全文获取类型
收费全文 | 389篇 |
免费 | 6篇 |
专业分类
化学 | 193篇 |
晶体学 | 4篇 |
力学 | 11篇 |
数学 | 83篇 |
物理学 | 104篇 |
出版年
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 11篇 |
2018年 | 12篇 |
2017年 | 18篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 16篇 |
2012年 | 21篇 |
2011年 | 18篇 |
2010年 | 15篇 |
2009年 | 17篇 |
2008年 | 12篇 |
2007年 | 20篇 |
2006年 | 13篇 |
2005年 | 6篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1968年 | 2篇 |
1965年 | 2篇 |
1958年 | 2篇 |
1956年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有395条查询结果,搜索用时 15 毫秒
21.
Tarek A. Salama Saad S. Elmorsy Abdel‐Galel M. Khalil Margret M. Girges Abdel‐Aziz S. El‐Ahl 《合成通讯》2013,43(8):1313-1319
A combination of tetrachlorosilane and potassium cyanide (in situ trichlorosilyl cyanide) was found to work efficiently for hydrocyanation of ketones to afford the corresponding cyanohydrins in high yield under mild conditions. 相似文献
22.
23.
Form factor axioms are derived in two dimensional integrable defect theories for matrix elements of operators localized both in the bulk and on the defect. The form factors of bulk operators are expressed in terms of the bulk form factors and the transmission factor. The structure of the form factors of defect operators is established in general, and explicitly calculated in particular, for the free boson and for some operator of the Lee–Yang model. Fusion method is also presented to generate boundary form factor solutions for a fused boundary from the known unfused ones. 相似文献
24.
C. J. Baddeley A. F. Lee R. M. Lambert T. Gie el O. Schaff V. Fernandez K. -M. Schindler A. Theobald C. J. Hirschmugl R. Lindsay A. M. Bradshaw D. P. Woodruff 《Surface science》1998,400(1-3):166-175
A quantitative structure determination of a newly discovered (2×2) adsorption phase of acetylene chemisorbed on Pd{111} has been performed by scanned-energy mode photoelectron diffraction: this phase corresponds to the threshold coverage for the catalytic conversion of acetylene to benzene. The carbon atoms in the C2H2 molecule are located almost over bridge sites with a C–C bond length of 1.34+0.10 Å, the centre of the molecule being positioned almost over a hollow site. Of the two hollow sites the hcp site (directly above a second layer Pd atom) is favoured, particularly by a subset of the data most sensitive to this aspect of the structure, but the full analysis indicates that the fcc site (above a third layer Pd atom) cannot formally be excluded. The adsorption site adopted by acetylene in the higher coverage
phase on Pd{111} is essentially identical. This is the dominant structure in the coverage regime which is catalytically active for the conversion of acetylene to benzene. The implications of these findings for acetylene coupling reactions over Pd{111} are discussed. 相似文献
25.
S.Abu el Ata-Doss 《Journal of Mathematical Analysis and Applications》1979,72(1):106-113
Control systems governed by linear parabolic evolution partial differential equations in the case of quadratic cost functions are considered. Sensitivity of the performance of the optimal systems to small parameter variations is studied. It is proved that the cost function sensitivity is the same if the optimal control is implemented in open-loop form or in feedbeck form. 相似文献
26.
27.
A fractional partial differential equation is derived for the spreading of matter in a saturated porous medium starting from precise hypotheses concerning the medium itself, which is a collection of intertwisted tubes with randomly distributed slopes, filled with quiescent fluid. Examining the fundamental solution of the fractional equation indicates that the second moment is not proportional to time, which is the signature of anomalous diffusion. The equation derived preserves non-negativity and also the total mass of matter. 相似文献
28.
Based on helium atom beam diffraction and scanning tunneling microscopy data, the coexistence of a meandering and a bunching instability during homoepitaxial step flow growth is established in a class of nonreconstructed, metallic vicinal surfaces, Cu (1,1,n), n=5,9,17. Specifically, the meandering instability is shown to act as a precursor to the bunching instability, indicating that a one-dimensional treatment of bunching in step flow growth is not sufficient. Our findings might be generic to step flow growth in kinetically restricted systems. 相似文献
29.
The longitudinal ultrasonic attenuation measurements have been made using pulse echo method at fundamental frequencies of 2, 4, 6 and 8 MHz in 20WO3–(80−x) TeO2–xPbO ternary tellurite glasses (x=10, 12.5, 15, 17.5 and 20 mol%) in the temperature range 160–280 K. The results showed the presence of a broad peak which shifts to higher temperature with increasing frequency. The ultrasonic attenuation peaks suggest that the experimental behavior is controlled by thermally activated structural relaxations. The internal friction, acoustic activation energy, deformation potential, relaxation strength, number of loss centers and density of state have been calculated both as a function of temperature and PbO content. The acoustic activation energy was found to decrease from 0.156 to 0.135 eV with the increase of PbO content. The results showed that both the number of loss centers and their activation energy decrease with the atomic ring size. An increase in the density of state is observed with addition of PbO content at the same frequency in the whole range of temperature which is associated with structural units formed when PbO is added. 相似文献
30.
H. Jensen J. Kröger N. Néel R. Berndt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):465-469
Clusters on surfaces have been investigated with low-temperature scanning tunnelling microscopy and spectroscopy. Constant
current spectra acquired on Ag oligomers and one-dimensional chains on a Ag(111) reveal a
single resonance peak whose energy shifts towards the Fermi level with increasing cluster size. Next, controlled and reproducible
contact between a STM tip and a C60 molecule adsorbed on Cu(100) is reported. The
transition from tunnelling to contact is discussed in terms of local heating of the tip-molecule junction. 相似文献