全文获取类型
收费全文 | 931篇 |
免费 | 31篇 |
国内免费 | 2篇 |
专业分类
化学 | 646篇 |
晶体学 | 7篇 |
力学 | 21篇 |
数学 | 153篇 |
物理学 | 137篇 |
出版年
2023年 | 7篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 16篇 |
2015年 | 19篇 |
2014年 | 12篇 |
2013年 | 36篇 |
2012年 | 42篇 |
2011年 | 45篇 |
2010年 | 25篇 |
2009年 | 26篇 |
2008年 | 50篇 |
2007年 | 42篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 41篇 |
2003年 | 33篇 |
2002年 | 37篇 |
2001年 | 22篇 |
2000年 | 25篇 |
1999年 | 14篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 21篇 |
1993年 | 11篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 8篇 |
1975年 | 12篇 |
1974年 | 14篇 |
1970年 | 5篇 |
排序方式: 共有964条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
ENDOR measurements on the19F? nuclei in the first four shells of KZnF3 containing Dy3+ ions in the cubic site are reported. The values and signs of the hyperfine and transferred hyperfine interaction parameters are determined. The local deformation of the crystal lattice in the vicinity of the impurity ion is estimated. The theoretical analysis of the THFI parameters for the first coordination shell of the F? ions has been carried out. For the Dy3+ ion the influence of spin polarization of the closed 5s and 5p shells is considered for the first time. Spin polarization is shown to play a significant role in the mechanisms of rare-earth ion-ligand coupling. 相似文献
105.
Summary Dynamic secondary ion mass spectrometry (DSIMS) investigations have been carried out with Cr, Mn, Fe, Co, Mo, Rh, W, Re, Os and Ir under 4 mPa N2O, NO and 3 mPa NO2 as reactant gases. Results indicate similar behaviour in adsorption for Cr, Mn, Fe, Mo, W on the one hand and for Co, Rh, Os and Ir on the other. For the first group of metals the nitrogen oxide molecules are always totally destroyed in adsorption whereas the second group shows evidence for surface compounds such as MeNO (Me=metal) indicating only a partial dissociation in the case of N2O and NO2, and molecular adsorption under NO respectively. Re does not belong uniquely to either group because it reacts with N2O and NO2 dissociatively whereas under NO only partial dissociation is observed.Abbreviations SIMS
Secondary ion mass spectrometry
- SSIMS
Static SIMS
- AES
Auger electron spectroscopy
- EELS
Electron energy-loss spectroscopy
- LEED
Low energy electron diffraction
- TDS
Thermal desorption spectroscopy
- XPS, UPS
X-ray/Ultraviolet photoelectron spectroscopy 相似文献
106.
By Petersen's theorem, a bridgeless cubic multigraph has a 2-factor. Fleischner generalised this result to bridgeless multigraphs of minimum degree at least three by showing that every such multigraph has a spanning even subgraph. Our main result is that every bridgeless simple graph with minimum degree at least three has a spanning even subgraph in which every component has at least four vertices. We deduce that if G is a simple bridgeless graph with n vertices and minimum degree at least three, then its line graph has a 2-factor with at most max{1,(3n-4)/10} components. This upper bound is best possible. 相似文献
107.
The chromatic polynomial PG(q) of a loopless graph G is known to be non-zero (with explicitly known sign) on the intervals (−∞,0), (0,1) and (1,32/27]. Analogous theorems hold for the flow polynomial of bridgeless graphs and for the characteristic polynomial of loopless matroids. Here we exhibit all these results as special cases of more general theorems on real zero-free regions of the multivariate Tutte polynomial ZG(q,v). The proofs are quite simple, and employ deletion–contraction together with parallel and series reduction. In particular, they shed light on the origin of the curious number 32/27. 相似文献
108.
Mark W. Beach Nelson G. Rondan Bruce B. Gerhart Bill G. Stobby Vladimir M. Shvartsberg 《Polymer Degradation and Stability》2008,93(9):1664-1673
Experimental methods as well as thermodynamic modeling techniques were utilized to explore potential gas and condensed-phase contributions of various flame retardant (FR) additives with polystyrene polymer. FR additives investigated include hexabromocyclododecane (HBCD), triphenyl phosphine oxide (TPPO), triphenyl phosphate (TPP), triphenyl phosphine sulfide (TPPS), and sulfur. Flame studies of fundamental FR activity were also employed using molecular beam mass spectrometry analysis of FR active species directly in a flame system. The flame studies show direct evidence for active bromine (HBr, Br) species for HBCD and active phosphorous species (HPO2, PO, PO2 HPO3) species for TPPO and TPP which provide high potential for gas-phase activity for these FR additives. Various experimental measurements were also done to assess the degradation species and the degree of degradation of polystyrene by the FR additives. These studies support enhanced degradation of the base polystyrene polymer by the FR additive as a major pathway for condensed FR activity for HBCD and sulfur FR additives. Phosphorous based structures appear to show little enhancement of polystyrene degradation. 相似文献
109.
The system of orthophosphate, magnesium and hydrogen ions in aqueous solution at 25 degrees and I = 0.2M chloride has been characterized by means of glass-electrode potentiometry. Protonation constants for orthophosphate species and formation constants for the complexes MgH(2)PO(+)(4), MgHPO(4), MgPO(4)(-) and MgOH(+) are reported. 相似文献
110.
E. Bill X. Q. Ding C. Haas H. Winkler A. X. Trautwein M. Zeppezauer 《Hyperfine Interactions》1988,42(1-4):877-880
The electronic structure of Fe(II) substituting Zn in Horse Liver Alcohol Dehydrogenase was investigated by Mössbauer spectroscopy at various temperatures and applied magnetic fields and by spin Hamiltonian analysis of the results. The novelty we found, is an unusually weak spin coupling of Fe(II) with a diradical (S=1). From ESR results and biochemical findings we conclude, that the corresponding chemical species is triplet oxygen (O2). Oxidation experiments, followed by Mössbauer spectroscopy, show that the spin-coupled species is an outer-sphere Fe(II)… O2 complex occuring as an intermediate of the dioxygen activation reaction, catalysed by Fe(II). A second Fe(II)?O2 complex could be detected, which corresponds to an inner-sphere complex with O2 directly bound to iron. The spin hamiltonian parameters in the coupled system describing the electronic properties of iron are presented. The results are compared with those of iron in other nonheme iron proteins. 相似文献