全文获取类型
收费全文 | 187篇 |
免费 | 3篇 |
专业分类
化学 | 110篇 |
力学 | 14篇 |
数学 | 53篇 |
物理学 | 13篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2015年 | 4篇 |
2013年 | 8篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 3篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1996年 | 3篇 |
1993年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1926年 | 1篇 |
1904年 | 2篇 |
排序方式: 共有190条查询结果,搜索用时 265 毫秒
41.
Py. Calvin O. Kinzey C. Glücksmann B. Hafner und Franz Zetzsche 《Fresenius' Journal of Analytical Chemistry》1904,43(2):125-134
Ohne Zusammenfassung 相似文献
42.
The equilibria and speciation of the proton cryptate polyoxometalate alpha-(H2)W(12)O(40)]6- (1) were examined by NMR following the phase-transfer cation metathesis of aqueous Na(6)1 with Q+Br-/CH(2)Cl(2), leading to the isolation of the (n-Bu)4N+ (Q+) salts Q(6)1 and alpha-Q5[(H3)W(12)O(40)](Q(5)2). Several groups report salts of the protonated anions H(x)1 (x = 1 and 2) with no consensus on proton numbers or locations. Reported herein, a combination of 1H and 183W NMR evidence, elemental analysis, acid titration measurements, and H/D isotopomer assignments establishes that in nonaqueous media the internal cryptand cavity of 1 reversibly accommodates only one more proton to form 2. Because an external proton must transfer across the close-packed tungsten oxide surface of 1, which should constitute a substantial activation barrier, it is significant that the transformation is instantaneous by 1H NMR (1 equiv of HBr in CH(3)CN), whereas the reverse process is slow (t1/2 approximately 17.4 h; 1 equiv of Q+OH-). 相似文献
43.
Amy F Chan CK Zhao W Hyung J Ono M Sueyoshi T Kera S Nesher G Salomon A Segev L Seitz O Shpaisman H Schöll A Haeming M Böcking T Cahen D Kronik L Ueno N Umbach E Kahn A 《The journal of physical chemistry. B》2006,110(43):21826-21832
Monolayers of alkyl chains, attached through direct Si-C bonds to Si(111), via phosphonates to GaAs(100) surfaces, or deposited as alkyl-silane monolayers on SiO2, are investigated by ultraviolet and inverse photoemission spectroscopy and X-ray absorption spectroscopy. Exposure to ultraviolet radiation from a He discharge lamp, or to a beam of energetic electrons, leads to significant damage, presumably associated with radiation- or electron-induced H-abstraction leading to carbon-carbon double-bond formation in the alkyl monolayer. The damage results in an overall distortion of the valence spectrum, in the appearance of (occupied) states above the highest occupied molecular orbital of the alkyl molecule, and in a characteristic (unoccupied state) pi resonance at the edge of the carbon absorption peak. These distortions present a serious challenge for the interpretation of the electronic structure of the monolayer system. We show that extrapolation to zero damage at short exposure times eliminates extrinsic features and allows a meaningful extraction of the density of state of the pristine monolayer from spectroscopy measurements. 相似文献
44.
Diaz-Marrero AR Austin P Van Soest R Matainaho T Roskelley CD Roberge M Andersen RJ 《Organic letters》2006,8(17):3749-3752
[structure: see text] The new meroterpenoids avinosol (1), 3'-aminoavarone (2), and 3'-phenethylaminoavarone (3) have been isolated from the marine sponge Dysidea sp. collected in Papua New Guinea, and their structures were elucidated by analysis of spectroscopic data. Avinosol (1), which is apparently the first example of a naturally occurring meroterpenoid-nucleoside conjugate, showed antiinvasion activity in a cell-based assay. 相似文献
45.
James Calvin Gražina Gimbutienė William O. Phillips Antanas Žilinskas 《Journal of Global Optimization》2018,71(1):165-191
The convergence rate of a rectangular partition based algorithm is considered. A hyper-rectangle for the subdivision is selected at each step according to a criterion rooted in the statistical models based theory of global optimization; only the objective function values are used to compute the criterion of selection. The convergence rate is analyzed assuming that the objective functions are twice- continuously differentiable and defined on the unit cube in d-dimensional Euclidean space. An asymptotic bound on the convergence rate is established. The results of numerical experiments are included. 相似文献
46.
The current and planned research in nanoscience and engineering will make possible a paradigm shift in nanoscale devices and structures. 相似文献
47.
Taylor R. Quinn Calvin N. Steussy Brandon E. Haines Jinping Lei Wei Wang Fu Kit Sheong Cynthia V. Stauffacher Xuhui Huang Per-Ola Norrby Paul Helquist Olaf Wiest 《Chemical science》2021,12(18):6413
Understanding the mechanisms of enzymatic catalysis requires a detailed understanding of the complex interplay of structure and dynamics of large systems that is a challenge for both experimental and computational approaches. More importantly, the computational demands of QM/MM simulations mean that the dynamics of the reaction can only be considered on a timescale of nanoseconds even though the conformational changes needed to reach the catalytically active state happen on a much slower timescale. Here we demonstrate an alternative approach that uses transition state force fields (TSFFs) derived by the quantum-guided molecular mechanics (Q2MM) method that provides a consistent treatment of the entire system at the classical molecular mechanics level and allows simulations at the microsecond timescale. Application of this approach to the second hydride transfer transition state of HMG-CoA reductase from Pseudomonas mevalonii (PmHMGR) identified three remote residues, R396, E399 and L407, (15–27 Å away from the active site) that have a remote dynamic effect on enzyme activity. The predictions were subsequently validated experimentally via site-directed mutagenesis. These results show that microsecond timescale MD simulations of transition states are possible and can predict rather than just rationalize remote allosteric residues.Transition state force fields enable MD simulations at the transition state of HMGCoA reductase that sample the transition state ensemble on the μs timescale to identify remote residues that affect the reaction rate. 相似文献
48.
Determination of oxidizable solutes in water is accomplished using amperometric detection in a solution exchange apparatus. The applied potential (Ea) used is + 0.5 V vs. SCE at a nickel working electrode. Electrode pretreatment is performed at −1.0 V vs. SCE. The background electrolyte is 0.1 M NaOH. Analyte solution drawn into the cell replaces background solution. No further convection occurs. Peak anodic current relative to the baseline is used as the analytical signal. The linear range extends down to 1 μM for sucrose, diethylenetriamine, phenol, and ethanolamine. The determination time is 2 min per sample. 相似文献
49.
50.
Static electric dipole and quadrupole moments were evaluated at the explicitly correlated second-order Møller–Plesset (MP2-F12) level for BH, CO, H2O, and HF molecules. The electron correlation contributions to the multipole moments were further decomposed into the direct (unrelaxed) and indirect (orbital response) components; we found that both components are equally important for the conventional (MP2) contribution, whereas the F12 correction to these properties originates primarily from the orbital response effects. Finally, the direct contribution dominates in the perturbative Hartree–Fock basis set incompleteness (CABS singles) correction. Two basis set families were employed: the standard aug-cc-pVXZ series and the cc-pVXZ-F12 series designed specifically for the F12 methods. The aug-cc-pVXZ MP2-F12 multipole moments usually have smaller basis set errors than the cc-pVXZ-F12 counterparts, albeit their differences are small at the triple (X = T) and quadruple (X = Q) zeta level. With the MP2-F12 calculations, the basis set errors of dipole and quadrupole moments can be reduced to ~0.001 a.u., or roughly 0.1%, at the aug-cc-pVDZ and aug-cc-pVTZ levels, respectively. 相似文献