全文获取类型
收费全文 | 348篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 201篇 |
晶体学 | 4篇 |
力学 | 7篇 |
数学 | 28篇 |
物理学 | 116篇 |
出版年
2023年 | 3篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2016年 | 12篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 17篇 |
2010年 | 8篇 |
2008年 | 10篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 15篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 4篇 |
1989年 | 4篇 |
1987年 | 4篇 |
1985年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1969年 | 3篇 |
1967年 | 2篇 |
1937年 | 2篇 |
1936年 | 2篇 |
1928年 | 2篇 |
1926年 | 2篇 |
1908年 | 2篇 |
1907年 | 4篇 |
1904年 | 2篇 |
1901年 | 2篇 |
1899年 | 3篇 |
1898年 | 2篇 |
1893年 | 2篇 |
排序方式: 共有356条查询结果,搜索用时 15 毫秒
141.
Development of Enantioselective Palladium‐Catalyzed Alkene Carboalkoxylation Reactions for the Synthesis of Tetrahydrofurans
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Brett A. Hopkins Zachary J. Garlets Prof. Dr. John P. Wolfe 《Angewandte Chemie (International ed. in English)》2015,54(45):13390-13392
The Pd‐catalyzed coupling of γ‐hydroxyalkenes with aryl bromides affords enantiomerically enriched 2‐(arylmethyl)tetrahydrofuran derivatives in good yield and up to 96:4 e.r. This transformation was achieved through the development of a new TADDOL/2‐arylcyclohexanol‐derived chiral phosphite ligand. The transformations are effective with an array of different aryl bromides, and can be used for the preparation of products bearing quaternary stereocenters. 相似文献
142.
John B. BrazierGreg P. Hopkins Meriem JirariShaun Mutter Ronan PommereuilLeopold Samulis James A. Platts Nicholas C.O. Tomkinson 《Tetrahedron letters》2011,52(21):2783-2785
Comparison of the relative reactivities of the benchmark catalysts for iminium ion catalysed Diels-Alder cycloaddition under optimised literature conditions showed the imidazolidinone scaffold to possess significantly superior levels of activity in the Diels-Alder cycloaddition when compared to diarylprolinol silyl ethers. 相似文献
143.
Hatzopoulos MH Eastoe J Dowding PJ Rogers SE Heenan R Dyer R 《Langmuir : the ACS journal of surfaces and colloids》2011,27(20):12346-12353
The physicochemical properties of a homologous series of sodium p-n-alkylbenzoates have been investigated. The objective was to determine whether there is a clear transition point from hydrotropic to surfactant-like behavior with increasing alkyl chain length n, so as to shed clear light on the aggregation mechanism of so-called "hydrotropes". Electrical conductivity measurements were used for a first estimation of the critical aggregation concentrations (cac). As for classical surfactants, log(cac) depends on alkyl chain length n, but two branches of behavior were observed: one having a gradient typical of long chain fatty acid salts and the other with a more shallow dependence. Surface tension (γ) measurements of high purity aqueous solutions were used to generate limiting headgroup areas A(cac), which were in the range (40-50 ?(2)) being consistent with monolayer formation. Small-angle neutron scattering conclusively shows that the lower chain length homologues (classed as hydrotropes) exhibit sharp transitions in aggregation as a function of bulk concentration, typical of regular surfactants. As such, there is little to suggest from this study that hydrotropes differ in association behavior from regular surfactants. 相似文献
144.
W. Scott Hopkins 《Molecular physics》2013,111(21):3151-3158
As our understanding of clusters has improved, we have found that rather than being models for surface and condensed phase phenomena, clusters often display chemical and physical properties that are quite distinct from those of their atomic constituents or associated bulk materials. Indeed, identifying and utilising the unique properties of dimensionally confined species is a major theme in nanotechnology. Consequently, numerous experimental and computational methods have been employed to investigate the structures and properties of cluster systems. In this article, the techniques of infrared multiple photon dissociation and differential mobility spectrometry are discussed using the examples of [Ag·B12F12]? and tetraalkylammonium/solvent ionic clusters, respectively. 相似文献
145.
Mary E. Hopkins 《代数通讯》2013,41(11):4333-4347
An integral domain D is weakly integrally closed if whenever x is in the quotient field of D, and J is a nonzero finitely generated ideal of D such that xJ ? J 2, then x is in D. We define weakly integrally closed (WIC) numerical monoids similarly. If a monoid algebra is weakly integrally closed, then so is the monoid. The characteristic function of a numerical monoid M can be thought of as an infinite binary string s(M). A pattern of finitely many 0's and 1's is called forbidden if whenever s(M) contains it, then M is not weakly integrally closed. The pattern 11011 is forbidden. We show that a numerical monoid M is WIC if and only if s(M) contains no forbidden patterns. We also show that for every finite set S of forbidden patterns, there exists a numerical monoid M that is not WIC and for which s(M) contains no stretch (in a natural sense) of a pattern in S. 相似文献
146.
Moore BC Glasberg BR Stoev M Füllgrabe C Hopkins K 《The Journal of the Acoustical Society of America》2012,131(2):1003-1006
Sensitivity to temporal fine structure (TFS) at low frequencies may be adversely affected by hearing loss at high frequencies even when absolute thresholds at low frequencies are within the normal range. However, in several studies suggesting this, the effects of hearing loss and age were confounded. Here, interaural phase discrimination (IPD) thresholds for pure tones at 500 and 750 Hz were measured for 39 subjects with ages from 61 to 83 yr. All subjects had near-normal audiometric thresholds at low frequencies, but thresholds varied across subjects at high frequencies. IPD thresholds were correlated with age. IPD thresholds for the test frequency of 750 Hz were weakly correlated with absolute thresholds at high frequencies, but these correlations became non-significant when the effect of age was partialed out. The results do not confirm that sensitivity to TFS at low frequencies is influenced by hearing loss at high frequencies, independently of age. 相似文献
147.
M.A. Knuth J.B. Johnson M.A. Hopkins R.J. Sullivan J.M. Moore 《Journal of Terramechanics》2012,49(1):27-36
Three-dimensional discrete element method (DEM) simulations were developed for the Mars Exploration Rover (MER) mission to investigate: (1) rover wheel interactions with martian regolith; and (2) regolith deformation in a geotechnical triaxial strength cell (GTSC). These DEM models were developed to improve interpretations of laboratory and in situ rover data, and can simulate complicated regolith conditions. A DEM simulation was created of a laboratory experiment that involved a MER wheel digging into lunar regolith simulant. Sinkage and torques measured in the experiment were compared with those predicted numerically using simulated particles of increasing shape complexity (spheres, ellipsoids, and poly-ellipsoids). GTSC simulations, using the same model regolith used in the MER simulations, indicate a peak friction angle of approximately 37–38° compared to internal friction angles of 36.5–37.7° determined from the wheel digging experiments. Density of the DEM regolith was 1820 kg/m3 compared to 1660 kg/m3 for the lunar simulant used in the wheel digging experiment indicating that the number of grain contacts and grain contact resistance determined bulk strength in the DEM simulations, not density. An improved correspondence of DEM and actual test regolith densities is needed to simulate the evolution of regolith properties as density changes. 相似文献
148.
The sound field in front of, and close to a building facade is relevant to the measurement and prediction of environmental noise and sound insulation. For simplicity it is often assumed that the facade can be treated as a semi-infinite reflector, however in the low-frequency range (50-200 Hz) this is no longer appropriate as the wavelengths are similar or larger than the facade dimensions. Scale model measurements and predictions using integral equation methods have been used to investigate the effect of diffraction on the sound field in front of finite size reflectors. For the situation that is commonly encountered in front of building facades, the results indicate that diffraction effects are only likely to be significant in the low-frequency range (50-200 Hz) when the façade dimensions are less than 5 m. This assumes that there is a point source close to the ground and microphones at a height of 1.2 or 1.5 m, at a distance between 1 and 2 m in front of the façade. 相似文献
149.
An analysis of 1385 K°μ3 decays observed in a heavy liquid bubble chamber is presented, and limits are obtained on the form factors ξ(0) and λ+. Assuming λ+ to be 0,025, ξ(0) is found to be ?0.90 ± 0.45. 相似文献
150.
F. F. Hopkins W. J. Courtney W. R. Coker C. F. Moore P. Richard 《Zeitschrift für Physik A Hadrons and Nuclei》1971,243(5):446-451
The (p, α) reaction was studied on a208Pb target at 16.475 MeV. Nineteen states were observed in205Tl, up to 3.6 MeV in excitation. Angular distributions were obtained for five strong proton-hole transitions, and DWBA fits made to determinelj values. Results are compared with previous206Pb(t, α)205Tl,206Pb(d,3He)205Tl,205Tl(p, p′), and205Tl(n, n′) work. 相似文献