全文获取类型
收费全文 | 328篇 |
免费 | 6篇 |
国内免费 | 5篇 |
专业分类
化学 | 178篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 93篇 |
物理学 | 64篇 |
出版年
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 22篇 |
2012年 | 17篇 |
2011年 | 12篇 |
2010年 | 15篇 |
2009年 | 4篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 14篇 |
2004年 | 5篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1943年 | 2篇 |
1942年 | 2篇 |
1935年 | 2篇 |
排序方式: 共有339条查询结果,搜索用时 406 毫秒
251.
252.
We investigate the mechanisms of fatigue behavior in nanocrystalline metals at the atomic scale using empirical force laws and molecular level simulations. A combination of molecular statics and molecular dynamics was used to deal with the time scale limitations of molecular dynamics. We show that the main atomistic mechanism of fatigue crack propagation in these materials is the formation of nanovoids ahead of the main crack. The results obtained for crack advance as a function of stress intensity amplitude are consistent with experimental studies and a Paris law exponent of about 2. 相似文献
253.
The adsorption and surface reactions of CH2I2 on the K-dosed Mo2C/Mo(1 0 0) have been studied by high resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy. Potassium is an effective promoter for the rupture of C-I bond in the adsorbed CH2I2. A partial dissociation of this compound occurred even at 100 K and was completed at 190 K at monolayer K coverage. The dissociation was further promoted by the illumination of coadsorbed layer at 100 K. As revealed by HREELS and XPS measurements the primary products of the dissociation are CH2 and I. Methylene was converted to π-bonded ethylene characterized by Tp = 160 K, and di-σ-ethylene with Tp = 350 K. Other products of the surface reaction are hydrogen and methane. The coupling reaction of CH2 species was clearly facilitated by potassium. The effect of potassium was explained by the extended electron donation to adsorbed alkyl iodide in one hand, and by the direct interaction between potassium and I on the other hand. 相似文献
254.
Morton E. Munk Margit Farkas Alan H. Lipkis Bradley D. Christie 《Mikrochimica acta》1986,89(1-6):199-215
The new generation of the CASE system described in this paper offers a promising approach to both spectrum interpretation and structure generation that allows for a natural linkage between them. The approach takes full advantage of the information contained in available spectral libraries, yet is not limited by the substructural deficiencies of these data bases. 相似文献
255.
256.
Edit Farkas István Szilágyi Sándor Dóbé Tibor Bérces Ferenc Márta 《Reaction Kinetics and Catalysis Letters》2003,80(2):351-358
The discharge-flow method with resonance fluorescence detection of OH radicals was applied to obtain the rate constant value
of k
D = 1.95 ± 0.14 (1σ) 1010 cm3 mol-1s-1 at 298 K. Combination with k
H from our previous study gives the kinetic isotope effect of k
H / k
D = 5.33 ± 0.41. OH + CH3C(O)CH3 → Products (H) OH + CD3C(O)CD3 → Products(D)
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
257.
Phase composition analysis of hydrous aluminium oxides by thermal analysis and infrared spectrometry
A general method for determination of the phase composition of hydrous aluminium oxides by thermal analysis and infrared spectrometry, and determination of the transformation temperature of mixtures of Al(OH)3 and AlOOH into -Al2O3 are described. 相似文献
258.
This study consists of two parts: The first part comprised an experimental determination of the kinetic parameters for the exchange of water between UO2(H2O)5(2+) and bulk water, including an ab initio study at the SCF and MP2 levels of the geometry of UO2(H2O)5(2+), UO2(H2O)4(2+), and UO2(H2O)6(2+) and the thermodynamics of their reactions with water. In the second part we made an experimental study of the rate of water exchange in uranyl complexes and investigated how this might depend on inter- and intramolecular hydrogen bond interactions. The experimental studies, made by using 17O NMR, with Tb3+ as a chemical shift reagent, gave the following kinetic parameters at 25 degrees C: kex = (1.30 +/- 0.05) x 10(6) s(-1); deltaH(not equal to) = 26.1 +/- 1.4 kJ/mol; deltaS(not equal to) = -40 +/- 5J J/(K mol). Additional mechanistic indicators were obtained from the known coordination geometry of U(VI) complexes with unidentate ligands and from the theoretical calculations. A survey of the literature shows that there are no known isolated complexes of UO2(2+) with unidentate ligands which have a coordination number larger than 5. This was corroborated by quantum chemical calculations which showed that the energy gains by binding an additional water to UO2(H2O)4(2+) and UO2(H2O)5(2+) are 29.8 and -2.4 kcal/mol, respectively. A comparison of the change in deltaU for the reactions UO2(H2O)5(2+)--> UO2(H2O)4(2+) + H2O and UO2(H2O)5(2+) + H2O --> UO2(H2O)6(2+) indicates that the thermodynamics favors the second (associative) reaction in gas phase at 0 K, while the thermodynamics of water transfer between the first and second coordination spheres, UO2(H2O)5(2+) --> UO2(H2O)4(H2O)2+ and UO2(H2O)5(H2O)2+ --> UO2(H2O)6(2+), favors the first (dissociative) reaction. The energy difference between the associative and dissociative reactions is small, and solvation has to be included in ab initio models in order to allow quantitative comparisons between experimental data and theory. Theoretical calculations of the activation energy were not possible because of the excessive computing time required. On the basis of theoretical and experimental studies, we suggest that the water exchange in UO2(H2O)5(2+) follows a dissociative interchange mechanism. The rates of exchange of water in UO2(oxalate)F(H2O)2- (and UO2(oxalate)F2(H2O)2- studied previously) are much slower than in the aqua ion, kex = 1.6 x 10(4) s(-1), an effect which we assign to hydrogen bonding involving coordinated water and fluoride. The kinetic parameters for the exchange of water in UO2(H2O)52+ and quenching of photo excited *UO2(H2O)5(2+) are very near the same, indicating similar mechanisms. 相似文献
259.
It is shown that the Explodator model of the BZ reaction can show bistability in CSTR. Conditions for multistationarity are formulated.
, - CSTR. .相似文献
260.
Synthesis of (?)-(R)-Nephthenol and (?)-(R)-Cembren A Starting for L -serine,(?)-(R)-nephthenol((?)- 2 ) and (?)-(R)-cembren A((?)- 3 ) were synthesized. 相似文献