全文获取类型
收费全文 | 335篇 |
免费 | 8篇 |
专业分类
化学 | 203篇 |
晶体学 | 5篇 |
力学 | 9篇 |
数学 | 39篇 |
物理学 | 87篇 |
出版年
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 27篇 |
2011年 | 25篇 |
2010年 | 21篇 |
2009年 | 15篇 |
2008年 | 18篇 |
2007年 | 19篇 |
2006年 | 20篇 |
2005年 | 9篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有343条查询结果,搜索用时 31 毫秒
101.
Yue-Ping Xiong Haruo Kishimoto Katsuhiko YamajiMasashi Yoshinaga Teruhisa HoritaManuel E. Brito Harumi Yokokawa 《Solid State Ionics》2011,192(1):476-479
The electronic conductivity of pure ceria with two different impurity levels is examined by dc polarization technique based on the Hebb-Wagner ion blocking method. The impurity level for the ceria with 99.999% purity (5N-CeO2) is about 1/100 of that with 99.9% purity (3N-CeO2) as confirmed by the fluorescence intensity of impurities obtained by Raman spectroscopy. The electronic conductivity for the 5N-CeO2 was measured at T = 973 K to 1173 K, and the results are essentially the same as those for the 3N-CeO2. The electronic conductivity increases with decreasing of P(O2) following slope values of − 1/4 to − 1/6. The − 1/4 dependent region becomes narrower for the 5N-CeO2 than that for the 3N-CeO2. For both types of ceria, the P(O2) independent region appears in the same region of higher than 10− 2 and 10− 3 MPa at T = 1073 K and 973 K, respectively. Activation energies for the 5N-CeO2 were 2.2 eV, 2.6 eV and 1.9 eV in P(O2) dependent regions of − 1/6, − 1/4 and 0, respectively. 相似文献
102.
This paper deals with solutions of the nonlinear Boltzmann equation for spatially uniform freely cooling inelastic Maxwell models for large times and for large velocities, and the nonuniform convergence to these limits. We demonstrate how the velocity distribution approaches in the scaling limit to a similarity solution with a power law tail for general classes of initial conditions and derive a transcendental equation from which the exponents in the tails can be calculated. Moreover on the basis of the available analytic and numerical results for inelastic hard spheres and inelastic Maxwell models we formulate a conjecture on the approach of the velocity distribution function to a scaling form. 相似文献
103.
In this paper we show how, under certain restrictions, the hydrodynamic equations for the freely evolving granular fluid fit within the framework of the time dependent Landau–Ginzburg (LG) models for critical and unstable fluids. The granular fluid, which is usually modeled as a fluid of inelastic hard spheres (IHS), exhibits two instabilities: the spontaneous formation of vortices and of high density clusters. We suppress the clustering instability by imposing constraints on the system sizes, in order to illustrate how LG-equations can be derived for the order parameter, being the rate of deformation or shear rate tensor, which controls the formation of vortex patterns. From the shape of the energy functional we obtain the stationary patterns in the flow field. Quantitative predictions of this theory for the stationary states agree well with molecular dynamics simulations of a fluid of inelastic hard disks. 相似文献
104.
105.
C. H. Brito Cruz H. L Fragnito R. Francalacci M. A. F. Scarparo Ramakant Srivastava 《Optical and Quantum Electronics》1983,15(6):487-496
We use a rate equation model to analyse a technique for the generation of picosecond duration laser pulses in argon pumped dye lasers. The system is based on passive mode-locking of the Ar+ laser by saturable absorption of the dye which is inserted in the Ar+ laser cavity. Simultaneously, the dye is forced to oscillate in a regime of synchronously pumped mode-locking. The system is relatively simple, does not require the use of an acousto-optical light modulator and can be easily implemented in commercially available lasers. Pulses shorter than 100 ps and having an average power of 20 mW were obtained at a repetition rate of 110 MHz. Good agreement between the model and experimental results was also obtained. 相似文献
106.
107.
Marques EF Brito RO Silva SG Rodríguez-Borges JE do Vale ML Gomes P Araújo MJ Söderman O 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):11009-11017
The use of amino acids for the synthesis of novel surfactants with vesicle-forming properties potentially enhances the biocompatibility levels needed for a viable alternative to conventional lipid vesicles. In this work, the formation and characterization of catanionic vesicles by newly synthesized lysine- and serine-derived surfactants have been investigated by means of phase behavior mapping and PFG-NMR diffusometry and cryo-TEM methods. The lysine-derived surfactants are double-chained anionic molecules bearing a pseudogemini configuration, whereas the serine-derived amphiphile is cationic and single-chained. Vesicles form in the cationic-rich side for narrow mixing ratios of the two amphiphiles. Two pairs of systems were studied: one symmetric with equal chain lengths, 2C12/C12, and the other highly asymmetric with 2C8/C16 chains, where the serine-based surfactant has the longest chain. Different mechanisms of the vesicle-to-micelle transition were found, depending on symmetry: the 2C12/C12 system entails limited micellar growth and intermediate phase separation, whereas the 2C8/C16 system shows a continuous transition involving large wormlike micelles. The results are interpreted on the basis of currently available models for the micelle-vesicle transitions and the stabilization of catanionic vesicles (energy of curvature vs mixing entropy). 相似文献
108.
Cluster emission and chemical reactions in oxygen and nitrogen ices induced by fast heavy-ion impact
Ponciano CR Martinez R Farenzena LS Iza P Homem MG Naves de Brito A Wien K da Silveira EF 《Journal of mass spectrometry : JMS》2008,43(11):1521-1530
Two ices, O2 and a mixture of O2 and N2, are bombarded by 252Cf fission fragments (FF) (approximately 65 MeV at target surface); the emitted positive and negative secondary ions are analyzed by time-of-flight mass spectrometry (TOF-SIMS). These studies shall enlighten sputtering from planetary and interstellar ices. Three temperature regions in the 28-42-K range are analyzed: (1) before N2 sublimation, in which hybrid chemical species are formed, (2) before O2 sublimation, in which the TOF mass spectrum is dominated by low-mass (O2)p cluster ions and (3) after O2 sublimation, in which (N2)p or (O2)p cluster ions are practically inexistent. In the first region, four hybrid ion series are observed: NOn-1+, N2On-2(+/-), and N4On-4(-). In the second region, two positive and negative ion series are identified: (O2)pO(+/-) and (O2)pO2(+/-). Their yield distributions are fitted by the sum of two decreasing exponentials, whose decay constants are the same for all series. It is observed that the cluster ion desorption from solid oxygen is very similar to that of other frozen gases, but its yield distribution oscillates with a three- or six-atom periodicity, suggesting O3 or 3O2 units in the cluster structure, respectively. 相似文献
109.
Le Guen K Miron C Céolin D Guillemin R Leclercq N Simon M Morin P Mocellin A Björneholm O Naves de Brito A Sorensen SL 《The Journal of chemical physics》2007,127(11):114315
We have studied the ultrafast dissociation of the H2S molecule upon S 2p3/2-->6a1 inner-shell excitation by combining high-resolution resonant Auger spectroscopy and energy-selected Auger electron-ion coincidence measurements. Auger final states have been correlated to the different fragmentation pathways (S+, HS+, and H2S+ ions). As an original result, we evidence a three-step mechanism to describe the resonant production of S+: the Auger recombination in the HS* fragment is followed for the A 3Pi and c 1Pi states by the S++H fragmentation mechanism. 相似文献
110.
Rodrigues CM Rinaldo D dos Santos LC Montoro P Piacente S Pizza C Hiruma-Lima CA Brito AR Vilegas W 《Rapid communications in mass spectrometry : RCM》2007,21(12):1907-1914
Direct flow injection electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS) was used to investigate the polyphenolic compounds present in an infusion from the barks of Hancornia speciosa Gom. (Apocynaceae), a native Brazilian plant popularly known as 'mangabeira', used as a source of nutrition and against gastric disorders. After a simple sample filtration pretreatment the characteristic fingerprint of the infusion was performed in negative ion ESI mode in a few minutes. At low capillary-voltage activation, the deprotonated molecules ([M--H]-) were observed and using collision-induced dissociation the product ion spectra showed the presence of a homologous series of B-type proanthocyanidins, as well as another series containing their respective C-glycosylated derivatives, with a degree of polymerization from 1 up to 6 units of interlinked catechins. Therefore, direct flow injection allowed us to identify the key compounds without preparative isolation of the components. 相似文献