全文获取类型
收费全文 | 633篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
化学 | 306篇 |
晶体学 | 11篇 |
力学 | 60篇 |
数学 | 47篇 |
物理学 | 221篇 |
出版年
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 14篇 |
2013年 | 19篇 |
2012年 | 29篇 |
2011年 | 44篇 |
2010年 | 15篇 |
2009年 | 24篇 |
2008年 | 44篇 |
2007年 | 30篇 |
2006年 | 23篇 |
2005年 | 36篇 |
2004年 | 18篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 12篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 18篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1971年 | 2篇 |
1922年 | 2篇 |
1906年 | 2篇 |
1882年 | 2篇 |
排序方式: 共有645条查询结果,搜索用时 406 毫秒
121.
This paper describes flow around a pair of cylinders in tandem arrangement with a downstream cylinder being fixed or forced to oscillate transversely. A sinusoidal parietal velocity is applied to simulate cylinder oscillation. Time-dependent Navier-Stokes equations are solved using finite element method. It is shown that there exist two distinct flow regimes: ‘vortex suppression regime’ and ‘vortex formation regime’. Averaged vortex lengths between the two cylinders, pressure variations at back and front stagnant points as well as circumferential pressure profiles of the downstream cylinder are found completely different in the two regimes and, thus, can be used to identify the flow regimes. It is shown that frequency selection in the wake of the oscillating cylinder is a result of non-linear interaction among vortex wakes upstream and downstream of the second cylinder and its forced oscillation. Increasing cylinder spacing results in a stronger oscillatory incident flow upstream of the second cylinder and, thus, a smaller synchronization zone. 相似文献
122.
We present numerical results on the distribution of forces in the central-force percolation model at threshold in two dimensions. We conjecture a relation between the multifractal spectrum of scalar and vector percolation that we test for central-foce percolation. This relation is in excellent agreement with our numerical data. 相似文献
123.
124.
Nicolas DesroyRémi Le Roux Phannarath PhansavathLucia Chiummiento Carlo Bonini Jean-Pierre Genêt 《Tetrahedron letters》2003,44(9):1763-1766
The stereocontrolled synthesis of a C15C24 fragment of dolabelides is reported. The C19 and C21 hydroxyl-bearing stereocenters were installed using ruthenium-mediated asymmetric hydrogenations of cyclic hemiketal 4 and β-keto ester 7. The C25C30 portion of dolabelides was prepared as well by ring opening of chiral epoxy alcohol 12 to set up the C27 stereogenic center. 相似文献
125.
Abboud JL Castaño O Dávalos JZ Jiménez P Gomperts R Müller P Roux MV 《The Journal of organic chemistry》2002,67(4):1057-1060
The standard enthalpy of formation of gaseous 2-adamantyl chloride(2-Ad-Cl) was determined by calorimetric techniques. The standard Gibbs energy change for the chloride anion exchange between 1-adamantyl (1-Ad+) and 2-adamantyl (2-Ad+) cations in the gas phase was obtained by Fourier transform ion cyclotron resonance spectroscopy (FT ICR). Theoretical calculations at the G2(MP2) level were performed on these and other relevant species. This and data from the literature provided three highly consistent independent estimates of the relative stabilities of 2-Ad+ and 1-Ad+. This difference in gas-phase stability was compared to the differential structural effects on the rates of solvolysis of the corresponding chlorides and tosylates, and it was shown that the thermodynamic stability of the secondary cation is the leading factor determining the solvolytic reactivity of the precursors in the absence of solvent effects. Thus, under these conditions, the previously established linear free energy correlation between carbenium ion stability and solvolytic reactivity of bridgehead derivatives applies also to secondary derivatives. 相似文献
126.
Socaciu-Siebert LD Hagen J Le Roux J Popolan D Vaida M Vajda S Bernhardt TM Wöste L 《Physical chemistry chemical physics : PCCP》2005,7(14):2706-2709
Femtosecond nuclear dynamics of mass-selected neutral Ag2 and Ag2O2 clusters are investigated with the 'negative ion-to neutral-to positive ion'(NeNePo) technique. For the bare silver dimer, wave packet dynamics occurring in the neutral electronic ground state and in the first excited triplet state are observed after photodetachment from the anion with 3.05 eV photon energy. While the dynamics in the ground state lead to an oscillatory structure in the NeNePo-pump-probe spectra with a vibrational constant of 185 cm-1, the dynamics in the triplet state are assigned to a bound-free transition leading to dissociation. Photodetachment from the Ag2O2- complex results in the desorption of O2. The experimental data clearly show the influence of the desorbing oxygen ligand on the nuclear dynamics of the silver dimer inducing a red shift in the vibrational frequency and an intensity enhancement of the oscillatory signal. 相似文献
127.
C. Bréchignac Ph. Cahuzac F. Carlier J. Ph. Roux 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,28(1):67-72
Rare earth clusters of europium, thullium and ytterbium were generated by gas aggregation technique and probed by photoionization mass spectrometry. Their relative intensities in mass spectra have shown that their stabilities are governed by compact geometrical structures. The addition of oxygen gas in the nucleation region was used to produce the reactive nucleation. Several stages of oxidation were observed as a function of oxygen pressure up to saturation. For the maximal degree of oxidation the observed oxide ion compositions enable one to follow the valence of metal atom in its oxide as cluster size increases. This exhibits a divalent to trivalent valence change with cluster size. Moreover it emerges from the data that the divalent to trivalent transition for Tm, Yb, and Eu occurs at different size values. 相似文献
128.
129.
Testemale D Hazemann JL Pokrovski GS Joly Y Roux J Argoud R Geaymond O 《The Journal of chemical physics》2004,121(18):8973-8982
The geometrical and electronic structure of the arsenious acid molecule As(OH)(3) in aqueous solutions has been investigated by x-ray absorption spectroscopy (XAS) within extended x-ray absorption spectroscopy (EXAFS) and x-ray absorption near edge structure (XANES), using realistic first-principle calculations in the latter case. This investigation was performed on aqueous solutions of arsenious acid from ambient to supercritical conditions (P = 250 and 600 bars, T 相似文献
130.
Rafael Notario Maria Victoria Roux Daniel A. Bors Joel F. Liebman 《Structural chemistry》2007,18(3):395-398
Acrylic acid is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious—even
ignoring “ancient” determinations, there is a 12 kJ mol−1 range of values reported for the gas phase quantity, −320 to −332 kJ mol−1. Our quantum chemical calculations using current methodology suggest the value of −321 ± 3 kJ mol−1. 相似文献