全文获取类型
收费全文 | 3645篇 |
免费 | 95篇 |
国内免费 | 15篇 |
专业分类
化学 | 2799篇 |
晶体学 | 60篇 |
力学 | 39篇 |
数学 | 115篇 |
物理学 | 742篇 |
出版年
2022年 | 19篇 |
2021年 | 27篇 |
2020年 | 23篇 |
2019年 | 34篇 |
2018年 | 18篇 |
2017年 | 26篇 |
2016年 | 51篇 |
2015年 | 50篇 |
2014年 | 54篇 |
2013年 | 144篇 |
2012年 | 182篇 |
2011年 | 211篇 |
2010年 | 120篇 |
2009年 | 123篇 |
2008年 | 219篇 |
2007年 | 209篇 |
2006年 | 183篇 |
2005年 | 200篇 |
2004年 | 183篇 |
2003年 | 167篇 |
2002年 | 131篇 |
2001年 | 116篇 |
2000年 | 85篇 |
1999年 | 72篇 |
1998年 | 40篇 |
1997年 | 56篇 |
1996年 | 48篇 |
1995年 | 36篇 |
1994年 | 33篇 |
1993年 | 36篇 |
1992年 | 51篇 |
1991年 | 35篇 |
1990年 | 45篇 |
1989年 | 31篇 |
1988年 | 30篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 48篇 |
1984年 | 47篇 |
1983年 | 35篇 |
1982年 | 47篇 |
1981年 | 45篇 |
1980年 | 40篇 |
1979年 | 57篇 |
1978年 | 36篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1975年 | 23篇 |
1974年 | 25篇 |
1973年 | 18篇 |
排序方式: 共有3755条查询结果,搜索用时 15 毫秒
31.
Book embedding of graphs is one of the graph layout problem. It is useful for the multiprocessor network layout or the fault-tolerant processor arrays. We show that the trivalent Cayley graphs proposed by Vadapalli and Srimani can be embedded in five pages, and show some additional results on cube-connected cycles. 相似文献
32.
Brick DH Widgoff M Beilliere P Lutz P Narjoux JL Gelfand N Alyea ED Bloomer M Bober J Busza W Cole B Frank TA Fuess TA Grodzins L Hafen ES Haridas P Huang D Huang HZ Hulsizer R Kistiakowsky V Ledoux RJ Milstene C Noguchi S Oh SH Pless IA Steadman S Stoughton TB Suchorebrow V Tether S Trepagnier PC Wadsworth BF Wu Y Yamamoto RK Cohn HO Calligarich E Castoldi C Dolfini R Introzzi G Ratti S Badiak M DiMarco R Jacques PF Kalelkar M Plano RJ Stamer PE Brucker EB Koller EL Alexander G Grunhaus J 《Physical review D: Particles and fields》1990,41(3):765-773
33.
34.
Norio Tsubokawa Yukio Shirai Hideyo Tsuchida Satoshi Handa 《Journal of polymer science. Part A, Polymer chemistry》1994,32(12):2327-2332
The photografting of polymers onto ultrafine inorganic particles, such as silica and titanium oxide, initiated by azo groups introduced onto these surfaces was investigated. The introduction of azo groups onto the particles was achieved by the reaction of 4,4′-azobis(4-cyanopentanoic acid) with surface isocyanate groups, which were introduced by the treatment with tolylene 2,4-diisocyanate. It was found that the photopolymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and N-vinylcarbazole, is initiated by ultrafine particles having azo groups. The corresponding polymers were effectively grafted onto these surfaces through the propagation of the polymer from the surface radicals formed by the photodecomposition of the azo groups: e.g., the percentage of grafting of PMMA and polystyrene onto silica was reached to 112 and 176%, respectively. The percentage of grafting onto silica in the graft polymerization initiated by photodecomposition of surface azo groups was much larger than that initiated by thermal decomposition. Polymer-grafted ultrafine particles thus obtained gave a stable colloidal dispersion in good solvents for the grafted chain. © 1994 John Wiley & Sons, Inc. 相似文献
35.
Gas-stirred propylene carbonate (PC) extraction can be performed by bubbling nitrogen without loss of volume. This extraction technique has proved to be highly useful for the separation and subsequent direct polarographic estimation of Tl(III) in the recovered PC phase. Tl(III) can be determined by differential-pulse polarography over the concentration range of 0.4 10 g ml–1 without any interferences due to most metal ions such as Pb(II), Bi(III), Cu(II), Sb(III) and As(III). This proposed technique would be possible to use as a simple extraction step prior to the final estimation by instrumental method of analysis such as atomic absorption spectrometry or spectrophtometry. 相似文献
36.
Toyoda M Ishihara M Yamaguchi S Ito H Matsuo T Roll R Rosenbauer H 《Journal of mass spectrometry : JMS》2000,35(2):163-167
A new type of multi-turn time-of-flight mass spectrometer was constructed, consisting of four cylindrical electric sectors and 28 electric quadrupole lenses, the size of the vacuum chamber being 60 x 70 x 20 cm. It was demonstrated that the mass resolution can be increased according to the number of cycles of the ions through the ion optical system. 相似文献
37.
38.
39.
Ohwada T Miura M Tanaka H Sakamoto S Yamaguchi K Ikeda H Inagaki S 《Journal of the American Chemical Society》2001,123(42):10164-10172
N-Nitrosamines can be considered as potential nitric oxide (NO)/nitrosonium ion (NO(+)) donors. However, the relation of the structures of N-nitrosamines, in particular of aliphatic N-nitrosamines, to the characteristics of release of NO or NO(+) remains unclear. Here we show that aliphatic N-nitrosoamines of 7-azabicyclo[2.2.1]heptanes can undergo heterolytic N-NO bond cleavage. On the basis of the observation of reduced rotational barriers of the N-NO bonds in solution and nitrogen-pyramidal structures of the N-nitroso group in the solid state, we postulate that N-NO bond cleavage of N-nitrosamines is enhanced by a reduction of the resonance in the N-NO group. Computational studies suggest that these structural features of the N-nitrosamines of 7-azabicyclo[2.2.1]heptane are derived from angle strain imposed on the CNC angles. 相似文献
40.
Kiitiro Utimoto Yukio Wakabayashi Yuho Shishiyama Masaharu Inoue Hitosi Nozaki 《Tetrahedron letters》1981,22(43):4279-4280
Title transformation is accomplished by the catalytic action of SnCl2 or BF3·OEt2 Lithio derivative of 2,2-dimethoxyacetonitrile is used as synthetic equivalent of methyl lithioformate. 相似文献