全文获取类型
收费全文 | 305篇 |
免费 | 11篇 |
国内免费 | 5篇 |
专业分类
化学 | 235篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 23篇 |
物理学 | 50篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 24篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 18篇 |
2007年 | 33篇 |
2006年 | 26篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1992年 | 5篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 3篇 |
1943年 | 2篇 |
1941年 | 1篇 |
1932年 | 1篇 |
1908年 | 1篇 |
1891年 | 2篇 |
排序方式: 共有321条查询结果,搜索用时 832 毫秒
31.
Abstract
In the title compound, [Cu(C34H52N4)](ClO4)2, the Cu(II) ion has a square-planar coordination somewhat distorted towards tetrahedral geometry. The macrocyclic ligand adopts a less stable trans-I (RSRS) configuration. The two benzyl groups and two secondary amine H atoms are oriented towards the same side of the macrocyclic plane. The two six-membered rings are in slightly distorted chair and unsymmetrical twist-boat forms while both five-membered chelate rings are in the gauche conformation. The longer distances (2.050(4) and 2.035(4) Å) of Cu–N(tertiary) compared to 2.017(4) and 1.990(4) Å for Cu–N(secondary) may be due to the steric effects of the attached two benzyl groups on the tertiary N atoms. The crystal structure is stabilized by hydrogen bonds between secondary NH groups and O atoms of perchlorate counter-ions. 相似文献32.
M. Tamura J. Luque J.E. Harrington P.A. Berg G.P. Smith J.B. Jeffries D.R. Crosley 《Applied physics. B, Lasers and optics》1998,66(4):503-510
Received: 10 June 1997/Revised version: 25 November 1997 相似文献
33.
C. F. Harrington 《应用有机金属化学》2007,21(11):999-1000
34.
Radiation and scattering from bodies of revolution 总被引:1,自引:0,他引:1
The problem of electromagnetic radiation and scattering from perfectly conducting bodies of revolution of arbitrary shape is considered. The mathematical formulation is an integro-differential equation, obtained from the potential integrals plus boundary conditions at the body. A solution is effected by the method of moments, and the results are expressed in terms of generalized network parameters. The expansion functions chosen for the solution are harmonic in ø (azimuth angle) and subsectional in t (contour length variable). Because of rotational symmetry, the solution becomes a Fourier series in ø, each term of which is uncoupled to every other term.Illustrative computations are given for radiation from apertures and plane wave scattering from bodies of revolution. The impedance elements, currents, radiation patterns, and scattering patterns for a conducting sphere are computed both from the general solution and from the classical eigenfunction solution. The agreement obtained serves to check the general solution. Similar computations for a cone-sphere illustrate the application of the general solution to problems not solvable by classical methods. 相似文献
35.
The problem of electromagnetic radiation and scattering from loaded bodies of revolution of arbitrary shape is considered. The analysis assumes the existence of an impedance function relating the tangential electric field to the surface current on the body. A solution is obtained by the method of moments applied to the potential integral formulation of the problem. The results are expressed in terms of generalized network parameters, using formulas previously obtained for unloaded bodies. Representative computations are given for plane-wave scattering and radiation from apertures in loaded cylinders and hemispheres. A general computer program for arbitrary bodies of revolution is available. 相似文献
36.
A series of experiments has been conducted to determine the effect of loading variables such as cyclic frequency, load ratio, and material on acoustic emission from fatigue-crack propagation. It is shown that the applied-stress intensity range (ΔK) is the controlling parameter for all materials studied while the other parameters have lesser effects. Two potential methods for engineering application of acoustic emission during fatigue loading are described. 相似文献
37.
38.
39.
Some metal ion complexing properties of the ligand PDAM (1,10-phenanthroline-2,9-dicarboxamide) in aqueous solution are reported. Using UV-visible spectroscopy to follow the intense π-π* transitions of PDAM as a function of metal ion concentration, log K(1) values in 0.1 M NaClO(4) and at 25 °C are, for Cu(II), 3.56(5); Ni(II), 3.06(5); Zn(II), 3.77(5); Co(II), 3.8(1); Mg(II), 0.1(1); Ca(II), 1.94(4); and Ba(II), 0.7(1). For more strongly bound metal ions, competition reactions between PDAM and EDTA (ethylenedinitrilo-tetraacetic acid) or tetren (1,4,7,10,13-pentaazatridecane), monitored following the UV spectrum of PDAM, gave the following log K(1) values in 0.1 M NaClO(4) and at 25 °C: Cd(II), 7.1(1); Pb(II), 5.82(5); In(III), 9.4(1); and Bi(III), 9.4(1). The very low log K(1)(PDAM) values for small metal ions such as Cu(II) or Zn(II) are unprecedented for a phen-based ligand (phen = 1,10-phenanthroline), which is rationalized in terms of the low basicity of the N donors of the ligand (pK(a) = 0.6) and the fact that PDAM has a best-fit size corresponding to large metal ions of ionic radius ~1.0 ?. Large metal ions with ionic radius ≥1.0 ? show large increases in log K(1) relative to their phen complexes, which in turn produces unparalleled selectivities, such as a 3.5 log units greater log K(1)(PDAM) for Cd(II) than for Cu(II). PDAM shows strong fluorescence in aqueous solution, suggesting that its carboxamide groups do not produce a fluorescence-quenching photon-induced electron transfer (PET) effect. Only Ca(II) produces a weak CHEF (chelation enhanced fluorescence) effect with PDAM, while all other metal ions tested produce a decrease in fluorescence, a CHEQ (chelation enhanced quenching effect). The production of the CHEQ effect is rationalized in terms of the idea that coordination of metal ions to PDAM stabilizes a canonical form of the carboxamide groups that promotes a PET effect. 相似文献
40.
Haines NR VanZanten AN Cuneo AA Miller JR Andrews WJ Carlson DA Harrington RM Kiefer AM Mason JD Pigza JA Murphree SS 《The Journal of organic chemistry》2011,76(19):8131-8137
2,4-Disubstituted furans are prepared by treating 2,3-dibromo-1-phenylsulfonyl-1-propene (DBP, 2) with 1,3-diketones under basic conditions. The furan-forming step involves a deacetylation, and the selectivity of this process depends upon the steric demand of the R group. The substituent in position 4 is elaborated by reaction of sulfonyl carbanions with alkyl halides, acyl halides, and aldehydes. Oxidative or reductive desulfonylation produces the 2,4-disubstituted furans in 60-92% yield. This strategy has been used to prepare rabdoketone A (12) and the naturally occurring nematotoxic furoic acid 13. 相似文献