全文获取类型
收费全文 | 645篇 |
免费 | 19篇 |
国内免费 | 6篇 |
专业分类
化学 | 330篇 |
晶体学 | 1篇 |
力学 | 35篇 |
数学 | 111篇 |
物理学 | 193篇 |
出版年
2022年 | 3篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 19篇 |
2013年 | 27篇 |
2012年 | 33篇 |
2011年 | 40篇 |
2010年 | 24篇 |
2009年 | 17篇 |
2008年 | 38篇 |
2007年 | 25篇 |
2006年 | 38篇 |
2005年 | 36篇 |
2004年 | 22篇 |
2003年 | 24篇 |
2002年 | 20篇 |
2001年 | 11篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1965年 | 4篇 |
1940年 | 2篇 |
1880年 | 2篇 |
排序方式: 共有670条查询结果,搜索用时 31 毫秒
21.
The influence of a partially filled conduction band on the magnetic properties of ferromagnetic semiconductors is studied within the framework of thes-f model. Allowing for magnon scattering to arbitrary order in the form of virtual electron- holecreation the magnon spectral density is derived, from which one gets magnon energies which are substantially renormalized by the presence of conduction electrons. In particular it is shown how the quasiparticle structure of the electronic excitation energies [4, 5] leads to scattering corrections in the magnon spectrum. These corrections are always negative and reduce the positive mean field part, which is proportional to the electron densityn. The calculated magnon spectrum is then used to determine the strikingn-dependence of the Curie-temperatureT
c
of Gd-doped EuO and EuS. 相似文献
22.
Preben C. Mrk John Ugelstad Jan Ole Aasen 《Journal of polymer science. Part A, Polymer chemistry》1995,33(11):1759-1765
Expressions for calculating the stationary state distribution of radicals in compartmentalized systems with a constant number of reaction loci containing an oil-soluble initiator are given. Besides pairwise formation of radicals in the particles, desorption and reabsorption, water phase termination, solubility of the initiator in the aqueous phase, and the possibility of formation of a single radical species are taken into consideration. The calculation is based on a probabilistic analysis leading to a third-order recurrence relation solved using confluent, hypergeometric Kummer functions. Some calculated curves illustrating the de-pendence of the average number of radicals per particle on various relevant parameters are included. © 1995 John Wiley & Sons, Inc. 相似文献
23.
Using Brion, Moser and Yamazaki's SCF LCAO MO the spin orbit splitting of the X
2
state of NO has been calculated using various potentials. Experimentally W (2
3/2) –W (2
1/2) is known to be 122 cm–1. Using an unscreened nuclear field we find a value of 328 cm–1. Inclusion of screening due to electronic repulsions reduces this value to 283 cm–1. Agreement with the experimental value may be obtained by reducing the orbital exponents in the 2 molecular orbital by 30% over the value given by Slater's rules.
Zusammenfassung Die Spin-Bahn-Aufspaltung des X 2 -Zustandes von NO wurde mit verschiedenen Potentialen unter Verwendung der SCF LCAO MOs von Brion, Moser und Yamazaki berechnet. Der experimentelle Wert für W (2 3/2) –W (2 1/2) beträgt 122 cm–1. Die Rechnung mittels eines reinen Kernfeldes liefert den Wert 328 cm–1 und unter Einschluß der Abschirmung durch die Elektronen 283 cm–1. Übereinstimmung mit dem experimentellen Wert läßt sich erzielen, wenn man den Exponenten des 2-Zustandes 30% kleiner als nach den Slater Regeln macht.
Résumé Avec les orbitals moléculaires SCF LCAO de Brion, Moses et Yamazaki, nous avons calculé le dédoublement spin-orbitale de l'état X 2 de NO. La valeur expérimentale W (2 3/2) –W (2 1/2) est 122 cm–1. Dans un champ nucléaire «sans écran» on trouve 328 cm–1. L'inclu-sion de l'effet d'écran dû aux répulsions interélectroniques réduit cette valeur à 283 cm–1. La valeur expérimentale s'obtient, si l'on réduit de 30% les exposants d'après Slater dans l'orbi-tale moléculaire 2.相似文献
24.
Ole J. Nielsen Matthew S. Johnson Timothy J. Wallington Lene K. Christensen Jesper Platz 《国际化学动力学杂志》2002,34(5):283-291
Pulse radiolysis techniques were used to measure the gas phase UV absorption spectra of the title peroxy radicals over the range 215–340 nm. By scaling to σ(CH3O2)240 nm = (4.24 ± 0.27) × 10?18, the following absorption cross sections were determined: σ(HO2)240 nm = 1.29 ± 0.16, σ(C2H5O2)240 nm = 4.71 ± 0.45, σ(CH3C(O)CH2O2)240 nm = 2.03 ± 0.22, σ(CH3C(O)CH2O2)230 nm = 2.94 ± 0.29, and σ(CH3C(O)CH2O2)310 nm = 1.31 ± 0.15 (base e, units of 10?18 cm2 molecule?1). To support the UV measurements, FTIR‐smog chamber techniques were employed to investigate the reaction of F and Cl atoms with acetone. The F atom reaction proceeds via two channels: the major channel (92% ± 3%) gives CH3C(O)CH2 radicals and HF, while the minor channel (8% ± 1%) gives CH3 radicals and CH3C(O)F. The majority (>97%) of the Cl atom reaction proceeds via H atom abstraction to give CH3C(O)CH2 radicals. The results are discussed with respect to the literature data concerning the UV absorption spectra of CH3C(O)CH2O2 and other peroxy radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 283–291, 2002 相似文献
25.
Rate constants for the reactions of OH radicals and Cl atoms with CH3ONO, C2H5ONO, n-C3H7ONO, n-C4H9ONO, and n-C5H11ONO have been determined at 298 ± 2 K and a total pressure of approximately 1 atm. The OH rate data were obtained using both the absolute rate technique of pulse radiolysis combined with kinetic spectroscopy and a relative rate method involving simultaneous measurement of the loss of the nitrite and the reference compound. The Cl rate constants were measured using the relative rate method. Values of the rate constants in units of 10?13 cm3 molecule?1 s?1 are:
When compared to rate data for the corresponding alkanes the results show that the -ONO group decreases the rate constant for H atom abstraction by the OH radical from groups bonded to the -ONO group and also decreases that for groups in the β position. Similar results were found for the reaction of Cl atoms with these compounds. The results are discussed in terms of reactivity trends. 相似文献
Relative Cl | Relative OH | Absolute OH | |
---|---|---|---|
CH3ONO | 94.4 ± 7.4 | 3.0 ± 1.0 | 2.6 ± 0.5 |
C2H5ONO | 295 ± 13 | 7.0 ± 1.5 | 7.0 ?1.1 |
n-C3H7ONO | 646 ± 58 | 11.0 ± 1.5 | 12.0 ± 0.5 |
n-C4H9ONO | 1370 ± 58 | 22.7 ± 0.8 | 27.2 ± 6.0 |
n-C5H11ONO | 2464 ± 444 | 37.4 ± 5.0 | 42.5 ± 8.0 |
26.
Hanne?Heiberg Odd?GropenEmail author Jon K.?Laerdahl Ole?Swang Ulf?Wahlgren 《Theoretical chemistry accounts》2003,110(3):118-125
Different density functional theory (DFT) functionals have been evaluated by studying geometries and bond strengths of YbH, YbF, EuF, GdF, and NdF and compared with accurate CCSD(T) results and, when available, experiment. The agreement between the CCSD(T) results and experiment, when available, is good. The agreement is also good between bond strengths calculated at the DFT level using relativistic effective core potentials and the CCSD(T) results. However, the all-electron ADF calculations systematically overestimate binding energies. The geometries obtained by both the all-electron and the effective-core-potential-based DFT calculations are generally in good agreement with the CCSD(T) results.Contribution to the Björn Roos Honorary Issue 相似文献
27.
The structure of 5-hydroxy-trans-2, trans-4-pentadienal acetate has been determined, using three-dimensional diffractometercollected X-ray data. The compound has the all-trans configuration with the atoms C-1 to C-5 in a plane. The charge distribution in the acetate and in the glutacondialdehyde anion have been calculated using the CNDO/2 approximation. In both compounds higher negative charges were found on carbon atoms C-2 and C-4 than on C-1, C-3 and C-5. 相似文献
28.
Robert Pendrill Ole W. Sørensen Göran Widmalm 《Magnetic resonance in chemistry : MRC》2014,52(3):82-86
Site‐specific 13C isotope labeling is a useful approach that allows for the measurement of homonuclear 13C,13C coupling constants. For three site‐specifically labeled oligosaccharides, it is demonstrated that using the J‐HMBC experiment for measuring heteronuclear long‐range coupling constants is problematical for the carbons adjacent to the spin label. By incorporating either a selective inversion pulse or a constant‐time element in the pulse sequence, the interference from one‐bond 13C,13C scalar couplings is suppressed, allowing the coupling constants of interest to be measured without complications. Experimental spectra are compared with spectra of a nonlabeled compound as well as with simulated spectra. The work extends the use of the J‐HMBC experiments to site‐specifically labeled molecules, thereby increasing the number of coupling constants that can be obtained from a single preparation of a molecule. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
29.
Computer-generated binary holograms are written on a polished copper surface using single 800-nm, 120-fs pulses from a 1-kHz-repetition-rate laser system. The hologram efficiency (i.e. the power in the holographic reconstructed image relative to the incoming laser power) is investigated for different laser-structuring parameters. Theoretical diffraction grating efficiencies for a binary amplitude grating show good agreement with the experimental measurements for diameters of the laser-formed holes below the pitch. Modelling based on straightforward geometrical arguments is used to find the optimal hole size. For a coverage (i.e. relative laser-structured area) of ~43 %, the efficiency reaches ~10 %, which corresponds to a relative power transferred to one reconstructed image of ~20 %. The efficiency as a function of pitch (for fixed coverage) is fairly constant from 2 to 6 μm. 相似文献