全文获取类型
收费全文 | 770篇 |
免费 | 38篇 |
国内免费 | 5篇 |
专业分类
化学 | 452篇 |
晶体学 | 2篇 |
力学 | 33篇 |
数学 | 173篇 |
物理学 | 153篇 |
出版年
2022年 | 14篇 |
2021年 | 14篇 |
2020年 | 28篇 |
2019年 | 15篇 |
2018年 | 21篇 |
2017年 | 8篇 |
2016年 | 21篇 |
2015年 | 14篇 |
2014年 | 27篇 |
2013年 | 54篇 |
2012年 | 57篇 |
2011年 | 51篇 |
2010年 | 30篇 |
2009年 | 23篇 |
2008年 | 45篇 |
2007年 | 30篇 |
2006年 | 34篇 |
2005年 | 35篇 |
2004年 | 28篇 |
2003年 | 26篇 |
2002年 | 23篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1996年 | 5篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1931年 | 4篇 |
1914年 | 4篇 |
1906年 | 4篇 |
1905年 | 3篇 |
1904年 | 11篇 |
1901年 | 5篇 |
1880年 | 3篇 |
1873年 | 3篇 |
排序方式: 共有813条查询结果,搜索用时 15 毫秒
51.
[reaction: see text] The organometallic intermediate obtained from halogen-metal exchanges of 4-iodo-6-phenylthieno[2,3-d]pyrimidine under Barbier-type conditions was reacted with aldehydes to form the corresponding alcohols in moderate yields. The reaction involving an organolithium intermediate proceeded only at low temperature, whereas the reaction involving a magnesium ate intermediate also proceeded at room temperature. A crystal structure confirms that the expected constitutional alcohol isomer is formed, where no migration has taken place. The conditions were also suitable for 9-benzyl-6-iodopurine. 相似文献
52.
We report on the direct imaging of s and d partial-wave interference in cold collisions of atoms. Two ultracold clouds of 87Rb atoms were accelerated by magnetic fields to collide at energies near a d-wave shape resonance. The resulting halos of scattered particles were imaged using laser absorption. By scanning across the resonance we observed a marked evolution of the scattering patterns due to the energy dependent phase shifts for the interfering s and d waves. Since only two partial-wave states are involved in the collision process the scattering yield and angular distributions have a simple interpretation in terms of a theoretical model. 相似文献
53.
Cladding structures of photonic bandgap fibers often have airholes of noncircular shape, and, typically, close-to-hexagonal airholes with curved corners are observed. We study photonic bandgaps in such structures by aid of a two-parameter representation of the size and curvature. For the fundamental bandgap we find that the bandgap edges (the intersections with the air line) shift toward shorter wavelengths when the air-filling fraction f is increased. The bandgap also broadens, and the relative bandwidth increases exponentially with f2. Compared with recent experiments [Nature 424, 657 (2003)] we find very good agreement. 相似文献
54.
Optical waveguide sensor for on-line monitoring of bacteria 总被引:2,自引:0,他引:2
A grating-coupled planar optical waveguide sensor is presented for sensing of bacteria by evanescent waves. The waveguide design results in increased depth of penetration into the sample volume, which makes it suitable for detecting micrometer-sized biological objects. We tested the sensor's performance by monitoring the adhesion of Escherichia coli K12 cells to the sensor surface. 相似文献
55.
Contrasts between beta relaxation in equilibrium viscous liquids and glasses are rationalized in terms of a double-well potential model with structure-dependent asymmetry, assuming structure is described by a single order parameter. The model is tested for tripropylene glycol where it accounts for the hysteresis of the dielectric beta loss peak frequency and magnitude during cooling and reheating through the glass transition. 相似文献
56.
[reaction: see text] Osmium tetroxide has been microencapsulated in a polyurea matrix using an in situ interfacial polymerization approach. These microcapsules have been effectively used as recoverable and reusable catalysts in the dihydroxylation of olefins 相似文献
57.
58.
59.
Evenson William E. Lu Jun Winz Michele W. Gardner John A. Zacate Matthew O. Lee Teresa Mommer Niels 《Hyperfine Interactions》1999,120(1-8):427-431
In order to explain PAC data for tetragonal zirconia at temperatures between 900 and 1300oC, we have developed a four-state
stochastic model. The model simulates vacancies which trap and detrap at a PAC probe nucleus. While trapped, the vacancies
hop around the probe in equivalent sites. The four states in this Winkler–Gerdau stochastic theory are three trapped states
with equivalent electric field gradients (EFGs) of different orientations and a detrapped state with a weaker EFG whose axis
of symmetry is oriented along the diagonal between the three trapped EFGs. There are three hopping rates in this model: w,
the rate a trapped vacancy hops around the probe, wD, the detrapping rate, and wt, the trapping rate. We report results of calculations for values of these hopping rates implied by our tetragonal zirconia
data, and we report heuristic fitting functions which summarize the computer results and can be used to fit data efficiently
for a wide range of parameters.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
60.
Niels Nielsen 《Monatshefte für Mathematik》1906,17(1):281-286
Ohne Zusammenfassung 相似文献