全文获取类型
收费全文 | 467篇 |
免费 | 7篇 |
专业分类
化学 | 306篇 |
晶体学 | 4篇 |
力学 | 8篇 |
数学 | 23篇 |
物理学 | 133篇 |
出版年
2023年 | 3篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 11篇 |
2014年 | 10篇 |
2013年 | 22篇 |
2012年 | 26篇 |
2011年 | 28篇 |
2010年 | 20篇 |
2009年 | 13篇 |
2008年 | 34篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 32篇 |
2004年 | 19篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 2篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1993年 | 7篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 5篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1961年 | 2篇 |
1928年 | 2篇 |
排序方式: 共有474条查询结果,搜索用时 31 毫秒
71.
Abécassis B Testard F Arleth L Hansen S Grillo I Zemb T 《Langmuir : the ACS journal of surfaces and colloids》2007,23(20):9983-9989
By means of small-angle neutron scattering and conductivity measurements, we study the microstructure of octylammoniumoctanoate/octane/water catanionic reverse microemulsions with an excess of anionic or cationic surfactant. Increasing the surface charge makes the microemulsion able to incorporate much more water than in the neutral case, up to 10 water molecules per surfactant. Even with charges in the surfactant film, wormlike micelles are present in the microemulsion domain. Along water dilution lines, the classical rod-to-sphere transition due to the minimization of the curvature energy of the rigid surfactant film is observed. When temperature is decreased, a re-entrant phase transition associated with the liquid-gas equilibrium of attractive cylinders is observed. Using the framework of the Tlusty-Safran theory, attraction could originate from junctions between wormlike reverse micelles. In any case, the spontaneous curvature of the catanionic surfactant film depends on both the temperature and the net charge, whatever the sign of the latter. 相似文献
72.
Resumé Le problème auquel on s'intéresse consiste à détecter parmi les formes réduites à l'origine deC
2 celles qui possèdent des intégrales premières liouvilliennes ou appartenant à la classe de Nilsson. Pour cela, on étudie l'espace des modules associé à une telle forme. 相似文献
73.
G. Chaboussant M. -H. Julien Y. Fagot-Revurat H. Mayaffre M. Horvati L. P. Lvy C. Berthier O. Piovesana 《Physica B: Condensed Matter》2000,280(1-4):315-316
CHCupCl is a two-leg spin-ladder where the Cu++ ions
are coupled by superexchange. Its magnetic properties change dramatically as a function of a magnetic field. Below the critical field Hc1, there is a singlet ground state separated from the triplet excited state by an energy gap. Between Hc1 and Hc2, several magnetic phases have been observed. Above 1 K, dynamical studies reveal a disordered quantum critical phase. At lower temperatures, a 3-D ordered phase has been observed in specific heat and NMR studies. New NMR results on the 3D-ordered and quantum critical phases are presented in this short report. 相似文献
74.
75.
76.
Vijay Singh R.P.S. Chakradhar Isabelle Ledoux-Rak Laurent Badie Fabienne Pelle Svetlana Ivanova 《Journal of luminescence》2009,129(11):1375-1380
New near-infrared luminescent, monoclinic CaAl2O4:Er3+ phosphor was prepared by using the combustion route at furnace temperatures as low as 500 °C in a few minutes. Combustion synthesized phosphor has been well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX) mapping studies. The luminescence spectra of Er3+-doped calcium aluminate were studied at UV (380 nm), vis (488 nm) and IR (980 nm) excitation. Upon UV and vis excitation, the CaAl2O4:Er3+ phosphor exhibits emission bands at ~523 nm and at ~547 nm, corresponding to transitions from the 2H11/2 and 4S3/2 erbium levels to the 4I15/2 ground state. A strong luminescence at 1.55 μm in the infrared (IR) region due to 4I13/2→4I15/2 transition has been observed in CaAl2O4:Er3+ phosphor upon 980 nm CW pumping. In the spectrum of IR-excited up-conversion luminescence, green (~523 and ~547 nm) and red (662 nm) luminescence bands were present, the latter associated with the 4F9/2→4I15/2 transitions of Er3+ ions. Both excited state absorption and energy transfer may be proposed as processes responsible for the population of the 4S3/2 and 4F9/2 erbium levels upon IR excitation. The mechanisms responsible for the up-conversion luminescence are discussed. 相似文献
77.
Loffreda D Delbecq F Vigné F Sautet P 《Journal of the American Chemical Society》2006,128(4):1316-1323
The usual empirical rule stating that the C=C bond is more reactive than the C=O group for catalytic hydrogenations of unsaturated aldehydes is invalidated from the present study. Density functional theory calculations of all the competitive hydrogenation routes of acrolein on Pt(111) reveals conversely that the attack at the C=O bond is systematically favored. The explanation of such catalytic behavior is the existence of metastable precursor states for the O-H bond formation showing that the attack at the oxygen atom follows a new preferential mechanism where the C=O moiety is not directly bonded with the Pt surface atoms, hence yielding an intermediate pathway between Langmuir-Hinshelwood and Rideal-Eley general types of mechanisms. When the whole catalytic cycle is considered, our results reconcile with experimental studies devoted to hydrogenation of acrolein on Pt, since the desorption step of the partially hydrogenated product (unsaturated alcohol versus saturated aldehyde) plays a key role for the selectivity. 相似文献
78.
Hoffmann-Emery F Hilpert H Scalone M Waldmeier P 《The Journal of organic chemistry》2006,71(5):2000-2008
A new efficient synthesis of two novel classes of NK1 receptor antagonists, among them befetupitant and netupitant, starting from 6-chloronicotinic acid is described. The introduction of the o-tolyl substituent at C4 of the pyridine ring was achieved by a one-pot selective 1,4-Grignard addition/oxidation sequence to 6-chloronicotinic acid or a derivative of it. The scope of this addition/oxidation sequence was examined. It was also shown that the carboxylic function can be converted to a methyl amino group by a Hofmann rearrangement followed by reduction. Furthermore, a new high-yielding synthesis of 2-(3,5-bistrifluoromethylphenyl)-2-methyl propionic acid based on the carbonylation of the tertiary alcohol obtained by Grignard addition of 3,5-bis(trifluoromethyl)bromobenzene to acetone was established. 相似文献
79.
Dimur C Pauzat F Ellinger Y Berthier G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(4):859-873
This paper looks at the possibility of astronomical detection of molecules of prebiotic interest containing phosphorus. Attention has been focused on the most stable species that can be formed with the four [C,H,O,P] atoms. Ab initio coupled cluster molecular orbital methods and density functional theory have been used. It is found that the best candidate for detection is singlet HPCO (corresponding to singlet HNCO), which lies 23.5 kcal/mol lower than the next isomer (HOCP) and has a non-negligible dipole moment of 0.8 D. Theoretical rotational constants and infrared (IR) spectra have been determined for HPCO and the closely related HPCS. By correcting the known inadequacies in the calculations with the average theoretical to experimental ratio from two benchmark molecules (HOCO+ and HNCO), it is possible to obtain rotational constants and IR frequencies of considerably higher accuracy. The corrected values of B = 5.5322 GHz and C = 5.4071 GHz for HPCO, and B = 3.0416 GHz and C = 3.0014 GHz for HPCS should be accurate to within a few tenths of a percent. It can also be predicted that only the 2000 cm(-1) (HPCO) and 1400 cm(-1) (HPCS) IR bands have sufficient intensity to be searched in the low-abundance conditions prevailing in space. 相似文献
80.
Tjasa Vrlinic Dominique Debarnot Gilbert Legeay Arnaud Coudreuse Benaissa El Moualij Willy Zorzi Armand Perret‐Liaudet Isabelle Quadrio Miran Mozetic Fabienne Poncin‐Epaillard 《Macromolecular bioscience》2012,12(6):830-839
New non‐fouling tubes are developed and their influence on the adhesion of neuroproteins is studied. Recombinant prion proteins are considered as a single component representative of hydrophobic proteins. Samples are stored for 24 h at 4 °C in tubes coated with two different coatings: poly(N‐isopropylacrylamide) as a hydrophilic surface and a plasma‐fluorinated coating as a hydrophobic one. The protein adhesion is monitored by ELISA tests, XPS and confocal microscopy. It appears that the highest recovery of recombinant prion protein in the liquid phase is obtained with the hydrophilic surface while the hydrophobic character of the storage tube induces an important amount of biological loss. However, the recovery is not complete even for tubes coated with poly(N‐isopropylacrylamide).