全文获取类型
收费全文 | 220篇 |
免费 | 4篇 |
专业分类
化学 | 157篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 32篇 |
物理学 | 30篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 7篇 |
2012年 | 13篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 21篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有224条查询结果,搜索用时 390 毫秒
91.
Luciano Lardicci Anna M. Caporusso Giampaolo Giacomelli 《Journal of organometallic chemistry》1974,70(3):333-338
The reaction between triisobutylaluminum and aliphatic 1-alkynes having alkyl groups of different structure on the 3-carbon atom has been investigated. At room temperature and in the absence of solvents, products which correspond to metallation, reduction and carbalumination processes, are isolated after hydrolysis. The extent of such reactions, and in particular the regiospecificity of the carbalumination is dependent on the experimental conditions adopted and on steric factors associated with the structure of the 1-alkyne used. On the basis of these results and the complete stereospecificity of the reaction when (+)(S-3,4-dimethyl-1-pentyne is used, possible mechanisms are discussed. 相似文献
92.
Mauro Biliotti Vikram Jha Norman L. Johnson Giampaolo Menichetti 《Geometriae Dedicata》1989,29(1):7-43
This paper is devoted to the study of translation planes of order q
2 and kernel GF(q) that admit a collineation group of order q
2 in the linear translation complement. We give a representation of this group by a suitable set of matrices depending on some functions over GF(q). Using this representation we obtain several results concerning the existence and the collineation group of the plane. 相似文献
93.
Gunaratne TC Gusev AV Peng X Rosa A Ricciardi G Baerends EJ Rizzoli C Kenney ME Rodgers MA 《The journal of physical chemistry. A》2005,109(10):2078-2089
Reported herein is a combination of experimental and DFT/TDDFT theoretical investigations of the ground and excited states of 1,4,8,11,15,18,22,25-Octabutoxyphthalocyaninato-nickel(II), NiPc(BuO)(8), and the dynamics of its deactivation after excitation into the S(1)(pi,pi) state in toluene solution. According to X-ray crystallographic analysis NiPc(BuO)(8) has a highly saddled structure in the solid state. However, DFT studies suggest that in solution the complex is likely to flap from one D(2)(d)-saddled conformation to the opposite one through a D(4)(h)-planar structure. The spectral and kinetic changes for the complex in toluene are understood in terms of the 730 nm excitation light generating a primarily excited S(1) (pi,pi) state that transforms initially into a vibrationally hot (3)(d(z)2,d(x)2(-)(y)2) state. Cooling to the zeroth state is complete after ca. 8 ps. The cold (d,d) state converted to its daughter state, the (3)LMCT (pi,d(x)2(-)(y)2), which itself decays to the ground state with a lifetime of 640 ps. The proposed deactivation mechanism applies to the D(2)(d)-saddled and the D(4)(h)-planar structure as well. The results presented here for NiPc(BuO)(8) suggest that in nickel phthalocyanines the (1,3)LMCT (pi,d(x)2(-)(y)2) states may provide effective routes for radiationless deactivation of the (1,3)(pi,pi) states. 相似文献
94.
A resin capture and release strategy for making a combinatorial array of 2,4,5-trisubstituted pyrimidines is demonstrated by capturing beta-ketoesters and beta-ketoamides on a solid-supported piperazine. Through a cyclocondensation reaction, the solid-supported enaminone is reacted with several guanidines under heating or microwave irradiation affording the corresponding pyrimidines in good yield and chemical purity directly on solution. After this final step, the support can be effectively recycled. 相似文献
95.
Bauer EM Donzello MP Ercolani C Masetti E Panero S Ricciardi G Rosa A Chiesi-Villa A Rizzoli C 《Inorganic chemistry》2003,42(2):283-293
Recrystallization of the previously reported monosolvated bis(phthalocyaninato)niobium(IV), [Pc2Nb].CINP (CINP = 1-chloronaphthalene), has allowed isolation of a single crystal of a new solvated form, i.e. [Pc2Nb]. 3.5CINP, whose structure has been elucidated by X-ray work: space group P2(1)/n (No. 14); a = 16.765(3), b = 23.800(4), c = 19.421(4) A; alpha = gamma = 90 degrees, beta = 92.51(2) degrees; Z = 4. The sandwiched material is a "stapled" molecule, characterized by the presence of two intramolecular interligand C-C sigma bonds and highly strained phthalocyanine units, as formerly observed by crystallographic work for its Ti(IV) analogue, [Pc2Ti], and the +1 corresponding fragment, [Pc2Nb]+, present in the species [Pc2Nb](l3)(l2)0.5.3.5CINP. [Pc2Nb] appears to be reluctant to undergo further oxidation above the +1 oxidation state. Detailed theoretical studies by DFT and TDDFT methods have been developed on [Pc2Nb] and [Pc2Nb]+, also extended for comparison to the Ti(IV) complex [Pc2Ti], and an adequate picture of the ground-state electronic structure of these species has been achieved. Moreover, the excitation energies and oscillator strengths calculated for the closed-shell systems, [Pc2Ti] and [Pc2Nb]+, provide a satisfactory interpretation of their characteristic visible optical spectra and help to rationalize the similar features observed in the visible spectrum of the open-shell "stapled" complex, [Pc2Nb]. Thin solid films (100-250 nm) of [Pc2Nb] deposited on ITO (indium-doped tin oxide) show a reversible redox process in neutral or acidic aqueous electrolytes. The electrochemical and electrochromic properties of the sandwiched complex, combined with impedance and UV/visible spectral measurements, are presented and discussed. The achieved electrochemical information, while substantially in keeping with the observed chemical redox behavior and theoretical predictions, qualifies [Pc2Nb] as an "optically passive" electrode and a promising material for its use in electrochromic devices. 相似文献
96.
97.
A microwave-enhanced procedure for the synthesis of substituted benzofurans starting from 2-(1-hydroxyalkyl)-phenols and using triphenylphosphine polystirene resin is reported. The benzofurans are isolated in good to high yields and purities by simple workup. The procedure can be applied to chiral alpha-alkyl-2-benzofuranmethanamines too. 相似文献
98.
99.
100.
Giampaolo Cicogna 《Physics letters. A》2008,372(20):3672-3677
The notion of λ-symmetries, originally introduced by C. Muriel and J.L. Romero, is extended to the case of systems of first-order ODEs (and of dynamical systems in particular). It is shown that the existence of a symmetry of this type produces a reduction of the differential equations, restricting the presence of the variables involved in the problem. The results are compared with the case of standard (i.e. exact) Lie-point symmetries and are also illustrated by some examples. 相似文献