全文获取类型
收费全文 | 936篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 643篇 |
晶体学 | 10篇 |
力学 | 27篇 |
数学 | 67篇 |
物理学 | 199篇 |
出版年
2023年 | 5篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 32篇 |
2012年 | 37篇 |
2011年 | 45篇 |
2010年 | 21篇 |
2009年 | 19篇 |
2008年 | 36篇 |
2007年 | 49篇 |
2006年 | 53篇 |
2005年 | 52篇 |
2004年 | 36篇 |
2003年 | 35篇 |
2002年 | 41篇 |
2001年 | 22篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 23篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1972年 | 5篇 |
1937年 | 4篇 |
1887年 | 4篇 |
排序方式: 共有946条查询结果,搜索用时 15 毫秒
71.
72.
Far-infrared absorption spectra of H216O, H218O, H16OD, H18OD, D216O, D218O have been observed between 10 and 40 cm?1 at a resolution of 0.07 cm?1. Experimental and calculated line positions agree within the accuracy of the experiment (±0.003 cm?1). The relative intensities of type a and type b transitions of H16OD and H18OD are used to estimate the ratio . 相似文献
73.
Abstract— The bioluminescent enzyme from Photobacterium fischeri is normally activated in vifro by reaction with FMNH2 and O2 . in the presence of a long-chain aldehyde. Emission from enzyme intermediates in this reaction continues for several seconds, and if the mixture is frozen just after initiation of the reaction, this presumptive emission may be delayed until the system is warmed again. Light is then emitted in a fashion analogous to thermo-luminescent emission, with a maximum intensity at — 10°C. The experiments described here show that the total amount of light which is emitted under these conditions no longer depends so much upon aldehyde, a relatively high quantum yield being obtained both with and without aldehyde.
It is further shown that bioluminescence may be activated by light, populating it is believed, the same state which is responsible for the emission in the case of the FMNH2 -induced emission. The light-induced reaction does not depend on flavin in the enzyme preparations, nor does the activation spectrum resemble that of a flavoprotein. Activation may be carried out in the solid state at temperatures down to at least — 100°C, and so does not involve the diffusion of large molecules. It is proposed that energy storage takes place by charge separation, and that the excited state from which emission takes place is associated with charge recombination. 相似文献
It is further shown that bioluminescence may be activated by light, populating it is believed, the same state which is responsible for the emission in the case of the FMNH
74.
Thomas Gibson 《Tetrahedron letters》1982,23(2):157-158
Hydrozirconation of internal olefins followed by oxidation with anhydrous t-butyl hydroperoxide generates primary alcohols in good yields and high purity. 相似文献
75.
Within the framework of a Faddeev formalism and an implicit hyperon channel approximation, we have calculatedK ? d elastic, total, and reaction cross sections for incident kaon laboratory momenta up to 120 Mev/c. We have used as input two different (slightly modified) multichannelM matrix fits to low-energy¯KN scattering, each of which contains explicitly theπ Y channels, as well as a single channel representation of the¯KN interaction in which the hyperon channels appear only through their contributions to the imaginary parts of the¯KN scattering lengths. TheK ? d cross sections obtained with the single channel¯KN input differ by only some 10% from those for which we used the multichannel¯KN input. TheK ? d cross sections calculated using¯KN input parameters from each of the two separateM matrix fits differ across the entire momentum range investigated by 25–35%. 相似文献
76.
S.F. Biagi M. Bourquin A.J. Britten R.M. Brown H. Burchhart A.A. Carter J.R. Carter Ch. Doré P. Extermann M. Gailloud C.N.P. Gee W.M. Gibson J.C. Gordon R.J. Gray P. Igo-Kemenes W.C. Louis T. Modis P. Mühlemann R. Weill 《Physics letters. [Part B]》1982,112(3):265-270
The α parameter for Ξ? → Λπ? decay has been determined to be αΞ?=?0.462 ± 0.015, from a sample of 1.5 × 105 events recorded in the CERN SPS hyperon beam. This value is 2.5 standard deviations higher than the current world average. 相似文献
77.
78.
H.H. Chang B.W. Ridley T.H. Braid T.W. Conlon E.F. Gibson N.S.P. King 《Nuclear Physics A》1978,297(1):105-124
The differential cross sections for the elastic scattering of 3He ions on targets of 40Ca and 58Ni have been measured at incident energies of 27.7, 51.4, 73.2 and 83.5 MeV. The results of optical model analyses showed that only one unique potential (JR ≈ 330 MeV · fm3) with a surface absorptive term can provide acceptable fits to the large angle elastic scattering cross sections at 83.5 MeV. The particular geometrical set found at 83.5 MeV could not, however, give an adequate fit to the data with energy less than 40 MeV. Subsequent analyses indicated that a break in the energy dependence of the real potential is observed for the low energy data. Explicit energy dependent terms were obtained by fitting all the data simultaneously. These phenomenological potentials were also compared with the folded nucleon-nucleus potential. The influence of the α-particle channels on the elastic scattering of 3He ions at 83.5 MeV was also examined. 相似文献
79.
Vogt FG Mattingly SM Gibson JM Mueller KT 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,147(1):26-35
A background-filtered version of the rotational-echo double resonance (REDOR) experiment is demonstrated. The experiment combines a traditional REDOR pulse sequence with a double-cross-polarization (DCP) sequence to select only those signals coming from spin pairs of interest. The relatively inefficient DCP sequence, which transfers polarization from (1)H to (15)N and subsequently to (13)C, is improved by the use of adiabatic passages through the (-1) sideband of the Hartmann-Hahn matching condition. The result is an efficient 2D-REDOR pulse sequence that does not require a reference experiment for removal of background signals. The data produced by the experiment are ideally suited to analysis by newly developed dipolar transform methods, such as the REDOR transform. The relevant features of the experiment are demonstrated on simple labeled amino acids. Relative efficiencies of several other potential filtering methods are also compared. Copyright 2000 Academic Press. 相似文献
80.
Cox AR Gibson VC Marshall EL White AJ Yeldon D 《Dalton transactions (Cambridge, England : 2003)》2006,(42):5014-5023
A series of metal complexes containing potentially tetradentate phenoxyamine ligands is described. The ligands are found to bind to main-group metals and first-row transition-metal centres with variable denticity depending upon the requirements of the particular metal centre. Bidentate [Al(III)], tridentate [Mg(II), Ca(II), Zn(II)] and tetradentate [K(I), Cr(III), Fe(II), Co(II)] binding modes have been established unambiguously through single-crystal X-ray structure determinations. 相似文献