全文获取类型
收费全文 | 219篇 |
免费 | 3篇 |
专业分类
化学 | 136篇 |
晶体学 | 7篇 |
力学 | 12篇 |
数学 | 5篇 |
物理学 | 62篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2020年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 6篇 |
2011年 | 15篇 |
2010年 | 2篇 |
2009年 | 7篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 187 毫秒
81.
The electronic structure of Al2O3 has been studied by electron energy loss spectroscopy (ELS), and an energy level model of both filled and empty states has been constructed from the ELS and available optical data. For the high temperature pyrolytic α-polycrystalline Al2O3 films, the transitions are assumed to originate at the two principal peaks in the valence band density of states and the O(2s) core state, and to terminate on two peaks within the conduction band density of states. We also report energy loss spectra due to excitations out of the deeper Al(2p), Al(2s), Al(1s), and O(1s) core levels. The excitations originating at the Al(2p), Al(2s), and Al(1s) core levels terminate on levels in the conduction band and on an exciton lying about 1 eV below the conduction-band edge. 相似文献
82.
R. A. Poirier R. Daudel P. G. Mezey I. G. Csizmadia 《International journal of quantum chemistry》1982,21(5):799-811
Uniform quality basis sets (UQ-NG ; N=3, 4, 5), with s = p and s ≠ p, and a 6-31 G* basis set have been optimized for the sulfur atom. These uniform quality basis sets in their uncontracted and contracted forms were used, together with other basis sets reported in the literature (a total of 40 basis sets), to study their accuracy in predicting the bond length and bond angle of H2S. 相似文献
83.
84.
85.
We report on the design and characterization of a highly coherent mid-IR source at 3.57mum based on a single-frequency optical parametric oscillator. Detailed frequency and amplitude noise spectra have been measured. The rms intensity noise from 1.2 to 1000 Hz was 0.03%, and a rms frequency drift of 8 kHz in 1 ms was observed. We have also demonstrated the utility of this source for coherent laser radar applications by measuring micro-Doppler spectra from vibrating targets. 相似文献
86.
Bill Poirier 《Foundations of Physics》2001,31(11):1581-1610
In an earlier article [Found. Phys.
30, 1191 (2000)], a quasiclassical phase space approximation for quantum projection operators was presented, whose accuracy increases in the limit of large basis size (projection subspace dimensionality). In a second paper [J. Chem. Phys.
111, 4869 (1999)], this approximation was used to generate a nearly optimal direct-product basis for representing an arbitrary (Cartesian) quantum Hamiltonian, within a given energy range of interest. From a few reduced-dimensional integrals, the method determines the optimal 1D marginal Hamiltonians, whose eigenstates comprise the direct-product basis. In the present paper, this phase space optimized direct-product basis method is generalized to incorporate non-Cartesian coordinate spaces, composed of radii and angles, that arise in molecular applications. Analytical results are presented for certain standard systems, including rigid rotors, and three-body vibrators. 相似文献
87.
Libraries of steroid derivatives with two levels of molecular diversity were prepared to optimize the antiproliferative activity
on leukemia HL-60 cells by first varying the amino acid (AA) at R1 (libraries A, B, C, and D: with 45, 45, 20, and 20 members, respectively) and, subsequently, the capping group at R2 (library E: 168 members). The screening of these aminosteroids revealed interesting structure–activity relationships. In
library A, the compounds bearing a tetrahydroisoquinolone residue as the first element of diversity showed potent cytotoxicity,
principally when isovaleric or cyclohexyl acetic acid was used as a capping group (>40% of cell growth inhibition at 1 μM).
In library B, the phenylalanine (Phe) derivatives bearing a cyano group induced a higher growth inhibition than the other
Phe derivatives. The screening of library C indicated the increase of hydrophobicity of proline (Pro) seems to preserve the
cytotoxic effect achieved by the lead compound. However, the synthesis of structural Pro variants (library D) clearly shows
weaker activities when compared to L-Pro building blocks. Finally, by incorporating some of the most active AA of libraries A–D in library E, we observed that
the amide coupling functionality gave stronger cytotoxic activity compared to the corresponding sulfonamides or benzylamines.
Six of the most active amide derivatives (E-37P, E-41P, E-42P, E-46P, E-48F, and E-12T) were selected and IC50 determined on HL-60 cells as well as on normal human lymphocytes. Among this series of new anticancer agents, good to high
selectivity indices (SI = IC50 (lymphocytes)/IC50 (HL-60 cells) = 5 - 55) were obtained. 相似文献
88.
Yu. M. Chumakov P. A. Petrenko T. B. Codita V. I. Tsapkov D. Poirier A. P. Gulea 《Crystallography Reports》2014,59(2):207-212
5-Bromo-2-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, and 2-hydroxynaphthalene-1-carbaldehyde 4-(2-pyridyl) thiosemicarbazones (I–III, respectively) were synthesized and their crystal structures were determined by X-ray diffraction. All these molecules are almost planar. The presence of bulky substituents at the terminal nitrogen atoms of these molecules does not lead to changes in the conformation of the thiosemicarbazide moiety. Depending on the nature of substituents in the phenol rings, the crystals are composed of either centrosymmetric dimers (I) or infinite chains (II and III). In the concentration range of 10?5–10?7 mol/L, thiosemicarbazones I–III selectively inhibit the growth of human myeloid leukemia HL60 cells. 相似文献
89.
Michel Maguet Yves Poirier Francis Garnier Robert Guglielmetti 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):193-194
Abstract The acid catalyzed rate for hydrolysis of methylphosponfluoridic acid has been determined at several hydrogen ion concentrations and temperatures. The acid hydrolysis is second order (in acid and substrate). Assumed rate expressions, observed rate constants, and hydrogen ion concentrations were used to calculate the thermodynamic equilibrium constant (K a=0.56) and rate constants for acid catalysis. The activation energy E a has been determined as 18.3 Kcal/mole. Finally, the acid catalyzed deuterolysis was determined to be about 1.47 times the rate of hydrolysis. The data suggest a two-step mechanism consisting of a rapid proton transfer, followed by slow hydration of the protonated complex. 相似文献
90.
E. Pahontu A. P. Gulea D. Poirier V. I. Tsapkov 《Russian Journal of General Chemistry》2014,84(9):1767-1770
o-Phenylenediamine reacts with 2-formyl-, 2-acetyl-, or 2-benzoylpyridine in ethanol in the presence of cobalt, nickel, copper, or zinc chlorides to form monomeric complexes ML1–3Cl2·nH2O {M = Co, Ni, Cu, Zn; L1 = N 1,N 2-bis(pyridin-2-ymethylidene)benzene-1,2-diamine, L2 = N 1,N 2-bis(pyridin-2-ylethylidene) benzene-1,2-diamine, L3 = N 1,N 2-bis[phenyl(pyridin-2-yl)methylidene]benzene-1,2-diamine; n = 0–3}. The condensation products (L1–L3) act in the complexes as tetradentate N,N,N,N-ligands. Thermolysis of the complexes occurs in two stages: dehydration (70–95°C) and complete degradation (320–450°C). At concentrations of 10?5–10?7 M, the complexes inhibit in vitro growth and proliferation of HL-60 human promyelocytic leukemia cells. 相似文献