 | 115篇 |
2006年 | 104篇 |
2005年 | 102篇 |
2004年 | 99篇 |
2003年 | 70篇 |
2002年 | 72篇 |
2001年 | 32篇 |
2000年 | 28篇 |
1999年 | 15篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 29篇 |
1995年 | 12篇 |
1994年 | 24篇 |
1993年 | 13篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1985年 | 24篇 |
1984年 | 27篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 24篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1967年 | 7篇 |
1966年 | 6篇 |
排序方式: 共有1751条查询结果,搜索用时 140 毫秒
91.
Otera J Fujita Y Sakuta N Fujita M Fukuzumi S 《The Journal of organic chemistry》1996,61(9):2951-2962
Mechanism of Mukaiyama-Michael reaction of ketene silyl acetal has been discussed. The competition reaction employing various types of ketene silyl acetals reveals that those bearing more substituents at the beta-position react preferentially over less substituted ones. However, when ketene silyl acetals involve bulky siloxy and/or alkoxy group(s), less substituted compounds react preferentially. The Lewis acids play an important role in these reactions. Enhanced preference for the more sterically demanding Michael adducts is obtained with Bu(2)Sn(OTf)(2), SnCl(4), and Et(3)SiClO(4) in the former reaction while TiCl(4) gives the highest selectivity for the less sterically demanding products in the latter case. These results are interpreted in terms of alternative reaction mechanisms. The reaction of less bulky ketene silyl acetals are initiated by electron transfer from these compounds to a Lewis acid. On the other hand, bulkier ketene silyl acetals undergo a ubiquitous nucleophilic reaction. Such a mechanistic change is discussed based on a variety of experimental results as well as the semiempirical PM3 MO calculations. 相似文献
92.
[reaction: see text] A new class of molecular machine exhibits a hingelike motion upon photoirradiation. The motion (close and open) can be operated by alternate irradiation with UV and visible light. The trans/trans and cis/cis isomers are thermally stable at 40 degrees C, and the photochemical closure reaction (from trans/trans to cis/cis isomer) is dependent on the intensity of the light used because of the short-lived intermediate (trans/cis isomer). 相似文献
93.
94.
N. Momoshima Y. Takashima M. Koike Y. Imaizumi T. Harada 《Journal of Radioanalytical and Nuclear Chemistry》1994,177(2):219-228
A determination procedure has been developed for210Bi and210Po in environmental samples and was applied for pine needles. Bismuth-210 and210Po separated from the parent nuclide210Pb as BiOCl precipitate were extracted simultaneously by TOPO/toluene containing PPO and POPOP. The separation of210Bi and210Po from210Pb was almost satisfactory. The activity of210Bi+210Po in the TOPO/toluene was measured periodically by liquid scintillation counting for about 20 days after separation. The time course of the decreasing pattern of the activity was determined by the initial activity ratio210Po/210Bi. The decreasing pattern of the activity was compared with theoretical patterns, and best estimates for210Po and210Bi were obtained by non-linear least-squares fitting. The activities of210Bi and210Po were determined for one-year and two-year old pine needles fro the same pine tree, and weathering half-time and deposition rate of these nuclides was discussed. 相似文献
95.
96.
We provide a classification method of weighing matrices based on a classification of self‐orthogonal codes. Using this method, we classify weighing matrices of orders up to 15 and order 17, by revising some known classification. In addition, we give a revised classification of weighing matrices of weight 5. A revised classification of ternary maximal self‐orthogonal codes of lengths 18 and 19 is also presented. © 2011 Wiley Periodicals, Inc. J Combin Designs 20:40–57, 2012 相似文献
97.
Sadayuki Mori Tetsuya Karita Koichi Komatsu Nobuyuki Sugita Terence S. M. Wan 《合成通讯》2013,43(9):1475-1482
Under high pressure conditions, fullerene C60 smoothly reacts with 2H-pyran-2-one to give a [4+2] cycloadduct, which can be reduced to an alcohol derivative. 相似文献
98.
Plasma-enhanced MOCVD in which metal-organic compounds are sublimated directly into the growth chamber is studied for the first time as a new low-temperature process for growing superconducting YBa2Cu3O--x thin films. Y(THD)3, Ba(THD)2, Cu(THD)2 and oxygen are used as metal sources and oxydizing agent. Emission spectroscopy reveals that activated metal-organic compounds and activated oxygen species are present during film growth. Superconducting YBa2Cu3O7-x films whose zero-resistivity temperature are 50 K and 82 K are grown at 550°C and 600°C. 相似文献
99.
100.