全文获取类型
收费全文 | 391篇 |
免费 | 10篇 |
专业分类
化学 | 218篇 |
晶体学 | 2篇 |
力学 | 39篇 |
数学 | 19篇 |
物理学 | 123篇 |
出版年
2021年 | 3篇 |
2020年 | 9篇 |
2019年 | 4篇 |
2016年 | 12篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 27篇 |
2012年 | 13篇 |
2011年 | 24篇 |
2010年 | 14篇 |
2009年 | 7篇 |
2008年 | 21篇 |
2007年 | 18篇 |
2006年 | 21篇 |
2005年 | 24篇 |
2004年 | 10篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1935年 | 2篇 |
1934年 | 2篇 |
排序方式: 共有401条查询结果,搜索用时 15 毫秒
81.
Arthur Maki Thomas A. Blake Robert L. Sams Nicolae Vulpanovici Jeffrey Barber Engelene T.H. Chrysostom Tony Masiello Joseph W. Nibler Alfons Weber 《Journal of Molecular Spectroscopy》2001,210(2)
New measurements are reported for the infrared spectrum of sulfur trioxide, 32S16O3, with resolutions ranging from 0.0015 cm−1 to 0.0025 cm−1. Rovibrational constants have been measured for the fundamentals ν2, ν3, and ν4 and the overtone band 2ν3. Comparisons are made with the earlier high-resolution measurements on SO3, and the high correlation among some of the constants related to the Coriolis coupling of the ν2 and ν4 levels is discussed in order to understand the areas of disagreement with the earlier work. Splittings of some of the levels are observed and the splitting constant for K=3 of the ground state is determined for the first time. Other observed splittings include the K=1 levels of 2ν3 (l=2), the K=2 levels of ν3 and ν4, and the K=3 levels of ν2. The analysis shows that there are level crossings between the l=0 and l=2 states of 2ν3 that allow one to determine the separation of the subband centers for these two states even though access to the l=0 state from the ground state is electric-dipole forbidden. This is a generalized phenomenon that should be found for many other molecules with the same symmetry. The l-type resonance constant, q3, that causes the splitting of the l3=±1, k=±1 levels of ν3 also couples the l3=0 and 2 states of 2ν3. 相似文献
82.
Connor J. Thomson David M. Barber Darren J. Dixon 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2491-2495
A scalable, one‐pot, enantioselective catalytic synthesis of 2‐pyrazolines from beta‐substituted enones and hydrazines is described. Pivoting on a two‐stage catalytic Michael addition/condensation strategy, the use of an aldehyde to generate a suitable hydrazone derivative of the hydrazine was found to be key for curtailing background reactivity and tuning the catalyst‐controlled enantioselectivity. The new synthetic method is easy to perform, uses a new and readily prepared cinchona‐derived bifunctional catalyst, is broad in scope, and tolerates a range of functionalities with high enantioselectivity (up to >99:1 e.r.). The significant scalability of this methodology was demonstrated with the synthesis of more than 80 grams of a pyrazoline product with 89 % catalyst recovery. 相似文献
83.
R.J. Ellis R.C. Barber G.R. Dyck B.J. Hall K.S. Sharma C.A. Lander H.E. Duckworth 《Nuclear Physics A》1985,435(1):34-42
The 1 m radius, high-resolution mass spectrometer at the University of Manitoba (“Manitoba II”) has been used to determine 11 atomic mass differences between some stable isotopes of Ge, As and Se. These values are of greater accuracy and precision than existing data. Their consistency has been checked by a major least-squares adjustment involving relevant data in the region. Results include improved S2n values for several nuclides and the energies available for the ββ decays of 76Ge and 74Se, respectively. 相似文献
84.
The molecular effect in the ionization of inner shell electrons of aluminum atoms by energetic H+2 molecules has been calculated. We distinguish between the molecular effect in Al and Al2O3. We conclude that in the case of Al the protons of the cluster have a definite orientation but in the case of Al2O3 the orientation is at random. 相似文献
85.
L C Collins-Gold D C Barber W J Hagan S L Gibson R Hilf D G Whitten 《Photochemistry and photobiology》1988,48(2):165-175
Abstract— Previous studies from our laboratories and elsewhere have shown that amides between fatty acids and the synthetic α, α, α, α -tetra (o-aminophenyl)-porphyrins exhibit good surfactant properties which facilitate their incorporation into structured assemblies characterized by hydrophobic-hydrophilic compartmentalization. This paper will focus on a number of aspects of our studies of these porphyrins at different interfaces. The α, α, α, α (4,0) isomers are readily incorporated into Langmuir-Blodgett films as either free base or metal complexes. Studies of assemblies containing free base and palladium (II) complexes have been carried out in which the porphyrin is irradiated in the presence of oxygen and nonexcited but oxidizable substrates. Much of the reactivity observed can be attributed to 1O2* generation. These studies reveal the migration range and reactivity of activated oxygen in a structure related to biomem-branes. Several of these synthetic porphyrins have also been examined in cell suspensions and in synthetic reversed micelle solutions. Studies in the former have shown that the porphyrins can mediate the photoinactivation of several enzymes located inside and within the mitochondrial membrane in tumor cells extracted from rats. They are found to compare favorably to hematoporphyrin derivative in effectiveness. Studies of the same porphyrins in their reactivity towards copper ion incorporation in anionic reversed micelles indicate striking rate differences which can be interpreted in part to structural variations between the porphyrins as well as to their orientation at the hydrophobic-hydrophilic interface. 相似文献
86.
87.
J. R. Barber 《Journal of Elasticity》1991,26(1):75-86
The classical formulation of the homogeneous problem of a curved bar loaded only by and end force involves the assumption of an appropriate stress function with four arbitrary constants and the determination of these constants from the boundary conditions. Since there are five boundary conditions, four on the curved edge and one at the end, the solution is only possible because the coefficient matrix of the resulting algebraic equations is singular. This in turn means that certain inhomogeneous problems in which the curved edges are loaded by sinusoidally varying tractions cannot be solved using apparently appropriate stress functions.Additional stress functions which resolve this difficulty are introduced and an example problem is solved, which exhibits qualitatively different behavior from that in more general cases of loading. The problem is then reconsidered as a limiting case of sinusoidal loading of arbitrary wavelength. It is shown that the solution of the latter problem appears to become unbounded as the special case is approached, but that when the end conditions have been correctly satisfied by superposing an appropriate multiple of the end-loaded solution, the limit can be approached regularly and the correct special solution is recovered. The limiting process reveals a general procedure for determining the additional stress functions required for the special case.Similar relationships between homogeneous and inhomogeneous solutions for other common geometries are discussed. 相似文献
88.
89.
Barberá J Gimeno N Monreal L Piñol R Ros MB Serrano JL 《Journal of the American Chemical Society》2004,126(23):7190-7191
The synthesis and characterization of reactive banana-shaped compounds have been carried out, and their ability to be photopolymerized in their SmCP mesophase has been assessed. The presence of a SmCP liquid crystalline phase in these compounds has been confirmed by X-ray studies. The polymerization of these molecules has been demonstrated by calorimetric techniques as well as by the preparation and characterization of SmCP-ordered free films that are mechanically stable at room temperature. Furthermore, polymerized films exhibit second harmonic generation activity at room temperature in the absence of an electric field. 相似文献
90.
Adams CJ Anderson KM Baber RA Connelly NG Kandiah M Orpen AG 《Dalton transactions (Cambridge, England : 2003)》2004,(20):3353-3359
The nominally square-planar coordination of the d(8) complexes [MClL(1)L(2)(p-XC(6)H(4)NNNHC(6)H(4)X-p)](M = Rh, L(1)= L(2)= CO, X = H, Me, Et or F; M = Ir, L(1)= L(2)= CO, X = Me; M = Pd or Pt, L(1)= Cl, L(2)= PPh(3), X = Me; M = Pd, L(1)L(2)=eta(3)-C(3)H(5), X = Me), with the triazene N-bonded via the imine group, is supplemented by an axial M...H-N interaction involving the terminal amino group. 相似文献