全文获取类型
收费全文 | 463篇 |
免费 | 12篇 |
专业分类
化学 | 334篇 |
晶体学 | 7篇 |
力学 | 2篇 |
数学 | 8篇 |
物理学 | 124篇 |
出版年
2021年 | 6篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 9篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 15篇 |
2007年 | 18篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 31篇 |
2003年 | 21篇 |
2002年 | 22篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1990年 | 4篇 |
1988年 | 3篇 |
1984年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1969年 | 4篇 |
1941年 | 4篇 |
1940年 | 3篇 |
1935年 | 7篇 |
1934年 | 5篇 |
1933年 | 4篇 |
1930年 | 3篇 |
1926年 | 6篇 |
1925年 | 6篇 |
1904年 | 3篇 |
1899年 | 4篇 |
1898年 | 3篇 |
1885年 | 5篇 |
排序方式: 共有475条查询结果,搜索用时 15 毫秒
101.
Simone Dill Jochen Glaser Markus Strbele Sonja Tragl H.‐Jürgen Meyer 《无机化学与普通化学杂志》2004,630(7):987-992
Beyond the Conventional Number of Electrons in M6X12 Type Metal Halide Clusters: W6Cl18, (Me4N)2[W6Cl18], and Cs2[W6Cl18] Black octahedral single crystals of W6Cl18 were obtained by reducing WCl4 with graphite in a silica tube at 600 °C. The single crystal structure refinement (space group R 3¯, Z = 3, a = b = 1498.9(1) pm, c = 845.47(5) pm) yielded the W6Cl18 structure, already reported on the basis of X‐ray powder data. (Me4N)2[W6Cl18] and Cs2[W6Cl18] were obtained from methanolic solutions of W6Cl18 with Me4NCl and CsCl, respectively. The structure of (Me4N)2[W6Cl18] was refined from X‐ray single crystal data (space group P 3¯m1, Z = 1, a = b = 1079.3(1) pm, c = 857.81(7) pm), and the structure of Cs2[W6Cl18] was refined from X‐ray powder data (space group P 3¯, Z = 1, a = b = 932.10(7) pm, c = 853.02(6) pm). The crystal structure of W6Cl18 contains molecular W6Cl18 units arranged as in a cubic closest packing. The structures of (Me4N)2[W6Cl18] and Cs2[W6Cl18] can be considered as derivatives of the W6Cl18 structure in which 2/3 of the W6Cl18 molecules are substituted by Me4N+ ions and Cs+ ions, respectively. The conventional number of 16 electrons/cluster is exceeded in these compounds, with 18 electrons for W6Cl18 and 20 electrons for (Me4N)2[W6Cl18] and Cs2[W6Cl18]. Cs2[W6Cl18] exhibits temperature independent paramagnetic behaviour. 相似文献
102.
103.
The paper describes the measurement and calculation of the primary statistical errors in the evaluation of TLC or HPTLC using in situ reflectance measurements. The primary errors are the errors of the sample volume spotted onto the plate, errors caused by the chromatographic process itself, the positioning error of the plate with respect to the centre of the light beam and the error in the light measurement. By scanning the same spot, the same track or the same plate under different conditions, the various errors can be determined. 相似文献
104.
Z--acetamidocinnamate esters were hydrogenated with neutral rhodium(I) complexes containing (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane. Increasing the steric bulk of the alcohol moiety in the unsaturated esters had little influence upon the optical purity of the N-acetylphanylalanine ester products. In the series Me, Et, i-Pr, and t-Bu the optical purity decreased from 44 % ee-(R) [Me] to 40 % ee-(R) [t-Bu]. The chiral cyclobutane diphosphine appears to be only slightly more effective than the heterocyclic DIOP when ring-substituted Z--acetamidocinnamic acids are hydrogenated with neutral rhodium(I) complexes without the addition of triethylamine. Addition of triethylamine to the solvent blend seems to be more beneficial to the cyclobutane analogue than to DIOP. 相似文献
105.
106.
107.
Homogeneous and electrochemical two-electron transfers within the Tl(aq)(3+)/Tl(aq)(+) couple are considered on a common conceptual basis. For the 2 equiv electrochemical reduction of Tl(aq)(3+) to Tl(aq)(+), the intermediate state with a formal reduction potential, E(1) = 1.04 +/- 0.10 V vs the normal hydrogen electrode, was detected, different from the established value of 0.33 V for a Tl(3+)/Tl(2+) couple. Examination of obtained electrochemical (cyclic voltammetry (CV) and rotating disk electrode techniques, along with the CV-curve computer simulation procedure) and literature data indicate that the detected formal potential cannot be the property of electrode-adsorbed species, but rather of the covalently interacting dithallium intermediate [Tl(II)-Tl(II)](4+) located at the outer Helmholtz plane. The analysis of microscopic mechanisms, based on the recent hypothesis of H. Taube and the Marcus-Hush theory extended by Zusman and Beratan, and Koper and Schmickler, revealed that the homogeneous process most probably takes place through the superexchange inner-sphere two-electron-transfer mechanism, via an essentially virtual (undetectable) dithallium intermediate. In contrast, the electrochemical process occurs through a sequential mechanism, via the rate-determining step of Tl(aq)(2+) ion formation immediately followed by activationless formation of the metastable (CV-active) dithallium state. The second electrochemical electron-transfer step is fast, and shows up only in the peak height (but not in the shape) of the observed CV cathodic wave. The anodic wave for a microscopically reverse process of the oxidation of Tl(aq)(+) to Tl(aq)(3+) cannot be observed within the considered potential range due to the blocking of through-space electron transfer by the competitor process of ion transfer to the electrode. 相似文献
108.
A Nexus between Theory and Experiment: Non‐Empirical Quantum Mechanical Computational Methodology Applied to Cucurbit[n]uril⋅Guest Binding Interactions 下载免费PDF全文
Jiří Hostaš Dr. David Sigwalt Marina Šekutor Haresh Ajani Dr. Matúš Dubecký Prof. Jan Řezáč Dr. Peter Y. Zavalij Dr. Liping Cao Christian Wohlschlager Prof. Kata Mlinarić‐Majerski Prof. Lyle Isaacs Prof. Robert Glaser Prof. Pavel Hobza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(48):17226-17238
A training set of eleven X‐ray structures determined for biomimetic complexes between cucurbit[n]uril (CB[7 or 8]) hosts and adamantane‐/diamantane ammonium/aminium guests were studied with DFT‐D3 quantum mechanical computational methods to afford ΔGcalcd binding energies. A novel feature of this work is that the fidelity of the BLYP‐D3/def2‐TZVPP choice of DFT functional was proven by comparison with more accurate methods. For the first time, the CB[n] ? guest complex binding energy subcomponents [for example, ΔEdispersion, ΔEelectrostatic, ΔGsolvation, binding entropy (?TΔS), and induced fit Edeformation(host), Edeformation(guest)] were calculated. Only a few weeks of computation time per complex were required by using this protocol. The deformation (stiffness) and solvation properties (with emphasis on cavity desolvation) of cucurbit[n]uril (n=5, 6, 7, 8) isolated host molecules were also explored by means of the DFT‐D3 method. A high ρ2=0.84 correlation coefficient between ΔGexptl and ΔGcalcd was achieved without any scaling of the calculated terms (at 298 K). This linear dependence was utilized for ΔGcalcd predictions of new complexes. The nature of binding, including the role of high energy water molecules, was also studied. The utility of introduction of tethered [‐(CH2)nNH3]+ amino loops attached to N,N‐dimethyl‐adamantane‐1‐amine and N,N,N′,N′‐tetramethyl diamantane‐4,9‐diamine skeletons (both from an experimental and a theoretical perspective) is presented here as a promising tool for the achievement of new ultra‐high binding guests to CB[7] hosts. Predictions of not yet measured equilibrium constants are presented herein. 相似文献
109.
Matthew A. Glaser Noel A. Clark David M. Walba Michael P. Keyes Marc D. Radcliffe Daniel C. Snustad 《Liquid crystals》2013,40(8):1073-1085
Mean field theory and Monte Carlo sampling are applied to the calculation of the spontaneous polarization density of ferroelectric liquid crystals by the ensemble averaging of single molecules confined in mean field potentials reflecting the SmC environment. Molecules are modelled with atomistic detail, using intramolecular interaction potentials derived from ab initio quantum mechanical calculations. This technique is applied to thirteen members of a family of novel fluoro ether-based compounds. Comparison with experiment shows that the observed variation of polarization density with chemical structure is well reproduced in most cases, but that the observed temperature dependence of polarization density is not captured by our model. The features of molecular organization responsible for the discrepancies between theory and experiment are discussed. 相似文献
110.