全文获取类型
收费全文 | 378篇 |
免费 | 8篇 |
国内免费 | 4篇 |
专业分类
化学 | 171篇 |
晶体学 | 3篇 |
力学 | 8篇 |
数学 | 60篇 |
物理学 | 148篇 |
出版年
2023年 | 3篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 10篇 |
2011年 | 18篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 15篇 |
2007年 | 7篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 7篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1968年 | 4篇 |
1944年 | 2篇 |
1943年 | 6篇 |
1932年 | 2篇 |
1931年 | 3篇 |
1922年 | 2篇 |
1880年 | 2篇 |
排序方式: 共有390条查询结果,搜索用时 15 毫秒
81.
82.
83.
Two-phase mixtures of diesel fuel and aqueous ethanol were microemulsified and data were collected on rheological properties, densities, water tolerance and critical solution temperatures. For the detergentless system of diesel fuel, aqueous ethanol and butanol it was found that the relative viscosity varied directly with the volume percent of the dispersed water phase and approximates Einstein's formula. With ionic systems it was found that relative viscosities varied with increasing volume percent of dispersed water by values greater than those predicted by Brinkman and Roscoe for suspensions of diverse particle size. Water tolerances for ionic systems were greater than those observed with 1-butanol. The nature of the surfactant and its concentration determine to a large degree the microemulsion's physical properties. 相似文献
84.
Antonio L. Braga Wolmar A. Severo Filho Ricardo S. Schwab Luciano Dornelles Diogo S. Lüdtke 《Tetrahedron letters》2009,50(25):3005-4730
The synthesis of selenium- and tellurium-containing nucleosides, derived from uridine is described herein. These compounds were prepared in a concise and short synthetic route in good yields, by nucleophilic substitution of a tosylate group by organoselenium nucleophiles. 相似文献
85.
S. Zein El Abedin P. Giridhar P. Schwab F. Endres 《Electrochemistry communications》2010,12(8):1084-1086
In this letter we show that nanocrystalline aluminium can be electrodeposited in the Lewis acidic ionic liquid based on AlCl3 (60 mol%) and 1-(2-methoxyethyl)-3-methylimidazolium chloride ([MoeMIm]Cl) (40 mol%). The study comprised cyclic voltammetry, potentiostatic polarization, and SEM and XRD measurements. The methoxy group in the side chain of the imidazolium cation significantly influences the electrodeposition pathway of Al in comparison to [EMIm]Cl/AlCl3. Cyclic voltammetry shows a significant current loop attributed to nucleation. Shiny Al layers are obtained with an average crystallite size of about 40 nm. 相似文献
86.
Schwab DE Tard C Brecht E Peters JW Pickett CJ Szilagyi RK 《Chemical communications (Cambridge, England)》2006,(35):3696-3698
X-ray absorption spectroscopic measurements and density functional calculations suggest that the hydrogenase H-cluster is best described as an electronically inseparable 6Fe-cluster due to extensive delocalization of frontier molecular orbitals of the iron centres, sulfide and the non-innocent dithiolate ligands. 相似文献
87.
A. J. Buras R. Fleischer S. Recksiegel F. Schwab 《The European Physical Journal C - Particles and Fields》2006,45(3):701-710
We analyze the B → ππ, πK modes in the light of the most recent B-factory data, and obtain the following new results: (i) the
modes prefer γ = (74±6)°, which - together with |Vub/Vcb| - allows us to determine the "true" unitarity triangle and to search for CP-violating new-physics contributions to B0d-
mixing; (ii) the B → πK puzzle reflected in particular by the low experimental value of the ratio Rn of the neutral B → πK rates persists and still favors new physics in the electroweak penguin sector with a new CP-violating phase ϕ ~ –90°, although now also ϕ ~ +90° can bring us rather close to the data; (iii) the mixing-induced
CP asymmetry is a sensitive probe of the sign of this phase, and would currently favor ϕ ~ +90°, as well as the direct CP asymmetry of
, which suffers, however, from large hadronic uncertainties; (iv) we investigate the sensitivity of our B → πK analysis to large non-factorizable SU(3)-breaking effects and find that their impact is surprisingly small so that it is indeed exciting to speculate on new physics;
(v) assuming that new physics enters through Z0 penguins, we study the interplay between B → πK and rare B, K decays and point out that the most recent B-factory constraints for the latter have interesting implications, bringing us to a few scenarios for the future evolution
of the data, where also the mixing-induced CP violation in
plays a prominent r?le. 相似文献
88.
Joshua Friedel Maren Krause Rose Jordan Ivn Maisuls Dana Brünink Dominik Schwab Nikos L. Doltsinis Cristian A. Strassert Axel Klein 《Molecules (Basel, Switzerland)》2022,27(22)
In a series of Pt(II) complexes [Pt(dba)(L)] containing the very rigid, dianionic, bis-cyclometalating, tridentate C^N^C2− heterocyclic ligand dba2– (H2dba = dibenzo[c,h]acridine), the coligand (ancillary ligand) L = dmso, PPh3, CNtBu and Me2Imd (N,N’-dimethylimidazolydene) was varied in order to improve its luminescence properties. Beginning with the previously reported dmso complex, we synthesized the PPh3, CNtBu and Me2Imd derivatives and characterized them by elemental analysis, 1H (and 31P) NMR spectroscopy and MS. Cyclic voltammetry showed partially reversible reduction waves ranging between −1.89 and −2.10 V and increasing along the series Me2Imd < dmso ≈ PPh3 < CNtBu. With irreversible oxidation waves ranging between 0.55 (L = Me2Imd) and 1.00 V (dmso), the electrochemical gaps range between 2.65 and 2.91 eV while increasing along the series Me2Imd < CNtBu < PPh3 < dmso. All four complexes show in part vibrationally structured long-wavelength absorption bands peaking at around 530 nm. TD-DFT calculated spectra agree quite well with the experimental spectra, with only a slight redshift. The photoluminescence spectra of all four compounds are very similar. In fluid solution at 298 K, they show broad, only partially structured bands, with maxima at around 590 nm, while in frozen glassy matrices at 77 K, slightly blue-shifted (~580 nm) bands with clear vibronic progressions were found. The photoluminescence quantum yields ΦL ranged between 0.04 and 0.24, at 298 K, and between 0.80 and 0.90 at 77 K. The lifetimes τ at 298 K ranged between 60 and 14040 ns in Ar-purged solutions and increased from 17 to 43 µs at 77 K. The TD-DFT calculated emission spectra are in excellent agreement with the experimental findings. In terms of high ΦL and long τ, the dmso and PPh3 complexes outperform the CNtBu and Me2Imd derivatives. This is remarkable in view of the higher ligand strength of Me2Imd, compared with all other coligands, as concluded from the electrochemical data. 相似文献
89.
Fabienne Schwab 《Helvetica chimica acta》2023,106(1):e202200136
Nanoagrochemicals conceived based on safe-by-design principles could provide, besides yield increases, real benefits for the environment due to lower losses of agrochemicals to wind drift and rainwater run-off, and lower toxicity to non-target organisms. As an emerging new technology rather than ‘just another’ active ingredient, nanoagrochemicals should be evaluated and compared to conventional products using multiple criteria, including the production costs, efficiency, mode of action, degradability, and (lack of) effects on non-target organisms. Current studies on nanopesticides suggest, on average, ca. 31 % more efficiency and ca. 43 % less toxicity on non-target organisms. Observations of a 5–10-fold increase in efficiency in laboratory studies need validation in the field. The most significant challenges for nanoagrochemicals today are to produce them at competitive costs and overcome the regulatory obstacles to register products containing nanomaterials. 相似文献
90.
Inequalities of Jackson and Bernstein type are derived for polynomial approximation on simplices with respect to Sobolev norms. Although we cannot use orthogonal polynomials, sharp estimates are obtained from a decomposition into orthogonal subspaces. The formulas reflect the symmetries of simplices, but analogous estimates on rectangles show that we cannot expect rotational invariance of the terms with derivatives. 相似文献