全文获取类型
收费全文 | 780篇 |
免费 | 32篇 |
国内免费 | 1篇 |
专业分类
化学 | 701篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 43篇 |
物理学 | 65篇 |
出版年
2021年 | 10篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 21篇 |
2015年 | 20篇 |
2014年 | 18篇 |
2013年 | 36篇 |
2012年 | 32篇 |
2011年 | 48篇 |
2010年 | 16篇 |
2009年 | 28篇 |
2008年 | 46篇 |
2007年 | 35篇 |
2006年 | 38篇 |
2005年 | 28篇 |
2004年 | 20篇 |
2003年 | 22篇 |
2002年 | 18篇 |
2001年 | 16篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 7篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 13篇 |
1992年 | 24篇 |
1991年 | 16篇 |
1990年 | 7篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1978年 | 12篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1943年 | 3篇 |
1930年 | 4篇 |
排序方式: 共有813条查询结果,搜索用时 15 毫秒
101.
Hj. Staudinger 《Fresenius' Journal of Analytical Chemistry》1956,150(2):154
Ohne Zusammenfassung 相似文献
102.
Claudia Mattheis Martin C. Schwarzer Gernot Frenking Seema Agarwal 《Macromolecular rapid communications》2011,32(13):994-999
The first example of phantom ring‐closing condensation polymerization for the synthesis of oligoguanidines is presented. A new oligoguanidine with a ring structure was achieved in one step by the condensation reaction of a triamine, like diethylenetriamine, with guanidine hydrochloride. The condensation reaction proceeded by selective ring‐closure towards the formation of five‐membered rings in the oligomer backbone. The resulting polymer repeat unit structure was different from the starting monomers (phantom polymer) and was formed by elimination of three molecules of ammonia per repeat unit. The inter‐, intra‐, and inter‐molecular reaction sequences led to the new structure as proved by different spectroscopic techniques (atmospheric pressure chemical‐ionization mass spectrometry, and one‐dimensional and two‐dimensional homo‐ and heteronuclear correlation NMR experiments) as well as supported by quantum chemical investigations. Preliminary results regarding antibacterial use of the resulting oligoguanidine were also promising and showed its effect within 15–30 min as an antibacterial material.
103.
104.
We compare analytic predictions of non-Hermitian chiral random matrix theory with the complex Dirac operator eigenvalue spectrum of two-color lattice gauge theory with dynamical fermions at nonzero chemical potential. The Dirac eigenvalues come in complex conjugate pairs, making the action of this theory real and positive for our choice of two staggered flavors. This enables us to use standard Monte Carlo simulations in testing the influence of the chemical potential and quark mass on complex eigenvalues close to the origin. We find excellent agreement between the analytic predictions and our data for two different volumes over a range of chemical potentials below the chiral phase transition. In particular, we detect the effect of unquenching when going to very small quark masses. 相似文献
105.
Qian Wang Sudip Pan Yan‐Bo Wu Guohai Deng Jian‐Hong Bian Guanjun Wang Lili Zhao Mingfei Zhou Gernot Frenking 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17526-17535
We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)3 (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D3 symmetric structure involving three equivalent η6‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n?1)d AOs of M and strong backdonation from the occupied (n?1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals. 相似文献
106.
Dr. Chaoxian Chi Dr. Sudip Pan Dr. Jiaye Jin Dr. Luyan Meng Prof. Mingbiao Luo Prof. Lili Zhao Prof. Mingfei Zhou Prof. Gernot Frenking 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(50):11772-11784
The octacarbonyl cation and anion complexes of actinide metals [An(CO)8]+/− (An=Th, U) are prepared in the gas phase and are studied by mass-selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (D4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (Oh) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8] (Oh; 1A1g) and [U(CO)8] (D4h; 5B1u) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium. 相似文献
107.
Dr. Xiaodan Chen Dr. Zhongshu Li Prof. Dr. Gernot Frenking Prof. Dr. Israel Fernández Prof. Lili Zhao Prof. Dr. Hansjörg Grützmacher 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(33):7912-7920
Phosphaheteroallenes R−P=C=L, with L = N-heterocyclic carbenes (NHCs), can be viewed to a certain extent as phosphaisonitriles stabilized with NHCs, R−P=C:←L. The suitability of these molecules as ligands for coinage-metal ions was investigated and coordination through the central carbon center was observed in most cases. A combination of experiments, spectroscopic methods, and DFT calculations indicates the presence of a hidden electron pair at the carbon center of R−P=C:←L. Remarkably, this lone pair also inserts intramolecularly in C−H bonds showing the carbene-type reactivity which is expected for phosphaisonitriles. 相似文献
108.
109.
Silicon carbide thin films, prepared by carbonization of Si-wafers are analysed by Auger depth profiling. The influence of atomic mixing is simulated with a Monte Carlo model. By using mixing simulations the dependence of the two mixing parameters (width of the mixing zone and recoil depth) on ion beam energy, incidence angle and ion mass can be calculated. For comparison of the simulated data with Auger measurements an Auger electron escape depth correction is necessary. The simulated and -corrected data of several layer structures show good qualitative agreement with Auger depth profiles of thin carbonized SiC-layers.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
110.
The geometry of Re2Cl82− has been optimized for the eclipsed (D
4h
) equilibrium conformation and for the staggered (D
4d
) conformation at BP86/TZ2P. The nature of the Re–Re bond which has a formal bond order four has been studied with an energy
decomposition analysis (EDA). The EDA investigation indicates that the contribution of the b
2 (δ
xy
) orbitals to the Re–Re bond in the ground state is negligibly small. The vertical excitation of one and two electrons from the bonding δ orbital into the antibonding δ* orbitals yielding the singly and doubly excited states and gives a destabilization of 17.5 and 36.1 kcal/mol, respectively, which is nearly the same as the total excitation energies.
The preference for the D
4h
geometry with eclipsing Re–Cl bonds is explained in terms of hyperconjugation rather than δ bonding. This is supported by the calculation of the triply bonded Re2Cl8 which also has an eclipsed energy minimum structure. The calculations also suggest that the Re–Re triple bond in Re2Cl8 is stronger than the Re–Re quadruple bond in Re2Cl82−. A negligible contribution of the δ orbital to the metal–metal bond strength is also calculated for Os2Cl8 which is isoelectronic with Re2Cl82−.
Contribution of the Mark S. Gordon 65th Birthday Festschrift Issue.
Theoretical Studies of Inorganic Compounds. 38. Part 37 (2006) Bessac F, Frenking G, Inorg Chem 45:6956. 相似文献